On certain aspects of strain rate sensitivity of sheet metals

The formability of a material depends upon the strain hardening and strain rate hardening of the material. In this study, constitutive parameters using the power law constitutive equation are determined for six different strength steels and two aluminum alloys over different strain ranges, including approximations of the postuniform elongation range. Constitutive parameters are found to be different at different strain ranges. The strain hardening of steels increases with strain at low strain levels (less than 5%) and decreases at high strain levels (greater than 10%). Strain rate hardening decreases with strain for all steels and aluminum alloys. Uniform elongation depends only on strain hardening, and postuniform elongation depends only on strain rate hardening. However, the total elongation depends on both strain hardening and strain rate hardening.     

Ti-22Nb-6Zr(at%)合金的超弹性和形状记忆效应

用弯曲法和拉伸法测定Ti-22Nb-6Zr（at％）合金的超弹性和形状记忆效应，研究固溶处理温度对Ti-22Nb-6Zr合金组织结构及性能的影响。结果表明：固溶处理后Ti-22Nb-6Zr合金的室温组织为单一的β相，晶粒尺寸随固溶处理温度升高而增大；合金的静态弹性模量小于30GPa；Ti-22Nb-6Zr合金具有良好的超弹性和一定的形状记忆效应。室温下变形，合金的超弹性和形状记忆效应随固溶处理温度升高而提高。900℃固溶处理后的合金在室温下拉伸变形，应变为5％时，总的最大回复应变达4．12％，其中超弹性回复应变为3．91％，记忆回复应变为0.21％。     

铸钢件准固态区域应力,应变数值模拟及热裂机制

对ＺＧ４５实验热裂试棒的数种工况进行了应力－应变的数值模拟，对热裂形成机制进行了讨论。研究认为：热裂起源于Ｂｉｎｇｈａｍ体，是塑性变形超过Ｂｉｎｇｈａｍ体塑性储备值所致。     

Analytical and experimental analysis of deep drawing process for bimetal elements

The paper presents the concepts of solving of deep drawing process for bimetal elements of sheet materials. The inertia forces, plastic hardening behaviour of the deformed material and dynamic stress are utilized in the problems of plasticity. The experimental results and general conclusion are presented at the end of the paper.     

基于有限元分析的轮胎胎圈耐久性能优化

以新开发的175/70R14半钢子午线轮胎为研究对象,针对胎体帘布反包端点裂口问题建立有限元仿真模型。根据有限元分析结果提出增大胎体帘布反包端点高度的改进措施。结果表明,增大胎体帘布反包高度能够有效改善胎圈裂口现象,提高胎圈耐久性能;有限元分析结果与试验结果有很好的一致性。     

细菌纤维素的功能化改性研究进展

细菌纤维素(BC)是微生物生长过程中产生的以葡萄糖为基本骨架的结构性碳水化合物,具有高纯度、高聚合度、高结晶度、高持水性、高抗张强度和良好的机械强度,在功能材料领域显示了巨大的应用潜力.综述了近年来BC合成菌种筛选的研究现状;分析了BC在透气、吸湿排汗、力学性能和染色与脱色性能调控方面的进展情况;重点总结了BC基材料在抗菌、防紫外线、防辐射、防静电、拒水拒油、导电和传感等功能化改性方面的研究进展;最后,指出BC大规模高效成模和成型技术、差异化高功能BC材料制备技术是未来的重点研发方向.     

Johnson-Cook dynamic constitutive relationship for TC 16 titanium alloy

The true stress--strain curves of TC16 alloy with a wide range of strain rates were investigated under uniaxial quasi-static tension and uniaxial dynamic compression with the lnstron 8032 test machine and the split Hopkinson bar respectively. The results indicate that the true stress increases with increasing strain rate, while decreases with increasing temperature. Under the 105 s^-1 high strain rate and temperature higher than 673 K, the true stress would even be less than that under quasi-static condition. A new method incorporating TCl6＇s stress strain curve developing item was proposed to determine the coefficients in J-C model easily and to avoid the estimation of the adiabatic temperature rising. The Johnson-Cook dynamic constitutive relationship for TC16 was obtained for the first time. Good agreement was obtained between the model prediction and the experimental stress--strain curves for TC16 under both quasi-static and dynamic loadings.     

含硅镍低密度钢的温拉伸力学行为及强韧机制

 为了分析硅镍合金化奥氏体基低密度钢在中温环境下的拉伸变形行为,采用Instron电子拉力试验机对Fe-28.64Mn-8.99Al-1.68Si-1.39Ni-1.0C(Mn29Al9Si2Ni,质量分数/%)低密度钢在23~300 ℃下进行了温拉伸试验,研究了该钢的温拉伸力学行为,并采用SEM、TEM和热力学计算对该钢的强韧化机制进行了研究。结果表明,随着应变的增加,温拉伸应力-应变曲线主要包括弹性变形、均匀塑性变形和断裂等几个过程,没有明显的屈服现象。随着温度的提高,该钢的强度逐渐降低,塑性(断后伸长率)先增加后减小再升高,于200 ℃时出现塑性低谷,此时该钢的应力-应变曲线和应变硬化率曲线均具有明显的锯齿状特征,应变硬化率随应变的增加变化不大。而该钢在其他温度下的应力-应变曲线和应变硬化率曲线没有发现明显的“锯齿状”特征,应变硬化率随应变的增加而平缓下降。试验钢在23~300 ℃下的主要强韧化机制为κ-碳化物强化、应变强化、孪生诱发塑性和动态应变时效强化。较低温度下位错可动性较差对孪生诱发的促进作用、镍元素和硅元素对孪生的抑制作用、较高温度下孪生现象的减弱和温度对动态应变时效的促进或抑制作用等使得试验钢在23、100和300 ℃时存在明显的孪生诱发塑性,而在200 ℃时存在明显的动态应变时效强化的主要原因。动态应变时效强化是该钢在200 ℃时出现塑性低谷的主要原因。     

应变速率对Q460连铸坯高温力学性能的影响

摘要：采用Gleeble-3500热模拟试验机和金相法测试了不同应变速率下建筑用钢Q460连铸坯的高温力学性能,获得了600~1200℃范围内Q460连铸坯的高温强度、热塑性和最终室温组织随拉伸温度和应变速率的变化规律。结果表明,当Q460连铸坯在较高的应变速率（10s-1）下进行高温拉伸时,试样的断面收缩率随着拉伸温度的升高而升高,没有出现高温脆性区;在较低的应变速率（10-3s-1）下进行高温拉伸时,试样的断面收缩率出现了2个脆性区,第1个在1100℃至熔点温度,第2个脆性区间在700℃附近。总体来说,实验钢种的高温断面收缩率均大于65%,表明建筑用钢Q460连铸坯具有较好的高温热塑性。此外,同一应变速率下,Q460连铸坯的抗拉强度随着拉伸温度的升高而降低,而伸长率随着拉伸温度的升高而升高。     

应变速率对闭孔泡沫铝力学性能和能量吸收性能的影响

采用分离式霍普金森压杆 (SHPB)技术 ,研究了应变速率 (1× 10 - 3s- 1 ～ 2 5 0 0s- 1 )对泡沫铝力学性能和能量吸收性能的影响。结果表明 :泡沫铝有较高的应变速率敏感性 ,随应变速率的增加 ,泡沫铝的屈服强度和吸能能力增加 ,泡沫铝的应变速率敏感性随应变、应变速率变化幅度的增加而增加。