Research On Influence Of Countersink Structure On Composite Joints Strength

With the widely use of composite materials in aerospace industries,it is important to improve joint technology and restrain damage generation and extension of composite materials for enhancing joint strength and ensuring structural reliability of aircraft.While in the process of assembly,there is always some machining tolerance which changes connecting–hole's geometry size.In this paper,research on the impact on structural connection strength of geometry parameters in composite mechanical connecting structure and analysis of fatigue failure process are adopted to study the rule of damage generation and propagation.The main research contents are as follows:First,based on characters of materials,applying three-dimension Hashin failure criterion and material deterioration model to construct a three-dimension damage accumulate evolution under fatigue load finite element simulation model of composite.Then researching the transfer path of load in different geometry size and verifying the model's accuracy by tests.Next,static strength tests and fatigue strength pre-tests of countersink bolt composite laminate joints are taken to research the fatigue life distribution of structures under different cyclic load.On this basis,conducting fatigue strength experiment of countersink bolt composite laminate joints structures in different countersink circular beads and countersink's depths and revealing the rule of force-displacement curve of composite connecting structures.Last,based on the microstructure of countersink bolt composite laminate joints indifferent circular beads and countersink's depth observed by SEM and the fatigue life prediction model of composite laminate joints,researching the effect law of circular bead and counter's depth on fatigue life,analyzing damage mechanism of composite and reveal the evolution of damage accumulation.In this paper,the prediction model of countersink bolt composite laminate joints' fatigue life and the change law of fatigue life are studied.The influence of circular bead and countersink's depth on fatigue life are provided to optimize joint technology and connection strength as theoretical reference and technical support.