15 research outputs found
Application of Polyurethane Foam Filled Aluminum Sandwich Structures in Blast Resistant Design
No full textWith the advancement of warfare weapons, terrorist attacks and failure of engineering structures due to impact of blast load has also frequented. Therefore, to protect the important structure and thereby human beings, scientists and engineers are proposing innovative solutions for mitigating the impact due to blast loading. Sandwich structure is one of the solutions that can be used for protecting the structure without much increase in overall weight of the structure. Therefore, present numerical analysis is performed to understand how sandwich structures filled with polyurethane (PU) foam responded as compared to bare honeycomb sandwich structure as well as equivalent weight plate. Due to the presence of foam filling in cells of honeycomb sandwich structure, the energy absorption capabilities are enhanced. The performance of PU foam filled honeycomb sandwich structure is evaluated based on peak backsheet deformation. Thus, an improved performance PU foam filled aluminum honeycomb sandwich structure is observed. Further, a parametric study is conducted considering different cell sizes (6, 12 and 19 mm), core depths (25 and 50 mm) and scaled distances. It is observed from this study that sandwich configuration with lesser cell size and higher core depth resisted the blast most effectively
Enhanced Single-Degree-of-Freedom Analysis of Thin Elastic Plates Subjected to Blast Loading Using an Energy-Based Approach
No full textSingle-degree-of-freedom (SDOF) models are known to represent a valid tool in support of design. Key assumptions of these models, on the other hand, can strongly affect the expected predictions, hence resulting in possible overconservative or misleading estimates for the response of real structural systems under extreme actions. Among others, the description of the input loads can be responsible for major design issues, thus requiring the use of more refined approaches. In this paper, a SDOF model is developed for thin elastic plates under large displacements. Based on the energy approach, careful attention is given for the derivation of the governing linear and nonlinear parameters, under different boundary conditions of technical interest. In doing so, the efforts are dedicated to the description of the incoming blast waves. In place of simplified sinusoidal pressures, the input impulsive loads are described with the support of infinite trigonometric series that are more accurate. The so-developed SDOF model is therefore validated, based on selected literature results, by analyzing the large displacement response of thin elastic plates, under several boundary conditions and real blast pressures. Major advantage for the validation of the proposed SDOF model is obtained from experimental finite element (FE) and finite difference (FD) models of literature, giving evidence of a rather good correlation and confirming the validity of the presented formulation
An Abridged Review of Buckling Analysis of Compression Members in Construction
No full textThe column buckling problem was first investigated by Leonhard Euler in 1757. Since then, numerous efforts have been made to enhance the buckling capacity of slender columns, because of their importance in structural, mechanical, aeronautical, biomedical, and several other engineering fields. Buckling analysis has become a critical aspect, especially in the safety engineering design since, at the time of failure, the actual stress at the point of failure is significantly lower than the material capability to withstand the imposed loads. With the recent advancement in materials and composites, the load-carrying capacity of columns has been remarkably increased, without any significant increase in their size, thus resulting in even more slender compressive members that can be susceptible to buckling collapse. Thus, nonuniformity in columns can be achieved in two ways—either by varying the material properties or by varying the cross section (i.e., shape and size). Both these methods are preferred because they actually inherited the advantage of the reduction in the dead load of the column. Hence, an attempt is made herein to present an abridged review on the buckling analysis of the columns with major emphasis on the buckling of nonuniform and functionally graded columns. Moreover, the paper provides a concise discussion on references that could be helpful for researchers and designers to understand and address the relevant buckling parameters
Effect of Geo-Material on Dynamic Response of Tunnel Subjected to Surface Explosion
No full textPrime materials involved in a problem such as underground structures are concrete, reinforcement steel, and geo-material surrounding the tunnel. Among these three materials, concrete and steel are manufactured materials and their properties can be controlled up to a certain extent. However, geo-material is a naturally occurring material whose constitutive properties vary from region to region, making it highly unpredictable. Findings from one study cannot be applied to other geotechnical problems directly, especially in the case of tunnels subjected to surface explosions. The blast wave generated has to travel through the geo-material before it interacts with the tunnel. As the shock wave propagates radially, its characteristics are likely to be altered by the geo-material. Limited study has been carried out considering this problem. In the present study, the effect of various types of geo-material on the blast response of tunnels subjected to surface explosions is investigated. Finite element analysis has been carried out using LS-DYNA®, wherein the problem has been modeled using the multi-material arbitrary Lagrangian–Eulerian (MM-ALE) method. Materials with fluid behavior such as air, explosives, and soil are modeled using ALE formulation. Other materials including tunnel lining, reinforcement steel, and rock are modeled using Lagrangian formulation. Blast loading is simulated using the Jones–Wilkins–Lee (JWL) equation of state. Geo-materials considered for the comparative study are sandy loam, saturated clayey soil, sandstone, and granite. Vertical displacement measured at the crown of the tunnel is used to determine the response of the tunnel. Sandy loam soil, being a highly compressible soil, exhibits non-linear and fluid-like behavior under high-strain loading such as explosions. Tunnels undergo extreme deformation in the case of sandy loam soil and clayey soil compared to rock cases. Further, the effect of saturation in sandy loam on tunnel stability is studied. It is observed that with the increase in saturation of soil, more blast energy is transmitted to the structure, which results in higher deformation. Lastly, the effect of the weathering of rock on the tunnel’s response is investigated in the case of sandstone and granite. It was observed that weathering in rock led to more displacement of tunnel crown when compared to intact rock
Blast resistance of stiffened sandwich panels with closed-cell aluminum foam
No full textIn 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
Dynamic Response of Stiffened Plates under Air Blast
No full text 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. </jats:p
