一种动光弹模型材料的制作方法及其应用

基于#618环氧树脂、甲基六氢苯酐、促进剂DMP-30、环氧树脂消泡剂四种原料,提出制作光弹性模型的新配方和新方法,并利用单轴压缩实验、电测法和动态光弹法分别测定了制作的光弹模型的动态力学参数。新方法工艺简单,制作周期短,对人体无害。制作的光弹模型初始应力小,表面光洁,质地均匀,透光性好,光学灵敏度高,具有良好的机械加工和切削性能。通过三点弯曲梁冲击实验,得到了清晰的光弹等差条纹图像,验证了该配方和方法制作的模型可以应用于动态光弹性实验。     

复合材料光弹性分析的工程方法

本文在推导均衡光弹性复合材料应力(应变)—光定律的基础上,导出了均衡光弹性复合材料的近似应变—光定律。然后加以推广,提出适用于一般光弹性复合材料的近似应变—光定律.精度分析及实验验证表明:作为工程计算,在采用本文推荐的参数时,光弹性复合材料可视作各向同性材料进行光弹性分析。     

正交异性动态光弹性方法的几个基本问题的研究

文章对适用于动态研究的正交异性光弹性复合材料进行了分析，详细说明了光弹性复合材料中残余双折射的确定方法；基于静态下Ｈｙｅｒ和Ｌｉｕ应力－光性定律，提出了正交异性动态应力－光性定律，并对正交异性材料的动态力学参数及动态光弹性常数给出了实用的标定方法；最后，利用三个单轴压缩试件（０°，９０°及４５°），采用动态应变测量方法，证实了单轴应力状态下正交异性动态应力－光性定律的正确性。     

Use of electrical-resistance strain elements in three-dimensional stress analysis

A method for constructing resistance-wire strain gages which may be imbedded in a plastic model without materially altering the stress pattern in the model is presented. The methods used to calibrate the gages and the photoelastic tests made to investigate the effect of the gages on the stress pattern are described. The application of this new three-dimensional technique to evaluate the stress distribution in a thick-walled cylindrical pressure vessel is discussed. Correlation between experimental data and calculated values is given.     

Mechanical characterization and modeling of polymeric materials for high-pressure sealing

The choice of a proper material is probably the most critical factor in the design of seals able to withstand extremely high pressure, and knowledge of material mechanical properties is essential for the finite-element model (FEM) simulations needed to understand and optimize seal behavior. The aim of this work is the mechanical characterization of polymeric materials for ultrahigh-pressure sealing applications (600 MPa). After a short presentation of seal design and materials commonly used, the testing of four thermoplastic materials is described: PA6, H-TPU and UHMWPE reinforced with glass or ceramic microspheres to enhance wear resistance. Uniaxial tension and compression, shear and planar tension test were performed as well as a stress relaxation test to gain information about viscoelastic effects. Experimental data are then discussed and elasto-plastic and hyperelastic constitutive models for polymeric materials reviewed, focusing on the application of these models at high pressure. The Young's modulus and yield strength are very sensitive to hydrostatic pressure for polymeric materials and a proposal for the implementation in the FEM of this effect is illustrated.     

Development of a Hybrid Method of Reflection Photoelasticity for Crack Problems in Anisotropic Plates

Reflection type photoelastic experiment can be used more effectively than a transmission type photoelastic experiment especially in industrial fields. Moreover, composite materials have been widely used in engineering applications and structures because of their outstanding advantages which individual isotropic components do not have. The development of these materials requires a promising technique such as reflection photoelasticity to analyze their behaviors in service. Unfortunately, there are few experimental studies based on this technique. Therefore, a hybrid method based on this technique was developed in this research to analyze the fracture behavior of opaque anisotropic materials. The application of this method will help to understand the fracture behaviors of anisotropic materials used in engineering components and structures. The validity of this method was verified by comparison of the results obtained from this method with ones obtained from the hybrid methods for isotropic material on the same isotropic specimen. The reflection type photoelastic experiment for orthotropic materials was then applied to orthotropic plates with a central crack of various inclination angles. Using this hybrid method for anisotropic materials, stress intensity factors and separated stress components were obtained at the vicinity of the crack-tip in orthotropic plates from only the isochromatic fringe patterns of the isotropic coating material.     

Tensile and compression testing under high pressures,and fluid-to-fluid extrusion of metals

The late Percy W. Bridgman emphasized the large increases in ductility made possible by a high-pressure environment. He also showed that many brittle materials became ductile under high pressures and could be plastically deformed without cracking or fracture. This work has led to tensile and compression testing as relatively routine under fluid pressures up to about 450,000 psi. Information so generated is employed to determine pressure levels at which working under pressure can be done without fracture or cracking. There is presented in this paper information on tensile and compressive tests under pressure and on application to the fluid-to-fluid extrusion process.     

动光弹性法中若干问题的近期研究进展

为适应解决工程中越来越多动态力学问题的需求,在近年来计算技术、高速摄影技术、图像处理技术等迅速发展的基础上,本文对动光弹性法中的若干关键问题近期的研究进展作简要叙述。内容包括：(1)新型数字式动光弹仪的研制,这种光弹仪以激光光源取代多火花放电式光源,实现了连续、实时的强光源,以高速摄影系统取代原来多个相机的拍摄系统,利用计算机软件对整个系统装置进行控制,实现了图像的优化采集,为数字化处理图像提供了有力的保障;(2)静、动光弹性材料的探索,重点介绍了动光弹模型材料的新配方和新工艺;该工艺采用硅橡胶模具,无需使用脱模剂,利用常温固化形成环氧树脂板材或块体,可精密浇注,一次到位,材料具有良好的光力学性能;(3)动光弹的工程应用,利用新型数字式动光弹仪器以及环氧树脂浇注新的工艺进行了实际工程的研究,取得了一些有价值的结果。文中以某舰船中的部件舵机和基座及海岸工程中港口关键部位柱、柱帽连接部位为实例进行了动应力分析,证明了新研制的仪器和新材料均满足试验要求,有广阔的发展前景。     

软弱地基上拱形围堰的光弹性研究

介绍目前水利水电工程设计中常遇到的软弱地基上拱形围堰的光弹性试验研究.其中包括异弹模组合模型浇制与粘结、水砂压荷载模拟及主要试验成果. 文中分析了在上述荷载作用下拱堰的受力特点和工作状态,探讨了低弹模基础和边界条件不对称性对堰体内力的作用和影响,提出了进一步改善应力和稳定条件的途径和措施.     

光弹性粘结材料的试验研究

在三维光弹性试验中，为模拟具有软弱夹层或由不同岩土构成的复杂地基问题，需用粘结材料将各种不同弹模的型材粘结成组合模型。本文提出三种新型光弹性粘结材料，并通过试验阐明其光学和力学性能，分析比较了它们的主要特点和差异，同时探讨了其粘结应力的作用与效果。     

Use of the holophotoelastic method for three-dimensional stress analysis

This paper suggests a new manufacturing and freezing technology for photoelastic materials which produces stress-optical coefficient ratios,B/A, different from ?0.5. By means of the absolute relardation method and the immersion method, the complete experimental stress solutions for the sphere under diametrical compression and for the closure head of a high-pressure vessel have been found.     

Stress-optic law in a single crystal and its application to photo-anisotropic elasticity

A general stress-optic law in a plate made of a single crystal with birefringence is developed, the plate has an arbitrary crystallographic direction. From the general stressoptic law, a condition for obtaining stress distributions in the plate under a plane stress state is derived. Some optical and mechanical properties when the plate is used as a photoanisotropic model are also explained. Experiments on silicon beams in pure bending are performed by using an infrared photoelastic method. Experimental results show that the stress-optic law is valid. The optical and mechanical properties of silicon beams are shown in tables.     

Remarks on properties of photoviscoelastic model materials

One of the basic problems of structural-model analysis, model photoelasticity and photoelastic coatings in the problem of mechanical and optical creep, relaxation and related phenomena. It is pointed out that, in spite of creep or relaxation, it is possible to achieve physical similarity between model and object if the model material behaves in a certain range as a linear viscoelastic material. Such a material is called a “momentarily linear material.” Several model materials behave in this way in a certain range of stress and time. Because of creep and relaxation, the common tensile tests are, in general, not quite adequate for evaluation of physical properties of plastics used for models. Also the bending test is not always adequate. It is shown how to obtain sufficiently accurate relations between stress, strain, birefringence and time, using tapered specimens. The problem of biaxial creep of model materials is discussed, and a simple method of evaluating the suitability of a given plastic as a model material is shown. Some conclusions concerning time-dependent factors are formulated, and some possible areas of investigation are shown.     

金川露天矿边坡岩体移动和变形的光弹性软材料模拟实验研究

通过对边坡岩体破坏机理的光弹性力学模拟实验研究, 岩体在地应力作用和自重体积力作用下, 对露天矿边坡的力学状态具有明显地影响。实验采用了明胶软材料, 模型比例1：1100。实验模拟了在自重应力和构造应力作用下, 边坡岩体的位移和变形。     

On the measurement of strain in the hostile environment of high-pressure water (80 MPa)

The measurement of strain on a structural member in the presence of high-pressure water environment requires waterproofing of the gages as well as understanding of the pressure effect on the foil gages. Two new waterproofing methods are developed to protect the gage under these extremely high pressures. This study has resulted in a new compensating method which eliminates the effects of temperature and pressure simultaneously. The waterproofing materials studied during this investigation are superior to other earlier techniques reported in literature since they provide protection up to 11,500 psi (80 MPa) while previously existing techniques failed before this pressure. Also, these studies on the pressure effect deal with the realistic situation of coated strain gages in a water environment, as compared to previous studies which dealt with uncoated strain gages in an oil environment.     

A stress-optic law for photoelastic analysis of orthotropic composites

The feasibility for utilizing transparent filament-resin composites for photoelastic stress analysis was investigated. Satisfactory photoelastic stress patterns were demonstrated in simple models with undirectional and bidirectional fiber orientations. A stress-optic law was formulated, based on the concept that the birefringence components contributed by each component of plane stress are combined according to a Mohr circle of birefringence. Applying this concept, the difference of the physical and optical principal directions was accounted for, and a general method of photoelastic solution for the plane-stress problem in orthotropic sheets was developed. The method of analysis is little more complex than the well-known procedures for isotropic materials, but at least three experimental measurements are required to characterize the optical response of the material to plane stress. Partial confirmation of the proposed stress-optic law was obtained by comparison of the theory to limited experimental data obtained in uniaxial-stress samples. It remains to establish a more positive verification by experiments in a variety of biaxial-stress conditions.     

The birefringent response of a potential photoelastic material with variable elastic properties

In photoelastic stress analysis, a need sometimes exists for a birefringent material in which the experimenter has the ability to vary its mechanical or elastic properties. It was the intent of this investigation to produce a homogeneous, isotropic solid with variable mechanical properties and which was suitable for photoelastic use. This goal is accomplished through the fabrication of a discontinuous composite where the birefringent constitutents have matched indices of refraction in the unstressed state. The constituents of this composite are solid-glass microspheres embedded in a polyester matrix. Three theories are formulated to define the stress-induced birefringent phenomena found in composites of this nature. Conventional photoelastic techniques were employed to produce data appropriate for comparison to the predictions of these theories.     

Suitability of the photoelastic implementation of polymers with material birefringence

Scattered photoelastic techniques would gain considerable momentum through better understanding of the nature and response of the available photoelastic materials. The influence of the prevailing birefringent effect in the state of load-free polymers on the radiated scattered light energy is investigated. Six different photoelastic materials are considered. The impact of material birefringences on the quality of reading the fringe orders of the scattered radiation in a stressed photoelastic medium is explored. Spectral dependence of the modulation of light vectors in acrylic materials (Plexiglas) is illustrated. The advantage of this characteristic as a convenient means of compensation in scattered photoelasticity is pointed out. Acrylic sheets, a relatively cheap transparent polymer, seem to be suitable for scattered photoelastic analysis. The moiré technique might find application in determining fringe orders in a material such as Homalite-100. Replacing the primary beam by a primary sheet saves the cost and effort consumed in the scanning process. Paper was presented at the 1988 SEM Spring Conference on Experimental Mechanics held in Portland, OR on June 5–10.     

Photoelastic investigation of large deflections by low-modulus photoelastic materials

Information is given to enable the experimental analysis of large deformations by application of photoelastic techniques. Promising photoelastic materials having low elastic modulus and high optical sensitivity were obtained for practical use at room temperature. The time and temperature dependence of the stress-fringe order and stress-strain relations of one of these viscoelastic materials is discussed. Photoelastic investigations of large deflected straight and circular beams are reported. Photoelastic technique seems to be a useful method for analysis of large deformations of models with complicated shapes.     

Determination of the full-field stress and displacement using photoelasticity and sampling moiré method in a 3D-printed model

The quantitative characterization of the full-field stress and displacement is significant for analyzing the failure and instability of engineering materials. Various optical measurement techniques such as photoelasticity, moiré and digital image correlation methods have been developed to achieve this goal. However, these methods are difficult to incorporate to determine the stress and displacement fields simultaneously because the tested models must contain particles and grating for displacement measurement; however, these elements will disturb the light passing through the tested models using photoelasticity. In this study, by combining photoelasticity and the sampling moiré method, we developed a method to determine the stress and displacement fields simultaneously in a three-dimensional (3D)-printed photoelastic model with orthogonal grating. Then, the full-field stress was determined by analyzing 10 photoelastic patterns, and the displacement fields were calculated using the sampling moiré method. The results indicate that the developed method can simultaneously determine the stress and displacement fields.