应力状态对无取向电工钢塑性变形和断裂行为的影响

Effect of stress state on deformation and fracture behavior of non-oriented electrical steel

以晶粒粗大的无取向电工钢为研究对象,通过改装的Arcan夹具和蝶形试样,研究了0°纯拉伸、45°拉伸-剪切复合、90°纯剪切3种应力状态下,应力三轴度Rσ对材料塑性变形和断裂机制的影响。采用万能拉伸试验机多次定点停车、SEM观察晶粒变形和裂纹扩展的试验方法,实现了对变形过程的＂准原位跟踪＂及其力学响应的动态分析。发现应力三轴度对晶粒的滑移阻力有决定性影响。应力三轴度Rσ越小滑移越容易进行,其断裂形式越接近于无空穴剪切型损伤,断面韧窝特征越少;反之,滑移越难进行,断裂形式越接近拉伸型空穴损伤,断面韧窝密集。对于无取向电工钢,当Rσ≈0时,随着变形损伤的加剧,材料最终发生剪切型断裂;当00.4时,材料为韧窝型断裂。

The non-oriented electrical steel with coarse grains was selected as the study object,and the three stress states of 0° pure tensile,45° tensile-shear composite,and 90° pure shear stress were constructed by the modified Arcan fixture and butterfly specimen to study the effect of stress triaxiality Rσon the plastic deformation and fracture mechanism of the material. The multiple programmed stop was carried out on the universal tensile tester,the grain deformation and crack propagation were observed by SEM,and then the quasi‘in situ tracking＇and dynamic tracking of mechanical response were realized. It is found that the stress thriaxiality has a decisive influence on the slip resistance of grain. The smaller the stress triaxiality Rσis,the easier the slip occurs,and the closer to non-cavity shear damage,the fracture is the less the dimple features are. Otherwise,the more difficult the slip occurs,the closer to the tensile cavity damage the fracture is,and the section has dense dimples. For the non-oriented electrical steel,when Rσ≈0,with the increase of the deformation damage,finally the material is shear fracture; when 0 Rσ≤0. 4,the material is shear and dimple mixed fracture; when Rσ 0. 4,the material is dimple-type fracture.