Community Research and Development Information Service - CORDIS

Residual stresses and hardening depth measurements: on line production testing

Mechanical components' performances are often improved by means of heat treatments and cold working processes, both preferred because of their good ratio cost/benefit. Industrial benefits involve improved fatigue resistance conferred to components by these processes. Equipment was developed which was able to measure: the in depth profile of residual stresses obtained via deep rolling on stub axles; the hardness profile on carbonitred gears (on the teeth's flank). The project resulted in two techniques the first (electromagnetic permeability based) able to supply consistent information on the residual stress state beneath the surface; the second (eddy current based) able to predict at which depth a given hardness value is positioned. An important application of artificial intelligence was pursued in the field of non destructive testing: a prototype of neural network for non destructive evaluation was also implemented.

Two pieces of equipment, implementing the addressed techniques, were prototyped and successfully tested. Demonstrator A was able to assess/measure the conventional hardness depth (the depth at which the hardness takes a given value). This task was reached also in presence of some micromorphological disturbances occurring near the surface due to trostite presence. The neural network based data treatment constituted an important by product of the project. Due to the circumstances it is not confined to the particular non destructive technique used, being suitable for application to the general problematics of measures where the final reject/accept rules cannot be simply established because many parameters have to be taken in account. Demonstrator B was able to assess/measure non destructively the in depth stress profile on stub axles to 0.5 mm. The measurements were taken on stub axles, some millimetres wide and double curvature shaped, and the probe was adapted to these specifications. Probably the technique could be better used on simpler geometry and/or larger objects.

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