Multi-Field Coupling Numerical Analysis Of Curing Of Composite Wound Structures

Hydrogen storage and transportation technology,which is one of the key technologies restricting the development of hydrogen energy industry,has been highly concerned.For their advantages of light weight and high specific strength,fiber wound composite vessels are the key components for the hydrogen storage and transportation industry.With the increase of operation pressure of hydrogen storage cylinder,the requirements of forming quality and process control of the gas vessels are also increasingly stringent.Curing process has significant influences on the forming quality and performance of composite vessels.The deformation mismatch between the liner and the composite wound layer during curing process may lead to interface debonding,and affects the long-term safety of the composite vessel.To give a sight into the internal deformation mismatch mechanism of composite wound vessel during cure,the following studies are carried out in this paper:(1)The evolutions of the physical and chemical properties of the resin during curing process were analyzed.The curing kinetics equation,mechanical properties,glass transition temperature,thermal expansion coefficient,chemical shrinkage coefficient and other physical and chemical properties of the resin were characterized by DSC,DMA,TMA and volume expansion method.Basic parameters were obtained for further development of the multi-field coupled finite element models of curing process of resin and its composites.(2)Curing experiment of pure Epoxy resin was adopted.The FBGs(Fiber Bragg Grating sensor)was used to monitor the strain development during curing process.Meanwhile,a multi-field coupled finite element model of the resin curing process was developed to study the strain transfer mechanism between the resin and the FBGs.The results show that the simulated changes of temperature,degree of curing and strain have little difference with the measured values,which proves the rationality of the characterizations of the resin properties and the multi-field coupled model.The strain transfer mechanism was explored by comparing the analysis results of pure resin model,FBGs model with interface simulated by tie constraint and FBSs model with interface simulated by cohesive behavior.A significant difference between the strain monitored by FBGs and the strain of resin was detected.Further studies reveals that the shear lag effect caused by the significant difference of stiffness between the matrix and FBGs at the early curing stage plays the main factor affecting the interfacial strain transfer efficiency,while the interface slip has little influence.(3)A multi-field coupled finite element model of the curing process for composite wound cylinder was further established.The feasibility of multi-field coupled numerical method to simulate the curing deformation of composite wound structure was validated by comparing the simulated and measured values of spring-in angle and chord length changes at cutting position of composite wound cylinder after cutting.The difference between simulation and experiment is small.The hoop stress of the winding layer reaches its maximum before the cooling,and gradually decreases during the cooling process.After the cooling,the direction of residual stress of the innermost layer and outermost layer of the winding cylinder is opposite.(4)Finite element model of curing process was also developed for the composite wound vessels by considering the interfacial interaction between liner and composite wound layers.The interfacial deformation behavior between the liner and composite wound layers during the curing process was explored.The results show that interface between the liner and composite wound layer is easy to debond during the cooling process.For type Ⅲ cylinder,the liner could be forced to compress on the composite wound layer during the self-tightening process.For type Ⅳ cylinder,the interfacial debonding tendency can be effectively reduced by using a larger metal boss and increasing the internal pressure in the cooling stage.At the same time,reducing the curing temperature can reduce the thermal deformation,significantly improve the bonding between the liner and the winding layer interface after curing.