Digital image correlation strain measurement of thick adherend shear test specimen joined with an epoxy film adhesive

Structural bonding and bonded repairs of composite materials become more and more important. Understanding the strain within the bondline leads to suitable bonding design. For new design approaches the strain distribution within the bondline has to be analyzed. Thus, often finite element analysis (FE) are used. However, a huge challenge is the availability of reliable material properties for the adhesives and their validation. Previous work has shown that it is possible to measure the small displacements resulting within thin epoxy film adhesives using high resolution digital image correlation (DIC). In this work a 2D DIC setup with a high resolution consumer camera is used to visualize the strain distribution within the bondline over the length of the joint as well as over the adhesive thickness. Therefore, single lap joints with thick aluminum adherends according to ASTM D 5656 are manufactured and tested. Local 2D DIC strain measurements are performed and analyzed. Two different camera setups are used and compared. The evaluation provides reliable material data and enables a look insight the bondline. The results of the full field strain data measured with DIC are compared with numerical simulations. Thus, material models as well as chosen parameters for the adhesive are validated. Compared to extensometers, giving only point-wise information for fixed measuring points, the DIC allows a virtual point-wise inspection along the complete bondline. Furthermore, it allows measuring close to the bondline to reduce the influence of adherend deformation.     

BFRP-钢板-混凝土组合双连梁抗震性能试验研究

为研究BFRP-钢板-混凝土组合双连梁的受力性能和破坏机理,完成了1个普通钢筋混凝土单连梁、1个普通钢筋混凝土双连梁、1个内置钢板的钢筋混凝土双连梁、1个外包BFRP布的钢板-混凝土组合双连梁的低周往复加载试验,研究了不同连梁形式和外包BFRP布对其抗震性能的影响,分析了各连梁的破坏形态、破坏特征、承载能力、变形能力和耗能能力等,并利用数字图像相关（DIC）测试技术分析了BFRP布应变随位移和时间变化的分布规律。结果表明：内置钢板和包裹BFRP布后,双连梁的延性、耗能和承载力均有显著提高;内置钢板显著提高了普通钢筋混凝土双连梁的承载能力和耗能能力,包裹BFRP布有效地提高了钢板-混凝土组合双连梁的持荷能力,BFRP布能较好地抑制混凝土裂缝的开展以及延缓混凝土的破坏速度。DIC测试技术能够较好地测定连梁外包BFRP布的变形以及应变变化,BFRP布在靠近梁墙交界处所受的力较大。     

肖特基二极管金属质量问题研究

介绍了出现在肖特基二极管金属膜上常见的几种异常情况,其中包括金属迸溅、金属“毛刺”以及金属DIC模式鼓泡现象.经过对不同问题的深入探究,分析出了各种现象产生的具体原因,并结合我所实际情况给出了有效的解决措施.     

Effects of physical aging on thermomechanical behaviors of poly(ethylene terephthalate)-glycol (PETG)

ABSTRACT

A series of experiments are performed to investigate the effects of physical aging on thermomechanical properties of poly(ethylene terephthalate)-glycol (PETG). The DMA, DSC and XRD tests are used to characterize the change of dynamic property, heat capacity and microstructure with annealing treatments. The uniaxial tension tests together with the DIC technique are employed to describe the failure behaviors of PETG. The results show that the annealed polymers exhibit a larger maximum local strain and fail at a smaller displacement. The type and size of the geometry defects can also affect the strain localization and final failure behaviors of PETG.     

Mechanics-aided digital image correlation for the investigation of piezoelectric and ferroelectric behaviour of a soft PZT

The strain response of a polarised PZT was characterised using Digital Image Correlation (DIC). The DIC algorithm is based on a global approach and regularises the displacement field using the balance equations of solid mechanics. The measurement error is reduced by correcting the displacements that are mechanically not admissible. A ferroelectric test showed that the standard deviations of strain fields remain mostly under 1.2 × 10^?4 for an element size of 64 px. The standard deviation on the average value is 3 × 10^?6. The strain field is homogeneous and its average value is consistent with the strain obtained from a CCD laser measurement device. The longitudinal strain, transverse strain and polarisation response of the PZT were measured for bipolar and unipolar loadings ranging from 50 to 5000 V/mm. Material properties were extracted from these measurements. This work shows the advantages of a novel 2D-DIC algorithm for piezoelectric strain characterisation.     

Classic and inverse compositional Gauss-Newton in global DIC

Today, effective implementations of digital image correlation (DIC) are based on iterative algorithms with constant linear operators. A relevant idea of the classic finite element (or, more generally, global) DIC solver consists in replacing the gradient of the deformed state image with that of the reference image, so as to obtain a constant operator. Different arguments (small strains, small deformations, equality of the two gradients close to the solution, etc) have been given in the literature to justify this approximation, but none of them are fully accurate. Indeed, the convergence of the optimization algorithm has to be investigated from its ability to produce descent directions. Through such a study, this paper attempts to explain why this approximation works and what is its domain of validity. Then, an inverse compositional Gauss-Newton implementation of finite element DIC is proposed as a cost-effective and mathematically sound alternative to this approximation.     

Study on the effect of DIC deformation sensor on mechanical property of substrate

The thin epoxy film with micro-scale speckle pattern as a digital image correlation (DIC) deformation sensor has been fabricated or transferred on the surface of sample in the previous study. When the thickness of the film cannot be ignored, it may have an influence on the validity of measurement results. And thus, the influence of the thin epoxy film on mechanical properties of substrates should be investigated. In this study, the mechanical behavior of thin film itself and surface strain of composite structure of thin film and substrate were measured using micro digital image correlation (MDIC) method. And theoretical and simulative results were also analyzed. From the comparison analysis of theoretical, simulative and experimental results, it is concluded that when the ratios of Young’s modulus and thickness between the film and substrate are smaller than 13 and 0.5 respectively, the influence from the thin film can be ignored, and thin epoxy film as DIC sensor can be used to measure the deformation of substrate.     

从2D到3D-创意电子创新的设计服务:SiP与SoC相辅相成

阐释系统封装(SiP)的定义、优缺点、使用上会遭遇的困难点及解决之道、与未来发展的趋势。     

支盘桩桩周土体位移场试验研究

挤扩支盘桩是一种新桩型,其承载能力和抗沉降变形性能远优于等直径桩,具有良好的经济和社会效益。在已有研究的基础上,利用数字图像相关技术(DIC)对模型试验各阶段的数码照片进行相关性分析,得到竖向荷载作用下挤扩支盘桩的桩周土体位移场及其破坏性状。     

基于DIC技术和无网格法的裂尖应变场分析方法

针对数字图像相关(DIC)技术难以获得精准的裂纹尖端应变场问题,提出一种基于DIC技术和伽辽金无网格法(EFG)的混合方法来分析裂尖应变场。该方法基于DIC技术导出场节点建立无网格模型,采用EFG法结合衍射法表示裂纹不连续性,进而计算全场应变值。以Q235qE钢材制成的紧凑拉伸(CT)试样为例开展了准静态循环拉伸试验,通过比较裂尖应变解析解和试验结果,证明该方法的有效性和稳定性。进一步研究DIC EFG法在裂尖塑性区域和应力强度因子(SIF)计算等方面的应用。研究结果表明：DIC EFG混合方法建模简单,不需要荷载和约束条件,能够获得准确的包括裂尖在内的全平面应变场。相较于传统DIC技术,DIC EFG混合方法解决疲劳裂纹附近结果缺失的问题,结合J积分法计算SIF结果更为精准,可应用于疲劳裂纹的塑性区域和SIF计算等断裂性能研究。