VDI VDI 3822 BLATT 2.1.7 PDF

The following types of stresses will be addressed in this guideline:

• effects of media (physical and chemical stresses due to media),
• effects of media in cases of pre-existing internal or external strains (crazing)

A physical effect of stress due media does not lead to a reaction between of the medium with the plastic material. Only the physical bonds are influenced (secondary valencies). This results in swelling even to the point of dissolution and in reversible changes in the properties of plastics.

Chemical effects of stress due to media lead to a reaction between the media and the primary valence bonds of the plastic and to irreversible changes in the properties. Even slight chemical changes can result in marked changes in the properties of plastics.

Since changes resulting from effects of stress due to media can also be influenced by other factors, such as low crystallinity or low molar mass, it must be clearly determined whether a failure was caused solely through the effects of stress due to media or whether the cause can be found in conditions that existed previous to the effects of stress due to media or in a combination of both.

This guideline initially deals only with failures caused by the effects of stress due to media and subsequently illustrates accompanying conditions that promote failure.