Mitigation Schemes for the Reduction of Fretting Wear and Fatigue

Fretting refers to wear damage at the asperities of contacting surfaces. This damage is induced under load and in the presence of repeated relative surface motion. Fretting degrades the surface quality producing increased surface roughness and micropits and cracks, which reduces the fatigue strength of the components. Fretting occurs in many electrical connectors subject to motion (e.g. a printed circuit board connector). Commonly most board-to-board (B2B) electrical connectors are especially vulnerable if there is any relative motion present between the mating connectors. Contact fretting can change the electrical contact resistance of such connectors from milliohms to ohms when vibration is present. Fretting decreases fatigue strength of materials operating under cycling stress. This can result in fretting fatigue, whereby fatigue cracks can initiate in the fretting zone. Then, crack propagate into the material and may cause total elemental failure. Common mitigation strategies rely on adding lubricants to the contact, or making contacts of soft materials. However, such contacts are susceptible to entrapped wear debris. Here a different mitigation strategy is offered that is based on pre-stressing the contacting elements. To mitigate the damage during the fretting motion, two main properties are focused on: plastic strain and wear volume. The plastic strain represents the plastic deformation in the bulk material, which will decrease the life of the component. The wear volume represents the damage at the interface, which will also decrease the life of the component. It is found that pre-stressing may be beneficial for the suppression fretting fatigue, however, if excessive it may increase the plastic strain in the contact.