M.K. Pandit

Analysis of Laminated Sandwich Plates Based on an Improved Higher Order Zigzag Theory

A finite element model based on an improved higher order zigzag plate theory developed by the authors is refined in this study and applied to bending and vibration response of soft core sandwich plates. The theory satisfies interlayer transverse shear stress continuity including transverse shear stress free condition at the plate top and bottom surfaces and transverse normal compressibility of the core. The in-plane displacements vary cubically through the entire thickness, while transverse displacement is assumed to vary quadratically within the core. In order to have a better computational benefit, a C0 finite element formulation is adopted. This is refined through satisfaction of certain constrains variationally using a penalty function approach. The performance of the model is demonstrated by comparing the present results with 3D elasticity solutions and other available results.

Free Vibration Analysis of Laminated Composite Rectangular Plate Using Finite Element Method

A nine-noded isoparametric plate-bending element has been used for the analysis of free undamped vibration of isotropic and fiber reinforced laminated composite plates. The effect of shear deformation has been incorporated in the formulation by considering the first-order shear deformation theory for the analysis. An effective mass lumping scheme with rotary inertia has been recommended. Two types of mass lumping schemes have been formed. In one lumping scheme rotary inertia has also been introduced. Numerical examples of isotropic and composite rectangular plates having different fiber orientations angles, thickness ratios, and aspect ratio have been solved. Examples of plates having internal cutout and uniformly distributed mass on the plates have also been studied. The results obtained have been compared with the available published literature. The present results are very close to the analytical solutions. Few examples have been presented as new results.

Vibration of Sandwich Plates with Random Material Properties using Improved Higher-Order Zig-Zag Theory

An improved higher-order zig-zag theory for vibration of soft core sandwich plates in random environment is proposed. It exploits all the merits of layer-wise theory, includes the effect of core transverse normal strain and simultaneously enjoys the benefits of single layer theory in terms of computational efficiency. The core is modeled as a 3-D elastic continuum. An efficient C 0 finite element is developed for the implementation of the proposed theory. A first order perturbation approach is employed to handle the randomness in the lamina material properties. Second order statistics of natural frequencies are computed and validated with independent Monte Carlo simulation.

Buckling of Sandwich Plates with Random Material Properties Using Improved Plate Model

An improved higher-order zigzag plate theory in a random environment is proposed and it is implemented in a stochastic finite element framework to study the buckling characteristic of sandwich plates with random material properties. The theory satisfies transverse shear stress continuity at all of the layer interfaces and the transverse shear-stress-free condition at the top and bottom surfaces. It also includes the effect of transverse deformability to the core. The through-thickness variation of in-plane displacements is assumed to be cubic, whereas transverse displacement varies quadratically within the core and it remains constant over the face sheets. Note that sandwich and composite structures are characterized by inherent uncertainties in their material properties. The effect of these uncertainties on the buckling characteristic of sandwich plates is studied by modeling the macromechanical material properties as basic random variables. A stochastic finite element method consisting of an efficient C° finite element in conjunction with a mean-centered first-order perturbation approach is developed, and the model is employed to evaluate the second-order statistics of the buckling loads. The published results are used to validate the deterministic part of the proposed approach, and its stochastic component is validated with an independent Monte Carlo simulation.

Effect of cenosphere on mechanical properties of bamboo–epoxy composites

Cenosphere is a ceramic-rich industrial waste produced during burning of coal in thermal power plants. This study deals with the effect of cenosphere as particulate filler on mechanical behaviour of natural fibre composites. The natural fibre composite consists of bamboo fibre as reinforcement and epoxy as matrix. The bamboo fibre is treated with alkali to improve its surface properties. The conventional hand lay-up technique is used to prepare different composite specimens. Twenty numbers of different composite specimens are prepared with varying number of laminae and filler content. The samples are analysed for their mechanical properties to establish the effect of varying filler content and the number of laminae. It is found that the mechanical properties are significantly influenced by addition of this waste-based ceramic filler.

Studies on water absorption behaviour of bamboo–epoxy composite filled with cenosphere

This paper deals with the evaluation of water absorption properties of natural fibre composites consisting of bamboo fibre as reinforcement, epoxy as matrix and cenosphere as particulate filler at different environmental conditions. Hand lay-up technique is used to fabricate the composites with varying number of layers of bamboo fibre and cenosphere filler content. Water absorption kinetics of the composites is presented in this paper. It is observed that the rate of water absorption depends on the fibre content as well as filler content. Addition of filler in the layered bamboo–epoxy composite decreases the moisture absorption capacity and maximum reduction is observed to be 21% and 32% for distilled and sea water conditions, respectively, in seven-layered composite with 3.0 wt% filler.

Vibration characteristic of laminated sandwich plates with soft core based on an improved higher-order zigzag theory

This paper presents an improved higher order zigzag theory for vibration of laminated sandwich plates. It ensures continuity of transverse shear stresses at all the layer interfaces and transverse shear stress-free condition at the top and bottom surfaces apart from core compressibility. The through-thickness variation of in-plane displacements is assumed to be cubic, whereas transverse displacement varies quadratically across the core, which is modelled as a three-dimensional elastic continuum. An efficient C0 finite element is developed for the implementation of the plate theory. The model is validated using three-dimensional elasticity solutions and some other relevant results available in the literature.

Behaviour of sandwich laminates subjected to thermal loading using higher-order zig-zag theory

In the present work, a higher-order zig-zag laminate theory is utilized to investigate the behaviour of sandwich laminates having low-density core materials subjected to thermal loading. The theory satisfies continuity condition of transverse shear stress at the layer interfaces and zero transverse shear stress at the top and bottom surfaces of the laminated plate. The assumed in-plane displacements are having cubic variations through the entire thickness of the plate. On the other hand, the variation of the transverse displacement is taken to be quadratic within the core and constant through the facesheets. In order to reduce the computation effort, an efficient C0 finite element formulation for the above sandwich plate model is adopted. Some examples of laminated composite and sandwich plate with different material properties, core thickness ratios, aspect ratios, boundary conditions, number of layers and ply orientations are considered for the analysis. The efficacy of the present model in predicting various responses is verified by comparing with three-dimensional elasticity solutions along with the available published results.

Performance of vertically reinforced 1-3 piezo composites for active damping of smart sandwich beams

This paper deals with the performance of vertically reinforced 1-3 piezoelectric composite material as a constraining layer for active constrained layer damping of sandwich beams. A finite element model, considering both in-plane and out-of-plane actuation of the constraining layer of the active constrained layer damping, has been developed for analyzing the active damping of sandwich beams integrated with the patches of such active constrained layer damping treatment. The analysis revealed that vertically reinforced 1-3 piezo composites, which are popularly used as sensor materials, can be used as distributed actuators of smart sandwich beam.

Low Velocity Impact Response of Composite/Sandwich Structures

Dent resistance of structures is one of the important design parameters to consider in automotive, aerospace, packaging and transportation of fragile goods, civil engineering and marine industries. It is important to study the dynamic impact response of various combinations of skin and core materials which can provide desired fracture toughness and highest strength to weight ratio for such applications. This paper discusses the low velocity impact response of sandwich structures having unique combination of mild steel as skin material bonded to thermoplastics/PU foam as core material. HDPE, LDPE and polypropylene were the choice of thermoplastics and an optimum combination of materials for the sandwich structure was evaluated using drop-weight experimental set up. It is observed that LDPE is the best choice of core material for the sandwich structures considered.