初始损伤对钢的延性起裂韧性影响的细观力学分析

Meso mechanical analysis of effect of initial damage on ductile fracture initiation toughness of steel

通过力学参数测量和微观观察研究了初始损伤对钢的延性起裂韧性影响.研究结果表明,随钢组织在预加载荷中产生的微孔洞初始损伤量的增加,其延性起裂韧性降低.并进一步对初始损伤孔洞在后续加载中的演化行为的细观有限元力学进行模拟计算及微孔洞初始损伤对钢的延性起裂韧性影响的机理进行了研究.计算结果表明,初始大尺寸孔洞长大速度比较快,且在这些孔洞之间存在变形局部化,容易诱发二次小孔洞的形核和长大,从而使一次初始大孔洞连接,使材料延性起裂,因而大尺寸初始损伤孔洞主导了材料的延性起裂.随初始损伤量的增加,大尺寸孔洞的数量和尺寸增加,使孔洞聚合(延性起裂)时的应变降低,这也就是随着预载荷比P0/Pgy的增加,材料的延性起裂韧性Pi/Pgy降低的细观力学原因.

By using measurement of mechanical parameters and microscopic observation, the effect of initial damage on the ductile fracture initiation toughness of steel was investigated experimentally. The results showed that with increasing the amount of the initial void damage, the ductile fracture initiation toughness of steel decreases. The mechanism of this effect was further investigated by using finite element method to simulate the evolution of pre-damage voids during the subsequent loading process. The computation results showed that the initial voids with large size grew faster and deformation localization took place among these large voids. The deformation localization could promote nucleation and growth of secondary voids, leading to coalescences of the large voids and the ductile fracture initiation of material, so that the large initial voids dominated the ductile fracture initiation of material. With increasing the amount of initial damage, the number and size of large voids increased. This caused the decrease of strain of void coalescence （ductile fracture initiation）, being the meso mechanical reason of decrease in ductile fracture initiation toughness Pi/Pgy with increase in pre-load ratio Po/Pgy.