Showing papers by "Vasudevan Rajamohan published in 2022"

Nonlinear buckling analysis of a semi-elliptical dome: Numerical and experimental investigations

Abstract: In this paper, non-linear buckling performance of a semi-elliptical steel dome under uniform external pressure is investigated numerically and experimentally. Numerical buckling analysis is performed on an ellipsoidal dome with various nonlinearities including geometric (GN) and material non-linearity (MN) to obtain the critical pressure. The option “Arc length method” available in ANSYS is implemented to solve the non-linear differential equations. Further, an experimental testing is performed on the prototype ellipsoidal dome subjected to external hydrostatic pressure to obtain the critical pressure. The effectiveness of the developed numerical modelling is demonstrated by comparing the critical buckling load evaluated using the present non-linear analysis with those available in literature and experimental analysis. Imperfections such as Force Induced Dimple (FID) and eigen affine imperfections are considered in the ellipsoidal dome to investigate their effects on collapse load. Non-linear (NL) buckling analysis of stringer reinforced semi-elliptical dome is performed to investigate the effect of stringers on critical buckling pressure. Various parametric studies are also performed to study the effect of the nature of imperfection, location of imperfection, aspect ratio on critical buckling pressure of the dome. It was observed that an increase in the amplitude of eigen affine imperfection significantly reduces the critical buckling pressure. FID at an apex of the dome causes a reduction in buckling pressure whereas FID located at the middle and bottom of dome do not affect the critical load significantly. It was also demonstrated that stringer reinforcement on semi-elliptical dome without modifying the mass of overall structure significantly increases the critical buckling pressure. The effect of geometric nonlinearity and material nonlinearity on the critical buckling pressure of the semi-elliptical dome is observed to be more significant in stringer reinforced domes.

Dynamic characterization of tapered composite sandwich plate with honeycomb core: Numerical and experimental investigations

Abstract: In the present study, the numerical and experimental investigations on the dynamic performance of tapered composite sandwich plates with various configurations of a honeycomb core material are presented. The tapered composite sandwich plates are considered with the tapered composite plates as face sheets and honeycomb structure with and without strip reinforcements as core materials. Various tapered composite face sheets are formulated by dropping the plies longitudinally at various locations. Further, the various honeycomb core materials are designed such that stiffeners are reinforced at various locations longitudinally and transversely within the honeycomb patterns to enhance the stiffness and damping properties. Higher order Shear Deformation Theory (HSDT) is used to derive the governing differential equations of motion of the various honeycomb tapered composite sandwich plate and solved numerically. Experimental tests are performed to identify the various mechanical properties of composite face sheets and core materials. Various composite sandwich plates are also fabricated to perform the modal analysis and identify the dynamic properties. The effectiveness of the developed numerical model is demonstrated by comparing the natural frequencies and loss factors identified through experimental tests on the prototype sandwich plates. Various parametric studies are also performed to investigate the effect of strip reinforcement in the honey comb patterns, ply drop off and taper angle of face sheets, aspect ratio of sandwich plates, ply orientation of face sheets and boundary conditions on the free vibration characteristics of the tapered composite sandwich plates. In addition, the transverse vibration responses of tapered composite sandwich plates under harmonic force excitation are examined at different types of the honeycomb core design and the performances are compared with those obtained without the addition of composite strips to demonstrate the effectiveness of strip reinforcement in optimizing the stiffness and damping characteristics of the structures. • Tapered sandwich plates are considered with the tapered composite plates as face sheets and honeycomb as core materials. • Various tapered composite face sheets are formulated by dropping off the plies longitudinally at various locations. • Stiffeners are reinforced at honeycomb core materials longitudinally and transversely within the honeycomb patterns. • Higher order Shear Deformation Theory (HSDT) is used to derive the governing differential equations and solved numerically. • Experimental tests are performed to identify the dynamic and mechanical properties of composite materials.

Nonlinear buckling analysis of a sandwich composite semi-ellipsoidal shell under hydrostatic pressure: A numerical and experimental investigation

Abstract: In this study, nonlinear buckling response of composite sandwich semi-ellipsoidal shell subjected to uniform hydrostatic external pressure is investigated numerically and experimentally. The face sheet of the sandwich shell is made up of laminated composite layers and the honeycomb core is considered as reinforced with and without strips. The various honeycomb core configurations with strip reinforcements are employed in the sandwich semi-ellipsoidal shell. The numerical buckling analysis of the sandwich shell is performed using the commercially available software ANSYS®. The geometric nonlinearity and material nonlinearity of the shell structures are included through the arc length method while solving the nonlinear differential equations and identifying the critical pressure of the structure. The efficacy of the numerical modeling and analysis are verified by comparing the critical pressure obtained through the experimental investigations performed on a composite semi-ellipsoidal sandwich shell and results available in the literature. The various parametric investigations are performed on the composite sandwich shell to study the effect of honeycomb configurations, ply orientation of face sheets, aspect ratio and slenderness of the structure, geometric imperfections on the critical pressure. It was seen that the semi-ellipsoidal sandwich shell having double strip reinforcement core yields higher critical pressure among the various configurations of honeycomb cores. However, the semi-ellipsoidal sandwich shell with the single strip reinforcement in between the core having [0°]6s face sheet composite ply configuration yields higher stiffness to weight ratio which leads to the highest critical pressure among the various configurations of sandwich shell.

Thermal buckling analysis of tapered laminated composite beam: Numerical and experimental investigation

Abstract: The present study focuses on the numerical modeling of the thermal buckling behavior of tapered laminated composite beams validated by experimentation. Lagrange's energy-based governing differential expression was derived utilizing classical laminated plate theory and higher-order shear deformation theory to analyze the tapered composite beam's thermal buckling property. The uniform temperature rise environment is employed to estimate the critical buckling temperature of the tapered laminated composite beam. The obtained results from the numerical approaches were validated with the experimental results and the previous results obtained from the literature associated with the fundamental frequencies of the structure and critical buckling temperature. The parametric study was incorporated in this present work to investigate the influence of the structural parameters and the geometrical parameters like taper angle, ply orientation, aspect ratio, and boundary constraints of the beam.

Structural–Acoustic Response Analysis of Variable Stiffness Laminates with Inherent Material Damping

Abstract: Sound radiation and transmission loss characteristics of variable stiffness composite plate reinforced with the curvilinear fibers are investigated numerically. The formulation is developed using higher-order shear flexible finite element model combined with Helmholtz wave equation. The governing equations obtained using Hamilton’s approach are further solved through the modal super position method to analyze the vibration response under steady state excitation. The inherent material damping of the laminate is accounted through the modal damping calculated using the modal strain energy approach. The acoustic pressure of the variable stiffness laminates is estimated using the Raleigh integral. Subsequently, acoustic response characteristics such as acoustic power level, radiation efficiency, directivity pattern, and transmission loss from the laminates are predicted using the estimated sound pressure for various forcing frequencies. A parametric study covering a wide range of design variables including center and edge fiber angles, lamination scheme, thickness ratio, and boundary conditions on the acoustic sound behavior arising from the vibration of curvilinear fiber composite plate is detailed. This study reveals that the acoustic response of the curvilinear fiber composite plate is significantly influenced by the curvilinear fiber angles at the center/edge fiber angle of the layers. It is hoped that the results obtained here will be useful for designers in developing structures with desired acoustic response characteristics.

Numerical and experimental investigations on nonlinear buckling response of a laminated composite shell

Abstract: In this study, a laminated composite shell with uniformly applied hydrostatic pressure on its external surface is investigated numerically and experimentally. A numerical buckling analysis is carried out on a laminated composite shell with various nonlinearities including geometrical nonlinearity, material nonlinearity and geometric imperfection to obtain the critical buckling pressure using the commercially available software ANSYS Ⓡ . The eigen mode shape imperfection in the geometry is considered for the nonlinear buckling analysis of composite shell. The force-induced inward dimple (FID) and eigen affine imperfections are also considered for the numerical analysis. The nonlinear governing differential equations of the buckling performance of the shell are solved using the arc-length method coupled with nonlinear finite element analysis. The developed nonlinear finite element modeling of the composite shell is validated by comparing the critical buckling pressures available in the literature obtained for the composite cylinder and prolate and oblate composite domes. Further, the effectiveness of the developed numerical modeling and analysis is demonstrated by performing an experimental investigation on a prototype shell made up of GFRP composites and subjected to external hydrostatic pressure. Various parametric studies are also performed to study the effect of aspect ratio of the shell and ply configuration of the composite shell. It was shown that the buckling pressure of the composite shell is decreased if the FIDs are located at the apex of the shell and eigen affine imperfection amplitude of the shell is increased. However, a substantial effect in the critical pressure of the composite shell could not be observed, if the position of FIDs is located towards the bottom of the shell. It is also found that the composite shell with all 90° ply orientation having aspect ratio of 0.5 yields higher critical buckling pressure.

A comprehensive damping study of variable stiffness composite rectangular/skew laminates reinforcement with curvilinear fibers by higher-order shear flexible model

Abstract: Abstract In this work, a comprehensive investigation of curvilinear fiber reinforcement on damping of rectangular and skew composite plates is computationally estimated using higher-order shear flexible model. A set of governing equilibrium equations developed here in form of eigenvalue analysis is solved by adopting the Q-R algorithm. The damping factors associated with different vibrational modes are evaluated from the complex eigenvalues. The proposed model is validated against the available analytical and experimental results. The damping capability of laminated rectangular/skew composite plates is thoroughly analyzed by varying the curvilinear fiber path angles in the layers, lay-up orientations, structural boundary conditions, skew angle of the laminate, and nature of the material. Results reveal that the damping pretending to the curvilinear fibers plate is better than the conventional composite laminate; it varies significantly according to the variation in center and edge of the curvilinear fiber angles. It is also noted that the damping increases with the skew angle of the plate. The study conducted here shows the suitability of such variable stiffness composite structure for safe design under dynamic/impact loading situation.