Design of a fretting fatigue test rig with compliant springs

摘要

Fretting is a small amplitude oscillatory movement which occurs between contacting bodies who are subjected to cyclic loading or vibrations. In the contact area arise stresses -normal and tangential- causing stress concentrations and surface degradation. Fretting in combination with ordinary fatigue will reduce the plain fatigue lifetime due to the additional stresses and surface degradation. Applications susceptible to fretting fatigue are for instance connections techniques. By nature they have contacting bodies and transfer loads or vibrations. Connection techniques commonly seen in the field of fretting fatigue are lap-joints, dovetail connections and spline connections. Although mitigating or managing fretting fatigue is industrially relevant, academic research is confined and only revealed basic insights. Therefore, we developed a fretting fatigue test rig at Soete Laboratory. The paper describes the design of the test rig and points out some important features. To study the general phenomenon of fretting fatigue we selected a coupon scale test rig rather than a full scale test rig where only one application can be studied. The specimens used are one dog bone specimen and two indentation pads which make contact with the dog bone specimen. The normal force FN between the specimen and the pads is close loop controlled with a hydraulic actuator. A second hydraulic actuator controls the dynamic force Ffat in the dog bone specimen. A third force FT is introduced during dynamic loading between the dog bone specimen and the pads by means of compliant springs. The combination of these three forces: FN, Ffat, FT in the contact area gives rise to the fretting fatigue phenomenon. The test rig at Soete laboratory can be used to study fretting fatigue and examine mitigations such as surface texturing, surface work hardening, etc.