一种韧性断裂模型的理论研究和实验验证

Theoretical research and experimental verification on a new ductile fracture criterion

为研究高强钢板成形过程中的损伤破裂机理,更准确地预测高强钢的断裂失效行为,基于细观损伤力学的空穴理论,并在屈服函数就是塑性势函数的通用性假设基础上推导了各向同性的韧性断裂模型;同时引入Lode参数以反映不同应变状态下空穴形核、长大以及聚合的差异,提出了一种包含应力三轴度和Lode参数的新模型.在Hill正交各向异性屈服假设下,描述了平面应力状态下应力比值、r值与应力三轴度、等效塑性应变的关系.最后,针对DP590进行了参数确定和实验验证.结果表明:应力三轴度在高强钢韧性断裂中仍然起主导因素,在低应力三轴下,材料主要是剪切型破坏,空穴的长大及聚合方式主要受剪应力影响,高应力三轴下,空穴损伤主要受拉应力影响,断裂是韧窝形的;Lode参数决定了应力组成形式,也间接地反映了应变状态,它与应力三轴度共同决定了空穴损伤的发展.新的模型能较准确地预测DP590的成形极限.

To study the damage mechanism and accurately predict the fracture failure behavior of high strength steel, a ductile fracture criterion for isotropic damage was proposed on base of the associated plastic flow law and the meso?damage mechanics. The Lode parameter was introduced into the criterion to describe the different mechanisms of nucleation, growth and coalescence of voids. The effects of the stress rate and the normal anisotropic coefficient r on the stress triaxiality and the equivalent strain were described considering Hill's criterion and plane stress state. The new criterion was checked experimentally by predicting the FLD of DP590. Experimental study shows that stress triaxiality still plays a dominant role in the ductile damage process. Fracture at low stress triaxiality is induced by the severe shear stress. And at the high stress triaxiality, the material suffers from the triaxial tension condition and voids coalesce quickly for the influences of the principal stresses. And the Lode parameter affects the evolution of the void?damage as well as the stress triaxiality. The criterion is quite reliable in the light of the comparison between the predicted FLD of DP590 and the experimental results.