Deformation and Spallation of Explosive Welded Steels under Gas Gun Shock Loading

We investigate deformation and spallation of explosive welded bi-steel plates under gas gun shock loading. Free surface histories are measured to obtain the Hugoniot elastic limit and spall strengths at different impact velocities.Pre-and post-shock microstructures are characterized with optical metallography, scanning electron microscopy,and electron backscatter diffraction. In addition, the Vickers hardness test is conducted. Explosive welding can result in a wavy steel/steel interface, an ultrafine grain region centered at the interface, and a neighboring high deformation region, accompanied by a hardness with the highest value at the interface. Additional shock compression induces a further increase in hardness, and shock-induced deformation occurs in the form of twinning and dislocation slip and depends on the local substructure. Spall damage nucleates and propagates along the ultrafine grain region, due to the initial cracks or weak interface bonding. Spall strengths of bimetal plates can be higher than its constituents. Plate impact offers a promising method for improving explosive welding.     

晶粒取向和晶界对双晶铜变形的影响

在扫描电子显微镜(SEM)下拉伸双晶铜样品,用数字图像相关方法(DIC)处理样品在不同应变状态下的SEM图片,得到正应变场E_(xx)和剪应变场E_(xy),并通过E_(xx)和E_(xy)的演化研究双晶铜的变形特征,以及晶粒取向和晶界对它的影响。正应变场E_(xx)显示两晶粒内部、晶界附近分别有单、双系滑移开启,滑移带会造成局部变形的不均匀。随着应变的增加,滑移带数量增多而强度减小,变形趋于均匀化。相比软取向晶粒,硬取向晶粒中的滑移带数量少而滑移带强度高。剪应变场E_(xy)幅值远小于E_(xx)幅值,因而观察不到滑移带。软取向晶粒比硬取向晶粒的平均正应变E_(xx)大,它们之间的差别在8%的拉伸应变后随着应变的增加而被放大,晶界产生更高的协调应力,使得晶界附近的剪应变E_(xy)开始急剧增加。