Engineering Elastic Properties in Glassy State

The bulk modulus K can be derived directly from an expression for the intermolecular energy potential u(d), where d is the intermolecular distance (Fig. 11.3). The most usual expression for u(d) is the Lennard-Jones relationship  

The bulk modulus can be derived from this equation, since 

Ultrasonic measurements (5 MHz) made at ambient temperature on amine-crosslinked epoxies (Morel et al., 1989), or styrene-crosslinked vinyl esters (Bellenger et al., 1994), show that K is effectively proportional to the cohesive energy density  

CED is determined by calculation, using the Van Krevelen increment values (Van Krevelen, 1990). There is no apparent effect of the crosslink density on K, which seems to depend (as CED), only on the molecular scale structure (polarity, hydrogen bonding). The following results were obtained with quasi-static tensile measurements (10 -10 s strain rate) in a temperature range 200 K-Tg, using a bidimensional extensometer to determine E and v (from which K and G could be determined) (Verdu and Tcharkhtchi, 1996)  

K values are of the same order as ultrasonic ones (typically 5 7 GPa). 

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