Characterization Of Prepreg Tack Behavior And Its Regulation By Placement Process Parameters

The tack of prepreg has a decisive influence on the forming quality of automated placement.The characterization of prepreg tack behavior and its regulation method based on the control of placement process parameters are mainly studied in this thesis.In the second chapter,the response features of the tack behavior between prepreg and the mould during the debonding process are characterized by the probe test firstly,it is found that there are two failure modes:interfacial failure mode(low temperature)and cohesive failure mode(high temperature).Subsequently,the exponential cohesive zone model(CZM)is used to describe the inelastic response of the prepreg bonding layer.Meanwhile,based on this model,the response laws of prepreg tack behavior under different placement process parameters are systematically discussed.The results show that the bond strength and the characteristic displacement of prepreg decline nearly linearly with the growth of the laying rate and go up nearly linearly with the rise of the laying pressure.With the growth of the laying temperature,the CZM parameters of prepreg tack increase at first and then decrease,reflecting approximately quadratic relationship.In the third chapter,the finite element model is established to further reveal the quantitative relationship between the tack of prepreg and the placement process parameters with the combination of the probe test and the peel test.First,the CZM parameters of prepreg tack which is required for the peel simulation are obtained by the probe test.Then,the debonding process of 90 degrees peel of prepreg under different placement process parameters are studied by simulation and experiment.The results reflect that the differences between the simulation values and the test values of the peel force between prepreg and the mould are all less than 15%,which proves that the CZM of prepreg tack based on the probe test can reveal the nonlinear debonding behavior of prepreg during the peel process under different placement conditions.The above results indicate that the laying temperature has a significant effect on the tack of prepreg.Therefore,the following emphasis is put on the method for regulating prepreg tack based on the control of the laying temperature.In the fourth chapter,the characteristics of the radiative heat flux distribution from the infrared lamp of the placement machine are studied.Based on the real geometric features of infrared lamp,a heat source equation considering the parameters of the heat source is established,on account of the systematic analysis of the heat flux from the lampshades indirectly and the tubes directly.After that,the finite element simulation of dynamic and static heating of infrared lamp is implemented based on the heat source equation,in which the radiative power of the tube is calibrated by the cylinder test.The results reflect that the temperature simulation results are in good agreement with the experimental data,thus verifying the accuracy of the heat source equation.In addition,the impact of the parameters of infrared lamp on its heat flux distribution is explored using the heat source equation.In the fifth chapter,the control rules of laying temperature is investigated by numerical simulation and experiment respectively.First of all,the thermal-mechanical coupling model using the finite element simulation approach is established to simulate the dynamic laying process of prepreg.At the same time,the CZM of prepreg tack and the heat source equation of infrared lamp are imported into the lay-up model for solving dynamic laying temperature.Then,the model is verified based on the dynamic laying temperature test.Finally,the influence of the laying rate and the heat source power on the temperature of the dynamic nip-point is studied using the approach of combining simulation and test.The results show that the laying temperature descends with the increase of the laying rate,and ascends with the climb of the heat source power.It provides a theoretical basis for the formulation of the constant temperature control strategy and the adjustment of prepreg tack.The above work has a certain engineering significance for revealing and regulating the tack behavior of prepreg and optimizing the automatic laying process.