| As a key component of the solid rocket motor structural power and fuel system,solid rocket motor cases are gradually developing towards high load capacity while maintaining structural efficiency and light weight.Carbon fiber composite materials have been widely used in solid rocket motor cases fabricated by filament winding due to their advantages of high specific strength,high specific modulus,and strong designability.Due to the problems of uncontrollable resin content and low trajectory accuracy,it is difficult to improve effective fiber strength of composite cases produced mainly through traditional wet winding process.Because composite cases have the characteristics of non-geodetic winding and complex stress field distribution,and the carbon fiber composite materials have high brittleness and low fracture toughness,it is prone to low-pressure burst arisen form the damage of the dome;the dome reinforcement plays a critical role in solving this problem.However,the existing reinforcement methods are deficient,and the coupling correlation mechanism between reinforcement process parameters and structural performance is not clear,resulting in difficult regulation of reinforcement structure performance,low precision and difficulty in overcoming the redundant mass brought by dome reinforcement,thereby seriously restricting the performance factor improvement of the composite case.Hence,it is very important to study the refined reinforcement mechanism of the composite case based on the prepreg tape winding process.In order to carry out dome reinforcement of composite cases,the method of combining numerical simulation and experiments were employed in this dissertation.It conducted the research on the regulation of prepreg winding process suitable for the case and the tensile strength of the composite materials.In the research,a refined finite element model of the composite case was established,and its RBF surrogate model was established to explore the influence mechanism of different dome reinforcement methods and reinforcement parameters on the structural performance of the case,so as to propose an appropriate dome reinforcement method.The main research work and achievements in present dissertation are as follows:(1)By establishing a coupled correlation model between the prepreg winding tension,roller pressure,temperature and winding rate and the degree of interlayer bonding,hoop tensile strength and residual stress,the effect mechanism of process parameters on structural performance was revealed.Based on the coupled correlation model,a non-dominated genetic algorithm was used to establish a multi-objective optimization model of process parameters to explore the coupling behavior between interlayer shear strength,hoop tensile strength and residual stress,and propose a method for performance regulation and optimization of composite structure using prepreg winding technology.In addition,the method was validated by experiments.Finally,a suitable prepreg winding process window is established to effectively improve the structural performance.(2)Based on the prepreg winding process,the interlaminar fracture toughness tests were accomplished.The interlaminar properties were characterized,and the mechanical property parameters of the interlaminar interface were obtained.Based on results of X-ray flaw detection test,a micro-scale model of the composite material was established,which was used to study the factors resulting in strength weakening of the composite case and to revise the hoop tensile strength model.According to the above analysis results,combined with the progressive damage theory,a refined finite element model of the composite case based on interlaminar damage constitutive was established.The damage process and failure law of the case were deduced and the coupling behavior of failure modes was revealed based on the finite element model.Therefore,the failure mode,failure position and burst pressure of the composite case were precisely predicted,and validated by hydraulic burst tests.Compared with the experimental results,the maximum error of the numerical simulation model is 8.1%.(3)Based on the refined finite element model of composite case,RBF surrogate model and Kriging surrogate model for dome reinforcement were established.The influence of different samples on the prediction accuracy of surrogate models was investigated by error evaluation methods,and then the RBF neural network surrogate model which has global approximation properties and high nonlinear prediction accuracy was obtained.According to the prediction results of the RBF surrogate model,a progressive damage failure analysis of the composite case was carried out to verify the reliability of the surrogate model.(4)Multi-objective optimization models of sectionalization-based dome reinforcement,variable-polar-radii reinforcement and variable-angle reinforcement were established respectively based on the RBF neural network surrogate model and the non-dominated genetic algorithm.The effect of reinforcement angle,reinforcement layers and reinforcement range on the performance of the case was investigated and the optimization design of the reinforcement parameters was carried out.A fine reinforcement optimization strategy for the dome that takes both manufacturability and structural performance into account was presented,which realized the target of high precision,quantification and high efficiency of the dome reinforcement.The results show that the sectionalization-based dome reinforcement can effectively improve the structural performance under the premise of meeting the requirements of process feasibility.Compared with the unreinforced cases,the performance factor of the composite case after sectionalization-based dome reinforcement is increased by 18.9%. |
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