A Study Of Crack Propagation And Life Perdiction About The Aluminum Alloy Specimen

Fatigue fracture is the main reason to failures of structural member,especiallyin the servo actuator of flight control system.Once the actuator crack because of itsown defects, crack propagation will lead to structral failures even if under lowalternate loading.So,it is particularly important to do the reaseach of crackpropagation rate and the residual life prediction of specimen.The first two chapters introduce the overseas and domestic research status ofcrack propagation and life prediction. Based on the basic theory of crackpropagation and life prediction, Pairs formula, combined with stress intensity factorof crack tip area,is adopted to analysis crack propagation rate and the residual lifeof aluminium alloy plate.In the third chapter, the issue of four-point bending specimen with centralthrough crack is simulated by finite element program(ANSYS). Stress intensityfactors (SIF) of specimen with different crack length are calculated and in crack tiparea is analyzed. The a Ncurve of the fracture process is derived by using thePairs formula.In the fourth chapter, The fatigue crack propagation experiment of four-pointbending specimen with central through and surface crack is carried out. The crackpropagation are recorded by camera. The crack lengths of different cycle index canbe measured by analyzing the photos to describe the curve. Then, the lawthat crack growth rate increased with increasing cycles can be derived bycomparing the he experimental and simulation results.