[6A4] Understanding of ultrasound behaviour from fatigue cracks under stress
Dr Jie Zhang, Roman Gorbanjov, Kobi Hazel and Dr Nicolas Larrosa
Department of Mechanical Engineering, University of Bristol, UK
Fatigue cracks are the most common form of damage in metallic structures which can lead to structural failure in a range of important industrial sectors such as aerospace, nuclear, transportation and petrochemical. Early stage fatigue cracks are typically difficult to detect with ultrasonic techniques, being tightly closed and with low acoustic contrast. A reliable ultrasound tool to detect closed fatigue cracks could provide early warning of damage, in turn allowing better scheduling of maintenance and/or the timely implementation of measures to extend material life. A barrier to the development of such reliable tools is a lack of understanding ultrasound behaviour from fatigue cracks under stress. The aim of this paper is to break this barrier and understand the ultrasound behaviour around fatigue cracks at their early development stage.
In this paper, a fatigue crack is generated from 3-point bending tests. The control of crack opening and closing is tested by a load machine. An ultrasonic array imaging system is used to rapidly capture ultrasonic data simultaneously with the load variation. Meanwhile, a digital imaging correlation technique is used to monitor the strain around the crack. Preliminary results show that ultrasonic arrays image can track crack opening under stress. How to combine finite element models for stress analysis and FMC data generation is also investigated.
In this paper, a fatigue crack is generated from 3-point bending tests. The control of crack opening and closing is tested by a load machine. An ultrasonic array imaging system is used to rapidly capture ultrasonic data simultaneously with the load variation. Meanwhile, a digital imaging correlation technique is used to monitor the strain around the crack. Preliminary results show that ultrasonic arrays image can track crack opening under stress. How to combine finite element models for stress analysis and FMC data generation is also investigated.
