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Results for “Compressive Strength”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Development of lightweight reinforced plastic laminates for spacecraft interior applications

Lightweight, Kevlar - reinforced laminating systems that are non-burning, generate little smoke in the space shuttle environment, and are physically equivalent to the fiberglass/polyimide system used in the Apollo program for non-structural cabin panels, racks, etc. Resin systems representing five generic classes were screened as matrices for Kevlar 49 reinforced laminates. Of the systems evaluated, the polyimides were the most promising with the phenolics a close second. Skybond 703 was selected as the most promising resin candidate. With the exception of compression strength, all program goals of physical and mechanical properties were exceeded. Several prototype space shuttle mobility and translation handrail segments were manufactured using Kevlar/epoxy and Kevlar-graphite/epoxy. This application shows significant weight savings over the baseline aluminum configuration used previous. The hybrid Kevlar-graphite/epoxy is more suitable from a processing standpoint.

Hertz, J.↗
NASA NTRS1978

Heat and moisture flow in concrete as a function of temperature

Due to temperature, reactors in operation cause heat and moisture flows in the thick walled prestressed pressure vessels. These flows were studied in three beams of concrete made with crushed limestone aggregate, and in three beams made of crushed gravel/sand aggregate. The flow phenomena were related to the structural development of the concrete by determining the amount of non-evaporatable water, the total porosity, and the pore size distribution. Local temperature and moisture conditions also influenced the technical properties. Compressive strength, changes in length due to shrinkage and contraction, thermal expansion, and thermal conductivity were determined.

Hundt, J.↗
NASA NTRS1979

Effects of low-velocity impact on Gr/Pi compression laminates

The results of low velocity impact tests conducted on a graphite-polyimide laminate are presented. The 48-ply orthotropic laminate tested during this investigation is typical of laminates being proposed for heavily loaded aircraft wing skins. The nature of the damage is described as well as the effect of that damage on the compression strength of the 48-ply orthotropic laminate. The results obtained for the graphite-polyimide laminate are compared to existing results of similar tests conducted on other graphite-epoxy laminates.

Garcia, R.↗
NASA NTRS1980

Regenerator matrix physical property data

Among several cellular ceramic structures manufactured by various suppliers for regenerator application in a gas turbine engine, three have the best potential for achieving durability and performance objectives for use in gas turbines, Stirling engines, and waste heat recovery systems: (1) an aluminum-silicate sinusoidal flow passage made from a corrugated wate paper process; (2) an extruded isosceles triangle flow passage; and (3) a second generation matrix incorporating a square flow passage formed by an embossing process. Key physical and thermal property data for these configurations presented include: heat transfer and pressure drop characteristics, compressive strength, tensile strength and elasticity, thermal expansion characteristics, chanical attack, and thermal stability.

Fucinari, C. A.↗
NASA NTRS1981

Design allowables for T300/5208 graphite/epoxy composite materials

Material coupon tests were conducted to formulate design allowables for T300/5208 graphite/epoxy unidirectional tape and bidirectional fabric composites. This paper gives a description of the tests conducted, representative ply level and laminate test data, and results of the statistical analysis. The design allowables for tension and compression strength are given and include the effect of notches, impact damage, temperature extremes and moisture absorption.

Ekvall, J. C.↗
NASA NTRS1982

Compression behavior of unidirectional fibrous composite

The longitudinal compression behavior of unidirectional fiber composites is investigated using a modified Celanese test method with thick and thin test specimens. The test data obtained are interpreted using the stress/strain curves from back-to-back strain gages, examination of fracture surfaces by scanning electron microscope, and predictive equations for distinct failure modes including fiber compression failure, Euler buckling, delamination, and flexure. The results show that the longitudinal compression fracture is induced by a combination of delamination, flexure, and fiber tier breaks. No distinct fracture surface characteristics can be associated with unique failure modes. An equation is described which can be used to extract the longitudinal compression strength knowing the longitudinal tensile and flexural strengths of the same composite system.

Sinclair, J. H.↗
NASA NTRS1982

Effects of thermal cycling on residual mechanical properties of C6000/PMR-15 graphite polyimide

An experimental study to determine the effects of thermal cycling on residual mechanical properties of a graphite/polyimide composite has been conducted. Interlaminar shear, flexure and compression strengths were measured at room temperature and 316 C on unidirectional and quasi-isotropic laminates subjected to 150 and 500 thermal cycles between -156 C and 316 C. Thermal cycling produced transverse microcracks and delaminations in the laminates. The linear density of the microcracks (35/cm) was about the same after 150 and 500 cycles. Although the crack density did not change from 150 to 500 cycles, crack growth did occur with intralamina cracks growing into adjacent lamina. The matrix controlled properties of the quasi-isotropic laminate at both room temperature and 316 C were significantly reduced by thermal cycling. However, the properties of the unidirectional laminate were significantly reduced only at 316 C.

Tompkins, S. S.↗
NASA NTRS1979

Advanced manufacturing development of a composite empennage component for L-1011 aircraft

Work in process verification and tooling development continued. The decision was made to redesign the ribs to a more producible design. The bead was eliminated and the truss ribs changed to plain C sections. The solid web rib stiffeners were eliminated as well as the beads and the webs are now reinforced with a syntactic core. Syntectic is an epoxy containing glass microballoons. Two cover specimens were successfully tested. The first specimen (H27) was designed to verify the stability and compression strength of the cover when it is hot and wet. Failure occurred at 120 percent of design ultimate load. As the failure appeared to be fixture induced and was limited to one end of the panel, the remainder of the panel will be tested. The second specimen (H28) was designed to verify the failsafe aspects of the design. The test verified the design. Preparation of the PRVT test facility is nearing completion and all ten spar durability specimens were installed in the test chambers.

Source record↗
NASA NTRS1984

Synthesis and toughness properties of resins and composites

Tensile and shear moduli of four ACEE (Aircraft Energy Efficiency Program) resins are presented along with ACEE composite material modulus predictions based on micromechanics. Compressive strength and fracture toughness of the resins and composites were discussed. In addition, several resin synthesis techniques are reviewed.

Johnston, N. J.↗
NASA NTRS1983

Rigid closed-cell polyimide foams for aircraft applications and foam-in-place technology

Significant accomplishments generated are summarized. Testing of closed cell foams, which has resulted in the characterization of compositions which produce rigid foams for use in galley structure applications is reported. It is shown that the density, compressive strength and shear strength of the foams are directly related to the concentrations of the microballoons. The same properties are also directly related to the resin loading. Prototype samples of rigid closed cell foams meeting the requirements of the program were submitted. Investigation of the apparatus to produce polyimide foams using foam in place techniques, resulted in the selection of a spray gun apparatus, capable to deliver a mixture of microballoons and resin binder on substrates which cures to yield a closed cell foam. It is found that the adhesion of the foam on aluminum, titanium and steel substrates is satisfactory. It is concluded that the material meets the mechanical and thermal requirements of the program.

Gagliani, J.↗
NASA NTRS1983

Compressive behavior of unidirectional fibrous composites

The longitudinal compressive behavior of unidirectional fiber composites was investigated by using the Illinois Institute of Technology Research Institute (IITRI) test method with thick and thin test specimens. The test data obtained are interpreted by means of stress/strain curves from back-to-back strain gages, examination of fracture surfaces by scanning electron microscope, and predictive equations for distinct failure modes including fiber compression failure. Euler buckling, delamination, and flexure. The results show that longitudinal compressive fracture is induced by a combination of delamination, flexure, and fiber tier breaks. No distinct fracture surface characteristics can be associated with unique failure modes. An equation is described that can be used to extract the longitudinal compressive strength from the longitudinal tensile and flexural strengths of the same composite system.

Sinclair, J. H.↗
NASA NTRS1984

The Chemical Nature of the Fiber/resin Interface in Composite Materials

Carbon fiber/epoxy resin composites are considered. The nature of the fiber structure and the interaction that occurs at the interface between fiber and matrix are emphasized. Composite toughness can be improved by increased axial tensile and compressive strengths in the fibers. The structure of carbon fibers indicates that the fiber itself can fail transversely, and different transverse microstructures could provide better transverse strengths. The higher surface roughness of lower modulus and surface-treated carbon fibers provides better mechanical interlocking between the fiber and matrix. The chemical nature of the fiber surface was determined, and adsorption of species on this surface can be used to promote wetting and adhesion. Finally, the magnitude of the interfacial bond strength should be controlled such that a range of composites can be made with properties varying from relatively brittle and high interlaminar shear strength to tougher but lower interlaminar shear strength.

Diefendorf, R. J.↗
NASA NTRS1985

Two-dimensional modelling of compressive failure in delaminated laminates

An analytical model is developed to assess the compressive strength criticality of near-surface interlaminar defects in laminated composites. The delaminated region is elliptic in shape, separating a thick isotropic plate from a thin orthotropic layer whose material axes coincide with the ellipse axes. The growth conditions and growth behavior of this defect are studied by breaking the overall problem into an elastic stability problem and a fracture problem. Post-buckling solution for the elliptic section is obtained using the Rayleigh-Ritz method while an energy balance criterion based on a self-similar disbond growth governs the fracture. The parameters controlling the growth or arrest of the delamination damage are identified as the fracture energy, disbond depth and elastic properties of the materials from both sides of the delaminating interface. By varying the degree of material anisotropy relative to the loading axis a range in growth behavior was found including stable or unstable crack growth parallel to or normal to the loading axis.

Chai, H.↗
NASA NTRS1985

Longitudinal compressive failure modes in fiber composites End attachment effects on IITRI type test specimens

The end-attachment effects on longitudinal compressive strength of IITRI type specimen unidirectional fiber composites are formally assessed using finite-element analysis (FEA) in conjunction with composite mechanics. Sixteen different cases were analyzed to evaluate end-attachment effects (such as degree of misalignment, type of misalignment, progressive end-tab debonding, and specimen thickness) on stress distribution, peak stresses, buckling loads, and buckling mode shapes. The results obtained from the FEA and comparisons with fractured specimens show that eccentricities induce bending-type stresses which peak near the end-tabs and cause flexural type fracture. Also, guidelines are included for placing back-to-back strain gages to measure the presence/absence of possible end-attachment and eccentricity effects.

Chamis, C. C.↗
NASA NTRS1986

New experimental and analytical results for diffusion and swelling of resins used in graphite/epoxy composite materials

The epoxy resins currently in use can slowly absorb moisture from the atmosphere over a long period. This reduces those mechanical properties of composites which depend strongly on the matrix, such as compressive strength and buckling instabilities. The effect becomes greater at elevated temperatures. The paper will discuss new phenomena which occur under simultaneous temperature and moisture variations. An analytical model will also be discussed and documented.

Hiel, C. C.↗
NASA NTRS1987

Hardness Tester for Polyur

Rubber-hardness tester modified for use on rigid polyurethane foam. Provides objective basis for evaluation of improvements in foam manufacturing and inspection. Typical acceptance criterion requires minimum hardness reading of 80 on modified tester. With adequate correlation tests, modified tester used to measure indirectly tensile and compressive strengths of foam.

Hauser, D. L.↗
NASA NTRS1987

High performance thermoplastics: A review of neat resin and composite properties

A review was made of the principal thermoplastics used to fabricate high performance composites. Neat resin tensile and fracture toughness properties, glass transition temperatures (Tg), crystalline melt temperatures (Tm) and approximate processing conditions are presented. Mechanical properties of carbon fiber composites made from many of these thermoplastics are given, including flexural, longitudinal tensile, transverse tensile and in-plane shear properties as well as short beam shear and compressive strengths and interlaminar fracture toughness. Attractive features and problems involved in the use of thermo-plastics as matrices for high performance composites are discussed.

Johnston, Norman J.↗