Experimental Study On Dynamic Compressive Properties Of Closed-cell Aluminum Foam

Aluminum foam is a typical porous metal material,which has several advantages as compared to the traditional metal and organic material,such as lightweight and more energy absorption capability.Therefore,it is widely used in the fields of transportation and aerospace.With the development of research in blast resistant design of civil building structures,aluminum foam is gradually used as energy absorbing material to reduce the blast effect on the main structures.In order to reveal the aluminum foam attenuation mechanism,and improve its attenuation design theory and method,it is of great significance to study mechanical properties of aluminum foam at high strain rates.In this thesis,the laboratory tests on dynamic compressive properties of closed-cell aluminum foam were carried out using INSTRON high speed loading system.The main research work and conclusions are as following:(1)Closed-cell aluminum foam specimens with appropriate size were prepared with considering the test results of previous studies.The Split Hopkinson Pressure Bar(SHPB)test method and the direct impact method and their applications are summarized.And the principles and assumptions for above methods are introduced.The INSTRON high speed loading system available in the laboratory are also presented.According to the performance parameters and working principle of test equipment,the problem of decelerating section in the process of high speed compression could be solved by adding an destructible organic glass(PMMA)tube with enough stiffness to the actuator,and the INSTRON would be suitable for dynamic compressive test of closed-cell aluminum foam.(2)To investigate the inertia effect of closed-cell aluminum foam at high speed compressive load,the forward and reverse test methods are utilized to do the dynamic compressive tests of 15 mm and 30 mm thick closed-cell aluminum foam specimen through the improved high speed loading system.The results show that the inertia effect on the test results will increase with the increase of the thickness of the closed-cell aluminum foam specimen.And once the maximum loading velocity is defined in the tests,the inertia effect could be eliminated by properly design of the specimen thickness.(3)Basing on the research results of inertial effect test,15 mm thick closed-cell aluminum foam specimens were selected to carry out high speed compression test under the strain rate of 10~1000s-1,and an energy efficiency method was used to process the experimental data.The results show that the dynamic stress-strain curve of closed-cell aluminum foam have three regions,the elastic region,the stress platform region and the compressive region,which is the same as the quasi-static case.Platform stress of the closed-cell aluminum foam has obvious strain rate effect under high speed compressive load,and densification strain at different strain rates show different trends.Preliminary interpretation is the interaction effect between the change of plastic deformation mechanism of aluminum foam cell wall and fluctuations effect.Energy absorption capability of the closed-cell aluminum foam improves significantly while increasing the strain rate.