Supporting Design

Supporting Design

Forces and stresses are key to design evaluation and optimization. What loads will be exerted on the bearings? Will the material be damaged by plastic deformation? How much wear will occur? Can this be avoided by changes to the geometry or material selection? 

Key aspects in rolling contacts are (mis-)alignment and tolerances. Misalignment leads to creepage, creepage leads to creep forces, these forces affect to the motion of the construction, which ultimately feeds back to misalignment. This leads to a catch-22 situation. A good design therefore needs good understanding of creepage and creep forces.

An example project concerns a design review of the rotation mechanism of the Extremely Large Telescope (ELT) that’s developed in Chili. This will be the world’s biggest “eye on the sky”. It needs to move slowly and precisely to track the stars in a desired portion of the nightly sky. Therefore, the telescope consists of a platform that’s supported on rollers. The question is, how should these rollers be designed, for a target lifetime of 50 years?

In this project, we considered the bending of the trolley structure, under the influence of wind loads for instance, and assessed the consequences for the contacts between the rail and the rollers. Estimating creepages and creep forces and the interaction of these with the ensuing motion. Next, we considered contact pressures and subsurface stresses, assessing the risk of waltzing and wear during the lifetime, guiding material selection. Further, we provided initial calculations for the optimization of gaps between rail segments, to avoid peak pressures and achieve a more gradual transition of the load.

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