A Prediction Research On S-N Curve Of Composite Materials Based On Energy Method Under Different Stress Ratios

With the research of composite materials fatigue going deeper and deeper, researchers hasstudied composite materials fatigue problems from a variety of different perspectives. How toaccurately predict the fatigue life of composite materials from external load conditions has becomethe focus of attention. S-N curve is commonly used in engineering to describe the fatigue life ofcomposite materials, but generally only for the S-N curve under a specific external stress ratio loadsbecause the measure of S-N curve under different stress ratio is very difficult, acquiring a lot ofexperiments. This paper constructed a predictable method for S-N curve of the composite materialsunder different stress ratio based on fatigue energy method.Firstly this paper outlines the fatigue problem, reviews the research status of composite materialfatigue problems described by different damage parameters and the background for the using offatigue energy method. Then a detailed analysis of the process of the composite material fatigueenergy dissipation mode was carried out, and the physical model for predicting the fatigue life ofcomposite materials based on fatigue energy method was constructed. Then the energy balanceequation was established with the energetic analytical expressions for fatigue process given in variousforms, and therefore casting process was obtained by introducing the stress ratio into the accumulatedplastic strain energy.This paper describes the tension–tension fatigue tests of glass fiber composite under differentstress ratios, and the use of infrared camera to accurately measure the specimen surface temperatureof the test piece in fatigue process in order to obtain the dissipative heat, getting various specificenergy values during the fatigue process. Finally, S-N curves for composite materials under differentstress conditions were predicted in the basis of a specific composite material S-N curve and the resultswere compared with the test results to verify the reliability of the method.