Manmohan Dass Goel

Comparative Performance of Stiffened Sandwich Foam Panels under Impulsive Loading

AbstractModeling and numerical simulation of foam sandwich panels subjected to impulsive loading are presented. The sandwich panels consist of steel sheets at front and back with two varieties of foam cores in between. Stiffeners are provided at the back sheet for improved response. The dynamic response of the stiffened steel plate (SSP), sandwich foam panel (SFP), and stiffened sandwich foam panel (SSFP) are compared. The foam material modeling accounts for elastic-plastic behavior with volumetric hardening. The finite element–based numerical simulation for dynamic analysis is performed using a combination of shell and solid elements for sheets and foam, respectively. Central point displacements caused from the impulsive load of peak pressure of 0.7 MPa and lasting for 15 ms applied uniformly to the sandwich panels are studied. The analysis is carried out with an objective of understanding the effects of foam thickness, type of foam, and the stiffener configurations. The results obtained indicate that th...

Titanium cenosphere syntactic foam with coarser cenosphere fabricated by powder metallurgy at lower compaction load

Abstract Titanium cenosphere syntactic foam of varying relative densities with coarse cenospheres was developed through powder metallurgy route at lower compaction loads. The cold compaction load was varied in the range of 60 to 75 MPa to obtain the foams of different relative densities. A function of cold compaction load between crushing tendency of cenosphere and relative density was investigated. The compressive deformation behavior of these foams was studied, and empirical relationships among plateau stress, elastic modulus, densification strains and energy absorption are formulated considering their practical significance. The performance indices of the developed foam in comparison with dense titanium were studied and it was found that the foam is superior alternative to titanium for engineering applications.

Dynamic Response of Stiffened Plates under Air Blast

A numerical investigation is presented to examine the effect of stiffener configuration on the response of rectangular plate subjected to air blast loading. Dynamic response of the plate, with various stiffener layouts under air blast is analysed. The plate is modelled using shell elements and the effect of strain rates are considered using Johnson-Cook (J-C) model, under air blast load applied in the form of an equivalent rectangular uniform pulse. A modal analysis is carried out to obtain the natural frequencies of the plates that help in assessment and influence on their dynamic response. Analysis is carried out from the perspective of understanding the dynamic response of the plate, with stiffener, in comparison with equivalently thickened unstiffened plate. The results indicate that the equivalently thickened unstiffened plates exhibit higher peak displacement as compared to the stiffened plate, signifying the importance of the stiffeners placed strategically. It is concluded that the stiffener layout and strain rate consideration governs the dynamic response of the plates subjected to small duration blast loading.

Strain rate sensitivity of closed cell aluminium fly ash foam

Abstract: With the increasing use of metal foams in various engineering applications, investigation of their dynamic behaviour under varying strain rate is necessary. Closed cell aluminium fly ash foam developed through liquid metallurgy route was investigated for its stress—strain behaviour at different strain rates ranging from 700 s −1 to 1950 s −1 . The numerical model of split Hopkinson pressure bar (SHPB) was simulated using commercially available finite element code Abaqus/Explicit. Validation of numerical simulation was carried out using available experimental and numerical results. Full scale stress—strain curves were developed for various strain rates to study the effect of strain rate on compressive strength and energy absorption. The results showed that the closed cell aluminium fly ash foam is sensitive to strain rate. Key words: high strain rate; metal foam; strain rate sensitivity; numerical simulation; split Hopkinson pressure bar 1 Introduction Metal foams had shown many interesting properties for their applications in blast resistance and crashworthiness [1]. To use metal foam efficiently in these applications, their characterization in terms of dynamic properties is of foremost importance. To investigate the mechanical behaviour of metal foams at higher strain rates, split Hopkinson pressure bar (SHPB) test is required. Several researchers in the past have experimentally investigated the deformation behaviour of aluminium foams at different strain rates ranging from quasi-static to high strain rates (about 5000 s

Blast-Resistant Design of Structures

AbstractThe strategy for dealing with the blast-induced threats against a structure requires attention from planning and design stages, as introducing or altering various blast response mitigation strategies becomes either difficult or impossible later on. Blast response mitigation strategies can be incorporated in the structural design at concept stage, leading to a well-designed and -constructed structure that can exhibit improved blast resistance and at the same time maintain its architecturally appealing appearance. This requires knowledge of (1) intelligent strategies in the form of blast source isolation strategies or using advanced engineered materials, (2) material behavior under such loading, and (3) postexplosion functioning of the structure and its elements. In this paper, various strategies for blast mitigation are reviewed and discussed with an emphasis on presenting a comprehensive assessment of blast response mitigation technologies beginning from the necessary discussion on fundamental asp...

Interaction of a shock wave with a closed cell aluminum metal foam

The present investigation examines the interaction of shock waves with closed cell aluminum foam samples in a conventional shock tube. The effect of the sample thickness on shock wave attenuation and/or enhancement and the use of the foam in the sandwich structure is studied. Results in terms of incident and reflected shock pressures are obtained, and the effectiveness of the samples with and without the foam is compared. It is demonstrated that the foam density and thickness, as well as the placement of cover plates of the same material in front of and behind the foam have the most significant effect on the reflected shock pressure. It is concluded that the closed cell aluminum metal foam can be effectively used as a sacrificial layer in blast protection of structures.

Characteristics and wear behavior of cenosphere dispersed titanium matrix composite developed by powder metallurgy route

Abstract The cenosphere dispersed Ti matrix composite was fabricated by powder metallurgy route, and its wear and corrosion behaviors were investigated. The results show that the microstructure of the fabricated composite consists of dispersion of hollow cenosphere particles in α -Ti matrix. The average pore diameter varies from 50 to 150 μm. The presence of porosities is attributed to the damage of cenosphere particles due to the application of load during compaction as well as to the hollow nature of cenospheres. A detailed X-ray diffraction profile of the composites shows the presence of Al 2 O 3 , SiO 2 , TiO 2 and α -Ti. The average microhardness of the composite (matrix) varies from HV 1100 to HV 1800 as compared with HV 240 of the as-received substrate. Wear studies show a significant enhancement in wear resistance against hardened steel ball and WC ball compared with that of commercially available Ti–6Al–4V alloy. The wear mechanism was established and presented in detail. The corrosion behavior of the composites in 3.56% NaCl (mass fraction) solution shows that corrosion potential ( φ corr ) shifts towards nobler direction with improvement in pitting corrosion resistance. However, corrosion rate of the cenosphere dispersed Ti matrix composite increases compared with that of the commercially available Ti–6Al–4V alloy.

Numerical investigation of the axial impact loading behaviour of single, double and stiffened circular tubes

ABSTRACT Thin-walled circular tubes are good in energy absorption and also light in weight. Energy absorption and deformation modes of these tubes depend on the geometry of the structure. Energy absorption can further be enhanced by implementing improved geometrical configurations. In the present investigation, an attempt is made to improve the energy absorption of thin concentric cylindrical tubes by replacing the inner tube with half cylindrical shells acting as stiffeners along the circumference of the external tube. The tubes have been test simulated under impact loading and their deformation and energy absorption is studied in view of bottoming-out and energy absorption effectiveness factor. The total mass of the stiffened and double tubes is kept identical for the purpose of comparison. It is found that energy absorption capacity of the double tube is 1.71 times higher than the single tube and for stiffened tube, it is 1.91 times higher than the single tube configuration. Moreover, energy absorption effectiveness factor is found to be 1.69 times higher for double and 1.89 times higher for stiffened tubes in comparison with the single tube configuration. Further, it is concluded that provision of longitudinal stiffeners results in higher energy absorption with higher energy absorption effectiveness factor for stiffened tube configurations in comparison with the single and double tube configurations. Further, it is found that provision of stiffeners influences the deformation modes considerably.

Blast resistance of stiffened sandwich panels with closed-cell aluminum foam

In the present investigation, response of the stiffened sandwich foam panels with closed-cell aluminum foam cores subjected to blast load is examined. The panels have the metal foam sandwiched between two steel sheets. To improve resistance of the sandwich foam panel against blast, stiffeners are provided and their dynamic response under varying blast load is studied. Blast load is applied using blast equations available in LS-DYNA which takes into account reflection of blast from surface of the sandwich foam panel. Finite element based numerical simulations for dynamic analysis are performed employing a combination of shell and solid elements for steel sheets and metal foam, respectively. Quantitative assessment of dynamic response of the sandwich foam panels is made, primarily focusing on peak central point displacement of back-sheet (opposite to explosion) of the panel. Several analyses are carried out with an objective to understand the effects of stiffener configuration, foam thickness, foam density, and standoff distance on the blast response. Results indicate that the provision of stiffeners along with metal foam considerably increases blast resistance as compared to the unstiffened panels with the metal foam.

Deformation and Energy Absorption of Aluminum Foam Filled Square Tubes

Modeling and numerical simulation of aluminum foam filled square tubes under axial impact loading is presented. The foam-filled thin-walled square tubes are modeled as shell wherein, foam core is modeled by incorporating visco-elastic plastic foam model in Altair® RADIOSS. Deformation and energy absorption studies with single, bi-tubular, and multi-tube structure with and without aluminum foam core are carried out for assessing its effectiveness in crashworthiness under the identical conditions. It is observed that the multi-tube structure with foam core modify the deformation modes considerably and results in substantial increase in energy absorption capacity in comparison with the single and multi-tube without foam core. Moreover, the multi-tube foam filled structure shows complicated deformation modes due to the significant effect of stress wave propagation. This study will help automotive industry to design superior crashworthy components with multi-tube foam filled structures and will reduce the experimental trials by conducting the numerical simulations.