Experimental Test And Analysis Of Dynamic Material Parameters Of Closed-cell Aluminum Foams

The metal foam material has many superior mechanical properties due to its special mesoscopic structure. It is widely used in automotive, aerospace and military protection and other fields for its specific strength, specific stiffness, and good energy absorption properties. Its performance is quite outstanding in the buffer endergonic structure design area. The metal foam material can be artificial designed, such as changing the relative density and its foam size, making it possible to be used in normal life. However, the relationship between its dynamic mechanical properties and the parameters of mesoscopic structure is unclear, and few experiments focusing on that relation have been carried out. The main difficulty of previous experiments is the failure of homogeneity assumption of the traditional Hopkinson experiments, as a result of its non-uniform deformation characteristics under high strain rate, causing an unreliable result. Another problem is about experimental technology: how to get the relation between structural parameters and dynamic mechanical properties through experiment.The method of accurate determination of quasi-static material parameters of foam aluminum is first discussed. Four optimization methods are given in this paper,from which we finally choose the R-PH model based on the physical meaning of the material parameters.In this paper, we used a method called direct impact and we introduce a related,rigid-plastic hardening rate (D-R-PH) model based on the dynamic mechanical properties of aluminum foam and the comprehensive study of its dynamic theory model. We can get a relationship between time and speed using the conservation relationship through wave front and Newton's laws of motion of rigid body, as shown in the following type:where L is the original length of aluminium foam specimen; v0 is the initial impact velocity and v is the history of impact velocity; which can be measured through experiment. Two parameters: b and c can be obtained by function fitting, which contains the parameters of the dynamic model: the initial crushing stress ?0d and strain hardening parameter D. The validity and correctness of D-R-PH model are verified through the contrast of the stress time history curve of D-R-PH model and stress time history curve measured by Hopkinson bar. We can conclude that aluminum foam is a loading rate sensitive material by comparing the stress-strain curve of quasi-static experiment. Besides, we can get a stress-strain relationship of aluminum foam including relative density by studying the influence of the relative density through experiment.The dynamic experiments were carried out on the foamed aluminum materials with different properties, and by comparing the two fitting schemes, we will obtain the better option to determine the material parameters of brittle foam aluminum and non-brittle foam aluminum, and related reasons were analyzed. The results show that both of the two fitting options can determine the parameters of the D-R-PH model. If the stress is large or not accurate enough in measuring process, the velocity and time fitting way should be taken. If the velocity and stress can all be measured accurately,the method which fitting by stress and velocity will be more accurate.