Ian W. Hall

Dynamics of metal foam deformation during Taylor cylinder–Hopkinson bar impact experiment

Abstract Analytical solutions for dynamic deformation of foam materials during the Taylor cylinder–Hopkinson bar impact experiment were obtained. It was shown that shock wave of foam collapse appears during the fast impact. The results of this experiment can be used in estimating the average material properties of the foam under dynamic loading conditions. Results show that the un-deformed and change in length of foam specimens are in good agreement between theory and experiment, as well as numerical analysis.

Crushing of aluminum closed cell foams: Density and strain rate effects

Potential applications of metal foams include light weight cores for sandwich panels, shells and tubes where the foam can increase the resistance to local buckling, increase the impact resistance, and improve the energy absorbing capacity of the structure [1,2]. This latter property offers potential uses in transportation applications where, for example, foam-filling of the hollow sections of automobiles, such as fenders, may reduce damage and injuries resulting from impact accidents. For this type of application, aluminum foam is more suitable than a polymeric foam, because it deforms plastically under impact and with essentially no spring back, preventing further damage [3]. Other important advantages of using aluminum foams over polymeric foams include high fire resistance and insensitivity to cold and hot weather and humidity [3]. Impact accidents produce loading rates which are higher than those of static or quasi-static rates and which may significantly alter mechanical response of the materials. Therefore, in designing with metallic foams as energy absorbing fillers, mechanical properties are needed for strain rates corresponding to those created by impact events. Quasi-static mechanical behavior of metallic foams has been fairly extensively studied and reported, e.g. [3–5], but data concerning high strain rate mechanical behavior of these materials are, however, only just becoming available and are rather sparse [6,7]. This study was initiated, therefore, to study the high strain rate mechanical behavior of a range of metallic foams, and to compare it with quasi-static behavior and, hence, determine any effect on energy absorbing capacity. Microscopic observations were also made in order to clarify the deformation mechanisms involved during crushing of the foam.

Fibre and fibre-surface treatment effects in carbon/aluminium metal matrix composites

A systematic study of the relationship between the microstructure of the interface in C/Al composites and its dependence on variations in squeeze-casting parameters has been undertaken. This research has shown that the amount of Al4C3 reaction product at the interface is dependent on the surface structure of the reinforcing fibre and the surface treatment of the fibre. Additionally, the interface shear strength increases with an increase in the amount of reaction product at the interface. An increase in interface shear strength leads to a decrease in composite longitudinal strength. High-resolution electron microscopy and X-ray photoelectron spectroscopy analyses indicate that carbide formation is a conventional two-step process of nucleation and growth. Nucleation occurs preferentially at graphite edge planes on the carbon fibre surface, and growth is restricted along certain matrix planes and directions.

Transverse and longitudinal crushing of aluminum-foam filled tubes

Abstract Al-foam filled and empty tubes of aluminum, brass and titanium were compression tested laterally. The specific energy absorption in filled tubes increased greatly in terms of percentages, and was greatest in aluminum tubes. In transversely tested tubes the foam deformed laterally showing a capability of spreading the deformation.

Interfacial reactions in titanium matrix composites

This letter presents some results of a study undertaken to determine the processing conditions necessary to produce acceptable composite microstructures using a variety of fibres and alloys, and to characterize the development of the interfacial reaction layers

The effect of thermal exposure on the microstructure an fiber/matrix interface of an AI2O3/AI composite

Samples of an α-Al2O3/Al-Li metal matrix composite have been exposed to a temperature of 500 °C for periods up to 100 hours and tensile tested in the longitudinal direction. The fracture surfaces were examined in the scanning electron microscope and specimens subsequently prepared, by ion-milling, for examination in the transmission electron microscope. It was found that the interfacial reaction layer increased in thickness with increasing exposure time but that the rate of thickening varied dramatically from one fiber to the next and even within a single fiber. The interfacial reaction was found to proceed preferentially along the grain boundaries of the polycrystalline α-Al2O3 fibers. Two compounds, namely, α-LiAlO2 and LiAl5O8, have been identified in the interfacial reaction layer by electron diffraction: the presence of the former phase has been confirmed in X-ray diffraction experiments. In the light of these microstructural modifications, the variations of mechanical properties with exposure time are considered. The mechanism of the interfacial reaction is also briefly considered.

Effect of strain rate on the compression behaviour of a woven fabric S2-glass fiber reinforced vinyl ester composite

Abstract Quasi-static (~10 −3 s −1 ) and high strain rate (>500 s −1 ) compression behavior of an S2-glass woven fabric/vinyl ester composite plate was determined in the in-plane and through-thickness directions. In both directions, modulus and failure strength increased with increasing strain rate. A higher strain rate sensitive modulus was found in the through-thickness direction while a higher strain rate sensitive failure strength was found in the in-plane direction. In the in-plane direction, the failure mode was observed to change from splitting followed by “kink banding” (localized fiber buckling) to predominantly splitting at increasing strain rates, while it remained the same in the through-thickness direction.

Dynamic properties of metal matrix composites: a comparative study

Abstract Three distinctly different metal matrix composites have been tested at strain rates from quasi-static to ≈3000 s −1 . It was found that the high strain rate response of each composite was determined primarily by (a) the response of the matrix in the absence of any reinforcement and (b) the damage formation and accumulation processes during deformation. High strain rate behavior of the short fiber composite was dominated by the matrix behavior at low strains but by fiber damage at high strains. The behavior of a whisker reinforced composite was dominated by the matrix properties at all strains. Re-loading tests produced increased fracture strains, indicating that adiabatic heating accelerates fracture of composites by permitting the development of local strain instabilities.

High strain-rate compression testing of a short-fiber reinforced aluminum composite

Abstract Compression behavior of 15–26 V f % Saffil ™ short-fiber reinforced Al-1.17wt.%Cu alloy metal matrix composites has been determined over a strain-rate range of approximately 10 −4 to 2×10 3 s −1 . The strain-rate sensitivity of composite samples at 4% strain, tested parallel and normal to the plane of reinforcement, was found to be higher than that of unreinforced alloy in the strain-rate range studied. Quantitative analysis of fiber fragment lengths from samples tested to different strain levels showed that, at small strains, high strain-rate testing induced a relatively shorter fiber fragment length distribution in the composite compared to quasi-static testing. At quasi-static strain rates, the fiber strengthening effect was found to increase with increasing V f % and was higher in samples tested parallel to the planar random array. The observed anisotropy of the composite at quasi-static strain rates was also observed to continue into the high strain-rate regime. Microscopic observations on composite samples tested quasi-statically and dynamically to a range of strains showed that the major damage process involved during compression testing was fiber breakage followed by the microcracking of the matrix at relatively large strains. Fiber breakage modes were found to be mostly shearing and buckling.

On the fibre/matrix interface in boron/aluminium metal matrix composites

The fibre/matrix interface of B; AI metal matrix composites (MMCs) has been examined by transmission and scanning electron microscopy (TEM and SEW. As-fabricated samples show no fibre/matrix reaction whereas isothermal exposure for increasing periods of time leads to the formation of at least four distinct borides. The extent and location of the fibre/matrix reaction is strongly influenced by the presence of an oxide layer which is present at all the interfaces. The effect of these reaction products upon mechanical properties is considered.