Peculiarities associated with testing polyetheretherketone (PEEK) in a model rolling contact

Commonly used four-ball testing configuration when used to investigate rolling contact behavior of polyetheretherketone (PEEK) produced some unexpected peculiarities, namely direct contact between ceramic balls. Direct contact between lower three balls is normally not expected to take place when elastic materials (ferrous or ceramics) are tested. However, due to the viscoelastic nature of PEEK surface damage of the ceramic balls were observed leading to the production of wear debris which in turn facilitated premature failure of PEEK components of the assembly. It is postulated that caution is required when using the four-ball testing configuration to assess rolling contact performance of viscoelastic materials, such as engineering polymers.Gdansk University of Technology, Gdansk, Poland(Grant DS-2012)

The Reach-Avoid Problem for Constant-Rate Multi-Mode Systems

A constant-rate multi-mode system is a hybrid system that can switch freely among a finite set of modes, and whose dynamics is specified by a finite number of real-valued variables with mode-dependent constant rates. Alur, Wojtczak, and Trivedi have shown that reachability problems for constant-rate multi-mode systems for open and convex safety sets can be solved in polynomial time. In this paper, we study the reachability problem for non-convex state spaces and show that this problem is in general undecidable. We recover decidability by making certain assumptions about the safety set. We present a new algorithm to solve this problem and compare its performance with the popular sampling based algorithm rapidly-exploring random tree (RRT) as implemented in the Open Motion Planning Library (OMPL).Comment: 26 page