Polycarbonate is tough, but stressed parts can be vulnerable to environmental stress cracking. Cracks may appear after cleaning, bonding, fastening, painting, machining, or exposure to an otherwise mild chemical.
Residual stress increases when sheet is formed too cold, incompletely formed, cooled unevenly, or forced across undercuts. Tight fasteners, drilled holes, sharp corners, and solvent-containing products add local stress.
Prevention
The grade-specific forming window and drying requirement should be followed. Tool contact and cooling should be uniform, and release must not force the part. Assembly loads should be distributed with suitable radii, washers, clearances, and joint design.
Cleaners, adhesives, paints, and thread-locking compounds must be checked for compatibility with stressed polycarbonate, not only with an unstressed coupon. A successful short exposure does not prove long-term compatibility under load.