3,885 research outputs found
A parametric study on the buckling of functionally graded material plates with internal discontinuities using the partition of unity method
In this paper, the effect of local defects, viz., cracks and cutouts on the
buckling behaviour of functionally graded material plates subjected to
mechanical and thermal load is numerically studied. The internal
discontinuities, viz., cracks and cutouts are represented independent of the
mesh within the framework of the extended finite element method and an enriched
shear flexible 4-noded quadrilateral element is used for the spatial
discretization. The properties are assumed to vary only in the thickness
direction and the effective properties are estimated using the Mori-Tanaka
homogenization scheme. The plate kinematics is based on the first order shear
deformation theory. The influence of various parameters, viz., the crack length
and its location, the cutout radius and its position, the plate aspect ratio
and the plate thickness on the critical buckling load is studied. The effect of
various boundary conditions is also studied. The numerical results obtained
reveal that the critical buckling load decreases with increase in the crack
length, the cutout radius and the material gradient index. This is attributed
to the degradation in the stiffness either due to the presence of local defects
or due to the change in the material composition.Comment: arXiv admin note: text overlap with arXiv:1301.2003, arXiv:1107.390
Adaptive unstructured meshing for thermal stress analysis of built-up structures
An adaptive unstructured meshing technique for mechanical and thermal stress analysis of built-up structures has been developed. A triangular membrane finite element and a new plate bending element are evaluated on a panel with a circular cutout and a frame stiffened panel. The adaptive unstructured meshing technique, without a priori knowledge of the solution to the problem, generates clustered elements only where needed. An improved solution accuracy is obtained at a reduced problem size and analysis computational time as compared to the results produced by the standard finite element procedure
Global/local stress analysis of composite panels
A method for performing a global/local stress analysis is described, and its capabilities are demonstrated. The method employs spline interpolation functions which satisfy the linear plate bending equation to determine displacements and rotations from a global model which are used as boundary conditions for the local model. Then, the local model is analyzed independent of the global model of the structure. This approach can be used to determine local, detailed stress states for specific structural regions using independent, refined local models which exploit information from less-refined global models. The method presented is not restricted to having a priori knowledge of the location of the regions requiring local detailed stress analysis. This approach also reduces the computational effort necessary to obtain the detailed stress state. Criteria for applying the method are developed. The effectiveness of the method is demonstrated using a classical stress concentration problem and a graphite-epoxy blade-stiffened panel with a discontinuous stiffener
Design of anisotropic plates for improved damage tolerance
An analytical study is presented showing the effects of the notch tip geometry on the location and direction of crack growth from an existing notch in a unidirectional fibrous composite modeled as a homogeneous, anisotropic, elastic material. Anisotropic elasticity and the normal stress ratio theory are used to study crack growth from elliptical notches in unidirectional composites. Sharp cracks, circular holes, and ellipses are studied under far-field tension and shear loading. The capabilities of a previously developed design code was upgraded to handle more generalized plate geometries and laminates under a more generalized loading and boundary conditions. Discussion of the developments of the design code is presented
Cutout reinforcements for shear loaded laminate and sandwich composite panels
This paper presents the numerical and experimental studies of shear loaded
laminated and sandwich carbon/epoxy composite panels with cutouts and
reinforcements aiming at reducing the cutout stress concentration and increasing
the buckling stability of the panels. The effect of different cutout sizes and
the design and materials of cutout reinforcements on the stress and buckling
behaviour of the panels are evaluated. For the sandwich panels with a range of
cutout size and a constant weight, an optimal ratio of the core to the face
thickness has been studied for the maximum buckling stability. The finite
element method and an analytical method are employed to perform parametric
studies. In both constant stress and constant displacement shear loading
conditions, the results are in very good agreement with those obtained from
experiment for selected cutout reinforcement cases. Conclusions are drawn on the
cutout reinforcement design and improvement of stress concentration and buckling
behaviour of shear loaded laminated and sandwich composite panels with cutouts
Compressive Failure Behaviour of Kevlar Epoxy and Glass Epoxy Composite Laminates Due to the Effect of Cutout Shape and Size with Variation in Fiber Orientations
The increasing trend of constructing components made of composite laminates is due to the flexibility in tailoring their properties and high strength-to-weight ratio. Nevertheless, most practical components involve cutout features for fastening and these cutouts could reduce significantly the strength of the laminate. Due to its importance, many studies were conducted to study the effect of circular cutouts however, there is lack of information regarding the effect of various cutout shapes. Therefore, this study aims to investigate the compressive failure behavior of Kevlar Epoxy and Glass Epoxy composite laminates due to the effect of cutout shape and size with variation in fiber orientations. Finite element software, ANSYS were used to simulate the deformation and failure behavior of the laminates under compressive load. Prior to that, mesh convergence analysis and numerical validation were performed. Failure analysis was conducted for various cutout shapes (square cutout, diamond cutout, and circular) and size, based on Maximum Stress Theory. The results show that the existence of the cutouts on the composite laminates have reduced up to ten times the strength of the laminated composite plates. This information in regards to the failure behavior is important when designing components made of composite laminates under compression
Detailed analysis and test correlation of a stiffened composite wing panel
Nonlinear finite element analysis techniques are evaluated by applying them to a realistic aircraft structural component. A wing panel from the V-22 tiltrotor aircraft is chosen because it is a typical modern aircraft structural component for which there is experimental data for comparison of results. From blueprints and drawings supplied by the Bell Helicopter Textron Corporation, a very detailed finite element model containing 2284 9-node Assumed Natural-Coordinate Strain (ANS) elements was generated. A novel solution strategy which accounts for geometric nonlinearity through the use of corotating element reference frames and nonlinear strain displacements relations is used to analyze this detailed model. Results from linear analyses using the same finite element model are presented in order to illustrate the advantages and costs of the nonlinear analysis as compared with the more traditional linear analysis. Strain predictions from both the linear and nonlinear stress analyses are shown to compare well with experimental data up through the Design Ultimate Load (DUL) of the panel. However, due to the extreme nonlinear response of the panel, the linear analysis was not accurate at loads above the DUL. The nonlinear analysis more accurately predicted the strain at high values of applied load, and even predicted complicated nonlinear response characteristics, such as load reversals, at the observed failure load of the test panel. In order to understand the failure mechanism of the panel, buckling and first ply failure analyses were performed. The buckling load was 17 percent above the observed failure load while first ply failure analyses indicated significant material damage at and below the observed failure load
Fast, accurate solutions for curvilinear earthquake faults and anelastic strain
Imaging the anelastic deformation within the crust and lithosphere using
surface geophysical data remains a significant challenge in part due to the
wide range of physical processes operating at different depths and to various
levels of localization that they embody. Models of Earth's elastic properties
from seismological imaging combined with geodetic modeling may form the basis
of comprehensive rheological models of Earth's interior. However, representing
the structural complexity of faults and shear zones in numerical models of
deformation still constitutes a major difficulty. Here, we present numerical
techniques for high-precision models of deformation and stress around both
curvilinear faults and volumes undergoing anelastic (irreversible) strain in a
heterogenous elastic half-space. To that end, we enhance the software Gamra to
model triangular and rectangular fault patches and tetrahedral and cuboidal
strain volumes. This affords a means of rapid and accurate calculations of
elasto-static Green's functions for localized (e.g., faulting) and distributed
(e.g., viscoelastic) deformation in Earth's crust and lithosphere. We
demonstrate the correctness of the method with analytic tests, and we
illustrate its practical performance by solving for coseismic and postseismic
deformation following the 2015 Mw 7.8 Gorkha, Nepal earthquake to extremely
high precision
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