Fatigue Life Prediction Method Of Laminated Structures Under Elevated Temperature

Composite laminate has become the key material and gains widely usage in the in the aerospace structures. Lower weight, good fatigue property and excellent curve shapes are achieved. With the excessive employment of the composite materials, it becomes urgent to understand their fatigue behavior in the elevated temperature environment.Firstly, this paper established the strength and fatigue prediction method based on the Weakest-link theory. By studying a layer of a laminate using the weakest-link theory which assumes that the laminate is in serial connection of each layer,once one single layer fails the whole laminate fails, the relationship between the strength/fatigue probability distribution of the unidirectional plies and the strength/fatigue probability distribution of the laminate is derived in forms of the characteristic life, fatigue cycles and the distribution factors. In such way, the strength and the fatigue life prediction method can be established. By using the strength/fatigue test data from references, a strength and fatigue life prediction of the T300/BMP316 laminate can be made. The strength prediction error is within 8% while the fatigue life predictions are in 3 times error band.Secondly, this paper extended the method to a region that can be applied with the FEM(finite element method) by assuming any node in the element fails the element fails. In this way the relationship of the element strength/fatigue distribution and the element characteristic life, life cycles and the distribution factors can be established. By using the strength/fatigue test data from references, a strength and fatigue life prediction of the T300/BMP316 laminated bolts can be made and the fatigue life predictions are in 3 times error band.After that, to apply the method into the elevated temperature environment, the paper employed Mivehchi’s strength/stiffness-temperature curve to describe the temperature depended behavior of the unidirectional plies. So that the equivalent life diagram under room temperature can be extend to the elevated temperature environments and the problems in prediction under temperature are solved.Meanwhile, to prove the validation of the method this paper provided, predictions and validations of the strength and fatigue life under elevated temperatures are carried out respectively. Furthermore, experiments are carried out under elevated temperatures. The strength and fatigue tests are performed using T300/BMP316 laminate and under 100°C 、 200°C respectively. After that, an ANSYS APDL program is established to predict the strength and the fatigue life of the laminate, the results are desirable. The strength results are within a 10% error band, and the fatigue results are within 2 times error band. The validation of the method is testified.