Key Engineering Materials Vols. 535-536

Abstract: In general, materials exhibit an increase of strength when loaded at high strain rates, which should be taken into account when dealing with structural impact. Kolsky developed an equipment operating based on elastic wave propagation capable of submitting a material sample to high strain rates. This paper presents some design features of such a tensile wave machine, including mechanical and electronic design issues, which may be helpful in a design phase.

Abstract: An analytic model is developed to obtain the dynamic response of beams with initial velocities of the upper beam which is clamped at both ends and fully supported by metal foam, as a representative arrangement for protective structures. In large deflection, plastic bending and stretching in deforming regions are considered and the membrane factor method is introduced in the model to take into account the effect of axial force in the yielding. The relationships between the final displacement of the center in the beam and the dimensionless parameters are obtained. This model can predict the dynamic effects of different initial velocities and beams with different lengths, thickness and yield strength of cores.

Abstract: The dynamic response of aluminum foam sandwich panels are studied experimentally by impacting the panels at mid-span with metal foam projectiles. Two types of core are considered: open-cell foam and closed-cell foam. By changing the launching speed of metal foam projectiles, different deformation/failure modes of sandwich panels are obtained. Strain history of face sheets in different positions is also recorded by strain gauges to observe its deformation mechanism. The experiment results indicated that when the strength of core is relatively small and the impulse exerted is large, erosion failure of front face and shear failure of core occurred.

Abstract: This paper is concerned with the failure characteristics and the failure loads of laser welds in a SPRC340 1.2t steel sheet under combined normal and shear loading conditions. The quasi-static and dynamic failure tests were carried out under nine different combined normal and shear loads including a pure-normal load and a pure-shear load. Especially for the pure-shear condition, a testing fixture was newly designed in order to evaluate the strength of a laser-welded region fabricated by the same welding condition as a two-layered lap joint. The failure load and the failure behavior of laser welds were investigated in each loading condition. Dynamic effects on the failure load of laser welds, which are critical for structural crashworthiness, were also examined based on the experimental data. In order to evaluate the effect of the strain rate on the failure contour of laser welds under the combined normal and shear loads, the failure loads measured from the experiment were decomposed into two components along the normal and shear directions.

Abstract: To examine the effect of elasticity in dynamic response of imperfect structures, by densely setting meshes in the vicinity of the imperfections, pre-cracked beams impinged by a striker are modeled and numerically investigated. The dynamic response patterns and failure history for two specific configurations are obtained. It is found that complex alternations of the elastic-plastic stress distribution exhibit, and the striker is rebounded and then separated from the beam, which well reflects the effect of material elasticity. The high stress and large deformation zones, corresponding to the plastic hinges in the rigid-plastic model, appear at the impinging position and the supporting ends, and the locations coincide with those in the modal pattern in rigid-plastic response. From comparison, it is concluded that when the impinging is intense, despite the effect of elasticity displaying in the early stage, the widely employed rigid-plastic analysis is still capable of providing favorable prediction on the final response parameters.

Abstract: 5083 aluminum alloy was investigated with respect to its uniaxial dynamic compressive properties over a range of strain rates using the split Hopkinson pressure bar (SHPB). The dynamic stress-strain curves of this alloy were obtained for strain rates from 1000 s-1 to 6000 s-1. Effects of strain rate, the samples size and anti-impact capability were analyzed. The experimental results show that under impaction loading, 5083 aluminum alloy has a remarkable strengthening response to strain rate and size; in particular, the responded stress increases with increasing strain rate, which implies that this alloy has high strength and high anti-impact capability.

Abstract: Similar blast loading characteristics can be obtained using impact of aluminium foam projectiles, which enables blast tests to be mimicked in a laboratory scale and in a safer environment. The purpose of this study is to determine the back-face deflection history of aluminium sandwich panels experimentally by aids of a laser displacement meter when panels are subjected to the impact of metal foam projectiles. This information was usually determined using finite element analysis (FEA) due to the difficulty in the experiment. The projectiles are cylindrical ALPORAS aluminium foam with diameter of 37 mm, length of 50 mm and nominal relative density of 10%. The sandwich panels consist of two 1 mm aluminium face-sheets and an aluminium honeycomb as the core. There are five different core configurations with a brand name of HEXCEL. The projectiles are fired towards the centre of the sandwich panels at different velocities using a gas gun. During the tests, a laser optical displacement measuring device is used to record the history of the back-face deflection experimentally. The deflection of the back-face is found to reach the maximum before coming to rest at a smaller value. The final back-face deflections of the sandwich panels show exponential relationship with the projectile impulse. The final deflections are compared with the deflection of monolithic plates with equal mass. The sandwich panels deflect less than the monolithic plate with an equal mass up to a critical value but continue to increase significantly afterwards. Care should be taken when using sandwich panels as protective structures against foam projectiles as beyond this point, the monolithic plates outperform the sandwich panels in absorbing the impact load.

Abstract: Experimental and numerical studies of the 2D woven composite laminates under low-velocity impact with different energy are discussed in this paper. The traditional Hashin failure criteria are improved to cover the failure modes of fiber rupture and delamination. It is found that the damage level depend on the impact energy. The matrix deformation is the main reason of delamination. The simulating results are in good agreement with the experimental phenomenon observed by nondestructive examination (ultrasonic C scanning) and cross-section examination

Abstract: The microstructure evolution of Ti-46.5Al-2Nb-2Cr with different microstructure types loaded under a large range of strain rates and elevated temperatures is investigated by TEM. The results show that deformation twins are the main deformation mode under high strain rate loadings and both ordinary dislocation and super-dislocation are the additional modes under quasi-static loadings. The proportion of twinned grains increases with the increased strain rates.

Abstract: Blast-resistant structures are traditionally designed and fabricated with solid materials of heavy weight to resist blast loadings. This not only increases the material and construction costs, but also undermines the operational performance of protective structures. To overcome these problems, new designs with either new structural forms or new materials are demanded against blast loads. A multi-arch double-layered unstiffened panel has been proposed as a new structural form in the previous study[1]. Its performance has been numerically demonstrated better than other forms of double-layered panels in resisting blast loads. In this study, to further improve the effectiveness of the multi-arch double-layered panel in resisting blast loads, responses of a five-arch double-layered panel with rectangular stiffeners to blast loads are investigated by using finite element code Ls-Dyna. Peak displacement, internal energy absorption, boundary reaction forces and plastic strain are extracted and used as response parameters to demonstrate the effectiveness of stiffened panel on the blast resistance capacities. The numerical results show that the stiffened panel outperforms the unstiffened panel of the same weight on the blast-resistant capacity. The stiffened multi-arch double-layered panel has great potential applications in the blast-resistant panel design.