Engineering topics

Farley, Gary L.

Publications and source records attributed to Farley, Gary L..

At least 55 records · Page 3

NASA NTRS1992

Mechanical response of composite materials with through-the-thickness reinforcement

An experimental investigation was conducted to identify the key geometrical parameters and quantify their influence on the mechanical response of through-the-thickness (TTT) reinforced composite materials. Composite laminates with TTT reinforcement fibers were fabricated using different TTT reinforcement materials and reinforcement methods and laminates were also fabricated of similar construction but without TTT reinforcement fibers. Coupon specimens were machined from these laminates and were destructively tested. TTT reinforcement yarns enhance damage tolerance and improve interlaminar strength. Thick-layer composites with TTT reinforcement yarns have equal or superior mechanical properties to thin-layer composites without TTT reinforcement yarns. A significant potential exists for fabrication cost reduction by using thick-layer composites with TTT reinforcement yarns. Removal of the surface loop of the TTT reinforcement improves compression strength. Stitching provides somewhat higher mechanical properties than integral weaving.

Farley, Gary L.↗

NASA NTRS1992

Absorption Of Crushing Energy In Square Composite Tubes

Report describes investigation of crash-energy-absorbing capabilities of square-cross-section tubes of two matrix/fiber composite materials. Both graphite/epoxy and Kevlar/epoxy tubes crushed in progressive and stable manner. Ratio between width of cross section and thickness of wall determined to affect energy-absorption significantly. As ratio decreases, energy-absorption capability increases non-linearly. Useful in building energy-absorbing composite structures.

Farley, Gary L.↗

NASA NTRS1992

Compression response of thick layer composite laminates with through-the-thickness reinforcement

Compression and compression-after-impact (CAI) tests were conducted on seven different AS4-3501-6 (0/90) 0.64-cm thick composite laminates. Four of the seven laminates had through-the-thickness (TTT) reinforcement fibers. Two TTT reinforcement methods, stitching and integral weaving, and two reinforcement fibers, Kevlar and carbon, were used. The remaining three laminates were made without TTT reinforcements and were tested to establish a baseline for comparison with the laminates having TTT reinforcement. Six of the seven laminates consisted of nine thick layers whereas the seventh material was composed of 46 thin plies. The use of thick-layer material has the potential for reducing structural part cost because of the reduced part count (layers of material). The compression strengths of the TTT reinforced laminates were approximately one half those of the materials without TTT reinforcements. However, the CAI strengths of the TTT reinforced materials were approximately twice those of materials without TTT reinforcements. The improvement in CAI strength is due to an increase in interlaminar strength produced by the TTT reinforcement. Stitched laminates had slightly higher compression and CAI strengths than the integrally woven laminates.

Farley, Gary L.↗

NASA NTRS1992

The effects of crushing surface roughness on the crushing characteristics of composite tubes

The effects of crushing-surface roughness on the energy-absorption capability of graphite and glass-epoxy composite tubes were investigated. Fifty different combinations of fiber, matrix, and specimen ply orientation were evaluated. Two different crushing surface roughnesses were used in this investigation. Crushing surface significantly influences the energy-absorption capability only of tubes that crush in the lamina bending crushing mode; tubes that crush in other modes are not influenced because their lamina bundles do not slide against the crushing surface. Those tubes that crush in the lamina bending mode can achieve higher, lower, or no change in energy-absorption capability as crushing surface roughness increases. If the fiber failure strain of tubes that crush in the lamina bending crushing mode exceeds the matrix failure strain then the energy-absorption capability increases as crushing surface roughness increases. However, if the matrix failure strain exceeds the fiber failure strain then the energy-absorption capability increases as crushing surface roughness decreases. Energy-absorption capability is uninfluenced by crushing surface roughness for tubes that have equal fiber and matrix failure strains.

Farley, Gary L.↗

NASA NTRS1992

Removal of surface loop from stitched composites can improve compression and compression-after-impact strengths

Stitching through-the-thickness (TTT) of composite materials produces a surface loop of yarn between successive penetrations. The surface loop is pressed into the surface layers of the composite material during the curing of the laminate, kinking the in-plane fibers near the surface of the material. The compression strength and compression-after-impact (CAI) strengths of carbon-epoxy specimens were measured with and without the surface loop. Removal of the surface loop had no influence on failure mode or failure mechanism, but did significantly increase the compression and CAI strengths.

Farley, Gary L.↗

NASA NTRS1992

Composite material shear property measurement using the Iosipescu specimen

A detailed evaluation of the suitability of the Iosipescu specimen tested in the modified Wyoming fixture is presented. Finite element analysis and moire interferometry are used to assess the uniformity of the shear stress field in the test section of unidirectional and cross-ply graphite-epoxy composites. The nonuniformity of the strain field and the sensitivity of some fiber orientations to the specimen/fixture contact mechanics are discussed. The shear responses obtained for unidirectional and cross-ply graphite-epoxy composites are discussed and problems associated with anomalous behavior are addressed. An experimental determination of the shear response of a range of material systems using strain gage instrumentation and moire interferometry is performed.

Ho, Henjen↗

NASA NTRS1992

Crushing characteristics of continuous fiber-reinforced composite tubes

Composite tubes can be reinforced with continuous fibers. When such tubes are subjected to crushing loads, the response is complex and depends on interaction between the different mechanisms that control the crushing process. The modes of crushing and their controlling mechanisms are described. Also, the resulting crushing process and its efficiency are addressed.

Farley, Gary L.↗

NASA NTRS1992

Analogy for the effect of material and geometrical variables on energy-absorption capability of composite tubes

Simplified procedures for determining the qualitative effect a variable has on structural response of a composite tube are very useful in both preliminary design as well as in providing insight into the general response. An analysis procedure is presented that can be used to determine the qualitative change in the sustained crushing load due to a change in specimen material properties or geometry. The analysis procedure is similar in form to the equation for the buckling load of a column on an elastic foundation.

Farley, Gary L.↗

NASA NTRS1992

Prediction of the energy-absorption capability of composite tubes

A method of predicting the crack-related energy-absorption capability of composite tubes is presented. The method is based upon a phenomenological model of the crushing process exhibited by continuous-fiber-reinforced tubes. A finite element method is used to model the crushing process. The analysis is compared with experiments on Kevlar-epoxy and graphite-epoxy tubes. Reasonable agreement is obtained between the analysis and experiment.

Farley, Gary L.↗

NASA NTRS1992

Crushing characteristics of composite tubes with 'near-elliptical' cross sections

An experimental investigation was conducted to determine whether the energy-absorption capability of near-elliptical cross-section composite tubular specimens is a function of included angle. Each half of the near-elliptical cross-section tube is a segment of a circle. The included angle is the angle created by radial lines extending from the center of the circular segment to the ends of the circular segment. Graphite- and Kevlar-reinforced epoxy material was used to fabricate specimens. Tube internal diameters were 2.54, 3.81, and 7.62 cm, and included angles were 180, 160, 135, and 90 degrees. Based upon the test results from these tubes, energy-absorption capability increased between 10 and 30 percent as included angle decreased between 180 and 90 degrees for the materials evaluated. Energy-absorption capability was a decreasing nonlinear function of the ratio of tube internal diameter to wall thickness.

Farley, Gary L.↗

NASA NTRS1992

A mechanism responsible for reducing compression strength of through-the-thickness reinforced composite material

A study was conducted to identify one of the mechanisms that contributes to the reduced compression strength of composite materials with through-the-thickness (TTT) reinforcements. In this study a series of thick (0/90) laminates with stitched and integrally woven TTT reinforcements were fabricated and statically tested. In both the stitching and weaving process a surface loop of TTT reinforcement yarn is created between successive TTT penetrations. It was shown that the surface loop of the TTT reinforcement 'kinked' the in-plane fibers in such a manner that they were made ineffective in carrying compressive load. The improvement in strength by removal of the surface loop and 'kinked' in-plane fibers was between 7 and 35 percent.

Farley, Gary L.↗

NASA NTRS1991

The effects of crushing speed on the energy-absorption capability of composite tubes

The energy-absorption capability as a function of crushing speed was determined for Thornel 300-Fiberite 934 (Gr-E) and Kevlar-49-Fiberite 934 (K-E) composite material. Circular cross section tube specimens were crushed at speeds ranging from 0.01 to 12 m/sec. Ply orientations of the tube specimens were (0/ +/- theta)2 and (+/- theta)2 where theta = 15, 45, and 75 deg. Based upon the results of these tests, the energy-absorption capability of Gr-E and K-E was determined to be a function of crushing speed. The magnitude of the effects of crushing speed on energy-absorption capability was determined to be a function of the mechanisms that control the crushing process. The effects of crushing speed on the energy-absorption capability is related to whether the mechanical response of the crushing mechanism that controls the crushing process is a function of strain rate. Energy-absorption capability of Gr-E and K-E tubes ranged between 0 and 35 percent and 20 and 45 percent, respectively, depending upon ply orientation.

Farley, Gary L.↗

NASA NTRS1991

Farley Three-Dimensional-Braiding Machine

Process and device known as Farley three-dimensional-braiding machine conceived to fabricate dry continuous fiber-reinforced preforms of complex three-dimensional shapes for subsequent processing into composite structures. Robotic fiber supply dispenses yarn as it traverses braiding surface. Combines many attributes of weaving and braiding processes with other attributes and capabilities. Other applications include decorative cloths, rugs, and other domestic textiles. Concept could lead to large variety of fiber layups and to entirely new products as well as new fiber-reinforcing applications.

Farley, Gary L.↗

NASA NTRS1991

A comparison of three popular test methods for determining the shear modulus of composite materials

Three popular shear tests (the 10 degree off-axis, the plus or minus 45 degree tensile, and the Iosipescu specimen tested in the modified Wyoming fixture) for shear modulus measurement are evaluated for a graphite-epoxy composite material system. A comparison of the shear stress-strain response for each test method is made using conventional strain gage instrumentation and moire interferometry. The uniformity and purity of the strain fields in the test sections of the specimens are discussed, and the shear responses obtained from each test technique are presented and compared. For accurate measurement of shear modulus, the 90 degree Iosipescu specimen is recommended.

Ho, Henjen↗

NASA NTRS1991

Damage assessment and residual compression strength of thick composite plates with through-the-thickness reinforcements

Damage in composite materials was studied with through-the-thickness reinforcements. As a first step it was necessary to develop new ultrasonic imaging technology to better assess internal damage of the composite. A useful ultrasonic imaging technique was successfully developed to assess the internal damage of composite panels. The ultrasonic technique accurately determines the size of the internal damage. It was found that the ultrasonic imaging technique was better able to assess the damage in composite panel with through-the-thickness reinforcements than by destructively sectioning the specimen and visual inspection under a microscope. Five composite compression-after-impact panels were tested. The compression-after-impact strength of the panels with the through-the-thickness reinforcements was almost twice that of the comparable panel without through-the-thickness reinforcement.

Smith, Barry T.↗

NASA NTRS1990

Effects Of Rapid Crushing On Composites

Experimental study described in NASA technical memorandum performed to determine whether crash energy-absorption capabilities of graphite/epoxy and Kevlar/epoxy composite materials are functions of speed of crushing. Additional objective to develop understanding of mechanisms of crushing. Technology applied to enhancement of safety and crashworthiness of automobiles, design of energy-absorbing devices in machinery, and problems involving explosions and impacts.

Farley, Gary L.↗

NASA NTRS1990

Angle-Ply Weaving

Bias-direction or angle-ply weaving is proposed new process for weaving fibers along bias in conventional planar fabric or in complicated three-dimensional multilayer fabric preform of fiber-reinforced composite structure. Based upon movement of racks of needles and corresponding angle yarns across fabric as fabric being formed. Fibers woven along bias increases shear stiffness and shear strength of preform, increasing value of preform as structural member.

Farley, Gary L.↗

NASA NTRS1990

Integrated Process For Insertion And Beatup Of Fill Yarns

Integrated apparatus and process devised for insertion and beatup of fill yarns during weaving of fabrics containing bias-oriented yarns. New technology supplants old shuttle method and modern water-jet method of insertion and conventional reed method of beatup. Intended for use in angle-ply or bias-direction weaving process.

Farley, Gary L.↗