| Prepreg tape winding is one of the advanced manufacturing technology for fabricating composite products.By virtue of the unique manufacturring characteristics,prepreg tape winding technology has become the main method for fabricating the cylindrical components.Moreover,the fabricating technique has been widely used in aviation,aerospace,marine and other industrial fields,especially for manufacturing shell of rocket motor and strategic missile.The rapid devlopment of composite materials has driven the prepreg tape winding to industrial automation for fabricating more complex components.However,compared with the mature winding mechanical systems,the manufacturing process still relies on the worker's experience.This will easily make the wound products with defects such as fiber wrinkles,delamination,cracks,etc.In addition,the unadvanced fabrication method also limits the innovation of winding processes and can dissatify the design of product with the desired performance.Therefore,the study and establishing reliable design method for process parameters are of great theoretical significance.Besides,it is of great importance to improve the performance of wound products and carry on the research of industrial automation.In order to solve the shortage in prepreg tape winding process,the problems existing in winding process are firstly analyzed based on the experimental platform.Then,the key process techniques are investigated during the prepreg tape winding.In this thesis,the friction system for prepreg tape transport,the residual stresses and hoop tensile strength for composite cylindrical part,and process parameters design and control are studied deeply.The main research work of this thesis is summarized as follows.(1)Establishment of the mapping relationship between wrapping tension and process parameters.Wrapping tension is the crucial factor to guarantee the product quality.The variation of wrapping tension is easily affected by friction force caused by the transport process of prepreg tape.Based on the prepreg tape transport characteristics in actual winding process,the friction system between prepreg material and hot compaction roller is discussed according to the frictioinal theory.Through the modified version of Howell's equation,the normal pressure can be measured in contact region,and further the pressure formula can be regarded as an indirect method to achieve the variable friction coefficient based on formula fitting method.The experimental results indicate that the friction coefficient between hot compaction roller and prepreg tape can be easily affected by process parameters including winding tension,temperature,speed and material.Moreover,the friction behavior transfers from resin-dominated friction to fiber-governed friction as the winding temperature rises.Meanwhile,increasing the winding tension or reducing the winding speed can reduce friction ability markedly.Then based on the experimental data,the mapping relationship between wrapping tension and winding process parameters is established using the regression fitting method.(2)Modeling of residual stress for prepreg tape wound cylinder.The residual stresses formation is inseperable from the manufacturing process which includes the winding and curing fabrication process.In these two process,the input of process parameters decides the stress variation of wound cylinder.Therefore,the stresses caused by winding and cure process stage are necessary to be investigated,respectively.Firstly,the stresses induced by wrapping tension in winding process stage are built by adopting the composite thick-walled theory and superposition principle.Then,the stresses caused by the resin chemical reaction and cure temperature are calculated by empolying the micromechanics model in curing process stage.Finally,the residual stresses of composite cylindrical part after mandrel removal are established according to the stress boundary conditions.Moreover,the strain gauge is used to measure the deformation of composite cylinder in slitting experiment,and then the model accuracy is validated.(3)Modeling of hoop tensile strength for prepreg tape wound cylinder.According to fabricating experience and the relationship between composite strength and fiber volume content,the effect of pressure from hot compaction roller on fiber volume content of prepreg tape is theoretically discussed in actual manufacturing process.The four models including resin continuity model,fiber consolidation model,Hertzian contact model and temperature-viscosity model are adopted to analyze fiber volume content in contact consolidation region.In addition,analyzing the fiber motion and combing the resin flow theory,the change of fiber volume content due to fiber motion is determined in curing process stage.Then through the maximum stress failure criterion,the model of hoop tensile strength is established.Experimetal result implies the prediction model is accuracy,and the fiber volume content of composite cylindrical part is higher in the inner layer than that in the outer layer.(4)Influence of process parameters on product performance.After the models of residual stresses and hoop tensile strength are obtained,the influence of process parameters on product performance would be discussed.The winding tension,temperature,speed and pressure are selected as the key parameters.And these parameters are limited wthin the range of actual process parameters,and inputed with constant value.Then the influence mechanisms of single-factor and multi-factor coupling on residual stresses and strength are revealed,respectively.Numerical analysis shows that the increase any of the winding tension,temperature and speed can improve wrapping tension and tensile strength,and make the residual stresses reduce.Besides,rising the winding pressure can also enhance the strength,but the ability of improvement is relativity low.Finaly,analyzing the sensetivity of process parameters,the degree rank of influence for controlled parameters on residual stresses is: temperature > winding tension > speed.While the sensetivity grade for hoop tensile strength is: winding tension > temperature > speed > pressure.(5)Winding process parameters design and control.The process parameters for fabricating composite cylindrical part can be designed by combining the models of residual stresses and hoop tensile strength.Based on the difference in structure of prepreg tape wound product,the formula is firstly established to design uniform hoop residual stress for composite cylindrical part with a linear.Secondly,for the composite part without mandrel,the design criteria for obtaining uniform hoop residual stress under the condition of internal pressure is proposed.The designed wrapped tension can be determined by combining the neural network algorithm based on the residual stresses model.And the solution sets of process parameters can be obtained by searching the model of wrapping tension.Then the parameter sets are selected to find the optimized parameter combination based on maximum tensile strength.Finally,in order to avoid the deviation between expectation and object caused by the parameter fluctuations,the models of residual stresses and hoop tensile strength are applied to control process parameters.The simulation result shows that the control method can reduce deviation by adjust process parameters in real-time. |
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