Experimental determination of thermal and adhesion stress in particle filled thermoplasts

The phenomena of dewetting in filled thermoplastics were studied by light microscopy and were correlated with variations in the slope of stress‐strain diagrams in constant strain rate tests. In such diagrams, kinks in the plots were found to correspond to the dewetting stress. The corresponding local stress at a filler particle is then equal to the sum of the thermal compressive stress and the adhesion stress. It was shown that the adhesion stress was proportional to the reciprocal root of the particle radius. Also, values of dewetting stress predicted for inorganic particles with radii smaller than 2–4 micrometers are higher than the stresses at which crazes and shear‐bands are formed near such particles, indicating that dewetting will not occur in those cases, and adhesion aids may be superfluous.