Design and development of fretting fatigue test apparatus

Abstract

A detail survey of the existing fretting fatigue test equipments used is given and a new fretting fatigue test apparatus has been designed and fabricated. The fretting fatigue test apparatus permits the examination of the contact zone during the test and allows the precise measurement of frictional force induced at the contact interface due to the fretting action. The fretting fatigue experiments have been carried out using 7075-T6-aluminium alloy specimen with the En24 steel pad with flat over flat contact condition. It has been observed that the life reduction factors increase with increase in normal stress for given maximum axial stress. For the specimens tested under fretting fatigue condition with normal stress in the range of 45 MPa to 90 MPa the average life reduction factors are 12.52, 6.71, and 2.28 for maximum axial stresses of 290 MPa, 300 MPa, and 325 MPa respectively. The micro cracks along the contact interface below the pads have been nucleated and these micro cracks later on link to other cracks to form a composite major crack which is considered as a leading cracks through the thickness, while other will be considered as non-propagating cracks. The crack initiation of the order of 20 micrometer is captured with the help of video microscope.