What is a stress crack?
A stress crack is a crack that forms because the stress in a material becomes greater than the material can take, without any obvious impact or external overload. The stress often arises within the material itself, for example from heating up or cooling down too quickly, from tensile stress already locked into the material, or from a combination of tensile stress and an aggressive environment. Stress cracks occur mainly in glass, rigid plastics and metals.
Causes by material
- Glass (thermal breakage). When part of a pane is warmed by the sun while the edge stays cold in the rebate or in shade, tensile stress develops at the edge. The crack then usually starts at right angles to the edge. Dark films, sun shading or radiators just behind the glass increase the risk.
- Plastic. Rigid plastics such as PVC or polycarbonate can crack around drilled holes, around screws that are too tight, or on contact with certain solvents and sealants.
- Metal (stress corrosion). Simultaneous tensile stress and corrosion can produce fine cracks, for example in stainless steel in a chloride-rich environment such as a swimming pool.
- Welding. Heating and cooling during welding leave residual stresses, which can lead to cracks under varying loads.
Application and prevention
- Have the glass assessed. For large panes with varying sun exposure, partial shade or solar control film, the glass supplier can calculate whether heat-strengthened or laminated glass is needed.
- No film without advice. Do not apply dark solar control film to existing glass without checking that the glass is suitable for it.
- Give plastic room. Drill oversized holes in plastic sheets, use spacer washers and do not overtighten screws, so the material can expand.
- Right materials. In aggressive environments, use a grade of stainless steel or a material suited to those conditions.
Common mistake: mistaking a thermal glass break for a break-in or a thrown stone. The tell-tale sign is a crack that starts at right angles from the edge, with no point of impact.
Related terms
- Crack
- Shrinkage crack
- Mechanical stress
- Building glass
- Corrosion
- Double glazing
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