铝合金自冲铆成形过程最大冲压载荷的反演模型

基于材料塑性变形虚功原理并结合上限定理,展开自冲铆成形过程最大冲压载荷的反演分析。以成形接头几何特征参数(钉脚张开度、铆钉几何尺寸参数、被连接材料的厚度)、铆钉和被连接材料力学性能参数以及冲头与铆钉的接触面接触条件为反演计算模型的控制量,建立最大冲压载荷的反演计算模型;同时,针对多种铝合金自冲铆成形开展最大冲压载荷的验证试验研究。结果表明:所建立的反演模型计算值与试验值的平均误差为7.82%,验证了最大冲压载荷反演计算模型的有效性;最大冲压载荷与铆钉的强度、长度成正比,与铆钉内腔深度成反比,为获得静力学性能较优的自冲铆接头应适当增加铆接最大冲压载荷。此外,在相近的最大冲压载荷作用下,较低硬度的被连接材料搭配较低硬度的铆钉,易获得大张开度的接头。

交叉结构在面内冲压载荷作用下的损伤变形机理研究

交叉构件在船舶与海洋工程舷侧及船底结构中广泛存在,在发生碰撞搁浅事故时,会受到面内冲压载荷作用发生损伤变形,影响船体结构的安全性,需在设计中予以关注。在初步设计阶段,解析计算方法的应用可以显著地提高结构设计效率。因此,以十字交叉结构为研究对象,通过设计开展交叉结构模型的准静态冲压试验及相应仿真,分析其变形机理,确定十字交叉结构在冲压载荷下的变形模式。以此为基础,运用塑性力学理论,推导出结构变形能、瞬时结构变形抗力及平均结构变形抗力的解析计算公式,并将计算结果与试验结果进行比较验证。研究得到的结构面内受压变形能和抗力解析计算公式,可以快速评估事故载荷下结构的响应情况,对船体耐撞结构设计及抗撞性能评估具有一定的指导意义。

基于冲压试验的聚乙烯力学性能预测

通过对5种不同曲率半径的高密度聚乙烯(PE-HD)圆棒试样进行单轴拉伸试验,重点分析了曲率半径对工程应力-位移曲线的影响;同时对PE-HD平板试样进行冲压试验,分析了压头直径和冲压速度对载荷-位移曲线的影响;建立了3种基于冲压载荷预测PE-HD单轴屈服应力的经验公式。结果表明,同一拉伸速度下,屈服强度随曲率半径的减小而增大;同一冲压速度下,最大冲压载荷随压头直径的增大而增大;同一压头直径下,最大冲压载荷随冲压速度的增大而增大;基于压头直径为变量的经验公式预测得到的屈服强度可靠性最高,可以较为准确地表征PE-HD的力学性能。

基于ANSYS的氧传感器夹紧套模具设计

针对汽车氧传感器夹紧套的质量问题,对氧传感器及夹紧套的结构特点进行了研究,设计出了一套能将氧传感器的敏感元件与夹紧套通过冲压成形固定在一起的夹紧套冲压模具。先利用夹紧套的径向塑性变形特点,确定夹紧套周向压缩加工的工艺方式;再由模具要将压力机的竖直运动转变为夹紧套径向塑性变形所需的水平运动,从而设计出了压盖式斜楔结构的模具结构;再对模具进行了冲压载荷校核,符合模具冲压载荷不超过冲压设备公称压力这一设计规范;选择模具中压块与连接螺杆做ANSYS应力分析,以施加载荷及约束并求解,获得了应力与应变等值线图。研究结果表明,压块与连接螺杆的强度及刚度均满足使用条件且具有较高的安全裕度。

A damage-based constitutive model for rock under impacting load

Using the Splitting Hopkinson Pressure Bar （SHPB） experimental system, investigations were made into the dynamic mechanical performances of underground soft rocks. The experiments proved that the measured stress-strain curves display the characteristics of plastic deformation. By making use of a revised overstress constitutive formula for the stress model and by taking into account that the strain rate and strain are a function of I - E（t）/Eo, a revised overstress constitutive formula for the stress model was simplified by applying dimensional analysis and consequently, a simplified overstress formula was obtained for the stress model. Then, by taking into consideration the effects of damage under a dynamic load on the dynamic loading strength of the rock, the continuous damage theory and the statistical strength theory were introduced into the development of the simplified overstress constitutive formula for the stress model. Hence, a damage-based constitutive formula for an overstress model, which can be appropriately applied to the analysis of full dynamic stress-strain curves, was developed. By using the simplified damage-based constitutive formula for an overstress model, the actually measured curves are fitted, indicating that the fitting curves and those actually measured are in good agreement.

Effects of thermal treatment on physical and mechanical characteristics of coal rock

To study the physical and mechanical properties of coal rock after treatment at different temperatures under impact loading, dynamic compression experiments were conducted by using a split Hopkinson pressure bar(SHPB). The stress–strain curves of specimens under impact loading were obtained, and then four indexes affected by temperature were analyzed in the experiment: the longitudinal wave velocity, elastic modulus, peak stress and peak strain. Among these indexes, the elastic modulus was utilized to express the specimens' damage characteristics. The results show that the stress–strain curves under impact loading lack the stage of micro-fissure closure and the slope of the elastic deformation stage is higher than that under static loading. Due to the dynamic loading effect, the peak stress increases while peak strain decreases. The dynamic mechanical properties of coal rock show obvious temperature effects. The longitudinal wave velocity, elastic modulus and peak stress all decrease to different extents with increasing temperature, while the peak strain increases continuously. During the whole heating process, the thermal damage value continues to increase linearly, which indicates that the internal structure of coal rock is gradually damaged by high temperature.