1.
Effect of low-speed impact damage and damage location on behavior of composite panels
Document ID: 19950022060
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Author: Jegley, Dawn
Abstract: An investigation of the effects of low-speed
impact damage on the compression and tension strength
of thin (less than .05 inches thick) and moderately thick (between .12 and .17 inches thick) composite specimens was conducted. Impact speeds ranged from 50 to 550 ft/sec (impact energies from .25 to 30.7 ft-lb) and impact locations were near or away from a lateral unloaded edge. In this study, thin tension-loaded or compression-loaded specimens with only 90 deg and +/- 40 deg plies which were impact ed away from the unloaded edge suffered less reduction in maximum load-carrying capability due to impact damage than the same specimens impact ed near the unloaded edge. Unlike the thin laminates, failure loads of thicker compression-loaded specimens with a similar stacking sequence were independent of impact location. Failure loads of thin tension-loaded specimens with 0 deg plies were independent of impact location while failure loads of thicker compression-loaded specimens with 0 deg plies were dependent upon impact location. A finite-element analysis of strain distributions across the panel width indicated that high axial strains occur near the unloaded edges of postbuckled panels, indicating that impact s near the unloaded edge would significantly effect the behavior of postbuckled panels.
Publication Year: 1992
Document Type: Conference Paper
Date Acquired: Dec 28, 1995
2.
Compression of thick laminated composite beams with initial impact -like damage
Document ID: 19920023247
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Author: Breivik, N. L.; Guerdal, Z.; Griffin, O. H., Jr.
Abstract: While the study of compression after
impact of laminated
composite s has been under consideration for
many years, the complexity of the damage initiated by low velocity impact has not lent itself to simple predictive models for compression strength. The damage modes due to non-penetrating, low velocity impact by large diameter objects can be simulated using quasi-static three-point bending. The resulting damage modes are less coupled and more easily characterized than actual impact damage modes. This study includes the compression testing of specimens with well documented initial damage states obtained from three-point bend testing. Compression strengths and failure modes were obtained for quasi-isotropic stacking sequences from 0.24 to 1.1 inches thick with both grouped and interspersed ply stacking. Initial damage prior to compression testing was divided into four classifications based on the type, extent, and location of the damage . These classifications are multiple through-thickness delaminations, isolated delamination, damage near the surface, and matrix cracks. Specimens from each classification were compared to specimens tested without initial damage in order to determine the effects of the initial damage on the final compression strength and failure modes. A finite element analysis was used to aid in the understanding and explanation of the experimental results.
Publication Year: 1992
Document Type: Technical Report
Report/Patent Number: NASA-CR-190573, NAS 1.26:190573, PB92-213487, VPI-E-92-15, CCMS-92-16
Date Acquired: Nov 07, 1995
3.
Effect of low-speed impact damage and damage location on behavior of composite panels
Document ID: 19920014738
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Author: Jegley, Dawn C.
Abstract: The effect of low speed
impact damage on the compression and tension strength of thin and moderately
thick composite specimens was investigated. Impact speed ranged from 50 to 550 ft./sec., with corresponding impact energies from 0.25 to 30.7 ft. x lb. Impact locations were near the center of the specimen or near a lateral unloaded edge. In this study, thin specimens with only 90 degree and + or - 45 degree plies that were impact ed away from the unloaded edge suffered less reduction in load carrying capability because of impact damage than of the same specimens impact ed near the unloaded edge. Failure loads of thicker compression loaded specimens with a similar stacking sequence were independent of impact location. Failure loads of thin tension loaded specimens with 0 degree plies was independent of impact location, whereas failure loads of thicker compression loaded specimens with 0 degree plies were dependent upon impact location. A finite element analysis indicated that high axial strains occurred near the unloaded edges of the postbuckled panels. Thus, impact s near the unloaded edge would significantly affect the behavior of the postbuckled panel.
Publication Year: 1992
Document Type: Conference Paper
Report/Patent Number: NASA-TP-3196, L-17031, NAS 1.60:3196
Date Acquired: Nov 07, 1995
4.
Investigation of low velocity impact damage on filamentary composite materials
Document ID: 19880006225
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Author: Bower, Mark V.
Abstract: Presented are the results of an investigation of the effect of low velocity
impact on the residual
modulus and residual strength of flat filamentary composite materials. Theoretical analysis of composite materials indicates that the modulus of the material must decrease as impact damage increases. This decrease must also correlate to the decrease in residual strength. This study attempts to verify these hypotheses. Graphite/epoxy laminates (AS4/3501-6) of various fiber orientations (8 (0 deg), 2 (+ or - 45 deg)sub 8) were impact ed using a falling weight impact tester. Impact energies ranged from 0.42 to 1.55 ft-lb, with impact velocities from 2.03 to 3.98 ft/sec. The results show that there is a reduction in residual modulus of the plate as the impact energy increases.
Publication Year: 1987
Document Type: Conference Paper
Date Acquired: Nov 04, 1995
5.
The influence of lay-up and thickness on composite impact damage and compression strength
Document ID: 19850048095
Author: Guynn, E. G.; Obrien, T. K.
Abstract: The effects of
composite stacking sequence, thickness, and percentage of zero-degree plies on the
size, shape, and distribution of delamination through the laminate thickness and on residual compression strength following impact were studied. Graphite/epoxy laminates were impact ed with an 0.5 inch diameter aluminum sphere at a specific low or high velocity. Impact damage was measured nondestructively by ultrasonic C-scans and X-radiography and destructively by the deply technique, and compression strength tests were performed. It was found that differences in compression failure strain due to stacking sequence were small, while laminates with very low percentages of zero-degree plies had similar failure loads but higher failure strains than laminates with higher percentages of zero-degree plies. Failure strain did not correlate with planar impact damage area, and delaminations in impact regions were associated with matrix cracking.
Publication Year: 1985
Document Type: Conference Paper
Report/Patent Number: AIAA PAPER 85-0646
Date Acquired: Nov 28, 1995
6.
Analysis and Characterization of Damage and Failure Utilizing a Generalized Composite Material Model Suitable for Use in Impact Problems
Document ID: 20170001285
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Author: Goldberg, Robert K.; Carney, Kelly S.; DuBois, Paul; Khaled, Bilal; Hoffarth, Canio; Rajan, Subramaniam; Blankenhorn, Gunther
Abstract: A material model which incorporates several key capabilities which have been identified by the
aerospace community as lacking in state-of-the art composite impact models is under development. In particular, a next generation composite impact material model, jointly developed by the FAA and NASA, is being implemented into the commercial transient dynamic finite element code LS-DYNA. The material model, which incorporates plasticity, damage , and failure, utilizes experimentally based tabulated input to define the evolution of plasticity and damage and the initiation of failure as opposed to specifying discrete input parameters (such as modulus and strength). The plasticity portion of the orthotropic, three-dimensional, macroscopic composite constitutive model is based on an extension of the Tsai-Wu composite failure model into a generalized yield function with a non-associative flow rule. For the damage model, a strain equivalent formulation is utilized to allow for the uncoupling of the deformation and damage analyses. In the damage model, a semi-coupled approach is employed where the overall damage in a particular coordinate direction is assumed to be a multiplicative combination of the damage in that direction resulting from the applied loads in the various coordinate directions. Due to the fact that the plasticity and damage models are uncoupled, test procedures and methods to both characterize the damage model and to covert the material stress-strain curves from the true (damage d) stress space to the effective (undamage d) stress space have been developed. A methodology has been developed to input the experimentally determined composite failure surface in a tabulated manner. An analytical approach is then utilized to track how close the current stress state is to the failure surface.
Publication Year: 2016
Document Type: Conference Paper
Report/Patent Number: GRC-E-DAA-TN33972
Date Acquired: Feb 07, 2017
7.
Incorporation of Damage and Failure into an Orthotropic Elasto-Plastic Three-Dimensional Model with Tabulated Input Suitable for Use in Composite Impact Problems
Document ID: 20160014871
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Author: Goldberg, Robert K.; Carney, Kelly S.; Dubois, Paul; Hoffarth, Canio; Khaled, Bilal; Rajan, Subramaniam; Blankenhorn, Gunther
Abstract: A material model which incorporates several key capabilities which have been identified by the
aerospace community as lacking in the composite impact models currently available in LS-DYNA(Registered Trademark) is under development. In particular, the material model, which is being implemented as MAT 213 into a tailored version of LS-DYNA being jointly developed by the FAA and NASA, incorporates both plasticity and damage within the material model, utilizes experimentally based tabulated input to define the evolution of plasticity and damage as opposed to specifying discrete input parameters (such as modulus and strength), and is able to analyze the response of composite s composed with a variety of fiber architectures. The plasticity portion of the orthotropic, three-dimensional, macroscopic composite constitutive model is based on an extension of the Tsai-Wu composite failure model into a generalized yield function with a non-associative flow rule. The capability to account for the rate and temperature dependent deformation response of composite s has also been incorporated into the material model. For the damage model, a strain equivalent formulation is utilized to allow for the uncoupling of the deformation and damage analyses. In the damage model, a diagonal damage tensor is defined to account for the directionally dependent variation of damage . However, in composite s it has been found that loading in one direction can lead to damage in multiple coordinate directions. To account for this phenomena, the terms in the damage matrix are semi-coupled such that the damage in a particular coordinate direction is a function of the stresses and plastic strains in all of the coordinate directions. The onset of material failure, and thus element deletion, is being developed to be a function of the stresses and plastic strains in the various coordinate directions. Systematic procedures are being developed to generate the required input parameters based on the results of experimental tests.
Publication Year: 2016
Document Type: Conference Paper
Report/Patent Number: GRC-E-DAA-TN30477
Date Acquired: Jan 03, 2017
8.
Analysis and Characterization of Damage Utilizing an Orthotropic Generalized Composite Material Model Suitable for Use in Impact Problems
Document ID: 20160010260
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Author: Goldberg, Robert K.; Carney, Kelly S.; DuBois, Paul; Hoffarth, Canio; Rajan, Subramaniam; Blankenhorn, Gunther
Abstract: The need for accurate material models to simulate the deformation,
damage and failure of polymer
matrix composite s under impact conditions is becoming critical as these materials are gaining increased usage in the aerospace and automotive communities. In order to address a series of issues identified by the aerospace community as being desirable to include in a next generation composite impact model, an orthotropic, macroscopic constitutive model incorporating both plasticity and damage suitable for implementation within the commercial LS-DYNA computer code is being developed. The plasticity model is based on extending the Tsai-Wu composite failure model into a strain hardening-based orthotropic plasticity model with a non-associative flow rule. The evolution of the yield surface is determined based on tabulated stress-strain curves in the various normal and shear directions and is tracked using the effective plastic strain. To compute the evolution of damage , a strain equivalent semi-coupled formulation is used in which a load in one direction results in a stiffness reduction in multiple material coordinate directions. A detailed analysis is carried out to ensure that the strain equivalence assumption is appropriate for the derived plasticity and damage formulations that are employed in the current model. Procedures to develop the appropriate input curves for the damage model are presented and the process required to develop an appropriate characterization test matrix is discussed
Publication Year: 2016
Document Type: Conference Paper
Report/Patent Number: GRC-E-DAA-TN29071
Date Acquired: Aug 15, 2016
9.
Analysis and Characterization of Damage Utilizing an Orthotropic Generalized Composite Material Model Suitable for Use in Impact Problems
Document ID: 20160002089
NTRS Full-Text: Click to View [PDF Size: 351 KB]
Author: Goldberg, Robert K.; Carney, Kelly S.; DuBois, Paul; Hoffarth, Canio; Rajan, Subramaniam; Blankenhorn, Gunther
Abstract: The need for accurate material models to simulate the deformation,
damage and failure of polymer
matrix composite s under impact conditions is becoming critical as these materials are gaining increased usage in the aerospace and automotive communities. In order to address a series of issues identified by the aerospace community as being desirable to include in a next generation composite impact model, an orthotropic, macroscopic constitutive model incorporating both plasticity and damage suitable for implementation within the commercial LS-DYNA computer code is being developed. The plasticity model is based on extending the Tsai-Wu composite failure model into a strain hardening-based orthotropic plasticity model with a non-associative flow rule. The evolution of the yield surface is determined based on tabulated stress-strain curves in the various normal and shear directions and is tracked using the effective plastic strain. To compute the evolution of damage , a strain equivalent semi-coupled formulation is used in which a load in one direction results in a stiffness reduction in multiple material coordinate directions. A detailed analysis is carried out to ensure that the strain equivalence assumption is appropriate for the derived plasticity and damage formulations that are employed in the current model. Procedures to develop the appropriate input curves for the damage model are presented and the process required to develop an appropriate characterization test matrix is discussed.
Publication Year: 2016
Document Type: Technical Report
Report/Patent Number: NASA/TM-2016-218959, E-19196, GRC-E-DAA-TN29072
Date Acquired: Feb 23, 2016
10.
Imparting Barely Visible Impact Damage to a Stitched Composite Large-Scale Pressure Box
Document ID: 20160007726
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Author: Lovejoy, Andrew E.; Przekop, Adam
Abstract: The Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS) is a concept that was developed by
The Boeing Company to address the complex structural design aspects associated with a pressurized hybrid wing body (HWB) aircraft configuration, which has been a focus of the NASA Environmentally Responsible Aviation Project. The NASA-Boeing structural development for the HWB aircraft culminated in testing of the multi-bay box, which is an 80%-scale representation of the pressurized center-body section. This structure was tested in the NASA Langley Research Center Combined Loads Test System facility. As part of this testing, barely visible impact damage was imparted to the interior and exterior of the test article to demonstrate compliance with a condition representative of the requirements for Category 1 damage d composite structure as defined by the Federal Aviation Regulations. Interior impact s were imparted using an existing spring-loaded impact or, while the exterior impact s were imparted using a newly designed, gravity-driven impact or. This paper describes the impact s to the test article, and the design of the gravitydriven guided-weight impact or. The guided-weight impact or proved to be a very reliable method to impart barely visible impact damage in locations which are not easily accessible for a traditional drop-weight impact or, while at the same time having the capability to be highly configurable for use on other aircraft structures.
Publication Year: 2016
Document Type: Conference Paper
Report/Patent Number: NF1676L-21716
Date Acquired: Jun 22, 2016