Dynamic failure of clamped metallic circular plates subjected to underwater impulsive loads

https://doi.org/10.1016/j.ijimpeng.2016.04.006Get rights and content

Highlights

  • Quantification of the failure of solid plates to water-based impulsive loads has been conducted.

  • Analyses focus on thickness, FSI parameter, and patch size of monolithic plates.

  • Comparisons are conducted between water-backed and air-backed conditions.

  • Scalding relations are developed considering different effects.

  • Parameters for constitutive model of the material have been provided.

Abstract

The dynamic response and failure of monolithic metallic plates subjected to water-based impulsive loads are investigated experimentally. The analysis focuses on the effects of plate thickness, fluid–structure interaction parameter, and patch size of loading area on deformation and failure modes in clamped solid 5A06 aluminum alloy plates under air-backed and water-backed loading conditions. The plates are subjected to impulsive loads of different intensities using a projectile-impact based underwater non-contact explosive simulator. 3D digital imaging correlation method is used to capture the dynamic response of plates to make comparison with postmortem analysis. Depending on the loading rate, the inelastic deformation is the primary failure mode of the plates. The different linear relationships between deflection resistance and applied impulse are identified experimentally, considering the influences of the effects of plate thickness, fluid–structure interaction parameter, and patch size of loading area. The results show that the effect of loading area is the most influential factor on transverse deflection. The results affirm that the plate under water-backed condition shows a 53% reduction in the maximum plate deflection compared with the plate under air-backed condition. Quantitative structure–load–performance relation is carried out to facilitate the advanced study on metallic structures and provides guidance for structural design.

Introduction

Military and civilian ship structures, such as the hull and keel structures, are exposed to various environmental loadings, which include high and low temperature extremes, transient impulsive loads, and corrosive sea water. Additionally, the structures are designed to survive from both surface and underwater explosions and weapons impact. The material properties, blast-resistant performances, and geometric design of sub-structures must be well-understood and quantified.

Clamped structures are representative of the underwater vessel, which have attracted a great amount of interest to investigate the dynamic responses. Recently, experimental and theoretical studies on the metallic and composite sandwich plates have been conducted by many researchers [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14]. Metallic solid and sandwich structures have been studied in terms of constituent material behavior, structural hierarchy, topological characteristics and complex loading involving fluid–structure interactions. Using light gas gun-based impact loading to generate exponentially underwater pressure impulses, Deshpande [2] and Espinosa [15] designed novel non-explosion impulsive simulators to exert planer pressure wave on targets. A number of topological cores were investigated, including the corrugated core, prismatic diamond core, honeycomb core, and metal foam [4], [8], [9], [16], [17]. Constitutive relations have been developed for sandwich structures, accounting for dynamic crush behavior of core and plasticity in constituents by Deshpande [18], [19] and Xue [20]. The deformation of sandwich is divided into three phases: phase I is the fluid–structure interaction, which is up to the point of the first cavitation of the fluid; stage II is the core compression until the front and back faces get an equal velocity, and is followed by the bending and stretching of stage III. McShane et al. [16] analyzed the three phases by making comparisons among the fully decoupled model, cross-coupled model, and fully-coupled model, to investigate the fluid–structure interaction effect during the deformation of plates. The results indicate that the Taylor's analysis based on a free-standing front face-sheet underestimated the transmitted momentum by 20–30% due to the continued fluid loading during the whole deformation of sandwich. Fleck and Deshpande [19], [21] examined the fully-coupled fluid–structure interaction in their analytical models to predict the transmitted momentum and deformation of the metallic sandwich. The parallel research [12] on different sandwich cores was based on the similar analytical model. These articles concluded that metallic sandwich structures outperform monolithic plates when the deformation is dominated by bending. However, Schiffer [5], [17] reported that sandwich plates may or may not outperform rigid plates of equal mass in terms of the impulse imparted to the structure in a blast event.

The solid metallic panels are the basic components of significant metallic structures, which have been studied experimentally and theoretically for several decades. Neglecting the elastic effect, Jones [22] studied the rectangular and circular solid metallic panels under different loading conditions and proposed the ‘bound’ solution for the structural dynamic response. Considering the bending and shearing, Schiffer [7] developed a model for elastic deformation of composite solid plates subjected to underwater impulsive loads, considering the effect of fluid–structure interaction. Nurick [23] conducted comprehensive experiments on fully clamped circular and rectangular steel plates subjected to blast loads. With the increase of impulsive intensities, failure modes are divided into three phases: mode I, inelastic deformation, which is caused by plastically bending and stretching; mode II, tearing at the supports. Plate stretching is followed by tensile rupture at the supports; mode III, shearing at supports. Shear failure occurs at the supports with negligible plastic deformation in the remainder of the beam. The typical discing and petalling failure modes in impulsively loaded clamped plates were analyzed by Lee and Wierzbicki [24], [25], and the tensile tearing modes were reminiscent mode II of failure modes for impulsively loaded beams. Balden [26] made experimental and numerical investigations into the shear rupture modes (mode III) of impulsively loaded clamped circular plates. Kazemahvazi [27] presented an experimental study on the failure modes of low strength copper plates subjected to underwater blast loads. It was concluded from the micrographs that the local failure mechanism is tensile necking, regardless of whether the macroscopic mode is petalling or shear-off. Zamani [28] presented the results of analytical and experimental studies on the response of steel and aluminum circular plates in two different media of air and water. A verified empirical prediction of normal deflection was presented considering the material strength, normal deflection, and intensity of impulses. Until now, detailed experimental validation needs to be attempted to provide more correct analysis and numerical predictions, especially in dynamic underwater situations for which the literature is scarce.

The high strength–weight ratios and high stiffness–weight ratios are the remarkable requirements of ship structures to resist transverse impulsive loads. Light structures, such as sandwich and some aluminum alloy solid panels, outperform the traditional steel plates in terms of these mechanical properties. To investigate the blast resistance and failure modes of the clamped plate as a function of applied impulses, the geometric property and loading configuration is important to the optimal design of vessel structures [4]. Despite recent advances in understanding the dynamic response of solid metallic plates, several issues remain. One is the lack of design relations that quantify the dynamic response as functions of both geometric parameters and load configurations. To obtain such relations, diagnostics that can provide in-situ, time-resolved measurements are required to record the dynamic deformation. Additionally, studies focused on plates that were in contact with water on only one side and with air on the opposite side, but the plates in contact with water on both sides were not considered especially in the experimental studies. The water-backed plate is the more common condition for most marine structures.

The objective of this work is to identify the dynamic response of solid metallic panels subjected to underwater impulsive loads experimentally. The focuses of present analysis are on understanding the deformation, failure modes and associated mechanisms, and quantifying the blast resistance of panels as functions of plate thickness, fluid–structure interaction parameter, and loading conditions. Experiments are conducted under three distinct loading conditions: (1) an air-backed condition, with the plate in contact with water on the impulse side; (2) a water-backed condition, with both sides of the plate in contact with water, and (3) the plates subjected to impulsive loading over a central loading patch, with the loading patch size r = 0.7. The results are presented in normalized forms to gain insight into underlying trends that can be used to design more blast-resistant structures.

Section snippets

Experimental detail

In order to generate predictable and controlled high-intensity underwater impulsive loads for testing marine structures, a projectile-impact based fluid–structure interaction experimental simulator was designed to measure temporal and spatial evolution and failure of structures, as shown in Fig. 1. A planar pressure pulse is generated by firing a projectile at a sliding piston. In order to obtain much higher intensity of underwater impulses, the dimensions of the water chamber similar to that

Experimental results

A parametric study was carried out, focusing on the effects of (i) loads intensity, (ii) thickness of plate, (iii) fluid–structure interaction parameter, (iv) patch size of central loading area, and (v) air-backed and water-backed conditions on dynamic response. The objective is to quantify the transverse deflection and failure mode of plates as functions of loads intensity, geometric thickness and load configuration. Although several input variables were considered, for brevity, this paper

Concluding remarks

Dynamic response and failure of 5A06 aluminum alloy solid plates subjected to water-based impulsive loadings have been evaluated experimentally in this paper. The effect of panel thickness, fluid–structure interaction parameter, loading patch size and intensity of underwater impulse on the dynamic deformation, failure modes and associated mechanisms of the solid plate in air-backed and water-backed conditions are examined respectively.

This study has yielded experimental data on the dynamic

Acknowledgments

The authors would like to thank the National Natural Science Foundation of China (Nos. 11372088, 51509115) for supporting the present work.

References (36)

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