Toughness arising from inherent strength of polymers

This study carries out spatial-resolved optical birefringence observations to quantify, for mode I (tensile opening) loading, the stress intensification at crack tip of brittle and ductile glassy polymers (polymethyl methacrylate—PMMA, polyethylene terephthalate—PET) as well one type elastomer: (ethylene propylene diene monomer—EPDM). We measure buildup in a precut specimen by correlating retardation with corresponding tensile stress. Given adequate spatial resolution under 10μm natural bluntness intentional through-cuts, we are able show that (a) during drawing different stages up onset fracture PMMA EPDM, local saturates, namely, ceases increase r−1/2 upon approaching cut (with r reaching rss range 0.05–0.15 mm), (b) σtip, i.e., saturation zone (r ≤ rss), linearly grows (operationally defined) intensity factor KI until fracture, level below breaking σb observed uncut specimen. Thus, inherent strength σF(inh) plane strain, taken be is only comparable σb. Moreover, characteristic length P, involved linearity between KI=σtipP1/2, found 2πrss. Here appears depend on sharpness, which may characterized radius curvature ρtip. toughness given critical KIc determined product ρtip1/2, energy release rate GIc specific work wF = [σF(inh)]2/2E