Core Compression Research Articles

Numerical study on the interaction between underwater explosion bubble and a moveable plate with basic characteristics of a sandwich structure

The dynamics of an underwater explosion bubble interacting with a moveable plate with basic characteristics of a sandwich structure are investigated numerically using boundary element method. The response of sandwich structures is assumed to be a moveable plate with a given velocity profile. The influence of the plate velocity profile, the standoff distance and the scale of the plate on the bubble behaviors are discussed. Within the scope of discussions, the bubble volume and period are a decreasing function of the maximum crushing velocity, the core compression, and the plate dimension, and an increasing function of the standoff distance. Three different regimes of bubble behaviors are distinguished: (1) jet directing towards the plate; (2) the bubble splitting into multiple bubbles or oscillating spherically without jet; (3) jet directing away from the plate. The results indicate that the sandwich plate which can provide larger deformation and larger maximum deformation velocity is beneficial for altering the jet direction to direct away from the plate.

Impulsive Response of Rectangular Metal Sandwich Plate with a Graded Foam Core

An analytical study considering inhomogeneous core compression is conducted to investigate the impulsive response of fully clamped rectangular metal sandwich plate with a graded foam (GF) core. The dynamic compressive properties of GF under impulsive loading are theoretically modeled antecedently. The approximate analytical predictions are achieved for the impulsive response of rectangular sandwich plate with a linear strength distributed GF core along the thickness by using the relevant loci of a new yield criterion. The analytical predictions agree well with the finite element (FE) results and indicate that the sandwich plates with negative gradient design outperform their uniform counterparts in impulsive resistance. The present study provides an insight into understanding the blast resistance of the sandwich structures with inhomogeneous cores.

Rectangular sandwich plates with Miura-ori folded core under quasi-static loadings

This research presents a parametric study by using ABAQUS/Explicit and analytical analysis of rectangular sandwich plates with Miura-ori folded core. Two loading conditions are studied: three-point bending and uniformly distributed pressure loading. Load-displacement curves are obtained and energy absorption performance is assessed. Under three-point bending and uniformly distributed pressure loading of small magnitude, performance of such sandwich plates has been found to be better than that of corresponding monolithic plates of the same mass. In addition, analytical modelling has been conducted based on the plastic hinge theory, which results in a good agreement with those from the finite element analysis (FEA). It has been found that the maximum bending strength is governed by the incipience or fully plastic yielding of the core material for relatively thick cores, or elastic buckling of the core compression for thin cores. Furthermore, the yielding moment, fully plastic bending moment and elastic buckling moment of the incipience of core buckling have been evaluated.

The effect of strain-rate sensitivity on dynamic response of impulsively loaded sandwich beam

ABSTRACTA theoretical analysis method is developed to study dynamic responses of clamped strain-rate-sensitive sandwich beam subjected to impulsive loading based on Cowper and Symonds constitutive model. The front sheet of the sandwich beam is normally loaded by a uniformly distributed impulse. The effect of strain-rate sensitivity is characterized by an influence factor independent of time history but related to initial impact kinetic energy. The relationship between this influence factor and initial kinetic energies is analyzed for three different materials. The dynamic response process of sandwich beam is divided into two stages: core compression stage and overall beam deformation stage. The strain-rate sensitivity of materials is considered only in the second stage of dynamic response analysis. From the comparison of the results of sandwich beam with that of monolithic beam, we can conclude that this method of introducing influence factor to characterize the strain-rate-sensitive effect is valid to analyze the dynamic responses of impulsively loaded sandwich beams.

Response of square honeycomb core sandwich panels to granular matter impact

The deformation of square honeycomb core, stainless steel sandwich panels by the impact of explosively accelerated granular matter has been investigated and compared to results from a previous study using equivalent (same material and mass per unit area) solid plates subjected to similar impulsive loadings. Spherical explosive charges surrounded by 25–150 kg mass annular shells of water-saturated granular media (either fused silica or zirconia particles) were suspended above the center of the edge clamped test panels. The radially expanding granular particle front velocities were measured from high-speed video images, and revealed that the granular matter had been accelerated to velocities of 500–1200 m/s after detonation. A Kolsky bar was used to measure the time-dependent pressure and impulse at a position equivalent to the panel center, while the permanent deflections of the sandwich panels were determined by profilometry after the experiments. Even though fracture of electron beam welds used to attach the back face sheet to the sandwich panel core occurred in all the tests, the permanent deflections of the sandwich panel back faces were significantly less than those of equivalent solid plates, and were accompanied by minimal core compression. Discrete particle simulations of the granular matter acceleration and impact loading of the sandwich panels indicated that their superior deflection benefit arose from their high bending resistance rather than particle-structure interactions. This benefit was offset when the rear face of the sandwich was kept the same distance from the impulsive source as that of the solid plate since the impact face of the sandwich panel was closer to the impulsive source, subjecting it to a higher impulse than the solid plate. However, a substantial deflection reduction was still achieved by use of a strong core sandwich design.

Spectroscopic Study of NGC 281 West

NGC 281 is a complex region of star formation at 2.8 kpc. This complex is situated 300 pc above the Galactic plane, and appears to be part of a 270 pc diameter ring of atomic and molecular clouds expanding at 22 km/s (Megeath et al. 2003). It appears that two modes of triggered star formation are at work here: an initial supernova to trigger the ring complex and the initial O stars and the subsequent triggering of low mass star formation by photoevaporation driven molecular core compression. To get a complete census of the young stellar population, we use observations from Chandra ACIS 100 ksec coupled with data from 2MASS and Spitzer. The Master X-ray catalog has 446 sources detected in different bandpasses. We present the spatial distribution of Class I, II and III sources to study the progress of star formation. We also determine the gas to dust ratio NH/AK to be 1.93 ± 0.47 ×1022 cm−2 mag−1 for this region. In this article, we present NGC 281 as a good target to study with the 3.6-m Devasthal Optical Telescope (DOT) in spectroscopy. With these spectra, we look for evidence for the pre-main-sequence (PMS) nature of the objects, study the properties of the detected emission lines as a function of evolutionary class, and obtain spectral types for the observed young stellar objects (YSOs). The temperatures implied by the spectral types can be combined with luminosities determined from the near-infrared (NIR) photometry to construct Hertzsprung–Russell (HR) diagrams for the clusters. By comparing the positions of the YSOs in the HR diagrams with the PMS tracks, we can determine the ages of the embedded sources and study the relative ages of the YSOs with and without optically thick circumstellar disks.

On physically asymmetric sandwich plates with metal foam core subjected to blast loading: dynamic response and optimal design

The dynamic response of physically asymmetric rectangular sandwich plates with metal foam core subjected to blast loading is investigated analytically and numerically. The so-called ‘bounds’ of analytical solutions for the maximum central deflection of back face-sheets and the structural response time are obtained, respectively, by employing the yield criteria for an asymmetric sandwich structure including core compression. Furthermore, an improved membrane mode analysis considering the ‘residual’ bending moment for asymmetric sandwich plates is presented and the membrane mode solutions are given. It is shown that there is a good agreement between the theoretical predictions and the numerical results. Based on the analytical formulae, optimal design charts are constructed to maximize the impulsive resistance of physically asymmetric sandwich plates for a given mass. Finally, the performances of optimally designed sandwich plates with various face-sheet material combinations are discussed.

Dynamic responses of metal sandwich beams under high velocity impact considering time inhomogeneity of core deformation

The objective of this paper is to establish a yielding criterion for a sandwich beam by considering the time inhomogeneity of foam core deformation, which results in the time-varied neutral surface and cross-sectional area. Taking into account of the bending and axial stretching, a unified dynamic yielding criterion for metallic sandwich beams considering the mass redistribution along with the core compression is established. A membrane factor is proposed and an analytical solution for the large deflection of the beam under high velocity impact is given. Different from the traditional yielding surface, when the core is partially densified, the yielding surface is asymmetric. Comparison of analytical solutions with numerical ones reveals that the present model improves the prediction accuracy of high-velocity impact responses of fully clamped sandwich beams. The present method can also be degenerated to predict the low velocity/energy impact responses of sandwich beams.

Degradation mechanisms of balsa wood and PVC foam sandwich core composites due to freeze/thaw exposure in saline solution

Structural engineers commonly use balsa wood and PVC foam as core materials for sandwich composite structures. These structures are frequently exposed to thermal cycling in sea water. The long-term performance and damage mechanism of these composite sandwich structures under such environmental conditions are still unclear. To simulate these effects, sandwich panels using balsa wood (SB100) and foam core (Airex C70.55) with fiber glass/vinyl ester face sheets were exposed to 100 days of freeze/thaw exposure (−20℃ to 20℃). The freezing and thawing occurred in presence of a saline solution. A total of 150 samples were tested for core shear, core compression, and peel tests. Results confirmed that exposure reduced the balsa wood core shear strength by 14%, compression strength by 36%, and compression modulus by 33%. Interestingly, the PVC foam core shear modulus increased by 25% after exposure, whereas the compression modulus reduced by 12%. Simulated lifetime core shear fatigue curves were developed and evaluated. Additional testing techniques such as scanning electron microscopy, optical microscopy, dynamical mechanical analysis, and X-ray computed tomography were used to rationalize the static and fatigue behavior of the core materials.

A study on different thermodynamic cycle schemes coupled with a high temperature gas-cooled reactor

With gradual increase in reactor outlet temperature, the efficient power conversion technology has become one of developing trends of (very) high temperature gas-cooled reactors (HTGRs). In this paper, different cycle power generation schemes for HTGRs were systematically studied. Physical and mathematical models were established for these three cycle schemes: closed Brayton cycle, simple combined cycle, and reheated combined cycle. The effects and mechanism of key parameters such as reactor core outlet temperature, reactor core inlet temperature and compression ratio on the features of these cycles were analyzed. Then, optimization results were given with engineering restrictive conditions, including pinch point temperature differences. Results revealed that within the temperature range of HTGRs (700–900°C), the reheated combined cycle had the highest efficiency, while the simple combined cycle had the lowest efficiency (900°C). The efficiencies of the closed Brayton cycle, simple combined cycle and reheated combined cycle are 49.5%, 46.6% and 50.1%, respectively. These results provide insights on the different schemes of these cycles, and reveal the effects of key parameters on performance of these cycles. It could be helpful to understand and develop a combined cycle coupled with a high temperature reactor in the future.

Response of Cylindrical Composite Structures Subjected to Underwater Impulsive Loading: Experimentations and Computations

The dynamic response of both thick-walled and thin-walled cylindrical composite structures subjected to underwater impulsive loads is analyzed. In the case of thick-walled structures, a novel experimental setup, the underwater shock loading simulator (USLS), is used to generate the impulsive loads. Deflection and core compression are characterized using high-speed digital imaging. The experiments are supported by fully dynamic numerical calculations which account for fluid–structure interactions (FSIs) and damage and failure mechanisms in the materials. The analysis focuses on the effect of varying structural attributes and material properties on load-carrying capacity, deformation mechanisms, and damage. Results show that cylindrical sandwich structures have superior blast-resistance than cylindrical monolithic structures of equal mass with only relatively minor increases in wall thickness. In the case of thin-walled structures, a unique computational framework based on a coupled Eulerian–Lagrangian (CEL) approach is developed to study the structural collapse and damage evolution under large impulsive loads which induces an implosion event. Simulations are carried out for a range of hydrostatic pressure and impulsive load intensity, with different loading configurations. Ply level stress analysis provides an insight on the stress–structural deformation–damage evolution relationship during the severe explosion-induced implosion event. The experiments, computations, and structure–performance relations developed in the current study offer approaches for improving the blast-mitigation capabilities of cylindrical composite sections in critical parts of marine structures, such as the keel, hull, and pipes.

Time Domain Spectral Element method to Study Response of a Sandwich Beam with Compliant Core Subjected to Under Water Explosion

A spectral element formulation is developed for a sandwich beam with stiff face sheets and a compliant core. Higher order displacement functions are taken for the core in order to incorporate the core compression effects. Highly efficient spectral element method is used for the study. Accuracy and the computational efficiency of this method are compared with the conventional finite element method in solving transient blast loading case. Using this spectral element method, under water blast loading response of a sandwich beam with composite face sheets and core is studied. A comparison is made between the response of stiff core and compliant core sandwich beam models. The study presents a design approach for an optimal configuration for under water blast resistant structures.

Analysis of the Failure Mechanism of the Sandwich Panel at the Supports

The paper presents the problem of static structural behavior of sandwich panels at supports. The panels have a soft core and correspond to typical structures applied in civil engineering. To analyze the failure propagation, the numerical 3-D model with non-linear material constitutive relations is applied. The numerical results are compared to the values obtained using simple engineering formulas. The obtained results show that the existing approach of assessing the failure by the level of the core compression is incorrect. The study verifies the assumption concerning the uniformity of normal stress distribution and describes the failure mechanism.

Structural design of face fabrics and the core as a premise for compression behavior of 3D woven sandwich fabric

In this work, an experimental study on compression properties of two E-glass 3D woven fabrics, known as integrally woven sandwich fabrics, has been presented. Compression properties of 2D face fabrics and the core, as structural parts of integrally woven sandwich fabric, have also been investigated. Compression behavior of the samples (compressibility, compression work, and compressive resilience) was analyzed from the aspect of the weave design of face fabrics and the core structure (shape and density of the pile yarns). Results of the investigation showed that “8” shaped core structure, the greater surface density of the pile yarns, and the less compact structure of face fabrics ensure better compression properties of 3D fabrics. Specific weave design of face fabrics and the structure of the core significantly influence the behavior of 3D fabrics during successive increases, followed by a gradual decrease of pressure. During the loading of 3D woven structures, three regions of curves can clearly be seen compared to two regions which are registered at 2D face fabrics. Concerning 3D woven fabrics, the first region represents compression of the core, the second region is prolonged core compression and the third region refers to the simultaneous compression of pile yarns in the core and face fabrics. The density of pile yarns plays an important role in the region 1. In region 2, both the shape and density of the pile yarns are significant. Influence of the weave of face fabrics on compression behavior of 3D fabric can be noticed to a lesser extent in the region 2 and, especially in the region 3, where highly packed yarns assemblies are created.

Fiber Element Model of Sandwich Panels with Soft Cores and Composite Skins in Bending Considering Large Shear Deformations and Localized Skin Wrinkling

AbstractThis paper studies the flexural performance of sandwich panels composed of a soft polyurethane foam core and glass-fiber-reinforced polymer (GFRP) skins. A robust numerical model is developed to predict the full load-deflection and strain responses of the panel. It is based on equilibrium and strain compatibility and accounts for the excessive shear deformation and material nonlinearity of the core. It also accounts for geometric nonlinearity in the form of localized deflection of the loaded skin using the principals of beam-on-elastic foundation and the change in core thickness due to its softness. The model incorporates various failure criteria, namely core shear failure, core flexural tension or compression failure, compression skin crushing or wrinkling, or tensile rupture of skin. The model has the advantage of being able to isolate quantitatively the individual contributions of flexure, shear, and localized skin deformations, to overall deflection. A parametric study is performed to examine ...

Numerical investigation of blanking for metal polymer sandwich sheets

Metal polymer sandwich sheets consist of materials with drastically different mechanical properties. Due to this fact and because of high local gradients in the cutting zone during the blanking process, traditional process strategies and empirical knowledge are difficult to apply. A finite-element simulation of the shear cutting process is used to predict the necessary force and the geometry of the cutting surface. A fully-coupled ductile damage model is used for the description of the material behaviour. This model considers the influence of shear and compression-dominated stress states on the initiation of damage. Experimental tensile and compression test data is used for the identification of material parameters. The results of the blanking simulation are compared with experimental data. Furthermore, the evolution of the stress state is analysed to gain understanding of the underlying physics. Finally this model enables the prediction of core compression and other quantities such as the acting stresses and corresponding triaxilities, which provide valuable information for the development of analytical models.

Creep relaxation and fully reversible creep of foam core sandwich composites in seawater

AbstractFoam core sandwich composites were subjected to (i) creep to failure, (ii) cyclic creep-relaxation and (iii) fully reversible cyclic creep loading in seawater in order to mimic an actual ship hull’s service lifetime scenario. The results indicate a strong dependence of lifetime on the mode of loading. A significant reduction in the overall life was observed under cyclic creep as compared with the conventional creep to failure. Creep relaxation (R=1) tests were performed at loading-relaxation periods of 24/24, 24/12, 24/6, 12/12 and 6/6 h, while the fully reversible (R=-1) creep tests were conducted at loading-reversed loading times of 36/36, 24/24, 12/12, 6/6, and 3/3 h. The results suggest that creep-relaxation lifetime characteristics depend predominantly on the relaxation time as opposed to loading times, i.e. longer relaxation periods lead to shorter life. Whereas, fully reversible creep appears to be dependent upon the number of reversals whereby, life is observed to reduce as the number of reversals increase. These significant observations are explained in terms of various possible paths to interface cell wall collapse. Modes of failure were predominantly indentation and core compression in the vicinity of the loading site.

The Response of Clamped Shallow Sandwich Arches with Metallic Foam Cores to Projectile Impact Loading

THE DYNAMIC RESPONSE AND ENERGY ABSORPTION CAPABILITIES OF CLAMPED SHALLOW SANDWICH ARCHES WITH ALUMINUM FOAM CORE WERE NUMERICALLY INVESTIGATED BY IMPACTING THE ARCHES AT MID-SPAN WITH METALLIC FOAM PROJECTILES. THE TYPICAL DEFORMATION MODES, DEFLECTION RESPONSE, AND CORE COMPRESSION OF SANDWICH ARCHES OBTAINED FROM THE TESTS WERE USED TO VALIDATE THE COMPUTATION MODEL. THE RESISTANCE TO IMPACT LOADING WAS QUANTIFIED BY THE PERMANENT TRANSVERSE DEFLECTION AT MID-SPAN OF THE ARCHES AS A FUNCTION OF PROJECTILE MOMENTUM. THE SANDWICH ARCHES HAVE A HIGHER SHOCK RESISTANCE THAN THE MONOLITHIC ARCHES OF EQUAL MASS, AND SHOCK RESISTANCE COULD BE SIGNIFICANTLY ENHANCED BY OPTIMIZING GEOMETRICAL CONFIGURATIONS. MEANWHILE, DECREASING THE FACE-SHEET THICKNESS AND CURVATURE RADIUS COULD ENHANCE THE ENERGY ABSORPTION CAPABILITY OF THE SANDWICH ARCHES. FINITE ELEMENT CALCULATIONS INDICATED THAT THE RATIO OF LOADING TIME TO STRUCTURAL RESPONSE TIME RANGED FROM 0.1 TO 0.4. THE PROJECTILE MOMENTUM, WHICH WAS SOLELY USED TO QUANTIFY THE STRUCTURAL RESPONSE OF SANDWICH ARCHES, WAS INSUFFICIENT. THESE FINDINGS COULD PROVIDE GUIDANCE IN CONDUCTING FURTHER THEORETICAL STUDIES AND PRODUCING THE OPTIMAL DESIGN OF METALLIC SANDWICH STRUCTURES SUBJECTED TO IMPACT LOADING.

Finite element analysis of sandwich panels with stepwise graded aluminum honeycomb cores under blast loading

This paper presents details and brief results of an experimental investigation on the response of metallic sandwich panels with stepwise graded aluminum honeycomb cores under blast loading. Based on the experiments, corresponding finite element simulations have been undertaken using the LS-DYNA software. It is observed that the core compression stage was coupled with the fluid–structure interaction stage, and the compression of the core layer decreased from the central to the peripheral zone. The blast resistance capability of sandwich panels was moderately sensitive to the core relative density and graded distribution. For the graded panels with relative density descending core arrangement, the core plastic energy dissipation and the transmitted force attenuation were larger than that of the ungraded ones under the same loading condition. The graded sandwich panels, especially for relative density descending core arrangement, would display a better blast resistance than the ungraded ones at a specific loading region.

Finite element simulation of metallic cylindrical sandwich shells with graded aluminum tubular cores subjected to internal blast loading

The LS-DYNA software was employed to analyze the dynamic responses of a sandwich cylindrical shell system under internal blast loading. The system consisted of metallic face sheets and graded aluminum tubular cores with different wall thicknesses. The response of this system was also compared with that of conventional ungraded ones. The dynamic response of graded cylindrical shells with a series of different core arrangements is reported in this paper. The deformation and blast resistance of the structures were discussed in detail, and the optimum sandwich configuration was obtained. The core layers, which had thickness-tapered arrangement from the inner to the outer layer, were favorable for the energy dissipation and the out face-sheet deflection. Finally, two new response types were defined based on the core compression consequence, which is unique to sandwich structures with graded cores.