TY - JOUR
T1 - Anomalous aging in two-phase systems
T2 - Creep and stress relaxation differences in rubber-toughened epoxies
AU - Lee, Andre
AU - McKenna, Gregory B.
PY - 1997/6
Y1 - 1997/6
N2 - From time-aging time superposition principles, similar to time-temperature superposition, one would expect similar shifting or superposition behaviors for both creep and stress relaxation responses. In particular, for isotropic homogeneous systems, in the linear viscoelastic regime, consideration of superposition in rheology by Markowitz1 or the discussion by Ferry2 from the Kramers-Kronig relation would seem to demand that creep and stress relaxation shift in the same way. Here we report on results from creep and stress relaxation measurements in two-phase, rubber-toughened epoxies that exhibit Boltzman additivity of creep or relaxation behaviors and follow the time-aging time superposition behavior in creep, but not in stress relaxation. While the lack of superposition in stress relaxation is, perhaps, not surprising, the finding that the creep responses at different aging times superimpose while the stress relaxation responses do not, presents an anomalous behavior that has not been previously reported. In addition, our findings show that the stress relaxation responses show short time "softening" upon aging. Possible reasons for the anomalous behaviors are briefly considered.
AB - From time-aging time superposition principles, similar to time-temperature superposition, one would expect similar shifting or superposition behaviors for both creep and stress relaxation responses. In particular, for isotropic homogeneous systems, in the linear viscoelastic regime, consideration of superposition in rheology by Markowitz1 or the discussion by Ferry2 from the Kramers-Kronig relation would seem to demand that creep and stress relaxation shift in the same way. Here we report on results from creep and stress relaxation measurements in two-phase, rubber-toughened epoxies that exhibit Boltzman additivity of creep or relaxation behaviors and follow the time-aging time superposition behavior in creep, but not in stress relaxation. While the lack of superposition in stress relaxation is, perhaps, not surprising, the finding that the creep responses at different aging times superimpose while the stress relaxation responses do not, presents an anomalous behavior that has not been previously reported. In addition, our findings show that the stress relaxation responses show short time "softening" upon aging. Possible reasons for the anomalous behaviors are briefly considered.
KW - Creep compliance
KW - Physical aging
KW - Rubber-toughened epoxies
KW - Stress relaxation
KW - Superposition
KW - Two-phase materials
UR - http://www.scopus.com/inward/record.url?scp=0031163485&partnerID=8YFLogxK
U2 - 10.1002/(SICI)1099-0488(199706)35:8<1167::AID-POLB1>3.0.CO;2-R
DO - 10.1002/(SICI)1099-0488(199706)35:8<1167::AID-POLB1>3.0.CO;2-R
M3 - Article
AN - SCOPUS:0031163485
SN - 0887-6266
VL - 35
SP - 1167
EP - 1174
JO - Journal of Polymer Science, Part B: Polymer Physics
JF - Journal of Polymer Science, Part B: Polymer Physics
IS - 8
ER -