Research And Numerical Simulation On Composite Unidirectional Laminates Stiffness Reduction

As the application of composites in main load-bearing structure of aircraft, its complex supported load condition and growing carrying levels make fatigue problems inevitable. Its complex damage mechanism under fatigue load makes failure analysis and life prediction very challenging. The keeping degradation of stiffness is an important part of macro mechanical property change. So research on stiffness degradation based on fatigue damage mechanism of composites is very important and valuable.In this article, research on stiffness degradation laws of unidirectional laminates under static tensile load and shear modulus degradation laws under fatigue load was carried out. At first, knowledge of fatigue failure mechanism was introduced and fatigue analysis models, especially residual stiffness models and numerical simulation models were concluded. And then a lot of fatigue experiments of different carbon fiber angel composites were carried out. And analysis on variable factors influencing stiffness degradation was made based on static attenuation models. Considering the influence of loading and fiber angle, static stiffness degradation model of composites was constructed and the static strength numerical simulation of unidirectional laminates was based on this model. According to failure model of unidirectional laminates, the influence of loading and fiber angle on shear modulus degradation in fatigue condition was studied. Next the fatigue shear modulus model was built and the fatigue numerical simulation analysis of unidirectional laminates was carried out based on this model. The simulation result fits the experiment result which proves that static stiffness degradation model and fatigue shear modulus model reasonably describe the degradation laws of relative composites.