Papers by Keyword: Energy Absorption

Abstract: A varying cell-size method based on Voronoi technique is extended to construct 3D graded cellular models. The dynamic behaviors of graded cellular structures with different density gradients are then investigated with finite element code ABAQUS/Explicit. Results show that graded cellular materials have better performance as energy absorbers. Graded cellular structures with large density near the distal end can protect strikers, and those with low density near the distal end can protect structures at the distal end. It is concluded that graded cellular materials with suitable design may have excellent performance in crashworthiness.

Abstract: The main objective of this paper was to present the results of experimental investigation carried out to study the structural behaviour of ferrogeopolymer elements under flexure. Initially the properties of geopolymeric binder prepared using the source materials such as Fly ash and Ground Granulated Blast Furnace Slag (GGBS) without conventional cement have been investigated. The different parameters considered in this study are the ratio of binder to fine aggregate (1:2 and1:3) and the ratio of Na₂SiO₃ to NaOH solutions (2.0 and 2.5). The various combinations of Fly ash and GGBS considered are 90% & 10% and 80% & 20%. The alkaline liquid to binder ratio is fixed as 0.45. The individual properties of mortar such as Compressive Strength and Density were determined as per relevant Indian standards. The geopolymer concrete mix that gives the highest compressive strength was used to cast the ferrogeopolymer structural slabs. Four numbers of rectangular slabs of size 800 mm x 300 mm x 25 mm were prepared with two types of meshes such as mild steel and galvanized iron weld mesh with single and double layers. Based on the test results Load-Deflection curves were drawn and the effectiveness of mild steel and galvanized iron weld meshes was compared from the characteristics such as first crack load, ultimate load, energy absorption and ductility.

Abstract: The effect of fibre type and fibre amount on physico-mechanical properties of slurry infiltrated fibre concrete (SIFCON) at both quasi-static and dynamic load was evaluated experimentally. SIFCON is a special type of cement-based composite with high fibre volume fraction, extremely strong and ductile. Test specimens were prepared with 7 types of steel fibres (with different shape and mechanical parameters) in four volume fractions (7.5-15 vol. %). High performance fibre-reinforced concrete (HPFRC) has also been cast and tested for comparison purposes. The impact test has been carried out by using an in-house manufactured impact testing machine based on drop test principle. The test results revealed that SIFCON slab with 15 vol. % fibre content exhibits superior energy-absorption characteristics when compared to other slab specimens. Diameter of the fibres plays an important role for both strength and energy absorption capacity of SIFCON - using of low-diameter fibres with higher aspect ratio leads to the best results.

Abstract: Ni-Ti foams of varying relative densities have been made by varying the size and volume fraction of NH₄(HCO₃), which was used as space holder. The green compacted pellets, after evaporation of NH₄(HCO₃), were sintered at 1100°C for 2 hrs. The XRD and EDX analysis confirms that there is no residual space holder. The extent of openness of cell walls increases with increase in porosity. The compressive stress-strain behavior of these foams varies with the relative density. The peak stress and energy absorption of these foam increases with relative density following power law and linear relationships respectively, and the densification strain decreases with relative density following a linear relationship. The pseudo elastic recovery strain and shape recovery strain decrease with increase in porosity. The overall recovery increases with decrease in degree of deformation. This phenomenological behavior indicates that these foams can be used for their shape memory effect.

Abstract: –The behaviour of extruded glass fibre reinforced thermoplastic pipe under axial crushing load was investigated experimentally. It was envisaged that the difference between the axial and hoop moduli and strengths as well as the volume fraction would influence the mode of collapses and energy absorption. The moduli could be varied using a new extrusion technology, which controls the fibre orientation pattern, hence, the mechanical properties. The ability to vary the moduli and the fibre volume fraction provide means of controlling the collapse mode in order to optimise specific energy absorption. Axial compression tests were performed on glass filled Polypropylene and Polyethylene composite pipes. The samples were chosen with a variety of fibre volume fraction, V_f = 5% to 20% and average angle of orientation, θ = 50^o to 80^o to evaluate the effect of anisotropy and V_f on the energy absorption capacity and collapse modes. The observations indicate that, the samples containing of higher V_f and θ, collapsed in brittle failure mode (fragmentation), while those with less V_f and θ angle collapsed in non-axis-symmetric (diamond) mode with local fracture. The galss fillet with polypropylene-60^o (GPP-60) displayed the highest specific energy absorption (E_s) compared to the other GPE, MDPE and LDPE pipe samples. However, the glass fillet polyethylene – 75^o (GPE-75) displayed the highest E_s and the glass fillet polyethylene – 65^o (GPE-65) displayed the lowest E_s compared with in the GPE pipes. The specific energy absorption of GPP-70 pipe (24 kJ/kg) and GPE-75 pipe (12 kJ/kg) is almost 50 % and 25% of the amount of specific energy absorption of aluminium tubes (60 kJ/kg), respectively. Moreover, it is close to the specific energy absorption of glass-epoxy 15^o (GE-15) / which is 30 kJ/kg, and much higher than aramid-epoxy-15^o (AE-15)/ which is 9 kJ/kg.

Abstract: Closed-cell superplastic Zn-22Al alloy foams were manufactured through the melt foaming process using sodium hydrogen carbonate powder as a foaming agent. Foaming tests were carried out under different foaming temperatures, times and additive amounts of foaming agent. The porosity of Zn-22Al alloy foams were between 30 and 70%. The cell wall consisted of fine equiaxial crystal grains after solution treatment. The compressive properties of the Zn-22Al alloy foams were investigated at room temperature and high temperature. Zn-22Al alloy foams exhibited high strain rate sensitivity, which was caused by superplastic deformation of the cell wall material.

Abstract: A conventional tube is considered in oblique position when its longitudinal is oblique. However, oblique attachments vary as the tube can be a straight or angulated tube. In the present study, impact responses of different oblique positioned tubes subject to axial loading were numerically studied. Next, the best oblique arrangements were proposed that have higher critical load angle and energy absorption capacity. Results show that specimen of Top-Bottom Angulated (TBA) from horizontal is the best choice for its lowest initial peak load and mean crush load. This data therefore has great potential for further enhance the new design of energy absorbers in oblique position.

Abstract: Cenospheres are very cheap, and are reasonably strong and thermally stable upto 1200°C. In view of this attempt has been made to use these cenosphere for making Titanium syntactic foams with varying relative densities. Precautions were taken for selecting cold compaction pressure to minimize cenosphere crushing. The sintered samples were then characterized in terms of microstructures primarily to see the extent of cenosphere crushing, distribution of cenosphere, and extent of sintering. The foams made using optimized pressure and sintering parameters, exhibits uniform distribution of cenosphere without any significant crushing. The plateau stress, energy absorption and modulus of these foams are varying with the cenosphere content or the relative density, and these parameters can be engineered by varying cenosphere content in the foam. These foams exhibit considerably higher strength and stiffness than the conventional foam and show the possibility of using them for biomedical and engineering applications.

Abstract: Aluminium foams are of interest due to their ultra low density, high structural stiffness per unit weight. Like conventional Al foams having Ca, ceramic particle (e.g. SiC, Al₂O₃) containing Al alloy metal matrix composite (MMC) foams can be produced. In this approach, parameters such as particle type, size, and volume fraction need to be optimized to get good quality foams with high foam expansions. However, the role of them on the compression properties of MMC foams is seldom reported. With this objective, the present study explores the effect of SiC_P size and vol. % on compression behavior of various Al-Si/SiC_P foams prepared at DMRL. From the large number of compression tests, it is observed that the reinforcement parameters don’t seem to play any effective role with respect to foam properties, although they are very important in foam manufacture.

Abstract: Long cylindrical tubes exhibit poor energy absorption due to Euler’s buckling mode when they are used to absorb impact energy. Circumferential grooves are introduced in the tube to force the plastic deformation which helps to control the buckling mode. Quasi-static and impact tests are performed and the load-displacement curves are studied. The results are also compared with the ones for the geometrically identical tubes. Non-linear finite element analyses are also carried out to simulate quasi-static and impact test conditions. The numerical predicted crushing force and fold formation are found to be in good agreement with the experimental results. The results revealed that grooves can stabilize the deformation behaviour and thus the proposed method could be a good candidate as a controllable energy absorption element.