ONR 25194 Determination of the resistance to slow crack growth of PE with CRB specimens 翻译.doc

Determination of the resistance to slowcrack growth of polyethylene withcracked round bar (CRB) specimens聚乙烯CRB试样抵抗慢速裂纹扩展的测试Content 目录FOREWARD前言1. Scope范围2. Normative references引用标准3. Terms and definitions术语和定义4. Principle原理5. Test equipment测试设备6. Test specimen测试试件7. Test procedure测试程序8. Test report测试报告Comparison of different specimen geometries不同试样几何形状对比Bibliography参考文献Foreword前言The knowledge about the resistance against long-term failure mechanisms caused by crack initiation and slowcrack growth (SCG) is an important information for the ranking and pre-selection of thermoplastic materials,especially for long-term applications like buried pipes made of polyethylene. Several tests to determine therelevant failure mechanisms are available today, where elevated temperatures and also the combination withstress cracking liquids are used to decrease the time frame for testing. 由裂纹萌生和慢性裂纹扩展引起的抵抗长期失效机制的认识，对于热塑性材料（特别是如埋于地下长期使用的聚乙烯管）的分类和预选，是一项重要信息。现阶段有测定相关失效机制的实验可利用，在这些实验中，通过提高实验温度和添加应力开裂液缩短了实验持续时间。However, developments in modern raw materials have led to a significant increase of the material resistanceagainst crack initiation and SCG, so that testing with available methods exceeds practical time frames. Therefore new acceleration methods preferably at application relevant temperatures and without additional time reducing liquids are required.然而，现代原材料的发展使得材料对于抵抗裂纹萌生和慢速裂纹扩展，有显著提高，使得已有方法的测试时间超出了实际合理时间范围。因此，现在要求应用一种新型快速合适的且在相关温度下无需添加时间缩短液的实验方法。This ONR, elaborated by the Technical Committee 005 “Thermoplastic pipes for the transport of fluids andgases”, provides a test method to achieve a significant decrease of testing time, even at ambient temperatures of 23 C, which is very close to those of many applications, and will not change the structural status ofthe polymer. On the one hand acceleration of material testing is reached by the specimen geometry. On theother hand the cyclic load is responsible for relatively short testing times.ONR提供了一种方法以实现测试时间的显著减少，甚至在周围环境温度23 C时（非常接近那些实际应用),并且不会改变聚合物的机构状态。ONR在“用以运输液体和气体的热塑性管路”技术会议上详细讲述。一方面，材料测试加快通过试样几何结构达到。另一方面，循环载荷也使测试时间相对缩短。1 Scope范围This ONR specifies a method for measuring the resistance against crack initiation and slow crack growth(SCG). This relevant long-term failure mechanism in mechanical loaded pipes will be tested with cylindricalnotched specimens subjected to a cyclic tensile load. The test results include the cycle number until failureoccurs as a function of the stress range.ONR对于测量抵抗裂纹萌生和慢性裂纹扩展（SCG)指定了一种方法。受机械载荷作用下的管路的相关长期失效机制可以通过对圆柱状缺口试样提供一个循环拉伸载荷测得。测试结果包括失效产生时的循环次数，作为应力范围方程。This method is suitable for an accelerated fracture-mechanics characterization at ambient temperatures of23 C of different polyethylene grades, especially for medium density (PE-MD) and high density (PE-HD)types for pipe applications, but can also be adapted for other thermoplastics materials, temperatures and applications. It can be used to evaluate specimens from compression-moulded sheets.这种方法适用于环境温度为23摄氏度的不同等级的聚乙烯材料的快速断裂力学特性，特别是中等密度（PE-MD)和高密度（PE-HD）类型的管路运用，同样也适用于其他热塑性材料、温度和实际应用。它能够用来评估压铸薄板试件。2 Normative references参考（引用）标准The following referenced documents are required for the application of this document. For dated references,only the edition cited applies. For undated references, the latest edition of the referenced document (includingany amendments) applies. Laws are to be applied in their current version.这篇文章应用了以下参考文件。对于注有日期的参考文件，仅当前版本适用。对于未注有日期的参考文件，最新版本（包括任何修订补充）均适用。规章适用当前版本。ISO 291, Plastics Standard atmospheres for conditioning and testingISO 291，塑料-标准大气条件和测试ISO 293, Plastics Compression moulding of test specimens of thermoplastic materialsISO 293，塑料-热塑性材料试件压缩铸模ISO 1872-2, Plastics Polyethylene (PE) moulding and extrusion materials Part 2: Preparation of test specimens and determination of propertiesISO 2818, Plastics Preparation of test specimens by machiningISO 16770, Plastics Determination of environmental stress cracking (ESC) of polyethylene Full-notchcreep test (FNCT)3 Terms and definitions术语和定义For the purposes of this ONR, the following definitions apply:对于ONR，适用以下定义3.1crack length, a 裂缝长度，adepth of the crack in mm at any time during a test measured from the specimen surface to the crack tip裂缝深度，单位mm，在一个实验任何时刻，从试件表面到裂缝尖端测量。3.2cycle, N 循环周期，Nsmallest segment of a load-time or stress-time function which is repeated periodically定期重复的载荷-时间或者应力-时间函数的最小时间段3.3failure cycle number, Nf 失效循环次数，Nftotal number of cycles from the beginning until the end of a test实验开始至结束循环总数3.4frequency, f 频率，fnumber of cycles within one second in Hz一秒内循环次数，单位HZ3.5initial crack length, aini 初始裂纹长度，ainimeasured depth of the crack in mm from the specimen surface through the crack tip at the beginning of the test实验开始时从试样表面到裂纹尖端的测量深度，单位mm3.6initial ligament diameter, Dini 初始韧带直径，Diniinner diameter of the cylindrical specimen in mm after notching刻痕后的圆柱时间的内径，单位mm Dini = D - 2 aini (1)3.7loading ratio, R 载荷比，Rratio of the minimum to the maximum load in one cycle在一次循环中最小载荷与最大载荷的比值s (2)s= =3.8load range, F 载荷幅度，Fdifference between the maximum and minimum load in N in one cycle一次循环中，最大载荷和最小载荷的差值，单位N3.9maximum ligament stress, max 最大韧带应力highest value of the calculated stress in MPa in the ligament area at the beginning of the test实验开始时韧性区域计算应力最大值，单位MPa3.10maximum load, Fmax 最大载荷， Fmaxhighest value of the applied load in N in one cycle在一次循环中施加载荷的最大值，单位N3.11minimum ligament stress, mins 最小韧带应力lowest value of the calculated stress in MPa in the ligament area at the beginning of the test实验开始时韧性区域计算应力最小值，单位MPa3.12minimum load, Fmin 最小载荷， Fminlowest value of the applied load in N in one cycle在一次循环中施加载荷的最小值，单位N3.13notch distance, Lmin 切口距离，Lminminimum distance from notch to clamping system in mm切口到夹紧装置的最小距离，单位mm3.14predicted initial crack length, aini* 预测初始裂纹长度，aini*foreseen depth of the crack in mm from the specimen surface through the crack tip after notching加工切口后预知裂纹深度（从试样表面到裂纹尖端），单位mm3.15predicted stress range, 0* 预测应力幅度, 0*foreseen difference between the maximum and minimum stress in MPa at the beginning of the test预测测试开始时的最大应力和最小应力的差值3.16specimen diameter, D 试样直径，Ddiameter of the cylindrical specimen in mm圆柱试样的直径，单位mm3.17specimen length, L 试样长度，Ltotal length of the test specimen in mm测试试样的总长度，单位mm3.18stress range, 0 应力幅度, 0applied difference between the maximum and minimum stress in MPa after notching at the beginning of the test加工切口后的试样在实验开始时所受最大应力和最小应力的差值，单位MPa3.19waveform 波形shape of the load-time curve within a single cycle一个循环内载荷-时间曲线形状4 Principle 原理A cyclic tensile test with constant load range is imposed on a cylindrical specimen under suitable test conditions within the range of linear visco-elasticity of the material. A pre-notched crack initiates the start of crack propagating until final failure of the specimen. The number of cycles until final failure Nf is recorded as a function of the stress range 0 at the initial crack length aini. The specimen geometry ensures quick crack initiation and short testing times due to the high constraint and low plastics deformations along the crack tip.合适的实验条件下在材料的线性粘弹性范围内，常载荷幅度下的循环拉伸实验采用圆柱试样。预刻制裂纹使裂纹扩展萌生直到试样最终失效。在初始裂纹长度aini下，记录下的最终失效循环次数Nf作为应力幅0的一种函数。试样的几何形状确保快速裂纹萌生和短的实验时间，原因是沿裂纹尖端的高约束和低塑性变形。5 Test equipment 实验设备5.1 Test machine 实验机械5.1.1 Loading system 加载系统The loading system shall be capable of imposing and recording a cyclic load varied by time between accurately defined limits (load control mode), in accordance to a specific waveform. Servo-hydraulically driven testmachines with electronic control are generally suitable for this purpose. However, mechanically driven machines may also be used if they meet the requirements.根据一个具体的波形，加载系统将能够施加并记录随时间变化的循环载荷，这是循环载荷在精确定义范围内（载荷控制方式）。带有电子控制系统的伺服-液压驱动实验机一般能满足这个要求。能够满足以上要求的机械驱动的试验机也可使用。5.1.2 Load-cycle waveform 载荷循环波形The cyclic load shall follow a sinusoidal waveform, which is characterized by the maximum load Fmax and theload ratio R. The maximum and minimum loading values shall be constant during the entire test with an accuracy of 1 %.循环载荷采用正弦波形，这个循环载荷具有最大载荷Fmax和载荷比R的特性。在整个实验中，最大和最小载荷值是常数，精度 1 %。5.1.3 Load-cycle frequency 载荷循环频率The load-cycle frequency (test frequency) f shall not exceed 10 Hz with an accuracy of 1 %. The hystereticheating at a frequency of 10 Hz usually causes no significant influence on Nf. In suspect of extraordinary hysteretic heating at the crack tip the frequency shall be reduced to 5 Hz or 1 Hz.载荷循环频率（测试频率）f不能超过10Hz，精度在1%。频率10Hz下的滞后热对循环次数Nf无显著影响。考虑到在裂纹尖端的特殊迟滞热，频率应该减小到5Hz或者1Hz。5.1.4 Cycle counter 循环计数器The test machine shall be equipped with a cycle counter displaying the number of load-cycles at any timeduring the test.5.1.5 Grips 夹具The machine shall be equipped with grips suitable to clamp cylindrical specimens. In any case a load distribution symmetrically to the specimen notch shall be ensured.5.1.6 Temperature chamber 热处理炉For testing at temperatures different from (23 2) C the test machine shall be equipped with a suitablechamber that contains the environment and ensures complete immersion of the specimen. The chamber shallbe constructed of materials which do not affect the environment and which are not affected by it. The temperature of the environment shall be controlled in order to maintain the test specimens within 2 C of the specified temperature.5.2 Microscope 显微镜A microscope or an equivalent device shall be used to measure the accurately initial crack length after thefinished cyclic tests. The device shall provide a resolution of at least 10 mm.5.3 Notching apparatus 刻痕装置The device shall be capable of producing a razor-sharp notch of accurately defined depth at the circumferenceof the cylindrical specimen. The notch tip radius produced shall be less than 10 mm. Usually razor blades meetthis requirement. A conventional lathe in combination with a razor blade tool may be suitable for this purpose.Buckling of the razor blade shall be avoided and notching perpendicular to the specimen axis shall be ensured.6 Test specimen 实验试件6.1 Specimen geometry and dimensions 试样几何结构和尺寸The specimen configuration of the cracked round bar (CRB) specimen is shown in Figure 1. A cylindrical barof the length L and a diameter D is prepared with a circumferential razor-sharp notch with a depth of aini* (predicted initial crack length) in the middle of the specimen resulting in an initial ligament diameter Dini.CBR试件外形已经在图1中展示，在长度L和直径D的圆柱棒的中间准备一个深度为aini（预测初始裂纹长度）的圆周形剃刀形成的锋利切口，形成初始韧带直径Dini。Useful specimen dimensions are L = 80 mm to 100 mm and D = 14 mm. The initial crack shall be perpendicular to the specimen axis with a depth of aini* = 1,5 mm. To avoid clamping effects at the crack tip, a notch distance Lmin of at least 20 mm from the grips to the notch shall be considered. To support specimen clamping,the specimen may be manufactured with e.g. M 14 1,0 metric fine thread.可采用的试样尺寸是长度L=80mm-100mm 且直径D=14mm。初始裂纹应当垂直于样本的轴线，深度为aini=1.5mm。为了防止避免夹紧力作用在裂纹尖端，夹具到切口距离Lmin至少为20mm。为了保证试样被夹紧，试样可以制造M14X1.0的公制细牙螺纹。 Figure 1 Principal configuration of CRB test specimen with optional metric fine thread 图1-CRB实验试样的主要结构（公制细牙螺纹可供选择）6.2 Specimen preparation 试样准备（外加工）The specimens shall be prepared from compression molded sheets. General guidelines for molding and cooling conditions are given in ISO 1872-2:1993, subclause 3.3, ISO 16770:2004, Table 1 and ISO 293. The use of different molding conditions will affect the results. The specimens shall be machined in accordance toISO 2818 at least 24 h after molding.试样应该用压制模塑板材制造。试样成型24小时后再进行机加工。6.3 Specimen notching 试样刻痕处理Specimens shall be notched at ambient temperature (23 2) C with a notching apparatus according 5.3. Toavoid frictional heating, which may lead to notch tip damage such as blunting and introduction of residualstresses, driving speed and feed shall be selected sufficiently low. Favorable values for the specimen notching are a driving speed of 80 rpm up to 100 rpm and a razor blade feed of approx. 0,03 mm/min. Special attention shall be paid to notching perpendicular to the specimen axis. A razor blade shall be used for no more than 10 notches.环境温度(23 2) C 防止摩擦生热导致开口尖端破坏例如变钝或者引入残余应力，操作速度和进给要选择的足够低（80 rpm100 rpm和0.03 mm/min） 切口要垂直于试件轴心 剃刀使用不能超过10次6.4 Specimen conditioningUnless otherwise specified, notched specimens shall be stored at 23/50, Class 2 according to ISO 291 prior totesting. Although the duration between notching and testing is not significant, it is recommended to precondition the specimens for a minimum of 24 h at 23/50, Class 2 according to ISO 291 prior to testing.按照ISO 291 23/50 等级2的规定存储试样，并推荐至少在实验开始前24小时预处理试样。7 Test procedure 实验过程7.1 Measurement of specimen dimensions 试样尺寸测量Before testing the diameter D in the vicinity of the notch shall be recorded with an accuracy of at least0,1 mm. Measuring D directly at the notch shall be avoided.实验前，刻痕附近的直径D要精确记录，精度0.1mm。禁止在刻痕处直接测量D。7.2 Specimen mounting 试样固定Depending on the clamping system specimen shall be mounted into the test machine without inducing additional forces. Bending or twisting of the specimen has to be avoided. The distance from the grips to the notch shall be in a sufficient distance Lmin (see Figure 1) to avoid any clamping effects at the crack tip.安装后不能有附加力，不允许弯曲和扭转。夹具到刻痕的近距离要满足最小距离Lmin ，以防止夹紧力影响裂纹尖端。7.3 Test atmosphere 实验环境 Usually the tests shall be done at 23/50, Class 2 according to ISO 291. In case of testing at elevated temperatures the unloaded specimen shall be conditioned at the test temperature for at least 2 h after mounting.安装后未加载荷的试样要在试验温度下适应2小时以防止实验在升高的温度下进行。7.4 Calculation of test load 实验载荷计算The test loads have to guarantee brittle failure by SCG and specimens failed in a ductile manner have to beexcluded. Specimens shall be tested with R = 0,1 at different Ds0 levels in the range of 10,5 MPa up to13,5 MPa depending on the density according to Table 1 (see also Pinter, et al. 2007 1). Loads aboveDs0= 13,5 MPa have to be avoided as this may result in ductile failure.试验载荷必须保证SCG脆性失效，必须排除试样韧性方式失效。根据表1（可见Pinter，er al.2007），依照密度，试样需按R=0.1在不同应力幅水平下进行测试，应力幅范围由10.5MPa至13.5MPa。防止超过Ds0= 13,5 MPa的载荷，这可能会导致韧性失效。表1-基于基础聚合物密度的循环CRB测试的典型应力范围（密度值符合未填充未着色基础聚合物）A comparison of different materials is only allowed for similar specimen geometry and test parameters. If CRBspecimens of different geometries as described in 6.1 are tested, the comparison of the results shall be doneusing the stress intensity factor as described in Annex A.只有在相似的试样几何结构和测试参数下才允许对不同材料进行对比。若几何结构不同与6.1所描述的CRB试样被实验，实验结果的对比应该使用在Annex A中描述的应力强度因子。At least four specimens shall be tested each at a different Ds0 regularly spread in the above specified loadrange. If an unknown material is tested, preliminary tests are recommended to ensure failure by SCG. Thecalculation of the maximum load Fmax and the minimum load Fmin shall be done according to Figure 2 and thefollowing equations.每个不同的Ds0内应该测试至少四个试样，这四个试样要有规律的分布在上述规定载荷范围内。如果一个未知材料被测试，推荐做最初实验以确保是SCG失效。最大和最小载荷的计算要根据图2和接下来的方程。7.5 Load application 载荷施加After mounting and conditioning of the specimen the cyclic load shall be applied immediately with the definedload-cycle frequency without exceeding the maximum load Fmax. Static loading prior the test shall be avoidedas this may cause creep. Simultaneous to the load application the load-cycle counter shall start for data acquisition. The cyclic load shall be applied and recorded continuously until specimen failure.试样安装和确保实验条件后，直接施加已定载荷循环频率的循环载荷，这个载荷不能超过最大载荷Fmax。防止实验前的静载荷引起蠕变。同步于载荷施加，载荷循环计数器开始数据捕捉。这个循环载荷将会被采用并连续记录直至试样失效。7.6 Notch depth measurement 切口深度测量The determination of the length of the razor blade notch on the unloaded specimens before testing may bedifficult. Therefore the initial crack length aini shall be measured after completion of the cyclic test by analyzingthe created fracture surface, where different surface textures usually allow a clear distinction between therazor-sharpened notch and the fatigue crack initiated from the notch. For this purpose a microscope accordingto 5.2 or an equivalent device shall be used.实验前未加载荷试样的剃刀切口长度的确定可能比较困难。因此初始裂纹长度aini将在循环测试完成后通过分析产生的断裂表面得出，剃刀切削开口和从切口萌生的疲劳裂纹之间的不同的表面纹理通常差别明显。为了这个目标，使用5.2所描述的显微镜或其他等功能装置。7.7 Calculation of results 实验结果计算To evaluate the results only specimens with a distinctive fraction of brittle fracture are allowed. Figure 3 showstypical microscope images of fracture surfaces of CRB specimens after testing. In both images the relativelysmooth ring-like surface from the initial notch aini is recognizable, which is a result of the specimen notching with a razor blade. The rough surface structure of the area with ductile failure (see Figure 3a) is significantly different to the area of brittle failure (see Figure 3b). In the second case a relatively smooth surface typical for brittle failure was created by SCG, which changes to ductile at small ligament diameter. The specimen with ductile failure only (see Figure 3a) was tested at too high stress levels and has to be rejected for data evaluation.评估实验结果，仅允许试样存在明显的脆性断裂区域。图3 展示了CRB试样实验后断裂表面的典型显微镜图像。在两个图像中，可以识别出初始切口aini 的相对光滑环形表面，这是试样用剃刀刻痕的结果。韧性失效（见图3a）断面的粗糙表面结构显著不同于脆性失效断面（见图3b）。在第二种情况中脆性失效的相对光滑表面类型是由SCG产生的，在小韧带直径处转变为韧性。韧性失效试样（见图3a）仅是在高应力水平下测试且不能用于数据评估。Key 关键1 razor blade notch 1剃刀刀口刻痕2 area with ductile failure 2韧性失效区域3 area with brittle failure 3脆性失