Optimization of Direct Biaxial Testing of Anisotropic Materials

Boehler, J. P.; Demmerle, S.

doi:10.1007/978-94-015-8494-4_1

Cited by 2 publications

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“…The laws of damage nucleation and accumulation in cross-ply laminates under biaxial loading have been poorly investigated primarily because of the difficulties involved in testing anisotropic plates under biaxial loading [4]. We may assume that the initial failure mechanism in cross-ply laminates under biaxial loading is the formation of tunneling macrocracks in both 0°-and 90°-plies.…”

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Deformation of Cross-Ply Composite Laminates with Cracked Ceramic Matrix

Kashtalyan

2005

Int Appl Mech

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The deformation of cross-ply ceramic-matrix composite laminates under biaxial loading is studied theoretically. Experimentally, microscopic damage evolution in cross-ply ceramic-matrix composite laminates has not been well characterized yet, mainly due to the difficulties involved in testing of anisotropic plates under biaxial loading. It is assumed that the initial damage mechanism observed in ceramic-matrix composite laminates is the formation of tunneling macrocracks both in the 90°-and 0°-plies. The paper addresses the stiffness-deterioration behavior of cross-ply ceramic-matrix laminates with transverse and longitudinal macrocracks. The analysis is based on the equivalent-constraint model of a damaged laminate. Numerical results for SiC/CAS cross-ply laminates of various lay-ups are presented and discussed Introduction. Composite materials with ceramic matrix and continuous fiber reinforcement have a great variety of advantages over solid ceramics. They possess higher crack, fatigue, and damage resistance and maintain load-bearing capacity even in the presence of internal damages [5].Failure of fibrous composites due to static or cyclic loading in the plane of reinforcement and due to thermal fatigue is a complex and multistage process of nucleation and accumulation of various internal damages. Theoretical and experimental studies into the internal damage mechanisms for ceramic-matrix fiber-reinforced composites are reviewed in [1]. Note that most of these studies are devoted to unidirectional composite materials. From the application standpoint, the advantage of composites reinforced in more than one direction (laminated or woven) is beyond question. However, their behavior has been studied poorly.It is generally recognized that the basic internal damage mechanism of fibrous ceramic-matrix composites at the initial stage of failure is matrix cracking. In cross-ply laminates under quasistatic or cyclic uniaxial loading, cracks occur and accumulate in both 90°-plies (perpendicular to the direction of load) and 0°-plies. In 90°-plies, cracking occurs in parallel to the fibers, producing tunneling macrocracks (Fig. 1). In 0°-plies, cracking occurs transversely to the fibers, which play the role of bridges, resulting in separation of fibers from the matrix (Fig. 1, inset).Matrix cracking in cross-ply laminates sets in at smaller strain than in a unidirectional material. Cracks appear first in 90°-plies. The cracks increase in number with increasing load, gradually reaching saturation. The saturation density of cracks in 90°-plies is less than in 0°-plies [8,22].Matrix cracking gradually reduces the stiffness and strength of the laminate and changes the values of the thermal-expansion coefficients and natural frequencies. Reduction in stiffness is more intensive in ceramic-matrix composites than in polymeric-matrix composites, since the elastic moduli of the ceramic matrix and the fibers are similar. The authors of [2, 3, 7, 8, 18-23, 25, 26] proposed a number of approaches to evaluate the influence of tunnelin...

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