Fatigue Life Of Spring Research Articles

Multiaxial fatigue and failure analysis of helical compression springs

Multiaxial fatigue criteria are applied to the analysis of helical compression springs. The critical plane approaches, Fatemi–Socie and Wang–Brown, and the Coffin–Manson method based on shear deformation, were used to predict fatigue lives of the springs under constant amplitude loading. Experimental fatigue lives are compared with the multiaxial fatigue criteria predictions. The stress analysis was carried out in the finite element code ANSYS, and the multiaxial fatigue study was performed using the fatigue software nCode. A failure analysis was conducted in order to determine the fatigue crack initiation point and a comparison of that location with the most damaged zone predicted by the numerical analysis is made. The Fatemi–Socie critical plane approach gives a good prediction of fatigue life. While the Wang–Brown criterion overestimates spring fatigue life, the Coffin–Mason model gives conservative results.

Fatigue Design Criterion of LCV Leaf Spring Based on Road Load Response Analysis

Suspension system of light commercial vehicle (LCV) has enough endurance to protect passenger and freight. Leaf spring is major part of LCV suspension system. Thus, fatigue strength evaluation of leaf spring based on road load response was carried out. At first, the strain of leaf spring was measured on the city mode driving condition and proving ground driving condition. And , the damage analysis of road load response was carried out. After that, fatigue test of leaf spring was also carried out. Based on ε-N life relation, fatigue life of leaf spring was evaluated at Belgian mode, city mode and drawing test specification called the 3 steps test mode. Next, it is compared the design life of leaf spring and evaluated fatigue life by the 3steps test mode. From the above, new target of Belgian mode and city mode was proposed to gratify design specification of leaf spring. It is expect that the proposed target can be satisfied leaf spring fatigue endurance at specific road condition.

１２００ＭＰａ級高強度ばね鋼“ＮＤ１２０Ｓ”

As for automotive suspension coil spring, its weight saving has been achieved by increasing the design stress, since the increasing of design stress requires higher fatigue strength and sag resistance. However, in the case of the conventional spring steel, the high tensile strength over 1900MPa can dramatically reduce the corrosion fatigue strength and delayed fracture strength. In this paper, a newly developed spring steel material, satisfying higher strength and corrosion fatigue life of spring, is proposed, and its application to automotive suspension coil spring under the appropriate spring manufacturing process is introduced. Carbon content of developed steel is less than conventional steels to increase of corrosion fatigue life and fracture toughness. Nickel is added to restrain corrosive pit forming. Boron and niobium are added to improve delayed fracture strength. Experimental results by both the test piece and spring under high strength design, shows that the developed spring material is effective for improving the corrosive fatigue life and delayed fracture strength, and can achieve the 20% weight saving under 1200MPa design stress, comparing with conventional spring steel.

Influence of Surface Flaws on Fatigue Life of Valve Springs

Surface flaws on valve springs in automobile engines are one of the crucial factors which affect the fatigue life of valve springs together with harmful non-metallic inclusions and surface decarburization. Through the fatigue tests of high tensile strength springs and nitrided springs with artificial longitudinal flaws, the influence of surface flaws on fatigue lives were investigated.Fatigue lives of both springs lowered as the depth of flaws increased, however, in this experiment, when flaw depth was not deeper than 0.05mm, no lowering of each fatigue strength was recognized. It was considered as this reason, that the large compressive residual stress of the surface layer effectively suppressed propagation of fatigue crack.

Fretting fatigue behavior of leaf springs under random loading.

Fretting fatigue tests on leaf springs and small axial-loading specimens were carried out under constant loading and random loading simulating field load spectra. The results of leaf springs were compared with the literature data for similar springs. The behavior of fretting fatigue crack initiation and propagation in the leaf springs was found to be almost the same as those in the small laboratory specimen. No significant differences between their fretted surfaces or between their fatigue fractured surfaces were observed. Random loading reduced the fretting fatigue lives by a factor of 1.5. The effects of shot peening on fretting fatigue were also investigated. Shot peening improved the fretting fatigue strength in both specimens by a factor of two. The residual compressive stress induced by the shot peening process was attributed as being the controlling factor to the improvement. It was suggested that the fretting fatigue life of leaf springs can be estimated from that of laboratory specimens, if the clamping pressures and the relative slip amplitudes of both the specimens have the same magnitudes.

Quenching of springs made of steel 60S2KhA in foam

Replacing oil for quenching cylindrical coiled compression springs of steel 60S2KhA with a water-base foam improves the hardenability without formation of cracks and increases the elestic properties and fatigue life of springs.

Effect of strain aging of martensite on relaxation resistance and service life of springs

Strain aging of steel 60S2A in the martensitic condition increases the relaxation resistance and fatigue life of springs.