FATIGUE LIFE PREDICTION OF LAMINATED COMPOSITES USING NORMALIZED S-N DATA

It is known that fatigue life prediction of laminated composites without conducting full-scale experimental work is quite an important practical task in the field of studying the fatigue strength of composites. Currently, the main volume of research in this direction is devoted to fatigue life prediction of composites using various constant-life diagrams. Unfortunately, despite a fairly large selection of such diagrams, it is not always possible to achieve acceptable labor intensity and accuracy of the results obtained using them. As a definite alternative to methods for fatigue life prediction of laminated composites using constant-life diagrams, we propose a method for fatigue life prediction using normalized S-N data. When forming the method, the main property of normalized S-N data is used – the ability to exclude the influence on fatigue life of different fiber strength, volume fractions and layings in laminated composites. It is assumed that normalized S-N data for the specimens under consideration can be obtained by processing experimental data on the fatigue life of the so – called "prototype specimens", without involving data on the fatigue life of the specimens under consideration. This is the practical value of the proposed method. Based on the equations for normalized S-N data, we propose equations for the formation of "classical" S-N fatigue curves of the specimens under consideration at various asymmetries of cyclic loading, using which we propose to perform the actual prediction of fatigue life characteristics. An example of fatigue life prediction of open-hole specimens made of GFRP T300/5208 Т300/5208 [45/0/-45/90]2s, demonstrating the capabilities of the proposed method, is presented.