Lake-Thomas model

Using trouser tear tests, Gent and Tobias [21] showed that the Lake-Thomas model held reasonably well for a number of elastomers. In their analysis, they took the molecular mass of a strand as that extracted from the elastic modulus and thereby incorporated the effect of entanglements (Section 9.8.2). More recent results on poly(dimethyl siloxane) (PDMS) elastomers using simple shear tests [22,23] over a wide range of structure (extent of cross-links and trapped entanglements) indicate that the role of entanglements in elastomer fracture needs to be elucidated further. 

The energy necessary to propagate the crack within the model described above can be obtained using the classic Lake-Thomas [65] model of elastomer failure. Within this model Qc = 2n 17 where n is the number of main-chain bonds between crosslink or entanglement points, and 17 is the energy needed to break a main-chain bond. This relationship predicts a fracture energy of 6 J/m2 when 2 is 0.075 chains/nm2,in reasonable agreement with the experimental results. 

The classic model that describes chain scission in elastomers was proposed many years ago by Lake and Thomas [26J. The aim of the model is to calculate the energy dissipated in breaking all the polymer strands that have adjacent cross-links on either side of the crack plane. The basic assumption of this model is that all the main chain bonds in any strand that breaks must be strained to the dissociation... 

Such a /Mc dependence has been observed for the threshold fracture energies in rubberlike materials [106,107] in accordance with the model of Lake and Thomas [108]. However, Eq. (7.10) is based on arrest energies and the reason for the use of arrest energies is not clear. 

Based on a measured Henry s Law Constant of 9.1x10 atm/m -mol (Ashworth et al. 1988), the volatilization half-life of 1,1,2-trichloroethane in a model river 1 m deep flowing 1 m/sec with a wind of 3 m/sec is estimated to be 4.5 hr, with resistance in the liquid phase primarily controlling volatilization (Thomas 1982). The half-life in a lake or pond would be much longer. The half-life of... 

---