Role of friction on the thermal development in ultrasonically consolidated aluminum foils and composites

Ultrasonic consolidation is a solid-state bonding process capable of producing metal and metal matrix composite parts. In this work a friction-based heat generation model is proposed to characterize the thermal development of ultrasonically consolidated aluminum foils and continuous fiber alumina reinforced aluminum metal matrix composite tape as a function of process control parameters. The friction coefficient between mating surfaces is determined experimentally, and the credibility of using both a constant friction coefficient and a process dependent friction coefficient is assessed. In most cases a constant friction coefficient is capable of producing results that are within 15% error; while a process dependent friction coefficient achieves an average error of 7%.     

The Pebble Bed Modular Reactor: An obituary

The High Temperature Gas-cooled Reactor (HTGR) has exerted a peculiar attraction over nuclear engineers. Despite many unsuccessful attempts over half a century to develop it as a commercial power reactor, there is still a strong belief amongst many nuclear advocates that a highly successful HTGR technology will emerge. The most recent attempt to commercialize an HTGR design, the Pebble Bed Modular Reactor (PBMR), was abandoned in 2010 after 12 years of effort and the expenditure of a large amount of South African public money. This article reviews this latest attempt to commercialize an HTGR design and attempts to identify which issues have led to its failure and what lessons can be learnt from this experience. It concludes that any further attempts to develop HTGRs using Pebble Bed technology should only be undertaken if there is a clear understanding of why earlier attempts have failed and a high level of confidence that earlier problems have been overcome. It argues that the PBMR project has exposed serious weaknesses in accountability mechanisms for the expenditure of South African public money.