A new partial finite element model for statics of sandwich plates

A new partial discretization formulation with four-noded bi-linear finite elements (FEs) has been developed in this study for flexural analysis of sandwich plates. Partial discretization results in solution of a two-point boundary value problem (BVP) governed by a system of coupled first-order ordinary differential equations (ODEs). Mixed degrees of freedom, displacements (u,v,w) and transverse stresses (tau(xz), tau(yz), sigma(z)) are the dependent variables and thus continuity of transverse stresses and displacements are implicitly enforced in the present formulation. Numerical investigations on symmetric and unsymmetric sandwich plates are performed and presented, involving both validation and solution of new problems

Nonlinear analysis of reinforced concrete beams strengthened with polymer composites

Strengthening of existing old structures has traditionally been accomplished by using conventional materials and techniques, viz., externally bonded steel plates, steel or concrete jackets, etc. Alternatively, fibre reinforced polymer composite (FRPC) products started being used to overcome problems associated with conventional materials in the mid 1950s because of their favourable engineering properties. Effectiveness of FRPC materials has been demonstrated through extensive experimental research throughout the world in the last two decades. However there is a need to use refined analytical tools to simulate response of strengthened system. In this paper, an attempt has been made to develop a numerical model of strengthened reinforced concrete (RC) beams with FRPC laminates. Material models for RC beams strengthened with FRPC laminates are described and verified through a nonlinear finite element (FE) commercial code, with the help of available experimental data. Three dimensional (3D) FE analysis has been performed by assuming perfect bonding between concrete and FRPC laminate. A parametric study has also been performed to examine effects of various parameters like fibre type, stirrup's spacing, etc. on the strengthening system. Through numerical simulation, it has been shown that it is possible to predict accurately the flexural response of RC beams strengthened with FRPC laminates by selecting an appropriate material constitutive model. Comparisons are made between the available experimental results in literature and FE analysis results obtained by the present investigators using load-deflection and load-strain plots as well as ultimate load of the strengthened beams. Furthermore, evaluation of crack patterns from FE analysis and experimental failure modes are discussed at the end

A general partial discretization methodology for interlaminar stress computation in composite laminates

A two-point boundary value problem (BVP) is formed in the present work governed by a set of first-order coupled ordinary differential equations (ODEs) in terms of displacements and the transverse stresses through the thickness of laminate (in domain -h/2 < z < h/2) by introducing partial discretization methodology only in the plan area of the three dimensional (3D) laminate. The primary dependent variables in the ODEs are those which occur naturally on a plane z=a constant. An effective numerical integration (NI) technique is utilized for tackling the two-point BVP in an efficient manner. Numerical studies on cross-ply and angle-ply composite plates are performed and presented, involving both validation and solution of new problems

An efficient semi-analytical model for composite and sandwich plates subjected to thermal load

A simple, semi-analytical model with mixed (stresses and displacements) fundamental variables starting from the exact three dimensional (3D) governing partial differential equations (PDEs) of laminated composite and sandwich plates for thermo-mechanical stress analysis has been presented in this paper. The plate is assumed simply supported on all four edges. Two different temperature variations through the thickness of plates are considered for numerical investigation. The accuracy and the effectiveness of the proposed model are assessed by comparing numerical results from the present investigation with the available elasticity solutions. Some new results for sandwich laminates are also presented for future reference

A NEW PARTIAL DISCRETIZATION METHODOLOGY FOR NARROW COMPOSITE BEAMS UNDER PLANE STRESS CONDITIONS

A partial discretization formulation With two-noded finite elements (FEs) under plane stress conditions has been developed for flexural analysis of composite and sandwich beams subjected to transverse loading. The methodology consists in defining a two-point boundary value problem (BVP) governed by a set of coupled first-order ordinary difrerential equations (ODEs) with four degrees of freedom (u,w, tau(xz) and sigma(z)) per node. Continuity of interlaminar transverse stresses and displacements at laminae interfaces is implicitly enforced in the formulation. All the fundamental elasticity relationships between the components of stress, strain and displacement fields are explicitly maintained throughout the elastic continuum. Results have been obtained for cross-ply composite and sandwich beams. Excellent agreement with available analytical, mixed semianalytical and FE solutions is observed. Some new results with clamped support conditions have also been obtained and are presented to serve as benchmark solutions for future reference and to show the generality of the formulation

2D semi-analytical solutions for single layer piezoelectric laminate subjected to electro-mechanical loading

Analysis of a piezoelectric laminate under plane strain condition of elasticity (cylindrical bending) has been performed with mixed semi-analytical model developed by Kant et al. (2007). The in-plane displacement, transverse displacement, transverse normal and shear stresses, electric potential and transverse electric displacement have been considered as fundamental dependent variables. The mathematical model consists of defining a two-point boundary value problem (BVP) governed by a set of coupled first order ordinary differential equations (ODEs). The accuracy and efficiency of the proposed model are assessed by comparing the numerical results from the present investigation with available elasticity solutions. (C) 2014 Elsevier Ltd. All rights reserved

Static solutions for functionally graded simply supported plates

In this article mixed semi-analytical and analytical solutions are presented for a rectangular plate made of functionally graded (FG) material. All edges of a plate are under simply supported (diaphragm) end conditions and general stress boundary conditions can be applied on both top and bottom surface of a plate during solution. A mixed semi-analytical model consists in defining a two-point boundary value problem governed by a set of first-order ordinary differential equations in the plate thickness direction. Analytical solutions based on shear-normal deformation theories are also established to show the accuracy, simplicity and effectiveness of mixed semi-analytical model. The FG material is assumed to be exponential in the thickness direction and Poisson's ratio is assumed to be constant

Design of cost effective epoxy + scrap rubber based composites reinforced with titanium dioxide and alumina fibers

In last decades, aerospace and automotive industries are in search of multi-functional high performance, low cost materials due to certain environmental regulations. Epoxy-recycled rubber based structural composites (ERCs) are used in these type of engineering applications thanks to their favorable properties such as corrosion resistance, low cost and light weight. In addition, the use of recycled materials gives an economic and environmental aspect to the manufacturers. The data for basic material parameters of these composites is essential in order to realize an efficient engineering development process. For this reason, this paper is focused on the design of ERCs reinforced with ceramic powders in different ratios in a matrix of epoxy-fresh scrap rubber. The mechanical and some physical properties of these composite systems were studied in this research. Titanium dioxide (titania-TiO2) and alumina fibers (Al2O3) are used as reinforcements in pre-defined weight percentages. During this study, mechanical and wear properties of these composite systems are studied. Three-point bending tests and nanoindentation were conducted to evaluate mechanical properties. After that, wear resistance is examined by means of nano-scratch tests. As the final step, fracture surfaces were observed with scanning electron microscopy (SEM) to identify damage mechanisms of these composites