Nondestructive evaluation of damage in SiC/Al metal matrix composite using x ray tomographic microscopy

Thesis/Dissertation · Tue Dec 31 23:00:00 EST 1991

OSTI ID:6838488

Breunig, T M

A fundamental understanding of damage evolution will be required before metal matrix composites (MMC) can be utilized safely for structural applications. Although macroscopic mechanical response to cyclic loading has been monitored in many mechanical and thermal test programs, little is known about the nucleation and growth of damage in MMC's. The goal of the present work is to improve the understanding of damage accumulation in SiC/Al using a new microscopic non-destructive volume-imaging technique, X-ray Tomographic Microscopy (XTM), which has resolution comparable to optical microscopy. Correlation of damage initiation and accumulation mechanisms and the macroscopic mechanical response of samples are discussed for continuous fiber SiC/Al MMC's. A series of mechanical tests were performed on a continuous, aligned fiber SiC/Al MMC, and the ensuing three-dimensional damage state was nondestructively characterized using XTM to map the x-ray absorptivity within the sample. The types of damage detected include: fiber fracture (SiC sheath, and C core), fiber-matrix interface microcracking, intra-ply matrix voids, and cracks. Quantitative three-dimensional measurements of damage are reported in as-fabricated, monotonically loaded and mechanically fatigue loaded SiC/Al. The XTM results indicate that increases in observed macroscopic structural stiffness during monotonic loading and the first few fatigue cycles of an MMC coupon correspond to elimination of processing-related matrix porosity and to displacement of the fibers from a somewhat irregular arrangement into a more nearly hexagonal array. The XTM of monotonically loaded samples also show that the carbon cores begin to fracture at or below 828 MPa, that is, at loads far less than those for fracture of the entire fiber. The fracture of the SiC sheath appears to be significantly affected by the fracture of the C cores.

• Research Organization: Georgia Inst. of Tech., Atlanta, GA (United States)
• OSTI ID: 6838488
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360603* -- Materials-- Properties
ABSORPTIVITY
CARBIDES
CARBON COMPOUNDS
CARBON FIBERS
COMPOSITE MATERIALS
CRACKS
DAMAGE
DIAGNOSTIC TECHNIQUES
ELEMENTS
EVALUATION
FATIGUE
FIBERS
MATERIALS
MATERIALS TESTING
MATRIX MATERIALS
MECHANICAL PROPERTIES
MECHANICAL TESTS
METALS
MICROSCOPY
NUCLEATION
OPTICAL MICROSCOPY
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
POROSITY
REINFORCED MATERIALS
RESOLUTION
SILICON CARBIDES
SILICON COMPOUNDS
TESTING
TOMOGRAPHY
VOIDS