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University of Nevada, Las Vegas

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Las Vegas (Nev.)

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The purpose of this collaborative research project involving the University of Nevada Las Vegas (UNLV) and Idaho State University (ISU) is to evaluate the feasibility of determining residual stresses of welded, bent (three-point-bend), and cold-worked engineering materials using a new nondestructive technique based on positron annihilation spectroscopy (PAS). The proposed technique is to use γ-rays from a small MeV electron linear accelerator (Linac) to generate positrons inside the test sample via 2 pair production. This method can be used for materials characterization and investigation of defects in thick samples that usually cannot be accomplished by conventional positron technique or other nondestructive methods. The data generated will be compared to those obtained by other nondestructive methods such as neutron diffraction (ND) and X-ray diffraction (XRD), and a destructive method known as ring-core technique. Materials tested so far include unirradiated austenitic (Type 304L) and martensitic (EP-823) stainless steels that were cold-reduced, bent (three point-bending) and welded prior to the evaluation of the resultant residual stresses.

While substantial progress has been made to evaluate residual stresses in all three specimen configurations of Alloy EP-823 and Type 304L stainless steel by the PAS and XRD methods, a large number of testing still needs to be performed by all four measurement techniques. Although, the Linac at ISU has been performing satisfactorily, some unforeseen problems related to the signal resolution are currently being experienced, which has delayed the desired measurements. Further, substantial measurements by ND and ring-core methods are yet to be performed. Collaboration has recently been established with the Atomic Energy of Canada Limited (AECL) to conduct residual stress measurements by the ND technique. Preliminary results obtained at AECL indicate a significant potential for the ND method to analyze residual stresses in thick specimens of different configurations. Microstructural evaluations by optical microscopy have just been initiated. However, a lot more metallographic studies will be performed involving cold-worked and welded specimens following future residual stress measurements. In addition, deformation characteristics in terms of dislocations and their movements resulting from welding and plastic deformation will be analyzed by transmission electron microscope (TEM), once this equipment is available at UNLV. Further, Alloys EP-823, HT-9, and austenitic materials (Type 316L stainless steel and Alloy 718) irradiated by low energy photon beam at ISU will be included in this program during the third year.


Austenitic stainless steel; Deformations (Mechanics); Martensitic stainless steel; Nuclear reactors — Materials — Testing; Plasticity; Strains and stresses; Welded joints — Fatigue

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Austenitic stainless steel; Martensitic stainless steel; Nuclear reactors--Materials--Testing


Materials Science and Engineering | Mechanical Engineering | Metallurgy | Nuclear Engineering | Oil, Gas, and Energy

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343 KB




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