Crazes

Crazes

Als Crazes (engl.: Haarrisse) werden mikroskopisch kleine Rissnetzwerke als Vorstufe einer Spannungsrissbildung in Kunststoffen bezeichnet.

In Kunststoffbauteilen, die unter mechanischer Spannung stehen, können sich die Polymerketten regelmäßig ausrichten. Wird die Spannung zu groß, kann es an den ausgerichteten Stellen zur Bildung von mikrorissartigen Strukturen kommen, die durch Fibrillen verbunden sind. Makroskopisch zeigen sie sich als weißbruchartige Muster auf der Oberfläche. Unter Einwirkung von Spannungen und Medien können sie zu größeren Rissen wachsen und schließlich zum Bruch des Bauteiles führen.

Einige amorphe Kunststoffe sind von diesem Effekt betroffen. Beispielsweise lässt er sich sehr gut beim Biegen von transparentem Polystyrol (Kunststofflineal) beobachten, welches durch Lichteinfall gealtert ist oder im Kontakt mit einem spannungsrissauslösenden Medium wie zum Beispiel Ethanol stand.


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