Study On Real-Time Observation Of Torsional Fretting Wear For Transparent Materials

Torsional fretting, the one that widely exists in industrial fields, is the relative motion, which happens between surfaces in contact, induced by reciprocating torsion movement under oscillatory and vibratory amplitudes. There is seldom research dedicated to torsional fretting that defined as one of four basic fretting modes. Some investigations have revealed the damage mechanism of torsional fretting, however, they are still incomplete. Up to now, the understanding of damage process of fretting wear is based on method of black-box. Therefore, dynamic real-time observation of different transparent materials is useful for revealing the occurrence and development of the microscopic phenomena occurred in the proceeding of damage, which has a significant effect to understand fretting wear mechanism deeply. At the same time, the real-time observation and friction vibration signal detecting can be treated as a new method to study the torsional fretting wear.In this paper, on a torsional fretting test rig with real time observation and fretting vibration recording systems, the experimental research of four wear contact paris (PMMA/GCr15, PMMA/PMMA, Glass/GCr15, Quartz/GCr15) were carried out. Based on the analysis of the frictional kinetics of torsional fretting and observational video in situ, combining with the analysis of friction vibration, the relation between the torsional fretting wear mechanisms, surface morpholohies and friction vibration has been revealed. The main conclusions obtained in this study are as follows:1. The friction torque vs. angular displacement amplitude curves (T-θ curves) of four contact pairs could be used to characterize the kinetic characteristics of rotational fretting wear. Under the test parameters in this study, for the material of PMMA, three types of T-θ curves curves could be obtained, i.e. linear, elliptic and parallelogram. Simultaneously, for the regular glass and quartz glass, it can be obtained two types of T-θ curves (i.e. elliptic and parallelogram).2. For the four contact pairs, the friction torque values climbed slowly in the partial slip regime. In the mixed and gross slip regimes, the friction torque curves can be divided into three stages:i.e. running-in, ascent and stable stages. The friction torque values in the gross slip regime were higher than that of in the partial slip and mixed regimes.3. Real time observation and wear mechanisms:a) Partial slip regime:the damage of the four contact pairs was slighter and the relative motion was accommodated by elastic deformation.b) Mixed slip regime:For the PMMA/GCr15contact, some fine crazes firstly emerged at the edge of contact zone. With the increase of the craze, the damage became more serious companied with the wear debris removing, and then the damage area displayed as annularity shape. The wear mechanism main was fatigue wear. For the PMMA/PMMA contact, the annular damage initially emerged at the edge of contact, which became severer and the contact center was still sticking, and the wear mechanism main was abrasive wear. c) Gross slip regime: For the PMMA/GCr15contact, some plastic flow traces were initially observed at the center of contact zone, and then a little of crazes appeared at the edge of the contact. And then, with the increase of the crazing and detaching of the material, some fusiform detached pits generated at the contact edge accompanied with a great deal debris removed.. The relative slip occurred at the whole contact zone, and the wear mechanism main was fatigue wear. For the PMMA/PMMA contact, the damage was firstly generated at the edge of contact zone, and with the increase of number of cycles the damage happened at whole contact zone, the wear mechanism main was abrasive wear. For the Glass/GCrl5contact, the damage firstly appeared at the inner side of the contact edge, then micro-crackle emerged and increased to form annular morphology. With the increment of damage area, the severer damage occurred gradually accompanied with removing of a great deal of debris the wear mechanisms main were abrasive and fatigue wear. For the Quartz/GCr15contact, the fretting damage processes and wear mechanisms were similarly to the former one, while micro-crackles could propagate circumferential and radial directions.4. Friction vibration signals:In the partial slip regime, both for the PMMA/GCr15and PMMA/PMMA contacts, the friction vibration signals were undetected. In the gross slip regime, for the PMMA/GCr15contact, the number of accumulated events in each cycle firstly increased and then decreased. In the different stages of the damage, the vibration apperared different characteristics. While for the PMMA/PMMA contact, the number of accumulated events in each cycle was just increased during the proceeding of the fretting. However, under the varied damage stages, the characteristics of vibration presented same feature. Both the lateral vibration and vertical friction of the two contacts in same cycle presented identical characteristics.