Watch the mechanical engineers measuring cheese and other soft materials with acoustic waves.
Soft materials are everywhere. In many applications, valuable information about the strength of these materials enables more precise control in everything from cutting and processing soft foods to designing new medical devices or assessing tissue properties for diagnostic applications. Current testing methods, such as 3- or 4-point bending, puncture/indentation and wire cutting, require lots of material and are destructive. An efficient, minimally invasive technique that works in real time is needed.
In hard materials like ceramics, concrete and composites, acoustic emissions (AE) testing detects the release of elastic energy in fractured materials and provides qualitative and quantitative data on crack nucleation, crack propagation, plastic deformation and dislocation motion. It has been used in applications like seismic and structural health monitoring. AE testing has yet to be widely studied in soft materials.
UW-Madison researchers Melih Eriten and Corinne Henak have developed a method for testing the mechanical and failure properties of soft materials using a non-contact, portable vibrometer that measures acoustic emissions. The team has established a direct link between the characteristics of emissions from failure in the materials and their properties. AE signals include maximum amplitude, frequency content, duration, rise time and energy. Vibrometers can measure the AE of incredibly small fractures – on the order of several micrometers – at multiple locations with high frequency, making them ideal for monitoring soft materials in real time.