ולדימיר סוקולינסקי - Academia.edu (original) (raw)

Papers by ולדימיר סוקולינסקי

Research paper thumbnail of Buckling of Debonded (Delaminated) Sandwich Panels With Transversely Flexible Core

Advances in Aerospace Materials and Structures, 1999

Buckling behavior of sandwich panels with a compressible core which are debonded at one of their ... more Buckling behavior of sandwich panels with a compressible core which are debonded at one of their face sheet-core interfaces is presented. The buckling analysis is based on the principles of the High-Order Sandwich Panel Theory (HSAPT). The effect of the delamination length and location on the critical loads and the buckling modes is studied numerically. Edge delamination as well as inner delamination results are presented. The effect of contact on the critical loads and the buckling modes is presented. A comparison with experimental buckling modes is discussed and conclusions are drawn.

Research paper thumbnail of Progressive Failure Analysis of Shuttle Reinforced Carbon-Carbon Plate Specimens

47th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference<BR> 14th AIAA/ASME/AHS Adaptive Structures Conference<BR> 7th, 2006

A progressive failure analysis of two reinforced carbon-carbon plate specimens subject to three-p... more A progressive failure analysis of two reinforced carbon-carbon plate specimens subject to three-point bending was carried out under contract to NASA by the Alpha STAR Corporation. The GENOA computer code was used to analyze both one and one-and-a-half inch long composite plate specimens. The failure propagation analysis revealed deep qualitative differences in the behavior of the short (one inch long) and long (one-and-a-half inch long) specimens. In the short plate, primary and secondary delaminations were predicted, progressive delamination being the cause of premature failure of the plate, whereas practically no delamination was predicted in the long specimen. The final failure at mid-span was predicted in both the short and long specimens. The predicted failure loads and damage mechanisms were in excellent agreement with the experiments.

Research paper thumbnail of Higher-order free vibrations of sandwich beams with a locally damaged core

International Journal of Solids and Structures, 2004

ABSTRACT The dynamical equations describing the free vibration of sandwich beams with a locally d... more ABSTRACT The dynamical equations describing the free vibration of sandwich beams with a locally damaged core are derived using the higher-order theory approach. The nonlinear acceleration fields in the core are accounted for in the derivations, which is essential for the vibration analysis of the locally damaged sandwich beams. A local damage in the core, arbitrarily located along the length of the sandwich beam, is assumed to preclude the transition of stresses through the core between the undamaged parts of the beam. The damage is assumed to exist before the vibration starts and not to grow during oscillations. The numerical analysis based on the derived equations has been verified with the aid of the commercial finite element software ABAQUS. The numerical simulations reveal that a small local damage causes significant changes in the natural frequencies and corresponding vibration modes of the sandwich beams. An important practical consequence of the present work is that the vibration measurements can be successfully used as a nondestructive damage tool to assess local damages in sandwich beams.

Research paper thumbnail of Special behavior of unidirectional sandwich panels with transversely flexible core under statical loading

International Journal of Non-Linear Mechanics, 2002

Special features inherent in the response of ordinary (fully bonded) and delaminated sandwich pan... more Special features inherent in the response of ordinary (fully bonded) and delaminated sandwich panels with a transversely exible ("soft") core subjected to external in-plane and vertical statical loads are analyzed. The analytical formulation is based on a higher-order theory for sandwich panels with non-rigid bond layers between the face sheets and the core. The central ÿnite di erence scheme is used for discretizing the continuous formulation. The de ated iterative Arnoldi scheme for solution of a large-scale generalized eigenvalue problem is employed, as well as the quasi-Newton global framework for the natural parameter and the arc-length continuation procedures. The numerical higher-order analysis reveals that the ordinary sandwich panel behaves as a compound structure in which the local=localized, overall or interactive forms of the response can take place depending on the geometry, mechanical properties, and boundary conditions of the structure. The non-sinusoidal modes conÿned to the support zones of the panel may occur at critical loads much lower than those predicted on the basis of presumed sinusoidal modes. Soft-core sandwich panels possess a complex branching behavior with limit points and secondary bifurcations. The thin-ÿlm-delamination approach used in the ÿeld of the composite plates is unsuitable for the analysis of delaminated sandwich panels and consideration of the interaction between the face sheets and the core is required. The complex response of the soft-core sandwich panels can be predicted only with the aid of the enhanced higher-order theory.

Research paper thumbnail of Branching behavior in the nonlinear response of sandwich panels with a transversely flexible core

International Journal of Solids and Structures, 2000

A branching behavior of sandwich panels with a transversely¯exible (``soft'') core subjected to l... more A branching behavior of sandwich panels with a transversely¯exible (``soft'') core subjected to longitudinal external forces is investigated using a geometrically nonlinear analysis. The study is based on a closed form highorder theory that allows for a general analysis without resort to the classical mode decoupling approach. The governing equations and the associated boundary conditions are presented, and the appropriate boundary conditions resulting from using edge beams are derived. An ecient path-following algorithm based on the quasi-Newton global framework has been developed. It provides a powerful numerical tool for determining the branching behavior which consists of a sequence of equilibrium states of the sandwich panel as a function of the external loading factor. Application of the general numerical analysis to the``soft'' core sandwich panels reveals that they possess a complicated branching behavior with limit points and secondary bifurcations. It is shown that the wrinkling of the face sheets does not necessarily identify the buckling of the panel as a whole and in many cases it is a result of the nonlinear response. The localized buckling modes are found in some cases to be the critical ones rather than the usual sinusoidal buckling patterns. It is further shown that variations in the geometry, boundary conditions and mechanical properties of the panel constituents can lead to a qualitative shift in its nonlinear response from an imperfection-sensitive,``shell-wise'' response, to an imperfection-nonsensitive,``plate-wise'' one.

Research paper thumbnail of Effects of Boundary Conditions in High-Order Buckling of Sandwich Panels with Transversely Flexible Core

Mechanics of Sandwich Structures, 1998

The effects of boundary conditions on the buckling behavior and bifurcation load level of sandwic... more The effects of boundary conditions on the buckling behavior and bifurcation load level of sandwich panels/beams with a “soft” core due to in-plane loads are presented. The study is conducted using a closed-form high-order linearized buckling analysis, that includes the influence of the transverse flexibility of the core as well as of the localized effects on the overall sandwich panel/beam behavior, and allows the use of different boundary conditions for the upper and the lower skin at the same section. The panel/beam construction is general and consists of two skins (not necessary identical), metallic or composite laminated symmetric, and a “soft” core made of foam or a low strength honeycomb which is flexible in the vertical direction. The closed-form high-order analysis yields the general buckling behavior of the structure which means that the solutions obtained allow for interaction between the skins and the core. The solutions are general and are not based on separation of the buckling response on several types of uncoupled buckling phenomena, such as overall buckling, skins wrinkling, etc., as commonly used in the literature. The finite differences technique has been applied to approximate the governing equations of the closed-form high-order formulation and transform the set of the linearized governing differential equations to an eigenvalue problem that is solved using the deflated iterative Arnoldi procedure. The influence of various boundary conditions, including the different support types throughout the height of the same section and non-identical conditions at the upper and the lower skin, as well as of the core properties, on the buckling behavior of the sandwich panels/beams is considered. The discrepancy between the Timoshenko-Reissner model and the present closed-form high-order formulation is discussed. In particular, a partial fixity phenomenon due to the existence of the pinned boundary conditions, i.e. simply-supported conditions, at the upper and the lower skins at the edge is demonstrated. It is shown that the core properties affect the buckling loads and the corresponding modes of the panel/beam in such a way that the structures with identical boundary conditions but with different cores may undergo different types of buckling such as overall and local as well as interactive loss of stability. The effect of edge concentrated moment induced by a couple of forces exerted on the skins only is also studied.

Research paper thumbnail of Simulating Composites Crush: From the Coupon Level to Full Vehicle Crashworthiness

52nd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, 2011

The initial usage of composites in the aerospace, automotive, and other industries was for the pr... more The initial usage of composites in the aerospace, automotive, and other industries was for the primary benefits of their high strength-to-weight ratios, the ability to mold complex shapes, and reduction in manufacturing time. Today, composites are also being utilized to take advantage of their excellent performance related to energy absorption during impact and crash events. Advances in commercial Finite Element Analysis (FEA) software have enabled engineers to accurately simulate the performance of composite structures in these high-speed, highly nonlinear events. Different methodologies and modeling approaches are needed for simulating composites crush at the coupon level versus simulating the full vehicle crash event. This paper presents new FEA technology and damage models related to composites crush analysis together with methodologies for performing physics-based simulations at the coupon level, phenomenological simulations at the full vehicle level, and for applying the two levels of modeling together. A discussion of the technology is illustrated by several examples.

Research paper thumbnail of Approach to Identify Debonding in Soft-Core Sandwich Beams

45th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics & Materials Conference, 2004

Most identification schemes require knowledge of the explicit functional form that describes the ... more Most identification schemes require knowledge of the explicit functional form that describes the phenomenon in question. Unlike conventional identification methods, the present approach does not require an explicit functional form and is conceived to work with numerical values. The approach requires both the measured natural frequencies of the debonded structure and the theoretical dependence of the natural frequencies on debond location and length. A “simply supported” sandwich beam is used to illustrate the proposed identification scheme. The information from the first three natural frequencies is found to be sufficient to uniquely identify the presence of debonding. This claim is validated for debonds of various length and location for the specified sandwich beam layout.

Research paper thumbnail of Prebuckling optimal design of orthotropic variable thickness plates for inplane loading

Structural Optimization, 1995

Research paper thumbnail of Analytical and Experimental Study of Free Vibration Response of Soft-core Sandwich Beams

Journal of Sandwich Structures & Materials, 2004

The natural frequencies and corresponding vibration modes of a cantilever sandwich beam with a so... more The natural frequencies and corresponding vibration modes of a cantilever sandwich beam with a soft polymer foam core are predicted using the higher-order theory for sandwich panels (HSAPT), a two-dimensional finite element analysis, and classical sandwich theory. The predictions of the higher-order theory are shown to be in good agreement with experimental measurements made with a simple experimental setup, as well as with finite element analysis. Experimental observations and analytical predictions show that the classical sandwich theory is not capable of accurately predicting the free vibration response of soft-core sandwich beams. It is shown that the vibration response of the cantilever soft-core sandwich beam consists of a group of five lower frequency shear (antisymmetric) modes that are followed by a group of four thickness-stretch (symmetric) modes. For the higher frequency range, the vibration modes alternate between groups of one-two antisymmetric and symmetric modes. For...

Research paper thumbnail of Boundary Condition Effects in Buckling of “Soft” Core Sandwich Panels

Journal of Engineering Mechanics, 1999

ABSTRACT

Research paper thumbnail of Optimal design of plates for shear buckling

Computers & Structures, 1997

This paper is concerned with the structural optimization problem of maximizing the shear buckling... more This paper is concerned with the structural optimization problem of maximizing the shear buckling load of rectangular plates for a given volume of material. Optimality conditions are first derived via variational calculus and a double cosine thickness varying plate and a hybrid double sine thickness varying plate are then fine tuned in a one parameter optimization search using a home coded program for an analysis that utilizes the Rayleigh-Ritz method until convergence. Results indicate an increase of 33% in capacity for an orthotropic plate having 50% of the fibers in the 0 ° direction and the other 50% in the 90 ° direction.

Research paper thumbnail of Numerical simulation of the crushing process of a corrugated composite plate

Composites Part A: Applied Science and Manufacturing, 2011

The significant potential of composite materials as highly effective energy absorbers has contrib... more The significant potential of composite materials as highly effective energy absorbers has contributed to their increasing usage in the aerospace, automotive, and railway industries. Traditionally, the development of crashworthiness composites design relies upon laborious and costly experimental testing. Therefore, the ability to simulate accurately the crushing response of composites and their energy absorption mechanisms can significantly reduce the product development

Research paper thumbnail of Consistent higher-order free vibration analysis of composite sandwich plates

Composite Structures, 2008

The consistent higher-order dynamic formulation for foam-type (soft) core sandwich beams was exte... more The consistent higher-order dynamic formulation for foam-type (soft) core sandwich beams was extended to the case of composite sandwich plates. Eight dynamic governing equations and the corresponding boundary conditions were derived through the application of Hamilton's principle. The extended formulation was applied to the free vibration analysis of soft-core and honeycomb-core sandwich plates with anti-symmetric and symmetric lay-ups. The vibration results for the thin and thick composite sandwich plates obtained using the extended formulation were consistent with the predictions of the higher order mixed layerwise theory for laminated and sandwich plates. To simplify the formulation for the case of symmetric sandwich plates, the general dynamic formulation was decoupled into two systems of equations representing symmetric and anti-symmetric vibrations. The numerical study demonstrates the importance of the present formulation for the prediction of higher mode vibration response of composite sandwich plates.

Research paper thumbnail of Experimental and analytical study of nonlinear bending response of sandwich beams

Composite Structures, 2003

The practical value of the geometrically nonlinear higher-order theory is demonstrated using four... more The practical value of the geometrically nonlinear higher-order theory is demonstrated using four-point bend tests carried out on sandwich beam specimens comprised of aluminum face sheets and a PVC foam core. The experimental results were compared with the predictions of classical sandwich theory, and with linear and geometrically nonlinear higher-order sandwich panel theory. The analytical predictions based on the higher-order theory are in excellent agreement with the experimental results. Response parameters show fundamentally distinct behavior with increasing external load, both in the particular section and along the span. Considering the longitudinal displacements, there is a significant geometrically nonlinear stage of the response that precedes the appearance of the material nonlinearity. The peeling stresses also exhibit significant geometrical nonlinearity in the vicinity of the internal supports. The linear higher-order theory can be used efficiently to estimate the vertical displacements of the soft-core sandwich beams up to high load levels with a great accuracy. Premature failure of sandwich beam specimens with weak adhesive layers is caused by high peeling stresses in the upper interface layer at the ends of the specimen, and the loading capacity decreases by more than 40%.

Research paper thumbnail of Accurate predictions of bending deflections for soft-core sandwich beams subject to concentrated loads

Composite Structures, 2004

Although computationally simple and physically perceptible, the formula for bending deflections u... more Although computationally simple and physically perceptible, the formula for bending deflections used by the classical sandwich theory is inaccurate when applied to sandwich beams with a transversely flexible (soft) core. Two correction factors to the classical deflection formula for sandwich beams are proposed based on the higher-order theory (HSAPT) approach. The influence of changes in the geometry and mechanical properties of soft-core sandwich beams on the proposed correction factors are studied numerically. The use of the correction factors reported in the present work offers a simple and accurate way of calculating the bending deflections in soft-core sandwich beams subject to quasi-static concentrated loads, and as such can provide a valuable tool for the designer.The proposed approach also can be used for accurate determination of the core shear modulus from the measurement of compliance in short beam shear tests of sandwich beams.

Research paper thumbnail of Assessment of sandwich models for the prediction of sound transmission loss in unidirectional sandwich panels

Applied Acoustics, 2005

The consistent higher-order approach and the two-parameter foundation formulation are used for th... more The consistent higher-order approach and the two-parameter foundation formulation are used for the derivation of sound transmission loss in symmetric unidirectional (infinitely wide) sandwich panels with isotropic face sheets. In both models, transmission loss is calculated using decoupled equations representing symmetric and anti-symmetric motions of a sandwich panel. The closed-form expressions for impedances and transmission coefficient of a symmetric sandwich

Research paper thumbnail of Consistent Higher-Order Dynamic Equations for Soft-Core Sandwich Beams

AIAA Journal, 2004

ABSTRACT

Research paper thumbnail of Boundary Condition Effects in Free Vibrations of Higher-Order Soft Sandwich Beams

AIAA Journal, 2002

ABSTRACT

Research paper thumbnail of Higher-Order Buckling of Debonded (Delaminated) Sandwich Panels with Soft Core

AIAA Journal, 2000

ABSTRACT

Research paper thumbnail of Buckling of Debonded (Delaminated) Sandwich Panels With Transversely Flexible Core

Advances in Aerospace Materials and Structures, 1999

Buckling behavior of sandwich panels with a compressible core which are debonded at one of their ... more Buckling behavior of sandwich panels with a compressible core which are debonded at one of their face sheet-core interfaces is presented. The buckling analysis is based on the principles of the High-Order Sandwich Panel Theory (HSAPT). The effect of the delamination length and location on the critical loads and the buckling modes is studied numerically. Edge delamination as well as inner delamination results are presented. The effect of contact on the critical loads and the buckling modes is presented. A comparison with experimental buckling modes is discussed and conclusions are drawn.

Research paper thumbnail of Progressive Failure Analysis of Shuttle Reinforced Carbon-Carbon Plate Specimens

47th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference<BR> 14th AIAA/ASME/AHS Adaptive Structures Conference<BR> 7th, 2006

A progressive failure analysis of two reinforced carbon-carbon plate specimens subject to three-p... more A progressive failure analysis of two reinforced carbon-carbon plate specimens subject to three-point bending was carried out under contract to NASA by the Alpha STAR Corporation. The GENOA computer code was used to analyze both one and one-and-a-half inch long composite plate specimens. The failure propagation analysis revealed deep qualitative differences in the behavior of the short (one inch long) and long (one-and-a-half inch long) specimens. In the short plate, primary and secondary delaminations were predicted, progressive delamination being the cause of premature failure of the plate, whereas practically no delamination was predicted in the long specimen. The final failure at mid-span was predicted in both the short and long specimens. The predicted failure loads and damage mechanisms were in excellent agreement with the experiments.

Research paper thumbnail of Higher-order free vibrations of sandwich beams with a locally damaged core

International Journal of Solids and Structures, 2004

ABSTRACT The dynamical equations describing the free vibration of sandwich beams with a locally d... more ABSTRACT The dynamical equations describing the free vibration of sandwich beams with a locally damaged core are derived using the higher-order theory approach. The nonlinear acceleration fields in the core are accounted for in the derivations, which is essential for the vibration analysis of the locally damaged sandwich beams. A local damage in the core, arbitrarily located along the length of the sandwich beam, is assumed to preclude the transition of stresses through the core between the undamaged parts of the beam. The damage is assumed to exist before the vibration starts and not to grow during oscillations. The numerical analysis based on the derived equations has been verified with the aid of the commercial finite element software ABAQUS. The numerical simulations reveal that a small local damage causes significant changes in the natural frequencies and corresponding vibration modes of the sandwich beams. An important practical consequence of the present work is that the vibration measurements can be successfully used as a nondestructive damage tool to assess local damages in sandwich beams.

Research paper thumbnail of Special behavior of unidirectional sandwich panels with transversely flexible core under statical loading

International Journal of Non-Linear Mechanics, 2002

Special features inherent in the response of ordinary (fully bonded) and delaminated sandwich pan... more Special features inherent in the response of ordinary (fully bonded) and delaminated sandwich panels with a transversely exible ("soft") core subjected to external in-plane and vertical statical loads are analyzed. The analytical formulation is based on a higher-order theory for sandwich panels with non-rigid bond layers between the face sheets and the core. The central ÿnite di erence scheme is used for discretizing the continuous formulation. The de ated iterative Arnoldi scheme for solution of a large-scale generalized eigenvalue problem is employed, as well as the quasi-Newton global framework for the natural parameter and the arc-length continuation procedures. The numerical higher-order analysis reveals that the ordinary sandwich panel behaves as a compound structure in which the local=localized, overall or interactive forms of the response can take place depending on the geometry, mechanical properties, and boundary conditions of the structure. The non-sinusoidal modes conÿned to the support zones of the panel may occur at critical loads much lower than those predicted on the basis of presumed sinusoidal modes. Soft-core sandwich panels possess a complex branching behavior with limit points and secondary bifurcations. The thin-ÿlm-delamination approach used in the ÿeld of the composite plates is unsuitable for the analysis of delaminated sandwich panels and consideration of the interaction between the face sheets and the core is required. The complex response of the soft-core sandwich panels can be predicted only with the aid of the enhanced higher-order theory.

Research paper thumbnail of Branching behavior in the nonlinear response of sandwich panels with a transversely flexible core

International Journal of Solids and Structures, 2000

A branching behavior of sandwich panels with a transversely¯exible (``soft'') core subjected to l... more A branching behavior of sandwich panels with a transversely¯exible (``soft'') core subjected to longitudinal external forces is investigated using a geometrically nonlinear analysis. The study is based on a closed form highorder theory that allows for a general analysis without resort to the classical mode decoupling approach. The governing equations and the associated boundary conditions are presented, and the appropriate boundary conditions resulting from using edge beams are derived. An ecient path-following algorithm based on the quasi-Newton global framework has been developed. It provides a powerful numerical tool for determining the branching behavior which consists of a sequence of equilibrium states of the sandwich panel as a function of the external loading factor. Application of the general numerical analysis to the``soft'' core sandwich panels reveals that they possess a complicated branching behavior with limit points and secondary bifurcations. It is shown that the wrinkling of the face sheets does not necessarily identify the buckling of the panel as a whole and in many cases it is a result of the nonlinear response. The localized buckling modes are found in some cases to be the critical ones rather than the usual sinusoidal buckling patterns. It is further shown that variations in the geometry, boundary conditions and mechanical properties of the panel constituents can lead to a qualitative shift in its nonlinear response from an imperfection-sensitive,``shell-wise'' response, to an imperfection-nonsensitive,``plate-wise'' one.

Research paper thumbnail of Effects of Boundary Conditions in High-Order Buckling of Sandwich Panels with Transversely Flexible Core

Mechanics of Sandwich Structures, 1998

The effects of boundary conditions on the buckling behavior and bifurcation load level of sandwic... more The effects of boundary conditions on the buckling behavior and bifurcation load level of sandwich panels/beams with a “soft” core due to in-plane loads are presented. The study is conducted using a closed-form high-order linearized buckling analysis, that includes the influence of the transverse flexibility of the core as well as of the localized effects on the overall sandwich panel/beam behavior, and allows the use of different boundary conditions for the upper and the lower skin at the same section. The panel/beam construction is general and consists of two skins (not necessary identical), metallic or composite laminated symmetric, and a “soft” core made of foam or a low strength honeycomb which is flexible in the vertical direction. The closed-form high-order analysis yields the general buckling behavior of the structure which means that the solutions obtained allow for interaction between the skins and the core. The solutions are general and are not based on separation of the buckling response on several types of uncoupled buckling phenomena, such as overall buckling, skins wrinkling, etc., as commonly used in the literature. The finite differences technique has been applied to approximate the governing equations of the closed-form high-order formulation and transform the set of the linearized governing differential equations to an eigenvalue problem that is solved using the deflated iterative Arnoldi procedure. The influence of various boundary conditions, including the different support types throughout the height of the same section and non-identical conditions at the upper and the lower skin, as well as of the core properties, on the buckling behavior of the sandwich panels/beams is considered. The discrepancy between the Timoshenko-Reissner model and the present closed-form high-order formulation is discussed. In particular, a partial fixity phenomenon due to the existence of the pinned boundary conditions, i.e. simply-supported conditions, at the upper and the lower skins at the edge is demonstrated. It is shown that the core properties affect the buckling loads and the corresponding modes of the panel/beam in such a way that the structures with identical boundary conditions but with different cores may undergo different types of buckling such as overall and local as well as interactive loss of stability. The effect of edge concentrated moment induced by a couple of forces exerted on the skins only is also studied.

Research paper thumbnail of Simulating Composites Crush: From the Coupon Level to Full Vehicle Crashworthiness

52nd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, 2011

The initial usage of composites in the aerospace, automotive, and other industries was for the pr... more The initial usage of composites in the aerospace, automotive, and other industries was for the primary benefits of their high strength-to-weight ratios, the ability to mold complex shapes, and reduction in manufacturing time. Today, composites are also being utilized to take advantage of their excellent performance related to energy absorption during impact and crash events. Advances in commercial Finite Element Analysis (FEA) software have enabled engineers to accurately simulate the performance of composite structures in these high-speed, highly nonlinear events. Different methodologies and modeling approaches are needed for simulating composites crush at the coupon level versus simulating the full vehicle crash event. This paper presents new FEA technology and damage models related to composites crush analysis together with methodologies for performing physics-based simulations at the coupon level, phenomenological simulations at the full vehicle level, and for applying the two levels of modeling together. A discussion of the technology is illustrated by several examples.

Research paper thumbnail of Approach to Identify Debonding in Soft-Core Sandwich Beams

45th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics & Materials Conference, 2004

Most identification schemes require knowledge of the explicit functional form that describes the ... more Most identification schemes require knowledge of the explicit functional form that describes the phenomenon in question. Unlike conventional identification methods, the present approach does not require an explicit functional form and is conceived to work with numerical values. The approach requires both the measured natural frequencies of the debonded structure and the theoretical dependence of the natural frequencies on debond location and length. A “simply supported” sandwich beam is used to illustrate the proposed identification scheme. The information from the first three natural frequencies is found to be sufficient to uniquely identify the presence of debonding. This claim is validated for debonds of various length and location for the specified sandwich beam layout.

Research paper thumbnail of Prebuckling optimal design of orthotropic variable thickness plates for inplane loading

Structural Optimization, 1995

Research paper thumbnail of Analytical and Experimental Study of Free Vibration Response of Soft-core Sandwich Beams

Journal of Sandwich Structures & Materials, 2004

The natural frequencies and corresponding vibration modes of a cantilever sandwich beam with a so... more The natural frequencies and corresponding vibration modes of a cantilever sandwich beam with a soft polymer foam core are predicted using the higher-order theory for sandwich panels (HSAPT), a two-dimensional finite element analysis, and classical sandwich theory. The predictions of the higher-order theory are shown to be in good agreement with experimental measurements made with a simple experimental setup, as well as with finite element analysis. Experimental observations and analytical predictions show that the classical sandwich theory is not capable of accurately predicting the free vibration response of soft-core sandwich beams. It is shown that the vibration response of the cantilever soft-core sandwich beam consists of a group of five lower frequency shear (antisymmetric) modes that are followed by a group of four thickness-stretch (symmetric) modes. For the higher frequency range, the vibration modes alternate between groups of one-two antisymmetric and symmetric modes. For...

Research paper thumbnail of Boundary Condition Effects in Buckling of “Soft” Core Sandwich Panels

Journal of Engineering Mechanics, 1999

ABSTRACT

Research paper thumbnail of Optimal design of plates for shear buckling

Computers & Structures, 1997

This paper is concerned with the structural optimization problem of maximizing the shear buckling... more This paper is concerned with the structural optimization problem of maximizing the shear buckling load of rectangular plates for a given volume of material. Optimality conditions are first derived via variational calculus and a double cosine thickness varying plate and a hybrid double sine thickness varying plate are then fine tuned in a one parameter optimization search using a home coded program for an analysis that utilizes the Rayleigh-Ritz method until convergence. Results indicate an increase of 33% in capacity for an orthotropic plate having 50% of the fibers in the 0 ° direction and the other 50% in the 90 ° direction.

Research paper thumbnail of Numerical simulation of the crushing process of a corrugated composite plate

Composites Part A: Applied Science and Manufacturing, 2011

The significant potential of composite materials as highly effective energy absorbers has contrib... more The significant potential of composite materials as highly effective energy absorbers has contributed to their increasing usage in the aerospace, automotive, and railway industries. Traditionally, the development of crashworthiness composites design relies upon laborious and costly experimental testing. Therefore, the ability to simulate accurately the crushing response of composites and their energy absorption mechanisms can significantly reduce the product development

Research paper thumbnail of Consistent higher-order free vibration analysis of composite sandwich plates

Composite Structures, 2008

The consistent higher-order dynamic formulation for foam-type (soft) core sandwich beams was exte... more The consistent higher-order dynamic formulation for foam-type (soft) core sandwich beams was extended to the case of composite sandwich plates. Eight dynamic governing equations and the corresponding boundary conditions were derived through the application of Hamilton's principle. The extended formulation was applied to the free vibration analysis of soft-core and honeycomb-core sandwich plates with anti-symmetric and symmetric lay-ups. The vibration results for the thin and thick composite sandwich plates obtained using the extended formulation were consistent with the predictions of the higher order mixed layerwise theory for laminated and sandwich plates. To simplify the formulation for the case of symmetric sandwich plates, the general dynamic formulation was decoupled into two systems of equations representing symmetric and anti-symmetric vibrations. The numerical study demonstrates the importance of the present formulation for the prediction of higher mode vibration response of composite sandwich plates.

Research paper thumbnail of Experimental and analytical study of nonlinear bending response of sandwich beams

Composite Structures, 2003

The practical value of the geometrically nonlinear higher-order theory is demonstrated using four... more The practical value of the geometrically nonlinear higher-order theory is demonstrated using four-point bend tests carried out on sandwich beam specimens comprised of aluminum face sheets and a PVC foam core. The experimental results were compared with the predictions of classical sandwich theory, and with linear and geometrically nonlinear higher-order sandwich panel theory. The analytical predictions based on the higher-order theory are in excellent agreement with the experimental results. Response parameters show fundamentally distinct behavior with increasing external load, both in the particular section and along the span. Considering the longitudinal displacements, there is a significant geometrically nonlinear stage of the response that precedes the appearance of the material nonlinearity. The peeling stresses also exhibit significant geometrical nonlinearity in the vicinity of the internal supports. The linear higher-order theory can be used efficiently to estimate the vertical displacements of the soft-core sandwich beams up to high load levels with a great accuracy. Premature failure of sandwich beam specimens with weak adhesive layers is caused by high peeling stresses in the upper interface layer at the ends of the specimen, and the loading capacity decreases by more than 40%.

Research paper thumbnail of Accurate predictions of bending deflections for soft-core sandwich beams subject to concentrated loads

Composite Structures, 2004

Although computationally simple and physically perceptible, the formula for bending deflections u... more Although computationally simple and physically perceptible, the formula for bending deflections used by the classical sandwich theory is inaccurate when applied to sandwich beams with a transversely flexible (soft) core. Two correction factors to the classical deflection formula for sandwich beams are proposed based on the higher-order theory (HSAPT) approach. The influence of changes in the geometry and mechanical properties of soft-core sandwich beams on the proposed correction factors are studied numerically. The use of the correction factors reported in the present work offers a simple and accurate way of calculating the bending deflections in soft-core sandwich beams subject to quasi-static concentrated loads, and as such can provide a valuable tool for the designer.The proposed approach also can be used for accurate determination of the core shear modulus from the measurement of compliance in short beam shear tests of sandwich beams.

Research paper thumbnail of Assessment of sandwich models for the prediction of sound transmission loss in unidirectional sandwich panels

Applied Acoustics, 2005

The consistent higher-order approach and the two-parameter foundation formulation are used for th... more The consistent higher-order approach and the two-parameter foundation formulation are used for the derivation of sound transmission loss in symmetric unidirectional (infinitely wide) sandwich panels with isotropic face sheets. In both models, transmission loss is calculated using decoupled equations representing symmetric and anti-symmetric motions of a sandwich panel. The closed-form expressions for impedances and transmission coefficient of a symmetric sandwich

Research paper thumbnail of Consistent Higher-Order Dynamic Equations for Soft-Core Sandwich Beams

AIAA Journal, 2004

ABSTRACT

Research paper thumbnail of Boundary Condition Effects in Free Vibrations of Higher-Order Soft Sandwich Beams

AIAA Journal, 2002

ABSTRACT

Research paper thumbnail of Higher-Order Buckling of Debonded (Delaminated) Sandwich Panels with Soft Core

AIAA Journal, 2000

ABSTRACT