| 1. |
- Ristinmaa, Matti
(författare)
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Void growth in cyclic loaded porous plastic solid
- 1997
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Ingår i: Mechanics of Materials. - 0167-6636. ; 26:4, s. 227-245
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Tidskriftsartikel (refereegranskat)abstract
- In low-cycle fatigue, where plastic strains are of great importance, final ductile fracture depends upon the mechanisms of void growth and coalescence of voids. A cell model is used to simulate a periodic array of initial spherical voids and this model is subjected to different loads that include cyclic loading. Three different types of matrix material are simulated: elastic-perfectly plastic, isotropic hardening and kinematic hardening. The cell model results are compared with the approximate constitutive equations for a voided material suggested by Gurson. The simulations show that the unspecified parameters introduced by Tvergaard in the Gurson yield function depend on the hardening behavior of the matrix material. For a perfectly plastic matrix material, the parameters q1 = 1.5 and q2 = 1.02 provide very close predictions for a variety of loadings. However, for isotropic or kinematic hardening matrix materials these parameters result in an inferior agreement and a much closer accuracy is obtained by adopting q1 = 1.5 and q2 = 0.82. This suggests that the parameter q2 depends on the hardening behavior of the matrix material. For kinematic hardening of the Gurson model, it is shown that Ziegler's hardening rule is superior to Prager's hardening rule. Finally, the void shape change due to loading is studied and it is found that this change has an insignificant effect on the response.
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| 2. |
- Akshantala, Nagendra V., et al.
(författare)
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A mechanistic model for fatigue damage evolution in composite laminates
- 1998
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Ingår i: Mechanics of materials. - 0167-6636 .- 1872-7743. ; 29:2, s. 123-140
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Tidskriftsartikel (refereegranskat)abstract
- We propose a mechanistic model which is capable of describing the evolution of transverse cracking in cross ply laminates subjected to cyclic tension in the longitudinal direction. The key feature of the model is that it incorporates delamination associated with transverse cracks in a manner that induces further formation of transverse cracks as delamination grows in fatigue. A variational approach is taken to estimate the stresses in the region between transverse cracks, and these are found to be accurate away from the crack planes when comparison is made with finite element computations. The evolution of transverse crack density and the associated overall elastic moduli changes predicted by the model are in agreement with experimental results
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| 3. |
- Ganghoffer, J.F., et al.
(författare)
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A micromechanical model of the martensitic transformation
- 1998
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Ingår i: Mechanics of Materials. - 0167-6636. ; 27:3, s. 125-144
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Tidskriftsartikel (refereegranskat)abstract
- A micromechanical model of the martensitic transformation at the grain scale has been established, considering the more specific case of ferrous alloys. The transformation proceeds through the formation of successive variants of the product phase within a unit cell representative of a grain; interactions between neighbouring grains are simulated by the choice of periodic boundary conditions. From a thermodynamical analysis, a selection rule for the order and orientation of the forming martensitic variants has been established, based on internal stresses anisotropy. These concepts have been implemented into a two-dimensional finite element simulation of the transformation, considering an elastoplastic behaviour of both parent and product phases. Morphological and crystallographical features of the transformation are considered: one variant consists of a thin layer of elements within the mesh that can form with four possible discrete orientations. Simulation results show the development of the plate pattern as a combination of the influence of both external load and internal stresses built during the progress of the transformation. These are related to global evolutions of transformation plasticity vs. transformation progress. Comparison with experiments show a similar form of the evolutions of the total strain; however, the model overestimates the strain levels. The possible reasons for this discrepancy are discussed.
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| 4. |
- 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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| 5. |
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| 7. |
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| 8. |
- Klarbring, Anders, 1957-, et al.
(författare)
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Asymptotic Modelling of Adhesive Joints
- 1999
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Ingår i: Mechanics of materials. - 0167-6636 .- 1872-7743. ; 28, s. 137-145
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Tidskriftsartikel (populärvet., debatt m.m.)
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