Residual stress cracking may appear during demolding, fabrication, assembly, cleaning, or service. The crack often begins at a corner, drilled hole, fastener, bond line, or other stress concentrator.
Forming a sheet before it is sufficiently pliable can lock high molecular orientation into the part. Incomplete tool contact, rapid uneven cooling, forced release, and sharp geometry add more stress. Chemicals that are harmless to an unstressed sample may trigger crazing or cracking in a stressed part.
Correction
The forming window should be verified with the actual grade. The sheet should reach complete shape before it cools, and demolding should not force the part across undercuts or inadequate draft. Fabrication and cleaning methods must be compatible with the polymer.
A stress-screening test using the approved service environment can help compare process changes. Aggressive solvent tests should not be applied without material-specific guidance because they may create failures unrelated to real use.