Investigation of the Damage Behavior of Polyurethane in Stress Relaxation Experiments and Estimation of the Stress-at-Break σb with a Failure Envelope
In stress relaxation experiments the investigated polyurethane exhibits an unexpected, but repeatable failure during the relaxation period. Images, taken by a camera and a high speed camera, displayed crack initiation several minutes before rupture occurred. The crack growth rate then accelerates and leads to failure rapidly. The present investigation indicates different methods for analyzing the damage evolution with focus on the appearance of damage at low strains, accumulation of damage processes at higher strains, the influence of time on damage evolution and the identification of recovery phenomena during unloading and in the unloaded state. The results show that not only long times at high strains but also the loading history, especially loading and unloading processes, accelerate damage evolution. In a preliminary study the characterization of the ultimate tensile properties by a failure envelope appears to provide an adequate method for estimating the stress-at-break σb and the time-to-break tb in stress relaxation experiments.
KeywordsDigital image correlation Crack initiation Crack growth Damage evolution Predeformation Failure envelope
We gratefully acknowledge the support of Prof. Dr. rer. nat. habil. Wulff Possart, Chair for Adhesion and Interphases in Polymers, Saarland University, for providing access to materials and equipment for sample preparation and to the dry box.
- 1.Tobolsky AV (1956) Stress relaxation studies of the viscoelastic properties of polymers. J App Phys 27:673–685Google Scholar
- 2.Bergström JS, Boyce MC (1998) Constitutive modeling of the large strain time-dependent behavior of elastomers. J Mech Phys Solids 46:931–954Google Scholar
- 3.Kahn AS, Lopez-Pamies O (2002) Time and temperature dependent response and relaxation of a soft polymer. Int J Plasticity 18:1359–1372Google Scholar
- 4.Tobolsky AV, Prettyman IB, Dillon JH (1944) Stress relaxation of natural and synthetic rubber stocks. Rubber Chem Technol 17:551–575Google Scholar
- 5.Kausch HH (2012) Polymer fracture. Springer Science & Business Media, BerlinGoogle Scholar
- 6.Friedrich L (2017) Untersuchungen zum Materialverhalten poröser Elastomere während der Relaxation. Bachelor thesis, Chair of Applied Mechanics, Saarland UniversityGoogle Scholar