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微型汽车变速器设计【两轴式四档手动】【8张CAD图纸和论文】【汽车专业】

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关键词：: 汽车变速器设计全套 cad 图纸毕业论文专业

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摘要
现代汽车的动力装置几乎都是采用往复活塞式内燃机，它具有体积小、质量轻、工作可靠、使用方便等优点，但其性能与汽车的动力性和经济性之间存在着较大的矛盾。
汽车需要克服作用在它上面的阻力，才能起步和正常的行驶。汽车变速器和主减速器，它们可以使驱动车轮的扭矩增大为发动机扭矩的若干倍，又可以使其转速减小到发动机转速的若干分之一。
传动系有两个功能：传送发动机到驱动轮之间的动力和改变转矩的大小。由此可见传动系统是汽车非常重要的组成部分，从而对汽车传动系的结构分析与设计计算也就显非常重要了。
主要设计内容有变速器的布置方案与设计，齿轮的强度计算与校核；主减速器主、从动锥齿轮的支承方案选择，主减速器主要参数选择与计算；差速器的设计。并且用AutoCAD绘出变速器和差速器的装配图还有部分零件图。
通过对微型轿车变速器的设计，不仅满足了现代汽车的动力性，也提高了其经济性，满足了市场现有的需求。

关键词：传动系；变速器；主减速器；差速器

Abstract
The Reciprocating Engine are almost used as the power plant of modern motor, which is advanced in the small volume, light weight, reliability and convenience. However, there is contradiction between the performance and the dynamic and economy of the vehicle.
As to start and drive smoothly, the vehicle has to come over the resistance. The torque of the wheels could be increased as several times of the engine or be decreased one of a number of points of the engine speed by the transmission and the main reducer.
The transmission has two function transmit the engine power to the wheels and change the torque. So the transmission is one of the most important parts of the vehicle. The Analysis and design of the transmission are also vital.
The design is consisted of Layout and design of the programme of the transmission, the strength calculation and checking of the gear, the support programme of the final drive active bevel gear and driven bevel gear, the main parameters choosing and calculation of the main reducer and the Differential design. The assembly of the main reducer and the differential and the parts must be drawn with the software AUTOCAD.
According to the transmission design of the mini vehicle, the dynamic ,economy and the market of the modern vehicle are satisfied.
Key words: Power train； Transmission； Final drive； Differential

目录
摘要 III
Abstract III
目录 V
1 绪论 1
1.1 本课题的研究内容和意义 1
1.2 国内外的发展概况 1
1.3本课题应达到的要求 2
2 变速器传动机构布置方案 3
2.1 传动机构布置方案分析 3
2.1.1 两轴式和中间轴式变速器 3
2.1.2 三轴式 3
2.1.3 倒挡的形式和布置方案 4
2.2 零部件布置方案分析 4
2.2.1 齿轮形式 4
2.2.2 换挡的结构形式 4
2.2.3 防止自动脱档的措施 5
2.2.4 轴承形式 5
2.3 本章小结 5
3 变速器主要参数的选择及设计计算 6
3.1 挡位数确定 6
3.2 传动比 6
3.3 中心距 8
3.4 齿轮参数 8
3.5 各档齿轮齿数的分配 9
3.6 齿轮的设计计算 11
3.7 本章小结 12
4 变速器主要结构元件的校核 13
4.1 齿轮损坏的原因及形式 13
4.2 齿轮材料的选择原则 13
4.3 轮齿强度校核 14
4.3.1 齿轮的接触强度 14
4.3.2 齿轮的接触强度 15
4.4 轴的强度校核 18
4.5 轴承的校核 22
4.5.1 输入轴轴承校核 22
4.5.2 输出轴轴承校核 23
4.6 本章小结 24
5 结论与展望 25
致谢 26
参考文献 26
附录 28

1 绪论
1.1 本课题的研究内容和意义
变速器的功能是在不相同的条件下，改变发动机传在驱动轮上的转矩和转速，使汽车得到不一样的牵引力以及速度，同时是发动机在最佳的工况范围内工作。此外，应保证汽车能倒退行驶和停车时使发动机和传动系保持分离。需要时还应有动力输出的功能。
随着我国千人汽车保有量的大副上升，高速公路，高级公路的不断建设，汽车正逐渐进入家庭，成为人们生活中的一部分。与此同时带来了燃料的大量需求，所以汽车的燃油经济性应给予重视。汽车的动力性、经济性能是车辆的重要性能，影响汽车的动力性、经济性能的因素很多，其中汽车的动力装置参数（发动机的参数；变速器的挡位及传动比）对上述性能的影响较大。因此对汽车变速器的研究有非常重要的社会意义和经济意义。
1.2 国内外的发展概况
手动变速器（MT：Manual Transmission）主要采用了齿轮传动的降速原理。变速器内有多组传动比不同的齿轮副，而汽车行驶时的换挡工作，也就是通过操纵机构使变速器内不同的齿轮副工作。
自动变速器（AT：Automatic Transmission）是由液力变矩器，行星齿轮和液压操纵系统组成，通过液力变矩器和齿轮组合的方式来达到变速变矩。
AMT是在传统干式离合器和手动齿轮变速器的基础上改造而成，主要改变了手动换挡操纵部分。即在MT总体结构不变的情况下改用电子控制来实现自动换挡。
无级变速器（CVT：Continuously Variable Transmission）,又称为连续变速式机械变速器。金属带式无级变速器主要包括主动轮组，从动轮组，金属带和液压泵等基本部件。主要靠主动轮，从动轮和传动带来实现速比的无级变化，传动带一般用橡胶带，金属带和金属链等。
无限变速式机械无级变速器（IVT：Infinitely Variable Transmission）采用的是一种摩擦板式变速原理。IVT的核心部分由输入传动盘，输出传动盘和Variator传动盘组成。它们之间的接触点以润滑油作介质，金属之间不接触，通过改变Variator装置的角度变化而实现传动比的连续而无限的变化[1]。
汽车的发展经历了三大革命，动力革命（内燃机

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内容简介：: 编号无锡太湖学院毕业设计（论文）题目：汽车变速器设计信机系机械工程及自动化专业学号： 0923180学生姓名：李超指导教师：黄敏（职称：副教授） 2013年5月25日编号无锡太湖学院毕业设计（论文）相关资料题目：汽车变速器设计信机系机械工程及自动化专业学号： 0923180 学生姓名：李超指导教师：黄敏（职称：副教授） 2013年5月25日目录一、毕业设计（论文）开题报告二、毕业设计（论文）外文资料翻译及原文三、学生“毕业论文（论文）计划、进度、检查及落实表”四、实习鉴定表无锡太湖学院毕业设计（论文）开题报告题目：汽车变速器设计信机系机械工程及自动化专业学号： 0923180 学生姓名：李超指导教师：黄敏（职称：副教授） 2012年11月12日课题来源自拟科学依据（包括课题的科学意义；国内外研究概况、水平和发展趋势；应用前景等）（1）课题科学意义变速器是关系汽车经济性和动力性的重要部件，变速器在汽车上的作用主要用来改变发动机传到驱动轮上的转矩和转速，目的是在原地起步、爬坡、转弯、加速等各种行驶工况下，使汽车获得不同的牵引力和速度，同时使发动机在最有利的工况范围内工作。在发动机旋转方向不变情况下使汽车能倒退行驶和利用空挡中断动力传递，以使发动机能够启动，怠速，并便于变速器换挡或进行动力输出。双座微型轿车的变速器的设计关系到微型轿车的动力性和经济性的协调，对其更进一步的发展起到至关重要的作用。（2）国内外的研究状况及其发展前景 AMT（Automated Mechanical Transmission）机械式自动变速器，是在原有的机械变速器离合器结构不变的情况下，通过加装微机控制的自动操作机构取代由驾驶员人工完成的离合器分离、接合、摘档与悬挂档以及发动机相应同步调节等操作，最终实现换档全过程操作的自动化。它既具有AT自动变速的优点又保留原来手动变速器MT齿轮传动效率高、成本底、结构简单、容易制造的长处。AMT系统是一个复杂的多输入多输出控制系统、参数多，变化快，时间历程短。当前，比较出名的AMT变速器有马瑞利的F1、selespeed变速器，奥迪的DSG，BMW的SMG。AMT以优越的动力性能，乘坐舒适性和简便的操作，在汽车工业中占有相当的地位。我国几种系列轿车上虽有应用，但限于技术和经济条件，独立开发，成批生产AMT的能力尚不具备。目前，国产轿车上使用的大多是手动变速器(MT)。手动变速器存在起动不平稳、发动机转速变化突然、发动机工况不稳、易对传动系统造成冲击、驾驶员操纵频繁等一系列缺点，满足不了人们的舒适性需求，因而正逐步被自动变速器所取代。目前，自动变速器新车装车率，在美国已达90%以上，日本为73%以上，欧洲则为25%左右。在我国，自动变速器的使用比例不高，但正在迅速上升，主要还是安装在档次较高的轿车上。我国现在使用的自动变速器，多数属于电控液力自动变速器（AT），存在着效率较低、结构和制造工艺复杂、成本较高、维修不方便等缺点。与此相比，AMT由于继承了齿轮传动固有的传动效率高、机构紧凑、工作可靠等优点，并可以实现手动和自动两种模式选择，因此有较强的可靠性和适应性。一些专家认为，它具有比AT更大的发展优势。研究内容本课题需完成的内容是：1. 了解汽车变速器的组成，原理，设计发展动态及我国现状，形成文献综述；2. 完成汽车变速器设计工作；3. 绘制汽车变速器的装配图及其有关零件图。研究计划及预期成果研究计划：2012年11月12日-2012年12月2日：按照任务书要求查阅论文相关参考资料，填写毕业设计开题报告书。2013年1月11日-2013年3月4日：填写毕业实习报告。2013年3月5日-2013年3月8日：按照要求修改毕业设计开题报告。2013年3月9日-2013年3月15日：学习并翻译一篇与毕业设计相关的英文材料。2013年3月22日-2013年4月15日：变速器参数的选择计算。2013年4月16日-2013年4月27日：变速器装配图和零件图。2013年4月28日-2013年5月20日：毕业论文撰写和修改工作。已具备的条件和尚需解决的问题已经找到相关资料对汽车变速器有所了解。相关数据的计算及装配图的画法存在问题。指导教师意见指导教师签名：年月日教研室（学科组、研究所）意见教研室主任签名：年月日系意见主管领导签名：年月日Experimental analysis of a composite automotive suspension arm M. PINFOLD and G. CALVERT (University of Warwick/Rover Group Gaydon, UK) Received 11 November 1992; revised 26 March 1993 In applications where weight saving and parts integration can be achieved, the Rover Group has been investigating the design and manufacture of components from composite materials. The methods used in the different steps in the design- to-manufacture cycle in the high volume automotive industry are relatively well known for a steel component, but are not so well established for a composite component. A design methodology for composites has been emerging in which a principal procedure is design analysis. One of the most established methods of analysisis that using the finite element technique, and this is being supplemented with experimental tests on prototypes using photoelastic analysis and stress pat- tern analysis by thermal emission, coupled with conventional strain gauge moni- toring. Little work has been undertaken to correlate the results obtained from these different test methods and to compare the results with measurements made on an actual component. This paper presents some of the work undertaken concerning the analysis and testing of a composite automotive suspension arm. The results obtained from the three different analysis techniques are compared with experi- mental test results, and their accuracy is discussed. Key words: autmotive suspension arm; stress analysis; finite element method; photoelastic analysis; SPA TE; strain gauges; sheet moulding compound Sol and de Wilde state that composite materials have been used increasingly as structural materials. A reason for this., is that composite materials have high strength to weight and high stiffness to weight ratios which can significantly reduce the weight of a structure. Perhaps the most important feature ofcomposite materials is that their mechanical p:operties can be tailored to meet a specific criterion. However, Johnson et al? suggest that composite design, analysis and fabrication technology must undergo major developments and successful demonstrations before significant structural components will be incorporated in production automobiles and trucks. Composite materials have to compete with steel within the engineering environment. Within the automotive industry this requires a certain amount of technology transfer from places such as the Advanced Technology Centre at the University of Warwick, which work with material manufacturers and automotive engineers to enable understanding about these materials as an alter- native to the traditional materials such as steel. If com- posites are to compete with traditional materials in a real sense, then automotive designers need to be fully aware 0010-4361/94/010059-05 of their strengths and limitations so that they can be one of perhaps many options considered at the concept stage of the design. For this to happen automotive engineers need to catch up on the techniques of designing, testing and manufacturing components from composites. This will include understanding how various methods such as finite element (FE) analysis, stress pattern analysis by thermal emission (SPATE) and photoelastic analysis can be applied to composite components in their design and development. Thus far little work appears to have been undertaken to study whether the results obtained from these different analysis methods correlate with one another or with actual experimental results obtained from testing a real component. In order to study the application and corre- lation of the different analysis methods to composite materials, a composite component - an automotive lower suspension arm - was manufactured. This com- posite component was analysed by the three methods described above and also tested under realistic loading conditions, with experimental results being obtained from strain gauges. 1994 Butterworth-Heinemann ktd COMPOSITES . VOLUME 25 . NUMBER 1 . 1994 59 , B a l l J o i nt Housing Fig. 1 The composite suspension arm DESIGN The existing steel lower suspension arm consists of nine pieces welded together whilst the re-designed composite component-which can be seen in Fig. 1-is a single moulded part. The material used to manufacture the suspension arm was a sheet moulding compound (SMC), comprising a polyester resin bonding agent with a 30% content of randomly arranged short glass fibres and cal- cium carbonate fiIler. The weight of the steel suspension arm is 2.53 kg whilst the re-designed SMC suspension arm complete with bushes and ball joint weighs 1.5 kg. The material properties used for the composite suspension arm in these analyses, obtained from tests carried out at Rovers materials laboratory, were Youngs modulus = 10.5 GPa, Poissons ratio = 0.26 and density = 1.8 x 10 -6 kg mm -3. EXPERIMENTAL TECHNIQUES Prior to undertaking experimental analysis of an actual engineering component, some initial validation work was required to gain confidence in the techniques when applied to sheet moulding compound. Therefore, fiat plates, beams and discs constructed from SMC were ana- lysed under various loading conditions before progress- ing on to the designed component. Most validation tests were carried out using strain- gauged specimens to correlate with the finite element analysis results. Although it is recognized that SMC is not an isotropie material due to some fibre orientation during processing, for the purposes of analysis the mater- ial was assumed to be isotropic. Also, when the actual SMC suspension arm was cut up and examined, signifi- cant fibre distribution was observed in the ribs. It is felt that the correlation between the experimental and analy- sis results validated this assumption in the case of this particular component. Strain gauge tests Before undertaking the experimental test work, the com- posite component was mounted via its rubber mounting bushes onto a relatively infinitely stiff structure. It is very difficult to cover all of the loading conditions when con- ducting experimental tests and thus a worst-case scenario is usually assumed. The worst-case loading condition on suspension components is known as pot-hole brake. This attempts to simulate the vehicle falling into a deep pot-hole at 30 mph with the brakes fully applied at the point of impact. The resultant fore/aft and lateral loads are then calculated based on the weight and velocity of the vehicle. Due to the limitations of the test rig the full pot-hole loads could not be applied to the component, and thus reduced loads with the same resultant direction as the pot-hole loads were applied and the results scaled. The loads applied for the full pot-hole brake case were 24.2 kN in X and 8.2 kN in Y, and for the reduced load case were 5.9 kN in X and 2.02 kN in Y - see Fig. 1. The strain gauges used consisted of six three-axis rosette gauges and 13 single-grid gauges, with 2.5 mm grid lengths, chosen to fit into the radii of the component in an attempt to measure the maximum strain, Gauges were situated near the ball joint housing, where the loads were applied, and around the radii of the body mounting bushes, where the component would be mounted to the car subframe. Additional strain gauges were situated on some of the strengthening ribs and close to the anti-roll bar mounting position. SPA TE analysis Stress pattern analysis by thermal emission (SPATE) can be used to determine the surface stresses of components by studying the small changes in temperature due to cyclic loading conditions. SPATE equipment comprises a detector unit with scanning head, an analogue signal processing unit and a digital electronic data unit. The system works by detecting the minute temperature changes which occur when a structure is cyclically loaded. The infra-red detector scans the structure and correlates the measured output with a reference signal from the loading system. An electronic data processing system correlates the detected stress-induced thermal fluctuations with the loading reference signal. A colour contour map of the sum of the principal stresses (cr + 4) is then plotted, together with a bar chart giving actual values. This correlation of signals effectively eliminates all signal frequencies other than those caused by the loading system, i.e., all ambient temperature fluctua- tions. The SPATE system has a temperature resolution of 0.001C, and a spatial resolution of less than I mm. This type of analysis has been shown by a number of authors TM to also be applicable to non-isotropic mater- ials such as composites, and the small errors (6%) demonstrated from such studies when compared with theoretical or FE results are felt to be due to inaccuracies in the material data used 4. It is apparent from the studies undertaken that the use of thermoelastic stress analysis to evaluate stresses and strains in anisotropic composite materials is more complex than for isotropic materials. However, it has been shown that the technique can provide valuable qualitative information on stress distri- bution, effects of surface defects and crack growth predictions. It has also been demonstrated that, given accurate details of material properties including expan- sion coefficients, quantitative results can be obtained depending upon the degree of anisotropy of the material. Prior to undertaking a full SPATE analysis of the suspen- sion arm it was necessary to determine a calibration factor for the material used. This can be achieved in two ways, either by loading a disc of the material in compres- sion and comparing the SPATE output with the theoreti- 60 COMPOSITES. NUMBER 1 . 1994 cal solution, or by strain gauging directly onto the component in an area of even stress distribution, thereby obtaining a direct comparison with the SPATE output. Both methods were used in this case, but direct calib- ration with strain gauges can overcome a lot of the problems, thus allowing significant information to be obtained from the SPATE output. Photoelastic analysis The majority of photoelastic work investigating the mac- romechanical behaviour of composite materials has been undertaken using photoelastic coating techniques. This is done to avoid the complexities of constructing a photo- elastic model with anisotropic properties and thus con- structing a composite like the original which would lose its transparency and could not be analysed. However, for complex fibre lay-ups this would be the only method of conducting photoelastic analysis, and thus some research has been undertaken investigating the use of the actual composites j7-30. Reasonable results have been obtained from such analyses, but with limitations due to the neces- sity for transparency within the composite. However, the composite component considered in this study was manufactured from SMC and the material was assumed to be isotropic, thus simplifying the creation of a photo- elastic model. A three-dimensional epoxy resin model of the suspension arm was constructed for the photoelastic analysis. The model was then loaded in a representative manner, with scaled-down loads, and subjected to a stress freezing cycle. This involves heating the model up to the mater- ials glass transition temperature, at which point the Youngs modulus changes, and the model deforms under the applied loads. The model is then slowly cooled, avoiding any uneven temperature distribution which could result in unwanted thermal stresses. During the cooling cycle the deformations and stresses are locked into the model. When viewed under polarized light the three-dimensional model is a jumble of interference fringes. In order to determine both magnitude and direc- tion of the principal stresses at any point, a slice is removed and observed under polarized light. By count- ing the fringes the stresses in the model can be calculated and converted into actual stress in the component. This is done by means of proportionality, between the model and component materials, and the loading and dimensio- nal parameters. The lower suspension arm is mounted to the rest of the car via rubber mounting bushes. Investigations were carried out as to the possibility of modelling these mounting bushes. However, experiments with silicon and foam rubbers showed that the required scaled-down stiffness of the bushes during stress freezing at elevated temperatures could not be maintained. The photoelastic analysis thus assumed that the suspension arm was solidly mounted. FINITE ELEMENT ANAL YSIS The composite suspension arm was modelled using approximately 1300 of the STIF45 ANSYS solid ele- ments. The suspension arm is mounted to the subframe via rubber mounting bushes; these were modelled with spring elements to represent the stiffness of the bushes and to create a realistic load distribution throughout the component. Loads were applied to the FE model via beam elements at the ball joint. Three load cases were analysed using the ANSYS FE software. The first load case simulated the full pot-hole brake loads. The second simulated the reduced load used in the tests due to the limitations of the test rig, to enable comparisons with the results from the experimental strain gauge analysis. These two load cases used spring elements to simulate the stiffness of the rubber mounting bushes. The third load case again used the reduced loads but this time omitted the spring elements; i.e., the suspen- sion arm was modelled as being solidly mounted. This third load case was required to correlate with the SPATE and photoelastic analyses. RESUL TS Finite element analysis Analysis of the suspension arm showed that the maxi- mum equivalent stress in the component for the load case considered is very close to the ultimate tensile strength of the proposed material for the pot-hole loading condition, which is the worst loading condition. This means that the component may need to be manufactured from a differ- ent material, or that other materials need to be posit- ioned in areas of high stress to strengthen the component locally. Due to constraints upon the amount of computer disc space available, the number of elements used within the FE model was relatively low and thus the size of the elements within the area of the radii around the body mounting bushes was too large to detect any large stress concentrations. Also, the types of element used around these areas, due to the geometry of the component, were a mixture of brick, wedge and tetrahedral. The latter shape tends to be too stiff to give good results and is not recommended. If more detailed results were required in these areas, then these radii would have to be modelled in greater detail with more and smaller elements in the areas of high stress gradient. Photoelastic analysis The analysis of the photoelastic model of the suspension arm was undertaken assuming that the directions of the maximum principal stresses lay in a horizontal plane through the model in the direction of the fore/aft load. Whilst this is not strictly true in practice due to local geometry effects in certain areas, the assumption gave sufficiently accurate results. If obvious discrepancies were found in particular areas then it was possible to take slices from different planes. Maximum stresses were seen to occur in the vicinity of the ball joint housing and the body mounts. Due to the ability of photoelastic analysis to pinpoint very small areas of high stress, the maximum stress values given by photoelasticity tended to be higher than the strain gauge results. For example, maximum stress levels in the internal radius of the leading body mount were found to be 43 MPa compared with a SPATE value of 26 MPa. This difference can be explained by examin- ing the slice taken through the photoelastic model which shows that the maximum stress only occurs at a position COMPOSITES. NUMBER 1 . 1994 61 Table 1. Stress results (MPa) for full load con- ditions Position Strain gauges FE Photoelastic Ball joint housing 176 165 176 spanning 3 mm and that the stress values either side of the maximum are around 25 MPa. SPA TE analysis The initial SPATE scan showed large bands of stress running across the mounting areas and some confusion as to whether these areas were in tension or compression. The problem was identified as excessive movement in the suspension arm body mounting positions due to distor- tion of the rubber bushes as experienced in the strain gauge tests. SPATE is equipped with a motion compen- sator device if required, which deflects the scanning mirrors inside the detector in time with the oscillations of the test-piece, thereby eliminating the movement. How- ever, in this particular case, the geometry and direction of movement could not be eliminated over the entire area at the same time, and thus it was necessary to remove the rubber bushes and to replace them with aluminium ones. The SPATE analysis was repeated with the solid bushes and showed areas of high tensile stress (26 MPa) along the leading edge and around the inner radius of the leading body mounting position. Unfortunately, no SPATE analysis could be undertaken at the ball joint end of the component as it was obscured by the large loading adaptor required to fit the hydraulic actuator supplying the cyclic loading. COMPARISON OF RESULTS It should be clarified that the stress values quoted in the tables from the strain gauge results were calculated from the rosette gauges to give a value of maximum principal stress. The photoelastic analysis also gives maximum principal stresses unless the values are taken inboard of a free edge in which case they are differences in principal stresses (o.- o-,). SPATE analysis gives an output in the form of the summation of the principal stresses (or. + a2) whereas the FE output can be in any form required (in this case yon Mises). Due to the geometry of the compo- nent and the way in which the loads were applied, the values of or2 and cr 3 were always small, and thus direct comparisons could be made between the different analy- sis methods without further conversion. Table l compares the results obtained for the maximum pot-hole load conditions. The maximum stress values all occur at the ball joint area and correlate very well. These resultant stresses for the strain gauges and photoelasti- city were calculated from the results obtained for the reduced load. The model stress was multiplied by a load- ing factor as the ratio between the fore/aft and lateral loading remained constant and in the same proportion as the full pot-hole brake load applied to the suspension arlTI. The results of the analyses undertaken with reduced Table 2. Stress results (MPa) for redTJced loads with mounting bushes Position Strain gauges FE Inner radius of body 25 20 mount Ball joint housing 49 40 Table 3. Stress results (MPa) for reduced loads without mounting bushes Position FE SPATE Photoelastic Inner radius of body 22 mount Ball joint housing 30 26 43 (25) 42 (25) loading but with the mounting bushes included can be seen in Table 2. Table 3 presents the results of the analyses undertaken with reduced loading and without the mounting bushes being used. The stress given by the photoelastic analysis is concentrated at a very small point whereas the stress given by FE analysis is averaged over a relatively large area. In the case of the photoelastic results, an average of the nominal stresses on both sides of the concen- tration point is also quoted in brackets to give a fairer comparison. Compared with the strain gauge results, the values given by SPATE are very similar for the maximum stress. In theory SPATE should be more effective than strain gauges when investigating stress concentration effects, as it is measuring values over a smaller area depending upon its distance from the object during scanning. In this case the measurement point of SPATE was set at I mm diameter compared with a 2.5 mm grid length on the strain gauges. However, in this instance the differences were small and movement of the component during load cycling inevi- tably blurred the image to some extent, thus the differ- ence in resolution was probably negligible. CONCLUSIONS All the analysis techniques used-i.e., SPATE, photoelas- tic, finite element and strain gauge analyses-showed that the area of highest stress was in the vicinity of the ball joint housing. All of the methods also showed signi- ficant stresses in the areas of the body mounting bushes. However, the FE analysis did not always accurately identify these high stresses due to the size of the elements within these areas being too large. If more detailed results were required for these areas from the FE analysis, then they would have to be modelled in more detail with a greater number of elements in the areas of high stress gradient. The overall pattern of stress distribution was the same for each analysis technique. The differences 62 COMPOSITES. NUMBER 1 . 1994 obtained between the strain gauge and the FE results can be explained by the accuracy of the gauges. As noted by Autio el al. 3t, the accuracy of strain gauge measurement depends upon many factors. An error of 5-10% is usually caused by the strain gauge itself and the measure- ment system, whilst further inaccuracies may be caused by orientation, location and gluing of the gauge. Strain gauges need a reasonably large area of uniform stress to obtain accurate results. In the case of the suspension arm this requirement was not always met due to the many changes in geometry, resulting in either steep stress gradients or areas of relatively very low or insignificant stresses. All the experimental techniques used presented similar pictures of stress distribution within the composite sus- pension arm. The methods all highlight the high tensile stress at the ball joint area (except for SPATE for the reasons already mentioned), as well as the high stresses around the body mounting bushes. If the areas of high stress are examined, they are all concentrated around geometry changes as would be expected. The photoelas- tic analysis effectively demonstrates how concentrated these stresses are and the small area that they cover. In contrast, the FE analysis consists of elements spanning several millimetres, thus averaging the stress intensity over that length and consequently presenting a signifi- cantly smaller value. Overall the experimental techniques give a good degree of correlation The patterns of stresses generated by photoelastic, SPATE and finite element analysis for the suspension arm were observed to be all very similar. It can also be concluded that the SPATE technique provides a valuable, non-contacting method for the determination of stresses within composite materials. REFERENCES 1 Sol, H. and de Wilde, W.P. Identification of elastic properties of composite materials using resonant frequencies Proc hit Confon Computer Aided Design in Composite Material Technology. South- anrptot, UK. 1988 (Computational Mechanics Publications, 1988) pp 273 280 2 Johnson, C.F., Chavka, N.G., Jeryan, R.A., Morris, C.J. and Babh- ington, D.A. Design and fabrication of a HSRTM crossmember module Proe Third Advanced Composites Conference. Detroit. M. USA (ASM International. September 1987) pp 197-217 3 Machin, A.S. Sparro,% J.G. and Stimson, M.G. The thermoelas- tic constant SPIE 731 (1987) pp 26-31 4 Stanley, P. and Chan, W.K., The application of thermoelastic stress analysis to composite materials J Strum Anal23 No 3 (1988) pp 137 143 5 Bowles, D.E. and Tompkins, S.S. Prediction of coefficients of thermal expansion for unidirectional composites J Composite Mater 23 (1989) pp 370 388 6 Potter, R.T. Stress analysis in laminated fibre composites by ther- moelastic emission SPIE 731 (1987) pp 110-120 7 Jones, R., Tay, T.E. and Williams, J.F. Thermomechanical behav- iour of composites in Proc US Army Workshop on Composite Materials Response: Constitutive Relations and Damage Mechanks edited by G.C. Sim. G.F. Smith, I.H. Marshall and .J. Wuh (Elsevier, New York, 1988) pp 49 59 8 Potter, R.T. and Greaves, L.J. The application of thermoelastic stress analysis techniques to fibre composites SPIE 817 (1987) pp 134-146 9 Kageyama, K., Ueki, K. and Kikuchi, M. Thermoelastic technique applied to stress analysis of carbon fibre reinforced composite materials Proc Sixth hit Congress on Experimental Mechanics. Portland, OR, USA, 1988 pp 931-936 10 Owens, R.H. Applications of the thermoelastic effect to typical aerospace composite materials SPIE731 (1987) pp 74-85 I 1 Cox, B.N. and Petit, D.E. Non-destructive evaluation of compo- site materials using the SPATE technique Proe SEM Spring Conf on Experimental Mechanics. 1987 (Society for Experimental Mechanics, Bethel, USA) pp 545-552 12 Bakis, C.E. and Reifsnider, K.L. Non-destructive evaluation of fibre composite laminates by thermoelastic emission in Review o

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