Comparative evaluation of potential NDE techniques for inspection of advanced composite structures

Comparative evaluation of potential NDE techniques for inspection of advanced composite structures Sheldon, W.H. Materials Evaluation 36 (February 1978) No 2 p 41 Ultrasonic resonance, focussed image ultrasonic holography, pulse-echo C-scan, B-scan and 3 D-scan, and laser holographic and radiographic techniques were evaluated as potential inspection systems for large carbon fibre/epoxy structures. These were a wing flap, bulkhead and wing section containing manufacturing flaws, a trunnion with a transverse crack, and several composites with simulated defects, The mobile systems were also applied to a stabiliser and composite panel undergoing fatigue testing, Ultrasonic techniques were superior in the detection of debonded areas, but radiography gave good rcsolution of core defects. Creep, repeated loading, fatigueand crack growth in 45 ° oriented carbon fibre reinforced plastics Sturgeon, J.B. Journal of Materials Science Vol 13 (1978) pp 1490-1498 Considerable creep occurs in room temperature tensile loading of 45 ° carbon fibre laminate, both static and repeated, and in each case is composed of a permanent and recoverable component, in fatigue cracking, temperature increases only become significant towards the end of the fatigue life, which is characterised by interlaminar cracking whose detection may be a useful indicator of lifetime, Monitoring of displacements due to cracking gives an indication of remaining fatigue lifetime, and allows an estimate of crack growth rate.

Designing for improved fracture strength in advanced composites Walter, R.W. and June, R.R. Sample Quarterly Vol 9 No 3 (April 1978) pp 26-33 The static and dynamic properties of glass/epoxy, graphite/epoxy and glass-graphite/epoxy laminates were investigated; the effect of laminate stacking sequence and basic static strength were studied. The use of glass in a graphite/epoxy laminate, as a glass/graphite hybrid reinforcement, was found to improve the strength and failure mode of the composite,

COMPOSITES. JANUARY 1979

Diamagnetic susceptibility of carbon fibre epoxy resin composites Arajs, S., Moyer, C.A. and Kote, G. Journal of Materials Science Vol 13 (1978) pp 2061-2063 This study confirms that the susceptibility behaviour as a function of fibre orientation is simply calculated from limiting values at 0 ° and 90 ° orientation. The magnetic susceptibility can be correlated with Young's modulus for two carbon fibre types. The technique is also sensitive to fibre misalignment. Evaluation of biaxial stress failure surfaces for a glass fabric reinforced polyester resin under static and fatigue loading Owen, M.J. and Griffiths, J.R. Journal of Materials Science Vol 13 (1978) pp 1521-1537 An extensive testing programme is described which has determined the plane stress surface in ol,o,,o6 space using thin walled tubes with axial and internal pressure loading. Evaluation of nine failure theories shows that satisfactory agreement is possible over a limited region of the surface only for theories incorporating complex stress properties. Application of these complex stress theories is usually governed by stability criteria which preclude discontinuities or intersections of the failure surface, but in practice such surfaces may be valid as damage mechanisms and failure modes change with load conditions. Separate evaluation of different regions of the failure surface is recommended,

Evaluation of the tensor polynomial failure criterion for composite materials Tennyson, R.C., MacDonald, D. and Nanyaro, A.P.JournalofComposite Materials Vol 12 (January 1978) p 63 A tensor polynominal failure criterion is developed for laminae and is shown to require cubic terms in addition to quadratic terms. Such a formulation is able to accommodate observed differences in positive and negative stress induced failures. Both experimental and analytical methods for ~he evaluation of the strength equation are described for glass/epoxy and graphite/epoxy composite tubes.

Experimental data for the longitudinal tensile strength of unidirectional fibrous composites Part 1: fibre and matrix Barry, P.W., Fibre Science and Technology Vol 11 No 4 (July 1978) pp 245-255 Experimental data are presented for three types of carbon fibre and two epoxy resin formulations. These data are considered suitable for checking the prediction of models for longitudinal tensile strength of unidirectional fibrous composites. A brief outline of the test methods used is also given. Fibre characteristics covered by experimental data include density, dimater, Young's modulus, and stength/length and strength/ modulus relationships. Expressions governing stres-strain curves in short fibre reinforced polymers Piggott, M.R. Journal of Materials Science Vol 13 (1978) pp 1709-1716 An extension of strength theories for short fibre-reinforced plastics enables complete stress/strain curves to be estimated. The friction between fibre and matrix, the residual stresses, and the fibre aspect ratio are critical parameters governing the shape of the stress/strain curve, but adhesion of the components is shown to be of minor importance in determining reinforcement, although it does extent.affect the elastic limit to a marked

Fatigue and residual strength degradation for graphite/epoxy composites under tensioncompression ioadings Yang, J.N. Journal of Composite MaterialsVol 12 (January 1978) p 19 A statistical model for fatigue life and residual strength of laminates is developed theoretically and verified for untouched graphite/epoxy composites in tension-compression fatigue and tension-tension fatigue. The approach can be extended to cover high loads, such as proof tests, and failure modes dominated by matrix failure. Fracture energy of epoxy resin under plane strain conditions Andrews, E.H. and Stevenson, A. Journal of Materials Science Vol 13 (1978) pp 1680-1688 Internal pressurization of a circular

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