We have connected viscoelastic recovery (healing) in sliding wear to free volume in polymers by using pressure-volume-temperature (P-V-T) results and the Hartmann equation of state. A linear relationship was found for all polymers studied with a wide variety of chemical structures, except for polystyrene (PS). Examination of the effect of the indenter force level applied in sliding wear on the healing shows that recovery is practically independent of that level. Strain hardening in sliding wear was observed for all materials except PS, the exception attributed to brittleness. Therefore, we have formulated a quantitative definition of brittleness in terms of elongation at break and storage modulus. Further, we provide a formula relating the brittleness to sliding wear recovery; the formula is obeyed with high accuracy by all materials including PS. High recovery values correspond to low brittleness, and vice versa. Our definition of brittleness can be used as a design criterion for choosing polymers for specific applications.

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Four different composite mixtures with varying amounts of expanded vermiculite were exposed to high temperatures of 300, 600, 900 and 1100uC for 6 h. Physical and mechanical properties including unit weight, porosity, water absorption, residual compressive strength, residual splitting tensile strength and also ultrasonic pulse velocity were determined after air cooling. Microstructures were investigated by scanning electron microscopy. Lightweight concrete with vermiculite shows a good performance at elevated temperatures. Expanded vermiculite is a significant lightweight aggregate for cementitious materials which are used for fire resistance applications. Concrete with vermiculite can be used as cement based refractory.