Proposed framework for thermomechanical life modeling of metal matrix composites

Technical Report · Thu Jul 01 04:00:00 EDT 1993

OSTI ID:6002599

Halford, G R; Lerch, B A; Saltsman, J F

The framework of a mechanics of materials model is proposed for thermomechanical fatigue (TMF) life prediction of unidirectional, continuous-fiber metal matrix composites (MMC's). Axially loaded MMC test samples are analyzed as structural components whose fatigue lives are governed by local stress-strain conditions resulting from combined interactions of the matrix, interfacial layer, and fiber constituents. The metallic matrix is identified as the vehicle for tracking fatigue crack initiation and propagation. The proposed framework has three major elements. First, TMF flow and failure characteristics of in situ matrix material are approximated from tests of unreinforced matrix material, and matrix TMF life prediction equations are numerically calibrated. The macrocrack initiation fatigue life of the matrix material is divided into microcrack initiation and microcrack propagation phases. Second, the influencing factors created by the presence of fibers and interfaces are analyzed, characterized, and documented in equation form. Some of the influences act on the microcrack initiation portion of the matrix fatigue life, others on the microcrack propagation life, while some affect both. Influencing factors include coefficient of thermal expansion mismatch strains, residual (mean) stresses, multiaxial stress states, off-axis fibers, internal stress concentrations, multiple initiation sites, nonuniform fiber spacing, fiber debonding, interfacial layers and cracking, fractured fibers, fiber deflections of crack fronts, fiber bridging of matrix cracks, and internal oxidation along internal interfaces. Equations exist for some, but not all, of the currently identified influencing factors. The third element is the inclusion of overriding influences such as maximum tensile strain limits of brittle fibers that could cause local fractures and ensuing catastrophic failure of surrounding matrix material.

• Research Organization: National Aeronautics and Space Administration, Cleveland, OH (United States). Lewis Research Center
• OSTI ID: 6002599
• Report Number(s): N-94-12449; NASA-TP--3320; E--7483; NAS--1.60:3320; CNN: RTOP 505-63-52
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360603* -- Materials-- Properties
360606 -- Other Materials-- Physical Properties-- (1992-)
CHEMICAL REACTIONS
CRACK PROPAGATION
CRACKS
ELEMENTS
EXPANSION
FAILURES
FATIGUE
FIBERS
FRACTURES
INTERFACES
MATERIALS
MATHEMATICAL MODELS
MATRIX MATERIALS
MECHANICAL PROPERTIES
METALS
OXIDATION
PHYSICAL PROPERTIES
REINFORCED MATERIALS
STRAINS
STRESSES
THERMAL EXPANSION
THERMODYNAMIC PROPERTIES