Research Directions in Computational Mechanics (1991) / Chapter Skim
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6 Materials Research: Numerical Modeling of New Materials
6 Materials Research: Numerical Modeling of New Materials
Pages 65-78
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From page 65... ...
For example, standard test procedures exist to measure a material's resistance to crack growth. Computational mechanics analyses are used to correlate performance in such a test with crack growth behavior under service conditions and relate the property measured in this test to material microstructure.
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From page 66... ...
A complete compact tension specimen was analyzed, but Figure 6.1 shows the mode of crack propagation in the region just ahead of the crack. The material is described by a porous plastic constitutive relation that allows for creation of a new free surface, and the elements in which there has been a complete loss of stress-carrying capacity are deleted from the mesh plot.
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From page 67... ...
~= ,, ·~^ ~ · ~ _ ~ ~ w 0 . 0 ~ ~ c 0~-~ 50 150 260 350 450 550 650 Grain Size ,um ;; FIGURE 6.1 Mode of crack propagation and comparison of predicted and experimental toughness and tearing modulus.
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From page 68... ...
Finite element analyses based on these models have successfully predicted toughness enhancements and the mode of fatigue crack growth at notches. Figure 6.2 shows that the direction of crack growth follows the predicted shape of the residual tensile stress contours near a notch-tip growth from a notch tip and predicted contours of constant normal stress at the notch tip.
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From page 69... ...
\ A 800 B 400 C 200 [) O \ \ C BOW / ~ l lick \ 69 FIGURE 6.2 Crack growth from a notch tip and predicted contours of constant normal stress at the notch tip.
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From page 70... ...
I ~ 1 1 1 ~ 1_ 0.4 0.6 0.8 Aa/(K~fac) 2 FIGURE 6.3 Sketch of facet microcracks and predicted crack growth resistance.
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From page 71... ...
~m) 1~ FIGURE 6.4 Debonding process and predicted particle debonding strain versus particle diameter.
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From page 72... ...
Figure 6.5 shows results from a finite element calculation of creep crack growth using a micromechanically based constitutive relation that allows for the loss of stress-carrying capacity due to grain boundary cavitation. The finer mesh is obtained by halving the grid spacing in each spatial direction.
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From page 73... ...
I . · ~ ~ ~' ~ ~ 1-' ' ' ' 1 0.0 0.5 1.0 1.5 2.0 t/t FIGURE 6.5 Creep crack growth versus time for two meshes.
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From page 74... ...
Since the governing equations have no natural length scale, the width of the shear band is arbitrary. Hence, numerical solutions to localization problems can exhibit an inherent mesh dependence because in a grid-based numerical solution the minimum width of the band of localized deformation is set by the mesh spacing.
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From page 75... ...
PROGRESSIVE CREATION OF NEW FREE SURFACE Fracture involves the creation of new free surface. In traditional approaches to fracture analysis, the presence of a single dominant flaw is presumed, and the key issue is whether that flaw will grow under the given loading conditions.
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From page 76... ...
The element vanish technique is applicable when the material constitutive relation allows for a complete loss of stress-carrying capacity and has been used successfully in a wide variety of circumstances where the failure mechanism is ductile void growth. However, other ductile separation mechanisms occur; for example, in machining operations, shear band-type localizations can occur and, the large strains within a band of localized deformation subsequently lead to the creation of new free surface.
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From page 77... ...
Mechanical effects on nonmechanical behavior will undoubtedly become an increasing concern. For example, an important problem in microelectronics, where significant advances have been made by finite element analyses, concerns the prediction of piezoelectrically induced threshold voltage shifts in gallium arsenide metal semiconductor field effect transistors.
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From page 78... ...
Available phenomenological inelastic constitutive models for composite materials are almost all based on a characterization of the distribution in terms of"a single parameter, the volume fraction. Computational studies of irregular distributions are being used to assess the extent to which the overall response of such materials does admit a one-parameter characterization.
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