Abstract
An increasing interest in lightweight metallic foams for automotive, aerospace, and other applications has been observed in recent years. This is mainly due to the weight reduction that can be achieved using foams and for their mechanical energy absorption and acoustic damping capabilities. An accurate knowledge of the mechanical behavior of these materials, especially under dynamic loadings, is thus necessary. Unfortunately, metal foams and in general “soft” materials exhibit a series of peculiarities that make difficult the adoption of standard testing techniques for their high strain-rate characterization. This paper presents an innovative apparatus, where high strain-rate tests of metal foams or other soft materials can be performed by exploiting the operating principle of the Hopkinson bar methods. Using the pre-stress method to generate directly a long compression pulse (compared with traditional SHPB), a displacement of about 20 mm can be applied to the specimen with a single propagating wave, suitable for evaluating the whole stress-strain curve of medium-sized cell foams (pores of about 1–2 mm). The potential of this testing rig is shown in the characterization of a closed-cell aluminum foam, where all the above features are amply demonstrated.
Highlights
For more than 20 years, metallic and aluminum alloy foams have become an interesting material class especially in aerospace and automotive industries [1,2]
Aluminum foams and soft materials in general exhibit some particular problems during high strain-rate mechanical testing, especially by means of Hopkinson bar techniques
Aluminum foam with a density of about 0.55 g/cm33 and an average pore size of 1 mm, manufactured aluminum foam with a density of about 0.55 g/cm and an average pore size of 1 mm, manufactured by Aluinvent. This cell size renders the specimen of 19 mm size suitable for the characterization of by Aluinvent. This cell size renders the specimen of 19 mm size suitable for the characterization of the foam with the modified Hopkinson pressure bar for soft materials (MHPB‐SM), as it constitutes a representative volume of the material
Summary
For more than 20 years, metallic and aluminum alloy foams have become an interesting material class especially in aerospace and automotive industries [1,2]. Particular problems can arise in this kind of testing due to the low acoustic impedance and strength of this material class Both strain-rate sensitivity and absence of it have been observed in a variety of different foams. An innovative apparatus is introduced, designed to perform compressive high strain-rate tests on metal foams or other soft materials by exploiting the operating principle of the Hopkinson bar methods. The current apparatus employs a pre-stressed bar method (instead of the striker bar of the conventional SHPB) to generate directly a long compression pulse («3 ms); a displacement of about 20 mm can be applied to the specimen with a single propagating wave, suitable for evaluating the whole stress-strain curve of medium-sized cell foams (pores of about 1–2 mm). Aluminum foams and soft materials in general exhibit some particular problems during high strain-rate mechanical testing, especially by means of Hopkinson bar techniques.
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