Investigation Of Composite Bolted Joints Under The Random Fatigue Loading

Composite bolted joints are widely used in aerospace structures,the joint is subjected to static load and random load in actual working condition,the corresponding fatigue problem is the focus of technical personnel in related fields.The investigation of random fatigue life prediction method can give full play to the anti-fatigue performance of composite materials.In this experiments,12 kinds of joints which have different geometric parameters and layer sequences will be tested.MTS testing machine is used for loading.The LoadDisplacement curves and static strength of joints will be obtained from static tensile and compressive experiments.Loading amplitude of constant amplitude fatigue experiments is related to the joints strength,different loading percent are selected for the experiments.The fatigue life data of joints can be drawn as S-N curve,the parameters of S-N curve is fitted from life data.The random fatigue loading spectrum is generated by Gaussian random process.This spectrum is including tensile and compressive loads,the stress ratio is R=-1.The random fatigue life can be counted by rain-flow counting method.The effect of parameters and layer sequence to the fatigue life and failure mode will be discussed in the analyzation.Prediction of joints life is consist of two parts: phenomenological model prediction and finite element model prediction.The phenomenological model is based on the Weibull distribution of random amplitude,the damage factor can be calculated by the SN curve function of constant amplitude fatigue.The prediction of random fatigue life is based on the Miner linear cumulative damage criterion.The finite element method of prediction is based on Puck criterion and Hashin criterion,VUMAT and UMAT subroutines are used to calculate the damage and the failure mode of joints.