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Advanced Composites Design and Applications

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Advanced Composites, Design and Applications


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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 fabrication 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 full-scale 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-fiber-reinforced 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 flaw- growth 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 loaded fracture critical structure.

Abstract: 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 pro- vide 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 Thome! 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 simul- taneously 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 determi- nations will be made. Data generated before and after exposure will be compared to identify any changes in physical or mechanical character- istics, particularly any unexpected changes. The ultimate output of the experiment will be either confirmation of predicted material behav- ior or the basis for revised prediction methods.

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

FOREWARD SESSION 1: AEROSPACE AND AIRCRAFT APPLICATIONS AND DESIGN A. Characterization and Application of Advanced 3 Composite Materials (abstract only) . Max Waddoups B. Physical and Mechanical Response of Graphite/ 4 Polyimide Materials to Long Term Exposure in a Space Environment; Material Preparation and Control Testing. J. H. Powell C. Effects of Room- Temperature Aging on Composite 17 Prepregs. H. C. Nash, C. F. Poranski, Jr.*, and R. Y. Ting

SESSION 2: AEROSPACE AND AIRCRAFT APPLICATIONS AND DESIGN A. Application of Instrumental Techniques to the Study 25 of the Cure of Phthalocyanine/Graphite Composites. Robert Y. Ting B. Moisture Diffusion Analysis for Composite Micro- 32 damage. C. L. Leung* and D. H. Kaelble C. Recent Work on Techniques and Applications of 47 Moisture Barriers to Graphite Epoxy Composites. James F. Haskins

SESSION 3: AEROSPACE AND AIRCRAFT APPLICATIONS AND DESIGN A. In-Service Ultrasonic Inspection System for 59 Composites (abstract only). F. H. Chang*, J. R. Bell, A. H. Gardner, C. P. Fisher and G. P. Handley B. Design Considerations for Graphite -Epoxy Laminates 60 of Low Thermal Expansivity. Dennis D. Smith IV C. Aircraft Composite Materials Selection and Appli- 72 cation. V. L. Reneau D. Composite Structures in Rotors and Propellers. 80 David F. Thompson

SESSION 4: AEROSPACE AND AIRCRAFT APPLICATIONS AND DESIGN A. Development of a Library Module for the Analysis of 91 Advanced Composite Materials. Karyn T. Knoll B. Structural SMC - Material, Process and Performance 108 Review. Ralph B. Jutte (presented by Joseph D. Feko, Owens-Corning Fiberglas Corporation) C. Development of a Graphite-Epoxy Spacecraft Precision 130 Mounting Platform (abstract only). Kathleen S. Budlong and Alvin W. Sheffler

SESSION 5: AUTOMOTIVE APPLICATIONS AND DESIGN A. Design Analysis of Automotive Composite Structures 133 (abstract only). M. F. Kowalski, D. S. Fine*, and R. K. Herrman B. Fiberglass Reinforced Plastics Use in Transporta- 134 tion Vehicles (abstract only) . R. D. Pistole C. Designing Automotive Components with Continuous 135 Fiber Composites. H. T. Kulkarni* and P. Beardmore SESSION 6: INDUSTRIAL APPLICATIONS AND DESIGN A. Fabrication of Large Composite Spars and Blades. 155 O. Weingart (presented by Robert Gordon, Structural Composite Industries, Inc.) B. The Effect of Fiber Orientation on the Design 173 Parameters of Reinforced and Filled Thermoplastic Compounds (abstract only) . Peter J. Cloud* and Robert T. Alvord V C. Quality Assurance of Manufactured Components 174 (abstract only). R. D. Margolis

SESSION 7: INDUSTRIAL APPLICATIONS AND DESIGN A. Degradation Data of Kevlar Pressure Vessels. 177 W. D. Humphrey B. Design Assurance of a Leak Failure Mode for 198 Composite Overwrapped Metal Tankage. W. W. Schmidt C. Composite Materials in Recreational Equipment 208 (abstract only) . David Ratchford

SESSION 8: INDUSTRIAL APPLICATIONS AND DESIGN A. Holographic Nondestructive Evaluation of Spherical 211 Kevlar/Epoxy Pressure Vessels. D. M. Boyd* and B. W. Maxfield B. The Air Force "Manufacturing Cost/Design Guide 226 (MC/DG) " (abstract only). Bryan R. Noton* and Captain Dan L. Shunk C. Tensile Strength and Failure Modes of Boron-Epoxy 228 Composites with a Notch. Charles E. S. Ueng

SESSION 9: FAILURE MODES IN ADVANCED COMPOSITES A. Failure Criteria for Composites under Complex 241 Loading (abstract only). P. W. Mast*, L. A. Beaubien, D. R. Mulville, S. A. Sutton, R. W. Thomas, J. Tirosh and I. Wo lock B. Failure Analvsis of an Idealized Composite Damage 242 Zone. Carl T. Herakovich* and David A. O'Brien C. Interlaminar Failure in Epoxy Based Composite 255 Laminates. A. S. Wang*, F. W. Crossman and G. E. Law, Jr. VI

SESSION 10: MARINE APPLICATIONS AND DESIGN A. Current Developments in Advanced Composites for 267 Naval Ship Application. J. J. Kelly* and H. H. Vanderveldt B. Environmental Effects on Fiber Reinforced Organic 276 Matrix Composites. M. Silvergleit* , A. B. Macander, F. A. Brauer, and H. P. Edelstein C. Composite Technology for Marine Application. 286 W. P. Couch APPENDIX List of Registrants for the 29th MFPG Meeting. 301 MFPG Publications 307 * Indicates speaker when a paper had more than one author.

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