Razor that doesn't get blunt could be on the horizon

A shaving razor that doesn't blunt could be on the horizon after scientists discover human hair can ' chip' metal blades, despite being 50 times softer than steel.

In shaving experiments, engineers closely studied shaving in ultra-fine detail with an electron microscope to see how a razor blade can be damaged as it cuts human hair. Despite hair's relative softness in comparison to the strength of steel, the edge of the blade dulls quickly after a few shaves.

Defects in the steel's microscopic structure combined with the angle of a shave can chip the blade even with a single stroke, researchers reveal.

The study suggests ways for current blade technology to be improved, thereby lengthening the lifetimes of commercial disposable razors and kitchen knives.

A single strand of hair can cause the edge of a blade to chip under specific conditions, the engineers say. Once this initial crack forms, the blade is vulnerable to further chipping, and as more cracks accumulate around the initial chip, the razor's edge can quickly dull.

'Our goal was to understand a problem that more or less everyone is aware of – why blades become useless when they interact with much softer material,' said study author C Cem Tasan at the Massachusetts Institute of Technology (MIT). 'We found the main ingredients of failure, which enabled us to determine a new processing path to make blades that can last longer.'

Razors, scalpels and knives are commonly made from stainless steel, which is honed to give a a razor-sharp edge and coated with even harder materials such as diamond-like carbon to increase its lifespan.

However, knives require regular sharpening and razors are routinely replaced, even when they've been cutting materials far softer than the blades themselves.

Researchers explored the microstructure of metals in order to design new materials with better damage-resistance.

'We are metallurgists and want to learn what governs the deformation of metals, so that we can make better metals,' Tasan said.

'In this case, it was intriguing that, if you cut something very soft, like human hair, with something very hard, like steel, the hard material would fail.'

The findings also apply to the sharpness of a kitchen knife's blade – for instance, when slicing vegetables, a chef might consider cutting straight down, rather than at an angle.

The study has been published in the journal Science.