Paper number 620


Xiaoming Wang1, Kelly Tsoi1, Lin Ye1, Yiu-Wing Mai1, Stephen C. Galea2 and L. R. Francis Rose2

1Centre of Expertise in Damage Mechanics/Centre for Advanced Materials Technology,
Department of Mechanical and Mechatronic Engineering,
The University of Sydney, NSW 2006, Australia
2Airframes and Engines Division, Aeronautical and Maritime Research Laboratory,
Defence Science and Technology Organisation, Melbourne, Victoria, 3001, Australia

Summary Many current bonded patch repairs are based on a concept that patches bonded on a structure reduce nominal stresses and provide crack bridging in order to reduce stress concentration or range of stress intensity factor and thus extend the service life of the structure. An alternative way to enhance repair efficiency is to apply crack closure stresses, which may be provided by external forces. Shape memory alloy (SMA) has an ability to recover its trained shape as a result of transformation from martensite to austenite when it is heated above a transformation temperature. Consequently, if pre-strained SMA fibres are embedded in a patch to form a SMA composite patch and then placed over the crack, closure stresses may be produced when the SMA fibres are activated. The benefit of the SMA composite patch comes from not only reducing the mean stresses in the cracked plate but also from a possible reduction in the cyclic amplitude relative to the standard patch with the same extensional stiffness. Therefore, this paper is concerned with an application of SMA composite patches on a cracked metallic plate. An upper bound model for the repair of a plate with a crack is presented to illustrate the reduction of energy release rate (G) caused by shape memory effect of SMA fibre reinforced composite patches. Association of the force transfer efficiency with a stress to retard crack growth is described. Some considerations on the design of SMA composite patches are also addressed.
Keywords shape memory alloy, polymer composites, repairs, SMA fibre reinforced composites, fracture mechanics, energy release rate, closure stresses.

Theme : Smart Materials and Smart Manufacturing

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