测试 测量残余应力的透明塑料2007/12/22
Residual stresses and molecular orientation throughout a product provide important information about how that product will perform.残余应力及分子取向整个产品提供了重要的资料，如何生产表演。 The presence or absence of residual stresses is a major concern in the production of plastics for applications such as medical devices and packaging, instrument manufacturing, optical components, and others.在场或缺席的残余应力是一个重大问题，在生产塑料的应用，如医疗仪器及包装，仪器制造，光学元件等。
Residual stresses are introduced by nearly all techniques used for polymer manufacturing.残余应力介绍了几乎所有技术用于聚合物制造。 They form as a result of extrusion, stretching, drawing, molding, casting, joining, or other strain-inducing processes.他们形成是由于挤压，拉伸，绘画，工艺，铸造，连接，或其他应变诱导过程。 Strains can be introduced by differential shrinkage, uneven cooling, or nonuniform flow.株，可引入微分收缩，冷却不均匀，或不均匀流量。
Stress evaluation can be quantified using a compensator. 强调评价的，可量化的使用补偿。 Photo: Strainoptic Technologies. 图片： strainoptic技术。
In some polymers, the process-induced orientation enhances mechanical properties.在一些高分子材料，工艺引起的方向，提高力学性能。 For example, biaxial orientation of PET or polystyrene film ensures improved strength and formability. 1 In other instances, residual tensile stress must be avoided, since the surface develops chemical susceptibility and cracks will occur in the presence of solvents and detergents.举例来说，双轴取向的PET或聚苯乙烯薄膜确保改善强度和成形性。 一日在其他情况下，残余拉应力，必须设法避免的，因为表面上的发展，化学敏感性及裂缝将出现在在场的溶剂和洗涤剂。 This is of particular concern to manufacturers of medical devices or containers for pharmaceutical products.这是特别令人关切的，以厂家的医疗器械或容器为药剂制品。
In a production environment, processes can change for a variety of reasons.在生产环境中，过程可以改变，出于各种原因。 Subtle increases in production rates or changes in cooling rates, temperature, or material composition can cause new problems.微妙增加产出率或改变冷却速度，温度，或材料成分，可以产生新问题。 Inspectors may find, for example, that molded polystyrene products warp or twist within a short time after emerging from the press, that machined acrylic surfaces crack, that oriented film can't be drawn without cracking, or that products discolor.检查人员可能会发现，例如，在模塑聚苯乙烯制品翘曲或扭曲很短的时间内出现后，从报章，即加工压克力表面裂纹，即面向电影不能得出无开裂，或产品变色。
These types of problems can often be traced to residual stresses or stress relaxation.这些类型的问题，往往可以追溯到残余应力或应力松弛。 Residual stresses must be evaluated at every stage of the product cycle, from product design to full production.残余应力必须加以评估，在每个阶段的产品周期，从产品设计到全面投入生产。 By carefully monitoring stresses, process and quality controllers help maintain both product quality and productivity, using direct measurements to assess the suitability of various approaches to eliminate undesirable stresses or to induce beneficial ones.仔细监测讲，工艺和质量控制人员帮助维持双方的产品质量和生产率，用直接测量，以评估是否适合各种办法，以消除不良讲或诱使有益的。 The uniformity and distribution of stresses in a product must also be carefully evaluated.均匀性和应力分布在一个产品还必须仔细评估。
While the effects of stresses in various materials are often reviewed and discussed, the methods and instruments available to evaluate stresses are not always well known or understood.而效果讲，在各种材料往往审查和讨论，方法和手段，以评估讲并不总是知名或理解。 Several methods are currently available to evaluate residual stresses in plastic parts.几种方法，目前可用来评估残余应力的塑料零件。 Users must first choose between destructive and nondestructive methods.用户首先必须选择具有破坏性和非破坏性的方法。 Most destructive methods are time-consuming, hard to use, difficult to interpret, and incapable of providing quantitative information for comparative purposes.最具破坏性的方法，耗费时间，很难使用，难以解释，并无法提供定量的资料，以便进行比较。 For nontransparent plastics, choices are limited to destructive tests such as layer removal, section removal, and stress-corrosion tests.对于缺乏透明度，塑料，选择是有限的破坏性试验，如层去除，第移除，以及应力腐蚀的考验。
Figure 1. 图1 。 Schematic illustrating the principle of polarized light transmission. 示意图说明的原则偏振光传输。 S 1 and S 2 represent the principal stresses at a point, and R is the retardation between vibration along S 1 , S 2 . s 1和2.0代表主应力在一个点，而R是迟缓之间的振动沿s 一 ，西二 。
For transparent plastics, nondestructive methods offer the better choice.为透明塑料，无损检测方法提供了更好的选择。 The methods discussed in this article apply the concept of photoelastic response of transparent materials, which has been known for well over a hundred years.该方法的讨论，在这篇文章中运用的概念，光反应的透明材料，它已经出名远远超过一百年。 Brewster's Law states that the index of refraction in a strained material becomes directional, and that the change of the index is proportional to stresses.布鲁斯特的法国表示，折射率，在紧张的物料定向，并改变该指数是成正比讲。 Plastic processing methods orient molecules and introduce birefringence--an orientation in the index of refraction--that can be effectively used for quality control.塑料加工方法东方分子和引进双折射-一个方向，在折射率-能够有效地用于质量控制。
MEASURING BIREFRINGENCE 测量双折射
Birefringence, or optical anisotropy, is related to the elastic stresses and orientation release stresses that prevail in oriented polymers (see Figure 1), so that双折射，或光学各向异性，是关系到弹性应力和定向释放强调占上风，在面向聚合物（见图1 ） ，使
(n 1 n 2 ) = C (S 1 S 2 ) , （ 一氧化二 ） = C的（ 1秒2 ） ，
where n 1 n 2 is in-plane birefringence, C is the material stress constant obtained from existing tables or by calibration, and S 1 S 2 is the difference in orientation stresses.其中N 一氧化二是在平面双折射， C是材料应力不断得到现有表或校准，和S 1秒2的差异方向讲。 As a result of the relative difference in their velocities, polarized rays vibrating in planes of principal stresses S 1 and S 2 will emerge with a relative phase shift and produce color interference fringes or multicolored bands.由于这一相对差，在其速度，偏振射线振动，在飞机的主应力s 一和S 2将会出现一个相对的相移，并产生彩色干涉条纹或彩色阶。 After crossing a thickness t, the relative retardation R between two polarized rays becomes之后穿越厚度t时，相对迟缓r之间的两个偏振射线变成
R = t (n 1 n 2 ) = C t (S 1 S 2 ) . r =吨（ 一氧化二 ） =的CT （ 1秒2 ） 。
Measuring the retardation R thus allows for the measurement of the birefringence at any desired location, so that测量迟缓r ，因此，可以用于测量的双折射在任何想要的位置，使
(n 1 n 2 ) = R t = C (S 1 S 2 ) . （ 一氧化二 ） = r吨= C的（ 1秒2 ） 。
Table I. Color versus retardation. 表一，彩色银两迟钝。
QUALITATIVE EVALUATION 定性评价
The most basic way to look at stresses in clear plastics is to place a sample of the material between two illuminated polarized sheets.最根本方法看讲清楚塑料，是把样本的物质之间的两个发亮的偏振板。 When these elements are properly aligned, the stress pattern becomes visible.当这些要素得到妥善不结盟，应力格局变得可见。 In some cases, the color fringes can be used to evaluate birefringence, since each color band correlates to the degree of stress in the inspected sample.在某些情况下，彩色条纹，可以用来评估双折射的，因为每种颜色波段关联度应力在检查的样本。 A color-versus-retardation chart is used to interpret the observed pattern (see Table I).彩色银两迟缓图是用来解释观察到的模式（见表一） 。
In a great majority of applications, the color pattern is difficult to interpret and can be misleading, since a "red" or a "green" fringe could be observed at multiple stress levels.在大部份的应用，色彩模式，是难以解释，并会导致误解，因为"红色"或"绿色"的边缘，可以观察到在多重压力水平。 However, this method can be very useful for a simple identification of maximum stress areas.不过，这个方法可以非常有用的一个简单的识别的最大应力区。 Today's quality control requirements, however, generally call for precise, reproducible, quantitative measurements that cannot be satisfied using this basic approach.今天的质量控制要求，但是，从总体要求精确，重复性好，定量测量，即不能满足于用这个基本方针。
QUANTITATIVE MEASUREMENTS 量化标准
Birefringence is easily measured quantitatively, and both off-line and on-line instruments are available to ensure product quality and maintain production uniformity.双折射是容易衡量，在数量上的，双方在离线和在线仪器，可确保产品质量，保持生产一致性。 The type of instrumentation selected largely depends on the application, degree of accuracy or reproducibility required, and level of operator skill.该类型的仪表选定在很大程度上取决于应用，其准确程度或重复性需要程度，以及操作人员的技能。
Measuring birefringence can be accomplished using a "compensator," a calibrated, graduated wedge that is placed in series with the measured item.测量双折射能够做到用"补偿" ，校准，毕业于楔这是摆在一系列与实测项目。 The operator adjusts the wedge until a black fringe appears at the point of interest, as shown in the photograph on page 16.经营者可以调整楔，直到一个黑色条纹会出现在兴趣点，显示在照片中第16页。 The black fringe becomes visible when the retardation in the compensator is equal and opposite to the retardation at the point of interest in the sample.黑色条纹可见当迟缓，该补偿是平等的和对面的迟缓，在兴趣点中的样本。 A scale then supplies a quantitative reading.其规模，然后提供了一个定量读。 Measuring with a compensator is a standard ASTM test procedure 2 and is a particularly effective laboratory tool for quality control of clear plastics.测量与补偿器是一个标准的ASTM标准测试程序2 ，是一种特别有效的工具，实验室的质量控制明确塑料工业。 This method is usually preferred over the so-called "Senarmont" or "analyzer rotation method," which can be difficult to learn and even more challenging to apply to high-stress products.这种方法通常是首选超过了所谓的" senarmont "或"分析器旋转法" ，我们不能因此就难以了解和更有挑战性的，以适用于高应力产品。
PC-BASED INSTRUMENTATION 基于PC的仪器
In today's industrial environment, quality production is required for survival.在今天的产业环境，优质的生产需要生存。 This is particularly true in the field of medical plastics.这一点尤为如此，在外地的医疗塑料。 In most companies, quality production dictates not only an ongoing upgrade of QC procedures, but also standardization of practices, calibration of measuring tools, and extensive training of personnel.在大多数公司，高质量的生产，决定了不仅是一个不断升级的质量控制程序，而且标准化的做法，校准测量工具，并进行广泛的人员培训。
Figure 2. 图2 。 PC-based spectral contents analyzer system. 基于PC的频谱分析仪的内容体系。
The use of PC-based methods for measuring stress helps simplify the implementation of quality control procedures.使用基于PC的测量方法应力有助于简化实施质量控制程序。 In particular, these methods can reduce the need for skilled operators and provide far greater speed, consistency, and precision.特别是，这些方法可以减少需要熟练的操作，并提供更大的速度，一致性和精度。 QC automation also offers a means to record and store measurement files for retrieval and to analyze trends over time.质量控制自动化，还提供了一个手段，以记录和存储测量档案检索和分析一段时间内的趋势。
Measuring can be greatly facilitated when a PC-based sensor is coupled with spectral contents analysis (SCA).测量，可以极大地便利时，基于PC的传感器，再加上谱内容分析（协议） 。 This technique works similarly to ordinary visual observation.这一技术工程同样普通的视觉观察。 First, polarized light is passed through the sample to be analyzed.首先，偏振光通过样品加以分析。 A scanner replaces the human eye, and channels light through a fiber-optic cable to a spectral contents analyzer spectrophotometer, as shown in Figure 2.扫描仪可以取代人眼，渠道光透过光纤电缆，一谱内容分析仪分光光度计，如图2所示。 The transmitted light intensity I is related to both retardation R and wavelength * i :该透光强度I是有关双方迟缓R与波长* 我 ：
I i =(I 0 )(sin 2 )( ¼R * i ).在我 = （ 1 0 ） （单2 ） （ ¼ r *时一 ） 。
Measurements of the transmitted light intensity are processed at multiple wavelengths * i , allowing for high-speed, totally automated measurements of retardation that are conveniently independent of the direction of stress. 3 Readout is nearly instantaneous, and can be reported for any selected point or along a scanned line.测量的透光强度进行处理，在多波长* 我 ，让具有高速，完全自动测量功能的迟缓是方便，独立的方向的压力。 三读，是近瞬时的，可报任何选定点或沿扫描线。
Figure 3. 图3 。 Off-line PC-based SCA stress scanner. 脱线的基于PC的政制事务局局长强调扫描器。
Figure 3 illustrates an off-line measuring station using the SCA method; this type of system can also be installed on-line.图3说明了一个离线计量站采用协议方式;这种类型的系统也可以安装上线。 For on-line installations, scanners can be mounted on a carriage as part of a linear-motion system, registering measurements across sheets, film ribbon, molded test samples, or finished parts.为上线装置，扫描器，可以安装在一个车厢的一个组成部分直线运动系统，测量，登记全国床单，电影丝带，浇铸试验样品，或成品零件。 After scanning an item, SCA systems show a graph of results (see Figure 4) that can be printed or stored.扫描后的一个项目，政制事务局局长系统的计算表明，一个图的结果（见图4 ）表示，可以打印或保存。 Reporting is immediate, making real-time process control a reality.报告是即时，使实时过程控制成为现实。
Figure 4. 图4 。 Retardation-versus-position graph produced with an SCA stress scanner. 迟缓尖锐对立的立场，图形制作与政制事务局局长强调扫描器。
MEASURING BIAXIAL ORIENTATION 测量双轴取向
In biaxially oriented products--such as blown tubular geometries or films produced by stretching in two directions--orientation stresses (S 1 and S 2 ) can be very large, but the difference (S 1 S 2 ) can be very small or even zero, leaving the in-plane birefringence (n 1 n 2 ) very small.在双向拉伸产品-如吹管状构型或电影制作的伸展在两个方向-定向讲（ 1和2 . 0），可以非常大，但差别（1秒2 ）可以很小，甚至零，留下在平面双折射（ 一 N 2 ）的非常少。 This presents a challenging measurement situation.这是一个具有挑战性的测量的情况。
Methods of measuring birefringence in biaxially oriented materials have been developed by Stein, Redner, and Drucker. 46 In these methods, light crosses the material at an angle, yielding birefringence in an oblique plane.测量方法的双折射在双向拉伸材料已研制施泰因， redner ，德鲁克46 ，在这些方法，光穿过物质上的一个角度来看，高产双折射在一个斜面。 Combining the retardation measured in the normal and oblique paths will yield both in-plane and out-of-plane birefringence.结合迟缓测量，在正常和斜路径，将收益率无论是在平面和出平面双折射。
Figure 5. 图5 。 PC-based stress scanners for biaxially oriented materials measure retardation in both normal and oblique paths. 基于PC的应力扫描器为双向拉伸材料举措迟缓，在正常和斜路径。
On-line and off-line scanners for QC of biaxially oriented films usually contain both normal and oblique light paths, combined with orientation-angle measurements. 7 Figure 5 shows an example of an off-line SCA measurement system for biaxially oriented film.上线与离线扫描器为御用大律师的双向拉伸薄膜中通常含有正常及斜光路径，加上方向角测量。 7图5显示的一个例子是一个离线协议测试系统的双向拉伸薄膜。
INSPECTION OF ANNEALED PARTS 检查退火零件
Materials like PMMA, optical elements, or other annealed plastics exhibit very low birefringence activity and thus require a different approach.材料如聚甲基丙烯酸甲酯，光学元件，或其他退火塑料很低的双折射活动，因此需要不同的方法。 For these materials, measured birefringence in a thoroughly annealed sample can be smaller than 2 * 10 -6 .对于这些材料，测定双折射在彻底退火样品可以小于2 × 10 -6 。 Even a small level of birefringence hampers optical properties and product performance.即使是一个小级别的双折射阻碍了光学性能和产品性能。
The annealing processes must be carefully and frequently monitored to ensure that residual stresses do not exceed tolerance limits.退火过程中，必须仔细，并经常监测，以确保残余应力不超过容许范围内。 This is particularly true of plastic materials of varying thicknesses or strong curvature.这是特别真实的塑胶原料的不同厚度或强烈曲率。 Undesirable stresses can also develop in machined parts.不可取的，可以讲，还可以发展在机械零件。 Similarly, stress concentrations around seals or welds can cause product failures, and therefore must be closely monitored (see Figure 6).同样，应力集中靠近海豹或焊缝可能导致产品失效，因此必须密切监测（见图6 ） 。
Figure 6. 图6 。 Examination of joint, seal, and weld stresses in a medical device. 考试的联合，印章，及焊接应力的医疗设备。
Figure 7. 图7 。 PC-based digital image analysis system. 基于PC的数字图像分析系统。
Visual methods for inspecting annealed parts often include a microscope and compensator.视觉方法检查退火零件往往包括显微镜和补偿。 For this type of inspection, a PC-based system using digital image analysis of the photoelastic image is preferred.对于这种类型的检查，一个基于PC的系统中的应用数字图像分析的光弹图像是首选。 Such a system offers consistent, precise, automated full-field inspection, with a maximum range of approximately 300 nm.这样一个系统提供了一致的，精确，自动化的全面实地考察，其最大射程大约为300 nm 。 The system acquires a full-field image of the inspection area using a polarimeter setup and a CCD camera with the appropriate magnification (see Figure 7).该系统具有全领域的形象，检查区用偏振设置和CCD相机与适当放大（见图7 ） 。 The CCD camera captures the image produced by the polarimeter. CCD相机拍摄的图像制作，由偏振。 A computer-based frame grabber splits the image into 512 * 512 measurement points (pixels), and the light intensity of each point is measured.以计算机为基础的帧抓取分裂的形象到512 * 512个测量点（像素） ，以及光照强度的每一个点，是衡量。 This light intensity is related to the retardation R and to the source intensity I 0 , so that这个光照强度，是关系到迟缓R和向源强度0 ，使
I=(I 0 ) (sin 2 ) ( ¼R * ) + I B , = （一0 ） （单2 ） （ ¼ r *时） + b ，
where I B is the amplifier zero or background, measured in absence of the specimen.我的B是放大器零或背景，在衡量缺乏标本。 Quantitative measurements are automatically computed by the system, and the operator selects the desired output format.量化标准是自动计算该系统，并将经营者选择理想的输出格式。 Measurements can be reported for a single point or along a line, or a full-field stress map can be selected for output.测量，可以报告为单点或沿一条线，或全额场应力图可以选择输出。 Each color of the full-field stress pattern corresponds to a narrowly defined stress range.每种颜色的全职场应力模式对应一个狭义界定应力范围。
Figure 8. 图8 。 Comparing residual stress in two copolymers using digital image analysis. 比较残余应力的两个共聚物用数字图像分析。
Figure 8 shows a digital image analysis system full-field stress map comparing residual stress in lenses produced from two different copolymers.图8显示的数字图像分析系统满场应力图比较残余应力的镜片制作，由两个不同的共聚物。 Useful in product development and materials analysis research, this type of system is also effective for day-to-day quality control; when supplied with a pass/fail software feature, operators can quickly and easily identify reject items.有用的，在产品开发和材料的分析研究，这种类型的体制，也是有效的日常质量控制;当提供一个通过/失败软件功能，运营商可以快速，轻松地找出拒绝的项目。 Inspection of this kind is also used to examine seals and welded joints between the same or different annealed materials.检查这种也被用来研究海豹和焊接接头之间的相同或不同的退火材料。
CONCLUSION 结论
Whatever the instrumentation or method used, the inclusion of stress measurement in QC procedures should be fundamental in monitoring, identifying, and fixing stresses before parts fail.无论仪表，或用何种方法，列入地应力测量在质量控制程序应基本监测工作，发现问题，并订定讲前部分失败的。 When stresses are identified, a variety of processing changes can be evaluated to improve product performance.当讲确定后，各种处理的变化，可以评价，以便改进产品性能。 The amount of residual stresses may point to one solution, while the distribution of stresses may suggest other required processing alterations.数额的残余应力可能指向一个解决方案，而应力分布，可以建议其他所需加工改建。 Depending on the production method, changes in material, temperature, cooling rates, airflow, gate placement, part thickness, and numerous other factors will cause variations in residual stresses or their distribution throughout a plastic part.依赖于生产方式的变化，材料，温度，冷却速度，气流，门配售，部分厚度，以及其他许多因素会导致变异的残余应力或其分布全国各地塑料零件。
When the perfect processing combination is identified, defects are substantially reduced.当完美的处理组合是确定的，缺陷的现象大幅减少。 Parts will maintain optical clarity, stability, and resistance to environmental stress factors.部分将保持清晰透明，稳定和耐环境应力因素。 Whether a manufacturer is simply putting together a design concept, developing prototypes, or in full production, a commitment to inspection of residual stresses will greatly contribute to product quality and consistency.不论制造商是简单地放在一起的设计理念，开发原型，或全面投入生产，全心全意为检查残余应力将大大有助于产品质量和一致性。
REFERENCES 参考文献
1. 1 。 Bakerdjian Z, "Preparation of Balanced HDPE Blown Films," SPE Technical Papers, 23:452454, 1977. bakerdjian z ， "配制均衡吹高密度聚乙烯薄膜， "固相萃取技术文件， 23:452454 ， 1977 。
2. 2 。 Standard Test Method D 4093-95 for Photoelastic Measurement of Birefringence and Residual Strains in Transparent or Translucent Plastic Materials, West Conshohocken, PA, ASTM, 1995.标准测试方法d 4093-95为光弹测量双折射和残余株，在透明或半透明的塑胶物料，西conshohocken ，坝，美国ASTM ， 1995 。
3. 3 。 Redner AS, "Photoelastic Measurement by Means of Computer-Assisted Spectral-Contents Analysis," Experimental Mechanics, 25(2):148153, 1985. redner作为， "光弹测量手段，以电脑辅助谱内容分析" ，实验力学， 25 （ 2 ） ： 148153 ， 1985 。
4. 4 。 Stein RS, "Measurement of Birefringence in Biaxially Oriented Films," Journal of Polymer Science, 24:383386, 1957.施泰因卢比， "测量的双折射在双向拉伸薄膜， 1999论文"高分子科学， 24:383386 ， 1957 。
5. 5 。 Redner AS, "A New Oblique-Incidence Method for Direct Photoelastic Measurement of Principal Strains," SESA Proceedings, 21(1):6769, 1963. redner因为， "一个新的斜入射法直接测量光的主要品种， "塞萨诉讼， 21 （ 1 ） ： 6769 ， 1963 。
6. 6 。 Drucker D, "The Method of Oblique Incidence in Photoelasticity," SESA Proceedings, 12:5160, 1955.德鲁克文字D "的方法，斜入射在光弹， "塞萨诉讼， 12:5160 ， 1955 。
7. 7 。 Redner AS, "Measurement of Biaxial Orientation and Orientation Release Stresses in Polystyrene Film Production," International Conference on Photoelasticity Proceedings, Kent, UK, Sira Communications Ltd., pp 124127, 1993. redner作为， "测量的双轴定向和定向释放应力聚苯乙烯薄膜生产中， "国际会议上光弹诉讼，肯特，英国，西拉通信有限公司，聚丙烯124127 ， 1993 。
