Cyclic creep and cyclic deformation of high-strength spring steels and the evaluation of the sag effect: Part I. Cyclic plastic deformation behavior

Abstract

The cyclic creep and cyclic plastic deformation behavior of two commercial suspension spring steels of high hardness levels, namely, SAE 9259 and SAE 5160, were studied under different testing conditions of cyclic peak stress and cyclic stress ratio. The experimental results indicate that both the cyclic stress ratio and cyclic peak stress have strong, but complicated, effects on the cyclic creep and cyclic plastic deformation behavior of these materials. It has also been found that the addition of silicon can increase the resistance of these steels to cyclic creep and cyclic plastic deformation, although the extent of this increase is also related to other cyclic deformation conditions. A transition in the relationship between the total plastic strain range and the cyclic stress ratio (R) has been detected at approximately R ϭ 0.5. The mechanism of such a transition is explained by the operation of cross-slip during the unloading process of cycling. Moreover, a cyclic softening behavior of these spring steels in the quench-tempered condition was also detected and is attributed to the activation and reorganization of obstacle dislocations introduced into the steels during the process of martensitic transformation. More importantly, this study has indicated that parameters such as the cyclic creep strain, the cyclic creep rate in the secondary creep stage, and the total cyclic plastic strain range can better reflect, and should be used to depict and characterize, the sag behavior of spring steels as well as other materials. Finally, the effect of silicon on sag behavior, in comparison with the results from the Bauschinger-effect test, has also been discussed through the influence of Si on carbide formation and distribution.

Optimization and Static Stress Analysis of Hybrid Fiber Reinforced Composite Leaf Spring

“…kumar and Vijayarangan [7] studied and tested monoleaf spring fabricated from a traditional E-glass/epoxy composite material for the static load conditions; fatigue life prediction was also done by these authors so as to ensure a reliable number of life cycles of that spring. Cyclic creep and cyclic deformation were also studied by Yang and Wang [8]. Fuentes et al [9], Clarke and Borowski [10], and Mayer et al [11] studied the premature failure in leaf springs so as to suggest remedies on application of composite leaf springs.…”

“…The loads are assumed to be applied at the infinity (for the sake of the problem of contact stresses and the Saint Venant principle to be turned away). Initially stress-free(8) The composite material is transversely isotropic[21]. The short fibers are randomly and homogeneously distributed throughout matrix material constituting the composite matrix such that it exhibits isotropic behavior[22].…”