Fatigue Life Enhancement of Welded Structures using Ultrasonic Needle Peening

Author:  Desfontaine, Montherat, Chateau, Briere
Source:  Conf Proc 2011: ICSP-11 South Bend, IN USA (pgs. 13-18)
Doc ID:  2011002
Year of Publication:  2011
ABSTRACT Ultrasonic Shot Peening technique is nowadays recognized as a mature process currently covered by 2 aerospace industries specifications (BNAE and SAE/AMS), and used worldwide for improving the resistance of high-value components. Ultrasonic Activation of media principle is also used for Needle Straightening and Forming of Metal sheet components. A recent development is the Needle peening of Welds (also called Ultrasonic Impact Treatment), a reliable, well-controlled and efficient technique for strengthening welded assemblies, especially as regards to fatigue damage due to cyclic loads encountered during service. Ultrasonic Needle Peening (Ultrasonic Impact Treatment) has been shown to bring significant life enhancement thanks to the introduction of beneficial Compressive Stresses combined with weld toe geometry reshape [2, 3, 4]. The process is able to increase the number of fatigue cycles before crack initiation by factors of ten. This process is also an alternative of toe grinding or TIG dressing. Target end-user applications are found or expected in a large range of industries, such as Transportation, Energy, Mining Exploitation, Oil & Gas, Heavy Industries and Infrastructures. In this article, we will describe experimental fatigue tests and characterization results [1] obtained on S355 steel welded specimens, that demonstrate and confirm life time enhancement. The ultimate goal of this program is to establish best practices to guarantee process repeatability and reliability whatever manual and automatic operations. KEYWORDS Ultrasonic Needle Peening (UNP), Ultrasonic Impact Treatment (UIT), Fatigue Life Enhancement, Welds, Residual Stresses, S355

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