一、疲劳计算 Solution:1. We can get three conclusions from the picture shown in Figure E14.4.a. the flaw shape is buried circular plate crackb. initial flaw size is 0.1 milimeter .c.critical dimension of fatigue crack is about 1 milimeter .So a0=0.1mm ac=1mma/2c=0.5 a/h=0.75 Look up the curves of Me shown in appendix D Me=1.1As Q=Φ2-0.212(σ/σs)2 Calculate Q=2.412. Estimate the remaining life of the part As da/dN=10-11 (Δk)4=10-11[Me*σ*(3.14*a/Q)1/2]4 The derivation of expression (1) is Nc is da/10-11[Me*σ*(3.14*a/Q)1/2]4Known:The maximum stress isσ, σ=300Mpa .Substitute Mc ,a0 ,ac ,and Q into expression (2) Integrate Nc.Nc=49 weeks.As the initiation stage of the flaw is 50 percent of the life of part , the total life time of the part is 49*2=98 .The above results are some larger ,because we uncondering stress frequency and other factors ,and it will be understood in Figure 1.1 Obviously , σe is larger than 300 Mpa ,because Nc cannot be boundlessly large. σs σeFrom the calculation above,it can be found in the process that the influence factors of the fatigue are:A, stress concentrationB, stress cycle timesC, stress ratioD, stress amplitudeE, the steel yield strength二、断裂分析根据上图 40Cr 断口金相照片，试分析：1. 断裂的影响因素主要有哪些？影响钢结构断裂的因素有以下几个方面：(1)、裂纹断裂力学认为，对脆性断裂必须从结构部存在的微小裂纹的情况出发进行分析。用断裂力学理论可以计算裂纹住荷载和侵蚀性介质下的扩展情况；当裂纹扩展剑临界尺寸时，脆性断裂就会发生。线弹件断裂力学指出，当一块板处于甲面应变状态下假如应力强度因子Ｋ１＝α❑√π aσ≥Ｋ ic 裂纹将迅速扩展而造成断裂。其中：σ 为板所受的拉力，ａ为裂纹尺寸，α 为系数，与裂纹形状、板的宽度以与应力集中等有关，Ｋ ic 裂韧性，代表材料抵抗断裂的能力，可由实验得到。（２）、应力集中的影响应力集中越严重，就越易发生脆性破坏，原因是...
