ISO 604 Compressive Properties of Plastics

ISO 604 Platens and Accessories 

Depending on your application, the following fixtures are commonly used for ISO 604 testing: 

• upper compression platen with integral spherical seat (diameters vary from 2" to 8”)
• lower rigid platen of matching size
• 2601-04X series LVDT (linear displacement transducer)
• LVDT mount for platens (2601-071)

Strain MeasurementThe preferred method of measuring strain when performing ISO 604 testing is by fixing an extensometer to the platens or the specimen itself. The instrument used must have 1% accuracy or better over the region it is being used. The LVDT is the recommended strain device for ease of use, but alternatively a small gauge length (0.5 inch or less) clip-on extensometer that will fit between the platens can be used during a modulus test. However, the preferred specimen dimensions of a compressive strength test do not allow for the use of a clip-on extensometer. If not using an extensometer, nominal compressive strain is to be measured using the distance between the platens and the test frame’s crosshead position. When calculating nominal strain, machine compliance must be corrected out of the frame’s displacement measurement. A complete explanation of compliance correction can be found in an annex of ISO 604 as well as this Instron whitepaper.

Helpful Tips and Tricks

• The ISO 604 method is included in the Plastics test method suite in Bluehill Universal.
• If the specimen is too thin, an anti-buckling support jig should be used to prevent the specimen from buckling.
• If reporting the modulus calculation, make sure the extensometer and load cell are both verified in the range where the calculation is being made. Labs commonly make the error of reporting calculations outside of the verified range of their devices.