| 1. |
- Paris, F., et al.
(författare)
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The fiber-matrix interface crack : A numerical analysis using Boundary Elements
- 1990
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Ingår i: International Journal of Fracture. - 0376-9429 .- 1573-2673. ; 82:1, s. 11-29
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Tidskriftsartikel (refereegranskat)abstract
- The calculation of the energy release rate of a debonding interface crack between fiber and matrix in plane strain requires a knowledge of the stress state and displacements at the neighbourhood of the crack tip. Analytical solutions which involve interpenetrations of the free boundaries of the fiber and matrix have classically been used to predict the variation of the energy release rate with the debonding angle. In this paper a numerical study of this problem as a contact problem, using Boundary Elements, is carried out. The singular stress components are modelled by means of singular discontinuous elements, a particular contact algorithm, which is very appropriate for cases like that under consideration where the fiber is much stiffer than the matrix, having been proposed. The numerical procedure shows the appearance of a contact zone with physical meaning starting at a certain value of the debonding angle, which implies the presence of a pure mode II of fracture. The values of G found by BEM are compared with those predicted by the use of an analytical solution showing clear discrepancies when the contact zone starts to develop, BEM always predicting smaller values of the energy release rate, in accordance with the absence of mode I in the presence of a contact zone.
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| 2. |
- Stehn, Lars, et al.
(författare)
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Fracture resistance determination of freshwater ice using a chevron notched tension specimen
- 1994
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Ingår i: International Journal of Fracture. - 0376-9429 .- 1573-2673. ; 65:4, s. 313-328
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Tidskriftsartikel (refereegranskat)abstract
- Crack growth resistance (R-curve behavior) measurements on large grained S1 type freshwater ice were conducted in the Ice Mechanics Research Laboratory at Clarkson University. To overcome previous difficulties in obtaining stable cracking in freshwater ice, a new crack geometry was developed. The short rod Chevron Notched Tension (CNT) specimen was found to be extremely favorable in the sense of promoting stable,stick-slip, crack growth over a large portion of the uncracked ligament. A negative fracture resistanceK R -curve was evaluated for this ice at -16°C.
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| 3. |
- Thesken, J.C., et al.
(författare)
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Application Of A Moving Variable Order Singular Element To Dynamic Fracture-Mechanics.
- 1991
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Ingår i: International Journal of Fracture. - 0376-9429 .- 1573-2673. ; 52:1, s. 47-65
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Tidskriftsartikel (refereegranskat)abstract
- An elasto-dynamic moving element formulation incorporating a variable order singular element to enhance the local crack tip description is presented. The moving mesh zone is embedded in a finite global mesh providing a functional tool for the analysis of dynamic crack growth experiments. In the following, the necessary numerical techniques are developed and tested using problems possessing analytical solutions. The promising results reported here motivate further work to include viscoplastic material behavior in the formulation.
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| 4. |
- Zang, W.L., et al.
(författare)
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Kinked cracks in bonded half-planes modeled by an integral equation method
- 1992
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Ingår i: International Journal of Fracture. - : Kluwer Academic Publishers. - 0376-9429 .- 1573-2673. ; 54:1, s. 65-78
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Tidskriftsartikel (refereegranskat)abstract
- Based on the integral equation for resultant forces along a crack, a boundary integral equation method for the solution of kinked cracks in bonded half-planes is presented. The equation only contains a weak logarithmic singularity and is valid for every point along the crack lines. Numerical results are presented to illustrate the efficiency and reliability of the method.
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| 5. |
- Östlund, Sören, 1961-
(författare)
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Large scale yielding for dynamic crack growth in a strip geometry
- 1991
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Ingår i: International Journal of Fracture. - : Springer. - 0376-9429 .- 1573-2673. ; 49:3, s. 219-237
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Tidskriftsartikel (refereegranskat)abstract
- Dynamic crack growth in a strip geometry has been studied by a convective formulation of the finite element method. The strip is assumed to be made of a material described by an elastic-viscoplastic constitutive equation and the loading conditions are plane strain mode I. The plastic strain-rates are characterized by a power-law overstress model giving an asymptotic elastic singularity at the crack tip. Two different types of loading on the strip geometry have been investigated. In the first geometry the horizontal boundaries parallel to the crack plane were subjected to prescribed displacements perpendicular to the crack plane and the crack tip was loaded in essentially the same way as for a crack in a plate subjected to tensile loading perpendicular to the crack. The second type of loading consisted of a prescribed rotation of the trailing edge in the moving finite element mesh. This created primarily bending loading of the structure.The crack tip energy flow has been calculated for different levels of yielding around the crack tip. The results are compared to the true small scale yielding solution obtained from a boundary layer analysis.The results reported indicate that for the tensile loading there exists a rather wide range of load levels for which the boundary layer solution gives a good description of the fields around the crack tip. For the bending loading the results indicate that the boundary layer solution is a correct description only in cases of extremely small scale yielding. Comparisons between large scale yielding and the boundary layer solution are also made for the effective stress and the effective plastic strain.
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| 6. |
- Östlund, Sören, 1961-
(författare)
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On numerical modeling and fracture criteria of dynamic elastic-viscoplastic crack growth
- 1990
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Ingår i: International Journal of Fracture. - : Springer. - 0376-9429 .- 1573-2673. ; 44:4, s. 283-299
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Tidskriftsartikel (refereegranskat)abstract
- Dynamic steady-state small-scale yielding crack propagation in an elastic-viscoplastic structure is studied by a convective formulation of the finite element method. The loading condition is mode I plane strain.The plastic strain-rates are characterized by a power-law overstress model based on a general theory by Perzyna. For values of the stress exponent less than 3, the elastic strain-rates are more singular than the plastic strain-rates and consequently the near tip fields will exhibit an asymptotic elastic behaviour. The size of the zone where this elastic singularity dominates is typically of the order 10–3–10–5 of the size of the active plastic zone. These relatively small dimensions severely complicate the finite element modeling. Although the energy flow is calculated with a path-independent integral of J-integral type, its value will be dependent on the size of the near-tip elements unless extremely small finite elements are used. This is an important difference compared with many other situations, for example the elastic case and a stationary crack in a power-law hardening material, where the use of a path-independent integral improves the numerical accuracy even if the crack tip region is modeled with a rather coarse mesh. This size effect is discussed in detail. An application of the results with numerical data for a realistic situation shows that the crack tip energy flow might be vanishingly small compared to the energy dissipation in the plastic region. This indicates that the energy flow to the crack tip is perhaps not an appropriate parameter for the description of small-scale yielding crack growth in the present type of material model.The paper also contains an investigation of the introduction of a variable order singular element at the element positions adjacent to the crack tip. It is shown that this type of element does not improve the numerical behaviour in the present formulation.
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| 7. |
- Melin, Solveig
(författare)
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Directional stability of an originally straight crack
- 1992
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Ingår i: International Journal of Fracture. - 0376-9429. ; 53:2, s. 121-128
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Tidskriftsartikel (refereegranskat)abstract
- The directional stability of an originally straight crack under symmetric remote loading is studied after introduction of an infinitesimal disturbance at one or both tips of the crack. The crack is assumed to grow slowly under vanishing mode II stress intensity factor. Directional stability is defined to prevail if the angle formed by the straight line between the crack tips and the original crack direction eventually decreases during crack growth. This is shown to be the case if, and only if, the principal stress perpendicular to the original crack is the largest of the two in-plane stresses. Another candidate for definition of directional stability is also discussed, even though it appears less logical, since it concentrates on the position of the crack tips rather than on the main direction of the crack. It assumes that directional stability prevails if the crack tips eventually move closer toward the line along the original crack. This definition leads to directional instability when the principal stress in the original crack direction is larger than the fraction 1-/4 of the other in-plane stress.
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| 8. |
- Melin, Solveig
(författare)
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On the directional stability of wedging
- 1991
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Ingår i: International Journal of Fracture. - 0376-9429. ; 50:4, s. 293-300
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Tidskriftsartikel (refereegranskat)abstract
- The directional stability of the crack path during wedging of a strip is investigated, using finite element methods. Linearly elastic material and plane conditions are considered. No dynamic effects are included. Stable crack growth in the direction of maximum mode I stress intensity factor at the tip of the crack is assumed. It is found that directional stability seems to prevail if the thickness of the wedge at the foremost point of contact between the wedge and the crack surfaces is less than about 1.69 K Ic% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaOaaaeaaca% WG3bGaai4laiaadweaaSqabaaaaa!3A93!\[\sqrt {w/E}\], where K Ic is the fracture toughness, w half the width of the strip and E the modulus of elasticity.
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| 9. |
- Melin, Solveig
(författare)
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Which is the most unfavourable crack orientation?
- 1991
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Ingår i: International Journal of Fracture. - 0376-9429. ; 51:3, s. 255-263
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Tidskriftsartikel (refereegranskat)abstract
- The most unfavourable orientation of a straight crack of given length is investigated, assuming mode I growth. It is shown that this orientation is not always the one perpendicular to the largest principal stress. If the smallest in-plane principal stress is compressive and its magnitude more than about one third of the largest (tensile) in-plane stress, then some other orientations are more unfavourable. Crack growth then takes place after kinking.
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