Wrinkling in Sandwich Structures With a Functionally Graded Core

2016 ◽  
Vol 84 (2) ◽  
Author(s):  
Victor Birman ◽  
Nam Vo
Keyword(s):  
Elevated Temperature ◽  
Sandwich Structures ◽  
Mass Density ◽  
Sandwich Beam ◽  
Functionally Graded ◽  
Effect Of Temperature ◽  
Uniform Temperature ◽  
Numerical Examples ◽  
The Core ◽  
Mode Of Failure

This paper illustrates the effectiveness of a functionally graded core in preventing wrinkling in sandwich structures. The problem is solved for piecewise and continuous through-the-thickness core stiffness variations. The analysis is extended to account for the effect of temperature on wrinkling of a sandwich beam with a functionally graded core. The applicability of the developed theory is demonstrated for foam cores where the stiffness is an analytical function of the mass density. In this case, a desirable variation of the stiffness can be achieved by varying the mass density through the thickness of the core. Numerical examples demonstrate that wrinkling stability of a facing can significantly be increased using a piecewise graded core. The best results are achieved locating the layers with a higher mass density adjacent to the facing. A significant increase in the wrinkling stress can eliminate wrinkling as a possible mode of failure, without noticeably increasing the weight of the structure. In the case of a uniform temperature applied in addition to compression, wrinkling in a sandwich beam with a functionally graded core is affected both by its grading as well as by the effect of temperature on the facing and core properties. Although even a moderately elevated temperature may significantly lower the wrinkling stress, the advantage of a graded core over the homogeneous counterpart is conserved.

Wrinkling of Functionally Graded Sandwich Structures Subject to Biaxial and In-Plane Shear Loads

2017 ◽  
Vol 84 (12) ◽  
Author(s):  
Victor Birman ◽  
Harold Costa
Keyword(s):  
Uniaxial Compression ◽  
Sandwich Structures ◽  
Sandwich Panels ◽  
Shear Loading ◽  
Functionally Graded ◽  
Biaxial Compression ◽  
Equal Weight ◽  
Plane Shear ◽  
The Core ◽  
Shear Loads

Benefits of a functionally graded core increasing wrinkling stability of sandwich panels have been demonstrated in a recent paper (Birman, V., and Vo, N., 2017, “Wrinkling in Sandwich Structures With a Functionally Graded Core,” ASME J. Appl. Mech., 84(2), p. 021002), where a several-fold increase in the wrinkling stress was achieved, without a significant weight penalty, using a stiffer core adjacent to the facings. In this paper, wrinkling is analyzed in case where the facings are subject to biaxial compression and/or in-plane shear loading, and the core is arbitrary graded through the thickness. Two issues addressed are the effect of biaxial or in-plane shear loads on wrinkling stability of panels with both graded and ungraded core, and the verification that functional grading of the core remains an effective tool increasing wrinkling stability under such two-dimensional (2D) loads. As follows from the study, biaxial compression and in-plane shear cause a reduction in the wrinkling stress compared to the case of a uniaxial compression in all grading scenarios. Accordingly, even sandwich panels whose mode of failure under uniaxial compression was global buckling, the loss of strength in the facings or core crimpling may become vulnerable to wrinkling under 2D in-plane loading. It is demonstrated that a functionally graded core with the material distributed to increase the local stiffness in the interface region with the facings is effective in preventing wrinkling under arbitrary in-plane loads compared to the equal weight homogeneous core.

scholarly journals Indentation failure of foam cored sandwich structures subjected to elevated temperatures

2017 ◽  
Vol 22 (2) ◽  
pp. 325-348
Author(s):  
Tobias Laux ◽  
Ole T Thomsen
Keyword(s):  
Elevated Temperature ◽  
Analytical Model ◽  
Elevated Temperatures ◽  
Sandwich Structures ◽  
Sandwich Beam ◽  
Design Tool ◽  
Image Correlation ◽  
Winkler Foundation ◽  
Simple Analytical Model ◽  
Polymer Foam

This research explores the detrimental effect of elevated temperatures on local indentation failure of polymer foam cored sandwich structures with laminated glass fibre reinforced epoxy face sheets. A simple analytical model to predict the critical indentation failure load at elevated temperatures is presented and validated against experimental observations. For this purpose, a sandwich beam loaded in three-point bending with an induced through-thickness elevated temperature profile was studied experimentally and by means of analytical and finite element models. In the experiment, the through-thickness temperature gradient was induced with an infrared lamp pointing on the top face sheet, while the local displacement and strain fields near the applied point load were recorded by digital image correlation. The analytical model proposed, which accounts for temperature degraded/reduced foam core properties, superimposes the local response, approximated by the classical Winkler foundation model, and the global response obtained by sandwich beam theory. The comparative study has shown that the critical load causing core crushing failure reduces significantly with elevated temperatures by as much as 50% at an elevated temperature of 90℃. It is shown that the simple analytical model can predict the local deflections and core stresses of foam cored composite sandwich structures subjected to simultaneous localized mechanical loading and elevated temperatures. Thus, the analytical model can be used as a preliminary design tool to determine the critical core crushing load at elevated temperatures.

The effect of temperature variation on the free vibration of a simply supported curved sandwich beam with a flexible core

2010 ◽  
Vol 225 (3) ◽  
pp. 537-547 ◽  
Author(s):  
R A Alashti ◽  
N Kashiri
Keyword(s):  
Free Vibration ◽  
Temperature Variation ◽  
Constant Width ◽  
Sandwich Beam ◽  
Effect Of Temperature ◽  
Geometrical Parameters ◽  
Simply Supported ◽  
The Core ◽  
Free Vibration Frequency ◽  
Flexible Core

In this article, the free vibration of a singly curved sandwich beam with a transversely flexible core under various temperature conditions is investigated. The beam is assumed to have a constant width with simply supported end conditions. The core and face sheets are considered to be made of materials with temperature-dependent mechanical properties. In this model, faces of the sandwich beam are treated as thin beams with negligible shear strain and flexural rigidities obeying Bernoulli's assumptions. The analysis is based on the high-order sandwich panel theory. The core is assumed to possess vertical normal and shear stiffness and act as a medium that transfers its inertia load to face sheets. Equations of motion and boundary conditions are derived using Hamilton's principle. The variation of free vibration frequencies and eigenmodes of the beam with temperature variation considering the temperature gradient across the thickness is studied. The effect of geometrical parameters such as the ratios of the length and the thickness to the mean radius of the beam on the vibration response of the beam is investigated. It is found that the free vibration frequency of the beam would decrease when its temperature is increased.

Analytical Solution for Free Vibration of Sandwich Structures with a Functionally Graded Syntactic Foam Core

2010 ◽  
Vol 636-637 ◽  
pp. 1143-1149 ◽  
Author(s):  
O. Rahmani ◽  
K. Malekzadeh ◽  
S. Mohammad ◽  
R. Khalili
Keyword(s):  
Free Vibration ◽  
Sandwich Panel ◽  
Sandwich Structures ◽  
Numerical Study ◽  
Sandwich Beam ◽  
Syntactic Foam ◽  
Beam Theory ◽  
Functionally Graded ◽  
Foam Core ◽  
The Face

In this study, after a brief introduction to recent investigations on syntactic foam, the free vibration of sandwich structures with syntactic foam as a functionally graded flexible core based on higher order sandwich panel theory is investigated. The formulation uses the classical beam theory for the face sheets and an elasticity theory for the functionally graded core. In the following a numerical study of free vibration of a simply-supported sandwich beam is carried out and corresponding eigenmodes are obtained.

Material Selection for CFRP-Aluminium-Foam-Sandwiches Manufactured by a PUR Spraying Process

2017 ◽  
Vol 742 ◽  
pp. 317-324
Author(s):  
Peter Rupp ◽  
Peter Elsner ◽  
Kay André Weidenmann
Keyword(s):  
Manufacturing Process ◽  
Sandwich Structures ◽  
Bending Stiffness ◽  
Effective Density ◽  
Sandwich Composites ◽  
Open Cell ◽  
The Core ◽  
Bending Modulus ◽  
The Face ◽  
Spraying Process

Sandwich structures are ideal for planar parts which require a high bending stiffness ata low weight. Usually, sandwich structures are manufactured using a joining step, connecting theface sheets with the core. The PUR spraying process allows to include the infiltration of the facesheet fibres, the curing of the matrix and the joining of the face sheets to the core within one processstep. Furthermore, this manufacturing process allows for the use of open cell core structures withoutinfiltrating the core, which enables a comparison of different material configurations, assembled bythe same manufacturing process. The selection of these materials, with the aim of the lowest possiblemass of the sandwich composite at a constant bending stiffness, is displayed systematically within thiswork.It could be shown that the bending modulus calculated from the component properties matched theexperimentally achieved values well, with only few exceptions. The optimum of the bending modulus,the face sheet thickness and the resulting effective density could be calculated and also matched theexperimental values well. The mass-specific bending stiffness of the sandwich composites with corestructures of open cell aluminium foams was higher than with closed cell aluminium foams, but wasexceeded by sandwich composites with Nomex honeycomb cores.

Probabilistic Oblique Impact Analysis of Functionally Graded Plates – A Multivariate Adaptive Regression Splines Approach

2021 ◽  
Author(s):  
P. K. Karsh ◽  
Bindi Thakkar ◽  
R. R. Kumar ◽  
Vaishali ◽  
Sudip Dey
Keyword(s):  
Material Properties ◽  
Mass Density ◽  
Plate Thickness ◽  
Functionally Graded ◽  
Multivariate Adaptive Regression Splines ◽  
Low Velocity Impact ◽  
Fe Model ◽  
Low Velocity ◽  
Velocity Impact ◽  
Mars Model

Purpose: To investigate the probabilistic low-velocity impact of functionally graded (FG) plate using the MARS model, considering uncertain system parameters. Design/methodology/application: The distribution of various material properties throughout FG plate thickness is calculated using power law. For finite element (FE) formulation, isoparametric elements with eight nodes are considered, each component has five degrees of freedom. The combined effect of variability in material properties such as elastic modulus, modulus of rigidity, Poisson’s ratio, and mass density are considered. The surrogate model is validated with the FE model represented by the scatter plot and the probability density function (PDF) plot based on Monte Carlo simulation (MCS). Findings: The outcome of the degree of stochasticity, impact angle, impactor’s velocity, impactor’s mass density, and point of impact on the maximum value of contact force (CFmax ), plate deformation (PDmax), and impactor deformation (IDmax ) are determined. A convergence study is also performed to determine the optimal number of the constructed MARS model’s sample size. Originality/value: The results illustrate the significant effects of uncertain input parameters on FGM plates’ low-velocity impact responses by employing a surrogate-based MARS model.

scholarly journals Extended exposure to elevated temperature affects escape response behaviour in coral reef fishes

PeerJ ◽  
2017 ◽  
Vol 5 ◽  
pp. e3652 ◽  
Author(s):  
Donald T. Warren ◽  
Jennifer M. Donelson ◽  
Mark I. McCormick
Keyword(s):  
Elevated Temperature ◽  
Escape Response ◽  
Community Dynamics ◽  
Thermal Exposure ◽  
Reef Fishes ◽  
Effect Of Temperature ◽  
Short Term ◽  
Physical Ability ◽  
Pomacentrus Amboinensis ◽  
Extended Exposure

The threat of predation, and the prey’s response, are important drivers of community dynamics. Yet environmental temperature can have a significant effect on predation avoidance techniques such as fast-start performance observed in marine fishes. While it is known that temperature increases can influence performance and behaviour in the short-term, little is known about how species respond to extended exposure during development. We produced a startle response in two species of damselfish, the lemon damselPomacentrus moluccensis,and the Ambon damselfishPomacentrus amboinensis,by the repeated use of a drop stimulus. We show that the length of thermal exposure of juveniles to elevated temperature significantly affects this escape responses.Short-term (4d) exposure to warmer temperature affected directionality and responsiveness for both species. After long-term (90d) exposure, onlyP. moluccensisshowed beneficial plasticity, with directionality returning to control levels. Responsiveness also decreased in both species, possibly to compensate for higher temperatures. There was no effect of temperature or length of exposure on latency to react, maximum swimming speed, or escape distance suggesting that the physical ability to escape was maintained. Evidence suggests that elevated temperature may impact some fish species through its effect on the behavioural responses while under threat rather than having a direct influence on their physical ability to perform an effective escape response.

Analysis of Elasticity Solution of Bi-Direction Functionally Graded Piezoelectric Beam Subject to Voltage

2012 ◽  
Vol 166-169 ◽  
pp. 824-827 ◽  
Author(s):  
Y Z Yang
Keyword(s):  
Hamiltonian System ◽  
Exact Solutions ◽  
Material Properties ◽  
Functionally Graded ◽  
Symplectic Method ◽  
Elasticity Solution ◽  
Numerical Examples ◽  
Piezoelectric Beam ◽  
Functionally Graded Piezoelectric

This paper presents symplectic method for the derivation of exact solutions of functionally graded piezoelectric beam with the material properties varying exponentially both along the axial and transverse coordinates. In the approach, the related equations and formulas are developed in terms of dual equations, which can be solved by variables separation and symplectic expansion in Hamiltonian system. To verify advantages of the method, numerical examples of bi-directional functionally piezoelectric beam are discussed.

Sign in / Sign up

Export Citation Format

Share Document