Research On The Damage Coupling Destruction Model And Energy-absorbing Mechanism Of Composite Thin-walled Structure

Crashworthiness is the ability of aerospace,rail transport and automobile,etc.to protect the safety of occupants and structures in the case of potentially survivable accidents.Compared with traditional metal material,composite material structures have been widely used in the crashworthiness design of engineering structure due to their higher specific strength,specific stiffness,specific energy absorption and light weight,etc.Because composite structures under axial crush loading not only have various complicated damage modes including fiber breakage,matrix cracking,delamination,etc.,but there also exists the coupling effect between different damage modes.The traditional damage models can not still accurately simulate the various coupled damage modes of composite thin-walled structures.Therefore,a deep study on failure mechanism of composite structures and establishing more accurate and reliable damage models are of great significance in researches on the impact dynamic characteristics and crashworthiness design of composite structures.In the thesis,based on continuum damage mechanics(CDM),a stiffness degradation method based progressive damage model is proposed to simulate the failure behaviors of three typical composite thin-walled structures under axial quasi-static loading condition.Subsequently,energy-absorbing characteristics of composite thin-walled structures are extensively studied based on finite element analysis.The main research contents are as follows:Initially,a nonlinear progressive damage model including the intra-and inter-ply damage is established.The maximum stress failure criterion,an exponential damage evolution and stiffness degradation method are adopted to simulate the intra-ply damage.The inter-ply cohesive damage model is modeled with the Traction-Separation constitutive model,quadratic nominal stress failure criterion,mixed-mode fracture energy based damage evolution and inter-ply stiffness degradation method.The damage model implemented by the user material subroutine(VUMAT)is used to simulate quasi-static crushing processes of three typical composite thin-walled structures such as UD composite waved plate,fabric composite waved plate and fabric composite square tube.Results show that the simulated results corresponding to three structures are respectively in agreement with corresponding experimental results.Thus,the validity of damage model is verified.Next,the effect of typical parameters,such as layer number,height and triggering mechanism,on the crashworthiness of fabric waved plate is analyzed.Thereinto,the W-like,wedge-like and sawtooth-like triggers are presented and corresponding impact energy-absorption characteristics are compared.Results show that the initial peak load,energy absorption and SEA of waved plate during impact process increase with the increase of layer number.The types of trigger have great effect on the impact behavior of composite waved plate and have the critical induced effect on damage modes.Finally,the effects of stacking sequence of UD and fabric composite waved plates on energy-absorption characteristics are respectively analyzed.Based on the similar layup family,the difference between the UD and fabric composite waved plate in energy-absorption characteristics is analyzed simultaneously.Results show that increasing the content of 45° fiber has the effect on increasing the energy absorption but slight effect for the content of 90° fiber.With the increase of 0 in[03/θ2/03]and[±θ]2s,the trend of the first increase and then decrease in impact loads and SEA is found in fabric waved plate.The impact loads and SEA of UD waved plate obviously increase with the decreasing of 0 in[0/(θ-90)]3s and[±θ]3s.There is much large difference between UD and fabric composite in crushing behaviors of waved plate using similar layup family.