Study On The Residual Strength Of Carbon Fibre Composite Overwrapped Pressure Vessels Subjected To Low Velocity Impact

Carbon fibre composite overwrapped pressure vessel(labeled as?CFCPOV?)has been increasing employed to fuel cell vehicles,aeronautics and astronautics because there exhibit many advantages such as high strength and stiffness-to-weight ratios,low density,excellent resistance to fatigue and strong designability.During the storage,handling,loading and unloading as well as usage of CFCPOVs,low velocity impact(LVI)loads such as impactor impact and accidental drops are easily encountered.CFCPOVs are susceptible to impact loads due to weaker load-bearing capacity in the transverse direction than in the longitudinal direction.Besides,the impact-induced damage reduces the load capacity of the vessels,which may cause a potential hazard.Thus,it is important to explore transverse impact responses and residual strength after LVI of vessels.This reaearch is supported by the National Key Research and Development Program of China?Research on Key Technologies of Damage Modes and Risk Identification for Mobile Pressure Equipment?(No.2017YFC0805601),and aims to explore on the progressive failure analysis method under LVI,residual strength prediction method after LVI,the damage mechanisms and energy dissipation mechanisms,and the impact-induced damage characterization of vessels.The main content and conclusions are as follows:(1)Based on the Puck failure criterion,considering the influence of inter-fiber failure fracture plane on the damage variables,the damage evolution criterion of the composite is proposed using the flexibility matrix method.Then a intralaminar damage model of composites is established,which improves the LVI progressive failure analysis method for composite materials.The accuracy of the model is verified by numerical simulation of the G₂₃ shear load.By solving the problem of explicit-implicit combined calculation of composites,a method for predicting the residual strength after LVI is established.Whole-process analysis of LVI and residual strength of composite is implemented based on VUAMT,UMAT user-defined subroutine and ABAQUS-Python scripting language.The accuracy of the predicting the LVI and residual strength models are verified by comparing the numerical and tests results of the LVI and the residual tensile strength of T300/YH69composite laminates.(2)Base on the mechanical analysis model of CFCOPVs,intralaminar damage and interlaminar delamination damage mechanisms are studied by using the progressive failure analysis method.Total energy dissipation mechanism,energy dissipation mechanism for each damage mode,and energy dissipation mechanism of the composite layers and the cohesive interfaces are also explored.Results show impact energy threshold exists during impact.There is no fiber damage below the energy threshold,but the fiber damage at hoop layers is obvious and the fiber compression is dominant above the energy threshold.Matrix damage is more serious than fiber damage under LVI.In the case of this paper,delamination mainly appears in the composite layers,but there is no delamination between the composite layers and the EPDM liner.Energy dissipation for interlaminar delamination,intralaminar damage and friction are reduced in turn,and no energy is dissipated by EPDM liner.Besides,the effects of liner type,impact direction and impactor diameter on the damage mechanism and energy dissipation mechanism of CFCOPVs are studied systematically.(3)The residual burst pressure of CFCOPVs after LVI is predicted based on the explicit-implicit combined whole-process analysis method.The damage mechanism during the burst process is also studied.Results show the residual burst pressure donot decrease below the impact energy threshold and impact-induced matrix damage mapped area becomes the potential burst area.However,the residual burst pressure gradually reduces with the increase of impact energy above the impact energy threshold,and the impact-induced fiber damage at the hoop layers is the potential burst area.Besides,the influence of liner type,impact direction and impactor diameter on the residual strength of CFCOPVs after LVI are studied systematically.By comparison,impact-induced fiber damage at hoop layers is the dominant influence mechanism affecting the residual strength of the CFCOPVs.Furthermore,the surface impact damage area is proposed as a LVI damage characterization method.