Modelling of cross-ply piezoelectric composite laminates in cylindrical bending with interfacial shear slip

An approximate theory for cross-ply piezoelectric composite laminates in cylindrical bending with interfacial shear slip is developed. This theory uses only 4 displacement and potential variables, the number of which is independent of the number of layers involved. The displacement and electric potential fields are depicted by the displacement and electric potential distribution functions through thickness, respectively. The two functions are formulated according to particular solutions to the three-dimensional elasticity equilibrium equations and electrostatics charge equation. In this shear slip modelling interfacial opening is neglected. The interfacial bonding conditions are characterised by a linear slip law and an electrically permeable assumption. A corresponding finite element is also developed to deal with piezoelectric laminates with local shear slip. The accuracy and effectiveness of the present theory are demonstrated in numerical examples.     

Interfacial delamination of thin-film PTFE (polytetrafluoroethylene) coatings

Interfacial adhesion is a major concern with respect to successful performance of thin polymer films in developing new thin-film processes. Micro-indentation was used to induce interfacial delamination of polytetrafluoroethylene (PTFE) films deposited on glass substrates using hot filament chemical vapour deposition (HFCVD). Film thickness (1, 2, 3, 5, 10 µm) and indentation load (0.5, 0.75, 1, 2, 3 N) effects on the delamination diameter were investigated. A three-dimensional finite element model using shear material failure criterion and cohesive zone model (CZM) was developed to simulate the delamination. A normalized load–delamination radius relationship was obtained to evaluate the interfacial fracture toughness. The experimental observations showed that the delamination diameter depends on film thickness and indentation load. The numerical simulation indicates the delamination diameter depends on film thickness, material properties, and indentation force. The predictions of interfacial fracture toughness for 5- and 10-µm PTFE films are much smaller than those values using Rosenfeld et al.’s equation, which excludes the energy spent during the penetration.     

Influence of the thermomechanical processing on the fracture mechanisms of high strength aluminium/pure aluminium multilayer laminate materials

The microstructure and mechanical properties, with emphasis in the impact fracture toughness behaviour, of two multilayer laminate materials have been investigated. The multilayer materials are constituted by alternated sheets of pure aluminium (Al 1200 or Al 1050) and high strength Al 7075 alloy. Stacked layers of these alloys have been successfully joined using two processing routes with different total hot rolling strains. Both laminates have been tested at room temperature under impact Charpy tests, three-point bend tests and shear tests on the interfaces. Both laminates exhibited more than eight times improvement in impact fracture toughness over the monolithic Al 7075-T6. The toughness increase in the higher rolling strained laminate is almost entirely due to crack blunting mechanism, while in the lower strained laminate, crack deflection by delamination and crack renucleation processes were active.     

Prediction and Minimization of Delamination in Drilling of Medium-Density Fiberboard (MDF) Using Response Surface Methodology and Taguchi Design

In this article, an attempt has been made to predict and minimize the delamination in drilling of medium density fiberboard (MDF). The experiments are carried out on LAMIPAN PB panel based on orthogonal array with feed rate and cutting speed as process parameters. The second order delamination factor models at entry and exit of the holes have been developed using response surface methodology. The parametric analysis has been carried out to study the interaction effects of the machining parameters. Taguchi's quality loss function approach has been employed to simultaneously minimize the delamination factor at entry and exit of the holes. From the analysis of means and analysis of variance, the optimal combination level and the significant parameters on delamination factor are obtained. The optimization results showed that the combination of low feed rate with high cutting speed is necessary to minimize delamination in drilling of MDF.     

Effect of deviation on delamination by saw drill

Various cutting techniques are available to drill holes, but drilling is the most common way in secondary machining of composite materials owing to the need for structure joining. Twist drills are widely used in the industry to produce holes rapidly and economically. Since the twist drill has a chisel edge, increasing the length of a chisel edge will result in an increase in the thrust force generated. Whereas, a saw drill has no chisel edge; it utilizes the peripheral distribution of the thrust force for drilling. As a result, the saw drill can achieve better a machining quality in drilling composite laminates than twist drill. The deviation of cutting edge that occurs in saw drill would result in an increase of thrust force during drilling, causing delamination damage when drilling composite materials in particular. A comprehensive model concerning delamination induced by the thrust force of a deviation saw drill during drilling composite materials has been established in the present study. For a deviation saw drill, the critical thrust force that triggers delamination increases with increasing β. A lower feed rate has to be used with an increasing deviation saw drill in order to prevent delamination damage. The results agree with real industrial experience. A guide for avoiding the drill deviation during drill regrinding or drill wear has been proved analytically by the proposed model, especially when the deviation ratio (β) affects the critical thrust force. This approach can be extended to examine similar deviation effects of various drills.     

有机印制板上倒装芯片的可靠性研究

对一种有机印制板上倒装芯片（Ｆｌｉｐｃｈｉｐ）进行温度循环试验,测出其失效分布曲线,然后通过扫描声显微镜、红外显微镜和剖面等失效分析手段,发现失效模式主要是合金焊点中的断裂以及下部填充料（Ｕｎｄｅｒｆｉｌ）中的损伤如分层（Ｄｅｌａｍｉｎａｔｉｏｎ）和内部裂缝（Ｃｒａｃｋ）。详细地阐述了倒装芯片中的下部填充料损伤在温度循环试验条件下的产生、发展及它们对合金焊点可靠性的影响。     

Local buckling of stitched composite laminate

Due to relatively low interlaminar strength, delamination is a common failure mode of composite laminates. Through-thickness stitching is shown to improve the delamination resistance of laminated composites. Under in-plane compressive loading, significant strength reduction occurs due to coupling between delamination and delamination buckling. In this paper, an energy-based model was developed to predict the effect of critical stitching parameters on the delamination buckling strength of stitched laminates. Excellent agreement was found between the model results and a corresponding finite element analysis.     

Effect of Delamination on Mechanical Properties of Al-Li Alloy Modified by Rare Earth Element Ce

１ＩｎｔｒｏｄｕｃｔｉｏｎＡｌｏｙ２０９０ｉｓｏｎｅｏｆｔｈｅｒｅｌａｔｉｖｅｌｙｗｅｌｄｅｖｅｌｏｐｅｄｈｉｇｈｓｔｒｅｎｇｔｈ,ｈｅａｔｒｅｓｉｓｔａｎｔｓｅｒｉｅｓａｍｏｎｇｃｏｍｍｅｒｃｉａｌＡｌＬｉａｌｌｏｙｓ．Ｔｈｅａｖａｉｌ...     

详谈PCB钻孔孔壁镀铜开裂问题及解决方案

PCB作为重要的电子部件,其钻孔质量的优劣直接关系到产品性能的稳定程度,尤其在航空、航天、军事等重要领域,钻孔质量在电气连接特性及使用可靠性方面起着至关重要的作用。文章针对PCB钻孔过程中出现的孔壁镀层开裂问题,结合金属切削理论基础,从钻孔参数、刀具选择、板材结构与叠层、分段钻孔、材料对比等方面进行了详尽的分析与交叉实验比较,下面对具体解决过程与结果进行阐述。     

2.25Cr-1Mo-0.25V钢148 mm厚板尾部分层缺陷分析及控制工艺

采用扫描电镜及电子探针对55 t钢锭成材148 mm厚2.25Cr-1Mo-0.25V钢板尾部分层缺陷进行观察分析,结果表明：分层缺陷是由于模铸保护渣卷入钢液造成的。为减少钢板尾部分层缺陷,对冶炼工艺进行优化,精炼过程中采用碳粉、电石及1.2～2.0 kg/t_钢Al线复合脱氧工艺,真空后软吹12～14 min,采用高粘度、低熔点、高熔速及膨胀系数较大的模铸保护渣。优化工艺后,钢板尾部分层缺陷出现概率分别为11.3%、9.6%、6.9%,分层缺陷导致钢板废品率由原8.1%降至1.7%。