相移数字散斑干涉计量系统

本建立了一套相移激光数字散斑干涉自动测量系统,运用一系列的图象处理方法,实现了高精度的自动测量,显地提高了数字散斑干涉计量技术的可靠性、实用性及自动化程度。该计量系统被应用于变形、振动等参数的测量中,取得了较为理想的结果。     

散斑干涉条纹图的总变分去噪方法

去除散斑条纹图中的噪声是电子散斑干涉测量技术的关键问题.提出将总变分图像去噪方法应用于电子散斑干涉条纹图滤波过程中,并对保真系数进行了改进.用总变分模型定义图像的能量函数,利用变分法求得满足能量函数的最优解,将图像去噪过程转化为求解偏微分方程的过程.分别对计算机模拟的条纹图和实验获得的条纹图进行了测试,定性和定量分析的结果表明该技术能够在显著滤波的同时保持条纹的对比度.     

流体温度场测量中的电子散斑干涉技术

电子散斑干涉是一种利用全电子记录和计算机图象处理系统替代传统照相干版进行测量的先进技术。本文在简要介绍其应用于流体温度场测量的理论与实验的基础上,着重描述了如何通过调整光学系统参数配置来获取最佳质量原始干涉图象的途径,并给出对比分析结果。     

Localisation Phenomenon Investigation on SMATed Stainless Steel Samples by Speckle Interferometry

Abstract: In‐plane Electronic Speckle Pattern Interferometry (ESPI) has been successfully used during tensile tests on SMA‐treated (Surface Mechanical Attrition Treatment) and as‐received 316L stainless steel in order to measure the strain rate field. The heterogeneity in the strain rate field can be observed from a stage of deformation which doesn’t coincide with the classic Considère’s criterion (dF = 0) for the diffuse neck initiation (or plastic instability). The initiation of this heterogeneity strongly depends on treatments undergone by the material. In this paper, a comparison was performed about the heterogeneity initiation of specimens SMATed during 30 min with 2 mm shot, 3 mm shot and a non‐treated sample. The formation of the two slip band system until fracture of the tensile specimen was also studied.     

焊接动态位移场的激光电子散斑法测量

为提供一种能够全场测量整个焊接过程动态位移场的工具,建立了激光电子散斑法测量系统.应用于实际TIG焊接过程中,获得了焊接位移场的散斑原始图像.利用自开发软件,对图像进行灰度变换和直方图均衡化处理后,采用频域同态滤波的方法对图像进行降噪滤波处理.经降噪、二值化、细化、平整、拟合、标定等一系列处理后,即可自动生成相对动态位移场.结果表明,激光电子散斑法能够胜任焊接动态位移场的测量,且具有非接触、测量精度高、对环境的防震要求低、可在明光下操作、能进行全场测量的特点.     

Damage characterization of a cross-ply carbon fiber/epoxy laminate by an optical measurement of the displacement field

Using Electronic Speckle Pattern Interferometry (ESPI), full-field displacement measurement was performed on the edge of a cracked cross-ply graphite/epoxy laminate subjected to a tensile loading. The displacement jumps corresponding to cracks are clearly visible and can be used to determine the crack opening displacement (COD) values along the cracks. The main objective of this study is to determine if the application of successive loads of increasing magnitude may have modified the existing cracks and thereby changed the COD dependence on the applied stress. Moreover, we have tested the applicability of the assumed linear elastic COD behavior in the presence of very high stress concentration at the crack tips. The profile of the opening along the crack was also studied.     

Automatic phase stepping in fiber-optic ESPI by closed-loop gainswitching

In this paper, we describe a new technique for automatic phase stepping in fiber-optic Electronic Speckle Pattern Interferometry (ESPI), useful in both single-point and imaging configurations. The proposed technique is based on closed-loop switching of the gain sign in the control loop used to stabilize the reference wavefront phase, with the aid of a Proportional-Integral (P.I.) controller. Simulation and experimental results are compared, showing that by a synchronization signal or by a proper choice of the feedback loop parameters, a sequence of π/2 steps of the reference wavefront phase, all of the same sign, is obtained, The residual fluctuation of each phase step amounts to ±2.5 mr over a bandwidth of 200 Hz. This level of phase stability is well suited for ESPI applications     

理想绝缘金属基板前处理工艺的研究

采用阳极氧化工艺制备理想绝缘金属基板阳极氧化绝缘层。利用激光干涉法测量阳极氧化膜层在热冲击过程中的开裂温度。研究了铝板表面不同前处理工艺对金属基板绝缘层热开裂温度的影响，利用扫描电子显微镜（SEM）观察裂纹萌生的位置，结果表明阳极氧化前铝表面微观不平将使阳极氧化膜中产生一种孔隙率高的界面，热冲击过程中这种界面上容易萌生裂纹。     

Strain rate measurement by Electronic Speckle Pattern Interferometry: A new look at the strain localization onset

In-plane Electronic Speckle Pattern Interferometry has been successfully used during tensile testing of semi-hard copper sheets in order to measure the strain rate. On one hand, heterogeneity in strain rate field has been found before the maximum of the tensile force (ɛ^t ≃ 19.4 and 25.4%, respectively). Thus, a localization phenomenon occurs before the classic Considère's criterion (dF = 0) for the diffuse neck initiation. On the other hand, strain rate measurement before fracture shows the moment where one of the two slip band systems becomes predominant, then strain concentrates in a small area, the shear band. Uncertainty evaluation has been carried out, which shows a very good accuracy of the total strain and the strain rate measurements.     

Stress singularity analysis in the restorations of premolar class ii cavities

Abstract

This paper presents the singular stress analysis near the apex of a structure formed during dental restoration of a premolar class II cavity. Based on the elasticity theory, the stresses may go to infinity at the junctions of different materials (e.g. dentine, enamel, restoration materials). Tensions will cause material separation and then material fracture. In order to reduce the failure probability, the degree of stress concentration has to be reduced. The stress singularity order and the stress intensity factor are two parameters, which are often used in fracture analysis. The objective of this paper is to find conditions such that non‐singular stress fields are possible. Three critical positions in the restoration structure are discussed.

They are the tips of interface between (1) enamel and restoration; (2) dentine and restoration; and (3) enamel, dentine and restoration. In the last two cases, the restoration may be bonded or debonded to enamel or dentine. After employing Kolosov‐Muskhelishvili complex functions together with the eigenfunction expansion method, the singularity orders are computed theoretically. Weak stress singularity conditions can be sought by properly selecting cutting angles or restoration materials.     

On the role of stress waves in dynamic rupture of cylindrical tubes

A systematic experimental/computational study was performed to investigate the role of stress waves in ductile fracture of cylindrical tubes. The stress waves were created by high‐speed moving load, which was produced by detonation of explosive cord inside two intact and two pre‐flawed steel tubes. Several distinct phenomena like cyclic crack growths in Modes I and III, crack flap bulging and crack curving/branching were observed and simulated by finite element (FE) method. The FE models were composed of 3D brick elements equipped with interface cohesive elements. The analysis results showed that the crack growths in Modes I and III were governed by the detonation‐induced stress waves. The crack speeds were obtained based on the increments of cyclic crack growth and the time period of the stress waves. The estimated crack speed range was 63–230 m s^?1 for the axial growth, whereas the average speed for growth in Mode III was 100 m s^?1.     

Laser Based Nondestructive Inspection Techniques

The most familiar laser based optical nondestructive methods are based on the interference of the wave fronts of monochromatic light reflected from a test surface. We explore the origins, applications, advantages and limitations of these techniques with a journey through the realm of Holographic Interferometry, Electronic Speckle Pattern Interferometry and Shearography. These methods are applied to the widest range of materials from metals to composites attempting to determine the conditions of the material that contribute to failure, in for example critical parts of a structure. These techniques are inherently of fairly high sensitivity, are non-contacting, they are able to inspect a whole field in a single procedure and results are obtained at almost real time. The inspection procedure on a test piece is identical for all three techniques. An image of the object??s surface is recorded and stored in a suitable medium; subsequently the object is perturbed mildly by mechanical or thermal means which results in its surface being deformed. At this stage a second image is captured and is made to interfere with the first image resulting in an image of the surface with zebra like stripes superimposed on it. This is known as a fringe pattern and abrupt changes in direction or spacing of these fringes may indicate a subsurface condition that affects the surface deformation. Thus porosity, voids, de-bonds, cracks, de-laminations etc. are detected. These techniques have also limitations particularly with the stability of the test piece and the inspecting instrument in relation to each other. Particular attention is paid in avoiding excessive test piece motion or environmental vibration both which will exceed the stringent requirements for fringe formation. It is well established that these laser based NDT techniques have found innumerable applications in the laboratory/field/factory environment and particularly Shearography but surprisingly it does not yet have a standard, like for example an ISO International Standard, hence we are calling for the involvement in this respect by the technical committee TC?135 of the ISO.     

双圆弧齿轮轮齿弯曲应力的研究

 用三维边界元法对GB12759—91双圆弧齿轮的轮齿弯曲应力进行了分析计算，并在此基础上得出齿根应力与法向载荷之间、齿腰应力与法向载荷之间、齿根应力与当量曲率半径之间及齿腰应力与当量曲率半径之间的关系曲线．研究表明，大螺旋角或小载荷时，齿腰应力大于齿根应力．因此，齿腰应力也是关键环节，需受到重视.     

Multi-segment FEA of the human lumbar spine including the heterogeneity of the annulus fibrosus

This study pursues the numerical validation of human lumbar spine segments. By means of the finite element (FE) method, computational analyses are carried out of various load cases. In particular Flexion–Extension, Lateral Bending and Axial Torque are considered. By means of a literature review the underlying constitutive data is verified. In this context, the heterogeneity of the annulus fibrosus, the transversely isotropic stress response of the spinal ligaments and aspects of the FE discretization are particularly emphasized. The numerical results show good agreement with experimental investigations for Extension and Axial Torque for a FE model that accounts for intact human lumbar spine response. In Flexion and Lateral Bending, however, the results of the intact FE-model do not properly account for the experimental data. A good correlation for these load cases can be found by taking disc degeneration into account in the FE-model. This fact shows that tissue degeneration plays a key role in the current validation process and must be accounted for if the lumbar spine specimen is employed for spinal implant evaluation. A degenerated FE-model that represents the stage of degeneration of the specimen and fits the experimental data for all load cases could not be found in this study and warrants further work in this area.The authors are deeply indebted to Centerpulse Orthopedics Ltd., Winterthur, Switzerland (www.zimmer.com) for financial aid and support of this research. Additionally, the authors thank Darrell Goertzen for his work involving the experimental testing.     

Study of Pd–Ag dental alloys: examination of effect of casting porosity on fatigue behavior and microstructural analysis

The goals of this study were to investigate the fatigue limits of two Pd–Ag alloys (Ivoclar Vivadent) with differing mechanical properties and varying proportions of secondary alloying elements, examine the effect of casting porosity on fatigue behavior, and determine the effect of casting size on microstructures and Vickers hardness. The alloys selected were: IPS d.SIGN 59 (59.2Pd–27.9Ag–8.2Sn–2.7In–1.3Zn); and IS 64 (59.9Pd–26.0Ag–7.0Sn–2.8Au–1.8 Ga–1.5In–1.0Pt). Tension test bars, heat-treated to simulate dental porcelain application, were subjected to cyclic loading at 10 Hz, with R-ratio of −1 for amplitudes of compressive and tensile stress. Two replicate specimens were tested at each stress amplitude. Fracture surfaces were examined with a scanning electron microscope (SEM). Sectioned fatigue specimens and additional cast specimens simulating copings for a maxillary central incisor restoration were also examined with the SEM, and Vickers hardness was measured using 1 kg load. Casting porosity was evaluated in sectioned fatigue fracture specimens, using an image analysis program. The fatigue limit (2 × 10⁶ loading cycles) of IS 64 was approximately 0.20 of its 0.2% yield strength, while the fatigue limit of d.SIGN 59 was approximately 0.25 of its 0.2% yield strength. These relatively low ratios of fatigue limit to 0.2% yield strength are similar to those found previously for high-palladium dental alloys, and are attributed to their complex microstructures and casting porosity. Complex fatigue fracture surfaces with striations were observed for both alloys. Substantial further decrease in the number of cycles for fatigue failure only occurred when the pore size and volume percentage became excessive. While the heat-treated alloys had equiaxed grains with precipitates, the microstructural homogenization resulting from simulated porcelain firing differed considerably for the coping and fatigue test specimens; the latter specimens had significantly higher values of Vickers hardness.     

The peak stress method applied to fatigue assessments of steel and aluminium fillet-welded joints subjected to mode I loading

The aim of this work is to present an engineering method based on linear elastic finite element (FE) analyses oriented to fatigue strength assessments of fillet‐welded joints made of steel or aluminium alloys and subjected to mode I loading in the weld toe region where fatigue cracks nucleate. The proposed approach combines the robustness of the notch stress intensity factor approach with the simplicity of the so‐called ‘peak stress method’. Fatigue strength assessments are performed on the basis of (i) a well‐defined elastic peak stress evaluated by FE analyses at the crack initiation point (design stress) and (ii) a unified scatter band (design fatigue curve) dependent on the class of material, i.e. structural steel or aluminium alloys. The elastic peak stress is calculated by using rather coarse meshes with a fixed FE size. A simple rule to calculate the elastic peak stress is also provided if a FE size different from that used in the present work is adopted. The method can be applied to joints having complex geometry by adopting a two‐step analysis procedure that involves standard finite element (FE) models like those usually adopted in an industrial context. The proposed approach is validated against a number of fatigue data published in the literature.     

Investigation of the Thermal Diffusivity of Human Tooth Hard Tissue

Experiments of two kinds have been performed in which the heat diffusion effects in human tooth hard tissues have been investigated. The first one has been carried out on an incisor tooth as a whole with the use of a bath system. Experiments of the second kind have been done on slice specimens cut out of a tooth. A laser flash apparatus has been utilized. The time dependence of the temperature response has been measured using tiny thermocouples. The experimental data are then used to calculate the effective overall thermal diffusivity of the tooth structures as well as the thermal diffusivity of enamel and dentine alone. A discrepancy between the calculated results and literature data has been discussed.     

Spherical indentation of tooth enamel

Spherical indentation measurements were made on enamel surfaces of intact human teeth. From the load versus depth of indentation curve Young's modulus was found to be typically 8.3×10¹⁰ Pa and the yield stress to be 3.3×10⁸ Pa. Young's modulus was observed to vary with moisture content and with the orientation of the enamel surface. Viscoelastic behaviour was evident, also depending on the moisture content of the enamel.     

绝缘搪瓷金属基板的研究

本文介绍了电子绝缘瓷釉的发展状况，测定了瓷釉的烧结温度、热膨胀系数、软化点、瓷层厚度、粒度分布等工艺性质以及耐击穿电压、体积电阻率、介电性能等电学性质；对瓷釉颗粒和瓷层进行了SEM分析，对瓷釉进行了TG—DTA和X衍射分析，明确了瓷釉中的析晶温度和结晶相；对比了绝缘瓷釉和ECA瓷釉的电性能；讨论了烧结温度和时间对瓷层形貌。温度和频率对介电性能的影响。     

Meshing characteristics of spur gear pair under different crack types

The effects of three different gear crack types such as, for example, the crack along tooth width uniformly and the crack propagating in the depth direction (crack type 1, CT1), the crack along tooth width non-uniformly and the crack propagating in both the depth and the tooth width directions (crack type 2, CT2), and the spatial crack propagating in the depth, the tooth width and the tooth profile directions (crack type 3, CT3) on the time-varying mesh stiffness (TVMS) of spur gear pairs are investigated in this study. Firstly, an analytical model for studying these three types of cracks is established based on potential energy method. A finite element (FE) model of the cracked spur gear pair is also built in the ANSYS software as well. In order to verify the analytical method, the TVMS obtained from analytical method is compared with that obtained from FE method under different crack types. Moreover, the effects of the depth, the length and the height of crack are discussed. The equivalent stress, contact pressure and displacement of tooth are also analyzed under different crack types by using the FE method. The results show that the effect of crack depth on TVMS is the largest, while that of the crack height is the smallest, and the non-penetrating crack for CT2 and CT3 will generate the non-uniform load distribution along tooth width.