Dr. Jacob Bortman, full professor of Mechanical engineering, head of the Prognostic and Health Monitoring (PHM) research center, Ben Gurion University of the Negev, Israel

Biography: Prof. Jacob Bortman studied for his D.Sc. in Washington University in St. Louis, MO, USA, Mechanical Engineering. Thesis title: "Nonlinear Models for Fastened Structural Connection Based on the p-Version of the Finite Element Method". He retired from the Israeli Air Force as Brigadier General after 30 years of service with the last position of the Head of Material Directorate . He is the chairman and member of several boards of start-up companies in Israel. In 1992 he received the Israeli Prime Minister National Prize for Excellency and Quality in the Public Service. Since 2010 he is the head of the BGU PHM lab. His specialties in the Dept. of Mechanical Engineering include: Health Usage Monitoring Systems [HUMS], Conditioned Based Maintenance [CBM]; Usage and Fatigue Damage Survey; Risk Analysis; and Finite Element Method [FEM].

Speech Title: A new model for spall-rolling-element interaction

Abstract: Evaluation of the spall size of a radially loaded rolling-element bearing is required for the assessment of the bearing damage severity and estimation of its remaining useful life. A new multi- body, nonlinear dynamic model of the interaction between the rolling-element and a spalled outer race is presented. The study focuses on the physics of rolling-element contact in a broader range of spall sizes than has been investigated to date, with intermittent contact between rolling- element and the outer race, which is a relevant defect size for diagnostics and prognostics query. The analysis is performed in several time intervals according to periods of rolling-element/race contact and periods when the rolling-element is not connected with the outer race. An explicit expression of the spall size as function of the time-to-impact has been developed by considering radial load, shaft speed, and gravity. The expression of the spall size was used in a sensitivity study of the effect of parameters such as geometry and radial load. The results obtained from the new model are in good agreement with a well-established general bearing model. The acceleration of the outer ring during the rolling-element/spall interaction with intermittent rolling-element race connection is a novel contribution, which allows verification of the model from direct observations using vibration sensors mounted on the structure.