An applications study of advanced composite materials to the C-130 center wing box
Applications of advanced composite materials to C-130 center wing box
Petit, P. H.↗
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Controlled intermittent interfacial bond concept for composite materials
Concept will enhance fracture resistance of high-strength filamentary composite without degrading its tensile strength or elastic modulus. Concept provides more economical composite systems, tailored for specific applications, and composite materials with mechanical properties, such as tensile strength, fracture strain, and fracture toughness, that can be optimized.
Marston, T. U.↗
Evaluation of hybrid composite materials in cylindrical specimen geometries
Static and fatigue properties of three composite materials and hybrids were examined. The materials investigated were graphite/epoxy, S-glass/epoxy, PRD-49 (Kevlar 49)/epoxy, and hybrids in angle-ply configurations. A new type of edgeless cylindrical specimen was developed. It is a flattened tube with two flat sides connected by curved sections and it is handled much like the standard flat coupon. Special specimen fabrication, tabbing, and tab region reinforcing techniques were developed. Axial modulus, Poisson's ratio, strength, and ultimate strain were obtained under static loading from flattened tube specimens of nine laminate configurations. In the case of graphite/epoxy the tubular specimens appeared to yield somewhat higher strength and ultimate strain values than flat specimens. Tensile fatigue tests were conducted with all nine types of specimens and S-N curves obtained. Specimens surviving 10 million cycles of tensile loading were subsequently tested statically to failure to determine residual properties.
Liber, T.↗
Effects of method of loading and specimen configuration on compressive strength of graphite/epoxy composite materials
Three test schemes were examined for testing graphite/epoxy (Narmco T300/5208) composite material specimens to failure in compression, including an adaptation of the IITRI "wedge grip" compression fixture, a face-supported-compression fixture, and an end-loaded-coupon fixture. The effects of specimen size, specimen support arrangement and method of load transfer on compressive behavior of graphite/epoxy were investigated. Compressive stress strain, strength, and modulus data obtained with the three fixtures are presented with evaluations showing the effects of all test parameters, including fiber orientation. The IITRI fixture has the potential to provide good stress/strain data to failure for unidirectional and quasi-isotropic laminates. The face supported fixture was found to be the most desirable for testing + or - 45 s laminates.
Clark, R. K.↗
Study of the influence of hole quality on composite materials
The influence of hole quality on the structural behavior of composite materials was investigated. From an industry survey it was determined that the most frequent imperfections encountered during hole fabrication are chipout, delamination, and oversize conditions. These hole flaw types were generated in critical areas of static, compression, and fatigue specimens fabricated from T300/5208 graphite/epoxy system. The specimens were tested in static and cyclic pin bearing modes in addition to compression loading. Results of these tests are presented and discussed. The hole chipout defect reduced the static and cyclic endurance characteristics. Oversize holes also lowered the cyclic pin bearing endurance, but had no influence of the static pin bearing characteristics. Delamination had no insignificant influence on the static tension and cyclic pin bearing characteristics. Compression tests demonstrated a deleterious effect for chipout of delamination defects. Hole quality requirements proposed are discussed.
Pengra, J. J.↗
Effect of the raw material composition of fabrics on the Limiting Oxygen Index (LOI)
The raw material composition of fabrics is one of the most important factors for LOI value. LOI value was determined in samples of varying composition composed of cellulose, protein, and synthetic fibers and their mixtures, based on ASTM D 2863-76. Cellulose fibers and their mixtures exhibited the lowest value, while synthetic fibers had the highest LOI value.
Jeler, S.↗
Response of composite materials to the Space Station orbit environment
The rationale for selecting composite materials with an anodized aluminum foil coating for the Space Station is presented. Data on the effects of the space service environment on these materials are given. Results are also presented on the effect of optical properties of an aluminum/aluminum oxide coating on the thermal balance of the cylindrical structural members. The resistance of this coating to solar ultraviolet degradation is discussed.
Tompkins, S. S.↗
The Iosipescu shear test method as used for testing polymers and composite materials
This paper describes a shear test method for polymers and composite materials, based on the Iosipescu (1967) shear test which was originally developed for use with homogeneous isotropic metals. Special attention is given to the loading fixture for the test, the standard specimen design and shear stress measurements. The range of the test applications is indicated. The method is in the final stages of being accepted as an ASTM standard.
Adams, Donald F.↗
Health, safety and environmental requirements for composite materials
The health, safety and environmental requirements for the production of composite materials are discussed. The areas covered include: (1) chemical identification for each chemical; (2) toxicology; (3) industrial hygiene; (4) fire and safety; (5) environmental aspects; and (6) medical concerns.
Hazer, Kathleen A.↗
A Critique of a Phenomenological Fiber Breakage Model for Stress Rupture of Composite Materials
Stress rupture is not a critical failure mode for most composite structures, but there are a few applications where it can be critical. One application where stress rupture can be a critical design issue is in Composite Overwrapped Pressure Vessels (COPV's), where the composite material is highly and uniformly loaded for long periods of time and where very high reliability is required. COPV's are normally required to be proof loaded before being put into service to insure strength, but it is feared that the proof load may cause damage that reduces the stress rupture reliability. Recently, a fiber breakage model was proposed specifically to estimate a reduced reliability due to proof loading. The fiber breakage model attempts to model physics believed to occur at the microscopic scale, but validation of the model has not occurred. In this paper, the fiber breakage model is re-derived while highlighting assumptions that were made during the derivation. Some of the assumptions are examined to assess their effect on the final predicted reliability.
Reeder, James R.↗
Fracture mechanics for delamination problems in composite materials
A fracture mechanics approach to the well-known delamination problem in composite materials is presented. Based on the theory of anisotropic laminate elasticity and interlaminar fracture mechanics concepts, the composite delamination problem is formulated and solved. The exact order of the delamination crack-tip stress singularity is determined. Asymptotic stress and displacement fields for an interlaminar crack are obtained. Fracture mechanics parameters such as mixed-mode stress intensity factors, KI, KII, KIII, and the energy release rate, G, for composite delamination problems are defined. To illustrate the fundamental nature of the delamination crack behavior, solutions for edge-delaminated graphite-epoxy composites under uniform axial extension are presented. Effects of fiber orientation, ply thickness, and delamination length on the interlaminar fracture are examined.
Wang, S. S.↗
A normal stress criterion for crack extension direction in orthotropic composite materials
A criterion for predicting the direction of crack extension in orthotropic composite materials is presented. The criterion is based upon the normal stress and the anisotropic tensile strength on arbitrary planes about the tip of a crack. Results are obtained, via finite element solutions, for: (1) isotropic mixed mode fracture, (2) cracks in unidirectional off-axis slotted composite tensile coupons and (3) cracks in cross plied laminates. Comparisons are made with other theories and experimental results.
Buczek, M. B.↗
Structural Framework for Flight: NASA's Role in Development of Advanced Composite Materials for Aircraft and Space Structures
This serves as a source of collated information on Composite Research over the past four decades at NASA Langley Research Center, and is a key reference for readers wishing to grasp the underlying principles and challenges associated with developing and applying advanced composite materials to new aerospace vehicle concepts. Second, it identifies the major obstacles encountered in developing and applying composites on advanced flight vehicles, as well as lessons learned in overcoming these obstacles. Third, it points out current barriers and challenges to further application of composites on future vehicles. This is extremely valuable for steering research in the future, when new breakthroughs in materials or processing science may eliminate/minimize some of the barriers that have traditionally blocked the expanded application of composite to new structural or revolutionary vehicle concepts. Finally, a review of past work and identification of future challenges will hopefully inspire new research opportunities and development of revolutionary materials and structural concepts to revolutionize future flight vehicles.
Tenney, Darrel R.↗
Delamination, durability and damage tolerance of laminated composite materials
Research exploring the role of delamination on the durability and damage tolerance of advanced composite materials is reviewed. Recent studies on the characterization of composite delamination are summarized. Recent analytical solutions for interlaminar stresses and strain energy release rates associated with common sources of delamination are also reviewed. The role of delamination in low velocity impact, residual compression strength, and in fatigue is highlighted. Delamination is shown to be the common damage mode observed in all of these problems. A Damage Threshold/Fail-safety concept for addressing composite damage tolerance is discussed.
O'Brien, T. K.↗
A Multiscale, Nonlinear, Modeling Framework Enabling the Design and Analysis of Composite Materials and Structures
A framework for the multiscale design and analysis of composite materials and structures is presented. The ImMAC software suite, developed at NASA Glenn Research Center, embeds efficient, nonlinear micromechanics capabilities within higher scale structural analysis methods such as finite element analysis. The result is an integrated, multiscale tool that relates global loading to the constituent scale, captures nonlinearities at this scale, and homogenizes local nonlinearities to predict their effects at the structural scale. Example applications of the multiscale framework are presented for the stochastic progressive failure of a SiC/Ti composite tensile specimen and the effects of microstructural variations on the nonlinear response of woven polymer matrix composites.
Bednarcyk, Brett A.↗
A Multiscale, Nonlinear, Modeling Framework Enabling the Design and Analysis of Composite Materials and Structures
A framework for the multiscale design and analysis of composite materials and structures is presented. The ImMAC software suite, developed at NASA Glenn Research Center, embeds efficient, nonlinear micromechanics capabilities within higher scale structural analysis methods such as finite element analysis. The result is an integrated, multiscale tool that relates global loading to the constituent scale, captures nonlinearities at this scale, and homogenizes local nonlinearities to predict their effects at the structural scale. Example applications of the multiscale framework are presented for the stochastic progressive failure of a SiC/Ti composite tensile specimen and the effects of microstructural variations on the nonlinear response of woven polymer matrix composites.
Bednarcyk, Brett A.↗
A test method to measure the response of composite materials under reversed cyclic loads
A test method to measure the response of composite materials under reversed cyclic loads is described. The method approximates the long-term response of a component by permitting the composite specimen to respond to the imposed loads and fail in an unconstrained mode rather than in a constrained mode. The method has been successfully used for the reversed cyclic loading of unnotched and notched graphite/epoxy and graphite/PEEK laminates of various stacking sequences. Included in the paper are monotonic tensile and compressive stiffness and strength data at several points in the fatigue lifetime, and damage development information obtained via X-ray radiography for quasi-isotropic T300/5208 and AS4/PEEK laminates with unloaded circular holes.
Bakis, Charles E.↗
Application of Raman Spectroscopy for Nondestructive Evaluation of Composite Materials
This paper will present an overview of efforts to investigate the application of Raman spectroscopy for the characterization of Kevlar materials. Raman spectroscopy is a laser technique that is sensitive to molecular interactions in materials such as Kevlar, graphite and carbon used in composite materials. The overall goal of this research reported here is to evaluate Raman spectroscopy as a potential nondestructive evaluation (NDE) tool for the detection of stress rupture in Kevlar composite over-wrapped pressure vessels (COPVs). Characterization of the Raman spectra of Kevlar yarn and strands will be presented and compared with analytical models provided in the literature. Results of testing to investigate the effects of creep and high-temperature aging on the Raman spectra will be presented.
Washer, Glenn A.↗