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Tactile Contact Pressure

During the design process, it is often necessary to calculate the distribution and magnitude of pressure between two touching or contacting surfaces. The pressure between such surfaces is termed Tactile Contact Pressure, where tactile means perceptible by touch or relating to the sense of touch. However, contacting surfaces are often not easily accessible, making it difficult to take accurate measurements.

At the 2006 International Conference on Tribology in Parma, Italy, M Conte, A Manuello, L Mazza, and C Visconte presented a paper titled, Measurement of Contact Pressure in Pneumatic Actuator Seals. This paper presented an experimental procedure for measuring tactile contact pressure between a pneumatic actuators lip seal and its counterpart. Static measurements were taken on a lip seal rectilinear specimen in a test fixture that was designed to reproduce actual operating conditions.

Tactile contact pressure was evaluated using Fuji tactile pressure indicating film that was placed between the seal and its contacting surface, and tests were carried out under different load conditions. Figure 1 shows the seal cross section, and Figure 2 illustrates the test fixture and the pressure indicating film results.

tactile contact pressure
Fig 1: Seal Cross Section and Dimensions
pressure test figure
Fig 2: Test Fixture and Fuji Pressure Indicating Film Results

The tactile contact pressure results compared favorably with predictions from Finite Element Analyses. Figure 3 shows the comparison of the FEA predictions and the pressure indicating film results at a load factor of 0.6 MPa. There is a good agreement in terms of pressure peaks, general trend, and normal force. The authors of this paper concluded that the Fuji pressure indicating film is ...a viable tool in design evaluation of lip seals.

test results
Fig 3: Comparison of Experimental and FEA Results

The terms Fuji Pressure Indicating Film®, Prescale Fuji Film, Fuji Paper®, or Fujifilm Prescale® are synonymous with Fujifilm Prescale® pressure indicating film that is distributed by Sensor Products. Fujifilm Prescale® is a unique, affordable and easy to use tool that reveals the distribution and magnitude of pressure between any two contacting, mating or impacting surfaces. Pressure indicating sensor film is extremely thin (4 to 8 mils) which enables it to conform to curved surfaces. It is ideal for invasive intolerant environments and tight spaces not accessible to conventional electronic transducers.

Fujifilm Prescale® is a Mylar®-based film that contains a layer of tiny microcapsules. The application of force upon the film causes the microcapsules to rupture, producing an instantaneous and permanent high-resolution topographical image of tactile contact pressure between two surfaces.

Simply place Fujifilm Prescale® between any two surfaces that touch, mate, or impact. Apply pressure, remove it, and immediately the film reveals the pressure distribution profile that occurred between the two surfaces. Like Litmus paper, the color intensity of the film is directly related to the amount of pressure applied to it. The color intensity is proportional to the pressure.