三边约束钢板的抗剪承载力

利用静力加载方法对4种宽厚比的三边约束钢板单元进行了试验研究,通过试验考察了三边约束钢板的破坏形态和抗剪极限承载力,分析了宽厚比对钢板抗侧性能的影响,试验结果表明：小宽厚比钢板的抗屈曲能力较强,但是对边界约束条件要求较高,易造成边界连接破坏。根据钢板破坏形态,对其抗侧性能进行了理论分析,建立了三边约束钢板的抗侧性能计算模型,给出了三边约束钢板极限抗剪承载力计算公式。文章最后对三边约束钢板的选择和设计提出了建议。     

The use of peel tests to examine the self adhesion of polyimide films

Peel tests were used to examine the adhesion between two layers of the polyimide pyromellitic dianhydride-oxydianiline (PMDA ODA). The main thrust of this work was to examine these tests with particular emphasis on yielding in bending of the peeled strips. Two peel geometries and a range of sample thicknesses were used to study interfaces whose strength could be varied over a wide range by changing the cure schedule. The peel strength varied with strip thickness and often reached a peak at an intermediate thickness. The results were shown to agree qualitatively with a combination of two theoretical models for the effects of yielding on peel tests. It was also found that a second problem of polyimide adhesion, the effect of solvent swelling, could significantly enhance the adhesion between polyimide layers.     

Yielding behaviour of thermoplastic/elastomer blends cured by gamma irradiation

Mechanical blends of thermoplastic medium density polyethylene (MDPE) and elastomeric ethylene propylene diene monomer (EPDM) have been prepared with a fixed composition of 60/40 wt%. They have been used either in their gum form or loaded with two different reinforcing fillers, high abrasion furnace (HAF) carbon black or precipitated SiO₂ (Hi Sil) of concentration 25–100 phr (parts per hundred parts of resin) with respect to the blend. Curing was achieved by gamma irradiation. Yielding properties (yield stress, yield strain and cold drawing) have been followed as a function of irradiation dose for different blend compositions. Yield stress values increased with irradiation dose and with the content of the reinforcing filler, but yield strain and cold drawing values decreased with irradiation dose and also with the filler content. The data obtained reveal that Hi Sil is more effective as a reinforcing filler, and the prepared blends are suitable for load‐bearing applications. © 2001 Society of Chemical Industry     

α—Fe 中氢致软化同氢致硬化机制的研究

本文研究了工业纯 α-Fe 中晶内同晶界对氢致软化同氢致硬化效应的不同贡献,发现其中仍以晶内贡献为主,并提出了相应的新机制。     

Cavitation Instabilities in Plastics and Rubber-Modified Plastics

Spherical void expansion in plastics and rubber-modified plastics is investigated under radial traction conditions. The plastics are modeled as elastic-plastic pressure-sensitive materials and the rubbers are modeled as nonlinearly elastic materials. First, the growth of a spherical void in an infinite plastic matrix is investigated under remote radial traction conditions. The results show that the cavitation stress of the plastic decreases significantly as the pressure sensitivity increases. Then, the growth of a spherical void located at the center of a spherical rubber particle in an infinite plastic matrix is investigated under remote radial traction conditions. The results indicate that without any failure criteria for the rubber, the cavitation stress does not exist when the void is small and the rubber is characterized by high-order strain energy functions. However, when a failure criterion for the rubber is considered at a finite stretch ratio, the results show that the cavitation stress for the plastic with the rubber particle becomes close to that for the plastic without the rubber particle. This revised version was published online in August 2006 with corrections to the Cover Date.     

Limitations on the use of the mixed-mode delaminating beam test specimen: Effects of the size of the region of K-dominance

The mixed-mode delaminating beam (MMDB) is a widely used test geometry designed to measure the fracture resistance of bimaterial interfaces under mixed-mode loading conditions. In the present work, linear-elastic finite element analyses are employed to determine the complex stress intensity factor, K, for an interfacial crack in this sample; results are found to confirm those of previous studies of the bilayer specimen. However, the numerical results further reveal that the region of K-dominance near the crack tip is very limited, extending merely 1/100 to 1/1000 of the sample height, about an order of magnitude smaller than for other common fracture-mechanics test samples. Analyses performed for this specimen geometry modified to include a thin sandwiched interlayer also indicate a very limited region of K-dominance, for example, extending 1/10 of the height of the sandwiched layer from the crack tip for very thin sandwiched layers. For the sandwiched geometry, two situations leading to a useful small scale yielding condition are described. Examples of the use of this specimen in the evaluation of the fracture toughness of ceramic joints are cited from the literature and comparisons are made between the size of the K-dominant region and the extent of crack tip plasticity. Based on these comparisons, the geometry-independent predictive power of linear-elastic fracture mechanics for common bimaterial couples and specimen dimensions using this geometry is challenged.     

A lattice‐shaped friction device and its performance in weak‐story prevention

Displacement‐dependent dampers with relatively low post‐yielding stiffness exhibits abrupt stiffness loss and can even induce notable damage concentrations under strong vibrations. A lattice‐shaped friction unit (LSFU) composed of steel strips and friction discs is proposed and it can dissipate most input energy through translational friction and rotational friction and provide post‐yielding stiffness through the axial strength of vertical strips. Measurements of the friction coefficient and torque coefficient ratio and quasi‐static analysis of the LSFU are conducted, the results indicate that the ratio rises first and then drops to a constant value. Under cyclic loading, the two friction mechanisms could work together effectively and the contribution of each component contained in the restoring force could be controlled by adjusting design parameters of the LSFU; the assembly accuracy of the components affect the resistance of vertical strips. The experiment results of two specimens are compared with those obtained from the developed formulas and numerical simulations. A design procedure and applicable style are proposed. Nonlinear seismic response analysis results show that these devices can reduce the displacement response effectively under small and moderate earthquakes and can also prevent concentrated damage and weak‐story occurrence in the structure relative to friction‐damped brace frame in strong earthquakes.     

基于锥形电极的三维型腔精确加工方法研究

提出并分析了在利用圆锥形电极定长补偿方法分层加工三维型腔实验时,其第一层第二道加工切除残余突起后形成的实际加工深度与理论分层厚度的差异,该差异存在于加工时采用的关键加工参数补偿长度的误差。进而探究并提出了精确计算第二道加工时补偿长度的方法,并通过实验验证了该补偿长度的准确性,从而使第一层两道加工后形成的加工深度达到理论值。最后,利用该方法进行两层的三维型腔加工实验,由此证明型腔加工效果良好,满足型腔尺寸及形状精度的要求。     

基于能量系数的损伤控制结构评估及其在钢框架中的应用

根据改进的能量平衡关系,推导了具有较大屈服后刚度系数的损伤控制单自由度体系的能量系数。采用非线性时程分析研究了地震作用下屈服后刚度系数及屈服时序对能量系数的影响。将能量平衡关系推广至多自由度体系,基于能量系数提出了用于判定损伤控制结构的评估方法,并将其用于损伤控制钢框架的评估。结合对损伤控制钢框架的评估分析说明了建议方法的应用,并通过非线性时程分析进行了校验。结果表明,能量系数对结构的屈服时序敏感,建议方法有良好的精度,可用于损伤控制结构的评估和优化设计。     

Microstructures and tensile behavior of carbon nanotube reinforced Cu matrix nanocomposites

Carbon nanotubes (CNTs) have been considered as an ideal reinforcement to improve the mechanical performance of monolithic materials. However, the CNT/metal nanocomposites have shown lower strength than expected. In this study, the CNT reinforced Cu matrix nanocomposites were fabricated by spark plasma sintering (SPS) of high energy ball-milled nano-sized Cu powders with multi-wall CNTs, and followed by cold rolling process. The microstructure of CNT/Cu nanocomposites consists of two regions including CNT/Cu composite region, where most CNTs are distributed, and CNT free Cu matrix region. The stress–strain curves of CNT/Cu nanocomposites show a two-step yielding behavior, which is caused from the microstructural characteristics consisting of two regions and the load transfer between these regions. The CNT/Cu nanocomposites show a tensile strength of 281 MPa, which is approximately 1.6 times higher than that of monolithic Cu. It is confirmed that the key issue to enhance the strength of CNT/metal nanocomposite is homogeneous distribution of CNTs.