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  • 1
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    GAMNAS- GEOMETRIC AND MATERIAL NONLINEAR ANALYSIS OF STRUCTURES (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: GAMNAS (Geometric and Material Nonlinear Analysis of Structures) is a two-dimensional finite element stress analysis program developed to support fracture mechanics studies of debonding and delamination. GAMNAS options include linear, geometric nonlinear, material nonlinear, and combined geometric and material nonlinear analysis. GAMNAS can analyze plastic deformations of isotropic materials. GAMNAS can calculate strain energy release rates using a virtual crack extension technique. The element available to the GAMMNAS user is a four-node isoparametric quadrilateral with full or reduced integration. GAMNAS has been used to investigate debonding and delamination of adhesively bonded composites. GAMNAS is written in FORTRAN 77 for batch execution and has been implemented on a PRIME 700 series computer. As currently dimensioned for a maximum global stiffness matrix of 1300 degrees of freedom and a bandwidth of 70, GAMNAS has a central memory requirement of approximately 603K of 16 bit words. GAMNAS was developed in 1983.
    Keywords: COMPOSITE MATERIALS
    Type: LAR-13279
    Format: text
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  • 2
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    Development of a laminate fatigue analysis (1980)
    In:  CASI
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    Publication Date: 2006-06-26
    Description: A fatigue analysis technique developed to predict damage growth in notched laminates is described. Features of the analysis include: criteria to relate matrix failure to cyclic stresses in and between plies; correlation of delamination growth with strain-release rate; and in-plane shear modulus change is related to cyclic shear stresses. A simplified finite element model is used to determine stresses in laminates that contain matrix damage. Failure criteria are integrated with the finite element model to form the fatigue analysis.
    Keywords: COMPOSITE MATERIALS
    Type: Selected NASA Res. in Composite Mater. and Struct.; p 79-106
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  • 3
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    A simple rectangular element for two-dimensional analysis of laminated composites (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A simple rectangular finite element was developed for two-dimensional analysis of laminated composite materials. The rectangular laminated composite element eliminates the need to add elements to a model simply to account for the material properties of various laminae. This is particularly advantageous for thick laminates with many lamina. Explicit integration in terms of generalized displacements minimizes the algebraic effort required to derive the element stiffness and the thermal load vector. A substitute shape function technique is used to improve the performance of the element in modeling bending type deformation. Results for several example problems are discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures (ISSN 0045-7949); 22; 3, 19; 387-393
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  • 4
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    Geometrically nonlinear analysis of adhesively bonded joints (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A geometrically nonlinear finite element analysis of cohesive failure in typical joints is presented. Cracked-lap-shear joints were chosen for analysis. Results obtained from linear and nonlinear analysis show that nonlinear effects, due to large rotations, significantly affect the calculated mode 1, crack opening, and mode 2, inplane shear, strain-energy-release rates. The ratio of the mode 1 to mode 2 strain-energy-release rates (G1/G2) was found to be strongly affected by the adhesive modulus and the adherend thickness. The ratios between 0.2 and 0.8 can be obtained by varying adherend thickness and using either a single or double cracked-lap-shear specimen configuration. Debond growth rate data, together with the analysis, indicate that mode 1 strain-energy-release rate governs debond growth. Results from the present analysis agree well with experimentally measured joint opening displacements. Previously announced in STAR as N83-13497
    Keywords: STRUCTURAL MECHANICS
    Type: ASME, Transactions, Journal of Engineering Materials and Technology (ISSN 0094-4289); 106; 59-65
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  • 5
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    Buckling of a sublaminate in a quasi-isotropic composite laminate (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The buckling of an elliptic delamination embedded near the surface of a thick quasi-isotropic laminate was predicted. The thickness of the delaminated ply group (the sublaminate) was assumed to be small compared to the total laminate thickness. Finite-element and Rayleigh-Ritz methods were used for the analyses. The Rayleigh-Ritz method was found to be simple, inexpensive, and accurate, except for highly anisotropic delaminated regions. Effects of delamination shape and orientation, material anisotropy, and layup on buckling strains were examined. Results show that: (1) the stress state around the delaminated region is biaxial, which may lead to buckling when the laminate is loaded in tension; (2) buckling strains for multi-directional fiber sublaminates generally are bounded by those for the 0 deg and 90 deg unidirectional sublaminates; and (3) the direction of elongation of the sublaminate that has the lowest buckling strain correlates with the delamination growth direction.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Composite Materials (ISSN 0021-9983); 19; 2-18
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  • 6
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    Parametric analytical study of instability-related delamination growth (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The effect of various parameters on instability-related delamination growth was studied analytially. The configuration studied consisted of a thick composite laminate with a single through-width delamination located near one surface. Both mechanical and thermal loads were considered. All conclusions were based on the assumption that GI and GII govern delamination growth. An approximate superposition stress analysis was developed which gives closed form expressions for GI and GII. The simplicity of the analysis permitted examination of numerous configurations. Both GI and GII were found to be very sensitive to delamination length and location through the thickness. The magnitude of GI was also very sensitive to initial imperfections, which might be the results of an inclusion of finite thickness in the delamination. Critical loads for delamination growth were calculated based on three growth criteria. Large differences in the predictions highlight the need for a verified mixed-mode delamination growth criterion.
    Keywords: COMPOSITE MATERIALS
    Type: Composites Science and Technology (ISSN 0266-3538); 25; 1, 19
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  • 7
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    Strain-energy release rate analysis of cyclic delamination growth in compressively loaded laminates (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Delamination growth in compressively loaded composite laminates was studied analytically and experimentally. The configuration used was a laminate with an across-the-width delamination. An approximate super-position stress analysis was developed to quantify the effects of various geometric, material, and load parameters on mode 1 and mode 2 strain energy release rates G sub 1 and G sub 2, respectively. Calculated values of G sub 1 and G sub 2 were then compared with measured cyclic delamination growth rates to determine the relative importance of G sub 1 and G sub 2. High growth rates were observed only when G sub 1 was large. However, slow growth was observed even when G sub 1 was negligibly small. This growth was apparently due to a large value of G sub 2.
    Keywords: STRUCTURAL MECHANICS
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  • 8
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    X-ray method shows fibers fail during fatigue of boron-epoxy laminates (1975)
    In:  Other Sources
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    Publication Date: 2011-08-16
    Description: A method proposed for studying progressive fiber fracture in boron-epoxy laminates during fatigue tests is described. It is based on the intensity of X-ray absorption of the tungsten core in the boron filaments as contrasted with that of the boron and epoxy matrix. When the laminate is X-rayed, the image of the tungsten in the born filaments is recorded on a photographic plate. Breaks in the boron laminates can be easily identified by magnifying the photographic plates. The method is suitable for studying broken boron filaments in most matrix materials, and may supply key information for developing realistic fatigue and fracture models.
    Keywords: COMPOSITE MATERIALS
    Type: Journal of Composite Materials; 9; Oct. 197
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  • 9
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    Approximate analysis of postbuckled through-width delaminations (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: (Previously announced in STAR as N81-27202)
    Keywords: STRUCTURAL MECHANICS
    Type: Composites Technology Review; 4; Fall 198
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  • 10
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    Reliability of the finite element method for calculating free edge stresses in composite laminates (1982)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The interlaminar normal stress distributions along the interface between the +45 deg and -45 deg plies of a graphite/epoxy laminate, obtained by various investigators, were found to disagree in both magnitude and sign. The reliability of the displacement-formulated finite element method in analyzing the edge-stress problem of a composite laminate is investigated. The history of the edge-stress problem is reviewed, and two well-known elasticity problems, one involving a stress discontinuity and one a singularity, are analyzed. The finite element analysis in these problems yields accurate stress distributions everywhere except in two elements closest to the stress discontinuity or singularity. Stress distributions for a + or -45 deg ply laminate near the singularity were similar to those of the two elasticity problems, demonstrating the methods, accuracy for calculating interlaminar stresses in composite laminates. The disagreement between the numerical methods was attributed to the unsymmetric stress tensor at singularity.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures; 15; 1, 19; 1982
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