Fatigue Strength Of Spring Steel Research Articles

Fatigue strength of spring steel with small scratches

AbstractIn compression coil springs subjected to cyclic load, fatigue cracks can sometimes initiate and propagate from scratch‐like small defects produced during the manufacturing process and degrade the fatigue strength. In this study, torsional and rotating bending fatigue tests were conducted to examine the fatigue behavior of a high‐strength spring steel (JIS G 3561, SWOSC‐V) in the presence of small scratches. The sensitivity of the HCF and VHCF strength to small scratches was evaluated based on the parameter model.

Effect of microshot peening on fatigue strength of spring steel

Effect of microshot peening on fatigue strength of spring steel

G0400401 ばね鋼の疲労強度に及ぼす硬質マイクロショットピーニングの影響

In shot peening, the surface of the material receives a so-called peening effect where strong local deformation forms a work-hardened layer or causes compressive residual stress. More recently, a new type of microshot has been developed to enhance the peening effect. In the present study, the effect of microshot peening on the surface characteristics and fatigue strength of spring steel was investigated. The workpiece was commercial spring steel SUP9. In the microshot peening process, the equipment was used an air-type machine. The microshots used were high-carbon cast steel and cemented carbide with an average diameter of 0.1mm. Air pressure was 0.6 MPa and peening time was in the range of 10-100s. Surface roughness and Vickers hardness for the peened workpiece were measured. The out-of-plane bending fatigue tests were also carried at a frequency of 200 rpm. As the peening time increased, surface roughness for the peened workpiece decreased. The use of microshot was the very effective means of reducing surface defect. The microshot peening process was very efficient in improving the fatigue life of spring steel, especially at a high number of cycles. It was found that the use of the hard microshot was found to cause a significantly enhanced peening effect for spring steel.

S0301-5-3 SUP10ばね鋼の疲労強度に及ぼすFPB処理による表面改質効果(軽合金と表面改質処理(2))

The FPB (Fine Particle Bombarding) process attracts attention as a new surface-preparation technique. The effect which the surface modification effect by this FPB process has on the fatigue strength of spring steel was investigated. It proved that surface roughness decreases and the hardness near surface rises rather than a shot peening process as compared with a shot peening process. As a result of comparing the shot time of a FPB process, hardness also increased as the shot time became long. The FPB process showed the value higher than a shot peening process by lowering of surface roughness, and the rise of hardness as a result of the fatigue test. These results showed that the FPB process was effective in the betterment in the fatigue strength of spring steel.

Fatigue strength of spring steel under axial and torsional loading in the very high cycle regime

The fatigue strength of an oil-tempered Si–Cr steel for valve springs (JIS G3561, SWOSC-V) was investigated. Smooth specimens without residual surface stresses were fatigued with two kinds of ultrasonic fatigue testing machines to clarify the fatigue properties up to very high numbers of cycles (giga cycle regime) under axial and torsional loading. The maximum inclusion size in the critical volume of a specimen predicted by the extremal statistics is 7.9 μm. Although scatter is somewhat large, the S– N data could be approximated by linear lines in double logarithmic plots for both loading conditions up to the giga cycle regime. The ratio of fatigue strength under torsional and axial loading at the same number of stress cycles is about 0.68 and is almost constant even in the giga cycle regime. Cracks were initiated from the specimen surface under tension–compression as well as torsion loading. No specimen showed crack initiation from the interior. Inclusions and granular facet areas could not be observed. Under torsional loading, cracks initiated either perpendicular or parallel to the longitudinal direction of the specimens. After shear crack propagation to a crack length of about 30 μm, crack branching and mode I propagation took place. The size of characteristic defects calculated on the basis of the propagation threshold of long cracks is much larger than the inclusion size calculated by the extremal statistics.

Effect of Shot Peening on Torsional Fatigue Strength of High Strength Spring Steel in Air and Corrosive Environments

Torsional fatigue tests were conducted for a spring steel, SUP7, with Vickers hardness of 480. The effect of shot peening on the torsional fatigue strength of smooth and artificially notched specimens in the corrosive environment and air was studied. The increase of the fatigue strength of smooth specimens in air by shot peening was relatively small, and the surface roughness due to peening did not reduced the fatigue strength. On the other hand, the fatigue strength of notched specimens increased greatly by shot peening and the notch sensitivity was reduced. In corrosion fatigue, the fatigue strength increased by shot peening in the medium life range. The strength of shot-peened specimens was reduced in the long life range around 107cycles and was approached to that of not-peened specimens. A similar improvement was observed for notched specimens in the medium life range, and the notch sensitivity was reduced by shot peening. The compression zone made by shot peening extended about 0.3mm below the surface, and relaxed by fatigue loading. The observation results on the cracking behavior and residual stress distribution were used to interpret the effect of shot peening on the fatigue strength of spring steel.

701 ばね鋼の疲労強度に及ぼす短時間誘導加熱焼戻しの効果

701 ばね鋼の疲労強度に及ぼす短時間誘導加熱焼戻しの効果

Fatigue strength of spring steel subjected to high-temperature thermomechanical treatment and ?inheritance? treatment

Fatigue strength of spring steel subjected to high-temperature thermomechanical treatment and ?inheritance? treatment