RESIDUAL STRESS IN ADDITIVE MANUFACTURED TITANIUM COMPONENTS
The major challenges in additive manufacturing are managing microstuctural and geometrical defects and also controlling distortion. Quantifying residual stresses in 3-D printed structures enables you to control distortion and demonstrate structural integrity.
StressMap has been working with Cranfield University to investigate residual stresses associated with Wire Arc Additive Manufacturing (WAAM) to control distortion and avoid cracking during the additive manufacturing process.
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) and because it can measure bulk stresses in relatively large parts.
Read the full article.
RESIDUAL STRESS IN TURBINE DISC
Traditionally, residual stresses in aero-engine parts have been measured using mature techniques such as Incremental Central Hole Drilling (ICHD) and X-ray Diffraction (XRD). But these techniques are limited to measuring the residual stresses at discrete locations at or near the surface of the component.
The use of process modelling for prediction of residual stress an input to life assessment of safety critical rotating parts requires a level of validation and experimental verification 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.
RESIDUAL STRESS MAPPING IN COBALT-CHROME ALLOYS
Distortion of bio-medical components due to residual stresses is an important concern. Dimensions are considered critical in order to ensure optimum fit to the patient’s body and therefore prostheses that fall out of specification are rejected resulting in significant environmental and business costs.
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.
SScanSS: Strain Scanning Simulation Software
Measuring residual stresses in complex geometries using neutron diffraction has historically been difficult. SScanSS is a powerful software that has been developed to enable residual strain or residual stress measurements by neutron diffraction in such challenging applications.
The SScanSS method was specifically designed to improve the quality of neutron diffraction measurements by maximising accuracy in strain measurements and providing a high level of traceability and QA.
Read the full article.
Reheat cracking in 316H stainless steel
Creep cavitation is an important failure mechanism in components operating at high temperature. Reheat cracking is associated with creep cavitation in weldments, which occurs either during high temperature service or during post-weld-heat-treatment.
StressMap and PhD candidate Rahul Unnikrishnan have been working with EDF Energy UK to investigate plastic deformation and creep cavitation around reheat cracking in order to provide a better understanding of reheat cracking and creep damage development mechanisms. This enables the improvement of models for predicting the life and structural integrity of susceptible welded components operating at high temperatures.