DSCM变形测定新技术在柔性包装力学性能测定中的应用

文中采用现代光测力学中的数字散斑相关(DSCM)新技术,测定了聚丙烯(PP)打包带的应力-应变曲线和泊松比、(牛皮)纸-塑(PE)复合材料的蠕变规律和F型瓦楞纸盒的侧向挤压变形.与传统的测试方法相比,显示了DSCM技术非接触式、零加强效应以及高精度全场全程测试的特点,并结合对象材料力学性态上的特殊性所提出的测量要求,展开了分析讨论.     

数字散斑相关法在高聚物领域中的应用

高聚物广泛地应用于人类生产和生活等各个领域，其力学性能研究在材料、工程结构的优化设计中起着重要的作用．数字散斑相关法(DSCM)是一种光测实验力学方法，该方法具有测量环境要求低、可直接测取位移和应变信息及细观结构、便于实现测量自动化等优点。文中综述了数字散斑相关法在高聚物领域中的应用。     

数字散斑相关方法在木材科学中的应用及展望

随着现代光电子和计算机技术的发展以及数字图像处理理论的深入，数字散斑相关方法（DSCM）迅速成为实验力学领域一种重要的测试方法。文章介绍了DSCM的基本原理，并对其在木材科学领域的应用进行了综述，包括在木材常规力学测试和木材断裂、微观力学以及复合材料力学测试等方面的应用及一些新的成果。最后根据木材材料的特点, 对DSCM在木材科学上的进一步应用提出了几点建议。     

含孔洞岩石单轴压缩下变形破裂规律的实验研究

采用数字散斑相关量测方法(DSCM)和数字照相量测软件系统PhotoInfor,通过观测表面位移场、应变场及总体变形在整个加载过程中的变化特点,对大小为100mm×100mm×100mm的含有孔洞的岩石试件在单轴压缩下的变形破裂演变规律进行了实验研究。结果表明:1)DSCM方法能够对岩石变形破裂的特点进行全程有效捕捉,有助于加深对岩石变形局部化过程的全面认识;2)含孔洞岩石试件局部化变形起始于峰值点处轴向位移的80%处,应力峰值点附近变形局部化最为剧烈;3)岩石表面平均最大剪应变随轴向位移的变化曲线,总体上能够很好地反映岩石变形破裂的演变过程和规律,可作为分析岩石变形演变的一个参考特征参数。     

基于数字散斑相关技术的沥青混合料老化特性实验研究

基于数字散斑相关技术DSCM(digital speckle correlation method),利用VIC-3D(video image correlate-3D)图像处理系统,通过半圆弯拉实验(semi-circular bending test,简称SCB实验),对温度老化前后的SBS改性沥青混合料和橡胶粉(CR)改性沥青混合料半圆试件的三点弯拉实验从加载到破坏的全过程进行图像采集,利用VIC-3D计算软件计算半圆试件全过程的水平应变、水平应变速率并通过荷载-位移曲线求出的断裂能指标,研究沥青混合料老化特性。结果表明,数字散斑相关技术,作为一种非接触、非干涉、全场变形的光学计量方法,可以很好地应用于沥青混合料的老化特性研究;在半圆试件从加载到开裂破坏的全过程中,温度老化后的沥青混合料的持荷能力和抵抗开裂破坏的能力与老化前相比明显削弱;温度老化后的CR改性沥青混合料比温度老化后的SBS改性沥青混合料有更好的抗裂性能。     

基于数字散斑相关法的紫外老化沥青混合料界面开裂特性

利用数字图像相关技术(DSCM)针对紫外光老化的沥青混合料(HMA)半圆试件弯拉试验中裂纹产生及扩展规律从细观角度进行表征,运用Vic-3D分析软件对沥青混合料半圆试件进行全场位移、应变计算,得到试件破坏过程的位移场、应变场。结果表明:通过对紫外光照的沥青胶浆、集料及界面水平方向应变场的对比分析,发现界面为沥青混合料最薄弱处,最易产生裂纹;进一步通过水平方向应变随载荷变化曲线的变化对HMA开裂时间进行分析,可以更好地将HMA微裂缝开裂时间与宏观裂缝开裂时间加以区分,且紫外老化后的HMA试样界面开裂时间明显缩短。同时,将相同的紫外老化前后的橡胶粉(CR)改性HMA试样与苯乙烯-丁二烯-苯乙烯(SBS)改性HMA试样的位移随载荷变化规律进行对比发现,经紫外老化后的CR改性HMA比紫外老化后SBS改性HMA具有更强的抗开裂能力及持荷能力。      

SOI集成中应变硅的外延工艺

在Si晶体中产生应变是提高载流迁移率的一个熟知的方法，为发挥其最佳效果，对PMOS晶体管的空穴导电，Si沟道中的应变是压缩应变，而NMOS Si沟道中是张(力)应变。由于非应变Si中空穴迁移率平均只是电子迁移率的1／3，所以开始集中努力于提高PMOS器件中(空穴)迁移率。为保持PMOS与NMOS器件中的迁移率比(为一定值)，就必须同时提高NMOS中的迁移率。     

非均匀载荷作用下偏心磨损套管稳定性准则

采用小参数摄动法建立了非均匀载荷作用下具有初始椭圆度的磨损套管稳定性准则,根据计算得到的磨损套管相对应变及其临界值之间的关系确定磨损套管是否发生挤毁失效。分析了磨损套管相对应变及其临界值与套管外径、壁厚、磨损深度、载荷非均匀度、初始椭圆度之间的关系。套管外径增加导致失稳临界应变减少,磨损套管保持其稳定的壁厚也随之增加。非均匀载荷作用下磨损套管相对应变与初始椭圆度之间是线性关系,套管初始椭圆度越大,相对应变越大。相对应变与载荷非均匀性之间是抛物线关系。磨损套管载荷非均匀性越大,相对应变越大。非均匀载荷作用下磨损套管的相对应变随磨损深度线性增加。该准则能够用于评价非均匀载荷作用下含磨损缺陷套管的井筒的完整性。     

考虑应变梯度及刚度劣化的剪切带局部变形分析

基于梯度塑性理论,研究了应变软化阶段的刚度劣化对剪切带内部的局部应变及相对剪切位移的影响。剪切带被看作一维剪切问题,本构关系为线弹性及线性应变软化。考虑刚度劣化后,剪切带的弹性应变由弹性剪切模量、损伤变量及残余剪切模量确定。剪切带的非局部总应变由双线性的本构关系确定。将非局部总应变减去弹性应变,可得剪切带的非局部塑性应变。剪切带非局部塑性应变与流动应力及损伤变量等参数有关,此关系即为在经典弹塑性理论框架之内的考虑刚度劣化的屈服函数。将二阶应变梯度项引入该函数,可得剪切带内部的局部塑性剪切应变及局部总剪切应变的分布规律。对局部塑性剪切应变积分,得到了局部塑性剪切位移。结果表明:考虑了刚度劣化后,剪切带内部的弹性剪切应变及位移增加,而局部塑性剪切应变及位移降低。若不考虑刚度劣化,理论结果可蜕化为以前的结果。理论结果与岩石局部变形的观测结果在定性是一致的。     

利用高精度激光干涉仪测量转动工件表面应变

通过对弹性固体表面的微观形貌进行建模，推导出切向应变与法向应变存在的线性关系，利用高精度激光表面粗糙度外差干涉仪对工件表面的法向应变进行测量，达到测量切向应变的目的，从而有助于新型非接触光学应变测量仪的研究。     

增材制造Ti合金数字散斑相关方法应变检测及成形极限构建综述

增材制造Ti合金的制件性能能否优于传统铸件、锻件的性能是研究人员关注的重点,亟需开展系统化的检测与评价方法研究.主要综述了增材制造Ti合金构件材料应变检测及相关成形性能基础理论研究中存在的不足和国内外研究现状,结合笔者的研究经历,围绕增材制造现阶段的研究热点,数字散斑相关方法(Digital Speckle Corre...     

Effect of mode III fracture on composite laminates

The digital speckle correlation method (DSCM) is preformed to study the inplane displacements along the x and y direction of laminated composite panels containing preset elliptical damage. The different principle axis of the ellipse and the different sequence of laminates are considered in the experiments. It is shown that the method is very useful to get the displacements on the laminate surface and between the adjacent plies. According to the experiment results, the deformations of x and y direction can be obtained. The conclusion that the mode III fracture may exist and may have an effect on the crack growth is formed. The total strain energy release rate is calculated by the finite element method. Using Mindlin plate theory and the virtual crack closure technique, the energy release rate of mode III fracture can be calculated by FEM. The results show that mode III fracture has an influence on the total energy release rate and also on the delamination growth. The energy release rate of mode III fracture cannot be ignored. The delamination growth also is influenced by the stacking sequence.     

Latent crack path and service life predictions for unnotched concrete under bending by digital speckle correlation method

The critical factor for flexural fracture of an unnotched concrete structure is the local damage with stress concentration. The latent critical crack path on the concrete surface is difficult to inspect using ordinary experimental methods. In the present paper, the digital speckle correlation method (DSCM) is employed to obtain the latent critical crack and to calculate the strain and displacement distributions on the surface of unnotched concrete under flexural load. The relationships of static flexural load versus longitudinal strain and load-direction displacement as well as fracture toughness are inherent material parameters. Furthermore, the cohesive energy density (CED) around the latent critical crack for unnotched concrete and the brittleness number are also determined by using the DSCM results. Then, the tensile performance of concrete and the residual service life are evaluated through the above material parameters. It is found that the latent crack path on the concrete surface depends on the strain fields after the bending force applied to the specimen reaches 30% of concrete flexural strength, and the cohesive stress does not rapidly increase until reaching 75% of concrete flexural strength. The service life of unnotched concrete without steel bars is dependent on the local cohesive performance around the latent crack path. Finally, the experimental results show that DSCM is useful to confirm the connection between the local damage of the material and the whole structure safety.     

Application of DSCM in prediction of potential fatigue crack path on concrete surface

Prediction of potential fatigue crack paths on the surfaces of concrete structures was a difficult task in the past. To complete this task a Finite Element Method simulation by computers is usually employed, but bearing in mind that the numerical results are not always consistent with the experimental ones because of the effects of various environmental factors and construction quality on concrete structures. In order to inspect the damage process during the service life of structures and to confirm their detailed plan of repair and reinforcement, a new non-destructive technology is used for on-line health inspection of many important concrete structures in the world. Fortunately, along with the development of Digital Speckle Correlation Method (DSCM) in the last two decades, this new non-destructive technique has presented many advantages. To testify the feasibility and accuracy of this system, two series of concrete specimens were tested under flexural fatigue loading and a software UU^© matched to DSCM was employed in this work. DSCM can get full-field and local displacements by comparing two speckle images on target surfaces before and after deformation. Then the full-field and local strain fields on these regions can be deduced from the longitudinal and transversal displacements. By analysis of these strain fields, the starts of potential fatigue crack paths can be predicted precisely. It is testified that DSCM system is accurate and effective in on-line prediction of potential fatigue crack path of specimens made of heterogeneous materials under flexural cyclic loading. The fractural mechanisms of the two concrete series under flexural cyclic loading were discussed. Note that the fatigue testing conditions should be kept still and clean in order to produce precise results of DSCM system.     

K‐dominance of static crack tip in functionally gradient materials

K‐dominance of static crack tip in functionally gradient materials (FGMs) with a crack oriented along the direction of the elastic gradient is studied through coherent gradient sensing (CGS), digital speckle correlation method (DSCM) and finite element method (FEM). In the direction of crack propagation, the shear modulus has a linear variation with constant mass density and Poisson's ratio. First, the CGS and DSCM governing equations related to the measurements and the elastic solutions at mode I crack in FGMs are obtained in terms of the stress intensity factor, material constants and graded index. Secondly, two kinds of FGMs specimens and one homogenous specimen are prepared to observe the influences of the property variation on the K‐dominance. Then, CGS and DSCM experiments using three‐point‐bending of FGMs and homogenous beams are performed. Thirdly, based on the results of the experiments, the stress intensity factors of three kinds of specimens are calculated by CGS and DSCM. Meanwhile, the stress intensity factors are obtained by FEM. Finally, comparing the results from CGS, DSCM and FEM, the K‐dominance of mode‐I static crack tip in FGMs is discussed in detail.     

Digital speckle correlation method based on wavelet-packet noise-reduction processing

Despite the advantages of being highly sensitive and nondestructive, the digital speckle correlation method (DSCM) may have difficulties in detecting tiny defects such as delaminations in multilayer ceramic capacitors. This is because the presence of background noise always complicates the data processing. We present a new algorithm, which employs the wavelet-packet noise-reduction process together with the improved DSCM, to improve data processing. Both the computational error and the noise are shown to be reduced successfully by this new algorithm. The accuracy (or precision) of the improved DSCM is increased after operation of the wavelet-packet noise-reduction process. The most important feature of this new algorithm is that it can extract a small hillock signal from a large noisy background in a DSCM deformation result. This helps to save time in the detection of tiny defects, such as delamination, in a miniaturized electronic component.     

An optical strain measurement system for asphalt mixtures

Knowledge of the conditions governing the initiation and propagation of cracks in hot mix asphalt (HMA) mixtures is a prerequisite for a comprehensive understanding of HMA cracking mechanisms. Traditional strain measurement sensors have proved to be not completely adequate in the sense that they do not provide pointwise measurements, thus not pinpointing the location of crack initiation, and not accounting for non-uniform strain distributions. This paper presents a digital image correlation (DIC) system for non-contact and full strain field measurements, conceived for the purpose of investigating the cracking behavior of HMA mixtures. The whole system was developed so as to account for the special nature of typical HMA testing configurations. An image matching technique (least squares matching) was employed for providing matches with sub-pixel accuracy. The performance of the method was investigated by several tests. The DIC system was shown to overcome the shortcomings of traditional on-specimen strain measurement devices achieving satisfactory accuracy compared to strain gauges.