【摘要】 韧性裂纹开始扩展的J积分值对于韧性断裂的工程构件是一个重要的材料性能指标。统计了三个钢种两种焊缝 2 0 0多个J积分值。发现当裂纹生长量Δa <0 .6mm时 ,Δa与J积分值存在线性关系 ,可以用J =J0 +K(Δa)表示 ,式中K =di dΔa(Δa =a0 +da) ,a0 是J—Δa曲线与钝化线的交点。当da =0时的J值以Ji 表示 ,它表示了韧性裂纹开始扩展时的J积分值。实验证明 ,只有Ji 与静拉伸发生颈缩时的颈缩比功有良好的线性相关性 ,从而由Ji 换算得KⅠC也应与颈缩比功线性相关 (相关系数 >99% ) ,而与静力韧度无关。而韧性裂纹开始扩展以后 ,各个扩展量下的JR 值与静力韧度、颈缩比功无任何相关性。从J积分的条件、裂纹尖端的特征、断裂的微观机理对试验结果进行了分析。从工程应用角度出发 ,说明Ji 与屈服强度与强度极限之比 (称屈强比 )无关 ,低屈强比不是保证缺陷 (或微裂纹 )抵抗其扩展的有效方法 ,有效的方法是提高强度的同时 ,不降低均匀塑性变形能力Ψb,这可以通过提高冶金质量如细化晶粒来实现。更多还原

【Abstract】 J integral value related to the initiation of ductile crack is important material properties for the engineering structure of ductile fracture. J values more than two hundred were treated by statistical method for three kinds of steel and two kinds of weldments. It is shown that J values behave linear relationship with Δ a as Δ a <0.6 mm.i.e J=J+K (Δ a ). Where K=d i/d Δ a , Δ a=a 0+d a, a 0 is the intersection of J -Δ a curve with blunting line, d a is the extent distance of ductile crack growth. When d a=0, J value is expressed by J i, J i is the value related to initiation of ductile crack. J i shows linear behaviour only with necking specific energy of tensile test, but do not have such kind relation with specific fracture energy. After initiation of crack, J value did not relate both the necking specific energy and specific fracture energy. The test results were analysed, which are based on both the characteristic of crack tip zone and the micro mechanism of crack fracture, J i did not relate to the ratio of yield stress to ultimate strength. The lower ratio of yield to ultimate strength can not provide higher fracture resistance. It is the effective way to increase strength in condition of maintaining the ability for homogeniously distributed deformation, which are achieved by improving metallurgical technology, for example, by fining the grain side.更多还原