Forensic determination of residual stresses
from fracture surface mismatch

After a part has fractured and the stresses have relaxed, can you still "measure" the residual stresses that were originally there? Yes!

Prime, M. B., DeWald, A. T., Hill, M. R., Clausen, B., and Tran, M., 2014, "Forensic Determination of Residual Stresses and K_I 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:

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

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!

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

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 K_I from the residual stresses during the EDM cut:

If crack closure effects are included, the K_I is consistent with typical K_Ic from values from the literature for 7050 Al of about 30 MPa m^0.5!

Managed by Triad National Security, LLC Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA
contact: Mike Prime at prime@lanl.gov | Copyright & Disclaimer
U.S. patent 6,470,756 | Last Modified:{date}