Acoustic emission spectral analysis of fiber composite failure mechanisms

K-calibration of unidirectional metal matrix composites Awerbuch, J. and Hahn, H.T. Jourhal of Composite Materials Vol 12 (July 1978)pp 222-237 Load/displacement curves were obtained for centre notched, unidirectional boron/aluminium and borsic/titanium specimens. The displacement was measured both with standard 1 inch (25.4 mm)and 0.25 inch (6.35 mm) clip gauges and with a laser interferometric technique, which measures the crack opening directly. The interferometric displacement gauge is more sensitive to damage at the crack tip, displaying a non-linear load displacement curve, and so gives a better characterization of the fracture behaviour of a composite,

The mechanical behaviour of porous austenitic stainless steel fibre structures Ducheyne, P., Aernaudt, E. and de Meesten, P. Journal o f Materials Science Vol 13 (1978) pp 2650 - 2658 Stainless steel (AISI 316L) fibres with diameters of 50 and 100 #m were compacted and sintered to form porous, metal fibre structures which were tested in tension and compression. The tensile behaviour is in agreement with theoretical predictions, with ultimate failure being caused by fibre breakage. In compression, however, plastic deformation occurs at very low applied loads,

The strength of carbon fibrereinforced nickel composites produced by electro-deposition and hot-pressing Shiota, I. and Watanabe, O. Journal o f Materials Science Vol 14 (1979) pp 699-704 By electro-plating nickel onto panbased carbon fibre yarn, and subsequently hot-pressing the coated fibre, the authors were able to achieve tensile strengths for the unidirectional material above that expected from the rule-of-mixtures, For constant current deposition, the properties of the plated metal change as the surface area increases and the current density decreases, and these differences persist even after annealing, and must be taken into account in assessing composite strength,

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Acoustic emission spectral analysis of fiber composite failure mechanisms Williams, J.H. and Egan, D.M. MaterialsEvaluation Vo137 No 1 (January 1979) The authors first review the literature on the frequency spectra of acoustics emission from fibre composites, and conclude that there is no statistically sound evidence for distinguishing between fracture mechanisms. Their experimental results from wide-band monitoring of graphite/polyimide composites are analysed statistically using a paired-sample t test, for 0°, 10°, 90 °, and + 45 ° fibre orientations. A table gives the percentage of specimen comparisons for which the acoustic emission spectra are statistically indistinguishable, Application of the average stress failure criterion. Part I Nuismer, R.J. and Labor, J.D.Jourhal of Composite Materials Vol 12 (July 1978)pp 238-249 Results are presented for the fract u r e st r e ng t h s o f se ve r a I graphite/epoxy (AS/3501-5) laminates containing countersunk holes and normal and slant slits. The countersunk holes behaved in the same manner as normal ones, and the normal and slanted slits produced similar results. It is shown that the average stress criterion leads to acceptable strength predictions for all cases considered.

Behaviour of integral composite joints - finite element and experimental evaluation Gillespie, J.W. and Pipes, R.B. Journal o f Composite Materials Vol 12 (October 1978) pp 408-421 Experimental evidence indicates that the incorporation of an insert increases the out-of-plane load transfer capability of an integral composite joint. A graphite/epoxy joint of this type has been studied using linear-elastic finite element techniques. Discussion of the finite element model, material properties and strength criteria for the noinsert, titanium insert and graphiteepoxy insert concepts, is presented and compared with experimental data.

Extrusion of self-reinforced thermoplastic composites illustrated by high density polyethylene Zachariades A.A., Ball, R. and Porter, R.S.JournalofMaterials Science Vol 13 (1978) pp 2671-2675 A method is described for solid state coextrusion of self-reinforced, transparent composites of high density polyethylene composed of core and sheath components. The co-cylindrical composites, formed below their melting points, have a high modulus and strength, a good orientation for both sheath and core components and possess considerable resistance to core/sheath separation. This resistance to pull-out is due to compressive radial stresses and not bonding by epitaxial crystallization. The fracture energy of hybrid earboa and glass fibre composites Kirk, J.N., Munro, M. and Beaumont, P.W.R. Journal o f Materials Science Vol 13 (1978) pp 2197 - 2204 Thefractureenergyofamodelcarbon fibre/glass fibre/epoxy resin hybrid composite system has been evaluated as a function of the carbon/glass ratio. Models of microscopic fracture behaviour, together with work of fracture and pull-out length measurements, were successful in quantitatively describing the observed fracture behaviour. The post debond friction energy and sliding mechanism were shown to be important.

Interconnected fibre masses precipitated from solutions of polymers Keller, L.B. and Jenkins, R.K. Nature Vol 278 (29 March 1979) pp 439-441 Three-dimensionally outerconnected fibre structures may be grown from polymer solutions by sonic agitation and simultaneous cooling. The fibre masses may be grown with isotacticpolypropylene, polyethylene, and polybutene-1. This has been extended to other polymers, both crystalline and noncrystalline, by a process termed 'seeding'. The fibre masses generally have greatly improved properties over bulk polymers, and havepotential application in the encapsulation of complex geometries where the in situ formation of fibres might be followed by polymerization of the sol-

COMPOSITES. JU LY 1979