Rapid cooling during the solidification process could trigger defects such as porosity formation inside and on the surface of manufactured components, which in turn means local variations of material properties. These variations can become the cause for unpredictable component behavior under load. Theoretical models such as the Niyama criterion have been widely adopted for the prediction of solidification defects and employed for decades. Today, the majority of simulation packages for casting process include such criteria.

The Niyama criterion is a local thermal parameter derived from the local thermal gradient and cooling rate. The Niyama value indicates the probability of local porosity defects after solidification. A plug-in has been developed in Abaqus to assess the Niyama criterion, in the form of post-processing of existing solidification simulation results. Visualizing the Niyama value as a field output provides great convenience for manufacturing engineers to better understand the potential casting outcome, and to pinpoint locations that need improvement of some form. The criterion has also been found to correlate with mechanical properties, such as yield strength, ultimate strength and rupture strain.  The implementation was tested on a qualification benchmark from the Steel Founder’s Society of America, with satisfactory results.

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RUM2022 ​​​​​​​R&D ​​​​​​​Abaqus ​​​​​​​