Study On Fatigue And Fracture Of Surface Crack For Plexiglass

Plexiglass is a transparent polymer material with excellent characteristics such as corrosion resistance,aging resistance,light weight and good mechanical strength.It is often used in various fields such as engineering construction,biomedicine,and aviation.Since the defects or inclusions generated during the processing of plexiglass will cause the initiation of surface cracks,and the crack propagation will lead to fatigue fracture under the action of alternating service loads,the study of the surface fatigue growth law of the material is very important for the safety life assessment of the structure.At present,the fatigue growth behavior of cracked structures is mainly studied based on the fatigue fracture theory under the two-dimensional frame.However,the use of two-dimensional theory to evaluate the fatigue life of materials has certain limitations,For example,the influence of the thickness effect on the fatigue growth rate and the fatigue growth behavior of complex curved cracks cannot be accurately predicted based on the two-dimensional theory.Therefore,this paper selects the typical DX 001 Mitsubishi plexiglass widely used in engineering as the research object,the surface fatigue crack growth rate and the fracture toughness of the curved crack specimens were experimentally studied,and the experimental data was systematically analyzed based on the three-dimensional fatigue fracture theory,and the growth model and fracture toughness suitable for the curved crack structure were determined.The main research contents and research results are as follows:1.Use standard test methods to perform fatigue growth tests on plexiglass with central penetration cracks under different stress ratios,revising the test data based on the three-dimensional fatigue fracture theory can solve the problem that the fatigue growth rate of plexiglass under different stress ratios is relatively dispersed.By fitting the fatigue propagation curve lg（da/d N）–lg(ΔK_eff),the material parameters in the Paris law are obtained.In addition,this article also uses the Matlab programming method to compare the fatigue crack growth rate curve obtained by the seven-point incremental polynomial and the secant method.2.An experimental study was conducted on the fatigue growth behavior of plexiglass surface cracks.Based on the three-dimensional fatigue fracture theory,the fatigue crack growth rate curve under different thicknesses and stress ratios was revised.The revised fatigue crack growth rate graph tends to be consistent,the fatigue crack growth rate curve that is independent of the stress ratio and thickness can be obtained,which avoids the use of multiple fatigue growth rate formulas to express the fatigue growth law under different stress ratios and thicknesses.In addition,we found that the fatigue growth behavior of plexiglass under different thicknesses and stress ratios has a certain law,and analyzed the relationship between surface crack length and internal crack length.3.The fatigue fracture analysis software Zencrack was used to simulate the fatigue growth behavior of plexiglass with surface cracks,and the fatigue growth rate and remaining life of the plexiglass surface cracks were obtained.We obtained the shape ratio,the total number of cycles,and the da/d N–ΔK and da/d N–ΔK_eff curves and compared them with the test results,which proves that the finite element method based on the three-dimensional fatigue fracture theory can well simulate the fatigue growth behavior of the surface cracks of plexiglass.4.The fracture toughness test of the plexiglass specimen with surface cracks was carried out,and the plexiglass fracture toughness value was obtained.The fatigue and fracture toughness section morphology of the plexiglass were observed and analyzed with the help of an optical microscope and a scanning electron microscope.The micro-mechanism of the fatigue crack growth and fracture behavior of plexiglass is discussed.Based on the three-dimensional fatigue fracture theory,a systematic experiment and simulation study on the fatigue growth and fracture behavior of plexiglass with surface cracks is carried out,it is realized that the material parameters measured by the penetrating straight crack are accurately applied to the life prediction of the surface crack based on the crack tip stress field analysis software,and the three-dimensional fracture toughness value of the plexiglass is obtained.This research provides a certain reference for damage tolerance design of plexiglass structure.