Research Of Temperature Effect On Mechanical Properties Of Multi-axial Glass Fiber Composites

Multi-axial warp-knitted fabrics are used widely in industry such as the environmental,transportation,civil engineering and wind turbine blades due to the lack of yarn undulations that exist in woven fabrics,provide better in-plane mechanical properties than the woven fabrics,and the use of through-thickness stitching in fabric allows for handling stability and delamination toughness,good tensile,bending,shearing and impact resistance properties in all directions,and simple production process and low price relatively.Industrial composite materials are exposed inevitably to various complicated environments in use.For example,the wind turbine blades are exposed to various environments all the year round,especially different temperature variations during the four seasons and day and night,the mechanical properties of composite materials are affected by the temperature.This topic is proposed in this context.This project has investigated the influence of temperature effects on the mechanical properties of composites in meso-scale and macro-scale.Firstly,tri-axial and quad-axial glass fiber warp-knitted composites were prepared by VARTM(Vacuum Assisted Resin Transfer Molding)process.Then the tensile,bending,compression properties in the 0°,90° and 45° directions at-30?,0?,20? and 40? were examined respectively.The stress-strain curves,(normalized)strength,(normalized)modulus and failure strain-temperature curves were obtained.The strength-temperature relationship of composite was obtained by fitting the curve and the failure mechanisms of composite at different temperature were analyzed with the fracture morphology with high power microscope and scanning electron microscope.Secondly,the finite element model of quad-axial warp-knitted composite under tensile loading at fiber/matrix meso-scale was developed and the stress distribution law and effect of stress concentration were analyzed by numerical calculation.Further explain the meso-structural failure characteristics of the materials and facilitate the structural optimization design of the tensile-resistant materials compared with the experimental results.The results show that the tensile properties have been decreased with the increasing of temperature.The ultimate strength of tri-axial and quad-axial warp-knitted composites was decreased as 14.18% and 18.13%,and the tensile modulus has maximum value at 20?,however the failure strain has smallest value.The bending performance has been decreased with the increasing of temperature,and the variation of bending strength and flexural modulus were not obvious between-30? and 20?,however,which reduced significantly at 40?,with 31.34% and 47.17% of tri-axial composite and 34.29% and 43.18% of quad-axial.The compression performance has also been decreased with the increasing of temperature,and the compression strength and modulus did not change significantly.However,the temperature effect of the compression property of quad-axial composite was significantly obvious than that of the tri-axial composite,with 23.41% and 29.00% of tri-axial composite and 26.94% and 31.41% of quad-axial by the most.The failure strain was the smallest at 20?,that is,the rigidity was optimal at normal temperature.The effect of temperature on mechanical properties were significantly reduced ascribed as the matrix shrinkage and the strong interface between fiber and matrix at low temperature,the different thermal expansion coefficients of the matrix and fiber at high temperature.This paper explores the influence of temperature on the mechanical properties of multi-axial warp-knitted composites,and analyzes the failure mechanism,and accurately predicts the tensile,bending and compression strength of composites at different temperatures.The results will provide a high-quality model which can be used to predict the effect of temperature on the dynamic or static mechanical properties of quad-axial warp-knitted composite in meso-scale,and reduce the experimental costs and time.It will provide theoretical support for structural design,material selection,and routine maintenance of industrial composite materials.It will reduce the cost and time and lay the theoretical foundation for the design of composite in production.