Development of a Hopkinson Bar Apparatus for Testing Soft Materials: Application to a Closed-Cell Aluminum Foam

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.

Size Dependence and Dynamic Properties of Adobe Masonry Bricks tested at high strain rates

“…3. For a detailed report of the dynamic test machine, the reader is referred to [6]. In the tests, the incident bar applies a constant velocity of about 4200 mm/s to the sample.…”

Dynamic behaviour of adobe bricks in compression: The role of fibres and water content at various loading rates

“…2(c). For a detailed report of the dynamic test machine, the reader is referred to [31,14]. In the tests, the incident bar applied a constant velocity of about 4200 mm/s to the sample.…”

Instrumented Dynamic Penetration of Sandwich Panels with Auxetic and Non‐Auxetic Core using Direct Impact Hopkinson Bar

“…In addition to the drop weight experiments [ 4 ] and the split Hopkinson pressure bar (SHPB) tests, [ 5,6 ] modifications of the direct impact Hopkinson bar (DIHB) [ 7,8 ] have been introduced for the medium‐to‐high strain rate compression of cellular solids under conditions similar to the potential applications of the materials, such as dynamic compression and dynamic penetration in auxetics in particular. With this method, the projectile directly impacts a specimen mounted on an instrumented transmission bar (the so‐called forward DIHB), or a specimen is mounted on a rigid mass projectile and launched toward a stationary instrumented transmission bar (the so‐called reverse DIHB).…”

“…All these aspects have to be taken into account during lattice optimization with respect to the given design scenarios characterized by the loading mode (e.g., compression or penetration), strain rate, and required absorbed deformation energy. [3] In addition to the drop weight experiments [4] and the split Hopkinson pressure bar (SHPB) tests, [5,6] modifications of the direct impact Hopkinson bar (DIHB) [7,8] have been introduced for the medium-to-high strain rate compression of cellular solids under conditions similar to the potential applications of the materials, such as dynamic compression and dynamic penetration in auxetics in particular. With this method, the projectile directly impacts a specimen mounted on an instrumented transmission bar (the so-called forward DIHB), or a specimen is DOI: 10.1002/adem.202300980 This article deals with the dynamic penetration of 3D-printed panels with auxetic and conventional honeycomb unit cell-based cores.…”