Department of Civil Engineering

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Subject: search.filters.subject.Buckling

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    Mechanism for Predicting the Progressive Failure of Natural Fiber-Based Composites
    (Springer, 2022-07) Singh, Shamsher Bahadur
    The present study deals with the numerical investigation of buckling and postbuckling responses and failure of natural fiber-based composites and synthetic fiber-reinforced polymer composites under uni-axial compression. The unidirectional fibers are used for the composite aligned with the (0/90) directions. The plates are modelled using general purpose software Abaqus. All the edges of the plate are simply supported. By implementing the linear buckling analysis, the buckling load has been determined. Using the non-linear analysis and static Riks procedure, the composite's postbuckling behavior has also been predicted. The Tsai hill failure criterion is incorporated in the numerical analysis to predict the first-ply failure in the composite. In this study, three different composite models, i.e., Glass, Carbon and Flax fiber-reinforced composites are considered for the analysis. It is observed that the carbon fiber composite has the better buckling load capacity and the first ply failure load compared to glass and flax fiber-reinforced composites. It is further observed that the flax fiber-reinforced composite performs comparatively similar to the glass fiber reinforced composite. Based on the results, it is expected that the glass fiber reinforced composite can be replaced by the flax fiber-reinforced composites. In this study, the ultimate load has been considered when the plate is unable to take any further load in analysis. To precisely predict the ultimate failure of a composite, a methodology has been proposed to undertake the progressive failure analysis of composite by incorporating the UMAT subroutine in the Abaqus.
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    Performance of FRP Bridge Deck Under Flexural Loading
    (Springer, 2022-07) Singh, Shamsher Bahadur
    Fibre-reinforced polymers or FRPs are durable materials that are highly resistant to corrosive activity, have a high stiffness-to-weight ratio and are ideally suited for the construction of assembly lines into compact modules which can be easily installed. FRP production costs are therefore considerably higher than conventional concrete and steel materials. Hence overall cost savings is either due to decreased weight, faster building speed or lower maintenance and improved life span. In this study, the optimum cross-section of the stiffeners of the deck slab is determined from different shapes and sizes of stiffener, which offers high stiffness and strength. Along with, effect of different longitudinal and transverse modulus of stiffeners on the flexural capacity of deck is determined. It is observed that by keeping longitudinal modulus (E1) constant while varying the E1/E2 ratio, the trapezoidal shape stiffener provides the highest strength and stiffness. On the other hand, keeping E2 constant and varying the E1/G12 ratio trapezoidal stiffener shape shows the best result.
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    Response of perforated H-pile subjected to coupled lateral displacement history and axial loading
    (Taylor & Francis, 2022-11) Kumar, Manoj
    The substructure of an integral abutment bridge is designed to accommodate the lateral demand induced by the expansion and contraction of the bridge deck. The assembly of H-piles oriented about their weak axis of bending and aligned in a single row with a rigid connection to the abutment is most preferred for supporting the integral abutment bridges. The weak axis orientation of H-pile allows for higher displacement capacity, thus accommodating the cyclic thermal demand induced by a superstructure. The hysteretic response of H-piles is suggestive of the early onset of the plastic hinge formation, which helps in accommodating the cyclic demand. The H-piles in the integral abutment bridge experience low cycle fatigue induced by cyclic thermal variations, resulting in the buckling of flanges at the critical zone. This study assesses the impact of perforation made on H-pile flanges at the critical buckling zone. In this study, six unique geometries of perforations are modelled and analysed using combined nonlinear kinematic and isotropic hardening formulation. The hysteretic response of the perforated H-pile models has been compared with an unperforated model to assess the proposed perforation geometry's impact on the H-pile's hysteretic response.
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    Buckling and free vibration analysis of randomly distributed CNT reinforced composite beam under thermomechanical loading
    (Elsevier, 2022-12) Kumar, Rajesh
    In this study, the buckling and free vibration characteristics of three-phase randomly distributed carbon nanotube (CNT) reinforced fiber composite (RD-CNTRFC) beams subjected to in-plane compressive loadings and thermal environment are discussed in-depth through a semi-analytical approach. Displacement-based governing equations of motion are derived using Lagrange equation considering higher-order shear deformation theory (HSDT). The effective material properties of RD-CNTRFC are determined in two stages; firstly, effective properties of hybrid matrix (CNTs + Polymer) are evaluated using the Eshelbhy-Mori-Tanaka approach. Finally, overall effective properties of CNTRFC are estimated by implementing different homogenization techniques. The influences of temperature-dependent material properties and CNT-agglomeration are included in the derived formulation. The buckling loads and natural frequencies of RD-CNTRFC beams are computed using a typical eigenvalue solution. The influence of various boundary conditions, CNT mass fraction, CNT-agglomeration, length-to-thickness ratio, and various ply sequences are also addressed.
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    Buckling behaviour of laminated composite skew plates with various boundary conditions subjected to linearly varying in-plane edge loading
    (Elsevier, 2015-09) Kumar, Rajesh
    In the present study, the buckling behaviour of laminated composite skew plates with different boundary conditions subjected to linearly varying in-plane loads are presented. The skew plate is modelled based on higher order shear deformation theory, which accurately predicts the buckling behaviour for the thick plate. The in-plane stress distribution within the skew plate due to linearly varying in-plane load is equal to the applied in-plane edge load in the pre-buckling range. Using these in-plane stress distributions, the total potential energy functional is formulated. Total potential energy is a function of the total strain energy of skew plate and potential energy due to in-plane stress distributions. The total strain energy of skew plate contains membrane energy, bending energy, additional bending energy due to additional change in curvature and shear energy due to shear deformation, respectively. The total potential energy functionals mapped from physical domain to computational domain over which a set of orthonormal polynomials satisfying the essential boundary conditions is generated by Gram–Schmidt orthogonalization process. Using a Rayleigh-Ritz method in conjunction with Boundary Characteristics Orthonormal Polynomials, the total potential energy functional is converted into sets of algebraic equations. Finally, these algebraic equations are rearranged as a linear eigenvalue problem, which is solved to obtain the critical buckling loads. The numerical results are presented for different skew angles, boundary conditions, length to thickness ratios, aspect ratios and in-plane loadings. It is observed that the critical buckling load increase with the increase of skew angle as well as change in the mode shape at a lower aspect ratio with the increase of skew angle.
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    Vibration and buckling of skew plates under linearly varying edge Compression
    (International Journal of Acoustics and Vibration, 2019-06) Kumar, Rajesh
    Pre-buckling vibration and buckling behaviour of composite skew plates subjected to linearly varying in-plane edge loading with different boundary conditions are studied. The total energy functional of the skew plate mapped from physical domain to computational domain over which a set of orthonormal polynomials satisfying the essential boundary conditions is generated by Gram-Schmidt orthogonalization process. Using Rayleigh-Ritz method in conjunction with Boundary Characteristics Orthonormal Polynomials, the total energy functional is converted into sets of algebraic equations for static stability problems and ordinary differential equation for free vibration problem. Pre-buckling vibration frequencies of the stressed skew plate are obtained by solving associated linear eigen value problem for free vibration and solution of the eigen value problem for static case results critical buckling load. From different parametric study, it is observed that the pre-buckling vibration frequency and critical buckling load increase with the increase of skew angle and edge restraint.
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    Dynamic instability analysis of laminated composite stiffened shell panels subjected to in-plane harmonic edge loading
    (Korea Science, 2006) Patel, S. N.
    The dynamic instability characteristics of laminated composite stiffened shell panels subjected to in-plane harmonic edge loading are investigated in this paper. The eight-noded isoparametric degenerated shell element and a compatible three-noded curved beam element are used to model the shell panels and the stiffeners respectively. As the usual formulation of degenerated beam element is found to overestimate the torsional rigidity, an attempt has been made to reformulate it in an efficient manner. Moreover the new formulation for the beam element requires five degrees of freedom per node as that of shell element. The method of Hill's infinite determinant is applied to analyze the dynamic instability regions. Numerical results are presented to demonstrate the effects of various parameters like shell geometry, lamination scheme, stiffening scheme, static and dynamic load factors and boundary conditions, on the dynamic instability behaviour of laminated composite stiffened panels subjected to in-plane harmonic loads along the boundaries. The results of free vibration and buckling of the laminated composite stiffened curved panels are also presented.
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    Dynamic stability analysis of stiffened shell panels with cutouts
    (ASCE, 2009-04) Patel, S. N.
    A finite element dynamic instability analysis of stiffened shell panels with cutout subjected to uniform in-plane harmonic edge loading along the two opposite edges is presented in this paper. The eight-noded isoparametric degenerated shell element and a compatible three-noded curved beam element are used to model the shell panels and the stiffeners, respectively. As the usual formulation of degenerated beam element is found to overestimate the torsional rigidity, an attempt has been made to reformulate it in an efficient manner. Moreover the new formulation for the beam element requires five degrees of freedom per node as that of shell element. Bolotin method is applied to analyze the dynamic instability regions. Numerical results of convergence studies are presented and comparison is made with the published results from literature. The effects of various parameters such as shell geometry, radius of curvature, cutout size, stiffening scheme, and dynamic load factors are considered in dynamic instability analysis of stiffened shell panels with cutout. The free vibration and static stability (buckling) results are also presented. With the consideration of radius of curvatures the panels reduce from deep shell case to shallow shell case and finally become flat plate.
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    Buckling response of laminated composite stiffened plates subjected to partial in-plane edge loading
    (Taylor & Francis, 2016-09) Patel, S. N.
    This article presents the buckling analysis of laminated composite stiffened plates subjected to partial in-plane edge loading. The finite element method is used to carry out the analysis. The eight-noded isoparametric degenerated shell element with C0 continuity and first-order shear deformation and a compatible three-noded curved beam element are used to model the plate skin and the stiffeners, respectively. The eigen value analysis is carried out to track the buckling load. The convergence study is performed for some specific problems and the results are compared with the available results in the literature. It is observed that the convergence of results is very fast for this finite element model. Effect of different parameters like orientation of fibers, number of layers, and loading types are considered in the present investigation. It is also observed that all these parameters have significant effect on the buckling response of the composite stiffened plate.
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    Postbuckling Response and Failure of Symmetric Laminated Plates with Rectangular Cutouts under Uni-axial Compression
    (Korea Institute of Science and Technology Information, 2008) Singh, Shamsher Bahadur
    This paper deals with the buckling and postbuckling responses and the progressive failure of square symmetric laminates with rectangular cutouts under uniaxial compression. A detailed investigation is made to show the effects of cutout size and cutout aspect ratio on prebuckling and postbuckling responses, failure loads and failure characteristics of (+45/−45/0/90)2s, (+45/−45)4s and (0/90)4s laminates. The 3-D Tsai-Hill criterion is used to predict the failure of a lamina while the onset of delamination is predicted by the interlaminar failure criterion. In addition, the effects of boundary conditions on buckling load, failure loads, failure modes and maximum transverse deflection for a (+45/−45/0/90)2s laminate with and without cutout have also been presented. It is concluded that square laminates with small square cutouts have more postbuckling strength than without cutout, irrespective of boundary conditions.