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| 2. |
- Isaksson, Per, et al.
(författare)
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Crack kinking under high pressure in an elastic-plastic material
- 2001
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Ingår i: International Journal of Fracture. - 0376-9429 .- 1573-2673. ; 108:4, s. 351-366
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Tidskriftsartikel (refereegranskat)abstract
- Directional crack growth criteria in compressed elastic–plastic materials are considered. The conditions at the crack tip are evaluated for a straight stationary crack. Remote load is a combined hydrostatic stress and pure shear, applied via a boundary layer assuming small scale yielding. Strains and deformations are assumed to be small. Different candidates for crack path criteria are examined. Maximum non-negative hoop stress to judge the risk of mode I and maximum shear stress for mode II extension of the crack are examined in some detail. Crack surfaces in contact are assumed to develop Coulumb friction from the very beginning. Hence, a condition of slip occurs throughout the crack faces. The plane in which the crack extends is calculated using a finite element method. Slip-line solutions are derived for comparison with the numerically computed asymptotic field. An excellent agreement between numerical and analytical solutions is found. The agreement is good in the region from the crack tip to around halfway to the elastic–plastic boundary. The relation between friction stress and yield stress is varied. The crack is found to extend in a direction straight ahead in shear mode for sufficiently high compressive pressure. At a limit pressure a kink is formed at a finite angle to the crack plane. For lower pressures the crack extends via a kink forming an angle to the parent crack plane that increases with decreasing pressure.
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| 3. |
- Isaksson, Per, et al.
(författare)
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Directional crack path criterion for crack growth in ductile materials subjected to shear and compressive loading under plane strain conditions
- 2003
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Ingår i: International Journal of Solids and Structures. - 0020-7683 .- 1879-2146. ; 40:13-14, s. 3523-3536
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Tidskriftsartikel (refereegranskat)abstract
- A directional crack growth criterion in a compressed elastic perfectly plastic material is considered. The conditions at the crack-tip are evaluated for a straight stationary crack with a small incipient kink. Remote load is a combined hydrostatic pressure and pure shear applied via a boundary layer. Crack surfaces in contact are assumed to develop homogenous Coulomb friction. The crack opening displacement of an extended kink is examined in a finite element analysis to judge the risk of opening mode failure. It has been found that the direction that maximizes the crack opening displacement of an extended kink tip coincides very well with a prediction of the crack growth direction obtained by using a criterion for continued crack growth direction discussed by the authors elsewhere [Int. J. Fract. 108 (2001) 351]. Moreover, the by the model predicted incipient crack growth directions are qualitatively comparable with reported crack paths obtained in ductile materials in a limited number of experiments performed under a combined load of inplane shear and compression.
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| 4. |
- Isaksson, Per, et al.
(författare)
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Mechanics of control element during irradiation
- 1997
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Ingår i: Structural mechanics in reactor technology : transactions of the 14th International Conference on Structural Mechanics in Reactor Technology, Lyon, France, August 17-22, 1997. - [Gif-sur-Yvette] : SMiRT 97.
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Konferensbidrag (refereegranskat)
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| 5. |
- Isaksson, Per, et al.
(författare)
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Mode II crack paths under compression in brittle solids : A theory and experimental comparison
- 2002
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Ingår i: International Journal of Solids and Structures. - 0020-7683 .- 1879-2146. ; 39:8, s. 2281-2297
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Tidskriftsartikel (refereegranskat)abstract
- A study of crack propagation paths in the situation where the crack is suppressed to open during growth due to high compressive forces has been performed. This problem was analyzed theoretically very recently by the authors and is here extended to involve a limited number of illustrative experimental results reported elsewhere in the literature. By analyzing the experimental crack growth patterns, the conclusion is that the model cannot describe the more realistic microscopic failure in detail. Since shear crack growth on the microscale strongly depend on inhomogenities in the material, like cavities, grains or inclusions; the closed crack growth patterns observed are not smooth or free of kinks. Nevertheless, the model show good agreement with the reported experimental observations of the paths of closed macroscopic mode II cracks on samples in brittle materials, induced under overall compression. Failure patterns experimentally observed supports the theory that the growth of mode II cracks under compression in brittle materials follow a propagation path described by a function y ¼ kxb, where b ¼ 3=2. This is strongly supported by the measured values obtained from various experiments. In all the studied experiments, the exponent b was found in the interval [1.43–1.58]. Further, an investigation of the curvature parameter k has been performed and the conclusion is that k does also agree with the simplified model, even though not as good as the exponent b. However, k differs in general <15% from the theoretical value predicted by the model. The process of crack growth is in the simplified model assumed to be controlled by the mode II stress intensity factor KII of the main crack and the difference between the compressive remote normal stress parallel with the crack plane (r111) and the compressive remote normal stress perpendicular to the crack plane (r122).
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| 6. |
- Isaksson, Per, et al.
(författare)
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Prediction of shear crack growth direction under compressive loading and plane strain conditions
- 2002
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Ingår i: International Journal of Fracture. - 0376-9429 .- 1573-2673. ; 113:2, s. 175-194
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Tidskriftsartikel (refereegranskat)abstract
- Abstract. A directional crack growth prediction in a compressed homogenous elastic isotropic material under plane strain conditions is considered. The conditions at the parent crack tip are evaluated for a straight stationary crack. Remote load is a combined biaxial compressive normal stress and pure shear. Crack surfaces are assumed to be frictionless and to remain closed during the kink formation wherefore the mode I stress intensity factor KI is vanishing. Hence the mode II stress intensity factor KII remains as the single stress intensity variable for the kinked crack. An expression for the local mode II stress intensity factor k2 at the tip of a straight kink has been calculated numerically with an integral equation using the solution scheme proposed by Lo (1978) and refined by He and Hutchinson (1989). The confidence of the solution is strengthened by verifications with a boundary element method and by particular analytical solutions. The expression has been found as a function of the mode II stress intensity factor KII of the parent crack, the direction and length of the kink, and the difference between the remote compressive normal stresses perpendicular to, and parallel with, the plane of the parent crack. Based on the expression, initial crack growth directions have been suggested. At a sufficiently high non-isotropic compressive normal stress, so that the crack remains closed, the crack is predicted to extend along a curved path that maximizes the mode II stress intensity factor k2. Only at an isotropic remote compressive normal stress the crack will continue straight ahead without change of the direction. Further, an analysis of the shape of the crack path has revealed that the propagation path is, according the model, required to be described by a function y = cxγ , where the exponent γ is equal to 3/2. In that case, when γ = 3/2, predicts the analytical model a propagation path that is selfsimilar (i.e. the curvature c is independent of any length of a crack extension), and which can be described by a function of only the mode II stress intensity factor KII at the parent crack tip and the difference between the remote compressive normal stress perpendicular to, and parallel with, the parent crack plane. Comparisons with curved shear cracks in brittle materials reported in literature provide limited support for the model discussed.
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| 7. |
- Massih, Ali R, et al.
(författare)
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Modelling the behaviour of a control-element blade during irradiation
- 1997
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Ingår i: Computers & Structures. ; 64:5-6, s. 1113-1127
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Konferensbidrag (refereegranskat)abstract
- The control-rod elements in a boiling-water reactor contain natural boron carbide (B4C) powder, used as neutron-absorber material and clad in stainless-steel blades. During in-reactor service, the internal production of helium gas and point defects in neutron-irradiated boron carbide cause swelling which can induce significant contact stresses in the blade causing, eventually, stress-corrosion cracking of the blades. In this work, a finite-element analysis of a control-rod blade consisting of B4C powder and stainless-steel cladding has been performed using ADINA. An algorithm for the finite-element calculation of a porous material such as B4C powder has been developed and which models both swelling and consolidation behaviour of B4C powder. The Drucker-Prager constitutive law has been used to model the consolidation effect. The model has been verified with an analytical solution for a simple geometry. A number of cases with B4C powder in contact with stainless steel and using the actual blade design have been studied for which contact stresses, the displacements and the effective stresses are calculated. Finally, the model has been used to predict the deformation of the blade during irradiation under B4C swelling and irradiation-induced creep of stainless steel.
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| 8. |
- Nilsson, Per, et al.
(författare)
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Plastic mechanisms during fast brittle fracture
- 1995
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Ingår i: Current topics in computational mechanics. - New York : American Society of Mechanical Engineers. - 0791813363 ; , s. 69-72
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Konferensbidrag (refereegranskat)abstract
- Careful studies of cleavage fracture surfaces show that parts of the surface consist of plastically formed ridges, presumably traces of plastically collapsed ligaments. These ligaments are assumed to be formed between the cleavage fractured areas. The collapse process of these ligaments is numerically examined. A finite element method and an asymptotic analysis are employed. The results shows that relatively large amounts of energy are consumed in this process and that the energy consumption is increasing rapidly with increasing crack tip speed. The implications for slow stable crack tip speeds at dynamic fracture are discussed.
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| 9. |
- Ståhle, Per, et al.
(författare)
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Slack Edges of Paper
- 2006
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Ingår i: Euromech Colloquium.
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Konferensbidrag (refereegranskat)
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| 10. |
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