PSI - Issue 7

Marton Groza et al. / Procedia Structural Integrity 7 (2017) 438–445 M. Groza et al. / Structural Integrity Procedia 00 (2017) 000–000

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7. Conclusions

• The following method is proposed for size and shape measurement of surface defects in an industrial environment via optical methods (calliper gauges, optical 3D scanning): 1) measuring the max. dimension on the surface (major axis – A), 2) measuring the max. dimension perpendicular to A (minor axis -B), 3) measuring or estimating depth of the defect (depth – C). The bounding ellipsoid with these dimensions is suitable for a reasonably simplified fatigue assessment of the given defect. • The application of the defect size parameter max area is advised instead of area , because the latter one depends on the first principal direction at the defect location, which is generally unknown at quality inspections. Since the fatigue assessment of defective material is closely linked with the quality assurance process, unified and clearly defined parameters should be used. The application of max area leads to conservative results both in terms of fracture mechanical methods and in the DSG approach. • Linear-elastic local FE stress results near the defect lead to slightly conservative results in the context of the DSG approach, and therefore well-suited for design purposes and quality assessment. The elastic plastic modelling of the local plasticity with the Chaboche nonlinear kinematic hardening material model at the defect offers a precise way to consider the effects of the cyclic loading on defective material. • EIM is a powerful tool for local stress computation near defects, which opens the way for an automatized surface defect assessment on an industrial level. • With the analysis of the stress distribution in surface normal direction from the hot-spot (point with the highest Crossland equivalent stress value) on the defect surface the DSG criterion can be evaluated for components with complex geometry under multiaxial loading conditions. • Comparing the stress fields with- and without defect directly in the FE calculation the stress gradient can be estimated in effective and automatized manner leading to visualizable results of the DSG approach. • The proposed DSG utilization factor helps in the interpretation of the calculated results, as a scalar predicting crack initiation at the value of 1, and also as result filed in the FEA post-processing environment.

Acknowledgements

The present paper has been realized within the Knorr-Bremse Scholarship Program supported by the Knorr-Bremse Railway Systems Budapest. We thank Dr. David Felhos and Szabolcs Jonas the active participation in the discussions related to this research.

References

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