| Fiber Metal Laminates(FMLs) are a kind of hybrid composites constituted by alternating layers of thin metal sheets and composite layers. FMLs have been widely used in aerospace industry due to their high specific strength and stiffness, excellent impact resistance, high damage tolerance and superb fatigue properties. With the development of the aerospace industry, aircrafts are being designed to operate at higher temperature than ever before. However, the epoxy-based FMLs cannot be used at such high temperatures. Thus, the high temperature FMLs need to be investigated. In this paper, the Ti/Cf/PMR laminates and Cf/PMR prepreg were prepared. Then, mechanical properties of the Ti/Cf/PMR laminates at high temperature were evaluated through tensile test, flexure test and inter laminar shear test. Moreover, the effect of overload on fatigue crack growth rate of the unidirectional Ti/Cf/PMR laminates was investigated. Furthermore, the fatigue crack growth behavior of Ti/Cf/PMR laminates at elevated temperature was discussed.Firstly, the preparation process of Ti/Cf/PMR laminates with 3/2 configuration was studied. The optimized parameters for the preparation of carbon fibre polyimide prepreg were obtained: yarn width was 3.7mm, tension force was 4-7N and wrapping speed was 18m/min. Prior to laminating, the titanium was surface-treated by sand blasting method and primed with polyimide matr ix. The prepreg was thereafter alternately stacked on the stacking sequence and placed in the mold. After curing in the hot-press system, the Ti/Cf/PMR laminates with good interface and stable performance were obtained.Secondly, the effects of temperature on the mechanical properties of Ti/Cf/PMR laminates with different layers were investigated. The results showed that tensile strength, flexure strength and inter laminar shear strength of the Ti/Cf/PMR laminates decreased with the increase of the testing temperature. The unidirectional laminates possessed the highest tensile strength and flexure strength among the three configurations while the laminates with ±45°fibre orientations showed the worst. The inter laminar shear strengths of the three laminates show ed no signif icant difference. Unidirectional laminates showed slightly higher interlaminar shear strengths than other two laminates.Thirdly, the influences of overload on the fatigue crack growth rate of the unidirectional laminates were studied. The fatigue crack propagation rate of the laminates presented an obvious decline after the application of the single overloads, which predominantly related to the crack growth retardation in metal layers. Fatigue crack growth rate decreased more obviously with the overload ratio increasing. Subsequent fatigue crack growth rate w ould gradually rise and return to its original level. Specimens were chemically etched to obtain the f inal delamination shapes after application of a single overload, multimodal over load and block load. The final delamination shape changed from a semi-elliptical shape to a shape containing a kink near the location of overload applied.Finally, the effects of temperature on the fatigue crack growth rate of Ti/Cf/PMR laminates were investigated. It was found that the fatigue crack growth rate increased with the increasing of the temperature. The unidirectional laminates possessed lower fatigue crack growth rate than the laminates with ±45°fibre orientations. Photographs on delamination shape between the outer metal layer and the prepreg layer were obtained by ultrasonic C scan and chemical etching, which were found much larger semi-elliptical with the increase of temperature. |
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