Fatigue Crack Propagation In Glass Fiber Reinforced Aluminium Laminates

Fiber reinforced aluminum laminates is a kind of lightweight structural materials, which have the advantage of the aluminum alloy and the advantage of composite materials. Fiber reinforced aluminum have the better comprehensive mechanical properties than aluminum alloy, which particularly are suitable to use as airframe skin material owing to light weight, high strength, excellent conductive performance, good impact resistance and damage tolerance.The optimization of layer structure can be achieved by changing the thickness, layer number and direction of the fiber. However, if such material is introduced into the aircraft’s main load-carrying structure, it needs greater thickness, and can work under more complex flight load.In view of the excellent fatigue crack propagation properties and future application prospect in the main load-carrying structure, the new type of glass fiber reinforced aluminum laminates were designed and prepared, which have the greater thickness in the whole and in components than GLARE. The experimental and theoretical studies were carried out for this new aluminum laminates under tension-tension loading and tension-compression loading.In Chapter 2, the 2/1 type and 3/2 type of glass fiber reinforced aluminum laminates were prepared using the vacuum bag autoclave curing system. The fatigue crack propagation tests were arranged under the tension-tension and tension-compression cyclic loading. The results show that the 3/2 type of laminates have the more excellent fatigue crack propagation properties than the 2/1 type of laminates. The fatigue crack propagation life of 3/2 type of laminates specimens increased by 80~100% than the aluminum specimens. And the fatigue crack propagation life of 2/1 type of laminates specimens increased by 20~50%. The 2024-T3 aluminium alloy has obvious stress ratio effect under tension-tension loading, but the less obvious compressive loading effects under tension-compression loading. However, the fiber reinforced aluminum laminates have obvious stress effect and compression loading effect under tension-tension loading and tension-compression loading.In Chapter 3, the method of the fatigue crack propagation was proposed to predicte the behavior of fatigue crack propagation in fibre reinforced aluminium laminates, to reflect the change of effective load in aluminium layer, the elastic-plastic behavior in the crack tip, the stress ratio effect and compressive load effect. In this method the plastic region size was used as the driving parameters of fatigue crack propagation by combining the method of increasing plastic damage theory and the finite element. By this method it was predicted of the fatigue crack growth rate of 2024-T3 aluminium alloy under the tension-tension and tension-compression cyclic loading. The stress ratio effect and the compressive loading effect have the unite explaining.In Chapter 4, the two-dimensional parametric model of fatigue crack propagation was proposed based on finite element software ABAQUS by combining the method of increasing plastic damage theory and bridging crack model of fiber metal laminates. It was realized to model the finite element and calculating bridging stress automatically, to simulate the fatigue crack propagation and delamination growth. The fatigue crack growth rate of the glass fiber reinforced aluminum laminates was predicted. The route of improving the fatigue crack propagation properties of the laminates was denoted by analyzing the lamination structure effect on the fatigue crack and delamination growth.In Chapter 5, it was analyzed of the stress ratio effect, compressive loading effect, delamination growth and bridging efficiency under the tension-tension and tension-compression loading for fiber reinforced alumimium laminates by the 2D parametric model. The results show that the stress ratio effect is caused by the positive plastic damage and the compressive loading effect is caused by the increasing of negative plastic damage.