Study On Effect Of Defects On Fracture Process Of Fiber Bundle Model

Defects that exist inside composites have conspicuous effects on mechanical properties of composites.It is an important subject in the fields of mechanics,physics and material science to study influence of defects on fracture process of materials.Fiber bundle model is a theoretical model commonly used to study tensile fracture properties of materials from the standpoint of physics.In order to study effect of the number of defects,limit defect size and spatial distribution of defective fiber inside defects on fracture process of composite materials in this thesis,extended fiber bundle model with cluster defects is constructed on basis of classical fiber bundle model.The effect of defect parameters on tensile fracture properties of model are analyzed by numerical simulations.The main research includes:Firstly,tensile fracture process of model is numerically simulated under equal load sharing,when considering lateral long range interaction limit.It is found that fracture strength of model decreases monotonically with the increase of the number of defects.However,maximum avalanche size has minimum value and the loading step has the maximum value at the extreme point.This indicates that the toughness of system is maximum.The fracture strength of system decreases monotonically with the increase of limit defect size.The results show that only when defect size is large enough,the influence of defect size on microfracture process appear.Defect parameters only change statistical distribution of fracture threshold in fiber bundles and have no effect on fracture statistical properties of model.In order to further study the effect of stress concentration at crack front on tensile fracture process of this model,the tensile fracture process of this model is simulated under local load sharing,when considering lateral short range interaction limit.It is found that when limit defect size is large,even if the number of defects is small,it will still have a great influence on fracture process of model.When maximum avalanche size has the maximum value and the loading step has the minimum value with the change of the number of defects,the system is most prone to brittle fracture.On the other hand,as the increase of limit defect size,model is more prone to macroscopic brittle fracture,and the corresponding fracture strength decreases monotonously.In addition,under the above two kinds of stress redistribution,the different distribution forms of damage degree inside defects and size of system have a certain influence on tensile fracture properties of the model.In conclusion,compared with fiber bundle model with single fiber defect,the number of defects and defect size have a significant influence on tensile mechanical properties of fiber bundle model with cluster defects due to the overlapping competition mechanism among defects.The simulation results in this paper have a certain theoretical significance for studying microscopic fracture mechanism of actual materials and improving mechanical properties of composites.