Department of Civil Engineering

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Author: search.filters.author.Kumar, RajeshHas files: No

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    A comprehensive review on mechanical performance and environmental resilience of fiber-reinforced polymer composites
    (Taylor & Francis, 2026-03) Kumar, Rajesh; Shrivastava, Sharad
    This review provides a comprehensive analysis of fiber-reinforced polymer composites (FRPCs), focusing on the enhancement of their mechanical properties and environmental resilience. This paper classifies key fiber types, such as glass, carbon, aramid, and basalt, and discusses their contributions to composite strength, stiffness, and durability. he paper highlights how manufacturing route and curing quality (e.g. hand lay-up, VARTM/RTM, pultrusion, prepreg/autoclave, and optimized compression molding) govern void content, fiber volume fraction, interlaminar consolidation, and interphase integrity, thereby strongly influencing tensile, flexural, interlaminar shear, fatigue, and impact responses. The critical role of the fiber-matrix interface is examined, with surface modification techniques and nanofillers, such as carbon nanotubes and graphene, highlighted for their impact on tensile, flexural, and shear properties. Environmental challenges, such as moisture absorption, chemical degradation, thermal aging, and UV exposure, are also addressed, with mitigation strategies such as surface coatings and modified resin systems. By integrating advanced interfacial engineering with environmental resilience techniques, this review outlines pathways for developing next-generation FRPCs for aerospace, automotive, marine, and civil infrastructure applications, while aligning with global sustainability goals.
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    Study on bending characteristics of CNT-reinforced metal Timoshenko composite porous beam exposed to transverse patch loading
    (Sage, 2025-03) Kumar, Rajesh
    Bending characteristics of porous composite beams reinforced by carbon nanotubes (CNTs) under localized transverse loading is examined in the current study. Initially, single-walled carbon nanotubes (SW-CNTs) are utilized as nanofillers within a metal matrix to enhance the beam’s mechanical properties. The effective mechanical properties of the beam are assessed using the Eshelby-Mori-Tanaka method. Next, the porosity of the beam is modeled as being distributed layer-by-layer through the beam’s thickness, either uniformly or in a non-uniform manner, with three distinct distribution types considered: uniform, symmetric non-uniform, and asymmetric non-uniform. The beam is mathematically modeled using theory of Timoshenko beam combining nonlinearity of von-Kármán. The governing nonlinear algebraic equations are derived from the principle of minimizing total potential energy. These equations are then simplified using the Galerkin method and solved implementing Newton-Raphson technique to determine the load-deformation path. Finally, the study is performed using different parameters to analyze their impact on the bending behavior of CNT-metal reinforced porous composite beams. This includes the mass fraction of SW-CNTs, porosity distribution types, agglomeration effects of CNTs, porosity coefficients, aspect ratio, types of transverse loading, and different metal matrices.
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    A semi-analytical method for non-linear instability analysis of variable stiffness laminated composite beams under thermo-mechanical loading
    (Elsevier, 2025-03) Kumar, Rajesh
    This investigation explores the non-linear instability phenomena of variable stiffness laminated composite (VSLC) beams subjected to thermo-mechanical loading. A semi-analytical model is developed to determine the post-buckling and post-buckled vibration behavior of VSLC beams based on trigonometric shear deformation theory. Non-linear strain equations are formulated based on von-Karman’s geometric non-linearity assumptions. Constitutive relations are modified for VSLC beam to account for various coupling effects that arise due to varying fiber orientation and Poisson effects that arise due to the development of zero-stress conditions in the width direction of beams. Using Gram-Schmidt orthogonalization process, an orthogonal basis for the displacement field is constructed to enhance accuracy and ease. The model employs a displacement-based Ritz approach to derive the matrix representation of the governing equations. The present model is developed assuming equivalent single-layer theory, and material properties and temperature variations are assumed to be constant across the thickness of the beam. Moreover, arc-length method is employed to obtain the non-linear response curves of VSLC beam. Pre-buckled and post-buckled vibration responses are obtained using a standard eigenvalue approach. A parametric analysis is conducted to investigate the effect of slenderness ratio, boundary conditions, and ply-sequence on post-buckling and post-buckled vibration characteristics of VSLC beam.
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    Nonlinear dynamics of axially functionally graded, porous sandwich panel subjected to periodic non-uniform in-plane excitation
    (Elsevier, 2025-06) Kumar, Rajesh
    The dynamic response of axially functionally graded (AFG) porous core sandwich panels under periodic non-uniform in-plane axial loads is investigated. The panel is a circular cylindrical shell with a rectangular base with simply supported, in-plane movable edges. The material properties of the face sheet are obtained using the rule of mixture, and porosity in the core is assumed to be randomly distributed. The core is modelled for compressibility with fourth and fifth-order expansions by neglecting the tangential displacement due to large rotations. Non-uniform in-plane stresses are obtained using the Airy stress function. The equations of motion are derived by using variational principles and multi-term Galerkin's approach. The region of dynamic instability is obtained using Bolotin's method; the novelty is that a proportional damping model of the panel is retained in this study. The Newmark-Beta technique is applied to calculate time-histories and phase-plane responses. Results show that damping plays a significant role in dynamic responses. Different from most of the semi-analytical solutions published in the literature, the present study satisfies both natural and essential boundary conditions. The functional gradation of material shows that by increasing the power law constant (k), the material properties present a softening character. Non-uniform in-plane loads are studied, which is another significant novelty for the problem under investigation. Porosity can play an important role in structural performance; it can be due to manufacturing defects or desired for the development of lightweight structures. Therefore, the influence of porosity is studied in detail by considering a random void distribution for both open and closed-type cellular structures.
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    Tunable thermal postbuckling response of imperfect skew sandwich plates with auxetic core and FGCNTRC facings using isogeometric approach
    (Elsevier, 2024-04) Watts, Gaurav; Kumar, Rajesh; Patel, Shuvendu Narayan
    The present work investigates the stability characteristics of skew sandwich plates with functionally graded (FG) facings reinforced with carbon nanotubes having temperature-dependent properties and a re-entrant auxetic core with tunable material properties using isogeometric analysis. The continuous function for material properties of the CNTs is obtained by interpolating the parameters at different temperature values using the fourth-degree polynomial, and resultant properties for the facings are determined using the modified rule of mixtures with the efficiency parameters. The mechanical and thermal properties of the reentrant auxetic core are based on modified Gibson’s relations. The equations of equilibrium are derived using the principle of virtual displacements, which are discretised through the approximation of solution and geometrical variables using B-spline basis functions. Several parametric studies are conducted to study the influence of type and magnitude of initial geometric imperfection, CNT distribution pattern in facings, cell angle of the auxetic core, rib length to thickness ratio, skew angle and boundary conditions on linear and nonlinear thermal post-buckling characteristics of the sandwich plate. New findings on the influence of geometric imperfection and auxetic core parameters on the thermal postbuckling behaviour of sandwich plates are presented for the first time, which may contribute towards a better understanding of the stability behaviour of lightweight structures.
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    Buckling of Laminated Composite Plate with Imperfections Subjected to In-Plane Pulse Loads
    (Springer, 2021-06) Kumar, Rajesh; Patel, Shuvendu Narayan
    In this article, the stability of a laminated composite plate when subjected to in-plane compressive pulse load is investigated in the finite element method framework. Convergence and validation studies are carried out using the current mathematical formulation and compared with the results from the existing literatures. The effects of loading duration, imperfection and ply orientation on the dynamic buckling behavior of the plate with irregular imperfection are studied in detail and the results are reported. It is observed that the plate having irregular imperfection of the order of 20% of the plate thickness has a lower non-linear dynamic buckling load than the plate with 15% irregular imperfection.
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    Parametric Instability Analysis of Functionally Graded CNT-Reinforced Composite (FG-CNTRC) Plate Subjected to Different Types of Non-uniform In-Plane Loading
    (Springer, 2021-06) Kumar, Rajesh; Patel, Shuvendu Narayan
    Carbon nanotube has attracted many researchers from last two decades due to its exceptional mechanical and multiuse properties. In this article, a semi-analytical study is performed to determine the dynamic instability of a Functionally Graded Carbon Nanotube Reinforced Composite (FG-CNTRC) plate exposed to uniform and various non-uniform in-plane loadings. The efficient mechanical properties for the plate are estimated using rule of mixture where CNTs are distributed aligned and distributed across the plates’ thickness such as Uniformly distributed (UD) and Functionally Graded (FG-X and FG-O). Here, The FG-CNTRC plate is modeled by means of higher order shear deformation theory (HSDT) and the stress distributions (σxx, σyy, τxy) within the plate because of non-uniform loadings are calculated using Airy’s stress method. Then, the Hamilton’s principle is applied to obtain the governing partial differential equations of the FG-CNTRC plate, and which is later solved with the help of Galerkin’s method to convert it to ordinary (Mathieu type) differential equations. Next, these Mathieu type equations are solved employing Bolotin’s method to trace the instability boundaries corresponding to period 2T. At last, the consequence of different parameters like volume fraction of CNT, types of non-uniform loading, static load factor, types of CNTs distribution on instability of the FG-CNTRC plate are examined.
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    Analytical and Numerical Study of Fractured Isotropic and Composite Plates Under Mode-I Crack Extension
    (Springer, 2022-04) Patel, Shuvendu Narayan; Kumar, Rajesh
    This paper deals with the study of fracture characteristics through the analytical method and FE (Finite Element) based methods of isotropic and anisotropic plates containing a central crack under uniform in-plane tensile load. In this study, mode I (opening mode) of fracture is considered. A governing differential equation is established for the plates and complex theory in terms of complex variables is employed to find stress functions to satisfy the equilibrium equation, compatibility equation and boundary condition at infinite distance and crack surfaces. An analytical solution which follows the Cauchy-Riemann conditions in the form of is introduced to study the stress characteristics at different positions of the plate. The effect of the uniform in-plane tensile load on the near field and far-field crack tip stress characteristics for mode-I crack is studied. ABAQUS/Standard software is used to carry out numerical analysis. The FEM results are compared with those of the analytical results. The damage parameters for composite plate is also studied.
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    Nonlinear Vibration of Functionally Graded CNT-Reinforced Composite Plate Under Nonuniform In-Plane Loading
    (Springer, 2022-04) Kumar, Rajesh
    In this study, a functionally graded carbon nanotube-reinforced composite (FG-CNTRC) plate exposed to uniform and different forms of nonuniform in-plane loadings is analyzed for the determination of plate’s nonlinear vibration behavior (frequency-amplitude curve). Firstly, to guesstimate the effective mechanical properties of the FG-CNTRC plate, the extended rule-of-mixture technique is implemented when CNTs are aligned and distributed throughout the thickness of the plate. The different forms of CNTs distributions are considered, like - uniformly distributed (UD) and functionally Graded (FG-X type and FG-O type). Secondly, the FG-CNTRC is modeled based on higher order shear deformation theory (HSDT) including von-Kármán nonlinearity. Then, the distribution of stresses (σxx, σyy, τxy) within the plate because of nonuniform in-plane loading is estimated by resolving the in-plane elasticity problem using Airy’s stress approach. Thirdly, the governing partial differential equations (PDEs) of the FG-CNTRC plate are derived by employing Hamilton’s principle and solved using Galerkin’s method to convert these PDEs to the nonlinear ordinary differential equations (ODEs). Lastly, the Incremental Harmonic Balance (IHB) method are used to solve these nonlinear ODEs to trace the non-linear vibration behavior (frequency-amplitude curve) of the FG-CNTRC plate. The effect of different parameters like volume fraction of CNT, types of nonuniform loadings, types of CNTs distribution, and dynamic load factors on nonlinear vibration behavior of the FG-CNTRC plate are examined.
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    Nonlinear Vibration of Functionally Graded Porous-Cellular Timoshenko Beam Subjected to In-Plane Periodic Loading
    (Springer, 2022-07) Kumar, Rajesh
    The present study deals with an open cell shear deformable functionally graded porous beam subjected to in-plane periodic loading to analyze its nonlinear vibration behaviour. The porous beam in this study is modelled based on Timoshenko beam theory i.e., first-order shear deformation theory (FSDT). The porosities are dispersed throughout the thickness of the beam considering uniform and non-uniform symmetric distribution models. For the two distribution systems, the mass density and elasticity moduli of porous beams are considered to vary in the thickness direction. Using Hamilton’s principle, the partial differential equations (PDEs) governing the behaviour of porous beams are derived for the simply supported boundary condition. Then, Galerkin’s method is employed to convert the PDEs to nonlinear ordinary differential equations (ODEs). Further to trace the non-linear vibration behaviour (frequency-amplitude curve) of the porous beam, these ODEs are solved by Incremental Harmonic Balance (IHB) method. A parametric study is presented to assess the influence of porosity, static and dynamic load factors on the vibrational characteristics of the porous beams. As anticipated, the porous beam with non-uniformly symmetric distribution exhibited a higher critical buckling load compared to the uniform distribution of porosity