Research Fellows Directory
Professor Fabrice Pierron
University of Southampton
In many areas of engineering, materials suffer deformation at high rates. This is the case when structures undergo impact, crash, blast, etc. but also in material forming like stamping or machining for instance. Therefore, it is essential for design engineers to have reliable mechanical models to predict the behaviour of the materials in such applications. Currently available experimental techniques to inform such models rely on very limited experimental information and fail to provide adequate model quality and complexity.
As part of his Royal Society Wolfson Research Merit Award, Professor Pierron is exploring new ways to inform the impact behaviour of materials based on ultra-high speed imaging (UHS). Thanks to new technological solutions, it is now possible to record images at an amazing frame rate of 5 million frames per second. Using a grid pattern at the surface of the test piece, it is possible to quantify the relative displacement of a very large number of points to produce a deformation map. Such maps can be obtained at every 0.2 microseconds (i.e., 0.2 millionth of a second). As a consequence, it is also possible to derive acceleration maps. As one knows from experience in roller coasters or cars, accelerations generate forces. Using this principle, the research developed here aims at using these acceleration maps as a load sensor to measure material deformation properties (stiffness, yield etc.). It is clear that for this to be feasible, sufficient acceleration needs to be induced in the specimen. Recent tests using UHS imaging have shown that a 40 mm x 30 mm x 3 mm carbon fibre composite impacted by a small 60 mm long 30 mm diameter projectile at 30 m/s (about 72 mph) undergoes up to about 1 million g’s (i.e., 1 million times more than the Earth’s gravity)! It is envisaged that within the next 10 years, this innovative route for impact material testing will bring a revolution in the engineering materials testing community.