Implementation Challenges for High-Temperature Composites (1997) / Chapter Skim
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Property Profiles
Property Profiles
Pages 7-15
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From page 7... ...
Technical factors arise from the important contributions to the costs originating with long cycle times for the high-temperature steps in the production, expensive chemicals and powders, and high capital costs. These can be systematically addressed through combinations of modeling, process optimization, lower-cost ingredients, and the matching of capital costs to product volumes.
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From page 8... ...
These mechanisms "blunt" and stabilize the damage emanating from failed fibers, by redistributing stresses in the surrounding material, thereby reducing the stress concentrations in the nearest fibers t40-421. The consequence is that multiple fiber failures can occur before the UTS is reached t43]
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From page 9... ...
FIGURE 7b Truncation of the strength at a minimum achieved either by proof testing or by developing inelastic mechanisms in the material that provide stress redistribution with an attendant insensitivity to large manufacturing flaws. efficiency increases as the interface debond and friction stresses decrease [42-451.
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From page 10... ...
Friction at the interfaces dictates the dimension over which stress concentrations around failed fibers are eliminated. This dimension becomes an internal scale parameter, which allows fiber failures to occur in a spatially uncorrelated manner.
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From page 11... ...
The key feature is that the stress concentration factor around the hole diminishes upon increasing the load, as an inelastic zone develops. This diminished stress concentration combines with an elevation in the local UTS arising from volume scaling [50,521.
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Brittle Matrix Composites For CMCs, multiple matrix cracking with interface debonding and friction enable appreciable inelastic strain in tension and shear [8] (see Figure 8~.
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Debond Crack Front ~ Debond Energy, Hi (b) FIGURE 10 Schematic of matrix cracking in CMCs and the associated cell models.
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From page 14... ...
This behavior is typical of that found for anisotropic materials that respond linearly in one direction, as previously elaborated for layered materials and coatings t42,59,601. This effect accounts for the relative notch sensitivity found for TMCs, differing dramatically from that for metals in which isotropic plastic deformation greatly diminishes stress concentrations.
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From page 15... ...
FIGURE 11 Stress concentrations around holes in unidirectional TMCs calculated using the constitutive law obtained from Figure 4. Also shown are the post-localization effects that enable bridging by the intact matrix that leads to the notch insensitivity found at larger notch sizes.
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