TY - JOUR
T1 - Criteria to predict the embrittlement of polycarbonate
AU - Engels, T.A.P.
AU - Breemen, van, L.C.A.
AU - Govaert, L.E.
AU - Meijer, H.E.H.
PY - 2011
Y1 - 2011
N2 - A direct correlation is found between the time evolution of the yield stress in unnotched tensile bars and that of the impact energy measured using notched tensile bars. In both cases a master curve can be constructed with an Arrhenius type of shift function, using the same activation energy. Combining these experimental findings with numerical simulations lead to a maximum hydrostatic stress as a criterion to predict the onset of failure, . Where aging kinetics is not dependent on the polymer’s molecular weight, embrittlement is, and for higher molecular weights a higher is found. Moreover, for high polymers we observe a more stable craze extension and crack propagation after cavitation, causing the computed impact energies to underestimate the experimental ones for all but the lowest molecular weight polymers. Because the maximum in hydrostatic stress under the notch, sh, increases with the polymer’s age, defined by the value of the state parameter Sa, and given the proportionality between Sa and the yield stress, sy, an alternative failure criterion is proposed which is a molecular weight dependent critical value of the evolving yield stress, sy,c. It predicts a product’s increased sensitivity to damage under the influence of progressive aging as enhanced by temperature.
AB - A direct correlation is found between the time evolution of the yield stress in unnotched tensile bars and that of the impact energy measured using notched tensile bars. In both cases a master curve can be constructed with an Arrhenius type of shift function, using the same activation energy. Combining these experimental findings with numerical simulations lead to a maximum hydrostatic stress as a criterion to predict the onset of failure, . Where aging kinetics is not dependent on the polymer’s molecular weight, embrittlement is, and for higher molecular weights a higher is found. Moreover, for high polymers we observe a more stable craze extension and crack propagation after cavitation, causing the computed impact energies to underestimate the experimental ones for all but the lowest molecular weight polymers. Because the maximum in hydrostatic stress under the notch, sh, increases with the polymer’s age, defined by the value of the state parameter Sa, and given the proportionality between Sa and the yield stress, sy, an alternative failure criterion is proposed which is a molecular weight dependent critical value of the evolving yield stress, sy,c. It predicts a product’s increased sensitivity to damage under the influence of progressive aging as enhanced by temperature.
U2 - 10.1016/j.polymer.2011.02.027
DO - 10.1016/j.polymer.2011.02.027
M3 - Article
SN - 0032-3861
VL - 52
SP - 1811
EP - 1819
JO - Polymer
JF - Polymer
IS - 8
ER -