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  • 1
    Electronic Resource
    Electronic Resource
    A dropped-weight apparatus for low-speed impact testing of composite structures (1995)
    Springer
    Experimental mechanics 35 (1995), S. 77-82 
    Details
    ISSN: 1741-2765
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A dropped-weight test apparatus has been developed that can be used to perform low-speed impact tests on composite aircraft structures. This vertical drop-weight test apparatus is simple, compact, inexpensive and has precision impact and self-arresting design features similar to the more sophisticated, expensive test machines. The test apparatus has been used to perform low-speed impact response studies on laminated composite plates to understand the influence of impactor and target parameters on structural response and to develop a validated analysis method. Some of the experimental results generated by using this test apparatus for composite laminated plates are presented in the present paper and compared with the corresponding analytical results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02325839
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    Paper (German National Licenses)
    Fulltext
  • 2
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    A dropped-weight apparatus for low-speed impact testing of composite structures (1995)
    Springer
    Details
    Publication Date: 1995-03-01
    Print ISSN: 0014-4851
    Electronic ISSN: 1741-2765
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Springer
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    PAPER CURRENT
  • 3
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    A stiffness tailored wing cover concept for structural efficiency and postbuckling application (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: The weight savings due to usage of composite materials in aircraft structural applications is well known. Significant weight and cost benefits are achievable by developing structurally tailored concepts and efficiently integrating them with suitable material and manufacturing technologies. The proposed paper will describe such an efficient concept for application to primary aircraft structures.
    Keywords: STRUCTURAL MECHANICS
    Type: The Third Air Force(NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization; p 353-356
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Technology integration box beam failure study (1992)
    In:  Other Sources
    Details
    Publication Date: 2013-08-29
    Description: Composite structures have the potential to be cost effective, structurally efficient primary aircraft structures. As part of the Advanced Composite Technology (ACT) program to exploit this potential for heavily loaded aircraft structures, the design and fabrication of the technology integration box beam (TIBB) was completed. The TIBB is an advanced composite prototype structure for the center wing section of the Lockheed C-130 aircraft. The TIBB was tested for downbending, upbending, torsion, and combined upbending and torsion load conditions to verify the design. The TIBB failed at 83 percent of design ultimate load for the combined upbending and torsion load condition. Current analytical and experimental results are described for a study of the mechanisms that led to the failure of the TIBB. Experimental results include load, strain, and deflection data. An analytical study was conducted of the TIBB structural response. Analytical results include strain and deflection results from a global analysis of the TIBB.
    Keywords: COMPOSITE MATERIALS
    Type: Second NASA Advanced Composites Technology Conference; p 99-111
    Format: text
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  • 5
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    Nonlinear Analysis of Bonded Composite Single-LAP Joints (2004)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: This study presents a semi-analytical solution method to analyze the geometrically nonlinear response of bonded composite single-lap joints with tapered adherend edges under uniaxial tension. The solution method provides the transverse shear and normal stresses in the adhesive and in-plane stress resultants and bending moments in the adherends. The method utilizes the principle of virtual work in conjunction with von Karman s nonlinear plate theory to model the adherends and the shear lag model to represent the kinematics of the thin adhesive layer between the adherends. Furthermore, the method accounts for the bilinear elastic material behavior of the adhesive while maintaining a linear stress-strain relationship in the adherends. In order to account for the stiffness changes due to thickness variation of the adherends along the tapered edges, their in-plane and bending stiffness matrices are varied as a function of thickness along the tapered region. The combination of these complexities results in a system of nonlinear governing equilibrium equations. This approach represents a computationally efficient alternative to finite element method. Comparisons are made with corresponding results obtained from finite-element analysis. The results confirm the validity of the solution method. The numerical results present the effects of taper angle, adherend overlap length, and the bilinear adhesive material on the stress fields in the adherends, as well as the adhesive, of a single-lap joint
    Keywords: Numerical Analysis
    Type: AIAA Paper 2004-1560
    Format: application/pdf
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  • 6
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    Combined In-Plane and Through-the-Thickness Analysis for Failure Prediction of Bolted Composite Joints (2004)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Although two-dimensional methods provide accurate predictions of contact stresses and bolt load distribution in bolted composite joints with multiple bolts, they fail to capture the effect of thickness on the strength prediction. Typically, the plies close to the interface of laminates are expected to be the most highly loaded, due to bolt deformation, and they are usually the first to fail. This study presents an analysis method to account for the variation of stresses in the thickness direction by augmenting a two-dimensional analysis with a one-dimensional through the thickness analysis. The two-dimensional in-plane solution method based on the combined complex potential and variational formulation satisfies the equilibrium equations exactly, and satisfies the boundary conditions and constraints by minimizing the total potential. Under general loading conditions, this method addresses multiple bolt configurations without requiring symmetry conditions while accounting for the contact phenomenon and the interaction among the bolts explicitly. The through-the-thickness analysis is based on the model utilizing a beam on an elastic foundation. The bolt, represented as a short beam while accounting for bending and shear deformations, rests on springs, where the spring coefficients represent the resistance of the composite laminate to bolt deformation. The combined in-plane and through-the-thickness analysis produces the bolt/hole displacement in the thickness direction, as well as the stress state in each ply. The initial ply failure predicted by applying the average stress criterion is followed by a simple progressive failure. Application of the model is demonstrated by considering single- and double-lap joints of metal plates bolted to composite laminates.
    Keywords: Composite Materials
    Type: AIAA Paper 2004-1703 , 45th AIAA/ASME/AHS/ASC Structures, Structural Dynamics and Materials Conference; Apr 19, 2004 - Apr 22, 2004; Palm Springs, CA; United States
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  • 7
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    Thermo-Elastic Triangular Sandwich Element for the Complete Stress Field Based on a Single-Layer Theory (2004)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This study presents a new triangular finite element for modeling thick sandwich panels, subjected to thermo-mechanical loading, based on a {3,2}-order single-layer plate theory. A hybrid energy functional is employed in the derivation of the element because of a C interelement continuity requirement. The single-layer theory is based on five weighted-average field variables arising from the cubic and quadratic representations of the in-plane and transverse displacement fields, respectively. The variations of temperature and distributed loading acting on the top and bottom surfaces are non-uniform. The temperature varies linearly through the thickness.
    Keywords: Structural Mechanics
    Type: AIAA Paper 2004-1770 , 45th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference; Apr 19, 2004 - Apr 22, 2004; Palm Springs, CA; United States
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  • 8
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    Nonlinear Analysis of Bonded Composite Tubular Lap Joints (2005)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The present study describes a semi-analytical solution method for predicting the geometrically nonlinear response of a bonded composite tubular single-lap joint subjected to general loading conditions. The transverse shear and normal stresses in the adhesive as well as membrane stress resultants and bending moments in the adherends are determined using this method. The method utilizes the principle of virtual work in conjunction with nonlinear thin-shell theory to model the adherends and a cylindrical shear lag model to represent the kinematics of the thin adhesive layer between the adherends. The kinematic boundary conditions are imposed by employing the Lagrange multiplier method. In the solution procedure, the displacement components for the tubular joint are approximated in terms of non-periodic and periodic B-Spline functions in the longitudinal and circumferential directions, respectively. The approach presented herein represents a rapid-solution alternative to the finite element method. The solution method was validated by comparison against a previously considered tubular single-lap joint. The steep variation of both peeling and shearing stresses near the adhesive edges was successfully captured. The applicability of the present method was also demonstrated by considering tubular bonded lap-joints subjected to pure bending and torsion.
    Keywords: Mechanical Engineering
    Type: 46th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference; Apr 18, 2005 - Apr 21, 2005; Austin, TX; United States
    Format: text
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  • 9
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    Optimal Design of General Stiffened Composite Circular Cylinders for Global Buckling with Strength Constraints (1998)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A design strategy for optimal design of composite grid-stiffened cylinders subjected to global and local buckling constraints and strength constraints was developed using a discrete optimizer based on a genetic algorithm. An improved smeared stiffener theory was used for the global analysis. Local buckling of skin segments were assessed using a Rayleigh-Ritz method that accounts for material anisotropy. The local buckling of stiffener segments were also assessed. Constraints on the axial membrane strain in the skin and stiffener segments were imposed to include strength criteria in the grid-stiffened cylinder design. Design variables used in this study were the axial and transverse stiffener spacings, stiffener height and thickness, skin laminate stacking sequence and stiffening configuration, where stiffening configuration is a design variable that indicates the combination of axial, transverse and diagonal stiffener in the grid-stiffened cylinder. The design optimization process was adapted to identify the best suited stiffening configurations and stiffener spacings for grid-stiffened composite cylinder with the length and radius of the cylinder, the design in-plane loads and material properties as inputs. The effect of having axial membrane strain constraints in the skin and stiffener segments in the optimization process is also studied for selected stiffening configurations.
    Keywords: Composite Materials
    Type: Composite Structures (ISSN 0263-8223); 41; 243-252
    Format: application/pdf
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  • 10
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    Low-Velocity Impact Response of Sandwich Beams with Functionally Graded Core (2006)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The problem of low-speed impact of a one-dimensional sandwich panel by a rigid cylindrical projectile is considered. The core of the sandwich panel is functionally graded such that the density, and hence its stiffness, vary through the thickness. The problem is a combination of static contact problem and dynamic response of the sandwich panel obtained via a simple nonlinear spring-mass model (quasi-static approximation). The variation of core Young's modulus is represented by a polynomial in the thickness coordinate, but the Poisson's ratio is kept constant. The two-dimensional elasticity equations for the plane sandwich structure are solved using a combination of Fourier series and Galerkin method. The contact problem is solved using the assumed contact stress distribution method. For the impact problem we used a simple dynamic model based on quasi-static behavior of the panel - the sandwich beam was modeled as a combination of two springs, a linear spring to account for the global deflection and a nonlinear spring to represent the local indentation effects. Results indicate that the contact stiffness of thc beam with graded core Increases causing the contact stresses and other stress components in the vicinity of contact to increase. However, the values of maximum strains corresponding to the maximum impact load arc reduced considerably due to grading of thc core properties. For a better comparison, the thickness of the functionally graded cores was chosen such that the flexural stiffness was equal to that of a beam with homogeneous core. The results indicate that functionally graded cores can be used effectively to mitigate or completely prevent impact damage in sandwich composites.
    Keywords: Composite Materials
    Type: International Journal of Solids and Structures (ISSN 0020-7683); 43; 2479-2496
    Format: text
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