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Forensic determination of residual stresses
from fracture surface mismatch

 
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Principle
   - make cut
   - measure surface
   - calculate stress
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   - bent beam
   - weld plate
   - quenched steel
   - impacted plate
   - alum. forging
   - friction stir weld
   - Ti FSW
   - Railroad rails
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Residual Stress
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After a part has fractured and the stresses have relaxed, can you still "measure" the residual stresses that were originally there? Yes!

download preprint Prime, M. B., DeWald, A. T., Hill, M. R., Clausen, B., and Tran, M., 2014, "Forensic Determination of Residual Stresses and KI from Fracture Surface Mismatch," Engineering Fracture Mechanics., Vol 116, pp. 158-171. DOI: 10.1016/j.engfracmech.2013.12.008. preprint (pdf).

An extension of this method to include shear stresses: Araujo de Oliveira, J., Kowal, J., Gungor, S., and Fitzpatrick, M. E., 2015, "Determination of normal and shear residual stresses from fracture surface mismatch," Materials & Design, 83, pp. 176-184.

A forging of 7050-T74 Aluminum alloy fractured in half during an EDM cut:

Sketch Photo of fracture surface

A laser scanner was used to map surface height on the two opposing fracture surfaces:

surface height map surf height map

The two surfaces looks like mirror images of each other (at least in the fracture region). Where one is low, the other is high.

When you average the two surface height maps the misfit is revealed!

misfit

From which you can calculate the residual stresses that were there prior to fracture:

stress map compare with neutron

Typical quenching stresses: compressive near the surface surrounded by a tensile core. The results were validated by neutron diffraction scans on another section of the same forging.

An FEM analysis can be used to calculate KI from the residual stresses during the EDM cut:

FEM

If crack closure effects are included, the KI is consistent with typical KIc from values from the literature for 7050 Al of about 30 MPa m0.5!

 

 

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contact: Mike Prime at prime@lanl.gov | Copyright & Disclaimer
U.S. patent 6,470,756 | Last Modified:{date}

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