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Medical application of fatigue life analysis

 

Connect, no.148, May/June 2007, p.2

Stents are inserted into the arteries around the heart to improve blood flow if the arteries have become damaged.

Biocompatibles UK Ltd, a TWI Industrial Member company, manufacture a stent from a solid tube of stainless steel. The tube walls of the stent are laser-cut into a lattice structure and the surfaces are then etched.

Once inserted in the patient, the lattice is expanded by an internal balloon which is later removed. It had been suggested that the fatigue loading applied by the heart beating could result in the failure of a stent. Therefore, Biocompatibles requested that TWI carry out a finite element analysis of the stent to enable the expected fatigue life to be calculated.

The stent was modelled using beam elements. The analysis involved simulating a heart beat by applying radial pressure loading to all the elements in the model. The stent is under compressive loading in-vivo because it pushes theartery open. The blood pressure changes the compressive loading approximately 60 times a minute. Therefore the stent experiences an in-service loading of 1 Hz.

The results of the analysis showed that the current design gave a predicted mean endurance of approximately an order of magnitude greater than the specified minimum target life. It was therefore concluded that the current design of stent was acceptable.

To find out how TWI's Finite Element Analysis section could benefit your company, contact fea@twi.co.uk

Photograph of a stent prior to expansion Finite element model of stent
Photograph of a stent prior to expansion Finite element model of stent
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contactus@twi.co.uk