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  • 1
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    A procedure for superposing linear cohesive laws to represent multiple damage mechanisms in the fracture of composites (2009)
    Springer
    Details
    Publication Date: 2009-06-30
    Print ISSN: 0376-9429
    Electronic ISSN: 1573-2673
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Springer
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    PAPER CURRENT
  • 2
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    Stable Tearing and Buckling Responses of Unstiffened Aluminum Shells with Long Cracks (1999)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The results of an analytical and experimental study of the nonlinear response of thin, unstiffened, aluminum cylindrical shells with a long longitudinal crack are presented. The shells are analyzed with a nonlinear shell analysis code that accurately accounts for global and local structural response phenomena. Results are presented for internal pressure and for axial compression loads. The effect of initial crack length on the initiation of stable crack growth and unstable crack growth in typical shells subjected to internal pressure loads is predicted using geometrically nonlinear elastic-plastic finite element analyses and the crack-tip-opening angle (CTOA) fracture criterion. The results of these analyses and of the experiments indicate that the pressure required to initiate stable crack growth and unstable crack growth in a shell subjected to internal pressure loads decreases as the initial crack length increases. The effects of crack length on the prebuckling, buckling and postbuckling responses of typical shells subjected to axial compression loads are also described. For this loading condition, the crack length was not allowed to increase as the load was increased. The results of the analyses and of the experiments indicate that the initial buckling load and collapse load for a shell subjected to axial compression loads decrease as the initial crack length increases. Initial buckling causes general instability or collapse of a shell for shorter initial crack lengths. Initial buckling is a stable local response mode for longer initial crack lengths. This stable local buckling response is followed by a stable postbuckling response, which is followed by general or overall instability of the shell.
    Keywords: Structural Mechanics
    Type: The Second Joint NASA/FAA/DoD Conference on Aging Aircraft; Pt. 2; 610-626; NASA/CP-1999-208982/PT2
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    NASA TECHNICAL REPORTS
  • 3
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    Nonlinear Local Bending Response and Bulging Factors for Longitudinal and Circumferential Cracks in Pressurized Cylindrical Shells (2000)
    In:  CASI
    Details
    Publication Date: 2018-06-05
    Description: Results of a geometrically nonlinear finite element parametric study to determine curvature correction factors or bulging factors that account for increased stresses due to curvature for longitudinal and circumferential cracks in unstiffened pressurized cylindrical shells are presented. Geometric parameters varied in the study include the shell radius, the shell wall thickness, and the crack length. The major results are presented in the form of contour plots of the bulging factor as a function of two nondimensional parameters: the shell curvature parameter, lambda, which is a function of the shell geometry, Poisson's ratio, and the crack length; and a loading parameter, eta, which is a function of the shell geometry, material properties, and the applied internal pressure. These plots identify the ranges of the shell curvature and loading parameters for which the effects of geometric nonlinearity are significant. Simple empirical expressions for the bulging factor are then derived from the numerical results and shown to predict accurately the nonlinear response of shells with longitudinal and circumferential cracks. The numerical results are also compared with analytical solutions based on linear shallow shell theory for thin shells, and with some other semi-empirical solutions from the literature, and limitations on the use of these other expressions are suggested.
    Keywords: Structural Mechanics
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    NASA TECHNICAL REPORTS
  • 4
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    Nonlinear Response of Thin Cylindrical Shells with Longitudinal Cracks and Subjected to Internal Pressure and Axial compression Loads (1998)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The results of an analytical study of the nonlinear response of a thin unstiffened aluminum cylindrical shell with a longitudinal crack are presented. The shell is analyzed with a nonlinear shell analysis code that maintains the shell in a nonlinear equilibrium state while the crack is grown. The analysis accurately accounts for global and local structural response phenomena. Results are presented for internal pressure, axial compression, and combined internal pressure and axial compression loads. The effects of varying crack length on the nonlinear response of the shell subjected to internal pressure are described. The effects of varying crack length on the prebuckling, buckling and postbuckling responses of the shell subjected to axial compression, and subjected to combined internal pressure and axial compression are also described. The results indicate that the nonlinear interaction between the in-plane stress resultants and the out-of-plane displacements near a crack can significantly affect the structural response of the shell. The results also indicate that crack growth instabilities and shell buckling instabilities can both affect the response of the shell as the crack length is increased.
    Keywords: Structural Mechanics
    Type: AIAA Paper 97-1144 , Stability Analysis of Plates and Shells; 197-207; NASA/CP-1998-206280
    Format: text
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    NASA TECHNICAL REPORTS
  • 5
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    Advances in Structural Integrity Analysis Methods for Aging Metallic Airframe Structures with Local Damage (2003)
    In:  CASI
    Details
    Publication Date: 2018-06-27
    Description: Analysis methodologies for predicting fatigue-crack growth from rivet holes in panels subjected to cyclic loads and for predicting the residual strength of aluminum fuselage structures with cracks and subjected to combined internal pressure and mechanical loads are described. The fatigue-crack growth analysis methodology is based on small-crack theory and a plasticity induced crack-closure model, and the effect of a corrosive environment on crack-growth rate is included. The residual strength analysis methodology is based on the critical crack-tip-opening-angle fracture criterion that characterizes the fracture behavior of a material of interest, and a geometric and material nonlinear finite element shell analysis code that performs the structural analysis of the fuselage structure of interest. The methodologies have been verified experimentally for structures ranging from laboratory coupons to full-scale structural components. Analytical and experimental results based on these methodologies are described and compared for laboratory coupons and flat panels, small-scale pressurized shells, and full-scale curved stiffened panels. The residual strength analysis methodology is sufficiently general to include the effects of multiple-site damage on structural behavior.
    Keywords: Aeronautics (General)
    Type: Ageing Mechanisms and Control: Specialists' Meeting on Life Management Techniques for Ageing Air Vehicles; 27-1 - 27-16; RTO-MP-079(II)
    Format: text
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    NASA TECHNICAL REPORTS
  • 6
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    An approximate solution for interlaminar stresses in laminated composites: Applied mechanics program (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An approximate solution for interlaminar stresses in finite width, laminated composites subjected to uniform extensional, and bending loads is presented. The solution is based upon the principle of minimum complementary energy and an assumed, statically admissible stress state, derived by considering local material mismatch effects and global equilibrium requirements. The stresses in each layer are approximated by polynomial functions of the thickness coordinate, multiplied by combinations of exponential functions of the in-plane coordinate, expressed in terms of fourteen unknown decay parameters. Imposing the stationary condition of the laminate complementary energy with respect to the unknown variables yields a system of fourteen non-linear algebraic equations for the parameters. Newton's method is implemented to solve this system. Once the parameters are known, the stresses can be easily determined at any point in the laminate. Results are presented for through-thickness and interlaminar stress distributions for angle-ply, cross-ply (symmetric and unsymmetric laminates), and quasi-isotropic laminates subjected to uniform extension and bending. It is shown that the solution compares well with existing finite element solutions and represents an improved approximate solution for interlaminar stresses, primarily at interfaces where global equilibrium is satisfied by the in-plane stresses, but large local mismatch in properties requires the presence of interlaminar stresses.
    Keywords: COMPOSITE MATERIALS
    Type: NASA-CR-190537 , NAS 1.26:190537 , AM-92-02
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    NASA TECHNICAL REPORTS
  • 7
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    Effects of Combined Loads on the Nonlinear Response and Residual Strength of Damaged Stiffened Shells (1996)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The results of an analytical study of the nonlinear response of stiffened fuselage shells with long cracks are presented. The shells are modeled with a hierarchical modeling strategy and analyzed with a nonlinear shell analysis code that maintains the shell in a nonlinear equilibrium state while the crack is grown. The analysis accurately accounts for global and local structural response phenomena. Results are presented for various combinations of internal pressure and mechanical loads, and the effects of crack orientation on the shell response are described. The effects of combined loading conditions and the effects of varying structural parameters on the stress-intensity factors associated with a crack are presented.
    Keywords: Structural Mechanics
    Type: FAA-NASA Symposium on Continued Airworthiness of Aircraft Structures; Aug 28, 1996 - Aug 30, 1996; Atlanta, GA; United States
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  • 8
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    Experimental Evaluation of Fatigue Damage Progression in Postbuckled Single Stringer Composite Specimens (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The durability and damage tolerance of postbuckled composite structures are not yet completely understood, and remain difficult to predict due to the nonlinearity of the geometric response and its interaction with local damage modes. A research effort was conducted to investigate experimentally the quasi-static and fatigue damage progression in a single-stringer compression (SSC) specimen. Three specimens were manufactured with a hat-stiffener, and an initial defect was introduced with a Teflon film embedded between one flange of the stringer and the skin. One of the specimens was tested under quasi-static compressive loading, while the remaining two specimens were tested by cycling in postbuckling. The tests were performed at the NASA Langley Research Center under controlled conditions and with instrumentation that allows a precise evaluation of the postbuckling response and of the damage modes. Three-dimensional digital image correlation VIC-3D systems were used to provide full field displacements and strains on the skin and the stringer. Passive thermal monitoring was conducted during the fatigue tests using an infrared camera that showed the location of the delamination front while the specimen was being cycled. The live information from the thermography was used to stop the fatigue tests at critical stages of the damage evolution to allow detailed ultrasonic scans.
    Keywords: Composite Materials; Structural Mechanics; Quality Assurance and Reliability
    Type: NF1676L-18235 , US-Japan Conference on Composite Materials, ASTM-D30 Joint Conference; Sep 08, 2014 - Sep 11, 2014; La Jolla, CA; United States|ASTM-D30 Committee Meeting; Sep 08, 2014 - Sep 11, 2014; La Jolla, CA; United States|American Society for Composites Technical Conference, 16th US-Japan Conference on Composite Materials, ASTM-D30 Joint Conference; Sep 08, 2014 - Sep 11, 2014; La Jolla, CA; United States
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  • 9
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    STAGS Developments for Residual Strength Analysis Methods for Metallic Fuselage Structures (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A summary of advances in the Structural Analysis of General Shells (STAGS) finite element code for the residual strength analysis of metallic fuselage structures, that were realized through collaboration between the structures group at NASA Langley, and Dr. Charles Rankin is presented. The majority of the advancements described were made in the 1990's under the NASA Airframe Structural Integrity Program (NASIP). Example results from studies that were conducted using the STAGS code to develop improved understanding of the nonlinear response of cracked fuselage structures subjected to combined loads are presented. An integrated residual strength analysis methodology for metallic structure that models crack growth to predict the effect of cracks on structural integrity is demonstrated
    Keywords: Structural Mechanics; Aircraft Design, Testing and Performance
    Type: AIAA Paper 2014-0848 , NF1676L-16748 , AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference; Jan 13, 2014 - Jan 17, 2014; National Harbor, MD; United States
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  • 10
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    Experimental Study of the Compression Response of Fluted-Core Composite Panels with Joints (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Fluted-core sandwich composites consist of integral angled web members spaced between laminate face sheets, and may have the potential to provide benefits over traditional sandwich composites for certain aerospace applications. However, fabrication of large autoclave-cured fluted-core cylindrical shells with existing autoclaves will require that the shells be fabricated in segments, and joined longitudinally to form a complete barrel. Two different longitudinal fluted-core joint designs were considered experimentally in this study. In particular, jointed fluted-core-composite panels were tested in longitudinal compression because longitudinal compression is the primary loading condition in dry launch-vehicle barrel sections. One of the joint designs performed well in comparison with unjointed test articles, and the other joint design failed at loads approximately 14% lower than unjointed test articles. The compression-after-impact (CAI) performance of jointed fluted-core composites was also investigated by testing test articles that had been subjected to 6 ft-lb impacts. It was found that such impacts reduced the load-carrying capability by 9% to 40%. This reduction is dependent on the joint concept, component flute size, and facesheet thickness.
    Keywords: Structural Mechanics
    Type: AIAA Paper-2012-1690 , NF1676L-13195 , 53rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference; Apr 23, 2012 - Apr 26, 2012; Honolulu, HI; United States
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