Study Of Low-velocity Impact Damage And Multi-scale Modeling Methods For Non-orthogonal Fiber Woven Thermoplastic Composites

Fiber woven thermoplastic composites(FWTC)are widely used in the aerospace industry due to their excellent properties such as high specific strength,high specific stiffness,fatigue resistance and corrosion resistance.However,they are inevitably subjected to impacts from foreign objects,such as tool falls,hail,debris impacts,etc.,in aerospace service,resulting in low-velocity impact(LVI)damage.Moreover,the FWTC are non-orthogonal due to the change of yarn angle during the manufacturing process,and this non-orthogonal structure will affect the mechanical properties of the material,thus changing the impact resistance of the material.Therefore,the study of LVI damage of non-orthogonal FWTC is of great importance for engineering applications.In this paper,the damage behavior of twill carbon fiber woven thermoplastic composites under LVI is systematically investigated using a combination of experimental analysis and numerical simulation.The main research contents and conclusions are as follows.(1)Experimental study of LVI damage of non-orthogonal FWTC.To investigate the impact response and damage patterns of composites with different yarn angles at different impact energies,three yarn angles(60°,75° and 90°)of FWTC laminates were prepared and subjected to two different impact energies(5J and 10J)of drop-weight impact tests.The results show that,the FWTC laminates with a yarn angle of 60° has better impact resistance,while the FWTC laminates with a yarn angle of 90° has better ductility.However,the yarn angle has less effect on the absorbed energy.Furthermore,the orthogonal laminate is more severely damaged at LVI and has weaker load carrying capacity.Moreover,the damage area of the FWTC laminate increases as the yarn angle decreases,thus the decrease in yarn angle facilitates the transfer of load and is therefore able to withstand greater impact forces.(2)A micro-meso-macro multi-scale model was constructed for simulating the LVI behavior of FWTC.In the framework of continuum damage mechanics,elastic damage constitutive models of carbon fiber and macro composite panels were constructed.Furthermore,elastic-plastic damage constitutive models were established for the matrix and yarn,respectively,considering the plastic effects of the micro-scale matrix as well as the meso-scale yarn and matrix.The mechanical properties of the matrix were first measured,then the mechanical properties of the yarn were obtained by virtual loading tests on the micro-scale representative volume element(RVE)model,and the mechanical properties of the macro composite panel were obtained by virtual loading tests on the meso-scale RVE model,and finally LVI simulations were performed on the meso-macro multi-scale model with the above parameters to predict the LVI damage behavior of FWTC.The impact force response curves of the numerical simulation results are within-10%error of the test results,and the damage patterns of the two are closer,which verifies the effectiveness of the multi-scale model.(3)The damage of FWTC with different yarn angles at LVI was revealed by numerical simulation.The results show that,the crack generation during impact is dominated by yarn damage and the damage range of the material gradually increases as the yarn angle decreases.In addition,all the damage spreads from the impact in all directions.Furthermore,for yarn damage,yarns damage on the back side of the impact is mainly caused by the fiber and matrix tensile,and yarns damage on the front side of the impact is mainly caused by the fiber and matrix compression.Meanwhile,the tensile damage and matrix damage of yarns are more extensive,and the tensile damage and fiber damage of yarns are the main causes of yarns failure.