Study On Fracture And Damage Performance Of Polypropylene Random Copolymer

Since the 1960s,Italian chemist,Giulio Natta,who had made polypropylene(PP)materials.A large numbers of scientific workers never stopped on the properties of mechanics,chemistry,electrical,etc,worldwide.Nowadays,the PP-R materials which were modified by it's structure are gradually used in daily life and industrial egengineering,and so on.For example,in the field of construction industry,supply and drainage pipes,bumper and other important components.It is found from the related papers no matter at home or abroad that there is little research on PP-R material in quasi-static and dynamic(impact loading)fracture performance(especially the performance of crack propagation)and damage mechanism.It brings some hindrance in application of PP-R.The research on the mechanism of fracture and damage have a great significance in the filed of anti-fracture design,structural failure assessment and structural residual life estimation.So,in this paper,PP-R materials were selected,and the mechanism of fracture damage was studied by experiment,digital image correlation method and finite element method.The main research work and achievements of this paper are as follows:1)First of all,for the specimen with different pre-crack location(center cracks,two types of off-center crack:one is 20mm,the other is 40mm),making I-mode fatigue pre-crack.Obtaining two types of PP-R specimens which have different pre-crack lengths.During the test,it was found that the PP-R materials still had toughening hysteresis under different spans.2)The three types of pre-crack specimens were subject to quasi-static loads with the same displacement speed,and obtaining graph of the relationgship between the load F and the crack propagation ?a.Analyze the fracture form of the materials under the three loading modes.It is found that the length of quasi-static crack propagation in the hystereis zone is less than that beyond the hysteresis zone.3)During the quasi-static test,using digital image correlation measurement technology.The crack tip displacement field and strain filed in initiation crack state and maximal propagation state under pure I and mixed-mode are calculated by VIC-2D software.And the feasibility is analyzed.4)Three types of specimens were under impact load of falling hammer.During the falling hammer test,the dynamic crack propagation path of these specimens were obtained by high speed camera,and get the speckle image of the specimens.Obtain the displacement field and strain field under the state of initial crack propagation of PP-R specimens by VIC-2D software.And the feasibility ia analyzed5)The Scanning Electron Microscopy(SEM)was used to analyze the fracture morphology of the three types of specimens which were under the quasi-static test and impact test conditions.And obtain the fracture and damage form of quasi-static crack stability state,crack fast propagation form under the quasi-static load,and fracture and damage form of crack propagation under the impact load.6)Franc3D and ABAQUS software were used to co-simulate crack tip's fractural parameter,such as stress field,strain field,displacement field,Crack Opening Displacement(COD)and Stress Intensity Factor(SIF).And compared with the result of digital image correlation method.