Impact Mechanical Behavior And Failure Mechanism Of Carbon/UHMWPE Hybrid 2.5D Woven Composites

Carbon fiber reinforced 2.5D woven composites have outstanding advantages such as excellent mechanical properties,design ability and near net forming,and have been widely used in aerospace,transportation,and wind turbine blade fields.In service,materials often undergo low velocity impact loads such as hail falls,tool drops,flying debris and stones.At present,due to the characteristics of high brittleness and poor transverse performance of carbon fiber,carbon fiber reinforced 2.5D woven composites present a low impact damage tolerance,which greatly limits its application.In this paper,the 2.5D woven structure is taken as the research object,and the hybrid structure design of UHMWPE fiber and carbon fiber is carried out.Carbon fiber reinforced 2.5D woven composites(C-2.5DWC)and Carbon/UHMWPE hybrid 2.5D woven composites(H-2.5DWC)are manufactured by vacuum assisted resin transfer molding process.The mechanical properties and damage mechanism of 2.5D woven composites under bending,single and repeated low velocity impact are studied by experimental tests or numerical simulation.The main research contents and conclusions are as follows:(1)Combined with acoustic emission(AE),digital image correlation(DIC)technology and micro-computer tomography(Micro-CT),three advanced real-time characterization techniques are used to test the three-point bending of warp(90°)and weft(0°)samples for carbon fiber reforinced 2.5D woven composites and Carbon/UHMWPE hybrid2.5D woven composites.The internal damage morphology and damage distribution are analyzed,the progressive damage evolution mode is discussed,and the failure mechanism is clarified.The results show that H-2.5DWC exhibits excellent toughness characteristics compared with C-2.5DWC.For hybrid 2.5D woven composites,the flexural mechanical responses of warp and weft direction specimens are quite different.Among them,the H-2.5DWC warp specimens show higher bending strength and specific energy absorption,but the H-2.5DWC weft specimens show smaller damage volume.(2)Single low velocity impact test is carried out for carbon fiber reforinced 2.5D woven composites and Carbon/UHMWPE hybrid 2.5D woven composites with 5 J/mm and 15J/mm impact energy levels.On this basis,the second and third repeated low velocity impacts of the same energy level are carried out respectively for specimens with 5 J/mm impact energy level.Then,Micro-CT is used to analyze the internal damage morphology,quantitatively describe the damage volume,and clarify the failure mechanism.The results show that the damage tolerance of the composite can be improved significantly by the hybrid method.Under single or repeated low velocity impact loads,H-2.5DWC has a smaller damage volume than C-2.5DWC,showing a more excellent impact damage tolerance.(3)Based on the "local" damage characteristics of 2.5D woven composites under low velocity impact load,a meso-macro hybrid mechanical analysis method is proposed.The stiffness damage reduction method is utilized to carry out numerical calculations of carbon fiber reforinced 2.5D woven composites and Carbon/UHMWPE hybrid 2.5D woven composites under 5 J/mm and 15 J/mm single low velocity impact.Compared with the experimental results,the progressive damage mechanism is clarified.The results show that the mechanical response curves and failure modes calculated by the proposed meso-macro hybrid model are in good agreement with the experimental results.Compared with C-2.5DWC,UHMWPE fiber in H-2.5DWC display higher stress level at 5 J/mm impact level,and UHMWPE fiber and carbon fiber bear load together at 15 J/mm impact level,showing a good synergistic effect.