Plastic parts can crack or fail for a variety of reasons. The part could be deformed beyond the mechanical properties of the material causing yield or break issues. Breakage can be characterized by brittle and and ductile mechanical failure. Brittle will typically show a sharp break and ductile will stretch and tear which may include stress whitening. Besides mechanical load based failures, UV may negatively decrease plastic performance over time. Parts may yellow and then crack due to UV exposure. The UV light attackss the polymer bonds