Composite tension damage

It is critical that surface treatment conditions be optimized to composite properties since overtreatment as well as undertreatment will degrade composite properties. Typically composite interlaminar shear strength (ILSS), in-plane shear, and transverse tension ate used to assess the effectiveness of surface treatment. More recently damage tolerance properties such as edge delamination strength, open hole compression, and compression after impact have become more important in evaluating the toughness of composite parts. 

Craddock, J.N. and Savides. I.S. (1994). Modeling elastic-plastic behavior of metal matrix composites with reaction zones under longitudinal tension. Ini. J. Damage Mech. 3, 308-311. 

Generally, when testing materials with a nonlinear stress-strain behavior, the tests should be conducted under uniform stress fields, such that the associated damage evolution is also uniform over the gauge section where the material s response is measured. Because the stress field varies with distance from the neutral axis in bending tests, uniaxial tension or compression tests are preferred when characterizing the strength and failure behavior of fiber-reinforced composites. 

Figure 6.1 shows a typical stress-strain curve for a unidirectional SiCf/CAS composite loaded in uniaxial tension parallel to the fibers. The features of this curve are represenative of many ceramic matrix composites. In order to distinguish between the various damage states that a composite undergoes, it is convenient to divide the stress-strain curve into several sequential parts. 

Daggumati S, Van Paepegem W, Degrieck J, Xu J, Lomov SV, Verpoest I. Local damage in a 5-hamess satin weave composite under static tension Part II — Meso-FE modelling. Compos Sci Technol 2010 70(13) 1934—41. 

Mollenhauer D, Ward L, larve E, Putthanarat S, Hoos K, Hallett S, Li X. Simulation of discrete damage in composite overheight compact tension specimens. Composites Part A 2012 43 1667-79. 

Takemura K, Fujii T. Fatigue strength and damage progression in a circular-holenotched GRP composite under combined tension/torsion loading. Compos Sci Technol 1994 52 519-26. 

Gray PJ, McCarthy CT. An analytical model for the prediction of through-thickness stiffness in tension-loaded composite bolted joints. Compos Struct 2012 94(8) 2450—9. Lapczyk I, Hurtado JA. Progressive damage modeUing in fibre-reinforced materials. Compos Part A-Applied Sci Manuf 2007 28 2333-41. 

Tension, compression, and shear are the three fundamental modes in which a composite lamina may fail. As the composite material is made up of multiple laminae (layers and plies) of various orientations, the stresses in the lamina s principal directions vary from lamina to lamina. As the load is increased, so do the various stresses in the laminae, and failure values may be attained in a certain lamina in a certain principal direction without the overall laminate experiencing actual failure in other words, the failure of the composite laminate is a progressive phenomenon. This progressive damage evolution is subcritical for a while, but eventually leads to ultimate failure of the composite laminate. 

Figure 15.1 Lxjngitudinal tension of a 0/90 composite laminate. Highlight of several damage modes matrix cracking in transverse (T) lamina, splitting of longitudinal (L) laminae, and delamination between T and L laminae [6],...

Figure 15.3 Composite damage due to fastener holes, (a) Tjfpical bolted junction between a composite wing skin and metallic connection (b) failure modes in a bolted joint under tension [6] and (c) compressive failure modes in a plate with an open hole.

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