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Type of Document	Dissertation
Author	Hanan, Jay C
URN	etd-05062003-123650
Persistent URL	http://resolver.caltech.edu/CaltechETD:etd-05062003-123650
Title	Damage evolution in uniaxial SiC fiber reinforced Ti matrix composites
Degree	PhD
Option	Materials Science
Advisory Committee	Advisor Name Title Ersan Ustundag Committee Chair Brent T. Fultz Committee Member I. Cev Noyan Committee Member Rob Phillips Committee Member William L. Johnson Committee Member
Keywords	strain Non-destructive testing Composite Models sin square psi Finite Element Model mechanical testing Residual Strain X-Ray Diffraction
Date of Defense	2002-06-18
Availability	unrestricted
Abstract Fiber fractures initiate damage zones ultimately determining the strength and lifetime of metal matrix composites (MMCs). The evolution of damage in a MMC comprising a row of unidirectional SiC fibers (32 vol.%) surrounded by a Ti matrix was examined using X-ray microdiffraction (?m beam size) and macrodiffraction (mm beam size). A comparison of high-energy X-ray diffraction (XRD) techniques including a powerful two-dimensional XRD method capable of obtaining powder averaged strains from a small number of grains is presented (HE?XRD?). Using macrodiffraction, the bulk residual strain in the composite was determined against a true strain-free reference. In addition, the bulk in situ response of both the fiber reinforcement and the matrix to tensile stress was observed and compared to a three-dimensional finite element model. Using microdiffraction, multiple strain maps including both phases were collected in situ before, during, and after the application of tensile stress, providing an unprecedented detailed picture of the micromechanical behavior in the laminate metal matrix composite. Finally, the elastic axial strains were compared to predictions from a modified shear lag model, which unlike other shear lag models, considers the elastic response of both constituents. The strains showed excellent correlation with the model. The results confirmed, for the first time, both the need and validity of this new model specifically developed for large scale multifracture and damage evolution simulations of metal matrix composites. The results also provided unprecedented insight for the model, revealing the necessity of incorporating such factors as plasticity of the matrix, residual stress in the composite, and selection of the load sharing parameter. The irradiation of a small number of grains provided strain measurements comparable to a continuum mechanical state in the material. Along the fiber axes, thermal residual stresses of 740 MPa (fibers) and +350 MPa (matrix) were found. Local yielding was observed by 500 MPa in the bulk matrix of the composite. Plastic anisotropy was observed in the matrix. The intergranular strains in the Ti matrix varied as much as 50%. In spite of this variation, the HE?XRD? technique powerfully provided reliable information from the matrix as well as the fibers.
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