Micromechanical modeling of unidirectional continuous sigma fiber-reinforced Ti-6Al-4V subjected to transverse tensile l
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NTRODUCTION
WITH the development of Ti/SiC composites and for their potential applications, the transverse properties of unidirectional continuous fiber–reinforced composites have received considerable attention. For instance, the transverse loading capability of metal-matrix composite (MMC) “blings” becomes a potential problem, since the maximum principal radial stress level could be one design limitation,[1] and experimental work[2] has shown transverse damage and failure of clad MMC testpieces. Additionally, finite-element analysis has shown that transverse stresses can be generated in clad titanium-matrix composite (TMC) testpieces containing cracks, even when they are subjected to (mode I) longitudinal loading.[3] Therefore, it is important to understand the response of such TMCs to transverse stresses, and many researchers have attempted to predict the transverse properties of MMCs by finite-element method (FEM) analysis.[4–9] It is commonly noted that the thermal stresses induced during the cooling of TMCs makes a characteristic contribution to the transverse behavior. These thermal stresses are beneficial to the transverse strength and deformation, because normally compressive stresses are induced at the interface between the fiber and matrix of the composite. Different interface conditions, such as perfect and weak bonding, have been considered and compared.[4,5] Adams[6] developed a model for a weak interface, which included layers of small elements at the fiber-matrix interface. Any of the material properties of a layer of these elements can be selectively reduced as desired, typically to some fraction of the corresponding matrix values, to model a “degraded” interface. The interface strength is found to be a very important parameter affecting the transverse strength. Wisnom[7] W. DING, Lead Engineer, is with Airbus UK Ltd., Bristol BS99 7AR, United Kingdom. P. BOWEN, Head, Department of Metallurgy and Materials, and Professor, School of Engineering, is with the University of Birmingham, Birmingham B15 2TT, United Kingdom. Manuscript submitted June 5, 2000. METALLURGICAL AND MATERIALS TRANSACTIONS A
designed a special interface element to enable separate shear and tensile strengths to be assigned, with linear and quadratic interactions. This represented a perfect interface until a certain state of stress is reached, when the interface is assumed to fail. Furthermore, Li and Wisnom[8] have investigated the effect of the fiber coating on the composite thermal residual stresses, elastic transverse tensile properties, and interface debonding. Two methods of estimating the interfacial tensile strength numerically are proposed. One method of determining the interfacial tensile strength is the combined analysis of the transverse tensile stress-strain curve with finite element modeling and an assumed interfacial failure criterion. The other method is to establish the interfacial tensile strength through simulation of a loading-unloading-reloading stressstrain curve. This latter method is amenable to experimental
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