The generic fracture response of polymers in uniaxial tension

4 The generic fracture response of polymers in uniaxial tension 

Correspondingly, eq. (13.2) representing the strain-rate dependence of the plastic resistance is taken to be given by a standard uniaxial reference experiment at a reference strain rate e gf, typically of magnitude 10 s that evokes a reference tensile uniaxial plastic resistance o-j-gf, which in this case would be the tensile yield stress o-q. The form of the idealized power law relating eg to Ug is given by the exponent m of the equivalent stress, which must be temperature-dependent in a form given in Chapter 8 as 

we note that the tensile strength uf is dependent on flaws, which for the purpose of illustration are characterized by the largest dimension Uf of the flaw, which is treated as a micro-crack. Without loss of generality, uf is considered to be defined by the Griffith relation 

As Fig. 13.1 depicts, the tensile toughness fkp per unit volume is the area under the stress-strain curve, terminated either when the flow stress reaches the tensile fracture strength uf or when the plastic strain reaches the fracture strain e , which we state simply in conformity with eqs. (13.1)-(13.5) as 

Noting that the initial uniaxial yield strength uo will be strain-rate-dependent, making sq (= ffg jE) also strain-rate-dependent, we note that the tensile toughness fkp will also be strain-rate-dependent. Thus, 

---