Fatigue of Composites—Fatigue Modulus Concept and Life Prediction

Fatigue behavior of glass fiber reinforced epoxy composite materials has been studied analytically. A new concept called "fatigue modulus," which is defined as a slope of applied stress and resultant strain at a specific cycle is introduced. Fatigue modulus degradation is studied using an assumption that the fatigue modulus degrada tion rate follows a power function of fatigue cycle. Theoretical equation for predicting fatigue life is formulated using the fatigue modulus and its degradation rate. This rela tion is simplified by strain failure criterion for the practical application. It is proved that the final formula predicts the fatigue life of a glass fiber epoxy composite material better than S-N curve or Basquin's relation. An attempt is made to find the relation ship between fatigue modulus and elastic modulus by the geometric relation from stress-strain curve under the cyclic loading.

[1]  Robert Croman,et al.  Residual Strength in Fatigue Based on the Strength-Life Equal Rank Assumption , 1978 .

[2]  R. Kim,et al.  Fatigue Behavior of Composite Laminate , 1976 .

[3]  K. Han.  Compressive fatigue behaviour of a glass fibre-reinforced polyester composite at 300 K and 77 K , 1983 .

[4]  J.N. Yang,et al.  Residual Strength Degradation Model and Theory of Periodic Proof Tests for Graphite/Epoxy Laminates* , 1977 .

[5]  H. Hahn,et al.  Proof Testing of Composite Materials , 1975 .

[6]  A. Dibenedetto,et al.  A study of the fatigue behavior of fiber reinforced nylons , 1975 .

[7]  W. S. Johnson,et al.  Mechanisms of fatigue damage in boron/aluminum composites , 1982 .

[8]  Pc Chou,et al.  Degradation and Sudden-Death Models of Fatigue of Graphite/Epoxy Composites , 1979 .

[9]  Shanyi Du,et al.  An Exploratory Study Into the Fatigue of Composites Under Spectrum Loading , 1983 .

[10]  J. N. Yang,et al.  Load sequence effects on the fatigue of unnotched composite materials , 1981 .

[11]  F. Chang,et al.  Real-Time Characterization of Damage Growth in Graphite/Epoxy Laminates , 1976 .

[12]  J. Dally,et al.  Fatigue behavior of glass‐fiber fortified thermoplastics , 1969 .

[13]  Su-Su Wang,et al.  Fatigue Damage and Degradation in Random Short-Fiber SMC Composite , 1983 .

[14]  Philip H. Francis,et al.  Biaxial Fatigue Loading of Notched Composites , 1977 .

[15]  S. Tsai,et al.  On the Behavior of Composite Laminates After Initial Failures , 1974 .

[16]  H. Hahn,et al.  Fatigue and Proof-Testing of Unidirectional Graphite/Epoxy Composite , 1977 .

[17]  Robert Croman,et al.  Scale Effect in Fatigue Of Composite Materials* , 1979 .

[18]  H. Corten,et al.  Shear Fatigue Degradation and Fracture of Random Short-Fiber SMC Composite , 1984 .

[19]  H. T. Hahn,et al.  Fatigue Behavior and Life Prediction of Composite Laminates , 1979 .

[20]  K. Reifsnider,et al.  Fatigue Damage Evaluation through Stiffness Measurements in Boron-Epoxy Laminates , 1981 .

[21]  A. Bunsell,et al.  Improved bending fatigue life of Kevlar 29 braid by the use of an impregnating medium , 1984 .

[22]  L. J. Ebert,et al.  Axial Fatigue Failure Sequence and Mechanisms in Unidirectional Fiberglas Composites , 1978 .

[23]  T. Kevin O'Brien.  Stiffness Change as a Nondestructive Damage Measurement , 1980 .

[24]  J. N. Yang,et al.  Fatigue and Residual Strength Degradation for Graphite/Epoxy Composites Under Tension-Compression Cyclic Loadings , 1978 .