Unloading of an elastic-plastic loaded spherical contact

ABSTRACT The process of unloading an elastic-plastic loaded sphere in contact with a rigid flat is studied by the Finite Element Method. The sphere material is assumed isotropic with elasticlinear hardening. The numerical simulations cover a wide range of loading interference deformations for various values of Young's modulus and Poisson ratios of the sphere material. The contact loads, stresses, and deformations in the sphere during both loading and unloading, are calculated for the range of interferences. Empirical dimensionless expressions are presented for the unloading load-deformation relation, the residual axial displacement and the residual curvature of the sphere after complete unloading

Design methodology for an air-lubricated seal

A methodology to design an air-lubricated piston seal for pneumatic actuators is described. Such a seal permits a small air leakage through a very narrow gap between the seal lip and the counterpart; this air film both avoids contact and ensures lubrication at the seal-counterpart interface thus permitting reduced friction and wear. Subsequently the use of grease could be limited or avoided. A seal geometry equipped with a self-pressurized balancing chamber was designed to make leakage as insensitive as possible to the supply pressure and to the barrel machining tolerances. A prototype was manufactured and tests were carried ou

Attachment ability of combined biomimetic adhesive micro-textures of different shapes

Abstract There are various potential applications of biomimetic adhesive solutions including climbing robotic systems, mobile sensor platforms, and biomedical applications such as patches for external use. Achieving resistance to both normal and tangential loads, however, is a critical issue that still needs to be addressed. Some animals have developed exceptional attachment mechanisms based on combined fibrillar elements of different shapes and functions. Experimental investigation of combined biomimetic adhesive micro-textures on tribological performances such as adhesion, friction, and peeling resistance is needed to apply this idea to the design of an artificial texture having similar “biomimetic” properties. In the present study, we demonstrate that combinations of different shapes of biomimetic adhesive micro-textures show increased efficiency under different contact environments and enable long-term adhesive solutions. Our work sheds light on combinations of different element shapes inspired by nature and their adhesive efficiency as a function of the ratio of each biomimetic element, as well as their spatial repartition

Flying Couplers Above Spinning Resonators Generate Irreversible Refraction

Creating optical components that allow light to propagate in only one direction - that is, that allow non-reciprocal propagation or \u27isolation\u27 of light - is important for a range of applications. Non-reciprocal propagation of sound can be achieved simply by using mechanical components that spin 1,2 . Spinning also affects de Broglie waves 3, so a similar idea could be applied in optics. However, the extreme rotation rates that would be required, owing to light travelling much faster than sound, lead to unwanted wobbling. This wobbling makes it difficult to maintain the separation between the spinning devices and the couplers to within tolerance ranges of several nanometres, which is essential for critical coupling 4,5 . Consequently, previous applications of optical 6-17 and optomechanical 10,17-20 isolation have used alternative methods. In hard-drive technology, the magnetic read heads of a hard-disk drive fly aerodynamically above the rapidly rotating disk with nanometre precision, separated by a thin film of air with near-zero drag that acts as a lubrication layer 21 . Inspired by this, here we report the fabrication of photonic couplers (tapered fibres that couple light into the resonators) that similarly fly above spherical resonators with a separation of only a few nanometres. The resonators spin fast enough to split their counter-circulating optical modes, making the fibre coupler transparent from one side while simultaneously opaque from the other - that is, generating irreversible transmission. Our setup provides 99.6 per cent isolation of light in standard telecommunication fibres, of the type used for fibre-based quantum interconnects 22 . Unlike flat geometries, such as between a magnetic head and spinning disk, the saddle-like, convex geometry of the fibre and sphere in our setup makes it relatively easy to bring the two closer together, which could enable surface-science studies at nanometre-scale separations