Session: OAC-06-01 Continued Safe Operation of Existing Assets-1

Paper Number: 122096

122096 - Bulk Metal Crack Tip Peening Using Acoustic Cavitation 

Bulk metal crack tip peening has traditionally been considered technically inadmissible because accessing the crack tip within bulk metal is extremely challenging. In the past, crack tip peening was limited to cracks formed in sheet or thin plate metals, which are more accessible compared to the crack tip within bulk metal. However, despite the inaccessibility of the crack tip in bulk metal, we introduce an innovative approach to peen the crack tip within bulk metal for the first time.

In this work, we demonstrate that acoustic cavitation can be localized at the tip of a crack when water is injected into the bulk metal crack specimen. This localized cavitation intensifies impact loadings, such as shockwaves and microjets produced when the cavities collapse, directly at the crack tip. These local impact loadings result in plastic deformation, leading to the formation of compressive residual stress in the region around the crack tip. The compressive stress at the crack tip mitigates tensile stress concentration, effectively peening the crack tip.

Given that cracks within bulk metal are typically only microscale wide, accessing the crack tips has been a significant challenge and limitation for crack repair. Our work predicts and demonstrates a unique acoustic condition that enables acoustic energy to effectively transfer to the crack tip, despite the limited accessibility. This energy is then used to create high-intensity cavitation at the crack tip, introducing shockwave or microjet impacts around the crack tip, thereby generating compressive residual stress. We experimentally verify this prediction and demonstrate acoustic cavitation at the crack tip, with a significant amount of compressive residual stress observed. Subsequently, we show that cavitation-induced compressive residual stress effectively retards crack growth.

To measure the residual stress at the crack tip, we develop a method that combines experimental strain measurements with finite element-based numerical computations, as the inaccessibility of the crack tip precludes the use of conventional residual stress measurement tools.

It's important to note that the present work implies that acoustic cavitation crack tip peening can also be uniquely used to repair already-grown deep surface cracks to retard their growth. Traditionally, peening has been only known as a method for preventing crack initiation, but our method can also be further useful for repairing existing cracks.

Presenting Author: Sunghwan Jung Dankook University

Presenting Author Biography: Sunghwan Jung received his B.S. degree in mechanical engineering from the University of Iowa, Iowa City, IA. He received his M.S. and Ph.D degrees in mechanical engineering from the Massachusetts Institute of Technology, Cambridge, MA, respectively. He is currently a Professor in Dankook University, Korea. His research interests include ultrasonic cavitation peening/cleaning, fracture mechanics, wafer spalling, and microfluidics.

Authors:

Sunghwan Jung Dankook University
Murugesan Prabhu Dankook UNiv.
Hyungyil Lee Sogang Univ.