复合型V形切口脆断的应变能密度因子准则

STRAIN ENERGY DENSITY FACTOR CRITERION FOR V-NOTCHED BRITTLE FRACTURE UNDER MIXED MODES

通过定义V形切口应变能密度因子,将V形切口尖端的奇异应变能密度转化为非奇异的应变能密度因子。基于V形切口尖端附近的线弹性奇异应力场,建立Ⅰ-Ⅱ复合型V形切口脆性断裂的应变能密度因子准则,并把裂纹作为切口张角为零的V形切口,从而将V形切口问题与裂纹问题的断裂准则统一起来。为了验证该准则,采用有机玻璃(polymethyl methacrylate,PMMA)板材加工了多种单边复合型V形切口试样进行拉伸破坏实验,应用上述准则对试样的起裂方向和临界载荷进行预测,并与最大周向应力准则和实验结果进行比较。结果表明,用所建立的应变能密度因子准则所预测的临界载荷在切口张角较小时更接近于实验结果。

The singular strain energy density near the sharp V-notch tip was converted into a non-singular strain energy density factor by defining the strain energy density factor for V-notch. Based on the singular stress field near the V-notch tip in the linear elasticity, the strain energy density factor criterion for the V-notch under mixed mode loading （mode Ⅰ and Ⅱ） was proposed. The crack can be looked as the V-notch with zero open angle, thus the fracture criterion for the crack problem is unified with that of the V-notch. To verify the above energy criterion, tensile fracture experiments were carried out using many kinds of single-edged V-notched specimens made out of polymethyl methacrylate （PMMA）. Meantime, applying this criterion, the predictions ofthe crack orientations and critical loads for the above experimental V-notched specimens under the mixed mode were compared with those calculated by the maximum circumferential stress criterion and the experimental results as well. The findings indicate that the values of critical loads predicted by the proposed strain energy density factor criterion are closer to the experimental results than those by the maximum circumferential stress criterion under small open angles.