Research On Extraction Methods Of Cohesive Zone Laws In Material Fracture

In recent years,cohesive zone model(CZM)plays an important role in simulating the crack,delamination and damage mechanical behavior in composite material.The traction-separation curve can describe the whole progress from crack initiation to fracture.Extraction methods of CZM parameters,an important topic in fields of composite material mechanics and fracture mechanics,were studied in this paper.Based on the theory of equivalent domain integral method,a numerical algorithm of J integral,M integral and interaction integral were provided in this paper.They were completed by Python program,and verified in finite element model.An improved direct method was proposed to extract the cohesive zone laws,which can measure the fracture toughness directly without the traditional beam theory.This method was applied into the extraction of bilinear and exponential cohesive zone law in numerical experiment.The result matches well with the numerical solution,which proves the reliability of this method.Combining the field projection method and digital image correlation method(DICM),two inverse methods based on interaction J integral and interaction M integral were proposed.Full-field displacement was measured by DICM to constitute the measurement field.Then,replace the dispersed traction in cohesive zone by uniform loads,constructing the auxiliary fields.According to interaction J(or M)integral conservation,equations were established to inversely solve the traction.A program was built by Python to complete the inverse method.And its reliability was proved by compact tensile numerical experiment.Improved direct method,interaction J integral inverse method and interaction M integral inverse method were applied into compact tensile experiment of 20% and 49% fiber volume content random spruce reinforced polypropylene.Three CZM tractionseparation curves were obtained by three methods.The results show good agreement in variation trend,cohesive strength,initial separation and debonding separation,which can make complete description of the mechanical behavior in cohesive zone.These three CZM extraction methods provide experimental bases for the application of CZM in theory and engineering analysis.