Study On Fatigue And Damage Of UPVC Materials

UPVC(Unplasticized PVC),is a polymer composite material,its superior performance,the characteristics of significant,Mainly reflected in the strong corrosion resistance,high mechanical strength,small fluid resistance,light texture,easy installation,non-toxic health,good watertight and so on.At present UPVC material products industry is developing rapidly,and is widely used in the key structure of the project.However,there are few studies on the mechanical properties of fatigue damage of polymer composites at present,especially in the field of damage fracture mechanics,and the fatigue damage mechanism of UPVC is less.The study of this mechanism can predict the propagation law of fatigue crack in PVC material and the fracture parameters,which is of great significance in carrying out anti-fatigue design,structural failure evaluation and structural residual life estimation.Therefore,in the study of this subject,the fatigue damage behavior of UPVC is studied by fatigue test and the fatigue fracture mechanism of UPVC material is discussed in depth.The main contents of this paper include:1)A reliable test system was established by using MTS 810 material fatigue tester and CCD camera system.The three-point bending test was carried out under different alternating loads,and the fatigue crack propagation in UPVC specimen was observed and recorded.The fatigue crack propagation data of UPVC specimen under different alternating loads were obtained(a,N).2)The seven-point incremental polynomial method is used to process the(a,N)data by mat lab programming.The crack length ai and fatigue crack growth rate da/dN are obtained.The ?K is obtained by the formula,finally the curves of a-N and fatigue crack growth rate da/dN-?K.As well as lg(da/dN)-lg(?K)curve.3)By analyzing the da/dN,-?K curves and lg(da/dN)-lg(?K)curves of different alternating loads,some laws of fatigue crack propagation of UPVC are obtained.4)The two important parameters C and m of the fatigue crack growth rate of the UPVC specimen under different alternating loads are calculated by the Paris formula,and the expression of the fatigue crack growth rate of the UPVC under different load is obtained.5)The crack tip displacement field and the strain field corresponding to the fatigue crack propagation were calculated by VIC 2D software when the fatigue crack was extended to 1mm?5mm?10mm?15mm?20mm.The displacement and strain field of crack tip under different crack propagation length are analyzed.6)The fatigue crack fracture morphology of UPVC specimen was analyzed by scanning electron microscopy(SEM).the fatigue damage characteristics of UPVC materials under different fatigue crack growth lengths are compared and the damage mechanism is studied.