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DC motors for Linearly Increasing Stress Test machine

Supplier: maxon motor australia By: Erin
23 July, 2010

A selection of brushless servo gear motors has been used for a University of Adelaide project.

Stress Corrosion Cracking (SCC) is a phenomenon that has caused gas pipelines to rupture catastrophically around the globe since the late 1960's.

SCC usually takes years to develop in the field, so accelerated testing needs to be carried out in order to study and understand the factors that affect SCC crack initiation and growth.

Soil environment, electrochemical fields, temperature, pipe metallurgy and applied stresses (static and fluctuating) have been found to affect SCC.

Project
In order to study these factors in the laboratory, a popular apparatus used is standard tensile testers, but they are usually bulky, expensive and slow. A new type of apparatus was developed to produce and study SCC in the laboratory, where the test is load controlled rather than displacement controlled.

This new apparatus is called the Linearly Increasing Stress Test (LIST), where a weight is moved along a beam, applying a load onto the sample to be studied by a lever principle. The position of the load needs to be carefully controlled in complex patterns so that it can represent real life pressure loading of the gas pipeline.

As the travelling load position is controlled, the beam that the load travels on needs to be kept horizontal at all times so as to not introduce undesirable stresses on the sample to be studied, requiring a complex dc motor control system to be in place that can simultaneously control the travelling weight in an active manner, whilst controlling the beam angle in a passive manner.

The selection of maxon brushless servo motors has been made because of their torque characteristics, high power and broad speed range.