EFFECT OF WEATHERING ON THE STRESS-DISTRIBUTION AND MECHANICAL PERFORMANCE OF AUTOMOTIVE PAINT SYSTEMS

The sources of stress in complete automotive paint systems have been i dentified and measured as a function of weathering In addition to the stresses developed during cure, the main sources of stresses developed during exposure are thermal expansion coefficient mismatch, humidity expansion mismatch,and densification of the clearcoat. Stresses genera lly increase during weathering due to a slow densification of the clea rcoat and increasing water absorption and desorption stresses. Finite element analysis (FEA) was used to compute the stress distribution in full paint systems. Stresses are typically in-plane and highest in the primer and clearcoat. Stresses approaching those required to propagat e cracks can be attained in weathered paint systems. The presence of f laws, either cracks or incipient delaminations, will lead to large str ess concentrations that can give rise to peeling forces not present in coatings without cracks.