This research aims to design and control a full scale gun recoil buffering system which works under real firing impact loading conditions. A conventional gun recoil absorber is replaced with a controllable magnetorheological (MR) fluid damper. Through dynamic analysis of the gun recoil system, a theoretical model for optimal design and control of the MR fluid damper for impact loadings is derived. The optimal displacement, velocity and optimal design rules are obtained. By applying the optimal design theory to protect against impact loadings, an MR fluid damper for a full scale gun recoil system is designed and manufactured. An experimental study is carried out on a firing test rig which consists of a 30 mm caliber, multi-action automatic gun with an MR damper mounted to the fixed base through a sliding guide. Experimental buffering results under passive control and optimal control are obtained. By comparison, optimal control is better than passive control, because it produces smaller variation in the recoil force while achieving less displacement of the recoil body. The optimal control strategy presented in this paper is open-loop with no feedback system needed. This means that the control process is sensor-free. This is a great benefit for a buffering system under impact loading, especially for a gun recoil system which usually works in a harsh environment.

Sapphire wafers are widely used as the substrates for fabricating GaN light-emitting diodes (LEDs). The quality of LEDs depends directly on the quality of the sapphire wafers. A series of machining processes is required to turn sapphire barstock into wafers with the desired geometry and surface quality. This paper reviews the literature on various machining processes for sapphire wafers: slicing (including outer diameter cut-off grinding, inner diameter cut-off grinding, loose abrasive multi-wire sawing, fixed abrasive slicing, and fixed abrasive multi-wire sawing), flattening (including lapping and grinding), and surface finishing (including mechanical polishing and chemical mechanical polishing). New machining technologies are also introduced.