高韧性合金钢断裂韧性及疲劳裂纹扩展门槛值的联合试验方法

A Combined Test Method to Determine Fracture Toughness and Fatigue Crack Growth Threshold of High-Toughness Steel Alloys

在柴油机曲轴、连杆等关键零部件的可靠性设计和失效评估中,断裂韧性及疲劳裂纹扩展门槛值分别是衡量材料抵抗裂纹失稳扩展和裂纹开始扩展的重要指标.但是,对于高韧性合金材料,难以通过常规试验所推荐的厚度确定平面应变断裂韧性,而门槛值的测定通常不但非常耗时,且难以直接应用于不同循环特性的实际结构.本文针对高韧性合金钢34CrNi3MoA,提出一种将断裂韧性和疲劳裂纹扩展门槛值试验合二为一的试验方法,即用同一个试件可以同时测定门槛值和断裂韧性.利用断裂韧性关于试件厚度的渐近特性,以几种较薄试件的试验,确定平面应变状态下的断裂韧性.试验结果还表明,裂纹扩展门槛值的试件厚度依存性可以忽略,并给出了任意循环特性(应力比)下的门槛值计算公式.

In the durability design and failure evaluation of key components such as crankshafts and connecting rods of diesel engines,fracture toughness and fatigue crack growth threshold are important parameters to measure the ability of the material to resist the crack instability growth and the beginning of crack growth,respectively.However,for high-toughness alloys,it is difficult to determine the plane strain fracture toughness through the thickness recommended by the conventional tests,and the determination of threshold is usually time-consuming and difficult to be directly applied to actual structures with different cyclic characteristics.This paper proposed a combined test method to determine the fracture toughness and the threshold simultaneously using one specimen,for evaluating the high-toughness steel alloy 34CrNi3MoA.It is found that the plane strain fracture toughness,which is defined under the plane strain state,can be well determined through comparison between several thin specimens utilizing the saturating behavior of toughness with specimen’s thickness,while the effect of specimen’s thickness on the threshold can be neglected.In addition,a formula to estimate the fatigue threshold for arbitrary stress ratio has also been given.