surface. (4) Since no abrasive particles are used, a clean working environment is maintained.

Surface characterization of optical materials, H. E. Bennett, SP562, pp. 337-350 (Oct. 1979).

Key words: Auger spectroscopy; corrosion films; ESCA; impurities; microroughness; optical microscopy; polishing defects; scattered light; SIMS; stylus instruments.

A complete description of the surfaces of optical materials involves their topography, presence of particulates, crystallinity and degree of disorder at the surface, impurities in the vicinity of the surface, stoichiometry at the surface, and surface films. The most direct method for observing small surface imperfections is by using electron or optical microscopy. Often transmission electron microscopy using replication has too high a lateral resolution and too low a depth resolution to ivestigate imperfections of greatest optical interest. Surprisingly, optical interference microscopy has one to two orders of magnitude higher depth resolution than electron microscopy, and techniques such as differential interference contrast, sometimes called Nomarski microscopy, are extremely useful in evaluating surfaces qualitatively. For quantitative results, stylus techniques and interometry using fringes of equal chromatic order are very useful and give results in good agreement with those obtained by scattered light measurements. Total integrated scattering provides a simple noncontact method for determining the rms height of surface irregularities and may be applied in various surface roughness determinations. Evaluating the roughness of ball bearings is one example.

Surface impurities and stoichiometry at the surface also affect the performance of optical materials. Impurity atoms in concentrations as low as 0.001 monolayer can be detected using Auger spectroscopy. There is a danger however, of disturbing the surface with the high energy electrons required to produce the Auger electrons unless very low electron currents are used. This problem is alleviated by using electron spectroscopy for chemical analysis (ESCA), which depends on photoemission induced by xray or vacuum ultraviolet irradiation rather than on electron bombardment. ESCA is also more sensitive to molecular forces than is Auger spectroscopy, so that compounds as well as the atomic constituents can often be detected. Even more sensitive is secondary ion mass spectroscopy. In many cases, surface impurity levels in the 10 range can be detected using this technique. Surface films also affect the optical properties of materials, often significantly. Their growth can be monitored using ellipsometry, which is insensitive to roughness introduced by the film and is sensitive to changes in average film thickness of a fraction of a monolayer. A new surface evaluation technique being developed is high fluence diagnostics and multithreshold analysis. Most of the techniques discussed are applicable to nonoptical surfaces as well as optical surfaces, and should be used more widely in analyses of surfaces produced by ceramic machining.

The nature of strength controlling machining flaws in ceramics, R. W. Rice and J. J. Mecholsky, Jr., SP562, PP. 351-378 (Oct. 1979).

Key words: brittle failure; flaw populations; flaws; fractography; fracture origins; grinding; machining; polishing; sanding; strength-size effects.

The nature of machining flaws introduced in a variety of glass, single crystal, and especially polycrystal bodies are reported, based on fractographic determination of such

flaws as the source of mechanical failure. Particular attenuation is given to grinding where the anisotropy of strength due to the direction of grinding relative to the tensile axis is shown to be due primarily to a dual population of flaws of differing shapes. One set of flaws form ~ perpendicular and another parallel to the grinding direction. The latter flaws are typically substantially more elongated and often larger than the former and thus give lower strengths for stressing perpendicular to the direction of grinding. Sawing, sanding, and polishing are also shown to result in similar dual flaw populations. The character of flaws are examined as a function of the type of material and machining, as well as specimen size and shape. The latter suggests a limited strength-size effect due to machining flaws. However, the key findings are that machining flaws do not vary greatly with typical variations of machining or material parameters, e.g., composition, grain size, or hardness.

Acoustic surface wave measurements of surface cracks in ceramics, B. T. Khuri-Yakub, A. G. Evans, and G. S. Kino, SP562, pp. 379-392 (Oct. 1979).

Key words: acoustic surface wave; ceramic; surface characterization; surface crack; turbine blade.

Acoustic surface wave techniques for detecting and characterizing surface cracks in ceramics have been devised. The techniques have been demonstrated to detect cracks at least as small as 60 μm in depth, on polished samples. The crack detectability was diminished by surface grinding, because of a background effect attributed to the backscattering from surface microcracks. Preliminary experiments conducted on turbine blades indicated that the techniques can be applied to components of complex shape.

Characterization of surface damage in ceramics using selected area electron channeling, J. Lankford and D. L. Davidson, SP562, pp. 395-404 (Oct. 1979).

Key words: electron channeling; plasticity; subsurface damage; surface damage.

The technique of selected area electron channeling has been applied to the problem of characterizing subsurface plastic damage introduced during ceramic machining and polishing operations. The surfaces of ceramics spanning a wide range in hardness were prepared under controlled grinding and polishing conditions. Subsurface regions of sectioned specimens were subjected to electron channeling analysis, enabling the boundaries of the subsurface damage (plastic) zones to be mapped out. It was determined that under conditions of constant applied load, the depth of damage during polishing is inversely proportional to the square root of the hardness; this finding is in good agreement with predictions based on indentation theory.

Y-deflection modulated secondary electron images in the evaluation of ceramic surface finish, L. P. Cook, E. N. Farabaugh, and C. D. Olson, SP562, pp. 407-415 (Oct. 1979).

Key words: ceramic; scanning electron microscope; secondary electron emission; silicon; surface roughness; y-deflection modulation.

Variations in secondary electron emission intensity as a function of surface topography have been examined for single crystal silicon surfaces of three different roughnesses. It is possible to calibrate absorbed current, and under carefully controlled conditions, to calibrate secondary emission for quantitative study of surface angu

lar variation. Such data can be statistically processed to give information on surface slopes analogous to that obtained from profilometry. The agreement between profilometer and preliminary SEM data appears to be good for the roughest of the silicon surfaces. The utility of this as a general method for the examination of ceramic surfaces is suggested for instances where specimen charging can be properly eliminated.

Latent scratches on optical glasses that appear after cleaning, T. Izumitani, E. Miyade, S. Adachi, and S. Harada, SP562, pp. 417-425 (Oct. 1979).

Key words: cleaning; chemical durability; glass surface; latent scratch; optical glass; polishing.

The latent scratch which appears on polished optical glass surfaces was studied. The latent scratch, as the word implies, can be hardly detected in polishing process, but becomes evident after cleaning or after antireflection coating. The appearance of the latent scratch is affected by (1) the polisher, (2) the polishing grains, (3) the mechanical condition of the polishing, and (4) the glass property. And it is also affected by the corrosion power of the cleaning solution. It is concluded that the latent scratches are the scratches which are formed as undetectable fine scratches in the polishing process and grow to the detectable size in cleaning process. On the basis of this fact, a method of preventing latent scratches was suggested.

Machining flaws and the strength grain size behavior of ceramics, R. W. Rice, SP562, pp. 429-452 (Oct. 1979).

Key words: brittle failure; flaw sizes; grain size dependence of strength; strength.

A model for the strength-grain size dependence of ceramics failing from machining flaws is presented based on the observation that the size of machining flaws (C) shows little or no dependence on grain size. Two regimes of behavior are seen. At finer grain sizes, little or no strength dependence on grain size (G) exists because flaws are > G. For large G, the significant decrease of strength with increasing G is attributed to a transition from polycrystalline to either lower single crystal or grain boundary (i.e. bicrystal) fracture energies was the constant (C) becomes significantly less than the G as G increases. The transition between the two regimes is when C and G are similar. Extensive analysis of strength-grain size data, and more limited directly correlated fractographic data support the proposed model. Spontaneous cracking in noncubic materials is shown to support the model, but not be an alternate explanation for the transitions seen in machined Al,O, or BeO. This analysis also further supports the observation that machining flaws do not vary greatly with typical variations in machining parameters.

Surface machining effects on the strength distributions of aluminas, T. E. Easler, T. A. Countermine, R. E. Tressler, and R. C. Bradt, SP562, pp. 455-462 (Oct. 1979). removal rate; Weibull function.

Three microstructurally different, dense polycrystalline aluminas were machined with 400-grit diamond at two different rates of surface removal. Flexural strengths were measued in four-point bending under toluene and the strength distributions analyzed by two-parameter Weibull statistics. Effects of edge-bevelling on the distributions were also examined. Machined surfaces and the bevelled and non-bevelled sample edges were examined by SEM. For all of the materials, the lesser rate of surface removal was less severe in edge chipping, and yielded higher average strengths and increased values of the Weibull parameters, m and σ..

Effect of surface finish on the strength of hot pressed silicon nitride, C. A. Andersson and R. J. Bratton, SP562, pp. 463474 (Oct. 1979).

Key words: finishes; flexure; fracture; fracture mechanics; grinding; silicon nitride; strength; surface.

Statistical flexural strenghts of hot pressed silicon nitride, Norton NC 132, were determined as functions of the stress axis to hot pressing direction, the coarseness of grinding and the stress axis to grinding orientation. The higher strengths of the material tested perpendicular to the hot pressing direction rather than parallel to it can be attributed to a proportional difference in the critical stress intensities between the directions. Coarser grinding media introduces larger flaws and reduces strength. Finally, transverse grinding produces stress concentrating grooves, effedtively deeper cracks and possibly wider ones which reduce the applied stress necessary to cause propagation.

The effect of surface finishing on the strength of commercial hot pressed Si ̧N, C. C. Wù and K. R. McKinney, SP562, pp. 477-481 (Oct. 1979).

Key words: fracture origin; fracture strength; machining of ceramics; oxidation and degradation; silicon-nitride.

Effects of diamond grit size on the as-ground and oxidized strength of commercial hot-pressed Si,N, were studied. Finer grit sizes gave higher as-ground strengths. Prolonged high temperature oxidation negates effect of machining on strength.

Surface condition and strength of silicon carbide-Silicon materials, T. J. Whalen and L. L. Terner, SP562, pp. 483488 (Oct. 1979).

Key words: coatings; SiC; strength; surfaces.

The measured strength of SiC-Si materials with as-silicided ground, and ground and polished surfaces was determined. The influence on strength of SiC and nickel coatings and the geometry of test specimens was studied.

The effect of grinding and polishing on the strength of annealed soda-lime-silica glass, R. Bowles, SP562, pp. 489-500 (Oct. 1979).

Key words: defects; etching; glass; grinding; polishing; strength.

As part of the continuing studies sponsored by the Procurement Executive, Ministry of Defence (UK), recent work at British Glass Industry Research Association has aimed at assessing the defects generated in glass during its working under conventional grinding and polishing procedures.

The assessment has been mainly based upon mechanical strength property measurements of lath specimens typically 150 x 25 x 3.5 mm either at specific stages of processing or after a controlled sequence of operations designed to produce a state of minimum surface damage.

The strength of laths was determined under four point flexure test, at a nominal stress rate of 5 MPa/s under normal ambient conditions of temperature and humidity.

The resulting fracture stress data was calculated on simple bending theory after bonded strain gauge tests indicated its adequacy under observed deflections to fracture. Group statistics were largely calculated assuming normal distribution theory but tests on aggregated groups of specimens were also examined by Weibull distribution theory to determine the probability of fracture under relatively lower stresses.

Surface flaw effects on crack propagation from subsonic water drop impact, Y. M. Ito and M. Rosenblatt, SP562, pp. 501-511 (Oct. 1979).

Key words: crack activation; numerical simulation; subsonic water drop impact; surface flaws.

The effects of surface flaws on ceramic target damage from subsonic water drop impacts are investigated using numerical code simulations based on fundamental wave propagation and fracture mechanics concepts. The water drop impact generates a tensile stress wave with a steep near-surface gradient. As a consequence of this steep stress gradient, crack activation is dependent on the depth of surface flaws. In addition, a relatively large flaw can perturb the stress field such that crack activation in its vicinity is suppressed.

Surface characteristics of diamond-machined ceramic surfaces evaluated by high fluence diagnostics, M. J. Soileau, J. O. Porteus, and D. L. Decker, SP562, pp. 513-518 (Oct. 1979).

Key words: ceramic surfaces; diamond single-point machining; high fluence; laser irradiation.

Ceramic surfaces prepared by precision diamondmachining are compared with surfaces prepared by conventional polishing. Comparison is made on the basis of high fluence diagnostics. The results indicate that the diamond-machined surfaces have as high or higher failure resistance under high fluence loading as surfaces prepared using conventional techniques. Failure of both diamondmachined and polished surfaces are strongly dependent upon surface structure and surface contamination. These findings indicate that diamond-machining is an attractive alternative for generating optical surfaces on ceramic materials.

SP563. MFPG-Advanced composites: Design and applications. Proceedings of the 29th Meeting of the Mechanical Failures Prevention Group, held at the National Bureau of Standards, Gaithersburg, MD, May 23-25, 1979, T. R. Shives and W. A. Willard, Eds., Nat. Bur. Stand. (U.S.), Spec. Publ. 563, 304 pages (Oct. 1979) SN003-003-02120-2.

Key words: advanced composites; applications of composites; composites; composite structures; design using composites; fiber composites; fiber glass; filament wound composites.

These proceedings consist of a group of thirty one submitted entries (twenty one papers and ten abstracts) from the 29th meeting of the Mechanical Failures Prevention Group which was held at the National Bureau of Standards in Gaithersburg, MD, May 23-25, 1979. The subject of the symposium was the design and application of advanced composites. Special emphasis was directed to aerospace, aircraft, automotive, marine, and industrial applications and design. Failure modes in advanced composites were also discussed. These proceedings include the following papers (indented):

Characterization and application of advanced composite materials, M. Waddoups, SP563, p. 3 (Oct. 1979).

Key words: aircraft structural components; composite materials; linear elastic materials; tensile fracture.

A technical understanding of the structural characteristics of composite materials and the critical issues in aircraft structural component development have been simultaneously generated. It is established that the strengthening concept, structural characteristics, and fabri

cation techniques are distinct from metals. These differences and the resultant structural implications are the subject of this lecture.

For practical purposes, composites are linear elastic. Tensile failure modes are brittle fracture governed, and compressive failure modes are micro and macro stability governed. Even though composites have no classical ductility, they are surprisingly tough materials. In most fullscale structures currently developed, tensile fracture constitutes the critical strength failure mode.

While generally tensile fracture governs strength, an equivalent-to-crack coalescence and monotonic growth in tension are not observed in composites (except glass-fiberreinforced plastics). In fact, tension-dominated cracking is not of serious consequence in advanced laminates. Weak plane (intralaminar and interlaminar) flaw propagation, predominantly in compressive and shear loadings, yields the lift limiting failure modes for composites. When modeled as strain-energy release-rate-driven flawgrowth processes, different growth rates and initial strengths generate competing failure modes in full-scale structures.

Simple structural forms that control the life-limiting failure processes will become the rule for successful structures. Only on stiffness critical or fairing type of structure will the complex shape moldability advantages of composites be used.

Because of the scale effects in the fracture process zone and the ability to react significant out-of-plane loads, simple mechanical fastening will dominate highly loaded, strength-critical structure. Secondary adhesive bonding will not be very successful in highly fracture critical structure.

Physical and mechanical response of graphite/polyimide materials to long term exposure in a space environment; material preparation and control testing, J. H. Powell, SP563, pp. 4-16 (Oct. 1979).

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Key words: cocured and precured laminates; mospheric exposure of composites; Long Duration Exposure Facility (LDEF); polyimide composite stability in space; polyimide/graphite mechanical properties; ultrasonic inspection.

Graphite/polyimide (Gr/PI) composite laminates are currently being prepared for deployment on NASA Langley Research Center's Long Duration Exposure Facility (LDEF). The experiment is intended to provide scientific and engineering design information on the response of Gr/PI composites to an actual exoatmospheric environment. Material systems to be exposed are a bismaleimide PI (Hexcel F-178) on Thornel 300 graphite fibers and a condensation PI (Monsanto Skybond 703) on HT-S graphite fibers, including both "precured" and "cocured" laminates. Initial physical characteristics determined on both exposure and simultaneously processed control panels include flatness, microcracking, void content, dry weight, and general appearance. Mechanical tests performed to date (on control panels only) are the basis for strength and elastic properties in tension, compression, and (rail) shear at ambient and elevated temperatures. Following in-space exposure of test panels and return to earth, identical physical and mechanical determinations will be made. Data generated before and after exposure will be compared to identify any changes in physical or mechanical characteristics, particularly any unexpected changes. The ultimate output of the experiment will be either confirmation of predicted material behavior or the basis for revised prediction methods.

Effects of room-temperature aging on composite prepregs, H. C. Nash, C. F. Poranski, Jr., and R. Y. Ting, SP563, pp. 17-21 (Oct. 1979).

Key words: aging of polymer; composite; fiber; mechanical properties; moisture; prepreg.

Prepreg materials of organic-matrix composites have very limited shelf-life, even under the required cold-storage conditions. A prepreg aging study has been carried out by storing prepreg materials at room temperature under three different controlled humidity levels. Exposed samples were examined periodically by proton NMR spectroscopy, and unidirectional 16-ply laminates were fabricated. Prepreg appearance, curing behavior, and laminate properties were found to change with prepreg out-time.

Application of instrumental techniques to the study of the cure of phthalocyanine/graphite composites, R. Y. Ting, SP563, pp. 25-31 (Oct. 1979).

Key words: cure; dielectric analysis; DSC; graphite-fiber; polyphthalocyanine; prepreg; TGA; V/STOL.

Work on resin evaluation in the NRL V/STOL aircraft program is directed toward the development of high temperature resins for application as potential composite matrix materials. As successful prepregging of the polyphthalocyanine/graphite-fiber system has recently been demonstrated, the processability of this material is now under study. Instrumental techniques including differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and dynamic dielectric analysis are employed to examine the thermal properties of unidirectional prepregs and the fabrication of unidirectional laminates. Results of these studies have led to the development of a cure cycle for this new resin system.

Moisture diffusion analysis for composite microdamage, C. L. Leung and D. H. Kaelble, SP563, pp. 32-46 (Oct. 1979). Key words: diffusion coefficents; iteration; moisture profile modeling; nondestructive evaluation; statistical estimation.

Because of their favorable performance characteristics, advanced composites using graphite fibers as reinforcement are increasingly being used in aerospace and commercial applications. There has been much concern, however, about the extent and mechanisms of strength degradation of these composites when exposed to moisture for long periods of time. In this paper, methods to obtain directional diffusion coefficients, i.e., D, D, and D, for the principal axis of a unidirectional fibrous composite are described by moisture absorption and effusion measurements. Additionally, analytical models have been developed to calculate, using the previously established diffusion coefficients, the moisture profile of the composite after periods of moisture exposure. The feasibility of the integration of the effusion rate measurement, moisture profiling, and strength prediction into a computer-aided analyzer for composite microstructure damage or defect is discussed.

Recent work on techniques and applications of moisture barriers to graphite epoxy composites, J. F. Haskins, SP563, pp. 47-56 (Oct. 1979).

Key words: advanced composites; dimensional stability; eutectic coating; graphite/epoxy; moisture barrier; space optics.

A number of space systems such as Thematic Mapper, MAGSAT and other space optical devices require that the components be dimensionally stable during both ground and space operation. It has been found that certain graphite/epoxy composite laminates can provide extremely low coefficient of thermal expansion (a < 0.05 × 10

in./in.F) and because of this are ideally suited to optical benches, telescope housings, and mirror substructures. However, the epoxy must be protected from moisture because it is hygroscopic and does change dimensions as it absorbs or desorbs moisture. Typically it may change as much as 100 microinches/inch over a period of several months when exposed to high relative humidity. This becomes a problem because most of the equipment will be manufactured, assembled, and operated in a humid environment before it is launched into space. Holding the humidity at low level lessens this problem but does not eliminate it.

A real advance in optical equipment for use in space can be made if graphite/epoxy can be sealed from moisture without substantially changing its weight and coefficient of expansion. The objective of this work was to test the effectiveness, develop inspection procedures, and check the reliability of a moisture barrier developed previously at General Dynamics Convair Division.

This paper gives the results of a critical evaluation of the effectiveness and reproducibility of the eutectic coating. Fifteen-inch long graphite/epoxy coated specimens were used to study processing variables, inspection techniques, and dimensional changes due to moisture pickup.

In-service ultrasonic inspection system for composites, F. H. Chang, J. R. Bell, A. H. Gardner, C. P. Fisher, and G. P. Handley, SP563, p. 59 (Oct. 1979).

Key words: composite structures; flaw simulation; semi-automated ultrasonic inspection; ultrasonic inspection system.

Advanced composite structures are presently used on high performance U.S. Air Force aircraft to save weight and increase performance. These structures are often difficult to inspect because of their complex/multi-bondline construction and because of the general lack of experience in the inspection of composite structures in the field environment. Ultrasonic techniques have generally been employed for the detection of service induced discontinuities such as disbonds and delaminations. They are not considered cost effective for inspection of large areas for small flaws or for monitoring areas containing known small flaws for propagation during service, primarily because of the lack of flaw position locating and permanent inspection result recording devices. An ultrasonic technique was developed under an AFML contract to record the position and flaw indication in a permanent manner and minimize operator dependence to obtain a high level of inspection reliability. The technique is simple to apply in the field environment by personnel without advanced training. In the program, specimens representing typical composite structures and containing implanted flaws simulating service induced or production type defects were fabricated. Improvements were made to the state-of-the-art ultrasonic inspection techniques to detect these defects. A follow-on program is being conducted to establish the producibility of the semi-automated ultrasonic inspection system for aircraft composite structure, based on the preliminary design developed in the previous contract, to provide a complete inspection system from inception to obsolescence.

Design considerations for graphite-epoxy laminates of low thermal expansivity, D. D. Smith, SP563, pp. 60-71 (Oct. 1979).

Key words: advanced composite materials; graphite-epoxy laminate design; laminate design sensitivities; thermal expansion.

The development of graphite-epoxy laminate designs for space missions requiring structural components with near zero coefficient of thermal expansion (CTE) is examined. The selection of fiber systems and laminate designs is approached by evaluating CTE sensitivities to material and process variabilities. Uniaxial and biaxial thermal stability laminates are considered. From this design approach, material and process specification tolerances can be determined to control laminate CTE within design objectives. Design examples are presented to illustrate this laminate design approach.

Aircraft composite materials selection and application, V. L. Reneau, SP563, pp. 72-79 (Oct. 1979).

Key words: aircraft; composites; design allowables.

Composite aircraft structure requires proof of safety and durability similarly to metallic structure. The proofs of structural analysis methods, reliable material properties, and of assembly methods are similar to those required for metal structure. The effects of environment, time and fatigue damage are different than for metal and must be compensated for when design properties (allowables) are developed. Design allowables are not as readily available for composites as for metals and frequently must be obtained by testing.

Composite structures in rotors and propellers, D. F. Thompson, SP563, pp. 80-88 (Oct. 1979).

Key words: blade aeroelastic behaviour; blade manufacture and quality control; composite propellers and rotors; failsafe blade design; propeller fatigue behaviour; propeller materials requirements.

A variety of composite rotor blade and propeller designs are reviewed. Desirable blade composite material qualities are enumerated. Various failsafe design features are shown for propeller blades. Multiple load path design features are discussed. Some manufacturing and quality control aspects of composite blade construction are discussed. Composite material properties versus cost factors are discussed.

Development of a library module for the analysis of advanced composite materials, K. T. Knoll, SP563, pp. 91-107 (Oct. 1979).

Key words: advanced composite materials; composite materials analysis; orthotropic materials; programmable calculators; solid state software.

Because of their orthotropic nature, advanced composite materials present some special problems to the engineer. The relation between the elastic constants of an orthotropic material is more complex than that of an isotropic material. In addition, composites exhibit coupling between normal and shear deformations as well as between bending and stretching load responses. The more complicated behavior of advanced composites is usually handled using techniques of matrix mathematics, but the required bookkeeping often overwhelms the isotropic-trained engineer who is used to working with fewer terms and less complicated equations. This paper discusses the development of a module, designed to be used with the Texas Instruments TI-58 and TI-59 desktop calculators which can be used to handle much of the required "bookkeeping." Given such input as the elastic constants of a single ply of composite material, the stacking sequence of a laminate, and the applied loads (or strains), the module will output desired information such as the physical properties of a laminate, the strains (or loads) in both the whole laminate and the individual plies, and the values of the laminate

properties as the laminate is rotated. The module will also provide "strength ratios" for particular laminate and load vector to indicate how close the material is to failure. It is hoped that this module will make the analysis and use of advanced composites seem less formidable to both research and developmental engineers.

Structural

SMC-Material,

process and performance review, R. B. Jutte, SP563, pp. 108-129 (Oct. 1979).

Key words: glass fiber reinforcement; polyester resin; structural sheet molding compound.

Sheet molding compound (SMC) has been used for functional or fascia automotive parts such as front and rear panels for several years. When properly formulated, processed, and molded, SMC has a potentially substantial role in the manufacture of more structurally demanding automotive parts.

Through variations in the materials, equipment and processing techniques, different types of SMC can be produced. These are random fiber SMC (SMC-R); continuous fiber SMC (SMC-C); and directional fiber SMC (SMC-D).

Representative formulations show how static mechanical properties are dependent upon glass content, glass orientation, and on the test temperature.

Based on equivalent performance, these systems are lighter in weight than steel and are generally less costly, on a material basis, than aluminum.

Development of a graphite-epoxy spacecraft precision mounting platform, K. S. Budlong and A. W. Sheffler, SP563, p. 130 (Oct. 1979).

Key words: composite design; graphite-epoxy; Precision Mounting Platform; resonant frequency.

A wide variety of spacecraft applications require structure which is ultralight in weight while satisfying tight stiffness (resonant frequency) criteria, along with critical pointing accuracy and thermal distortion requirements. This paper presents the design, analysis, and test of a graphite-epoxy precision mounting platform intended to replace the current aluminum platform being flown on an Air Force satellite program.

The Precision Mounting Platform (PMP) provides an instrument mounting surface which is defined and controlled for each instrument to within 0.01 degree. It maintains a mutual alignment of the instruments to within 0.003 degree through the full range of thermal gradients occurring on orbit. While the aluminum PMP uses active thermal controls to minimize thermal gradients and maintain alignment, the composite design takes full advantage of the near zero coefficient of thermal expansion of the GY70/X30 graphite-epoxy, thus eliminating active control. The ultra-high stiffness of the composite is also critical in maintaining the resonant frequency range defined by overall spacecraft dynamics for the aluminum PMP. The graphiteepoxy PMP provides in addition a weight savings of 32 percent while fulfilling all the requirements of a direct replacement for the current aluminum version.

Design analysis of automotive composite structures, M. F. Kowalski, D. S. Fine, and R. K. Herrman, SP563, p. 133 (Oct. 1979).

Key words: automotive structures; composite material; composite material analysis program; Tsai-Wu tensor polynomial lamina strength failure criterion.

Advanced composite materials offer potential for structural mass reduction in automotive structures due to their