The effect of 'running-in' on the tribology and surface morphology of metal-on-metal Birmingham hip resurfacing device in simulator studies

It is well documented that hard bearing combinations show a running-in phenomenon in vitro and there is also some evidence of this from retrieval studies. In order to investigate this phenomenon, five Birmingham hip resurfacing devices were tested in a hip wear simulator. One of these (joint 1) was also tested in a friction simulator before, during, and after the wear test and surface analysis was conducted throughout portions of the testing. The wear showed the classical running in with the wear rate falling from 1.84 mm 3 per 10 6 cycles for the first 10 6 cycles of testing to 0.24 mm 3 per 10 6 cycles over the final 2 x 10 6 cycles of testing. The friction tests suggested boundary lubrication initially, but at 1 x 10 6 cycles a mixed lubrication regime was evident. By 2 x 10 6 cycles the classical Stribeck curve had formed, indicating a considerable contribution from the fluid film at higher viscosities. This continued to be evident at both 3 x 10 6 and 5 x 10 6 cycles. The surface study complements these findings

Chapter 4: Mobility Support

Wireless access allows independency between the user’s position and the physical bearer used to access services from the network. However, this independency does not imply that wireless networks show a full ability to cope with any degree of mobility. This is because other constraints can limit the mobility when accessing the network. The main constraints are registration and addressing (e.g., of user, terminal, application) and handover. In general, procedures needed to cope with those issues have a cost in terms of quality degradation, need for more resources, or both; this is known as mobility cost. Performance evaluation of mobility related issues in wireless networks requires a precise knowledge and understanding of the way in which terminals move, the impact of the movement on performance and quality, and the procedures and resources allocated in the network to minimize the impact of the mobility.Postprint (published version

Chapter 4: Mobility Support

Wireless access allows independency between the user’s position and the physical bearer used to access services from the network. However, this independency does not imply that wireless networks show a full ability to cope with any degree of mobility. This is because other constraints can limit the mobility when accessing the network. The main constraints are registration and addressing (e.g., of user, terminal, application) and handover. In general, procedures needed to cope with those issues have a cost in terms of quality degradation, need for more resources, or both; this is known as mobility cost. Performance evaluation of mobility related issues in wireless networks requires a precise knowledge and understanding of the way in which terminals move, the impact of the movement on performance and quality, and the procedures and resources allocated in the network to minimize the impact of the mobility