Compressible Core Research Articles

Large deformation of sandwich wide panel

This work addresses the general nonlinear static and dynamic formulations of sandwich panels with compressible cores under large deformation, within the framework of Extended High-order Sandwich Panel Theory. The commonly-used assumption named large displacement with moderate rotation, is assessed. Within a total Lagrange manner, the weak form of the nonlinear equation of equilibrium is derived via the principle of virtual work and further linearized through the Newton-Raphson iteration. Both the static and dynamic governing equations are acquired with respect to the nodal degrees of freedom. Numerical techniques involving Newton-Raphson method for the static analysis, and Newmark-Beta method for the time domain integration are employed to get the solutions. The static and transient mechanical response of simply supported sandwich panels under static pressure and dynamic blast is conducted respectively. The closed linear solutions and finite element models are accomplished to validate. Conclusions are drawn that the deformation gradient, as well as the displacement and rotation, critically determines the structural stiffness and internal force, and their relationship is originally provided in this paper. The structural stiffness at large deformation is stronger than that at small deformation. The assumption of large displacement with moderate rotation is inadequate for sandwich structure in large deformation.

Effect of confining pressure on shear fracture behavior and surface morphology of granite by the short core in compression test

The study on shear fracture behaviour at elevated confining pressure is very meaningful for a lot of practical activities in underground works. To understand the influence of confining pressure on shear fracture behavior, a series of confined rock fracture tests were performed on the short core in compression (SCC) specimens. Uniform confining pressure was applied on the entire surface of the rock specimen in the tests. The results show that the peak load, shear modulus, nominal shear strength and mode II fracture toughness of SCC specimens increase approximatively linearly with confining pressure. The shear fracture surfaces after confined SCC tests were measured by a three-dimensional (3D) optical scanner. Based on fractal and statistical theories, the effect of confining pressure on the morphological characteristics in shear fracture surfaces has been studied in depth. The results indicate the fracture surface roughness decreases slightly with the increase of confining pressure, which can be attributed to the restraining effect on fracture expansion and the friction effect on the two new shear fracture surfaces under large confining pressure. Generally, standard deviations and means for asperity height and standard deviations of slope angle decline with increasing confining pressure. Frequency distributions of aspect orientation become more evenly with confining pressure. Moreover, the feasibility of applying the Mohr-Coulomb criterion in the SCC approach was assessed. It is found that the cohesion and internal friction angle determined by the SCC method are very closed to the values calculated from uniaxial compression tests, indicating that the SCC method are feasible for estimating shear parameters of rock.

Experimental study on shear performance of steel shell-concrete composite structure in immersed tunnel

Based on local arrangement details in the top slab of Shenzhen–Zhongshan Link immersed tunnel, steel shell-concrete (SSC) composite specimens with 1:2.5 scale were prepared and tested under shear, to investigate the effects of transverse T-shape stiffeners on shear capacities, crack development, and relative slip. Finite element models were also built and verified by the experimental results. For the specimen without transverse stiffeners, the failure at the steel plate-concrete interface occurred firstly, and then top and bottom steel plates were separated from the compression concrete core. While for the specimen with transverse T-shape stiffeners, the concrete cracks developed diagonally from the flange edge of T stiffeners near the bottom steel plate in sequence, and the corresponding tension field in the steel web enlarged gradually until full web yielding, as the shear force increased. Compared to specimens without transverse stiffeners, when transverse T stiffeners were placed in SSC composite specimens, the shear force at initial cracking was much smaller, but the yielding and ultimate shear capacities were increased by 12.2% and 14.6%, respectively. Although earlier cracking induced, the transverse T stiffeners were beneficial to improve shear capacities of SSC composite structures. The maximum relative slip at steel plate-concrete interface of specimens with and without transverse T stiffeners were 0.28 mm and 0.62 mm before the structure reaching the yielding stage, respectively, indicating that transverse T stiffeners could reduce the relative slip and separation between steel plates and concrete core, ensuring the effective composite action of steel plates and filled concrete. T stiffeners could improve the compressive behavior of concrete. With transverse T stiffeners placed in SSC composite structure, and the shear force could be resisted by both the diagonal compressive core in concrete and the arch system formed with the T stiffeners.

Influence of thermal treatment on dynamic mode Ⅱ fracture properties of rocks using the short core in compression (SCC) method

The effect of thermal-induced damage on the dynamic mode II fracture properties is crucial for evaluating the long-term safety and stability of underground rock-related infrastructures. Thus, it is significant to quantify systematically and accurately the dynamic mode II fracture parameters of rocks under elevated temperatures. Recently, the short core in compression (SCC) has been successfully adopted to measure the dynamic mode II fracture toughness KIIC of rocks due to its easy preparation and simply assembly. However, the dynamic mode II fracture parameters of rocks under various high temperatures have not been systematically determined. In this study, the dynamic SCC specimen was adopted to investigate the influence of thermal treatment on the dynamic mode II fracture parameters of a homogeneous biotite gabbro (BG). The SCC specimens were thermally treated at 25 °C, 100 °C, 300 °C, 500 °C and 700 °C. The P wave velocity and CT value were measured to characterize the thermal-induced damage within the BG specimens. The XRD analysis was employed to examine chemical changes in BG treated at elevated temperature. A split Hopkinson pressure bar (SHPB) apparatus was used to conduct the dynamic SCC tests and the momentum-trap system was utilized to ensure that the dynamic energy absorbed by the SCC specimen can be accurately determined. The SCC specimen was sheared along the upper and lower notch-tips, and the fracture surface of the SCC sample is relatively smooth. The failure pattern is valid mode II fracture. For five different temperatures, the dynamic KIIC of BG increases linearly with the loading rate. At the same loading rate, the dynamic KIIC of BG specimen treated at the temperatures lower than 300 °C is much higher than that without thermal treatment. With the increase of the heat-treatment temperature, the dynamic KIIC of BG decreases gradually under the same loading rate. The combination of the thermal expansion, the phase transformation and the oxidation in BG could generate the increase of the number of microcracks and the growth of microcracks, further reducing the dynamic KIIC of BG at high treatment temperatures. Furthermore, at the same temperature, the dynamic fracture energy of BG demonstrates the rate dependence. Another important observation is that, at the same loading rate, the dynamic fracture energy of BG increases when the temperature increases from 25 °C to 100 °C, whereas the dynamic fracture energy of BG decreases with the increase of temperature when the temperature is higher than 100 °C.

Bending behavior of pyramid lattice sandwich beams with non-uniform truss cores

To improve the three-point bending capacity of the pyramid lattice sandwich beam, a non-uniform pyramid lattice sandwich structure is proposed in this paper by assigning different diameters to the tensile and compressive core rods and setting the ratio of the diameters of the two kinds of core rods as a non-uniform coefficient. The influence of the non-uniform coefficients on the three-point bending performance of the pyramid lattice sandwich beam is analyzed theoretically and numerically. Results show that the introduction of the non-uniform coefficients can significantly improve the bending ultimate bearing capacity of the structure. Compared with the uniform lattice sandwich beam, the optimal non-uniform coefficients increase the bending ultimate bearing capacity by 39%. Moreover, it is revealed that the optimal non-uniform coefficient ([Formula: see text]) decreases with the increase of the total mass of the structure. The research on the three-point bending performance of non-uniform lattice sandwich beams in this paper can provide guidance for the optimal design of lightweight lattice sandwich structures.

Adaptation of the CCSDS 123.0-B-2 Standard for RGB Video Compression

The integration of video sensors on-board satellites is becoming a trend in the space industry, since they provide extra information in the temporal domain when compared with traditional remote sensing imaging acquisition equipment. The inclusion of the temporal dimension together with the constant increase in the sensor resolution supposes a challenge for on-board processing, taking into account the limited computational and storage resources on-board satellites and that it is unfeasible to directly transmit raw video to ground, due to downlink bandwidth limitations. For these reasons, on-board video compression is needed. However, the inherent complexity of the video encoders used on ground limits their implementation on environments with high constraints in terms of computational burden, area, and power consumption. This article proposes an extended compression chain that implements as compression core the CCSDS 123.0-B-2 standard, originally developed for near-lossless compression of multi- and hyperspectral images. In addition, some preprocessing stages are included to manage the temporal dimension of RGB videos efficiently. The proposed solution guarantees low complexity and flexibility to compress both multi- and hyperspectral images and panchromatic and RGB videos by using a single compression instance, which is adapted by adding or removing the appropriate stages. Results demonstrate the viability of this solution to be implemented on space payloads, since high compression ratios are achieved without incurring in a penalty in terms of video quality.

Failure characteristics of the active-passive damping in the functionally graded piezoelectric layers-magnetorheological elastomer sandwich structure

The active-passive damping of the functionally graded piezoelectric layers-magnetorheological elastomer (FGPE-MRE) sandwich structures may fail due to the compressibility of the core. This work provides a unified modeling method for the failure characteristics of the active-passive damping in the FGPE-MRE sandwich structure. The unbounded condition and normal magnetic field are considered to approximate the practical applications of the active-passive damping. To clarify the failure mechanism of the active-passive damping, a novel compressible core method is proposed. To illustrate the effect of the normal magnetic field, the strain-stress relation with in-plane Lorenz force is developed by employing the Maxwell's equation. Moreover, to realize the unbounded condition of the FGPE-MRE sandwich structure, the classical boundary condition of sandwich structures is modified. To avoid the failure of the active-passive damping, the traditional feedback control law is improved by constructing a fractional negative feedback equation. Finally, numerical investigations are conducted to show the failure characteristics of the active-passive damping and the effectiveness of the proposed control law.

Deformation and fracture behavior of granite by the short core in compression method with 3D digital image correlation

AbstractBased on three‐dimensional digital image correlation (3D‐DIC) technique, the deformation behavior, damage and fracture characteristics of the granite specimens have been tested and observed by the short core in compression (SCC) method. The test results show that (1) the damage degree of rock in the region of interest (ROI) increases with axial stress. Before peak stress, damage factor based on apparent principal strain increases slowly, then rises rapidly; (2) relative displacements in both horizontal and vertical directions are observed, indicating that the fracture mode for SCC specimens subjected to uniaxial compression is the tensile‐shear mixed mode fracture; (3) new fracture initiates from the middle part of the expected shear fracture band (ESFB) then propagates along the loading direction. A dominant macro‐fracture, linking up the tips of two notches, eventually forms. Meanwhile, a calculation method based on the energy conservation law for the fracture energy of SCC specimens is proposed. The fracture energy of granite is estimated as 1760.4 J/m2.

Hemoglobin microbubbles for in vivo blood oxygen level dependent imaging: Boldly moving beyond MRI

Microbubbles are gas-filled, micron-sized particles stabilized by lipid, protein, or polymer shells. They scatter ultrasound energy efficiently due to their compressible gas cores, making them excellent blood pool contrast agents in ultrasound imaging. In this project, we have developed a novel oxygen-sensitive hemoglobin-shell microbubble designed to acoustically detect blood oxygen levels in vivo. We hypothesized that structural changes in the hemoglobin in response to varying oxygen levels will alter the mechanical properties of the bubble shell, resulting in detectable changes in the bubble acoustic signature. In this project, we have (1) optimized the hemoglobin bubble formulation for in vivo circulation, (2) demonstrated that the hemoglobin shell is still responsive to oxygen after formulation, and (3) characterized the acoustic response of the microbubbles at varying oxygen levels. Our preliminary results show a strong correlation between the oxygen concentration in the solution and the acoustic response of bubbles, suggesting that they would serve as excellent oxygen sensors. If successful, in vivo sensing of oxygen levels would have numerous benefits, including evaluating the hypoxic regions in tumors and in the brain, among other blood-oxygen-level-dependent (BOLD) imaging applications.

Compressible EULAG Dynamical Core in COSMO: Convective-Scale Alpine Weather Forecasts

AbstractThis paper presents the semi-implicit compressible EULAG as a new dynamical core for convective-scale numerical weather prediction. The core is implemented within the infrastructure of the operational model of the Consortium for Small-Scale Modeling (COSMO), forming the NWP COSMO-EULAG model (CE). This regional high-resolution implementation of the dynamical core complements its global implementation in the Finite-Volume Module of ECMWF’s Integrated Forecasting System. The paper documents the first operational-like application of the dynamical core for realistic weather forecasts. After discussing the formulation of the core and its coupling with the host model, the paper considers several high-resolution prognostic experiments over complex Alpine orography. Standard verification experiments examine the sensitivity of the CE forecast to the choice of the advection routine and assess the forecast skills against those of the default COSMO Runge–Kutta dynamical core at 2.2-km grid size showing a general improvement. The skills are also compared using satellite observations for a weak-flow convective Alpine weather case study, showing favorable results. Additional validation of the new CE framework for partly convection-resolving forecasts using 1.1-, 0.55-, 0.22-, and 0.1-km grids, designed to challenge its numerics and test the dynamics–physics coupling, demonstrates its high robustness in simulating multiphase flows over complex mountain terrain, with slopes reaching 85°, and the flow’s realistic representation.

Experimental and Finite Element Study of Polymer Infilled Tube-in-Tube Buckling Restrained Brace

This study presents a tube-in-tube buckling-restrained brace (BRB) infilled with lightweight and rapid hardening polymer. The proposed BRB consists of a circular or square tube core encased with a tube of similar shape and polymer infill. The tube-in-tube arrangement minimizes the filler material volume and enables the use of rolled steel section as opposed to welded profiles commonly utilized when large BRB axial strength is required, although welded profiles suffer from low assembly accuracy resulting from welding deformation. The infilled polymer has a density of approximately half that of mortar and requires a curing time of 24 h, enabling weight and fabrication time reduction. The stability and inelastic deformation capability of the BRB were investigated through brace and subassembly tests of six circular and four-square full-scale specimens, followed by finite element analysis. The test results show that circular BRB designed with a Pcr/Py ratio of 1.46 exhibited a stable hysteresis up to 1.42% and 1.06% core strain in tension and compression, respectively. Circular and square specimens designed with Pcr/Py ratios ranging from 0.82 to 1.06 exhibited stable hysteresis before failing by global buckling at compressive core stains ranging from 0.86% to 1.09%. The slot weld detail adopted for welding core projection stiffener displayed a stable performance in circular BRB specimens, while it resulted in large plastic strain demand in square BRB specimens, leading to core fracture at tensile core strains ranging from 0.64% to 0.71%.

Dynamic Mode Ⅱ fracture behavior of rocks under hydrostatic pressure using the short core in compression (SCC) method

The shear failure of rocks under both a static triaxial stress and a dynamic disturbance is common in deep underground engineering and it is therefore essential for the design of underground engineering to quantitively estimate the dynamic Mode Ⅱ fracture toughness KⅡC of rocks under a triaxial stress state. However, the method for determining the dynamic KⅡC of rocks under a triaxial stress has not been developed yet. With an optimal sample preparation, the short core in compression (SCC) method was designed and verified in this study to measure the dynamic KⅡC of Fangshan marble (FM) subjected to different hydrostatic pressures through a triaxial dynamic testing system. The formula for calculating the dynamic KⅡC of the rock SCC specimen under hydrostatic pressures was obtained by using the finite element method in combination with secondary cracks. The experimental results indicate that the failure mode of the rock SCC specimen under a hydrostatic pressure is the shear fracture and the KⅡC of FM increases as the loading rate. In addition, at a given loading rate the dynamic rock KⅡC is barely affected by hydrostatic pressures. Another important observation is that the dynamic fracture energy of FM enhances with loading rates and hydrostatic pressures.

159. Midterm 4-year outcomes for single-level total disc replacement with a novel viscoelastic artificial cervical disc compared to ACDF

<h3>BACKGROUND CONTEXT</h3> The M6-C artificial cervical disc, with a compressible viscoelastic nuclear core and an annular structure, is substantially different from first generation articulating surface designs and has previously demonstrated favorable clinical outcomes out to 2-years post-implantation. <h3>PURPOSE</h3> To evaluate the safety and effectiveness of the M6-C artificial cervical disc compared with ACDF. <h3>STUDY DESIGN/SETTING</h3> A prospective, multicenter, controlled, IDE clinical trial is ongoing. Twelve M6-C sites and 11 ACDF sites are participating in the study, with preoperative assessments followed by assessments at 6 weeks, 3 months, 6 months, 1 year and annually out to 10 years postimplantation. <h3>PATIENT SAMPLE</h3> Study subjects presented with one-level symptomatic degenerative cervical radiculopathy, and received either M6-C or ACDF at a single level. <h3>OUTCOME MEASURES</h3> Neck Disability Index (NDI), neck pain and shoulder/arm pain visual analog scale (VAS) scores. <h3>Methods</h3> The M6-C and ACDF cohorts were propensity matched. Follow-up assessments are ongoing and planned out to 10-years postop. <h3>Results</h3> A total of 160 M6-C and 189 ACDF subjects were enrolled. NDI scores are available for 124 M6-C and 148 ACDF subjects at 3 years, and 116 M6-C and 133 ACDF subjects at 4 years postop. At 3 years postop, M6-C subjects had a mean NDI score of 10.9 - significantly better than the mean of 17.2 observed in the ACDF group. A significant difference was observed at 4 years postop (M6-C mean of 10.3 compared to 19.2 for ACDF.) M6-C subjects experienced a mean improvement from baseline of 43.9 points at 3-years and 45.2 points at 4-years postop, compared to 36.0 and 36.0, respectively, for the ACDF cohort, with the 4-year results being significantly better for the M6-C group. More M6-C subjects experienced a 15-point improvement from baseline (93.6% at 3 years and 95.7% at 4 years,) compared to the ACDF cohort (86.6% and 82.7%, respectively,) with the 4-year results being significantly better for the M6-C group. Neck pain and shoulder/arm pain VAS scores are available for analysis for 124 M6-C and 148 ACDF subjects at 3 years, and 116 M6-C and 134 ACDF subjects at 4 years postop. At 3 years postop, M6-C subjects had a mean neck pain VAS score of 1.1, which was significantly better than the mean of 2.0 observed in the ACDF control group. Similarly, a significant difference was observed at 4 years postop (M6-C mean of 1.0 compared to 2.3 for ACDF.) M6-C subjects experienced a mean improvement from baseline of 6.1 points at 3-years and 6.2 points at 4-years postop, compared to 5.2 and 4.8, respectively, for the ACDF cohort, both significantly better for the M6-C group. Similarly significant results were observed in shoulder/arm pain VAS scores (worst side) at 3-years (0.9 for M6-C and 2.2 for ACDF) and 4-years postop (0.6 for M6-C and 2.7 for ACDF.) One M6-C subject (0.6%) had the device removed in the first 4 postop years (chronic neck pain.) <h3>Conclusions</h3> The significant benefits in NDI and neck pain and shoulder/arm pain VAS scores associated with M6-C in earlier follow-up periods, compared to ACDF controls, appear to be maintained at 3- and 4-years postop, with no concerns for durability of the surgical outcome or the prosthesis at 4 years. Both NDI and neck pain and shoulder/arm pain will continue to be monitored in this cohort via annual assessments out to 10-years postop. <h3>FDA DEVICE/DRUG STATUS</h3> M6 TDR (Approved for this indication)

In-plane lateral cyclic behaviour of lime-mortar and clay-brick masonry walls in dry and wet conditions

This paper presents an experimental investigation into the structural and material response of ambient-dry and wet clay-brick/lime-mortar masonry elements. In addition to cyclic tests on four large-scale masonry walls subjected to lateral in-plane displacement and co-existing compressive gravity load, the study also includes complementary tests on square masonry panels under diagonal compression and cylindrical masonry cores in compression. After describing the specimen details, wetting method and testing arrangements, the main results and observations are provided and discussed. The results obtained from full-field digital image correlation measurements enable a detailed assessment of the material shear-compression strength envelope, and permit a direct comparison with the strength characteristics of structural walls. The full load-deformation behaviour of the large-scale walls is also evaluated, including their ductility and failure modes, and compared with the predictions of available assessment models. It is shown that moisture has a notable effect on the main material properties, including the shear and compression strengths, brick–mortar interaction parameters, and the elastic and shear moduli. The extent of the moisture effects is a function of the governing behaviour and material characteristics as well as the interaction between shear and precompression stresses, and can lead to a loss of more than a third of the stiffness and strength. For the large scale wall specimens subjected to lateral loading and co-existing compression, the wet-to-dry reduction was found to be up to 20% and 11% in terms of stiffness and lateral strength, respectively, whilst the ductility ratio diminished by up to 12%. Overall, provided that the key moisture-dependent material properties are appropriately evaluated, it is shown that analytical assessment methods can be reliably adapted for predicting the response, in terms of the lateral stiffness, strength and overall load-deformation, for both dry and wet masonry walls.

Flax FRP tube and steel spiral dual-confined recycled aggregate concrete: Experimental and analytical studies

Using fibre reinforced polymer (FRP) tube as outer confining material of recycled aggregate concrete (RAC) column improved its compressive strength and deformation capacity although the RAC core still behaved in a brittle failure manner. To achieve a ductile failure mode of RAC core in compression, outer flax FRP tube (FFRP) and inner steel spiral reinforcement (SR) were used in this study to confine the RAC cylinders, i.e., to form an FFRP tube-SR-confined RAC column, which is shortened as FFRP-SR-RAC. To evaluate the effects of spacing of the inner steel spiral (i.e., 25 and 50 mm), strength of RAC (i.e., 26.3 and 33.7 MPa), and the FFRP tube thickness (i.e., 3, 6 and 9 layers of FFRP) on the compressive behaviour of FFRP-SR-RAC, 36 concrete cylinders were constructed and tested in uniaxial compression. The test results indicated that comparing with unconfined RAC or FFRP tube confined RAC cylinders, the FFRP-SR-RAC specimens possessed higher compressive strength and failed in a ductile manner. When the number of FFRP layer increased and the spacing of SR decreased, the FFRP-SR-RAC cylinder gained more pronounced enhancement in the compressive strength. Based on the experimental results, stress and ultimate strain models were developed to predict the axial compressive behaviour of FFRP-SR-RAC in uniaxial compression.

STRUCTURAL EVALUATION OF REINFORCED CONCRETE COLUMN WITH COMPOSITE GFRP SHELL -- A STRUCTURAL ELEMENTOF BRIDGE PIER

Statement of the problem. It’s considered the problem of developing a methodology for structural evaluation of hybrid design - a reinforced concrete column combined with external composite GFRP (glass-fiber-reinforced-plastic) shell. This hybrid design is intended for bridge piers. Results. As a result of a study, theoretical relationships were formulated to determine the longitudinal and transverse stresses and relative deformations of hybrid column structural elements. The developed formulas take into account the cooperation of triaxial compressed concrete core and an anisotropic composite GFRP shell. Conclusions. The obtained theoretical dependences of the hybrid column’s elements behavior make it possible to develop a structural evaluation methodology of bridge piers hybrid columns. The findings of the investigation are proposed to be applied in the structural evaluations of the bridges piers hybrid columns with composite GFRP elements.

Dendroids, Discrete Covalently Cross-Linked Dendrimer Superstructures.

A versatile method is presented to form dendrimer superstructures by exploiting coacervate-core micelles as a template to confine and organize the hyperbranched macromolecules. First, complex coacervate-core micelles are formed from negative–neutral block copolymers and positively charged polyamidoamine dendrimers. The dendrimers inside the micellar core are then covalently cross-linked with each other upon addition of glutaraldehyde. After removal of the block copolymer from the assembly by increasing the salt concentration, consecutively, the formed Schiff bases cross-linking the dendrimers are reduced to amines, followed by a final dialysis step. This leads to well-defined covalently cross-linked nanostructures, coined dendroids, with a size of around 30 nm in diameter and a molecular weight of approximately 2.5 MDa. By incorporating dendrimer-encapsulated gold nanoparticles (AuDENs) into the micelle template strategy, the aggregation number of dendrimers inside the dendroids is determined by counting the nanoparticles in TEM micrographs. Furthermore, TEM performed at different tilt angles and AFM analysis corroborate formation of stable, covalently linked three-dimensional structures. Reconstruction of the TEM tilt series results in a tomogram further illustrating the 3D distribution of the gold nanoparticles, and hence the individual dendrimers, in the nanostructure. These dendroids appear to have a hard, poorly compressible core and a relatively soft outside. The versatility of the hierarchical building up of the supermolecules is illustrated by the controlled and synchronous incorporation of empty dendrimers and AuDENs into a single hybrid dendroid structure. The presented strategy allows for the preparation of a variety of classes of supermolecules, depending on the type of micellar-core macromolecule, e.g., dendrimer, cross-linker, and nanoparticles, used. Considering the broad interest in dendrimers as well as micelles in a plethora of research areas, e.g., (targeted) drug delivery, biomedical imaging, theragnostics, and catalysis, there is a great potential for dendroids and related classes of covalently linked macromolecules, viz., supermolecules.

Free vibration analysis of a laminated composite sandwich plate with compressible core placed at the bottom of a tank filled with fluid

The paper addresses the free vibration problem of a laminated composite sandwich plate with compressible core, placed at the bottom of a tank filled in with fluid. The analysis is performed based on the extended higher order sandwich plate theory (EHSAPT). First-order shear deformation theory (FSDT) is used for the face sheets. Cubic and quadratic polynomials are used to describe the in-plane and transverse displacements of the core, respectively. The fluid is assumed inviscid, incompressible, and irrotational. To obtain the kinetic energy of the fluid, its velocity potential is expressed by using the compatibility and boundary conditions. The governing differential equations and corresponding boundary conditions are derived from Hamilton’s principle. A single series expansion is considered with two-variable orthogonal polynomials as a set of admissible functions satisfying the boundary conditions. The natural frequencies of the coupled sandwich plate-fluid system are calculated by using the Rayleigh-Ritz method. Convergence of the adopted strategy is first investigated. Then, comparisons are conducted with previous results reported in the literature. Also, the effects are investigated of several parameters, such as the plate side-to-thickness ratio, the core-to-face sheets thickness ratio, the face sheet-to-core flexural modulus ratio, the height and aspect ratio of the tank.

Three-dimensional pulse response of curved composite sandwich panel with compressible core using non-linear higher-order theory

In this paper, the dynamic response of cylindrical sandwich panels with compressible core is obtained using the extended non-linear higher-order sandwich panel theory. It is assumed that the sandwich panel has simply supported boundary at all edges and is consisted of orthotropic face sheets and viscoelastic core layer. To describe the mechanical properties of the viscoelastic foam core, the Kelvin-Voigt linear viscoelastic model was applied. Three-dimensional linear equations of motions were used to describe the sandwich panel deformations. The effects of various parameters including the panel span, core and facing thickness, the viscous damping factor, pulse duration, and maximum pressure on the dynamic response of the sandwich cylindrical panel are studied. The results obtained from present method are compared with finite element solutions and those reported in the literature, and consequently, agreement among the results could be observed. The results shown that applied viscoelastic model has a signification effect on the panel response and reduces the magnitude of vibrations. The presented programming code (DQ) needs less computational time and computer hardware capacity and is faster than finite element solution.

Free vibration analysis of rectangular sandwich plates with compressible core and various boundary conditions

Extended higher-order sandwich plate theory is used to analyze the free vibrations of rectangular sandwich plates with compressible core. Accordingly, first-order shear deformation theory is used to model the laminated face sheets. Besides, the in-plane and transverse displacements of the core are assumed to be cubic and quadratic functions of the thickness coordinate, respectively. To deduce the governing equations, Hamilton’s principle is used. Then, based on the Rayleigh-Ritz method, single series expansions with two-variable orthogonal polynomials – namely, the orthogonal plate functions – are considered to approximate the displacement components. Lastly, a generalized eigenvalue problem is solved to obtain the free vibrational characteristics of sandwich plates with both symmetric and anti-symmetric lay-ups subjected to various boundary conditions. The method is validated against the results obtained by different methods in the literature. Finally, the effects of the plate side-to-thickness ratio, in-plane aspect ratio, and core-to-face sheets thickness ratio on the natural frequencies are discussed.