Projects

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StressMap has been working with Cranfield University to investigate residual stresses associated with Wire Arc Additive Manufacturing (WAAM).

The grain size in these materials is particularly large due to the nature of the process which present challenges for non-destructive techniques such as X-Ray and neutron diffraction. The contour method is ideal for measuring these components as it is insensitive to microstructural variations (grain size, texture, anisotropy).

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The use of process modelling residual stress predictions as an input to lifing assessment of safety critical rotating parts requires a level of validation not just at the surface but also in the bulk of the material. In this context, the 2D contour method maps are particularly useful for validating finite element predictions.

StressMap have successfully measured the residual stresses in Nickel superalloy turbine discs using the contour method. Using our results, organisations have been able to optimise the processing route (forging, machining and heat treatment cycles) to control remaining internal residual stresses and thereby improve damage tolerance.

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Together with the University of Limerick, residual stresses at different manufacturing stages of a femoral knee implant made from Cobalt-Chrome-Molybdenum (Co-Cr-Mo) was investigated.

As part of this study, a number of residual stress determination methods, such as centre-hole drilling, ring coring, neutron diffraction, X-ray diffraction and the contour method were assessed. Many of the techniques used require flat surfaces and were therefore not suitable for application to the articulating surface of the femoral (the area of interest). The application of neutron diffraction to coarse-grained, complex-shaped, cobalt alloys is challenging. The contour method proved to be the most suitable residual stress determination technique for this application.

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