Search results

The purpose of this paper is to investigate the effect of peening on the fatigue limit of steels for welded structure with a crack in the weld toe zone.

An artificial semi-circular slit was created in the weld toe, and peening was conducted. Then, bending fatigue tests were carried out.

First, owing to the shot peening, the maximum slit depths that can be rendered harmless were 1.0 and 1.2 mm in SUS316 and SM490, respectively. Second, during the fatigue test, the fracture of a peened specimen originated outside the slit, which indicated that peening eliminated the effect of the slit on the fatigue limit. Third, the fatigue limit of a slit specimen was improved by the enhanced residual stress distribution and the decreased stress concentration due to plastic deformation at the weld toe.

There are very few studies about which a fatigue crack is rendered harmless by residual compressive stress, as a result the structures could be continued to use. Moreover, the study defining the concept about rendering crack harmless and systematic investigation was not able to be found.

The purpose of this study was to investigate the effect of overload (bending moment with plastic deformation: Mp) on three point bending specimen at the fatigue limit of high-tensile-strength steel containing a crack in the stress concentration zone.

An artificial semi-circular slit was introduced and Mp was applied after which bending fatigue tests were carried out.

The relationship between the level of Mp and the fatigue limit (σ_w) was proportional; the fatigue limits of specimens containing 0.2- and 0.3-mm-deep slits are improved by the Mp process as much as twice the original values; the slit size that can be rendered harmless by the Mp process is a=0.05 mm in depth; and all non-propagating cracks appeared around the artificial slit.

Very few studies have been conducted on the fatigue limit of materials containing crack-like surface defects after overload in the stress concentration zone. This study elucidated the effect of Mp on the fatigue limit.

The purpose of this paper is to investigate the effect of shot peening (SP) on the fatigue limit of high‐tensile‐strength steel containing a crack in the stress concentration zone.

An artificial semi‐circular slit was introduced into the bottom of notch, and SP was performed. Bending fatigue tests were then carried out.

First, the fatigue limits of specimens containing a slit of 0.2 or 0.3 mm in depth were improved up to approximately twice their original values. Second, in the case of shot‐peened specimens with a crack of 0.2 mm in depth, the fractures occurred from outside the slit. Moreover, the specimens recovered to fatigue limits up to those of non‐slit specimens. Finally, the effect of stress concentration (Kt=1.9) on the slit size could be rendered harmless by SP was not found in the fatigue test.

There are very few examples of evaluations of the fatigue limit of materials containing crack‐like surface defects after SP has been performed in the stress concentration zone. The study elucidated the effect of SP on the fatigue limit in such materials, compared with that of a smooth zone.

The paper's aim is to investigate the effects of shot peening (SP) on the bending fatigue limit of high‐strength steel containing an artificial semi‐circular slit.

SP and stress SP (SSP) were conducted on the specimens containing an artificial semi‐circular slit with a depth of a=0.1, 0.2 and 0.3 mm. Then, bending fatigue tests were conducted on the specimens.

The fatigue limit was improved by SP and SSP. In the case of SP and SSP specimens, the specimens with a semi‐circular slit under a=0.2 mm fractured outside the slit, and they had considerably high fatigue limits. Therefore, a semi‐circular slit with a depth of under a=0.2 mm could be rendered harmless by SP or SSP. It was found that the fatigue limit of specimens with a semi‐circular slit that received SP or SSP was determined by the threshold condition for non‐propagation of fatigue cracks that emanated from outside the slit. Whether the semi‐circular slit is rendered harmless or not is decided by the relationship between the stress intensity factor range of semi‐circular cracks and the threshold stress intensity factor range.

The proposed method can be applied to mechanical parts used in vehicles, aircraft and trains.

There are very few examples of evaluations of fatigue limits after SP in materials containing crack‐like surface defects. This study calcifies the effect of SP on the fatigue limit having crack‐like surface defects.

The purpose of this paper is to estimate the acceptable defect size amax after needle peening (NP) and predict the fatigue limit improvement through the use of NP for an austenitic stainless steel welded joint containing an artificial semi-circular slit on a weld toe.

Residual stress and hardness distribution were measured. Microstructures around the weld toe were observed to clarify the cause for the change in hardness after NP. Finite element method analysis was used to analyze the change in the stress concentration following NP. Fracture mechanics was used to evaluate amax after NP. The fatigue limits before and after NP were predicted by determining amax for several levels of stress amplitude.

The tensile residual stress induced at the surface of the weld toe prior to NP changed to a compressive residual stress after NP. The residual stress near the surface layer after NP exceeded the yield stress prior to NP due to the increase in yield stress as a result of work hardening as well as the generation of a deformation-induced martensitic structure. The stress concentration was reduced due to the shape improvement caused by NP. The estimation value of amax after NP and the prediction results of fatigue limits were in good agreement with the fatigue test results.

The proposed method is useful in improving the reliability of welded joints used in large steel structures, transportation equipments and industrial machines.

From an engineering perspective, it is essential to estimate amax and the fatigue limit of welded joints with crack-like defects. However, it is unclear as to whether it is possible to predict amax and the effects of NP on the fatigue limit for stainless steel welded joints.

The purpose of this study is to clarify the influence of stress ratio (R) on the effects of shot peening (SP) on the fatigue limit of high-strength steel containing an artificial small defect.

SP was subjected on the specimens with a semi-circular slit with a depth of a=0.1, 0.2 and 0.3 mm. Then, bending fatigue tests were carried out under R=0.4.

The fatigue limits of specimens with a semi-circular slit were improved by SP under R=0.4. The fatigue limits of the SP specimens with a semi-circular slit under a=0.2 mm fractured outside the slit, and they had considerably high fatigue limits equal to specimens without a slit. Therefore, a semi-circular slit with a depth of under a=0.2 mm could be rendered harmless by SP under R=0.4. Compared to the results of R=0, the increasing ratios of fatigue limits under R=0.4 were lower than those under R=0. However, the size of semi-circular slit that could be rendered harmless by SP was same. In addition, it was found that whether the semi-circular slit is rendered harmless or not is decided by the relationship between the stress intensity factor range of semi-circular cracks and the threshold stress intensity factor regardless of stress ratio.

The proposed method can be applied to mechanical parts used in vehicles, aircraft and trains.

This is the first paper to investigate the fatigue limits after SP in materials containing a surface defect under positive stress ratio. In this study, the authors investigated the influence of stress ratio on the effects of SP on the fatigue limit containing a surface defects.

The purpose of this paper is to clarify the effects of shot peening (SP) on the torsional fatigue limit of high‐strength steel specimens containing an artificial small defect.

Specimens containing a drilled hole 0.1‐0.4 mm deep or a semi‐circular slit 0.15 or 0.3 mm deep were subjected to SP. Torsional fatigue tests were then carried out.

The torsional fatigue limits of specimens containing a drilled hole and those with a semi‐circular slit were increased 25‐64 per cent and 156‐186 per cent by SP, respectively. The torsional fatigue limits of the specimens subjected to SP and containing a drilled hole less than 0.1 mm in depth or a semi‐circular slit less than 0.15 mm in depth were almost equal to those of SP specimens without a defect. Based on these results, it can be concluded that a drilled hole less than 0.1 mm in depth and a semi‐circular slit less than 0.15 mm in depth could be rendered harmless by SP.

The proposed method can be applied to mechanical parts subjected to cyclic torsion, such as coil springs, crank shafts and drive shafts.

This is the first paper to investigate the torsional fatigue limits after SP in materials containing a surface defect. In this paper, the effect of SP on the torsional fatigue limit having a surface defect is investigated.

It has been known for many years that apparently brittle failures of mild‐steel plates and rivets can take place in apparatus used for the concentration of caustic soda. These failures invariably reveal the presence of a network of fine intergranular cracks which have their origin at parts where high concentrations of stress can occur; that is under rivet heads, alongside caulked seams and in the vicinity of welded joints which have not been stress relieved. Failures of a similar type have occurred from time to time in steam boilers, frequently by the formation of fine intergranular cracks in the vicinity of riveted seams.

The above Congress, being held at the Imperial College of Science and Technology, London, from April 10–15, has been described as likely to be the corrosion event of the decade. Size alone is no criterion, though over 80 papers are being presented, but the standing of many of the corrosionists associated with the Congress is, perhaps, the best indication of the truth of this statement. Summaries and abstracts of some of the papers appear in the following pages. More will be published in next month's issue.

Although under many conditions a carefully made weld should introduce no special corrosion risk, the fact remains that welding raises special corrosion problems. The reasons are discussed by Dr. Evans in the first part of his article. He then considers in particular the corrosion of welded stainless steel and aluminium alloys, corrosion fatigue, and hydrogen blistering and cracking.