Changing colours reveal the pressure

An American company has developed a sheet-like material that changes colour when it is placed between solid surfaces and subjected to pressure. The intensity of the colour indicates the precise pressure, allowing the material, called Pressurex, to be used in a variety of applications where the pressure between mating or impacting surfaces needs to be measured and there is not enough room for traditional sensors such as loadcells.

For example, the material can be used to measure pressure distribution between gear teeth, shafts and frames. It can also be used to decide where to place strain gauges, to determine drawing pressure in dies, and to control processes such as punching, bending, rolling and flanging.

The material consists of a sandwich with two outer sheets of polyester film containing a layer of microcapsules which burst under pressure and react with a colour developing layer. It comes in large thin sheets, 25-50 microns thick, and in five sensitivities from 2-1,300 kg/cm2. When placed between mating or impacting surfaces, the material changes colour instantly and permanently with an intensity proportional to the force applied. The force can be measured by comparing the colour to a calibration chart (providing an accuracy of ±10%) or by using an imaging system (giving an accuracy of ±1%).