Mustafa Güden

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.

Material parameters of quaternary III - V semiconductors for multilayer mirrors at wavelength

Nine quaternary (Al,Ga,In) - (P,As,Sb) semiconductor compounds lattice matched to InP are investigated theoretically. Direct bandgap, refractive index at wavelength, and thermal conductivity are calculated as a function of the composition. These material properties are important, e.g. in distributed Bragg reflectors of vertical-cavity lasers. The alloy systems AlGaAsSb, AlGaPSb and GaInPSb are found to promise better performance of those mirrors than the common InGaAsP system.

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.

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.

Effect of adhesive on the strengthening of aluminum foam-filled circular tubes

Studies of the crushing behavior of closed-cell, aluminum foam-filled aluminum and steel tubes have shown an interaction effect between tube wall and foam filler [1, 2, 3]. The crushing loads of foam-filled tubes are, therefore, found to be higher than the sum of the crushing loads of foam (alone) and tube (alone) mainly due to this effect. Santosa et al. [1], based on FEM results, proposed the following equation for the average crushing load of foam-filled square tubes of length b,

Stress Wave Propagation Effects in Two- and Three-Layered Composite Materials

Multilayer materials consisting of ceramic and glass/epoxy composites have been subjected to high strain rate compression testing using the Split Hopkinson Pressure Bar. The samples were extensively strain gaged so that dynamic data were generated directly from the samples during testing. Output data from the experiments were compared with numerical simulations of the same experiments and good agreement was noted. It was found that the stress distribution within samples was quite inhomogeneous and that stresses were highest in the region of the bar-sample interface. The presence of a rubber interlayer between the ceramic and glass/epoxy decreased the stress in both components but dramatically increased the degree of stress in homogeneity.

High strain rate deformation behavior of a continuous fiber reinforced aluminum metal matrix composite

Abstract An aluminum metal matrix composite reinforced with continuous unidirectional α-Al 2 O 3 fibers has been compression tested at quasi-static and dynamic strain rates. In the transverse direction, the composite showed increased flow stress and maximum stress within the studied strain rate regime, 10 −3 to 3500 s −1 . The strain rate sensitivity of the flow stress in this direction was found to be similar to that of a similar, but unreinforced, alloy determined from previous work. In the longitudinal direction, the maximum stress of the composite increased with increasing strain rate within the range 10 −5 to 700 s −1 . The strain rate dependent maximum stress in this direction was described by the strain rate dependent fiber buckling stress.