This case study is part of a set reflecting the impact of ISIS science reported as part of the UK Research Excellence Framework (REF 2021).
REF Case Study: Application of laser shock peening in aerospace applications
Principal Investigator: Prof Michael Fitzpatrick
Institution: Coventry University
Funding: Science and Technology Facilities Council through an ISIS Facility Development Studentship
Company involved: Airbus
The Challenge
Technologies for extending the lifetime of airframe structures, both for new designs and for aircraft types already in operation, are a key priority for the aerospace industry. A critical factor in structural integrity of metallic structures is parts that are subject to fatigue cracking. This is an issue in aerospace because of those parts of the structures that are highly-stressed under cyclic loading conditions. Damage-tolerant design requires a complete understanding of the fatigue behaviour of the structure, where cracks will initiate and grow, and implementing robust systems of inspection to detect cracks before they can grow and cause failure.
Laser shock peening (LSP) is a surface treatment technology that uses a sequence of high-power-density laser pulse to locally vaporise a sample surface, generating a plasma and associated shock wave that is driven into the surface by use of a confinement layer, usually a water film. The method is applied extensively in aero-engine applications by the major manufacturers, but its cost, relative inflexibility in application, and the effort required to optimise it for deployment on a new material, have meant that there are few other large-volume commercial applications, including aerospace structures.
Evidence of Impact
The impact of the research carried out using IMAT included the safe implementation of laser shock peening in repair and life extension operations in aircraft: reducing the cost of developing new repair solutions to the US Air Force; and the commissioning of a bespoke system for airframe repair by Airbus.
The work by Prof Fitzpatrick's group at Coventry has advanced understanding on how commercial laser shock peening technology generates residual stress in aerospace aluminium alloys; how that residual stress can be tailored to slow the growth of fatigue cracks; and how models of the process need to account for cyclic hardening properties of the material peened. The outcomes of the research have informed the application of laser shock peening as a manufacturing tool, as well as for use in repair, either where fatigue hotspots are identified in-service, or as a means to arrest growing cracks.
“The adoption of laser shock peening has allowed the aerospace industry to safely extend the life of aircraft parts by identifying how cracks form and grow in response to mechanical stress. Key to this is understanding how laser shock peening generates residual stress in aluminium alloys, and how this can be tailored to slow the growth of fatigue cracks. Using neutron diffraction and imaging at ISIS gave unique insights into the internal stresses with high resolution, contributing to our overall understanding and allowing development of accurate models for life prediction and assurance of structural integrity," Professor Mike Fitzpatrick, Coventry University.
The role of ISIS
Coventry University, supported by Airbus and the US Air Force Research Laboratory, used IMAT to both carry out conventional analysis and, taking advantage of the high spatial resolution, to perform novel Bragg-edge strain imaging which rapidly demonstrated the influence of process parameters. STFC funded an ISIS Facility Development Studentship to enable research on IMAT to be carried out to the value of £41,380.
ISIS Instrument(s): IMAT
ISIS Technique(s): Neutron diffraction and imaging
References: R. S. Ramadhan, D. Glaser, H. Soyama, W. Kockelmann, T. Shinohara, T. Pirling, M. E. Fitzpatrick, A. S. Tremsin, 'Mechanical surface treatment studies by Bragg edge neutron imaging'. Acta Materialia:2022:118259. DOI:
Ramadhan, R.S., Syed, A.K., Tremsin, A.S., Kockelmann, W., Dalgliesh, R., Chen, B., Parfitt, D., Fitzpatrick, M. E. (2018) 'Mapping Residual Strain Induced by Cold Working and by Laser Shock Peening using Neutron Transmission Spectroscopy', Materials and Design, 143, 56-64.
