Study On Impact Resistance Of Laminated Woven Composites In Salt Spray Environment

Carbon fiber reinforced plastics(CFRP)which have the characteristics of high specific strength,high specific modulus and corrosion resistance,are used in marine field widely.The effect of corrosion and impact in marine environment has put forward strict requirements on the corrosion resistance and impact resistance of materials.Multi-layer woven composites overcome the disadvantage of low interlaminar strength of traditional laminated composite materials and have developed rapidly.The paper compared the impact property of multi-layer woven composites with different structures before and after salt-spray aging so as to provide technical theoretical support for the application of such materials in the marine environment.Firstly,the hypothesis of the convex shaped weft cross-section with quadratic function was proposed based on the analysis of the micro-morphology of the multi-layer woven structure to obtain the coefficient of variation of the convex shaped weft cross-section and the mathematical relationship between the structural parameters.The Micro-CT technology was used to observe and analyze the yarn morphology in the cross section of multi-layer woven preform.The hypothesis which contained the convex shaped weft cross-section with quadratic function and rectangular warp cross-section was proposed.The equation for solving the coefficient of variation of weft yarn cross section was derived,the mesoscopic model of the multi-layer woven structure was established and the mathematical relationship between the structural parameters of the preform was obtained.The results of the comparative analysis showed that the thickness and fiber volume fraction of the multi-layer woven preform,and the theoretical calculated values were in good consistency with the experimental results,which verified the validity and rationality of the mesoscopic model.Secondly,Charpy impact tests was applied to compare and analyze the impact property of three kinds of structure of multi-layer woven composites with line weft twill,twill and line warp twill.The high energy single impact test and low energy multiple impact test were carried out on three kinds of structure of multi-layer woven composites,and the impact property of them were compared and analyzed through load-deflection curves and damage morphology observation.Under the high energy single impact test,the main failure mode of three kinds of structure of multi-layer woven composites was fiber fracture.The structure with line warp twill has the highest maximum impact force,the structure with line weft twill has the second highest and the structure with twill has the lowest.The structure with line warp twill has the largest impact fracture energy and crack forming energy,the structure with twill has the second largest and the structure with line weft twill has the smallest.Under the low energy multiple impact test,the main failure modes of three kinds of structure of multi-layer woven composites were matrix cracking and interfacial failure.The structure composites with line warp twill have the strongest multiple impact resistance,the structure with line weft twill has the second strongest,and the structure with twill has the weakest.Finally,Charpy impact property of three kinds of structure of multi-layer woven composites before and after salt-spray aging was compared.The study found that the weight of composites was increased because of the absorption of moisture after the salt-spray aging.The salt-spray aging reduced the glass transition temperature(Tg)of the resin.After 8 days of the salt-spray aging,the maximum impact force of three kinds of structure of multi-layer woven composites was almost unchanged,but the impact fracture energy of line weft twill,twill and line warp twill decreased by13.07%,8.04% and 11.51% respectively,which was showed by the reduction of crack propagation energy and the unchanged crack forming energy.Through the analysis of the impact damage morphology of three kinds of structure of multi-layer woven composites before and after salt-spray aging,it was showed that the bond strength of the fiber/resin interface was reduced by the salt-spray aging and the crack propagation energy was reduced,so the impact fracture energy was reduced.After the comprehensive analysis of the impact property of three kinds of structure of multi-layer woven composites,it was shown that the multi-layer woven composites with line warp twill structure all had excellent impact resistance property before and after salt-spray aging.