Research On The Dynamic Energy Absorption Property Of Composite Materials

Fiber reinforced plastics(FRP)have excellent mechanical properties such as high specific strength and high specific modulus.They are increasingly used in structural design in many fields such as manned spaceflight,rail transportation and other sea,land and air transportation.The detailed study of the mechanical behavior of composite materials under impact loading,such as failure criteria,failure modes,energy absorption mechanisms,etc.,has important theoretical significance and application value for guiding the design of composite structures,improving their energy absorption properties and crash safety.In this paper,the mechanical behavior of glass fiber and carbon fiber reinforced composite energy-absorbing structures under impact loading is studied experimentally and numerically.Optimization design on the energy absorption structures was also carried out.The main research contents include:(1)The effects of geometrical parameters,filling materials,and multi-material mixing of composite thin-walled energy-absorbing structures under axial compression loading on their energy absorption characteristics were studied.Firstly,experimental research was carried out on the thin-walled energy absorption structure of glass fiber reinforced composite materials with and without foam filling.Based on the experimental data,a numerical analysis model was established and calibrated.After that,based on the numerical model,the influence of continuous changes in geometric parameters,foam density,and metal-composite mixing on the energy absorption characteristics of the structure was analyzed and the coupling effects of these factors was considered.The results show that the energy absorption per unit mass(specific energy absorption,SEA)of the thin-walled glass fiber reinforced plastics(GFRP)structure can be improved by changing the structural parameters,filling foam and compositing metal materials.(2)The effects of the layup sequences and layup orientations of the thin-walled energy-absorbing structure of composite materials on its energy absorption characteristics under dynamic and quasi-static compression loading were studied.Based on the calibrated numerical model,the influences of various layup sequences and layup orientations on the energy absorption characteristics of GFRP structures were analyzed.Based on the statistical analysis and mathematical regression model,the layup sequences and layup orientations was optimized,and the optimal layup sequences and layup orientations in the design interval were obtained.Furthermore,the optimal structures were manufactured and tested under impact loading to validate the numerical optimization results.Considering the randomness and uncertainty of the load direction in practical engineering problems,numerical models under a variety of inclined angle of loading was established to study the energy absorption performance of thin-walled structures with circular cross-sections,considering the effcet of simultaneous change of the loading inclination and the ply angle.Finally,the results of the drop weight impact tests are compared with those of the quasi-static compression tests.The results show that properly increase of the ratio of the axial layer can obviously increase the specific energy absorption of the structure;foam filling can significantly improve the energy absorption performance of the structure under inclined compression loading;the energy absorption performance of the GFRP circular structure under dynamic load is reduced.(3)The effects of the layup sequences and layup orientations of carbon fiber reinforced composites(CFRP)on their strain rate effects were studied.T700 carbon fiber reinforced epoxy resin-based composite laminates with two layup sequences were tested subjected to impact tests at high strain rates and the macro and meso failure modes of the laminates were obtained.At the same time,the effect of the angle between fiber and load direction on their mechanical properties under various strain rates was considered.The impact performance of carbon fiber laminates under different strain rates was analyzed by using the efficiency coefficient method.The results show that the mechanical behavior of carbon fiber laminates under impact loading shows a significant strain rate effect.When the fiber direction is consistent with the loading direction,the strain rate enhancement effect of the strength and modulus is the largest for both cross ply laminates and unidirectional ply laminates.It it observed by scanning electron microscope that with the increase of the strain rate,the failure mode of the fiber-matrix interface has a obvious change,and the deformation of the matrix material at the interface is greater,which indicates that the strain rate effect of the structure is related to the mechanical properties of the interface between the fiber and matrix.(4)The influence rule of the mechanical properties of the fiber-matrix interface and the mechanical properties of the matrix material on the overall structural properties of the fiber-reinforced composites were studied.Based on the experimental results,a ratedependent macroscopic constitutive model of the material is modified.Multi-layer shell elements was used to establish a macro-scale numerical model of the carbon fiber laminate under the impact loading.The dynamic mechanical properties of the material under different impact angles and different strain rates are predicted.The fiber and matrix in the composite were simulated separately,and a micro-scale numerical model of the carbon fiber reinforced composite was generated.The effects of interface strength and Poisson's ratio of the matrix material on the mechanical properties of the composite structure were analyzed.The results show that the greater the strength of the interface between the fiber and the matrix,the greater the strength and toughness of the overall structure.The influence of the Poisson's ratio of the matrix on the strength and toughness of the overall structure shows a significant nonlinear characteristic.