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991.
R. LUNDÉN 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(10):905-914
Propagation of small subsurface cracks subjected to shear under repeated rolling contact load is studied. An analytical crack model (Dugdale) with plastic strips at the two crack tips is employed. Compressive stresses promoting crack closure and friction between crack faces are considered. The triaxial stress state is used in the yield criterion. A damage criterion is suggested based on experimental LCF data. In a numerical study, critical crack lengths are found below which propagation of an existing crack should be effectively suppressed. 相似文献
992.
R. RODRÍGUEZ-MARTÍN I. OCAÑA A. MARTÍN-MEIZOSO 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(7):664-670
High-strength steels are used to increase the load carrying capacity of components. However, to guarantee a safe design, it is also necessary to combine high strength with adequate fracture toughness. In this paper, fracture toughness of three high-strength steels with yield strengths ranging from 460 to 890 MPa has been studied at very low temperatures. Taking into account experimental evidence, a new mechanism of cleavage at very low temperatures is proposed. This mechanism considers the possibility of reaching the ideal strength (the stress at which the lattice of a single crystal losses its stability) in the immediate vicinity of the fatigue crack tip. Moreover, a computational model able to calculate the external load needed to produce a catastrophic failure of these steels has been developed. 相似文献
993.
Crack closure in fibre metal laminates 总被引:1,自引:0,他引:1
H.M. PLOKKER R.C. ALDERLIESTEN R. BENEDICTUS 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(7):608-620
GLARE is a fibre metal laminate (FML) built up of alternating layers of S2-glass/FM94 prepreg and aluminium 2024-T3. The excellent fatigue behaviour of GLARE can be described with a recently published analytical prediction model. This model is based on linear elastic fracture mechanics and the assumption that a similar stress state in the aluminium layers of GLARE and monolithic aluminium result in the same crack growth behaviour. It therefore describes the crack growth with an effective stress intensity factor (SIF) range at the crack tip in the aluminium layers, including the effect of internal residual stress as result of curing and the stiffness differences between the individual layers. In that model, an empirical relation is used to calculate the effective SIF range, which had been determined without sufficiently investigating the effect of crack closure. This paper presents the research performed on crack closure in GLARE. It is assumed that crack closure in FMLs is determined by the actual stress cycles in the metal layers and that it can be described with the available relations for monolithic aluminium published in the literature. Fatigue crack growth experiments have been performed on GLARE specimens in which crack growth rates and crack opening stresses have been recorded. The prediction model incorporating the crack closure relation for aluminium 2024-T3 obtained from the literature has been validated with the test results. It is concluded that crack growth in GLARE can be correlated with the effective SIF range at the crack tip in the aluminium layers, if it is determined with the crack closure relation for aluminium 2024-T3 based on actual stresses in the aluminium layers. 相似文献
994.
A. MONSALVE M. PÁEZ M. TOLEDANO A. ARTIGAS Y. SEPÚLVEDA y N. VALENCIA 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(8):748-758
The S-N-P (stress, number of cycles, failure probability) curves for 2024 T3 and 7075 T7351 aluminium alloys were obtained. Previously, surface treatments of degreasing and different types of anodizing were applied to samples, evaluating the influence of these treatments on the fatigue life of the alloys. The determination of the S-N-P curves was done using Maennig's method. Rotary fatigue was used because this technique produces greater stress on the sample surfaces, the zone in which it is important to evaluate fatigue resistance. Both the transition range and the finite life range were evaluated, calculating the 1, 50 and 99% fracture probability. SEM was performed in order to characterize the fracture micromechanism. The conclusions were that Maennig's method is useful to evaluate fatigue life of these materials in a fast and efficient manner. Moreover, surface treatments produce a decrease in the fatigue life of both alloys, associating this effect with the surface damage produced on each sample during the treatment. 相似文献
995.
L. T. MO M. HUURMAN S. P. WU A. A. A. MOLENAAR 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(9):823-831
Tensile fatigue behaviours of bitumen–stone adhesion were investigated using a dynamic mechanics analyser under stress‐controlled mode at two temperatures of 5 and 25°C and various controlled‐stress levels. Failure characteristics including interfacial failure and cohesive failure were examined using image analysis of fracture surfaces. Finite‐element analysis on stress distributions was conducted under different temperatures, film thickness and interfacial bonding conditions. A Coulomb–Mohr like criterion in combination with shear and normal stresses is proposed to deal with the extreme thin adhesive layer, which can be further simplified into an adhesive zone without significant loss of accuracy for stress analysis. 相似文献
996.
The thermal evolution of defects produced by ion irradiation is studied by kinetic Monte Carlo and Rate Theory approaches. An isochronal annealing is simulated to evidence the different thermally activated mechanisms that govern defect evolution. KMC simulations show that in the case of ion irradiation, additional recovery peaks should be expected, in comparison to electron irradiation conditions. A comparison between kMC and RT results indicates that some of these peaks are due to spatially – correlated recombinations that occur at low temperature. Therefore kMC and RT approaches differ at low temperature. However, at higher temperature results obtained by both models are in near perfect agreement. In addition, we studied the influence of vacancy cluster mobility on the evolution of damage. KMC simulations show that the mobility of V2, V3 and V4 clusters does not significantly affect the evolution of defects and can be neglected in these conditions. 相似文献
997.
The Modified Embedded Atom Method model for Pu metal is revised so that it more accurately captures the behavior of the Ziegler-Biersack-Littmark
model of ion-ion interactions. Two revision are tested with somewhat different stiffnesses in the 2-1000 eV range. The revised
models show higher damage levels at 20 KeV than an earlier model, suggesting that the behavior of the models above 100 eV
is dominating damage production, at least in the earlier stages of the cascade.
Work was performed at Los Alamos National Laboratory under the auspices of the US Department of Energy, under contract DE-AC52-06NA25396. 相似文献
998.
999.
1000.
Sinéad C. Mac Namara Maria M. Garlock David P. Billington 《Canadian Metallurgical Quarterly》2007,21(2):152-156
Steam generator replacement at nuclear power plants requires large construction openings in nuclear containment structures. This study examines the effects of such openings placed in a 61?cm (2?ft) thick dome of a shield building. The dome is cast in two layers, and the limiting cases of the two layers acting as one and the lower layer carrying the entire load are considered. Without openings, the stresses due to dead load in the structure are very low when compared to the material strength. With openings, the loads are easily redistributed around the opening, and the maximum stresses for the conservative case are between three and four and one-half times larger than in the original structure with no openings. The extent of the affected area around the holes is relatively small. Smooth corners in the openings are necessary to avoid high local stress concentrations. 相似文献