Failure analysis on a surgical instrument

Having been approached by a member company, TWI undertook a confidential and independent failure analysis exercise on a surgical instrument that had failed during an operation. TWI’s breadth of expertise and capabilities offer a vital and unrivalled service to material scientists working in areas such as process optimisation, corrosion, failure investigation and more.

As a first step, the product documentation and drawings were reviewed in order to understand the exact design specifications and the manufacturing engineering processes. The team examined the instrument itself using light microscopy to identify the character of the failed areas and to determine the location for subsequent metallographic sectioning. Light microscopy involves the observation of the light reflected from carefully prepared metallographic specimens. This can reveal different features of the microstructure, including grain size, inclusions, presence of intermetallics, corrosion, impurities and local changes in composition.

TWI’s light microscopy facilities examine samples at up to 1000x magnification with different etches revealing different features of the sample structure. In addition, by analysis of these images, accurate measurements may be made of features including pits, cracks, coatings, grain sizes and volume/area fractions of the different microstructural features.

The fracture faces were examined using light microscopy and also a scanning electron microscope(SEM) equipped with an energy-dispersive X-ray (EDX) detector. There are two high quality scanning electron microscopes at TWI. The first of these, an environmental SEM can analyse relatively large samples without extensive cleaning, allowing the characterisation of surface deposits, fracture surface topography and microstructure. The attached EDX detector maps chemical compositions both locally and globally. Imaging of features is possible up to 5,000x.

The FEG-SEM can image samples at up to 100,000x magnification, revealing the sample structure in extremely fine detail. Local and global elemental analysis is possible by EDX spectroscopy. The recent addition of an electron back-scattered diffraction detector means that crystal structures, crystallographic orientation, and phase identification can be characterised at a microscopic level. A metallographic section through the fracture site was also prepared and hardness measurements were taken. Finally, chemical analysis was carried out on the material.

As a result, TWI was able to determine and explain the causes of failure and provide recommendations to the company that would enable them to prevent any re-occurrence, minimise the risks and limit associated costs.

For further information, or to find out more about failure analysis please email contactus@twi.co.uk.

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Failure analysis on a surgical instrument

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