基于3D打印技术的岩体复杂结构与应力场的可视化方法外文文献翻译、中英文翻译、外文翻译.docx
基于3D打印技术的岩体复杂结构与应力场的可视化方法外文文献翻译、中英文翻译、外文翻译
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河海大学文天学院本科毕业设计（论文）Visualization of the complex structure and stress field inside rock by means of 3D printing technologyYang Ju . Heping Xie . Zemin Zheng . Jinbo Lu . Lingtao Mao . Feng Gao . Ruidong Peng Received: 18 June 2014 / Accepted: 14 July 2014 / Publishedonline: 21 August 2014.Science China Press and Springer-Verlag Berlin Heidelberg 2014AbstractAccurate characterization and visualization of the complex inner structure and stress distribution of rocks are of vital significance to solve a variety of underground engineering problems. In this paper, we incorporate several advanced technologies, such as CT scan, three-dimensional (3D) reconstruction, and 3D printing, to produce a physical model representing the natural coal rock that inherently contains complex fractures or joints. We employ 3D frozen stress and photoelastic technologies to characterize and visualize the stress distribution within the fractured rock under uniaxial compression. The 3D printed model presents the fracture structures identical to those of the natural prototype. The mechanical properties of the printed model, including uniaxial compression strength, elastic modulus, and Poissons ratio, are testified to be similar to those of the prototype coal rock. The frozen stress and photoelastic tests show that the location of stress concentration and the stress gradient around the discontinuous fractures are in good agreement with the numerical predictions of the real coalY. Ju (&) L. Mao R. Peng State Key Laboratory of Coal Resources and Safe Mining, China University of Mining Technology, Beijing 100083, China e-mail: Y. Ju F. Gao State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining Technology, Xuzhou 221116, China H. Xie College of Hydraulic and Hydroelectric Engineering, Sichuan University, Chengdu 610065, China Z. Zheng J. Lu School of Mechanics and Civil Engineering, China University of Mining Technology, Beijing 100083, China sample. The proposed河海大学文天学院本科毕业设计（论文）method appears to be capable of visually quantifying the influences of discontinuous, irregular fractures on the strength, deformation, and stress concentration of coal rock. The method of incorporating 3D printing and frozen stress technologies shows a promising way to quantify and visualize the complex fracture structures and their influences on 3D stress distribution of underground rocks, which can also be used to verify numerical simulations.Keywords Fractured rock3D printingFracturestructure modelStress field Visualization河海大学文天学院本科毕业设计（论文）1 IntroductionAccurately characterizing and visualizing the complex interior structures and stress distribution of solids are a long-term goal for scientists and engineers in various engineering and technical fields. This objective is also of critical significance to solve many engineering problems. For instance, in the fields of petroleum and mining engineering, efficient and safe exploration of oil, natural gas, coalbed methane, and mineral resources greatly relies on the knowledge and characterization of the structures and stress fields of underground reservoirs 15; in geological and environmental engineering, resolving the problems of waste geological disposal, CO2 geological storage, geothermal energy utilization, water resource conservation, and contaminant transportation and diffusion highly depends on the recognition and grasp of the geological structures and underground stresses 611; in civil and hydroelectric engineering, the stability of dam foundations, slope of reservoir banks, and underground tunnels is closely associated with the structures and the distribution and transformation of stress fields of surrounding rocks 12 15; inmechanical and manufacturing engineering, it is critical to well understand the defects, crack propagation, and stress distribution in each component for accurately evaluating and predicting the mechanical properties, safety, and service life of complex workpieces 1619. Achieving these goals, however, confronts many thorny difficulties and challenges. Among a key problem is, for the vast majority of theapplications, that the interior structures, stress fields, and the physical processes that essentially govern the apparent performance of solids are invisible and intangible, appearing to be as much as a blackbox problem. One of typical examples among the applications is the underground rock. Being buried deep underground means that it is extremely hard to explore and represent the complex structures of interior fractures or pores, and the internal physical processes of rocks, such as stress-induced deformation, fluid flow, and coupling effects of stress andfluid flow, by means of the existing methods and techniques. The current in-situ probing techniques are technically difficult, costly, and risky. To some extent, solving this problem seems to be as difficult as or even more difficult than exploring a distant河海大学文天学院本科毕业设计（论文）unknown planet! It has become a bottleneck that impedes the development of relevant engineering techniques and analytical theories.In fact, an amount of work has been done regarding the characterization of interior structures and stress fields of underground rocks. Most of the work focuses on specification of the physical and mechanical properties of rocks by means of a variety of experimental and analytical methods, using the measurement results to indirectly represent the interior structures and their influences on these properties 2025. Owing to the difficulties in theoretical modeling and computation, as well as in visualization and quantification of the interior structures and those governing mechanisms, including spatial morphologies of pores orfractures, connectivity of pores, capillary pressure, stress distribution on pore walls, crack initiation, bifurcation and coalescence, stress intensity at crack tips, fluid flow, the influences of pore or fracture structures on the fluid flow, and the interaction of seepage and stress, it leads to an embarrassing reality that the inherent nature and laws that determine the apparent performance of rocks are unclear and have not been precisely quantified. People have to face such a dilemma that, on the one hand, the data of the mechanical properties of rocks show wide scatterness, poor applicability and comparability, and limited predictive accuracy; on the other hand, design and evaluation of an engineering application requires a large number of core samples, resulting in long cycles, high costs, and difficulties in applicability.It is noteworthy that numerical simulation provides an effective way to visualize and quantify the complex structures and internal physical and mechanical processes of rocks. Beingquantitative, intuitive, controllable, repeatable, predictable, and low cost, it has become a powerful tool to solve the problems that experimental or theoretical methods cannot overcome 2631. However, a fair number of controversies have been raised about the numerical solutions of the complex structure and the mechanical behavior of rock due to a series of problems that have not been solved satisfactorily, including the inconsistency between the simplified numerical models and the real bodies, meshing patterns, contact and separation of elements, calculation algorithms,河海大学文天学院本科毕业设计（论文）material parameters chosen, determination of constitutive relationships, computation scale and efficiency, and especially, laboratory or in-situ validations of the numerical solutions. The answers to how to build up a computational model that accurately represents the real structure of rock, to find the solutions to the aforementioned problems, and to verify the numerical results have become the key part of driving power of promotion of numerical analysis of rock behavior.In recent years, CT imaging technology has become a powerful tool to identify and extract the information of interior composition and structure of solids 3235. Three-dimensional (3D) digital models have been developed to represent the real rock structures by means of CT imaging and the reconstruction algorithms 3641, which makes it possible to quantify the complex interior structure, stress fields, energy fields, distribution of flow speed, and the associated governing mechanisms of underground rocks via numerical approaches 4248. Neither the existing macroscale laboratory measures nor the in-situ field tests can achieve these goals. Nevertheless, verifying the accuracy and reliability of numerical solutions still remains a great challenge for researchers worldwide.The frozen stress method, based on the unique property of photoelastic materials, that is, the inside stress can be recorded by frozen when exposed to high temperature, has been widely applied to quantitatively analyze the 3D stresses of a complex solid.When a heated object made ofphotoelastic materials recovers to room temperature, the isochromatic and isoclinic fringes caused by exerted loads as the temperature increases can be frozen, based on which, the stress distribution inside a model can be extracted and analyzed through photoelastic experiments 4951. With rapid development of photomechanical techniques, the 3D frozen stress method has achieved significant progress in various aspects, covering the properties of photoelastic materials, model preparation, 3D optical measuring principles, fringe identification and discrimination, and measurement of stresses on free surface, etc. 5255. This method turns to be a convenient, economic, and effective tool to quantify the complicated stress fields of solids. However, several河海大学文天学院本科毕业设计（论文）difficulties arise when preparing a 3D photoelastic model. The conventional preparation procedure is that one first casts a 3D model using a mold and then modifies manually or by a machine. This involves not only the processing difficulties but also a complicated, expensive mold and a long preparation cycle. Moreover, when replicating a complicated structure using this preparation procedure, some sophisticated details of the real structure have to be omitted due to the manufacturing difficulties and limits. It results in the distortion in analysis of stress and deformation of the entity. Especially, using the conventional manufacturing technique can hardly duplicate the solids that embrace complex substructures. For instance, it is extremely hard to realize duplication of the rock involving a number of pores and fractures, as shown in Figs. 1 and 2. This has become a significant barrier to applying the 3D frozen stress method to quantify and visualize the inner stress field of complex solids and to verify the reliability of numerical analysis.It is especially interesting that the emerging 3D prototyping or printing technology in recent years has realized a rapid manufacturing of a complicated 3D solid. This advanced method, adopting the digital files of a target body, forms the 3D body through spraying powder (or liquid) photopolymer, ceramic, or even metal, layer by layer, and curing by laser 5660. Nowadays, this technology as been rapidly applied in the fields of industrial design, manufacturing, medicine, automotive, aerospace, building design, and construction. It is shown, from the authors preliminary laboratory investigation, that comparing with the conventional photoelastic material, i.e., epoxy resin, the adopted photopolymer possesses similar composition, photoelasticity, and stress-frozen characters, which makes it possible, from the theoretical point of view, to apply 3D printing technique and frozen stress method to study the stress distribution of a complex solid. This indicates that incorporating 3D printing and frozen stress method could provide a promising way to accurately quantify and visualize the complex interior structures and Fig. 1 Natural fractured coal rock: a the picture of the sample, b CT image of the cross section of the sample. The black cracks refer to the fractures without fillings, the gray cracks stand for the fractures with fillings, and the rest represents the河海大学文天学院本科毕业设计（论文）rockmatrixFig. 2 (Color online) 3D and 2D representations of fracture network of the coal rock: a xz cross section, b xy cross section, c yz cross section, d 3D perspective view of the fracture network. The black parts refer to the fractures without fillings; white parts represent the fractures with fillings. The dark gray parts in 2D images and the transparent parts in 3D model stand for the rock matrix3D stress fields of solids, and to verify the reliability of the numerical solutions aswell. To achieve the goal, this paper adopts a series of advance technologies, including 3D reconstruction, 3D printing, 3D frozen stress, and photoelastic tests, to probe the method of quantifying and visualizing the complex interior structure and stress field of fractured rock. The tested coal rocks are sampled from an underground coal seam with a depth of 490 m. We intend to seek an effective way to quantify and visualize those invisible and intangible physical and mechanical processes or mechanisms, such as fracture of porous structures, excavation-induced structural deformation, seepage, and coupled stressfluid interaction, of rocks underground.河海大学文天学院本科毕业设计（论文）2 CT identification of the fractured structure of natural coal rockFigure 1 shows the tested cubic specimen (size 50 mm 9 50 mm 9 50 mm) of natural coal rock drilled from a depth of 490 m underground. The specimen involves two types of fractures and/or joints: One is dark without fillings, and the other is gray white with fillings. For the sake of simplification, we roughly call the two types of fractures the fractures and hereinafter. To Cunderstand the rock behavior, we conducted a series of X-ray diffraction and uniaxial compression tests to analyze the mineral compositions, mixture proportions, and mechanical properties of the coal matrices and the fillings in fractures 61. It is shown that the test rock possesses average uniaxial compression strength of 22.2 MPa and average elastic modulus of 2.93 GPa. More details of the tests can be found in Ref. 61.In order to acquire the accurate information of the fractures, we employed a high-resolution micro-CT with a spatial resolution of 4 lm to consecutively scan the coal specimen along its height from top to bottom at an interval of 200 lm. A total of250 grayscale images (512 9 512 pixels) were gained. As an example, Fig. 1b demonstrates a CT image of the twenty-fourth cross section of the specimen. To identify and extract the fractures, we applied the self-developed identification algorithms and computer codes 62 to process all the CT images via binarization threshold methods. Figure 2 presents the obtained fractures, in which the black pixels with a gray value of zero comprise the the fractures without fillings, the gray pixels with a gray value between zero and 255 represent the coal matrix, and the bright white pixels with a gray value of 255 consist of the fractures with fillings. Same procedure was applied to all the 250 CT images of the cross sections, and all the fractures were extracted. We employed the self-developed 3D reconstruction algorithm and MIMICS software as a platform to build up the 3D fracture network of the rock 6164, shown in Fig. 2d. The high precision of CT images ensures the complete and accurate digital representation of the河海大学文天学院本科毕业设计（论文）spatial morphology of the real fractures, thereby enabling preparation of the 3D physical model of natural fractured coal rock.河海大学文天学院本科毕业设计（论文）3. 3D physical model of the fractured coal rockIn this study, we employed the Object Connex 500 3D printer to produce the 3D models of the fractured coal rock shown in Figs. 1 and 2. The device has a print resolution up to 600 9 600 9 1,600 dpi with a dot accuracy of 1050 lm, and a molding thickness ranging 1630 lm. The printer can utilize 17 different types of basic photo-polymer materials to generate hundreds of composite digital materials by specific mixing ratios, thus allowing the mechanical properties of composite materials to match with those of the natural sample. This facilitates the production of a multi-component material model. The Object Connex 500 3D printer (shown in Fig. 3) has the advantages of high precision and automation, and ease of creating complex 3D solid models. In order to accurately reflect the characteristics and changes of internal stress fields of solids via 3DFig. 3 (Color online) Photograph of Object Connex 500 3D printer photoelasticity and frozen stress method, it is crucial to select appropriate materials to represent the fractured coal rock. Thus, we compared the similarity of models made from different photopolymer materials, as shown in Fig.Based on the experimental results of compositions of matrix and fillings of the coal rock 61, for the model in Fig. 4a, we adopted the transparent photopolymer Vero Clear to produce the matrix, and the white opaque photo-polymer Vero White Plus to produce the fractures with fillings. The lite-type latticed supporting materials Fullcure 705 were adopted to form the fractures河海大学文天学院本科毕业设计（论文）without fillings. The lite-type supporting material features loose structure, low transparency, and small strength. In default, there are three types of looseness of Fullcure 705, among the lite-type is the loosest and has the mechanical properties close to zero. It is shown that the model is solidified and cured evenly by lasers, and the fractures with fillings integrate seamlessly with the matrix. The two pictures display the printed model from different perspectives, respectively. In contrast, Fig. 4b presents the model of which the matrix was made from the transparent photopolymer Vero Clear, and both the fractures with and without fillings were made from Fullcure 705. It is shown that there are clear interfaces between the matrix and the fractures in the model. The observation indicates that the printed 3D model involves the same geometrical and distribution characteristics asthose of the natural prototype no matter what types of materials were adopted for preparation.In order to verify the similarity of the mechanical properties between the printing materials and the natural rock, we produced a series of cylindrical specimens (size U25 mm 9 50 mm) made from matrix materials Vero Clear and Vero White Plus, respectively, and a group of cubic specimens (side lengths 39 and 50 mm, respectively) of which the matrix was made from transparent materials Vero Clear, and fractures were made from soft, latticed, supporting materials Fullcure 705. The uniaxial compression and tension tests were carried out on these specimen河海大学文天学院本科毕业设计（论文）F ig. 4 3D printed model of fractured coal rock. a Model with the fractures made from white opaque materials Vero White Plus. The left and right images display the model from different perspectives. b Model with the fractures made from the latticed supporting materials Fullcure 705. The left and right models are the same o measure the basic mechanical properties of the materi-Clear are similar to those of the natural rock, but the unials. Table 1 lists the measured results. It indicates that the axial compression strength and the tension strength uniaxial compression strength and the Poissons ratio of the remains big gaps. The overall properties, including uniaxial material Vero White Plus for fractures are close to those of compression strength, elastic modulus, and Poissons ratio, the fillings of nature fractures, but their uniaxial河海大学文天学院本科毕业设计（论文）tension are fairly close to thoseof the natural coal rock. It means strength and elastic modulus are apparently different. The that the overall mechanical properties of the model shown elastic modulus and the Poissons ratio of the material Vero in Fig. 4b are much closer to those of therealprototype.Table 1 Comparison of the mechanical properties of the printing materials and the natural coal rockBasic mechanical properties Matrix material Fracture material Coal rock Natural Fillings of natural fractures Vero Clear Vero White plus model coal rock (main composition: calcites) Uniaxial tensile strength ft (MPa) 54.4 48.7 5.06.0 25.0Uniaxial compression strength fc (MPa) 76.7 86.1 20.8 22.2 75.4 Elastic modulus E(GPa) 3.1 3.0 1.4 2.9 34.0 Poissons ratio m 0.38 0.36 0.32 0.38 0.25 Therefore, the printing materials for the model in Fig. 4b are adopted for representing the fractured rock. The general procedure for preparing a 3D model of fractured coal rock is as following. First, we employed MIMICSto process the CT images of the coal sample and output to the STL files. Second, we input the STL files into the Objet Studio software to create a 3D model. Note that the fractures and the matrix have independent STL files, from which the Objet Studio software automatically assembles the whole model in accordance with the location coordinates of the parts. Third, the material properties were accordingly assigned to the matrix and fractures in line with the experimental results of the physical characteristics of the matrix and the fractures of coal rock 61. Using the Objet Studio, we were able to set the additional printing parameters, such as河海大学文天学院本科毕业设计（论文）the material properties of contact surfaces and the thickness of supporting materials, to finalize the printing setup. In the end, all the data of the model were transmitted to the 3D printer, which incrementally deposited the materials layer by layer and cured by laser to form the 3D solid model.河海大学文天学院本科毕业设计（论文）4 Frozen stress testsThe stress-frozen property of photoelastic materials refers to the property that the isoclinic or isochromatic fringes occurring under loading when the temperature increased can be recorded or frozen when the temperature recovers to ambient temperature 4951. Using this property, we cut the model into slices and adopted the reflection-type photoelastic techniques 6567 to extract and identify the 3D stress distribution of the fractured coal rock subjected to uniaxial compressions.Figure 5 illustrates the experimental setup and loading method. A dead vertical load of 47 kg was placed on the cubic coal model (size 50 mm 9 50 mm 9 50 mm) via the vertical guide bar. No lateral constraints applied to the specimen.河海大学文天学院本科毕业设计（论文）Figure 6 plots the curve of temperature for the freezing tests. To determine the freezing temperature, we conducted a series of preliminary tests of the photopolymer materials. The critical freezing temperature of the material was found to be 120 C. We therefore set the freezing temperature for the frozen stress test to be 125 C. In order to eliminate the influence of nonuniform temperature gradient on stress-frozen effect, the temperature was increased slowly from ambient temperature to 40 C with the rate that was designed by the heating device setup. The temperature was kept constant for 0.5 h at 90 C and for 1.5 h at the freezing temperature and then kept constant for 0.5 h againwhen it decreased to 90 C. Figure 6 illustrates the complete temperature arrangement Through thefrozen strestests.河海大学文天学院本科毕业设计（论文）Figure 7 diagrams the setup of reflection-type photoelastic tests and devices. In order to identify the 3D internal stress distribution, the stress-frozen model was cut into slices. The slices were then polished and placed in the optical path consisting of polariscopes (shown in Fig. 7)to identify the stress fringes. The thickness of the slice, which greatly affects the orders of fringes, was determined considering the following aspects: (1) It should meet the minimum requirement to assure the necessary optical-path difference for light traveling; (2) it should keep an enough thickness to ensure a quality manufacture with less impact on the original fractures; (3) there are enough slices in order to get a complete picture of 3D stress distribution over the body. After we tried it repeatedly, the thickness of the slice was set to be 5 mm. In the meantime, we performed a series of tests to compare the definition and sharpness of the fringes that represent the stress distribution around the fractures by applying theXXXXXXtransmission-type and reflection-type polariscope systems, respectively. As a result, we found out that the stress fringes in the reflection-type polariscope system are better than those in the trans-mission-type path system. Accordingly, the reflection-type photoelastic testing system was set up to identify and extract the stress fringes of the frozen rock model. For plane photoelasticity, the principal stress difference at any point can be determined as 6567: where r1 and r2 are the principal stresses at a certain point under plane stress state, n refers to the fringe order of isochromatic of the point, f0 means the fringe constant of the photopolymer material at freezing temperature, and t is the thickness of the slice Fig. 5 The device and loading scheme for the frozen stress tests. a Stress-frozen equipment and loading devices; b direction of the uniaxial loads Time (h) Fig. 6 Curve of temperature for freezing modelsSimilarly, for 3D photoelasticity, we have where r0 and r0 are stress components at a certain point on the plane perpendicular to the light direction, which are also referred to as the secondary principal stresses, f 0stands for the fringe constant of the material at freezing temperature, m is the isochromatic fringe order at the point, and t is the thickness of the slice. The secondary principal stresses satisfy the following equations: It indicates that the difference of stress components at each point of any slice of the model can be obtained by the isochromatic fringe orders.XXXXXXXXX5 Results and analysisResults of frozen stress tests The frozen stress tests were carried out on two types of printed model with identical geometry but different fillingsof fractures (shown in Fig. 4). The results show that themodel with the matrix made from the material Vero Clear and the fractures filled with the material Vero White Plus, shown in Fig. 4a, does not reflect the influences of the fractures on the 3D stress distribution. The main reason, from the authors point of view, seems to be that the white opaque material Vero White Plus is composed of photo-polymer material and portion of rigid additions. After the laser solidification, the strength of the Vero White Plus increases, getting close to that of the Vero Clear that comprises the matrix. Moreover, due to the effect of laser curing, the filling material was melt and integratedseamlessly with the matrix material, meaning that there were no discontinuous weak interfaces between them. The results of the photoelasticfringes also indicate that no stress concentration takes place around the fractures. Theoretically, this does not conform to the known mechanical performance of naturally fractured coal rock. This can also be verified by the subsequent numerical simulation results. In contrast, the model of fractured rock with the matrix made from the Vero Clear and the fractures filled with the low-strength, loose-structure supporting material (as shown in Fig. 4b) explicitly presents the apparent discontinuous weak interfaces between matrix and fractures. The frozen stress test results show the high orders of fringes around the ractures,indicatingprominentstressconcentrationattheselocations.XXXFigure 8 demonstrates the results of stress fringe distribution on the slices at different heights of the printed model subject to uniaxial compressions using the 3D frozen stress technique and photoelastic measures. 5.2 Numerical simulation of stress distribution To verify the accuracy of the stress distribution around the fractures in the model obtained by the frozen stress method, we performed the numerical analysis of the stresses using a 3D numerical model of the fractured system shown in Fig. 4b. MIMICSsoftware was employed as a tool to establish a 3D finite element model from the 3D entity model of fractured coal (see Fig. 2d). The stress河海大学文天学院本科毕业设计（论文）distribution inside rock as the maximum uniaxial compression achieved was obtained using the so-called Birth Death Element algorithm in ANSYS61. Figure 9 illustrates the simulation results. In the numerical approach, the loading method and boundary conditions were set to be the same as those shown in Fig. 5b. The material parameters for the matrix were adopted in accordance with their experimental results listed in Table 1. The elastic constitution relationship was used in the calculation. Considering that the fracture-filling material Fullcure 705 has low strength and loose structure, we assigned null to the value of material parameters of the fracture elements. In order to effectively reflect the stress concentration, the elements around the fractures were refined and densified Fig. 8 Distribution of stress fringes on the slices at different heights in the fractured rock model under uniaxial compressions using the frozen stress technique and 3D photoelastic method. a Spatial locationofphotoelastic slicing; b slice at x = 4 mm; c slice at x = 12 mm; d slice at x = 20 mm; e slice at x = 28 mm; f slice at x = 36 mm; g slice at x = 44 mm. x represents the coordinate at 1/2 thickness of the slicFig. 9 Numerical results of stress distribution on the slices at different heights in fractured rock model under uniaxial compressions. a Spatial location of photoelastic slicing; b slice at x = 4 mm; c slice at x = 12 mm; d slice at x = 20 mm; e slice at x = 28 mm; f slice at x = 36 mm; g slice at x = 44 mm properly. Considering the problems that could impede the execution of computation, including small element size, large element number, distort element deformation, and intractable irregular interfaces, due to the complicated geometry, intersection or overlap, roughness and irregularity of the fractures (see Fig. 2), we adopted a several measures to optimize the initiated surface meshes by regulating the errors of geometrical configuration to reduce the element number. The embedded and repeated triangle elements that were generated in preliminary mesh optimization were repaired automatically using MIMICSsoftware. These optimization procedures initiated a surface-element mesh model with dense elements around the interfaces between fractures and matrix and relatively loose elements in matrix. Then, the optimized surface mesh model was transformed into 4-node tetrahedron mesh model using the mapping algorithm integrated in MIMICS.河海大学文天学院本科毕业设计（论文）Using similar optimization methods to control the number and quantity of tetrahedron elements, we fulfilled the establishment and calculation of the finite element model of coal rock with irregular fracture structures. The distribution of stress field around the fractures was explicitly displayed through this method and could be used to verify the results obtained by photoelastic measurements. Owing to the limit of paper length, more details about the numerical modeling and calculations for the fractured coal rock refer to the literature 61. Analysis of results Comparing the results of frozen stress tests with the numerical simulation, we find out that: The method incorporating the 3D printing, frozen stress, and photoelastic technologies is able to visualize and quantify the stress distribution around complex fractures inside coal samples. As shown in Figs. 8 and 9, the photoelastic test results of stress concentration and the stress gradient show a good agreement with the numerical predictions of the real coal sample. The results of both the photoelastic test and the numerical simulation indicate that high stress concentration takes place around the irregular fractures. The irregular, discontinuous fractures are the primary reason for the occurrence of nonuniform stress distribution, low strength, large deformation, and being vulnerable to collapse of fractured coal rock. Incorporating the 3D printing technique and the frozen stress method provides an effective way to visualize and quantify the complex structure and stress field of fractured coal rock. The method can also be used to verify thenumerical solutions of stress distribution. The photoelastic results of the stress amplitude and distribution range from the frozen stress methodpresent a certain amount of variance from the numerical predictions. This is mainly attributed, fromthe authors point of view, to that the slice of the 3D printed photoelastic model has to keep a minimum thickness in order to acquire a clear pattern of stress fringes. On the contrary, the numerical slice showing the stress distribution actually has no physical thickness.In the other words, the stress result on each physically frozen slice actually represents a superposition or overlap of the stress distribution of several numerical slices. This leads to the observable discrepancies in the occurrence of fractured structures, stress河海大学文天学院本科毕业设计（论文）amplitudes, and distribution areas. In addition, to accomplish the numerical calculation of the ractured rock model, considering the impact of complex structures on the implementation, we took some measures to optimize the elements around the fractures, i.e., smooth the local, sharp substructures of the fractures to keep clear of no convergence due to the presence of small size, large number of elements and element distortion. This optimization of meshes could bring about a certain amount of impact on the numerical simulation, leading to the difference from the experimental results. Conclusions and discussions A 3D photopolymer model of natural coal rock involving complex fractures is constructed using CT imaging technology, 3D reconstruction, and 3D printing techniques. The distribution of stress fields inside the fractured coal rock subject to uniaxial compressive loads is quantified and visualized by means of the 3D frozen stress method and photoelastic tests. The experimental test and numerical analysis show that: ) The 3D printed model of real rock with matrix made from the photopolymer material Vero Clear and the fractures filled by the loose material Fullcure 705presents the consistent characteristics of the fracture structures as compared to those of the prototype rock. The mechanical properties of the printed model, such as uniaxial compressive strength, elastic modulus, and Poissons ratio, are close to those of the prototype rock. (2) The materials used for the printed models show good photoelastic properties. Incorporating the frozen stress method and photoelastic tests is able to visualize and quantify the distribution of inside stresses around the complex fractures in fractured rock. The experimental tests and the numerical results show good consistency in terms of the distribution area of high stresses and the stress gradients in the vicinity of discontinuous fractures. The proposed method can be used to visualize the influences of discontinuous, irregular fractures on the strength, deformation, and stress concentration of fractured coal rock. The method of incorporating 3D printing and frozen stress technique could provide a new, promising way to quantify and visualize the complex fracture structures and the 3D distribution of stress field inside rock, and to verify their numerical solutions as well. However, it should be pointed out that, despite河海大学文天学院本科毕业设计（论文）the preliminary attempts having been conducted in this paper for the 3D display and visualization of internal stress field and complex fracture structures, further research efforts are needed for more precisely and quantitatively describing the stress field, the fractures (or fracture network) caused by mining, and the evolution and coupling mechanisms of stress and fluid, etc. To a large extent, solving these problems heavily relies on in-depth and intensive study on the photo-elastic materials, 3D printing-related technologies (e.g., the optical and mechanical properties of model materials, the precision of 3D printing, the similarity in geometry and mechanics between 3D models and natural prototypes), the frozen stress technique, the identification of stress fringes, and the separation methods of 3D stresses as well. Acknowledgements This work was supported by the National Natural Science Foundation for Distinguished Young Scholars of China (51125017), the National Natural Science Foundation of China (51374213), and the National Basic Research Program of China河海大学文天学院本科毕业设计（论文）References1. Zhou XG, Cao CJ, Yuan JY (2003) The research actuality and major progresses on the quantitative forecast of reservoir fractures and hydrocarbon migration law. Adv Earth Sci 18:398404 (in Chinese)2. Hou QL, Li HJ, Fan JJ et al (2012) Structure and coalbed methane occurrence in tectonically deformed coals. Sci China Earth Sci 55:175517633. Zhang LK, Wang ZL, Qu ZH et al (2007) Physical simulation experiment of gas migration in sandstone porous media. Acta Geol Sin 81:5395444. Mazumder S, Wolf K (2008) Differential swelling and permeability change of coal in response to CO2 injection for ECBM. Int J Coal Geol 74:1231385. Song HZ, Zeng HR, Sun JX et al (1999) Methods of reservoir tectonic fracture prediction and its application. Seismol Geol6. Wang J (2014) On area-specific underground research laboratory for geological disposal of high-level radioactive waste in China. J Rock Mech Geotech Eng 6:991047. White CM, Smith DH, Jones KL et al (2005) Sequestration of carbon dioxide in coal with enhanced coalbed methane recoverya review. Energy Fuels 19:6597248. Shaika AR, Rahmana SS, Trana NH et al (2011) Numerical simulation of fluid-rock coupling heat transfer in naturally fractured geothermal system. Appl Therm Eng 31:16001606 Chin. Sci. Bull. (2014) 59(36):535453659. Xu TF, Sampera J, Ayorab C et al (1999) Modeling of non-isothermal multi-component reactive transport in field scale porous media flow systems. J Hydrol 214:14416410. Liu J, Wang H, Nie Y (2004) Fractal model for predicting effective diffusion coefficient of solute in porous media. Adv Water Sci 15:458462 (in Chinese)11. Kim SO, Kim JJ, Yun ST et al (2003) Numerical and experimental studies on cadmium (II) transport in kaolinite clay under electrical fields. Water Air Soil Pollut 150:13516212. Li YS, Yin JM, Ai K (2006) Experimental study of borehole elasticity and geostress in Xiaowan hydropower plants dam foundation rock mass. Chin J Undergr Sp Eng河海大学文天学院本科毕业设计（论文）2:912915 (in Chinese)13. Cai YQ, Zhu YW, Li JG et al (2002) Influence of geological flaw on mechanical behaviors of arch dam and dam foundation. Chin J Rock Mech Eng 21:18051809 (in Chinese)14. Liu X, Fu Y, Wang Y et al (2009) Stability of reservoir bank slope under waterrock interaction. Rock Soil Mech 30:613616 (in Chinese)15. Yang SX, Li H, Bai MZ et al (2010) The wall-rocks stress releasing regularity arose by cavern excavation in the high stress condition. J China Coal Soc 35:2630 (in Chinese)16. Zhu H, Zhu L, Chen JH et al (2007) The study of deformation and damage mechanism of aluminium alloy (6063) under different stress states. Rare Metal Mater Eng 36:597601 (in Chinese)17. Tarpania JR, Ruckerta, COFT, Milana MT (2004) Estimating fatigue life under variable amplitude loading through quantitative fractography: a case study. Engng Failure Anal 11: 54755918. Zheng ES, Wang ZG, Ai SH (1995) Dislocation structure of fatigue crack tip. Acta Metall Sin 31:105114 (in Chinese)19. Morgeneyer TF, Starink MJ, Sinclair I (2008) Evolution ofvoids during ductile crack propagation in an aluminium alloy sheet toughness test studied by synchrotron radiation computed tomography. Acta Mater 56:1671167920. Nelson RA, Handin J (1977) Experimental study of fracture permeability in porous rock. AAPG Bull 61:22723621. Bai M, Roegiers JC, Elsworth D (1995) Poromechanical response of fractured-porous rock masses. J Petrol Sci Eng 13:15516822. Degueldre C, Pleinert H, Maguire P et al (1996) Porosity and pathway determination in crystalline rock by positron emission tomography and neutron radiography. Earth Planet Sci Lett 140:21322523. Liu J, Elsworth D, Brady BH (1999) Linking stress-dependent effective porosity and hydraulic conductivity fields to RMR. Int J Rock Mech Min Sci 36:581596河海大学文天学院本科毕业设计（论文）24. Maguire RP, Missimer JH, Emert F et al (1997) Positron emission tomography of large rock samples using a multiring PET instrument. IEEE Trans Nucl Sci 44:263025. Pingguang X, Tomota Y (2006) Progress in materials characterization technique based on in-situ neutron diffraction. Acta Me-tall Sin 42:68168826. Dimas LS, Giesa T, Buehler MJ (2014) Coupled continuum and discrete analysis of random heterogeneous materials: elasticity and fracture. J Mech Phys Solids 63:48149027. Farhat C, Avery P, Chapman T et al (2014) Dimensional reduction of nonlinear finite element dynamic models with finite rotations and energy-based mesh sampling and weighting for computational efficiency. Int J Numer Methods Eng 98:62566228. Wang SY, Sloan SW, Sheng DC et al (2014) Numerical study of failure behaviour of pre-cracked rock specimens under conventional triaxial compression. Int J Solids Struct 51:1132114829. Lisjak A, Liu Q, Zhao Q et al (2013) Numerical simulation of acoustic emission in brittle rocks by two-dimensional finite-discrete element analysis. Geophys J Int 195:42344330. Ghotbi RE, Rahmannejad R, Feili MAE et al (2013) Application of numerical modeling and genetic programming to estimate rock mass modulus of deformation. Int J Min Sci Tech 23:73373731. Hart R (2003) Enhancing rock stress understanding through numerical analysis. Int J Rock Mech Min Sci 40:1089109732. Yun TS, Jeong YJ, Kim KY et al (2013) Evaluation of rock anisotropy using 3D X-ray computed tomography. Eng Geol 163:111933. Raynaud S, Fabre D, Mazerolle F et al (1989) Analysis of the internal structure of rocks and characterization of mechanical deformation by a non-destructive method: X-ray tomodensitometry. Tectonophysics 159:14915934. Nasseri MHB, Rezanezhad F, Young RP (2011) Analysis of fracture damage zone in anisotropic granitic rock using 3D X-ray CT scanning techniques. Int J Fract 168:11335. Mori S, Endo M (2007) Candidate image processing for real-time volumetric CT河海大学文天学院本科毕业设计（论文）subtraction angiography. Eur J Radiol 61:33534136. Kawakata H, Cho A, Kiyama T et al (1999) Three-dimensional observations of faulting process in Westerly granite under uniaxial and triaxial conditions by X-ray CT scan. Tectonophysics 313:29330537. Birk M, Dapp R, Ruiter NV et al (2014) GPU-based iterative transmission reconstruction in 3D ultrasound computer tomography. J Parallel Distrib Comput 74:1730174338. Hajizadeh A, Safekordi A, Farhadpour FA (2011) A multiple-point statistics algorithm for 3D pore space reconstruction from 2D images. Adv Water Resour 34:1256126739. Gomi T, Koshida K, Miyati T (2007) Development of a nonlinear weighted hybrid cone-beam CT reconstruction for circular trajectories. Comput Med Imaging Graph 31:56156940. Geiger J, Hunyadfalvi Z, Bogner P (2009) Analysis of small-scale heterogeneity in clastic rocks by using computerized X-ray tomography (CT). Eng Geol 103:11211841. Ru Z, Ting A, Hegui L et al (2013) 3D reconstruction method and connectivity rules of fracture networks generated under different mining layouts. Int J Min Sci Tech 23:86387142. Rani HP, Divya T, Sahaya RR et al (2013) Numerical investigation of energy and Reynolds stress distribution for a turbulent flow in an orifice. Eng Fail Anal 34:45146343. Jafarian Y, Sadeghi AA, Vakili R et al (2011) On the efficiency and predictability of strain energy for the evaluation of liquefaction potential: a numerical study. Comput Geotech 38:80080844. Latief FDE, Biswal B, Fauzi U et al (2010) Continuum reconstruction of the pore scale microstructure for Fontainebleau sandstone. Phys A: Stat Mech Appl 389:16071618 45. Ju Y, Yang YM, Song ZD et al (2008) A statistical model for porous structure of rocks. Sci China Ser E Technol Sci 51:1026104146. Hossain MM, Rahman MK (2008) Numerical simulation of complex fracture growth during tight reservoir stimulation by hydraulic fracturing. J Petrol Sci Eng河海大学文天学院本科毕业设计（论文）60:8610447. Ju Y, Wang HJ, Yang YM et al (2010) Numerical simulation of mechanisms of deformation, failure and energy dissipation in porous rock media subjected to wave stresses. Sci China Technol Sci 53:1098111348. Piri M, Blunt M (2005) Three-dimensional mix-wet random pore-scale network modeling of two-and three-phase flow in porous media. I. Model description. Phys Rev E 71:02630149. Pappalettre C, Galietti U (1995) Polycarbonate for frozen stress photoelasticity. Strain 31:697450. Epstein JS, Post D, Smith CW (1984) Three-dimensional photoelastic measurements with very thin slices. Exp Tech 8:343751. Schroedl MA, McGowan JJ, Smith CW (1972) An assessment of factors influencing data obtained by the photoelastic stress Chin. Sci. Bull. (2014) 59(36):53545365 freezing technique for stress fields near crack tips. Eng Fract Mech 4:80180952. Hyde TH, Warrior NA (1990) An improved method for the determination of photoelastic stress intensity factors using the Westergaard stress function. Int J Mech Sci 32:26527353. Buckberry C, Towers D (1996) New approaches to the full-field analysis of photoelastic stress patterns. Opt Laser Eng 24:41542854. Pinit P, Umezaki E (2007) Digitally whole-field analysis of isoclinic parameter in photoelasticity by four-step color phase-shifting technique. Opt Laser Eng 45:79580755. Baldi A, Bertolino F, Ginesu F (2007) A temporal phase unwrapping algorithm for photoelastic stress analysis. Opt Laser Eng 45:61261756. Kruth JP, Leu MC, Nakagawa T (1998) Progress in additive manufacturing and rapid prototyping. CIRP Ann Manuf Technol 47:525540 57. Campbell TA, Ivanova OS (2013) 3D printing of multifunctional nanocomposites. Nano Today 8:11912058. Jee HJ, Sachs E (2000) A visual simulation technique for 3D printing. Adv Eng Softw 31:9710659. Miller BW, Moore JW, Barrett HH et al (2011) 3D printing in X-ray and gamma-ray河海大学文天学院本科毕业设计（论文）imaging: a novel method for fabricating high-density imaging apertures. Nucl Instrum Methods Phys Res Sect A 659:26226860. Kostakis V, Papachristou M (2013) Commons-based peer production and digital fabrication: the case of a Rep Rap-based, Lego-built 3D printing-milling machine. Telem Inform 31:43444361. Sun HF, Yang YM, Ju Y et al (2014) Numerical analysis of deformation, failure and energy release mechanisms of fractured coal rock under unloading conditions. J China Coal Soc 39:258272 (in Chinese)62. Ju Y, Xing MX, Sun HF et al (2013) Computer program for extracting and analyzing fractures in rocks and concretes. Software Copyright Registration (#0530646) Chinas National Copyright Administration, Beijing (in Chinese)63. Ju Y, Zheng JT, Epstein M et al (2014) 3D numerical reconstruction of well-connected porous structure of rock using fractal algorithms. Comput Methods Appl Mech Eng 279:21222664. Ju Y, Zheng JT, Yang YM et al (2012) Computer programs for fractal reconstruction and analysis. Software Copyright Registration (#0449190) Chinas National Copyright Administration, Beijing (in Chinese)65. Shin DC, Hawong JS (2011) Development of a hybrid method of reflection photoelasticity for crack problems in anisotropic plates. Exp Mech 51:18319866. Dally JW, Riley WF (1991) Experimental stress analysis, 3rd edn. McGraw-Hill, New York67. Ramesh K (2000) Digital photoelasticity: advanced techniques and applications. Springer, Berlin河海大学文天学院本科毕业设计（论文）基于3D 打印技术的岩体复杂结构与应力场的可视化方法鞠杨*, 谢和平, 郑泽民, 卢晋波, 毛灵涛, 高峰, 彭瑞东 中国矿业大学煤炭资源与安全开采国家重点实验室, 北京 100083; 中国矿业大学深部岩土力学与地下工程国家重点实验室, 徐州 221116; 四川大学水力水电学院, 成都 610065; 中国矿业大学(北京)力学与建筑工程学院, 北京 1000832014-06-18 收稿, 2014-07-14 接受, 2014-08-01 网络版发表中国科学出版社和施普林格出版社柏林海德堡2014摘要准确表征与直观显示岩体复杂的内部结构与应力场是解决诸多地下工程问题 的基础和关键. 本文运用CT 成像、三维重构和3D 打印技术制备了包含复杂裂隙的天然煤岩模型, 借助三维应力冻结和光弹技术, 直观定量地显示了单轴压缩载荷作用下复杂裂隙煤岩内部的应力场分布特征. 研究表明: 通过3D 打印技术制备的煤岩模型具有与天然煤岩一致的裂隙结构特征; 3D 模型的单轴抗压强度、弹性模量和泊松比等力学性能指标接近于天然裂隙煤岩; 在不连续裂隙周边的高应力分布区域以及应力级差等方面, 3D 模型的实验结果与数值模拟结果具有较好的一致性; 该方法能够直观定量地显示不连续不规则裂隙对煤岩的强度、变形以及应力集中区的影响. 3D 模型打印与应力冻结技术相结合为实现地下岩体内部复杂结构与三维应力场分布的定量表征与可视化, 以及印证数值模拟结果提供了新途径.关键词 裂隙岩体 3D 打印 裂隙结构模型 应力场可视化准确表征与直观显示固体复杂的内部结构与应力场是众多工程 技术领域内科学家和工程师长期追求的目标, 也是解决诸多工程实际问题的基础和关键. 例如, 石油、天然气和矿业工程领域中, 高效安全地开采储层中的石油、天然气、煤层气和矿物资源依赖于对地下储层结构及地应力场的准确认知与科学描述15; 地质与环境工程领域中, 解决废弃物地质处置、CO2 地质封存、地热利用、水资源保护、有害溶质的运移和扩散等重要问题取决于对地质结构及地应力环境的准确把握611; 土木与水电工程领域中, 坝基、库岸边坡和地下硐室围岩的稳定问题与地下岩体结构及围岩应力场的分布演化规律密切相关1215; 机械与制造工程领域中, 评估与预测复杂工件的机械性能、安全性及使用寿命需河海大学文天学院本科毕业设计（论文）要准确地掌握和表征工件的复杂结构、内部缺陷、裂纹扩展和应力场变化规律1619. 然而, 实现上述目标面临众多困难与挑战, 其中一个关键难题是, 对绝大多数工程而言, 所关注的工程对象的复杂结构、应力场以及对其表观现象起控制作用的内部物理力学过程“看不见、摸不着”, 属于典型的“黑箱”问题. 例如, 上述一系列工程问题涉及的岩体介质, 它深埋于地下, 其内部复杂的孔隙/裂隙结构、由地应力及开采应力引发的结构演化与形变、流体渗流、应力-渗流 相互作用等物理力学过程或机制, 在现有的方法和技术条件下, 难以准确地获知与定量表征, 现场探测的技术难度大、成本高、可靠性低. 从某种程度上讲, 其难度不亚于探测遥远的未知星球, 甚至可能更高. 这已成为制约相关工程技术与基础理论取得突破的瓶颈.实际上, 地下岩体介质的内部结构与应力场分析的问题, 人们已开展了大量研究, 但主要集中在通过各种实验和分析手段获取工程所需要的岩体物理力学性质, 并根据这些性质的变化来间接地反映介质内部结构特征及其影响2025. 由于理论建模与计算的困难, 以及无法直观准确地显示和定量表征岩体介质的内部结构以及对表观物理力学行为起控制作用的内禀机制, 如岩石孔隙/裂隙的空间形态、孔隙连通状态、毛细管压力、孔壁应力分布、裂隙起裂、分叉和汇聚机 制、裂隙尖端应力特征、流体渗流、孔隙或裂隙结构对渗流机制的影响、渗流与 应力相互作用等, 人们难以准确地把握岩体复杂多变物理力学行为的内在规律与实质, 因而不得不面对依据有限采样样本获得的岩体物理力学性质离散性大、适用性差、难以准确预测的尴尬局面, 每次工程建设都要依赖于大量采样样本的测试结果, 周期长、花费高且难以广泛应用.值得重视的是, 数值模拟为人们开辟了一条直观显示和定量分析岩体复杂结构与内在物理力学过程的途径, 由于具有定量、直观、可控、可重复、可预测和低成本等优势, 数值模拟已发展成为解决实验或理论方法无法克服的难题的有力工具2631. 然而, 由于计算模型简化造成的几何模型与岩体真实结构之间的偏差、网格覆盖模式、单元接触与分离、求解算法、材料参数选取、本构关系确 定、计算规模与效率等一系列问题未得到圆满解决, 特别是计算结果难以得到实验或现场验证, 以及岩体复杂结构与物理力学行为的数值分析引发了大量的争议或质疑. 如何构建准确反映岩体真实结构的计算模型、解决模拟计算中的关键问河海大学文天学院本科毕业设计（论文）题和有效地验证数值计算结果成为推动地下深部岩体物理力学行为数值分析方法 发展的关键.近年来, CT 成像成为获取和识别固体复杂内部组成与结构信息的有力工具3235, 人们利用CT 成像以及数字重构算法建立了表征岩石真实结构的3D 数字模型3641, 使利用数值模拟手段定量研究地下岩体介质复杂的内部结构、应力场、能量场、渗流场及相关内禀机制成为可能4248. 这些是以往实验室宏观实验或现场实验所难以实现的. 尽管如此, 如何实验验证基于三维重构模型的岩体物理或力学性质数值分析的准确性与可靠性仍是世界范围内科学家面临的重大 挑战.应力冻结技术是定量分析复杂固体三向应力场的有效方法, 它利用光弹材料的应力冻结特性, 即升温环境下外载所引起的应力等差线或等倾线条纹在温度恢复室温时可以被“冻结”记录下来的性质, 通过光测实验提取和分析空间中任一点的应力状态4951. 随着光测力学实验技术的发展, 固体三维应力冻结法在光弹材料性质、模型制备、三向光测理论、条纹拾取与分辨分析、自由表面应 力测定等方面取得较大的发展5255, 成为直观和定量分析固体结构复杂应力场的方便、经济和有效的途径. 然而, 三维光弹分析中传统的模型制备方法, 主要是通过制作模具后浇注成型, 再辅以手工或机加工进行修整.这不仅需要解决许多铸型工艺难题, 而且模具费用高、制备周期长. 更重要的是, 对于复杂的固体结构,利用传统方法制作三维光弹模型时, 不得不省略那些复杂的局部特征, 导致在应力或变形分析中出现失真. 特别是对于固体内嵌复杂结构, 传统方法难以制备. 例如, 内部含有孔隙或裂隙的地下岩体介质(如图1 和2 所示), 现有方法和技术难以制备其光弹性模型. 这已成为无法通过三维应力冻结法直观显示复杂固体结构内部应力场以及验证其数值分析可靠性的瓶颈难题.近年发展起来的3D 成型(也称3D 打印)技术使得快速制作复杂三维固体模型成为现实. 这项技术以数字模型文件为基础, 采用粉末状(或液态)光敏树脂、陶瓷或金属材料, 利用激光快速固化技术, 逐层喷涂(类似传统激光打印)堆叠累积的方式来构造三维固体5660. 目前该技术已迅速在工业设计、机械制造、医疗、汽车、航空航天、建筑设计与施工等领域得到应用. 就其应用的成型材料之一光敏树脂而言,作者研究发现, 与传统的光弹材料环氧树脂相比, 光敏树脂材料具有相似的成分构成、光弹性和应力冻结特性, 这从理论上保证了利用光敏树河海大学文天学院本科毕业设计（论文）脂和3D打印技术制作复杂固体结构光弹模型以及开展三维应力冻结实验的可行性. 因此, 综合应用3D 打印技术和三维应力冻结法将为实现固体复杂结构与内部三维应力场的定量表征与可视化以及验证数值模型分析的可靠性提供极具前景的发展道路.本文以采自地下490 m 深处的天然裂隙煤岩为例, 尝试采用三维重构、3D 成型、三维应力冻结等方法和技术, 研究煤岩体内部复杂的裂隙结构与应力场的定量表征与可视化的方法, 意在为探索地下岩体复杂的孔隙/裂隙结构、地应力及开采引发的结构演化、渗流、应力-渗流相互作用等“看不见、摸不着”的物理力学 过程或机制的定量描述与可视化方法提供参考和途径.(a) (b)图1 天然裂隙煤岩(a) 样品的实物照片; (b) 样品横截面的CT扫描图像. 其中, 黑色裂纹为不含填充物的裂隙, 灰白色裂纹为含填充物的节理/裂隙, 其余为煤岩基体河海大学文天学院本科毕业设计（论文）1 天然煤岩体的裂隙结构与CT 识别图1 为实验用的采自地下490 m 深度处天然煤岩的立方体样本, 尺寸50 mm50 mm50 mm. 肉眼可见两类节理/裂隙: 一类是深黑色节理/裂隙, 不含填充物; 另一类是灰白色节理/裂隙, 含填充物. 为简化分析, 作者将上述节理/裂隙统称为“裂隙”(以下相同). X-射线衍射、单轴压缩实验等方法, 测量分析了样品煤岩的基质、裂隙填充物的组分、配比及物理力学性质61. 结果显示: 煤岩的单轴抗压强度平均值为22.2 MPa, 弹性模量平均值为2.93 GPa, 详细测试结果参见文献61.为了获得准确的裂隙结构信息, 利用高精度微焦点CT(空间分辨率4 m), 沿煤岩高度自上而下间隔200 m 连续扫描250 层, 得到一组尺寸512512像素的灰度图像, 图1(b)显示了第24 层横截面的CT图像. 为识别和提取裂隙, 利用自主研发的裂隙识别算法和程序62对CT 图像进行二值化处理, 获得图2所示的裂隙图像, 其中, 灰度值等于0 的像素(黑色)代表不含填充物的裂隙, 中间灰度值像素(灰色)代表煤岩基体, 灰度值等于255 的像素代表含填充物的裂隙.采用相同方法处理250 层横截面CT 图像, 提取出全部裂隙. 利用三维重构方法并借助MIMICS程序建立了煤岩体的三维裂隙网络模型6164, 如图2(d)所示. 由于CT 扫描精度较高, 因而可以获得天然裂隙完整、真实的空间形态等信息, 这为制备天然裂隙煤岩的三维物理模型创造了条件.河海大学文天学院本科毕业设计（论文）2 天然裂隙煤岩的3D 物理模型本文采用Object Connex 500 3D 打印机制备图1和2 所示的裂隙煤岩体的三维物理模型. 设备打印分辨率为6006001600 dpi, 精度1050 m, 成型厚度1630 m. 配备了17 种基本光聚合物材料和按一定配比生成的百余种复合数字材料. 当模型含不同材料成份时, 可根据不同成分的物理力学性能选用两种基本材料, 再由这两种基本材料按比例配比生成其他复合材料, 方便多组份材料模型的制作. 设备具有成型精度高、自动化程度高和便于制作复杂固体三维模型等优点. 图3 为本实验室的Object Connex 5003D 设备的片照.图2 (网络版彩色)煤岩体裂隙结构的三维实体模型与二维剖面图(a) X-Z 截面; (b) X-Y 截面; (c) Y-Z 截面; (d) 三维裂隙结构的透视图. 图中黑色部分为不含填充物的裂隙, 白色部分为含填充物的裂隙, 2D 剖面图中的深灰色部分和3D 透视图中的透明部分代表煤岩基体为了能够应用三维光弹与应力冻结法准确地反映固体内部应力场的特征与变河海大学文天学院本科毕业设计（论文）化规律, 选择恰当的模型材料来制备裂隙煤岩模型至关重要. 为此, 本文研究了不同光敏材料制备煤岩裂隙结构的效果, 图4给出了采用不同光敏材料(Photopolymers)制备的两组裂隙煤岩结构三维模型. 依据天然煤岩的基质与裂隙填充物的物性实验结果61, 图4(a)模型: 采用透明光聚合物材料Vero Clear 制备基体, 含填充物的裂隙采用白色不透明材料Vero White Plus; 采用网格支撑材料Fullcure 705 制备不含填充物的裂隙, 网格疏密类型为Lite. 网格支撑材料透明度低、结构疏松、强度小, 系统默认有3 种疏密程度, Lite 类型为最疏松, 力学性质接近于零. 模型经激光照射后均匀固化, 含填充物裂隙与基体之间无缝融合, 没有明显分离的交界面. 作为对比, 图4(b)模型: 基体采用透明光聚合物材料Vero Clear 制备, 但含填充物和不含填充物的裂隙均采用网格支撑材料Fullcure 705 制备, 此种模式下模型固化后裂隙与基体之间可见明显的分界面. 从图4 可以看出, 无论哪种制备模式, 3D 打印模型具有与天然煤岩裂隙结构相同的几何与分布特征.图3 Object Connex 500 3D 打印机河海大学文天学院本科毕业设计（论文）图4 裂隙煤岩的3D 打印模型(a) 裂隙采用白色不透明材料Vero White plus 的模型, 左右图片为同一模型的不同视角照片; (b) 裂隙采用网状支撑材料Fullcure 705 的模型, 左右两个模型完全相同为检验模型材料与天然煤岩基本力学性质的相似程度, 利用3D 打印机分别制备了基质材料VeroClear、裂隙材料Vero White Plus 的圆柱体试件(尺寸25 mm 50 mm)以及用Vero Clear 模拟基质、用网格支撑材料Fullcure 705 模拟裂隙的煤岩立方体试件(尺寸分别为39 mm 39 mm 39 mm, 50 mm 50 mm 50 mm 两种), 分别进行了试件单轴受压和受拉实验,测得了模型材料的基本力学性质, 实验结果如表1 所示. 对比可以看出: 裂隙材料Vero White Plus 的单轴抗压强度、泊松比与天然裂隙填充物较接近, 而单轴受拉强度、弹性模量的差距较河海大学文天学院本科毕业设计（论文）大. 基质材料VeroClear 的弹性模量、泊松比与天然煤岩的指标较接近,但单轴受压和受拉强度的差距较大. 采用Vero Clear模拟基质和用网格支撑材料Fullcure 705 模拟裂隙的立方体模型的单轴抗压强度、弹性模量和泊松比与天然裂隙煤岩的指标较接近. 这表明图4(b)煤岩模型的整体力学性质与天然裂隙煤岩的较接近. 为此,本文采用了图4(b)模型所用材料来制备裂隙煤岩3D模型.打印制备裂隙煤岩三维模型的基本方法和流程是: 首先, 利用MIMICS程序对煤岩CT 扫描图像进行处理, 输出STL 格式文件. 运行Objet Studio 程序并导入STL 文件创建三维立体模型, 其中, 裂隙和基质分别导出各自的STL 文件, 由Objet Studio 程序按照各自的位置坐标自动组装形成完整的含裂隙的立方体模型. 导入完整模型后, 根据天然煤岩基质与裂隙的物性实验结果61, 对模型的基质和裂隙分别赋予选定的材料属性. 通过Objet Studio 设置其他相关的打印属性, 例如, 各部分接触面的材料属性、支撑材料的厚度等, 优化模型打印效果. 对各部分结构分别设置属性后, 将模型数据发送到3D 打印机并开始逐层喷涂堆叠、经激光照射固化后形成三维固体模型.河海大学文天学院本科毕业设计（论文）3 应力冻结实验本文利用光敏材料的应力冻结特性, 即升温环境下外载所引起的应力等差线或等倾线条纹当温度恢复室温时可以被“冻结”记录下来的性质4951, 通过分层切片和反射光弹技术6567提取并分析单轴压缩荷载下裂隙煤岩的三维应力状态. 图5 显示了冻结实验装置与加载方案, 通过竖向移动的导向杆对立方体煤岩模型(尺寸50 mm 50 mm 50 mm)施加均匀竖向压力47 kg, 侧面无约束. 图6 为冻结实验的温度控制曲线. 首先通过预备实验测得模型用光聚物材料的临界冻结温度为120, 据此将本次冻结温度设定为125. 为了使模型均匀“冻结”, 消除不均匀温度梯度对冻结应力分布的影响, 从室温到40过程中, 温度按照变温箱内设的升温速率进行; 升温至90时保温0.5 h, 达到“冻结”温度时保温1.5 h; 温度降至90时再保温0.5 h. 整个“冻结”过程的升降温按照图6 程序控制进行.图7 为反射光弹实验布置方案. 为了直观清晰地显示受载时煤岩体内部的三维应力分布, 我们对“应力冻结”后的煤岩模型进行分层切片, 将适当厚度的切片经双面磨平抛光处理后置于图7 所示的反射光路中观察应力条纹级数. 确定切片厚度时我们考虑了以下因素: (1) 为获得清晰的等差条纹, 光经过切片时须具有足够的光程差, 即切片最小厚度; (2) 能够确保切片加工的质量, 减小加工制河海大学文天学院本科毕业设计（论文）备对裂隙结构的损坏; (3) 有足够多的切片以反映应力在不同空间位置处的分布特征. 经反复试验对比, 切片厚度确定为5 mm. 同时, 为了更好地显示煤岩内部裂隙周边的应力集中状况、增强可观察的条纹级数, 我们分别进行了透射光弹和反射光弹实验的对比, 发现反射光弹条纹较清晰, 为此采用了图7 所示的反射光弹布置方案来识别和提取“冻结”煤岩模型中的应力分bu河海大学文天学院本科毕业设计（论文）平面光弹中, 任一点的主应力差值可由下式确定6567:其中, 1 , 2 表示平面应力状态下某点的两个主应力, n 为某点主应力等差线条纹级数, f0 表示光敏材料的冻 结 条 纹 值 ,t为 切 片 的 厚 度 . 类 似 地 ,三 维 光 弹 有其中, 1, 2表示三维模型中与光线照射方向垂直的平面内某一点的应力分量, 也称次主应力, f0表示冻结条纹值, m 表示切片中某点的条纹级数. 次主应力满河海大学文天学院本科毕业设计（论文）足:这表明三维冻结模型中任意切面上某一点的应力分量差可以通过识别等差线条纹级数获得.河海大学文天学院本科毕业设计（论文）4 结果与分析4.1 应力冻结实验结果进行图4 所示两种不同的裂隙煤岩模型的应力冻结实验, 结果发现: 采用Vero Clear 模拟基体和Vero White Plus 模拟填充物裂隙制备的图4(a)所示模型未能清晰地反映出裂隙对三维应力分布的影响. 主要原因在于: 白色不透明Vero White Plus 是由基质光敏材料中加入一部分刚性材料而构成的, 激光固化后强度有所增强, 但与基质材料Vero Clear 的强度相差不大. 同时, 模型经激光照射固化后, 填充裂隙材料与基质材料之间无缝融合, 无不连续弱面. 光弹条纹分布表明: 节理裂隙处没有不均匀应力集中现象, 从理论上讲, 这与天然煤岩节理裂隙的力学特征不一致(后续的数值模拟也证明了这一点). 与此相反, 图4(b)所示模型由于采用低强度、结构疏松的支撑材料制备裂隙, 裂隙与基质之间存在明显的不连续低强度弱面, 冻结实验显示: 裂隙面周围存在高阶条纹级数, 应力集中现象显著. 图8 给出了通过“应力冻结”和三维光弹实验获得的裂隙煤岩模型单轴压缩时不同位置层面的应力条纹结果.4.2 应力数值模拟结果为了进一步分析应力冻结法获得的煤岩裂隙周边应力分布的有效性, 建立图4(b)所示的煤岩裂隙结构的三维数值模型, 借助MIMICS程序将图2(d)所示的煤岩三维实体模型转换为有限单元模型. 运用ANSYS“单元生死”技术61, 分析得到了单轴压缩荷载达到峰值时裂隙煤岩内部的应力分布, 如图9 所示.数值模拟中, 模型的单轴压缩方式和边界约束与图5(b)所示一致, 基质参数取模型材料的实测值(见表1),采用弹性本构关系. 由于裂隙填充材料Fullcure 705 强度低、结构疏松, 故数值模型中裂隙单元材料取值取空. 为了能够反映应力集中程度, 裂隙周边单元网格适当加密. 考虑到裂隙的几何形态复杂、相互交叉切割, 且交界面粗糙和不规则(见图2), 有限元计算时会遇到单元尺寸小、数量多、网格畸变和交界面难处理等问题, 导致数值计算难以进行. 为此, 本文采用控制几何误差来减少单元数量的方法对初始面网格进行优化, 利用程序自动修复功能修复初级网格优化中产生的嵌入三角网格和重复三角网格, 经过上述网格优化处理后形成一个裂隙和基体界面处网格密集、基体网格相对疏散的初始面网格模型. 然后,将河海大学文天学院本科毕业设计（论文）优化好的面网格模型通过映射算法生成四节点四面体网格, 并在裂隙处生成密网格. 通过控制网格尺寸来控制四面体单元网格的数量和质量. 尽管裂隙结构复杂、单元数目众多(约一百万单元), 由于采用了上述多种优化方法, 本文顺利实现了不规则裂隙结构的有限元建模与高效运算以及裂隙邻近区域应力场分布的直 观显示. 考虑本文目的和篇幅所限, 裂隙煤岩的数值模型建模方法与运算的更多详细内容参见文献61.4.3 结果分析对比应力冻结实验与数值模拟的结果, 不难发现:(1) 运用3D 打印模型、应力冻结与光弹方法可以直观显示出煤岩内部复杂裂隙结构的周边应力场分布, 在高应力分布区域以及应力级差等方面(见图8 和9), 3D 模型的应力冻结实验结果与数值模型结果具有较好的一致性. 实验与数值分析均表明: 不规则裂隙周边具有较高的应力集中水平, 不规不连续裂隙是造成煤岩的应力场分布不均匀、强度低、变形大、易发生破坏的主要内因. 3D 模型打印与应力冻结技术为实现裂隙岩体复杂结构与内部三维应力场分布的定量分析与可视化以及印证数值模拟分析结 果提供了有效途径.(2) 应力冻结切片显示的应力幅值和分布范围与数值模拟切片显示的结果有一定差距, 这主要是因为: 为了保证合适的光程差获得清晰的应力条纹,3D 物理模型切片具有一定的厚度; 而数值模型切片显示的是沿数值模型某横截面位置剖开后的应力分布, “切片”本身没有厚度. 因此, 相比数值模型切片而言, 应力冻结实验切片显示的是多个数值切片应力“叠加”的结果, 这是造成数值模型切片显示的裂隙结构、应力幅值和分布范围与应力冻结模型切片显示的结果不完全 一致的主要原因. 此外, 由于裂隙结构复杂, 为了完成数值运算, 利用MIMICS 对裂隙周围单元网格进行了优化, 对部分裂隙的局部微结构进行了平滑处理, 以消除单元尺寸小、数量多和网格畸变等造成的计算不收敛问题. 这种处理一定程度上也会影响裂隙周边主应力的数值计算结果, 造成与实验结果相比的差距.河海大学文天学院本科毕业设计（论文）5 结论与讨论本文运用CT 成像、三维重构和3D 打印技术制备了包含复杂裂隙的天然煤岩模型, 借助三维应力冻结和光弹技术, 直观定量地显示了单轴压缩载荷作用下复杂裂隙煤岩内部的应力场分布特征. 实验与数值模拟结果表明:采用基质材料Vero Clear 和疏松材料Fullcure 705, 通过3D 打印技术制备的煤岩模型具有与天然煤岩一致的裂隙结构特征, 煤岩模型的单轴抗压强度、弹性模量和泊松比等力学性能指标与天然裂隙煤岩的较为接近.(1)(2)图8 应力冻结和光弹实验获得的单轴压缩下裂隙煤岩模型不同位置层面的应力条纹(a) 光弹切片的空间位置; (b) x=4 mm 处的切片; (c) x=12 mm 处的切片; (d) x=20 mm 处的切片; (e) x=28 mm 处的切片;(f) x=36 mm 处的切片; (g) x=44 mm 处的切片; 其中, 坐标x 表示的是切片厚度1/2 处的坐标河海大学文天学院本科毕业设计（论文）图9 单轴压缩下裂隙煤岩不同位置层面的应力分布的数值模拟结果(a) 应力切片的空间位置; (b) x=4 mm 处的切片; (c) x=12 mm 处的切片; (d) x=20 mm 处的切片; (e) x=28 mm 处的切片; (f) x=36 mm 处的切片; (g) x=44 mm 处的切片(2) 模型材料具有较好的光弹性性质, 运用3D打印模型、应力冻结与光弹方法可以直观显示出煤岩内部复杂裂隙结构的周边应力场分布, 在不连续裂隙周边的高应力分布区域以及应力级差等方面, 3D模型的实验结果与数值模拟结果具有较好的一致性.该方法能够直观定量地显示不连续不规则裂隙对煤岩的强度、变形 以及应力集中区的影响. 3D 模型打印与三维应力冻结技术相结合为实现裂隙岩体复杂结构与内部三维应力场分布的定量分析与可视化, 以及印证数值模拟结果提供了新的途径.需要指出的是, 尽管本文对煤岩体内部复杂的裂隙结构及应力场的三维显示与可视化进行了初步尝试和探索, 但距离准确定量地表征人们广泛关注的复杂岩体结构的应力场、开采引发的裂隙结构(或裂隙场)、应力场、渗流场的演化与耦 合机制或过程尚有很长的路要走. 解决这些问题很大程度上依赖于对模型材料的光学-力学特性、3D 打印成型精度与工艺、3D 模型与天然原型之间的几何与力学河海大学文天学院本科毕业设计（论文）相似性、应力冻结技术、应力条纹识别以及三向应力分离方法等诸多方面更深入 和全面的研究.河海大学文天学院本科毕业设计（论文）参考文献1 周新桂, 操成杰, 袁嘉音. 储层构造裂缝定量预测与油气渗流规律研究现状和进展. 地球科学进展, 2003, 18: 3984042 侯泉林, 李会军, 范俊佳, 等. 构造煤结构与煤层气赋存研究进展. 中国科学: 地球科学, 2012, 42: 148714953 Zhang L K, Wang Z L, Qu Z H, et al. Physical simulation experiment of gas migration in sandstone porous media. Acta Geol Sin, 2007,81: 5395444 Mazumder S, Wolf K. Differential swelling and permeability change of coal in response to CO2 injection for ECBM. Int J Coal Geol,2008, 74: 1231385 Song H Z, Zeng H R, Sun J X, et al. Methods of reservoir tectonic fracture prediction and its application. Seismol Geol, 1999, 21:2052136 Wang J. On area-specific underground research laboratory for geological disposal of high-level radioactive waste in China. J Rock MechGeotech Eng, 2014, 6: 991047 White C M, Smith D H, Jones K L, et al. Sequestration of carbon dioxide in coal with enhanced coalbed methane recoveryA review.Energy Fuels, 2005, 19: 6597248 Shaika A R, Rahmana S S, Trana N H, et al. Numerical simulation of fluid-rock coupling heat transfer in naturallsystem. Appl Thermal Eng, 2011, 31: 160016069 Xu T F, Sampera J, Ayorab C, et al. Modeling of non-isothermal multi-component reactive transport in field scale porous media flowsystems. J Hydrol, 1999, 214: 14416410 刘建国, 王洪涛, 聂永丰. 多孔介质中溶质有效扩散系数预测的分形模型. 水科学进展, 2004, 15: 45846211 Kim S O, Kim J J, Yun S T, et al. Numerical and experimental studies on cadmium (II) transport in kaolinite clay under electrical fields.Water Air Soil Pollut, 2003, 150: 13516212 李永松, 尹健民, 艾凯. 小湾水电站坝基岩体弹模与地应力测试研究. 地下空间与工程学报, 2006, 2: 91291513 蔡元奇, 朱以文, 李金光, 等. 地质缺陷对拱坝及坝基力学行为的影响. 岩石力学与工程学报, 2002, 21: 1805180914 刘新荣, 傅晏, 王永新, 等. 水-岩相互作用对库岸边坡稳定的影响研究. 岩土力学, 2009, 30: 61361615 杨树新, 李宏, 白明洲, 等. 高地应力环境下硐室开挖围岩应力释放规律. 煤炭学报, 2010, 35: 263016 朱浩, 朱亮, 陈剑虹. 不同应力状态下铝合金变形及损伤机理的研究. 稀有金属材料与工程, 2007, 36: 59760117 Tarpania J R, Ruckerta C O F T, Milana M T. Estimating fatigue life under variable amplitude loading through quantitative fractographyA casestudy. Eng Failure Anal, 2004, 11: 54755918 郑冶沙, 王中光, 艾素华. 疲劳裂纹尖端的位错结构. 金属学报, 1995, 31: 10511419 Morgeneyer T F, Starink M J, Sinclair I. Evolution of voids during ductile crack河海大学文天学院本科毕业设计（论文）propagation in an aluminum alloy sheet toughness teststudied by synchrotron radiation computed tomography. Acta Mater, 2008, 56: 1671167920 Nelson R A, Handin J. Experimental study of fracture permeability in porous rock. AAPG Bull, 1977, 61: 22723621 Bai M, Roegiers J C, Elsworth D. Poromechanical response of fractured-porous rock masses. J Petrol Sci Eng, 1995, 13: 15516822 Degueldre C, Pleinert H, Maguire P, et al. Porosity and pathway determination in crystalline rock by positron emission tomography andneutron radiography. Earth Planet Sci Lett, 1996, 140: 21322523 Liu J, Elsworth D, Brady B H. Linking stress-dependent effective porosity and hydraulic conductivity fields to RMR. Int J Rock MechMin Sci, 1999, 36: 581596 24 Maguire R P, Missimer J H, Emert F, et al. Positron emission tomography of large rock samples using a multiring PET inst
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