Computational analysis of mixed-mode delamination crack growth in a woven laminated ceramic-matrix composite G.M. Newaz a, *, N. Bonora b , M. Krishnappa a a Mechanical Engineering Department, Wayne State University, 5050 A. Wayne Drive, Detroit, MI 48202, USA b Industrial Engineering Department, University of Cassino, Via G. Di Biasio 43, 03043 Cassino, Italy Received 4 August 1998; received in revised form 15 February 1999; accepted 23 July 1999 Abstract Mixed-mode delamination crack growth characteristics in a Nicalon/glass (barium magnesium alumino-silicate, BMAS) woven laminated ceramic-matrix composite (CMC) have been analyzed. Delamination crack growth under mixed-mode conditions was investigated by the use of a computational mechanics approach. For the purpose of this study the CMC specimen considered was in four-point bending. A T-crack configuration was investigated with particular attention to determining the influence of notch depth and delamination crack length on the eective strain-energy release rate. # 1999 Elsevier Science Ltd. All rights reserved. 1. Introduction Ceramic-matrix composites (CMC) are a class of composite materials which have low thermal expansion coecient and low density, are corrosion resistant, have high electrical resistivity and can withstand very high temperatures. For high-temperature applications, sili- con-carbide-fiber-reinforced glass-matrix composites oer potential which cannot be matched by polymer- matrix composites (PMC). In addition, higher tempera- ture Nicalon-reinforced silicon-carbide matrix (SiC) CMCs oer good potential for applications above 1000  C. As a result of their high-temperature perfor- mance, ceramic-matrix composites are finding a number of civilian and military applications [1,2] such as advanced heat-engine rotors, flame holders, combus- tors, casings, flaps, shrouds and vanes of jet engines [3]. As structural materials, monolithic (unreinforced) ceramics inherently suer from two important reliability issues: high sensitivity to processing and service-gener- ated flaws (low fracture toughness) and the inability to tolerate stress overloads without catastrophic brittle failure. Although whisker reinforcements enhance toughness in CMCs, they do not eliminate the possibi- lity of failure, a problem that severely restricts their use in heat engines. Continuous-fibre ceramic-matrix compo- sites, however, can provide significant toughness increases along with the ability to fail in a non-catastrophic manner similar to metal. One of the typical fracture modes that limit the use of CMCs is delamination damage that may occur in pro- cessing or which can be induced as a result of service loads. Delamination is also the most prevalent type of life-limiting failure in advanced composites that may also result from impact damage or from three-dimen- sional interlaminar stresses that develop at the stress- free edges or discontinuities such as the free surface of a hole. Delamination between plies has been found to have considerable impact on the structural integrity of the system. It causes a loss in the structural stiness which in turn leads to very large deflections. Moreover, experiments with composites indicate that the suscept- ibility to delamination cracking is usually associated with low transverse-fracture resistance and low inter- laminar shear strength [4–6]. Furthermore, delamina- tion cracking in many instances exhibits a mixed-mode fracture condition. The relative contribution of Mode I and Mode II components depends on various factors, such as the location and configuration of loading and boundary conditions, material properties, etc. [4]. As indicated in the literature, a complete under- standing of delamination in CMCs, particularly in woven laminated CMCs, is lacking. In this paper, an 0266-3538/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S0266-3538(99)00086-X Composites Science and Technology 59 (1999) 2287–2292 * Corresponding author. Tel.: +1-313-577-3843; fax: +1-313-577- 8789. E-mail address: gnewaz@hub.eng.wayne.edu (G.M. Newaz).