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焊接接头应具有一定的变形量和承载能力。在整体屈服阶段,结构部件会产生明显的变形。为了从工程评定的观点来评价所选材料的焊接接头性能,重要的问题是考虑存在缺陷的焊接接头在失稳整体屈服断裂中的判据和变形量。在本文中,着重研究了超过整体屈服而开始失稳断裂时的COD判据,并在考虑到COD-gloval实际应变ε_∞(在足够长标距内的总应变)的前提下,研究了带缺口板材缺口顶端附近的变形特征。研究结果搞清,在塑性拘束系数不大于1的范围内,可以采用COD概念作为整体屈服后断裂起始工程断裂判据。依据弹塑性断裂力学理论,均匀材料的COD与总应变是成比例的,而且比例常数N是试样几何形状和应变硬化指数n的函数。对宽板而言,低强度C-Mn系钢和高强度钢(如HT80钢)的N值,约分别等于1和2。对焊接接头而言,变形特征会受到机械性能不均匀性的影响,而且COD与总应变的关系曲线是非线性的,并主要取决于应变硬化指数比。
Welded joints should have a certain amount of deformation and carrying capacity. In the overall yield stage, the structural components will have obvious deformation. In order to evaluate the performance of a welded joint of a selected material from the standpoint of engineering evaluation, an important issue is to consider the criteria and the amount of deformation of the welded joint under total instability in yield failure. In this paper, we focus on the COD criterion that begins to exceed the overall yielding and start to destabilize the fracture, and on the premise of considering COD-gloval actual strain ε_∞ (total strain within a long enough gauge) Deformation features near the notched top of notch plate. The research results show that the concept of COD can be used as the criterion for the initiation of fracture after yielding in the range of plastic restraint coefficient not greater than 1. According to the elasto-plastic fracture mechanics theory, the COD of a homogeneous material is proportional to the total strain, and the proportional constant N is a function of the sample geometry and the strain hardening index n. For wide plates, the N values for low strength C-Mn steels and high strength steels (such as HT80 steels) are approximately equal to 1 and 2, respectively. For welded joints, deformation characteristics are affected by mechanical inhomogeneities and the relationship between COD and total strain is nonlinear and depends mainly on the strain hardening index ratio.