The role of frictional power dissipation (as a function of frequency) and test temperature on contact temperature and the subsequent wear behaviour in a stainless steel contact in fretting

Temperature is known to affect the fretting wear behaviour of metals; generally, a critical temperature is observed, above which there are substantial reductions in wear rate, with these being associated with the development of protective oxide beds in the fretting contact. This work has examined the gross sliding fretting behaviour of a stainless steel as a function of bulk temperature and fretting frequency(with changes in the fretting frequency altering the frictional power dissipated in the contact amongst other things). An analytical model has been developed which has suggested that at 200 Hz, an increase in the contact temperature of more than 70°C can be expected, associated with the high frictional power dissipation at this frequency (compared to that dissipated at a fretting frequency of 20 Hz). With the bulk temperature at either room temperature or 275°C, the increase in contact temperature does not result in a transition across the critical temperature (and thus fretting behaviour at these temperatures is relatively insensitive to fretting frequency). However, with a bulk temperature of 150°C, the increase in temperature associated with the increased frictional power dissipation at the higher frequency results in the critical temperature being exceeded, and in significant differences in fretting behaviour

The role of geometry changes and debris formation associated with wear on the temperature field in fretting contacts

The temperature of a fretting contact is known to be a key factor in its development. However, as a test proceeds, the wear scar changes, both geometrically and through the formation of oxide-based debris-beds. Accordingly, the effects of these on the near-surface temperature field resulting from frictional heating in fretting has been analysed via numerical modelling. Under the test conditions examined, it was predicted that (i) the development of the wear scar geometry would result in a significant (up to ~ 25%) reduction in the mean-surface temperature rise, and (ii) the formation of a typical oxide debris bed would result in a significant (up to ~ 80%) increase in the mean-surface temperature rise

The role of temperature and frequency on fretting wear of a like-on-like stainless steel contact

The influences of environmental temperature and fretting frequency on the mechanisms and rates of wear in a like-on-like 304 stainless steel contact were examined, and mainly attributed to changes in the mechanical response of the bulk material and to changes in the behaviour of the oxide debris formed in the fretting process. At low temperatures, wear proceeds by continual oxide formation and egress from the contact, whilst at high temperatures, the rate of wear is much reduced, associated with the development of oxide formed into a protective bed within the contact. The temperature at which the change between these two behaviours took place was dependent upon the fretting frequency, with evidence that, at this transition temperature, changes in behaviour can occur as the fretting test proceeds under a fixed set of conditions. An interaction diagram has been developed which provides a coherent framework by which the complex effects of these two parameters can be rationalised in terms of widely accepted physical principles

Reactions to urbanisation in New Zealand during the nineteen twenties.

The nineteen twenties were years of rapid urban growth in New Zealand. City populations increased, urban areas expanded, and an even greater proportion of the country's people were officially designated "urbanites". 1918 - 1930 was the key period in the social transformation. The perceived implications of this change became matters of intense social and political debate. This thesis examines the debate as found in contemporary publications to determine how New Zealanders reacted to urbanization. In New Zealand urbanization was perceived as a threat to the economy, by upsetting the balance between urban "non-producers" and the rural "producer", population, and as a threat to the national identity of being the outlying farm of the Empire. Although reactions to urbanization in the twenties were coloured by romantic ideas introduced from Britain, the main thrust of reaction in times of recession and doubt was against the economic effects of urbanization, coupled with an outburst of nostalgia for the "true" New Zealand of the pioneering period. Land settlement was widely advocated as a solution to the problems of recession and unemployment believed to be caused by urbanization. In times of prosperity attempts were made to improve the urban environment by combining the "virtues" of the country to the "convenience" of the city. The garden suburb was one outcome of these attempts

The effect of temperature on wear and friction of a high strength steel in fretting

This paper investigates the effect of temperature (between 24 °C and 450 °C) on the wear rate and friction coefficient of a high strength alloy steel (Super-CMV) in gross sliding fretting in air. It was found that whilst there was significant loss of material from the contact during fretting at room temperature, the overall loss of material from the contact had become negative even with a modest increase in temperature to 85 °C. At temperatures greater than 85 °C, negative wear was maintained, with the coefficient of friction dropping monotonically with increasing temperature up to 450 °C. It is proposed that the changes in wear rate and friction coefficient were due to changes in the way that the oxide particles sintered to form a protective debris bed, with sintering of the oxide debris particles at these low temperatures being promoted by the nano-scale at which the oxide debris is formed