Research On Biaxial Strength And Fatigue Life Of Composite

Composite laminates have been widely used in the field of aerospace for its superior mechanical properties.In the process of designing actual composite structure,it is inevitable to meet some requirements such as observation holes and pipeline.The composite components of aircraft generally work under complex multiaxial loading conditions,however,the research on the static and fatigue characteristics of open-hole composite laminates under multiaxial loading is not sufficient.It is of great practical significance to make a research on static strength and fatigue life prediction of laminates with opening holes.The main work and conclusions of this article has been listed as follows:（1）Developing multiaxial tests of laminates with an opening hole under biaxial tensile loading.For rectangular and cruciform specimens with a stacking sequence of[45/0/-45/90]_2s,biaxial tensile testing research at biaxial tensile loading ratios of 0 and 1 has been made respectively to obtain the strength properties in each axis;developing proportional fatigue testing at biaxial tensile loading ratios of 0 and 1,non-proportional fatigue testing at biaxial tensile loading ratios of 1 and different phase angles of 45°and 90°.Comparing and analyzing different effects of loading ratio and phase angles on the biaxial tensile-tensile fatigue life of open-hole laminates.（2）Based on the classic theory of laminates and the principle of virtual displacement,deriving the stress and strain analysis formula with progressive damage for laminates under biaxial tensile loading.Establishing a method of progressive damage analysis of composite laminates under biaxial tensile loading.Applying energy-type fatigue damage parameter in cruciform laminates under biaxial tensile loading and establishing the concrete formula between fatigue parameters and life.Developing suitable programs based on the established analysis method and ANSYS software.（3）For predicting biaxial tensile strength of cruciform laminates with an opening hole,the progressive damage expanding of the open-hole laminate under uniaxial（biaxial ratio equals to 1）and biaxial tensile loading has been simulated,and the static tensile strength in each direction is effectively predicted.By comparing it with the testing strength,it has been found that the maximum predicting error of static strength in the X axis under uniaxial tensile loading is-5.05%,and the maximum predicting error of static strength in the X axis under biaxial tensile loading is-4.50%and Y axis under biaxial tensile loading is-5.48%,high predicting accuracy proves the effectiveness of progressive damage analyzing method used in this article.（4）For predicting fatigue life of cruciform laminates with an opening hole under biaxial tensile loading,studying the fatigue parameter distribution around hole under proportional loading and the change of which with time in a working cycle under nonproportional loading.Based on the proportional fatigue testing data under biaxial loading ratio of 1 and phase angle of 0°,an appropriate biaxial fatigue life predicting model formula has been fitted,and the accuracy of the model has been verified by other biaxial fatigue testing data of laminates with an opening hole under different loading paths.