| 1. |
- Bjerkén, Christina, et al.
(author)
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A tool to model short crack fatigue growth using a discrete dislocation formulation
- 2003
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In: International Journal of Fatigue. - : Elsevier. - 1879-3452 .- 0142-1123. ; 25:6, s. 559-566
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Journal article (peer-reviewed)abstract
- A method is presented that combines the modelling of cracks by distributed dislocation dipoles with developing plasticity represented by discrete dislocations moving along slip bands. Crack growth is due to the emission of dislocations from the crack tip along preferred slip planes. Eventual annihilation of dislocations occurs by reunion with the corresponding displacement steps of the crack surface. Crack surface overlap is not allowed. The equilibrium state for each load increment is solved iteratively, allowing various crack geometries. The method is applied to the problem of a short edge crack growing in mode I due to fatigue loading. It is shown that the development of a local plastic zone and the propagation of the crack can be monitored in detail.
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| 2. |
- Alfredsson, Bo, et al.
(author)
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Applying multiaxial fatigue criteria to standing contact fatigue
- 2001
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In: International Journal of Fatigue. - 0142-1123 .- 1879-3452. ; 23:6, s. 533-548
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Journal article (peer-reviewed)abstract
- The ability of some multiaxial fatigue criteria to predict initiation of standing contact fatigue cracks is investigated. In the standing contact fatigue test an indenter subjects a case-hardened rest specimen to a stationary but pulsating contact load. The initiation of two axi-symmetric crack types appearing in the test specimen is investigated. The surface initiated ring/cone cracks circumscribe the contact area, whereas the lateral cracks are horizontal sub-surface cracks. The effect of the stress-state history at possible crack Locations is evaluated through the Sines, Haigh principal stress, Findley, Me Diarmid and Dang Van multiaxial fatigue criteria. The material fatigue parameters of each criterion are determined from independent bending and torsion fatigue testing. Finally, the mean and spread in radial position of the ring/cone crack are evaluated by considering the statistical effects of a weakest link assumption using a three parameter Weibull distribution. The investigation shows that it is hard to distinguish a single criterion that well describes all aspects of the experimental results. For the current contact situation with highly compressive mean stresses in combination with tensile maximum values the Findley criterion shows the best overall performance followed by the Haigh principal stress criterion
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| 3. |
- Ericsson, Mats, et al.
(author)
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Influence of welding speed on the fatigue of friction stir welds, and comparison with MIG and TIG
- 2003
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In: International Journal of Fatigue. - : Elsevier BV. - 0142-1123 .- 1879-3452. ; 25:12, s. 1379-1387
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Journal article (peer-reviewed)abstract
- The objective of this investigation was to determine whether the fatigue strength of friction stir (FS) welds is influenced by the welding speed, and also to compare the fatigue results with results for conventional arc-welding methods: MIG-pulse and TIG. The Al-Mg-Si alloy 6082 was FS welded in the T6 and T4 temper conditions, and MIG-pulse and TIG welded in T6. The T4-welded material was subjected to a post-weld ageing treatment. According to the results, welding speed in the tested range, representing low and high commercial welding speed, has no major influence on the mechanical and fatigue properties of the FS welds. At a significantly lower welding speed, however, the fatigue performance was improved possibly due to the increased amount of heat supplied to the weld per unit length. The MIG-pulse and TIG welds showed lower static and dynamic strength than the FS welds. This is in accordance with previous comparative examinations in the literature on the fatigue strength of fusion (MIG) and FS welds. The TIG welds had better fatigue performance than the MIGpulse welds. The softening, of the alloy around the weldline has been modelled. Using a model without adjustable parameters, a fair description of the hardness profiles across the weld as a function of welding speed was obtained. The softening in front of the Friction Stir Welding tool was also estimated. At the low and high welding speeds a full and partial softening is predicted, respectively.
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| 4. |
- Gamstedt, E. Kristofer, et al.
(author)
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An experimental investigation of the sequence effect in block amplitude loading of cross-ply composite laminates
- 2002
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In: International Journal of Fatigue. - 0142-1123 .- 1879-3452. ; 24:04-feb, s. 437-446
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Journal article (peer-reviewed)abstract
- The Palmgren-Miner rule has been shown to be inexact in many cases for various composite materials. Several empirical models have been conceived to account for this discrepancy, as well as the effect of block sequence. The approach taken here is based on the underlying mechanisms. A cross-ply laminate was used as a model material. In general, composites show both initiatory and progressive mechanisms under fatigue loading. The former is active at high static stresses, whereas the latter predominates at lower stress amplitudes where they are given sufficient time to propagate, Initiatory mechanisms give rise to damage from which the progressive mechanisms can start, and conversely the progressive mechanisms continually alter the local stress state which results in further damage accumulation caused by the initiation controlled mechanisms. In a cross-ply laminate, the initiatory mechanism is the formation of transverse cracks, and the progressive mechanism is mainly delamination growth initiated from the transverse cracks. In an experimental investigation of carbon fiber/epoxy cross-ply laminates, the interaction of these mechanisms has shown why a sequence of high-low amplitude levels results in shorter lifetimes than a low-high order. Such a sequence effect seems to be a common behavior for many other composite materials, and can be mechanistically explained by a similar kind of interaction. Advantages and drawbacks of the mechanistic approach compared with empirical rules are also discussed.
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| 5. |
- Linder, Jan, et al.
(author)
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Fatigue strength of spot welded stainless sheet steels exposed to 3% NaCl solution
- 1998
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In: International Journal of Fatigue. - 0142-1123 .- 1879-3452. ; 20:5, s. 383-388
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Journal article (peer-reviewed)abstract
- Fatigue properties of spot welded stainless sheets steels have been investigated in a 3% NaCl solution and, for comparison, also in air at ambient temperature. Corrosion fatigue tests have been conducted both for one austenitic Stainless steel type AISI304, and for one duplex (similar to 50% austenite, 50% ferrite) stainless steel SAF2304. For the duplex steel, the effect of preexposure of unloaded specimens to a 3%NaCl solution before corrosion fatigue testing was also investigated. Corrosion fatigue strength in 3% NaCl for the stainless steels investigated was found to be reduced by approximately 30-40% compared to fatigue strength in air. Preexposure of unloaded specimens prior to fatigue testing was shown not to reduce fatigue strength further.
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| 6. |
- MackAldener, M., et al.
(author)
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Tooth Interior Fatigue Fracture - computational and material aspects
- 2001
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In: International Journal of Fatigue. - 0142-1123 .- 1879-3452. ; 23:4, s. 329-340
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Journal article (peer-reviewed)abstract
- The hypothesis of the gear failure mode Tooth Interior Fatigue Fracture (TIFF), i.e. a fatigue crack is initiated in the interior of the tooth, is analysed by numerical simulations using FEM and the critical plane fatigue initiation criterion according to Findley. The residual stress profile in the gear is simulated and calibrated versus a neutron diffraction residual stress measurement. Fatigue properties are determined experimentally and are taken to vary with depth in the numerical analysis. In addition, the effect of shot peening is included. The analysis shows that a TIFF-crack is initiated approximately mid-height of the tooth and slightly below the case-core boundary. Furthermore, the analysis shows that TIFF is more pronounced in idlers than in single stage gears.
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| 7. |
- Mansson, T., et al.
(author)
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High temperature fatigue crack growth in two metals under constant and variable amplitude loading
- 2002
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In: International Journal of Fatigue. - 0142-1123 .- 1879-3452. ; 24:11, s. 1159-1168
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Journal article (peer-reviewed)abstract
- Results are presented for fatigue crack growth at elevated temperatures during both constant amplitude and variable amplitude loading. A careful experimental investigation is presented to show that the concept of the effective stress-intensity factor range DeltaK(I)(eff) can be used to eliminate the load ratio effect on fatigue data and produce one single set of crack growth data. The fatigue crack propagation data corrected for crack closure is then used for comparison of mean crack propagation rates for variable amplitude loads with simple time histories. It is concluded that measured crack closure can not fully explain the discrepancies between measured and predicted propagation rates. A reduction factor fitted to the experimental data could be used to successfully correlate the results.
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| 8. |
- Melin, L.G., et al.
(author)
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Fatigue testing and buckling characteristics of impacted composite specimens
- 2002
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In: International Journal of Fatigue. - 0142-1123 .- 1879-3452. ; 24:2-4, s. 263-272
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Journal article (peer-reviewed)abstract
- Fatigue testing has been performed in constant amplitude tension-compression loading on impact damaged carbon fibre/epoxy composite laminates. Two layups were tested. The shape and the amplitude of the buckles were measured using an optical whole field measurement technique. The experimental conditions were chosen to be representative of damages in aircraft structures. The R-value was found to have a small influence on the fatigue life indicating that the compressive part of the load cycle has more importance than the tensile part, this because the compressive load caused local buckling around the damage zone. The buckling was inward on the impact side and outward on the backside with larger buckles on the backside. Also the backside buckles showed a larger growth. Fatigue lives were compared with an analytical model that was found to give conservative predictions. © 2002 Elsevier Science Ltd. All rights reserved.
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| 9. |
- Ringsberg, Jonas W., et al.
(author)
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Rolling contact fatigue analysis of rails inculding numerical simulations of the rail manufacturing process and repeated wheel-rail contact loads
- 2003
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In: International Journal of Fatigue. - 0142-1123 .- 1879-3452. ; 25:6, s. 547-558
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Journal article (peer-reviewed)abstract
- The present work is an investigation on how an initially introduced residual stress-state affects the service life of a rail, i.e. the time to fatigue crack initiation. The finite element (FE) method was used to make two-dimensional thermo-mechanical analyses of the rail cooling and roller straightening processes. The results became the initial conditions in a three-dimensional elastic-plastic rail model; the model is part of an FE tool developed for rolling contact fatigue (RCF) analysis of rails. The results from this tool were analysed for fatigue, for eight wheel passages, according to a method which incorporates a critical plane approach that evaluates fatigue damage on a cycle-by-cycle basis. A heavy-haul (30 tonne) train traffic situation on the Iron-ore Line in Sweden was studied with respect to subsurface fatigue crack initiation in straight track. Three examples using the rail model in the FE tool were assessed: (a) an initially stress-free rail, (b) a measured residual stress field in a newly manufactured rail, and (c) a calculated residual stress field from the cooling and roller straightening analyses. The results from the thermo-mechanical FE analyses of the rail manufacturing process showed tensile residual stresses in the longitudinal direction of the rail; this was validated with experimental measurements on newly manufactured rails. The FE tool and fatigue calculations revealed only small differences in results for the three examples. It was concluded that, because of the very high axle load in the present traffic situation, the local wheel-rail contact loads governed the fatigue life to crack initiation. Additional FE tool calculations were made to show the axle load at which rail manufacturing stresses reduce the fatigue life to crack initiation.
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| 10. |
- Schon, J., et al.
(author)
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Spectrum fatigue of composite bolted joints
- 2002
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In: International Journal of Fatigue. - 0142-1123 .- 1879-3452. ; 24:2-4, s. 273-279
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Journal article (peer-reviewed)abstract
- The new Swedish fighter JAS39 Gripen has a large number of primary structures made of composites. On those structures a large number of bolted joints are used which during the aircraft's service life will be subjected to spectrum fatigue loading. Consequently it is important to study the spectrum fatigue life of bolted joints. Specimens with a double-lap configuration and six bolts have been fatigue loaded at the load ratios R=-0.2 and R=-5. Specimens were also fatigue loaded with a vertical fin spectrum which had different amounts of elimination of load cycles. A linear damage rule, Miner's rule, was used to predict the spectrum fatigue life. The experimental results show that the shortest fatigue life occurs for specimens loaded at R=-1 followed by specimens loaded at R=-0.2. The longest fatigue life occurred for specimens loaded at R=-5. It was found that 50% elimination of load cycles in the spectrum can be used without affecting the fatigue life. The Miner's rule predictions appeared to overestimate the spectrum fatigue life. From bolt failure it was found that the first bolt row transfers the largest amount of load in the specimens. © 2002 Elsevier Science Ltd. All rights reserved.
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