Periodic Compressive Loads Research Articles

Parametric instability analysis of sandwich plates with composite skins and LPRE based viscoelastic core

In the present analysis, the parametric instability regions of a three-layered sandwich plate with thin composite skins and leptadenia pyrotechnica rheological elastomer (LPRE) core under axial periodic compressive load is studied for five different boundary conditions. The governing equation of motion is derived using finite element method (FEM) which is in the form of a parametrically excited system. The instability regions of the sandwich plate are found using modified Hsu method. The shear storage modulus and loss modulus of the newly developed LPRE core is determined experimentally and used in this analysis. The dynamic properties of the LPRE based sandwich plates are observed to be better than those of the room temperature vulcanised elastomer core based sandwich plates. The critical dynamic loads and the corresponding frequencies are found which will find various applications in structural design.

Non-linear parametric vibration responses of composite plates on Pasternak foundations using extended dynamic stiffness method

ABSTRACT In this work, the non-linear parametric vibration responses of rectangular laminated composite plates subjected on Pasternak foundation, under in-plane periodic compressive load applied along two opposite edges, are theoretically studied using the extended dynamic stiffness method. The authors present the new method to establish the exact dynamic stiffness matrices of rectangular laminated composite plates subjected to in-plane periodic forces based on general Von-Kármán large deflection plate theory. A set of second-order ordinary differential non-linear equations of extended Mathieu–Hill type with periodic coefficients is formed to determine the regions of dynamic instability and non-linear parametric vibration responses based on Bolotin method. The effects of various parameters such as static load, dynamic load, aspect ratio, boundary conditions, orthotropy and foundation stiffness factor on the dynamic instability regions and non-linear parametric vibration characteristics are investigated and discussed. For linear theory, the present results are found to be in agreement with available conclusions in the literature which was obtained based on the linear analysis.

Assessment of dynamic instability of laminated composite-sandwich plates

The current work deals with the assessment of dynamic stability behavior of laminated composite and sandwich plates subjected to in-plane static and periodic compressive loads based on a recently developed zigzag theory by the authors. This theory satisfies the traction-free boundary conditions at top and bottom surfaces of the laminate as well as the inter-laminar stress continuity at layer interfaces. Also, it obviates the need of artificial shear correction factor. The theory is based upon shear strain shape function assuming non-linear distribution of transverse shear stresses. An efficient C0 continuous, eight-noded isoparametric element with seven field variables is employed for the dynamic stability analysis of laminated composite and sandwich plates. The boundaries of principal instability domains are obtained following Bolotin's approach and are represented either in the non-dimensional load amplitude-excitation frequency plane or load amplitude-load frequency plane. A series of numerical examples on the dynamic stability analysis of laminated composite and sandwich plates are studied to demonstrate the effects of modular ratio, span to thickness ratio, boundary conditions, thickness ratio, static load factor and various load parameters on the principal instability regions. The predicted results are compared with the available existing results in order to ensure the performance of the proposed model.

Dynamic Instability of Laminated Composite and Sandwich Plates Using a New Inverse Hyperbolic Zigzag Theory

AbstractThe present study deals with the dynamic stability behavior of laminated composite and sandwich plates subjected to in-plane static and periodic compressive loads based on a recently developed inverse hyperbolic zigzag theory by the authors. The present model satisfies the traction-free boundary conditions on the surfaces of the plate and interlaminar continuity conditions at the layer interfaces, thus obviating the need for a shear correction factor. An efficient C0 continuous isoparametric serendipity element with seven field variables is employed for the usual discretization of the plate structure. The effect of span-thickness ratio, modular ratio, boundary conditions, static load factor, and thickness ratios are examined by solving a variety of numerical problems on laminated composite and sandwich structures. The principal instability regions of plate structures are obtained using Bolotin’s approach and are represented either in the nondimensional load amplitude-excitation frequency plane or ...

Vascular Endothelial Growth Factor Release from Alginate Microspheres Under Simulated Physiological Compressive Loading and the Effect on Human Vascular Endothelial Cells

Bone tissue engineering has generated promising results in bone defect repair, but is limited by the inherently poor nutrient supply to nonvascularized tissue-engineered bone grafts. In this study, we investigated the delivery of vascular endothelial growth factor (VEGF) and the effect on in vitro cultured human umbilical vein endothelial cells (HUVECs), in an attempt to provide experimental basis for promoting the vascularization of tissue-engineered bone grafts. A mechanical stimulator was developed to generate a periodic compressive load analogous to goat locomotor characteristics, simulating the mechanical stimulation applied on the fracture ends of the load-bearing bone. Poly-l-lysine-coated VEGF/alginate microspheres were combined with demineralized bone matrices into composites, and the in vitro release of VEGF from these composites was evaluated under periodic compression. The effect of the release media on HUVECs was also investigated. Compression slightly accelerated VEGF release at the early stage (<11 days) compared with noncompressed composites, although the release profiles of the two composite groups were generally similar. The released VEGF promoted HUVEC proliferation. In addition, the periodic compression applied on composites containing both HUVECs and VEGF/alginate microspheres promoted the expression of matrix metalloproteinases-2/9 in HUVECs. This study provides a model for investigating VEGF release under simulated in vivo biomechanical conditions and without the disadvantage of the rapid degradation of VEGF in in vivo investigation of VEGF release. The results also provide important guidelines for future in vivo experiments.

VIBRATION AND STABILITY BEHAVIOR OF LAMINATED COMPOSITE CURVED PANELS WITH CUTOUT UNDER PARTIAL IN-PLANE LOADS

The present paper is concerned with the vibration, buckling and dynamic instability behavior of laminated composite, cross-ply, doubly-curved panels with a central circular hole subjected to in-plane static and periodic compressive loads. A generalized shear deformable Sanders' theory is used to model the curved panels, considering the effects of transverse shear deformation and rotary inertia. Bolotin's approach is used for studying the dynamic instability regions of doubly-curved panels. The effects of non-uniform edge loads, curvature with different cutout ratios, static and dynamic load factors, and lamination parameters on curved panels are investigated with the results discussed.

Dynamic Stability of Laminated Composite Curved Panels with Cutouts

The present investigation deals with the dynamic stability behavior of laminated composite curved panels with cutouts subjected to in-plane static and periodic compressive loads, analyzed using the finite element method. A generalized shear deformable Sanders’ theory with tracers is used in this study. Numerical results obtained for vibration and buckling of composite panels with cutouts compare well with literature. The principal dynamic instability region of composite perforated panels is obtained using Bolotin’s approach. The study reveals that curved panels with cutouts depict higher stiffness with the addition of curvatures. The laminated hyperbolic paraboloid panel shows the highest stiffness with the onset of instability at higher excitation frequencies. The effect of curvature in laminated composite curved panels is reduced with an increase in size of the cutout. The principal instability regions are influenced by the lamination parameters. Thus, the laminate construction, coupled with cutout geometry, can be used to the advantages of tailoring during design of composite structures for practical applications.

Dynamic stability analysis and control of a composite beam with piezoelectric layers

A slender laminated composite beam with piezoelectric layers subjected to axial periodic compressive loads is considered. The dynamic stability behaviors of the laminated composite beam are investigated. The top and bottom piezoelectric layers act as actuators. The beam is restrained at both ends, and the piezoelectric actuators induce in-plane stresses affecting the dynamic behavior of the beam. The stress stiffening effects on the dynamic stability of the beam with piezoelectric layers are examined. While the top piezoelectric layer acts as an actuator, the bottom layer works as a sensor. A simple negative velocity feedback control algorithm that couples the direct and converse piezoelectric effects is employed to actively control the dynamic response of the beam through a closed control loop. The influence of the feedback control gain on the response of the beam is evaluated.

Implementation of strain rate as a bone remodeling stimulus.

Strain rate is implemented as a stimulus for surface bone remodeling. Using idealized models for trabecular bone structures, the surface remodeling predictions using the strain rate as the stimulus are compared with the predictions using the peak strain magnitude as the stimulus. For a uniaxially loaded cruciform shape, the comparison shows that the two surface remodeling stimuli predict the same final shape under a periodic compressive load, but the two evolutionary paths to final shapes are different. Two biaxially loaded regular grid models of trabecular structure were considered, one a grid of square diamond shaped elements and the other a brick wall patterned grid. For both of these idealized trabecular structures, the comparison shows that the two surface remodeling stimuli predict the same final shape under a periodic compressive load, even from these distinctly different initial grid patterns, and the evolutionary paths to final shapes are quite different. In general the two stimuli do not predict the same remodeling and the conditions under which they do are derived. The models developed are also applied to the data from the animal experiments reported in Goldstein et al. (1991), and it is shown that the strain rate stimulus predicts bone remodeling similar to what was experimentally observed.