TWIP钢的动态力学性能及变形机制研究

利用Zwick/Roell Z100万能材料试验机和Hopkinson拉杆对TWIP钢进行了准静态及动态力学性能的研究。基于力学实验结果,修正了Johnson-Cook动态本构模型中应变硬化项以及应变强化项。采用X射线衍射(XRD)、扫描电镜(SEM)、电子背散射衍射(EBSD)技术对TWIP钢拉伸变形前后的组织进行了观察与分析。结果表明：TWIP钢在准静态加载下表现为负应变率敏感性,动态加载时表现为正应变率敏感性。拉伸过程中,孪生诱发塑性是TWIP钢的主要变形机制,同时滑移也起到重要作用;动态加载下TWIP钢中形变孪晶的起始应变和孪晶体积分数均小于准静态加载过程;形变孪晶的生成以及孪晶相互作用导致的晶粒细化,使TWIP钢兼具高强度、高塑性及高动态吸能性能,在抗冲击、抗爆领域具有广泛的应用前景。     

富CoCr含量CoCrNiAlTi中熵合金的高温强韧化行为及微观机制

本工作研究了富CoCr含量的CoCrNi基中熵合金的高温力学性能及其变形机制。研究发现,经过热锻以及时效热处理,成分为Co_33.3Cr_30.6Ni_26.1Al₅Ti₅ (at%)中熵合金在600～800℃的温度范围内具有优异的瞬时拉伸性能。特别是,在700℃条件下出现反常屈服,屈服强度高达为944 MPa,拉伸塑性为16%,优于大多数镍基以及钴基高温合金。通过X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和三维原子探针(3D-APT)等手段,发现高体积分数的多主元γ′[(Ni,Co,Cr)₃(Al,Ti)]相的有序强化以及晶界处生成的多主元富(Co,Cr)面心立方相(fcc)结构相引起的晶界强化是该合金在高温条件下实现强韧化的主要因素。     

Effects of Nb Addition on Charpy Impact Properties of TiVTa Refractory High-Entropy Alloy

In the present study, the effects of Nb addition on Charpy impact properties of TiVTa refractory high-entropy alloy with high strength-ductility trade-off were systematically studied by using the instrumented Charpy impact testing machine. The experimental results showed that the impact toughness was remarkably improved by Nb addition in TiVTa to form TiVTaNb alloy. The crack initiation energy and propagation energy of TiVTaNb were 67.3% and 24.9% higher than that of TiVTa, indicating that Nb addition simultaneously reinforced the resistance to crack initiation and propagation. The impact fracture of TiVTaNb exhibited larger bending degree of shear lips, deeper dimples and more secondary cracks which effectively dissipated more impact energy. The deformation mechanism of TiVTa alloy was dominated by dislocation activities. While in TiVTaNb, the deformation mechanism was synergized by dislocation activities and deformation twinning, which were the main contributors for the improved impact properties and the stronger crack resistance of TiVTaNb alloy under impact loading.     

Cyclic properties of dense to very dense silica sand

This paper presents results of a series of cyclic laboratory test performed on dense to very dense silica sand. Triaxial and direct simple shear tests were performed on reconstituted sand. The test program aimed to determine the cyclic shear strength and soil deformation properties for foundation design of offshore wind turbine structures on the Dogger Bank site, offshore United Kingdom, but is also applicable for foundation design of other offshore structures and other locations. Two sand batches were used, one with clean silica sand and one with 20% silt content. Normally consolidated specimens from both batches were reconstituted to a target relative density approximately equal to 100% and 80%. On the clean sand with a target relative density of 80%, tests were also performed on specimens with an overconsolidation ratio of OCR = 4. Various contour diagrams, presenting cyclic shear strength and average and cyclic shear strains for different number of cycles, are presented. These diagrams can be used in the front-end engineering design (FEED) stage of commercial design projects on similar soil conditions, to define soil behavior when limited cyclic data is available, or in the planning stage of a cyclic laboratory test program. Effects of precycling and fines content on the cyclic behavior of triaxial and DSS specimens are discussed.     

土钉墙变形与稳定性关系初探

本文对土钉墙的变形影响因素进行分析和简化 ,并通过与土钉墙稳定性分析影响因素的比较 ,得出两者在参数上的近似一致性 ;利用土钉墙位移监测资料和稳定性分析结果 ,总结出工程意义上的土钉墙变形和整体稳定安全系数之间的关系曲线 ,可以用于土钉墙的变形预测     

卸荷应力状态下玄武岩变形破坏特征的试验研究

本文采用卸荷三轴试验．在实验室研究了玄武岩在卸荷状态下的变形和破坏特征．     

利用回归平面确定建筑物的倾斜变形状态

本文利用回归平面进行建筑物倾斜变形分析，对用来确定回归平面的沉降观测点的布设要求和观测精度作了说明，并结合算例验证了该方法的可靠性。     

深基坑支护结构变形规律分析

以青岛市某深基坑工程的变形监测为例,分析深基坑支护结构变形在复杂条件下的时空效应变化规律。     

Effect of the moment transfer efficiency of a beam web on deformation capacity at box column-to-H beam connections

This paper investigates the effect of moment transfer efficiency of a beam web on deformation capacity at beam-to-column connections. Non-linear finite element analysis of five connection models was conducted. Analytical results showed that the moment transfer efficiency of the connection with a box column was poor when compared to a connection with an H-column; this was due to the out-of-plane deformation of the column flange. Based on previous test data, analytical results were compared with experimental results. Analytical and experimental results showed that the deformation capacity of the connection with a box column decreased due to the poor moment transfer efficiency of a beam web, followed by strain concentration at the beam flange.     

钢筋混凝土现浇薄板变形裂缝的形成机理及其防治方法

钢筋混凝土现浇薄板 (ld 3 5>h >相似文献