Department of Civil Engineering

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Author: search.filters.author.Kumar, RajeshSubject: search.filters.subject.Civil engineering

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Now showing 1 - 4 of 4
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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.