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本文企图从宏观和微观相结合的观点分析和讨论K_(1c)的物理意义及其影响因素。对于脆性断裂,通过表面能密度、裂纹尖端凝聚力场以及点阵“捕捉”作用说明K_(1c)的意义。用热力学原理分析了K判据的必要性和充分性,指出只有在裂纹尖端半径小于临界尺寸时,K判据才是必要和充分条件。 对于小范围屈服,裂纹尖端的钝化是通过尖端放射位错和吸引周围异号位错而形成的,这是最可能的物理过程。同时,着重指出Vitek的理论结果。 在弹塑性连续理论中,采纳了Orowan—Irwin有效断裂能密度的概念。用这概念及能量原理,本文建议要从试样塑性变形功中抽出属于K_(1c)组成部分的裂纹尖端塑性功。可以导出K_(1c)的表达式,形式上和陈篪的结果以及Hahn—Rosenfield的结果相似。影响K_(1c)的主要因素有:硬化率,杨氏樸量,抗拉强度,平面应变断裂真应变和一个适当的长度参数,其意义随断裂机制而异。其它冶金因素,例如晶粒度,可能通过断裂真应变影响K_(1c)。
This paper attempts to analyze and discuss the physical meaning of K_ (1c) and its influencing factors from the macroscopic and microscopic perspectives. For brittle fracture, the meaning of K_ (1c) is explained by the surface energy density, the crack tip cohesion field, and the lattice “catch” effect. The necessity and sufficiency of K criterion are analyzed by thermodynamics principle. It is pointed out that K criterion is necessary and sufficient condition only when the radius of crack tip is smaller than the critical size. For small-scale yielding, passivation of the crack tip is formed by tip-emitting dislocations and attracting the surrounding allotopic dislocations, which is the most likely physical process. At the same time, highlighting the theoretical results of Vitek. In the elasto-plastic continuum theory, the concept of effective fracture energy density of Orowan-Irwin was adopted. Using this concept and energy principle, this paper proposes to extract the crack tip plastic work which belongs to the component of K_ (1c) from the plastic deformation work of the specimen. We can derive the expression of K_ (1c), which is similar in form to that of Chen Chi and Hahn-Rosenfield. The main factors affecting K_ (1c) are: hardening rate, Young’s modulus, tensile strength, true strain of plane strain fracture and an appropriate length parameter, the significance of which varies with the fracture mechanism. Other metallurgical factors, such as grain size, may affect K_ (1c) by true strain at break.