Holography - Potential nondestructive testing tool
Holography as nondestructive testing tool, considering application in vibration analysis, stress/strain measurement, bond inspection, internal flaw detection and displacement measurement
Erf, R. K.↗
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Criteria for selecting resin matrices for improved composite strength
Criteria are presented which can be used a priori to select matrices to yield composites with improved unidirectional strength. The criteria evolved from an investigation including both theoretical and experimental efforts. Composite micromechanics were used in conjunction with suitable experiments and reference data to identify those matrix properties which influence composite strength properties. Composites of graphite fibers and low, intermediate and high-modulus resins were investigated. It was found that the area under the matrix stress/strain diagram limited to one percent strain is a good index for an a priori assessment of the matrix contribution to composite strength. The corresponding initial modulus is a useful parameter in translating matrix properties to composite properties. Matrix properties such as ultimate strength, ultimate elongation, toughness, and fracture toughness are misleading in translating matrix properties to composite strength.
Chamis, C. C.↗
Criteria for selecting resin matrices for improved composite strength.
Criteria are presented which can be used a priori to select matrices to yield composites with improved unidirectional strength. The criteria evolved from an investigation including both theoretical and experimental efforts. Composite micromechanics were used in conjunction with suitable experiments and reference data to identify those matrix properties which influence composite strength properties. Composites of graphite fibers and low, intermediate and high-modulus resins were investigated. It was found that the area under the matrix stress/strain diagram limited to one percent strain is a good index for an a priori assessment of the matrix contribution to composite strength. The corresponding initial modulus is a useful parameter in translating matrix properties to composite properties.
Chamis, C. C.↗
Design of mechanical components for long-term performance
Review of the results of a NASA program designed to study advanced techniques for determining the long-term performance of rocket engine components. Aging and operational degradation mechanisms of metal valve seats are identified. Characterization of metal valve seat surfaces by optical signature analysis is described. The results of the development of a long-life 'zero leakage' metal valve seal designed to avoid failure by contamination, stress/strain, fatigue, and the deterioration of the surface by wear is reported. An analysis of a specific seat design showed that material strain prevention along all axes would prevent these failures. The design provided for refurbishment of the sealing surfaces during each valve cycle, thereby preventing cumulative surface damage.
Salvinski, R. J.↗
Elastic modulus of the human intact left ventricle - Determination and physiological interpretation
The left ventricle (l.v.) is represented as a shell of muscle whose performance is characterized in terms of the chamber pressure and stress/strain in the ventricular wall; the effective elastic modulus of the l.v. relates these performance variables, and hence represents the transfer function of the left ventricular physiological system. A method is presented for indirectly determining the effective modulus E for the left ventricle. The method employs a thick-walled mathematical model of the l.v. having a homogeneous isotropic medium. Instantaneous values of E are determined for subjects with heart diseases of varied etiologies, in order to assess the responses of the l.v. to chronic overloads of pressure and volume. Resulting values for E are used diagnostically to characterize the physiological state of the l.v. Normal values of E, at systole, indicate that the strength of contraction exercised by the l.v. is normal, and hence is an indication of the l.v. having adjusted to the heart disease.
Ghista, D. N.↗
Yield-pressure determination
Stress/strain relationship of complex-shape vessel is recorded under hydrostatic pressure. Technique is used to test pressurized gas cylinders and tubular transition joints made of dissimilar metals and to determine burst or system-failure pressures.
Wakefield, M. E.↗
Efficient measurement of shear properties of fiber composites
Intralaminar (in-plane) shear characterization (shear stress/strain relationships) of unidirectional fiber composites has been hampered by difficulty of producing state of pure shear in practical paboratory test specimens. Proposed method uses 10 deg off-axis tensile specimen (fiber oriented 10 deg from load direction) in conjunction with simple transformation equations for intralaminar shear characterization of fiber composites.
Chamis, C. C.↗
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.↗
Vibration Analysis With Finite Dynamic Elements
To enhance usefulness of computers in solving engineering problems, new techniques are being developed for numerical analysis of structural dynamics. Two aspects of this analysis--structural discretization with finite dynamic elements and solution of resulting equations--have been applied in detail to membrane and plane stress/strain continua.
Gupta, K. K.↗
Inexpensive Bolt-Load Gage
"Built-in" gage determines whether large bolt or stud has been torqued to desired load and provides for continuous inspection to ensure proper load is being maintained. Gage detects longitudinal stress/strain bolt; requires no electronic or sonic test equipment.
Long, M. J.↗
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.↗
Synthesis and characterization of a melt processable polyimide
A melt processable polyimide which contains sulfur and oxygen bridges between the aromatic rings (BDSDA/APB) was synthesized and characterized. Its physical, mechanical, thermal and flow properties were determined as was its resistance to some of the more commonly used solvents. The melt flow properties were measured for the temperature range 250 C - 350 C and under the conditions (stress/strain) encountered in commercial processes.
Burks, H. D.↗
For operation of the Computer Software Management and Information Center (COSMIC)
Computer programs for degaussing, magnetic field calculation, low speed wing flap systems aerodynamics, structural panel analysis, dynamic stress/strain data acquisition, allocation and network scheduling, and digital filters are discussed.
Carmon, J. L.↗
Calculating Strain Relief in Electronic-Component Leads
Stress/strain formulas applicable to design of electronic-component leads compiled in report. Such things as factors of safety and whether or not lead is likely to fall in service determined in advance. Set of formulas is simple enough to be solved on programable hand-held calculator.
Snytsheuvel, H.↗
ICAN: Integrated composites analyzer
The ICAN computer program performs all the essential aspects of mechanics/analysis/design of multilayered fiber composites. Modular, open-ended and user friendly, the program can handle a variety of composite systems having one type of fiber and one matrix as constituents as well as intraply and interply hybrid composite systems. It can also simulate isotropic layers by considering a primary composite system with negligible fiber volume content. This feature is specifically useful in modeling thin interply matrix layers. Hygrothermal conditions and various combinations of in-plane and bending loads can also be considered. Usage of this code is illustrated with a sample input and the generated output. Some key features of output are stress concentration factors around a circular hole, locations of probable delamination, a summary of the laminate failure stress analysis, free edge stresses, microstresses and ply stress/strain influence coefficients. These features make ICAN a powerful, cost-effective tool to analyze/design fiber composite structures and components.
Murthy, P. L. N.↗
Proceedings of the Flat-plate Solar Array Project Research Forum on the High-speed Growth and Characterization of Crystals for Solar Cells
The High-Speed Growth and Characterization of Crystals for Solar Cells Research Forum was held on July 25-27, 1983, at the Sandpiper Bay Hotel in ort St. Lucie, Florida. The Research Forum was arranged into eight interactive sessions and addressed theoretical and experimental phenomena, applications, and characterization including stress/strain and other problem areas that limit the rate of growth of crystals suitable for processing into efficient, cost-effective solar cells. The Flat-Plate Solar Array Project of the Jet Propulsion Laboratory sponsored the meeting: Thirty-five invited papers were presented. Discussion periods followed each presentation. These Proceedings are a record of the papers and the discussions.
Katherine A. Dumas↗
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.↗
Predicting the Cyclic Response of High-Temperature Materials
Simplified analytical procedure for estimating local stress/strain response in high-temperature structural component developed. Simplified procedure relies on assumption local inelastic response in hightemperature structure constrained by surrounding elastic material. Procedure assumes local response composed of elastic, time-independent plastic, and creep components. Conventional yield surface concept used to determine onset of plastic action.
Moreno, V.↗