Journal Published Online: 25 May 2018
Volume 7, Issue 4

Effects of Laser Shock Peening over Minimally Detectable Partial Through-Thickness Surface Cracks



Laser shock peening (LSP) has evolved as a viable alternative to other surface treatments (shot peening, burnishing, etc.) that induce beneficial residual stress in structural components. While fatigue life improvements have been recognized by the aerospace industry, in-service components may have surface flaws with sizes below current inspection limits. A concern is that the application of LSP over an existing crack may cause unintended detrimental consequences. To address this concern, two different LSP processes were applied over a 0.25 in. (6.35 mm) partial through-thickness surface fatigue crack in 7075-T651 aluminum. The resulting residual stresses were measured using combinations of included X-ray diffraction with layer removal, incremental center-hole drilling, and neutron diffraction. Both LSP processes resulted in a through-thickness residual stress profile in which compressive stresses at either surface were balanced by tensile stresses in a band centered in the mid-thickness of the specimen. Peened and unpeened (baseline) specimens were then tested under constant-amplitude cyclic loading to assess the fatigue response. The average fatigue life of the baseline specimens was about 49,000 cycles. The peened specimens (both treatments) survived to runout, exhibiting no crack growth when examined with an optical microscope even when the crack tip was either very close to or inside the region of tensile residual stress.

Author Information

Eisensmith, David L. A.
Structures Validation Branch, Air Force Research Laboratory, Wright-Patterson AFB, OH, USA
Palazotto, Anthony N.
Department of Aeronautical Engineering, Air Force Institute of Technology, Wright-Patterson AFB, OH, USA
Langer, Kristina
Structures Technology Branch, Air Force Research Laboratory, Wright-Patterson AFB, OH, USA
Gharghouri, Michael A.
Neutron Scattering Section, Material Sciences Branch, Canadian Nuclear Laboratories, Chalk River, ON, Canada
Coratella, Stefano
Aerospace Mechanics Division, University of Dayton Research Institute, Dayton, OH, USA
Pages: 20
Price: $25.00
Reprints and Permissions
Reprints and copyright permissions can be requested through the
Copyright Clearance Center
Stock #: MPC20170134
ISSN: 2379-1365
DOI: 10.1520/MPC20170134