Elastic Core Research Articles

Use of the Finite Element Method in Predicting Vibrations of Sandwich Beams and Plates Resting on Deformable Foundations Subjected to Moving Loads

AbstractThis paper presents the capabilities of ABAQUS finite-element program [1] in modelling sandwich beams and plates resting on deformable foundations. Specific systems of sandwich beams and plates separated by an elastic core layer were subjected to the action of point and distributed moving loads. A few theoretical examples are provided to present different techniques of modelling the foundations and the moving loads. The effects of the boundary conditions and of the foundation parameters on the deflections of the analysed structures are also presented.

Shear and bending performance of new type enhanced lattice truss structures

In this work, the new type enhanced lattice (defined as hourglass) truss structures with the improved resistance of their core members and attached face sheets have been fabricated by an innovative interlocking method. The shear and bending properties of the produced sandwich structures characterized by three different relative densities have been investigated using various analytical methods and the obtained results were in good agreement with the experimental data. The truss failure under shear loading was dominated by the inelastic buckling of the truss members, while the four possible analytical models describing the bending properties and failure mechanism of the hourglass truss beams included elastic face sheet buckling, face sheet yielding, elastic core member buckling, and core member yielding were studied. The bending specimens, which were designed by constructing failure mechanism maps, were used to examine the yielding behavior of the truss core members as well as the elastic buckling and yielding of the face sheet members. The obtained results revealed that the specific shear strengths and bending failure loads of the studied hourglass truss structures were superior to those of pyramidal truss structures, and that the former could be considered promising candidates for manufacturing lightweight structures with high specific strength.

INTERVENSI DUMBBELL LUNGES DAN CORE STABILITY EXERCISE LEBIH BAIK DARIPADA INTERVENSI ELASTIC BAND DAN CORE STABILITY EXERCISE TERHADAP PENINGKATAN KESEIMBANGAN DINAMIS PADA PEMAIN SKATEBOARD DENGAN KONDISI CHRONIC ANKLE INSTABILITY

Among skateboarders frequently faced with recurrent injury especially on ankle region. They seldom take attention to their injury and if the condition left untreated, it will turn into chronic ankle instability. This condition will disturb dynamic balance while playing skateboard. The purpose of this research is to find if dumbbell lunges intervention and core stability exercise are more effective than elastic band and core stability exercise for the improvement of dynamic balance. This experimental research using pre and post test two group design. Sample was taken with simple random sampling. Total of 24 samples were divided into 2 groups, each group contain 12 samples. Group I had dumbbell lunges intervention and core stability exercise while Group II had elastic band intervention and core stability exercise. The exercise was done 3 times per week for 6 weeks. Data was taken with measurement dynamic balance using modified bass test of dynamic balance before and after exercise to each group. The mean difference test increasement of dynamic balance with paired sample t-test results p value 0.001 (p<0.05) within treatment Group I and p value 0.001 (p<0.05) within treatment Group II. which mean there is significantly difference of increasing value dynamic balance before and after intervention within both group. Difference test before intervention in treatment Group I and Group II with independent t-test result p value 0.818 (p>0.05) in which there is no significant difference between groups before intervention. and difference test after intervention in treatment Group I and Group II with independent t-test shows significant difference with p value 0.001 (p<0.05). This study shows that dumbbell lunges intervention and core stability exercise result in better improvement of dynamic balance than elastic band intervention and core stability exercise among skateboarders.

Developing a semi-analytical model for thermomechanical response of SMA laminated beams, considering SMA asymmetric behavior

In this study, thermomechanical behavior of a beam reinforced with Shape Memory Alloy (SMA) elements is investigated (an elastic core with upper and bottom SMA layers). The improved Brinson constitutive model is used in order to account for the asymmetric behavior of SMA in tension and compression. Assuming a plane stress model for the beam reinforced with SMA layers, a semi-analytical formulation is proposed. This formulation has two parts: the first part consists of a linear distribution of strain along the cross section and the second part is an iterative numerical procedure to satisfy classical equilibrium equations. For the numerical procedure, bisection method is used. Moreover, the semi-analytical results are compared with a 2D Finite Element (FE) solution. The proposed model is applicable for Euler–Bernoulli beams with any material and geometric features. For example, for a composite beam including both superelastic and shape memory SMA layers the proposed model can be employed. Regarding the results, there is more than 95% agreement between the present numerical solutions and those of 2D FE method. Also, for the numeric examples discussed in this paper, it is shown that considering the asymmetry between the tension and compression behavior of SMA, leads to at least 25% change in the force–displacement plot with respect to the cases when considering symmetric behavior and also, there is 8% (of the width of the structure) shift in the location of the neutral axis from the centerline. In addition, hysteresis inner loops are investigated, using the asymmetric proposed model and compared against 2D FE solution, where results show a good agreement between two solutions.

Axisymmetric bending of circular and annular sandwich plates with nonlinear elastic core material

This paper compares the analytical model of the axisymmetric bending of a circular sandwich plate with the finite element method (FEM) based numerical model. The differential equations of the bending of circular symmetrical sandwich plates with isotropic face sheets and a nonlinear elastic core material are obtained. The perturbation method of a small parameter is used to represent the nonlinear differential equations as a sequence of linear equations specifying each other. The linear differential equations are solved by reducing them to the Bessel equation. The results of the calculations with the use of the analytical and FEM models are compared with the results obtained by other authors by the example of the following problems: (1) axisymmetric transverse bending of a circular sandwich plate; (2) axisymmetric transverse bending of an annular sandwich plate. The effect of the nonlinear elasticity of the core material on the strained state of the sandwich plate is described.

Superhydrophobic, Reversibly Elastic, Moldable, and Electrospun (SupREME) Fibers with Multimodal Functions: From Oil Absorbents to Local Drug Delivery Adjuvants

Surface hydrophobicity has served as a core means for governing the spatial behaviors of numerous substances depending on their affinities to oil or aqueous phases. Exploiting systems that can maximize hydrophobic features contributes to the development of versatile supports capable of spatially separating, guiding, or protecting target materials in defined manners. Herein, superhydrophobic, reversibly elastic, moldable, and electrospun (SupREME) fibers, which exhibit multimodal functions for arranging spatial responses of substances with distinct affinities to oil phases, are fabricated by coaxially electrospinning polysulfone and poly(glycerol sebacate) (PGS), followed by a thermal process. The exterior PSF layers enable volumetric expansion of the fibers, further reinforcing the overall superhydrophobicity (contact angles >150°). The elastic core PGS networks confer reversibly compressible properties (>100 cycles) to the fibers, ultimately enhancing their hydrophobic performance and extending their durability. The SupREME fibers demonstrate superiorities as absorbents for selectively separating oil‐based substances, sealants for blocking the leakage of aqueous fluids, and adjuvants for temporarily enhancing the local residence of drugs by repelling ambient fluidic environments. The SupREME fibers can be versatile platforms in many applications that require the spatial regulation of specific substances with affinities to oil or water phases, ranging from environmental industries to medical fields.

Size-dependent free vibration and dynamic analyses of piezo-electro-magnetic sandwich nanoplates resting on viscoelastic foundation

In this paper, size-dependent free vibration analysis of a sandwich nanoplate is presented. The sandwich nanoplate is including an elastic nano core and two piezo-electro-magnetic face-sheets as sensor and actuator actuated by electric and magnetic potentials. The sandwich nanoplate is resting on visco-Pasternak's foundation. Hamilton's principle is employed to derive the governing equations of motion based on Kirchhoff plate and nonlocal elasticity theory. The numerical results are presented to study the influence of important parameters of the problem such as applied electric and magnetic potentials, nonlocal parameter and visco-Pasternak's parameters. Furthermore, the influence of various boundary conditions is discussed on the vibration characteristics of the sandwich nanoplate.

Electro-magneto-elastic analysis of a three-layer curved beam

In this paper, based on first-order shear deformation theory, the governing equations of motion for a sandwich curved beam including an elastic core and two piezo-magnetic face-sheets are presented. The curved beam model is resting on Pasternak\'s foundation and subjected to applied electric and magnetic potentials on the piezo-magnetic face-sheets and transverse loading. The five equations of motion are analytically solved and the bending and vibration results are obtained. The influence of important parameters of the model such as direct and shear parameters of foundation and applied electric and magnetic potentials are studied on the electro-mechanical responses of the problem. A comparison with literatures was performed to validate our formulation and results.

Dislocation core effects on slip response of NiTi- a key to understanding shape memory

The understanding of the non-Schmid behavior in shape memory alloy NiTi is considered a significant breakthrough because this alloy still remains enigmatic. We utilize an Eshelby-Stroh formalism in conjunction with Molecular Statics-Peierls stress calculation to predict the experimental CRSS results for three different crystal orientations and tension-compression cases. These combination of tools incorporating elastic anisotropy and core displacements are necessary to develop a precise understanding of non-Schmid behavior. We note the different extents of core spreading produce a highly asymmetric tension-compression behavior and strong orientation dependence governed by the non-glide shear and normal stress components. The experimental results and empiricism free modeling produces excellent agreement, and most importantly enlisting scientific insight into the shape memory response.

Coupled thermo-electro-mechanical analysis of sandwiched hybrid functionally graded elastic material and piezoelectric plates under thermal loads

Based on Reissner’s mixed variational theorem, a weak-form formulation of finite layer methods is developed for the three-dimensional coupled thermo-electro-mechanical analysis of simply-supported, functionally graded elastic material plates integrated with surface-bonded piezoelectric layers and under thermal loads. The material properties of the functionally graded elastic material core are assumed to obey the power-law distributions varying through-the-thickness coordinate of the core according to the volume fractions of the constituents, and those of the functionally graded elastic material core and piezoelectric face sheets are also temperature dependent. The effective material properties of the functionally graded elastic material are estimated using the Mori-Tanaka scheme. Two different thermal conditions, i.e. the convection conditions and specified temperature conditions, on the top and bottom surfaces of the plate are considered. The accuracies and convergence rates of the finite layer methods with various orders used for expanding the elastic and electric variables in the thickness direction are assessed by comparing their solutions with the exact three-dimensional ones available in the literature.

Electromechanical properties of a yarn strain sensor with graphene-sheath/polyurethane-core

This paper reports on the fabrication of a new yarn strain sensor based on commonly used polyurethane yarn which is easily incorporated into textile structures by using textile technologies for wearable applications. By integrating graphene/poly(vinyl alcohol) composites as the conductive sheath around yarn, and polyurethane yarn as the elastic core by using a layer-by-layer assembly method that is simple, scalable and low in cost, the merits of both types of materials are incorporated to fabricate sensors with enhanced performance. The combined effects of graphene concentration and number of coatings on sensor properties are elucidated, and on that basis, the electromechanical properties can be modified by adjusting the parameters. The sensors are characterized in terms of sensitivity, resistivity, linearity, repeatability, hysteresis and thermal stability. There are two sensors (graphene concentration of 0.8 wt% and 1.0 wt%, and 12 and 9 cycles of coating respectively) with high sensitivity (gauge factor of 28.48 and 86.86, respectively), good linearity between the change in relative resistance and applied strain (correlation coefficient of 0.95 and 0.97, respectively), good repeatability (repeatability error of 2.03% and 1.81%, respectively), low hysteresis (hysteresis error of 7.03% and 9.08%, respectively) and excellent thermal stability (within the range of 25 °C–310 °C).

Helical Piezoelectric Energy Harvester and Its Application to Energy Harvesting Garments

In this paper, we propose a helical piezoelectric energy harvester, examine its application to clothes in the form of an energy harvesting garment, and analyze its design and characteristics. The helical harvester is composed of an elastic core and a polymer piezoelectric strap twining the core. The fabricated harvester is highly elastic and can be stretched up to 158% of its initial length. Following the experiments using three different designs, the maximum output power is measured as 1.42 mW at a 3 MΩ load resistance and 1 Hz motional frequency. The proposed helical harvesters are applied at four positions of stretchable tight-fitting sportswear, namely shoulder, arm joint, knee, and hip. The maximum output voltage is measured as more than 20 V from the harvester at the knee position during intended body motions. In addition, electric power is also generated from this energy harvesting garment during daily human motions, which is about 3.9 V at the elbow, 3.1 V at the knee, and 4.4 V at the knee during push-up, walking, and squatting motions, respectively.

Development Behavior for Post-Tensioned Self-Centering Steel Connection under Cyclic Loading

One of the newest steel beam-column joints to replace conventional welded connections, post-tensioned connection steel is with the upper and lower angles. In this connection are high-strength steel strands that parallel beam web and angles between beams and column. Actually high resistance strands and upper and lower angles respectively are provider centralization properties and energy dissipation capacity of the connection. The benefits of post-tensioned steel can be used in connection with the centralization and lack of relative displacement (drift) persistent, stay elastic core components such as connecting beams, columns and fountains connection, appropriate initial stiffness and joint manufacture with materials and traditional skills. . In this study, numerical modelling in Abaqus software, the results of the analysis were compared with the results of laboratory samples and the results showed that the two together are a perfect match. After validation, parameters influential centrist connection then pulled the thick angles in three numerical models were evaluated. The results show that by increasing the thickness of the angles, increase energy dissipation capacity and ductility connection and the β₁ value does not experience tangible changes with changes in angle thickness.

Free vibration of composite sandwich plates and cylindrical shells

Sandwich plates and cylindrical shells composed of two composite laminated faces and an ideally orthotropic elastic core are considered in this paper. Since the natural frequencies of sandwich structures may not be affected by the accuracy of local behaviors, to avoid the complexity involved in the higher-order shear deformation theory and layerwise theory and to supplement the loss of the transverse shear deformation in the classical lamination theory, a modified first-order shear deformation theory was employed to obtain the closed-form solutions of natural frequencies of certain particular problems of sandwich plates and shells such as a rectangular composite sandwich plate with symmetric cross-ply laminates with all edges simply supported. Mathematical formulation extended by the classical methods used in isotropic thin plates was also established to deal with the general cases of sandwich plates and cylindrical shells. Numerical results show that the solutions obtained by the present methods are accurate enough to serve as a quick check for the other numerical solutions.

Effect of applied magnetic field on sound transmission loss of MR-based sandwich panels

This study aims to investigate the sound transmission loss (STL) capability of sandwich panels treated with Magnetorheological (MR) fluids at low frequencies. An experimental setup has been designed to investigate the effect of the intensity of applied magnetic field on the natural frequencies and STL of a clamped circular panel. It is shown that the fundamental natural frequency of the MR sandwich panel increases in proportion to the applied magnetic field. In addition, the STL of the panel at the resonance frequency increases as the magnetic field is amplified. Furthermore, the classical plate theory and Ritz method have been utilized to develop the governing equations of motion of the finite multilayered circular panels comprising two elastic face sheets and MR fluid core layer. The radiated sound power from the panel is derived using Rayleigh integral as a function of the transverse velocity of the panel which is subsequently used to evaluate the STL. The theoretical study is validated comparing the simulation results with the experimental measurements. Experimental and analytical parametric study have also been conducted to study the effect of the core layers’ thickness on the natural frequency and the STL of sandwich panel.

Power Law of Critical Buckling in Structural Members Supported by a Winkler Foundation

AbstractIn the fields of engineering, nanoscience, and biomechanics, thin structural members, such as beams, plates, and shells, that are supported by an elastic medium are used in several applications. There is a possibility that these thin structures might buckle under severe loading conditions; higher-order, complicated elastic buckling modes can be found owing to the balance of rigidities between the thin members and elastic supports. In this study, we have shown a new and simple ‘power law’ relation between the critical buckling strain (or loads) and rigidity parameters in structural members supported by an elastic medium, which can be modelled as a Winkler foundation. The following structural members have been considered in this paper: i) a slender beam held by an outer elastic support under axial loading, ii) cylindrical shells supported by an inner elastic core under hydrostatic pressure (plane strain condition), and iii) complete spherical shells that are filled with an inner elastic medium.

Polishing-pad-free electrochemical mechanical polishing of single-crystalline SiC surfaces using polyurethane–CeO2 core–shell particles

A novel method for electrochemical mechanical polishing (ECMP) of the single-crystalline SiC surface, which has extremely high mechanical and chemical strength compared to conventional electronic materials, is reported. The method does not employ a polishing pad; it comprises electrochemical oxidization of the SiC surface and subsequent removal of the oxide by CeO2 from the polyurethane–CeO2 core–shell particles. The core–shell particles are used to maintain a gap between the polishing plate (cathode) and the SiC wafer (anode), which enables efficient anodic oxidation of the inert SiC surface. The core–shell particles, composed of the elastic polyurethane core covered with an abrasive layer of small and soft CeO2 particles prepared by a simple and low-cost process, can be used to obtain a smooth SiC surface without using a polishing pad. The ratio of polyurethane to CeO2 in the core–shell particles is optimized to obtain core particles that are fully covered with the shell particles without leaving excess CeO2 particles. Using the fabricated core–shell particles, the conventional CMP process is unable to remove the SiC surface without anodization. While a continuous bias during polishing produces a rough SiC surface owing to the oxide film remaining on the treated surface, as confirmed by current measurements and X-ray analysis, a periodically applied bias, whose conditions were determined by the theoretical growth rate and residual thickness of the oxide film, reduces the number of scratches, and a smooth surface with sub-nanometer roughness is obtained. The obtained value of surface roughness is in good agreement with the calculated value determined using conventional grinding theory. Compared to a conventional polishing process with a colloidal SiO2 slurry, the proposed method shows superior polishing efficiency without the need for a polishing pad. SEM observation of the core–shell particles shows that the particles have durability against the strong electric field between the electrodes.

Study on structural failure of RPV with geometric discontinuity under severe accident

A severe accident management strategy known as ‘in-vessel retention (IVR)’ is widely adopted in most of advanced nuclear power plants. The IVR mitigation is assumed to be able to arrest the degraded melting core and maintain the structural integrity of reactor pressure vessel (RPV) within a prescribed period of time. This traditional concept of IVR without consideration of internal pressure effect wasn’t challenged until the occurrence of Fukushima accident on 2011, which showed that the structural behavior had not been appropriately assessed, and a certain pressure (up to 8.0MPa) still existed inside the RPV. Accordingly, the paper tries to address the related issue on whether lower head (LH) integrity can be maintained, when the LH is subjected to the thermal-mechanical loads created during such a severe accident. Because of the presence of the high temperature melt (∼1300°C) on the inside of RPV, some local material is melted down to create a unique RPV with geometric discontinuity, while the outside of RPV submerged in cavity water will remain in nucleate boiling (at ∼150°C). Therefore, the failure mechanisms of RPV can span a wide range of structural behaviors, such as melt-through, creep damage, plastic yielding as well as thermal expansion. Through meticulous investigation, it is found that the RPV failure is mainly caused by creep and plasticity, especially for the inside of highly-eroded region. The elastic core (or layer) is found to exist in the proximity of mid-section of the highly-eroded wall. However, the elastic core is squeezed into a smaller size with the internal pressure increase. Besides, the multiaxial state of stress is found to accelerate the damage evolution on the thinnest site.

On the energy harvesting via doubly curved piezoelectric panels

This article presents an analytical solution for power output from a doubly curved piezoelectric energy harvester. The energy harvester is made of an elastic core layer coupled with one or two surface-bonded piezoelectric layers. Five mechanical equations of motion together with Gauss’s equation are derived on the basis of first-order shell theory and solved simultaneously for simply supported mechanical boundary conditions. The influence of structural damping is taken into account using Rayleigh damping. The electromechanical frequency response functions that relate the power output and circuit load resistance are identified from the exact solutions. Finally, the performance of the system is analyzed extensively for different parameters such as type of energy harvester including unimorph and bimorph panel in series or parallel connections of piezoelectric layers, circuit load resistance, geometrical parameters, and material properties of core and piezoelectric layers.

High-performance stretchable yarn supercapacitor based on PPy@CNTs@urethane elastic fiber core spun yarn

Yarn supercapacitors, as knittable and weavable energy storage devices, are attracting more and more attention in recent years. Similar to various yarns with different physical and mechanical properties available in textile industry, different yarn supercapacitors should be developed as well. However, as a device, stretchable yarn supercapacitors suffer a lot from limited stretchability, complicated and high cost fabrication, which greatly restrict their wide adoptions. Here, we use urethane elastic fiber core spun yarns (UY) with intrinsic high stretchability for the first time, as a wearable scaffold for hosting conductive CNT and electrocapacitive PPy to fabricate large-scale highly stretchable yarn electrodes via a simple two-step process (CNTs dipping and PPy electrodeposition). The yarn supercapacitor keeps the excellent stretchability of the UY without using any extra stretchy substrate or wavy structure as most stretchable yarn supercapacitors used, and at the same time, exhibits a high areal capacitance of 69mFcm−2 (normalized to two electrodes) as well as a good rate capacity. Furthermore, the capacitive performance of the yarn supercapacitor remains nearly unchanged even at a high strain of 80%. The high-performance stretchable yarn supercapacitor with the use of intrinsically stretchable yarns paves a way for the production of large-size fabrics for wearable electronic applications.