Composite impact damage

Many of the inspection problems posed by composites can be dealt with effectively by ultrasonic. Delaminations, bonding defects, impact damage, cavities and porosities are among the typical defects which can de detected by ultrasonic inspection. 

There are, of course, many more aspects of composite hardware design that differ from metallic bonded structure but do not necessarily involve adhesive bonding. For instance there are many types of reinforcement tape and fabric to choose from, the orientation of the plies must be chosen, the ply stackups must be balanced to avoid part warping after cure, a minimum number of plies must be used to prevent non-visible impact damage that significantly affects the load carrying capability of the part, etc. 

I ig. X.ll. Residual stillness a.s a funetion crack length as measured from double cantilever beam specimens after impact damage carbon fiber composites containing (O) unmodified epoxy ( ) rubber-... 

Caneva, C., Olivieri, S Santulli, C. and Bonifazi, G. (1993). Impact damage evaluation on advanced stitched composites by means of acoustic emission and image analysis. Composite Structures 25, 121-128,... 

Masters. J.E. (1987b). Characterisation of impact damage development in graphite/epoxy laminates. In Fractography of Modern Engineering Materials Composites and Metals, ASTM STP 948, ASTM. Philadelphia, PA, pp. 238-258. 

Poon, C., Benak, T. and Gould, R. (1990). Assessment of impact damage in toughened resin composites. Theor. Appl. Fract. Mech. 13, 81-97. 

Rechak, S. and Sun, C.T. (1990). Optimal use of adhesive layer in reducing impact damage in composite laminates. J. Reinforced Plasl. Composites 9, 569 582. 

Sun. C.T. and Rechak. S. (1988). Effect of adhesive layers on impact damage in composite laminates in Composite Materials Testing and Design (8th Conf.) ASTM STP 972 (J.D. Whitcomb ed.), ASTM, Philadelphia, PA, pp 97-123. 

Fig. 10.2. Successive ply layers of a glass-fibre-reinforced composite (GFRP) damaged by impact of a missile from an air-gun 50 MHz (sample from Kyoto University,...

Many applications of ceramic composites will expose the material to impact damage. Here again, the amount of work which has been done in this arena is limited, and needs to be increased. Impact tests can be performed using drop towers or Charpy impact testing apparatus. Such measurements have been done at room temperature30 and the apparatus can be adapted for use at elevated temperatures. 

W. H. Green, J. M. Wells, Nondestructive characterization of impact damage in metallic/nonmetallic composites using X-ray computed tomography imaging, NASA ARL-TR-2399, February 2001. 

Broken fibers, a result of impact damage, cause a reduction in tensile strength and thus shorten the life of composite laminates. Under cyclic loading, fiber fractures begin within the first third of the expected life of cross-ply laminates [6], If carbon or boron fibers are used, these tend to be more brittle, and cracking may occur more easily during onset of impacts, which reduces the structural integrity of composites made with such materials. 

Che.ster, R. J.. and Clark. G. (1992), Modelling of impact damage features in graphite epoxy laminates. Damage Detection in Composite Materials. ASTM, STP. 

Greszczuk, L. B.. and Chao, H. (1976). Impact damage in graphite-fiber-reinforced compo-sitc.s. Proc. of the 4th Conf on Composite Materials testing and design. AST Pub. 617. May 1976. pp, 389-408. 

Opiinger. D. W.. and Slepetz, J. M. (1975), Impact damage tolerance of graphite, epoxy sandwich panels. Foreign Object Impact Damage to Composites, ASTM STP 568, pp. 30 48. 

Cantwell. W. J.. and Morton, (1985). Detection of impact damage in CFRP laminates. Composite Structures, 3, 3-4, 241-257. 

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