Clamping Hardware

The mechanical arrangement used to obtain a steady, nonshifting clamping force obviously depends on the nature of the test object and the gage installation. Sometimes a simple spring clamp will suffice. In other cases, it may be necessary to devise a more elaborate clamping fixture. For any type of clamp, the assembly generally consists of four components:

1. A release film is used between the gage/adhesive and the pressure pad . It prevents the pressure pad from adhering to the adhesive layer. For low-temperature-curing epoxies [<150 deg F (66 deg C)] such as AE-10 or 15 and GA-2 , this film is usually cellophane tape ( PCT-2A ). For higher-temperature-curing epoxies, such as 600 , 610 , 43-B and GA-61 , it is usually a sheet of Teflon film ( TFE-1 ) or Mylar tape ( MJG-2 ).
    
2. A resilient rubber pressure pad is used to provide a uniform clamping pressure over the gage area. It should be soft enough to conform to slightly irregular surfaces but not so soft as to extrude from under the clamping plate. Recommended hardness is durometer A40-60. Silicone gum or silicone rubber are preferred because of their high-temperature capability.
    
3. A metal clamping plate serves to distribute the clamping force over the entire area of the pressure pad. It should be formed to match the contour of the pressure pad or test part and should have sufficient thickness to prevent deformation under normal clamping force.
    
4. A force application device is used to apply steady force on the metal clamping plate. It could range from simple dead weights to sophisticated vacuum pads with integral heaters.

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