Failure Behavior Study Of Single Lap Joints In Laminated Composites Under Thermal-mechanical Coupling Effect

Composite materials have been applied widely in various fields due to its outstanding features, like in aerospace, car manufacturer, civil construction fields. In many engineering applications, the connection between structures is necessary for realizing the load transfer behavior. Adhesive-bonded joints and mechanical joints have become the two main forms of connection used in composite structures as their advantages. Structure failures often occur in connected position, thus finding out the joints failure mechanism and the factors that influence joints strength are very important to promote application of joints in engineering. However, joints often service in a certain environmental temperature, in this paper, numerical simulation is used to research and analyze the impact of temperature on the joints strength performance.A3D model for adhesively bonded single lap joints in laminated composites is established by using finite element software ANSYS, and strength performance of adhesively bonded joints is analyzed and evaluated under temperature and adhesive viscoelastic effects. By introducing interface failure criterion and cohesion failure criterion, the crack position and failure mode are analyzed at different temperature. Comprehensive analysis indicates that failure index increases with rising temperature, and then reduces the load transfer capacity of bonded joints. Bonded joints failure mode relates to temperature strongly. The feasibility of analysis methods are proved to be effective by comparing the previous test results.Finite element model containing pre-crack of adhesively bonded single lap joints in laminated FRP composites is established to analyze the impact of viscoelasticity on crack propagation. Each model strain energy release rate (SERR) of crack tip is calculated by the virtual crack closure technique (VCCT) under different temperature load. Mode Ⅱ SERR decreases first and then increases with temperature, mode I SREE and mode III SREE show the considerably positive correlation with temperature. SREE of free boundary is sensitive to temperature, the increase of temperature promotes crack propagation and the crack extension firstly occurs in the free boundary.Damage analysis of single-bolted-lapped joints in laminated FRP composites is done by referencing Hashin failure criterion and the corresponding stiffness degradation criterion, the load transfer capacity is calculated in two different conditions that without temperature and considering the influence of temperature. Joints failure mainly includes matrix failure and fiber-matrix shear failure. In the three failure modes of composite materials, matrix failure is greatly influenced by temperature, whereas fiber-matrix shear failure and fiber failure are not affected nearly by temperature.