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- Lacy, Thomas E., et al.
(författare)
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Effects of damage distribution on evolution
- 1997
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Ingår i: Applications of continuum damage mechanics to fatigue and fracture. - : ASTM International. - 0803124732 ; , s. 131-149
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Bokkapitel (refereegranskat)abstract
- Recent micromechanically inspired phenomenological theories using internal state variable (ISV) representations of damage have been used to predict the thermomechanical behavior of microcracked solids. These models do not, in an explicit manner, account for distributions of microcracks in a representative volume element (RVE) and have been used success-fully only to determine the effective moduli of damaged solids. It has been demonstrated that while the distribution and interaction of damage entities within an RVE generally have a minor effect on the effective moduli, it has a significant effect on the evolution of damage and failure at the macroscale. Damage evolution rates, in general, cannot be described adequately by such theories because of their inability to account for interactions between damage entities in an arbitrary distribution. Key issues pertaining to the development of viable damage evolution equations using a continuum damage mechanics approach are addressed. In particular, limitations associated with the use of ISVs that can be expressed either in terms of macroscopically measurable quantities or through a spatial average of the geometric features of individual damage entities are discussed. Numerical simulations of evolving crack systems in two-dimensional perfectly brittle solids indicate that "effective stress" models may have difficulty in characterizing damage evolution in brittle microcracked solids when the damage consists of cracks of variable size or spatial distributions. An argument for implementing ISVs based on higher-order moments of the damage distribution within an RVE is presented.
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| 3. |
- Lacy, Thomas E., et al.
(författare)
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Gradient concepts for evolution of damage
- 1999
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Ingår i: Mechanics of materials. - 0167-6636 .- 1872-7743. ; 31:12, s. 831-860
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Tidskriftsartikel (refereegranskat)abstract
- While low-order measures of damage have sufficed to describe the stiffness of bodies with distributed voids or cracks, such as the void volume fraction or the crack density tensor of Vakulenko, A.A., Kachanov, M., 1971., addressing the growth of distributed defects demands a more comprehensive description of the details of defect configuration and size distribution. Moreover, interaction of defects over multiple length scales necessitates a methodology to sort out the change of internal structure associated with these scales. To extend the internal state variable approach to evolution, we introduce the notion of multiple scales at which first and second nearest-neighbor effects of nonlocal character are significant, similar to homogenization theory. Further, we introduce the concept of a cutoff radius for nonlocal action associated with a representative volume element (RVE), which exhibits statistical homogeneity of the evolution, and flux of damage gradients averaged over multiple subvolumes. In this way, we enable a local description at length scales below the RVE. The mean mesoscale gradient is introduced to reflect systematic differences in size distribution and position of damage entities in the evolution process. When such a RVE cannot be defined, the evolution is inherently statistically inhomogeneous at all scales of reasonable dimension, and the concept of macroscale gradients of internal variables is the only recourse besides micromechanics. Based on a series of finite element calculations involving evolution of 2D cracks in brittle elastica arranged in random periodic arrays, we examine the evolution of the mean mesoscale gradients and note some preliminary implications for the utility of such an approach.
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| 4. |
- Lacy, Thomas E., et al.
(författare)
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On representation of damage evolution in continuum damage mechanics
- 1997
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Ingår i: International journal of damage mechanics. - : SAGE Publications. - 1056-7895 .- 1530-7921. ; 6:1, s. 62-95
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Tidskriftsartikel (refereegranskat)abstract
- The effect of damage patterning on elastic moduli and damage evolution in ideal brittle cracked solids is examined. Key limitations associated with typical continuum damage mechanics approaches are addressed. Critical shortcomings arising from the use of spatially-averaged damage descriptors in the evaluation of effective moduli and thermodynamic forces are investigated using numerical simulations of evolving two-dimensional crack systems. Fundamental elements of a higher-order continuum description of damage based on distribution functions are discussed, which directly include damage interaction effects.
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