Effect of contact pad rigidity and fretting fatigue design curve

Abstract

In fretting fatigue the nucleation and early propagation of fatigue crack depends on the state of stress near the contact edge. Contact pad rigidity is one of the factors that influence the stress state near the contact edge, there by influencing fretting fatigue strength. In the present study the effect of contact pad rigidity on fretting fatigue strength of turbine steels (Ni-Cr-Mo-V steel specimen with 12 Cr steel contact pads) were investigated. To study the effect of contact pad rigidity, contact pads with different pad foot height were used. FEA was performed to evaluate the stress distribution near the contact edge. The results showed that with increase in contact pad rigidity the fretting fatigue strength decreased. The results obtained were explained based on the stress distribution near the contact edge evaluated by using FEA. By combining the experimental results and FEA, fretting fatigue design curves were proposed. relationship between rigidity of contact pad and fretting fatigue strength is also clarified and then fretting fatigue design based on rigidity of contact pad can be developed. These design curves helps in real industrial applications to avoid FF failures.In the present study the effect of contact pad rigidity on fretting fatigue strength was investigated by using the contact pads with different foot height and contact length. Finite element analysis (FEA) was also performed to evaluate the stress distribution and the relative slip amplitude at the contact edge. From the results, it is confirmed that the contact pad rigidity influences the stress state at the contact edge (tangential stress and compressive stress) and then plays a dominant role in determining FF strength. Finally, by combining the experimental and FEA results fretting fatigue design curves were proposed, based on the dependence of FF life on both the tangential stress and compressive stress at the contact edge. Experimental procedure 2.1 MaterialThe material used in the present study was Ni-Cr-Mo-V steel, which was commonly used for steam turbine rotors. The contact pads were made of 12 Cr steel, which was commonly used for steam turbine blades. To study the effect of contact pad rigidity, contact pad with four different foot heights were used. The dimensions of the specimen and the contact pads are shown in Figs. 1 and 2, respectively. The chemical composition and mechanical properties of the specimen and the pad materials are shown in Table 1 and 2, respectively.

A Review of Research Progress on the Fretting Fatigue Mechanism and Protection Measures of Metal Matrix Composites

“…In 2009, Wagle and Kato [142] further investigated the effect of torque on fretting fatigue in bolts and rivets. Jayaprakash et al [143] investigated different shear and compressive stresses to predict the fretting fatigue life of bolted joints [144,145]. The results showed that the introduction of grooves at the edges of the contact zone could effectively improve the fretting fatigue life of the joint.…”

Fretting Fatigue in Mechanical Joints: A Literature Review

“…A couple of years later, Jayaprakash et al [95] investigated the possibility of predicting the fretting fatigue life of an S355mc (hot rolled low-alloy steel) automotive bolted joint using the tangential stress range (TSR)-compressive stress range (CSR) diagram previously developed by them [84,96].…”