Fatigue crack initiation life prediction for aluminium alloy 7075 using crystal plasticity finite element simulations

An experimentally-validated approach for predicting fatigue crack initiation life of polycrystalline metals is developed based on crystal plasticity finite element (CPFE) simulations. In this approach, the microstructure used in the simulations possesses statistically the same grain size and crystallographic orientations as those obtained from electron back-scatter diffraction experiments. A backstress model is incorporated into the CP constitutive model to describe the mechanical behaviour of aluminium alloy (AA) 7075 under cyclic loading. The key variables of the prediction model, the energy efficiency factor and plastic strain energy density, are calibrated using a fatigue test on a round-notched AA7075 specimen at room temperature. The proposed approach is then validated by using another fatigue test to predict 69.1–87.3% of the experimentally measured fatigue crack initiation life. The effects of the microstructure and texture on the energy efficiency factor and fatigue life prediction are quantitatively determined. It is shown that for a given range of energy efficiency factors a similar range of life prediction is obtained. Since the proposed approach considers the heterogeneity of the microstructure, it can well capture the grain scale deformation localisation and therefore improve the precision of fatigue life prediction.     

金属塑性成形缺陷的数值模拟预测研究

论述了基于有限元的金属塑性成形过程缺陷预测涉及到的理论基础、数值模拟实现和具体的缺陷预测技术，最后以某零件的挤压成形过程为例，通过数值模拟结果显示了金属的充填情况和存在的缺陷，并分析了产生缺陷的原因。     

高速钢薄片状圆刀热处理畸变控制

在高速钢薄片状圆刀热处理过程中，利用相变塑性原理，采用限形冷却工艺，较好地控制了高速钢薄片状圆刀的热处理畸变。     

钛合金热氢处理技术及其应用前景

钛合金热氢处理技术是利用氢致塑性、氢致相变以及钛合金中氢的可逆合金化作用以实现钛氢系统最佳组织结构、改善加工性能的一种新体系、新方法和新手段，利用该技术不仅可以改善钛合金的加工性能，而且可以提高钛制件的使用性能，降低钛产品的制造成本，提高钛合金的加工效率。综述了钛合金中氢对改善压力加工、扩散加工、机械加工和铸造钛合金变质加工的组织、力学性能和加工性能的作用，简要分析了其改性机理，展望了钛合金热氢处理技术的应用前景。     

Springback characteristics of tailor-welded strips in U-draw bending

The purpose of this study is to investigate the springback characteristics of tailor-welded strips in U-draw bending. Two different welded strips were adopted to compare the effects of weld-line locations on the springback. One was welded along the centerline of the strip-width and the other was welded along the centerline of the strip-length. To investigate the effect of different thickness combinations on the springback, the tailorwelded strips were joined by a laser welding process. Three sheet thickness combinations were assessed, SCP1 0.8 t^* SCP1 1.2 t, SCP1 0.8 t^* SCP1 1.6 t and SCP1 0.8 t^* TRIP 1.0 t. Three punch profile radii of 3, 6, and 9 mm and three die profile radii of 5, 10, and 15 mm were prepared and three blank holding forces (BHF) of 125 kg_f, 250 kg_f, and 500 kg_f were applied to investigate the effects of punch profile radius (R_p), die profile radius (R_d), and BHF on the springback of tailor-welded strips. With consideration for the thickness of the sheet and the material properties, the extent of the springback on the sidewall of unloaded sheet shapes increases as the thickness and the yield strength of the sheet increase in the U-draw bending process. For longitudinally welded strips, the amount of springback of the TRIP steel sheet in TWB could be reduced through a springback combination of the thinner side and weld-line. For the thinner side (0.8 t) of the centrally welded strips, the deformed shapes after the springback were almost the same regardless of the thickness com|bination, and the extent of the springback decreased compared with that of non-welded SCP1 0.8 t. Some experimental results are compared with analytical results obtained by using the finite element method.     

塑性加工技术前沿综述

分析提出了塑性加工的若干技术前沿 ,包括虚拟塑性加工技术、基于知识的塑性加工技术、精密塑性加工技术、基于新能源、新介质和不同加载方式的塑性加工新技术、模具制造新技术。对各技术前沿的研究现状、存在的问题和发展趋势做了科学的分析论述 ,对塑性加工技术的发展具有一定指导意义     

冲击荷载作用下饱和软粘土的一些性状

在己有对饱和软粘土再固结性状研究的基础上，重点讨论饱和软粘土在偏压应力状态下的再固结性状、土性及塑性指数对再固结变形的影响、冲击荷载作用下超固结土的孔压和变形性状、残余孔压与剪应变之间的相互关系及其变化机理、扰动固结问题以及偏压应力状态下地基土沉降和强度计算等问题。     

地质缺陷对拱坝及坝基力学行为的影响

  通过对一个坝址地质结构较为发育的拱坝作三维有限元非线性分析,分析了温度、渗流,地形地貌,地基上的地质缺陷等对拱坝及大坝运行时地基的力学行为的影响。并给出了复杂地基的拱坝的位移场、应力场的分布规律和传力特性。对大坝及基岩上塑性区产生的机理,形式和发展趋势作了分析。     

岩样失稳回跳与直剪试验机-岩样系统失稳回跳关系研究

研究了岩样及直剪试验机-岩样系统的弹性回跳不稳定性。将试验机简化为具有一定高度和剪切模量的钢块，利用梯度塑性理论得到了直剪试验机．岩样系统的剪应力．剪应变的理论关系。当不考虑钢块的高度时，这一关系便蜕化为岩样的剪应力-平均剪应变的理论关系。如果试验机-岩样系统回跳，那么岩样可能失稳回跳，也可能不失稳回跳；当钢块高度及剪切模量比值越大，试验机-岩样系统越容易发生失稳回跳。当这一比值较大时，纵然岩样不回跳，系统也会回跳：当这一比值较小时，只有当岩样回跳，系统才会回跳；当系统不回跳时，试样必不回跳。试样回跳，必然导致系统回跳：如果试样不回跳，则系统可能回跳，也可能不回跳。理论结果可解释若干常见的实验现象。     

论防空地下室结构设计的“八性”

文章对防空地下室结构设计中的特点做了系统总结,概括为延性、塑性、波动性、动静荷载等效性、抗力相协调性、防护密闭性、平战兼顾性、经济合理性等八个特性。对广大工程人员学习和理解人防结构设计有指导价值。