Monday  |  Salon 13  |  05:30 PM–05:50 PM

#16120, Fracture Behavior Study of PMMA in Quasi-Static and Dynamic Regime

The toughness and the fracture energy are the well-known material parameters of the LEFM considered for a predictive behavior model. Few studies have examined the complete achievement of the full PMMA kinetic law of fracture, from quasi-static to dynamic regime. In the same way, very few studies deduce these laws from displacement field measurements realized by digital image correlation (DIC). It is the case of this study which established, the evolution of the stress intensity factor (SIF) according to the PMMA crack speed using a fast camera allowing the acquisition of 1280*800 resolution images at 60 000 frame/s. Kinetic laws representing KID and GID according to the crack speed are thus compared with those from the literature by considering dynamical effects induced by rapid crack propagation.

Results from fracture tests with strip band specimen type geometry indicate that dynamic stress intensity factor (KID), for v = 0.23 cR, is lower than in quasi-static regime. Indeed, from experimental stabilized fracture tests, with « compact tension » type geometry, a material toughness of 1.25 MPa.m0.5 and a material fracture energy of 0.5 kJ/m2 were measured for a crack speed from 0.1 to 3.0 mm/min. This decrease is attributed to viscous effects, to a local rise in temperature at the crack tip [1]. PMMA needs to be view as a visco-elastic material which is not always considered in the literature. Besides, a rather linear evolution of KID was obtained for 0.23 < v/cR < 0.60. The increase of KID for v > 0.60 cR seems to be due to not considering the created surface area in calculations. Besides, the stress factor KID, obtained by a local approach, is compared to the fracture energy GID, obtained by a global approach.

Surface quantification induced by PMMA fracture was also highlighted in this study and correlated to the cracking mechanisms. At approximately 0.6 cR, the amount of fracture surface created is higher than twice the projected fracture surface on the average fracture plane, close to the “mirror” zone. Lastly, the dynamic fracture energy must be considered as a function of created surface since the microcrack branching velocity has been reached.

[1] K. N. G. Fuller, P. G. Fox, and J. E. Field. The Temperature Rise at the Tip of Fast-Moving Cracks in Glassy Polymers. Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences, 341(1627) :537-557, 1975.

Vincent Fournier   University of Bordeaux
Jean-Benoit Kopp   University of Bordeaux
Jérémie Girardot   University of Bordeaux