摘要:

Abstract—The corrosion fatigue crack growth characteristics of small surface and corner cracks in aluminium alloy 2024 is established. The damaging effect of salt water on the early stages of small crack growth is characterized by: (1) crack initiation at constituent particle pits, (2) intergranular microcracking for a≤100μm, and (3) transgranular small crack growth for a≥100μm. In aqueous 1% NaCl and at a constant anodic potential of −700 mVSCE, small cracks exhibit a factor of three increase in fatigue crack growth rates compared to laboratory air. Small cracks exhibit accelerated corrosion fatigue crack growth rates at low levels of ΔK(<1 MPa√m) below the long crack ΔKthvalue. When exposed to Paris regime levels of crack tip stress intensity, small corrosion fatigue cracks exhibit growth rates similar to that observed for long cracks. Similar small and long crack growth behavior at various levels ofRsuggest that crack closure effects influence the corrosion fatigue crack growth rates of small cracks for a≥100 μm. Contrary to the corrosion fatigue characteristics of small cracks in high strength steels, no pronounced chemical crack length effect is observed for alloy 2024 expos

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00213.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—The influence of precracking history on the subsequent fatigue crack growth thresholds for branch cracks has been studied for AISI 316 stainless steel and BS4360 50D under mixed mode I/II loading. The work has examined: (1) the influence of precrack length; (2) the influence of stress intensity factor range at the final stage of precracking; (3) the influence of precracking loadR‐ratio; and (4) the influence of precracking unloading schemes. A computer controlled precracking test system has been set up in the current investigation and comparisons have been made between the results of computer controlled work and those published previously using a manually controlled technique. The results show that a computer controlled precracking method generally gives more conservative and more repeatable growth threshold values for branch cracks than a manually controlled precracking proced

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00214.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—Micro‐crack behaviour under axial and torsional loading at 550°C was observed by replica techniques. Cracking behaviour and micro‐damage observations were correlated using several parameters that are based on equivalent strain parameters. From the observations, micro‐cracking of the oxide films at the crack tip in the strain localized regions seems to be a dominant micromechanism of fatigue crack growth. The maximum principal strain has been identified as an important parameter in multiaxial fatigue at high temperature. A good correlation was obtained between the principal strain range and the crack growth rate. Finally, a life prediction method was proposed based on maximum crac

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00215.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—Conventional mechanical tests and fracture mechanics experiments were carried out at – 196°C on a low alloy steel (A508 class 3) which was investigated under two different conditions: (i) a reference condition in which the failure mode was cleavage and (ii) an embrittled condition in which the fracture mode was either partly or predominantly intergranular fracture. These experiments, performed with a new specimen geometry, a ring specimen instrumented to measure also the crack velocity, were used to determine the fracture toughness at crack initiation (KIc) and at crack arrest (KIa). It is confirmed that the reduction inKIcmeasured in the embrittled material is associated with the appearance of intergranular fracture. It is also shown thatKIa, determined by a static analysis decreases rapidly with crack velocity when the fracture mode is predominantly cleavage. On the other hand,KIa, corresponding to intergranular fracture seems to be much less dependent on crack speed. This difference in the sensitivity of both modes of brittle fracture to crack velocity is briefly discu

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00216.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—Fracture mechanics analyses are carried out on a cracked machine element of complex geometry to predict its fatigue behaviour. Usually, in order to obtain reliable values of stress intensity factors, it is necessary to realize three‐dimensional meshes or to utilize the energy approach. An alternative, simplified and approximate approach is proposed here. It is based on the construction of simple two‐dimensional models to obtain accurate values of the geometry factors of the component at the deepest point of the crack. Experimental tests show that the relation between the depth and the length of the crack on the free surface is linear. Hence it is possible to reduce the problem to two dimensions with a consequent saving of calculation time. A comparison with experimental data indicates that a satisfactory prediction is obtained by the proposed m

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00217.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—Calculated fatigue lives, based on three criteria for multiaxial random fatigue, were compared with lives obtained from tests on cylindrical specimens of 30CrNiMo8 steel subjected to in‐ and out‐of‐phase bending and torsion at variable amplitudes. In the chosen fatigue criteria the expected position of the fracture plane, determined from a variance method for the equivalent stress, were taken into account. The equivalent stress history was related to the rain flow method and fatigue damage was evaluated from the Palmgren–Miner hypothesis. It has been shown that the expected fatigue fracture planes agree with those determined by experiments. The most realistic estimations of fatigue life were obtained by the criterion of maximum shear and normal stresses on the fracture plane using a modified she

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00218.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—Low cycle fatigue (LCF) testing of powder metallurgy (PM) superalloys has determined that LCF cracks initiate from defects such as pores and ceramic inclusions located either at the surface or internally. The ratio of surface‐to‐internal crack initiation sites depends upon experimental conditions. In the current work, a probabilistic model is presented that describes the competition between these two failure mechanisms from a single experimental parameter, μ. The model predicts the size distribution of defects which initiate LCF cracks, as well as the proportion of specimens which fail as a result of internally located defects. Model predictions were found to correlate well with experimental LCF data obtained from a N18 PM Ni‐base superalloy. The model further enables evaluation of a “size effect”, as it predicts that internal crack initiation is favoured for larger componen

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00219.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—The low‐cycle fatigue crack propagation behaviour of surface cracks in SUS316 stainless steel at 700°C, in both the surface direction and the in‐depth direction, has been studied with special emphasis on the role of oxidation. The coalescence behaviour of surface cracks is essential for the process of crack propagation in high temperature low cycle fatigue, irrespective of the existence of oxidation effects. For sub‐surface cracks the process of crack propagation is divided into two stages characterized by differences in fracture mode. In both stages, the in‐depth crack propagation rate in air is higher than that in vacuum. This difference in crack propagation rate is the main reason for the decrease of fatigue life in air compared with that in vacuum. The crack propagation behaviour in the in‐depth direction can be estimated from the conversion of the surface crack length into the subsurface depth by the use of an

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00220.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—A fatigue scatter band has been computed for laser welded austenitic stainless steel joints. These laser welded steels have a very small heat affected zone. The unified scatter band provided by standards for welded structural steels does not adequately describe the trend of the experimental data of laser welded steels and this makes their design parameters scarcely realistic. The scatter band proposed in this paper has been computed by re‐sorting experimental data relative to joints with high stress concentration factors and has subsequently been assessed with data relevant to butt welded joi

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00221.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract—The opening and closure behaviour of surface, corner and through‐thickness cracks in thin notched plates of FeE460 (Kt= 2.5) and A15086 (Kt= 3.4) was experimentally studied. The cracks were initiated and examined under uniaxial fully reversed constant amplitude and two‐step loading. Crack opening load values were measured during crack growth in notch sections with a nonuniform stress distribution using small strain gauges glued to the specimen surface, very close to the crack tip. The results represent a comprehensive set of experimental data for crack opening load values in dependence on crack lengthsa, cand load level including the influence of overloads and covering all types of cracks. The results indicate uniform relationships between crack opening load levels and all crack types. Crack opening and closure occur at nearly the same strain level, which depends on the applied load level. The crack opening load values measured at large notched specimens differ from those measured at similar smaller specimens because of the different local stress grad

ISSN:8756-758X    

DOI:10.1111/j.1460-2695.1994.tb00222.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY