High strain-rate compression test on metallic foam using a multiple pulse SHPB Apparatus

The high strain-rale compressive behaviour of a structural aluminium foam (manufactured by IFAM) has been investigated using both the Split Hopkinson Pressure Bar (SHPB) and the direct impact tests. The tests have been carried out with the Hopkinson bar set up in the Experimental Mechanics Laboratory of the 2nd Engineering Faculty of the Politecnico di Torino. In order to obtain high level of strain in the specimen (70-80%), a multiple pulse test technique has been developed. With this solution the specimen is subjected, within the same test, to repeated pulses due to the reflection of stress waves in the input bar. A multiple point strain-gage measurement and a third bar positioned after the output bar allow a correct reconstruction of the dynamic stress-strain characteristic of the foam specimen. Correction for wave propagation by means of the Pochhammer-Chree method was used to improve the quality of the response and to correct errors. Tests with strain-rate up to 3000 s-1 were performed and quasi-static tests comparison has been carried out. The influence of several parameters, especially density, has been examined. \ua9 EDP Sciences

Advanced experimental investigation and numerical simulation of polycarbonate behaviour at different strain-rate and temperature

Modelling the mechanical behaviour of plastics in simulating large strains and large displacements (as in impact simulations) is a complex task due to the highly non-linear characteristics of these materials. Moreover, non negligible influences of strain-rate, multiaxial loading, and temperature are present and must be taken into account accordingly. This work presents some results about the modelling of these effects for a thermoplastic used in automotive components. The model was developed based on experimental results obtained in different loading conditions, with different temperature and strain-rate. In this work the characterization of a polycarbonate for automotive applications has been carried out. A detailed experimental tests campaign covering the main influencing factors has been first fulfilled. The experimental results were used to obtain parameters for a suitable model implemented in a numerical code. The explicit and implicit LS-DYNA solvers for dynamic simulations have been used. Good fitting between numerical and simulation results has been obtained and the results provide a very useful tool for the design of plastic body parts

The mechanical behaviour of aluminium foam structures in different loading conditions

The use of foam has the potential for energy absorption enhancement. Many types of materials can be produced in the form of foams, including metals and polymers. Of the metallic based foams, aluminium based are among the most advanced. Aluminium foams couple good specific mechanical properties with high thermal stability. Among the various aspects still to be investigated regarding their mechanical behaviour is the influence of a hydrostatic state of stress on yield strength. Unlike metals, the hydrostatic component affects yields. Therefore, different loading conditions have to be considered to fully identify the material behaviour. Another important issue in foam structure design is the analysis of composite structures. The mechanical behaviour of an aluminium foam has been examined. The foam was subjected to uniaxial, hydrostatic stress, pure deviatoric stress, and combinations thereof. Results obtained will be presented as quasi-static and dynamic uniaxial compression and quasi-static bending and shear loading. Moreover, composite structures were made by assembling the foam into aluminium cold extruded closed section 6060 aluminium tubes. The results show that the energy absorption capability of the composite structures is much greater than the sum of the energy absorbed by the two components, the foam and the tube