δ₂₅ Crack opening displacement parameter in cohesive zone models: experiments and simulations in asphalt concrete

Abstract

A B S T R A C T Recent work with fracture characterization of asphalt concrete has shown that a cohesive zone model (CZM) provides insight into the fracture process of the materials. However, a current approach to estimate fracture energy, i.e., in terms of area of force versus crack mouth opening displacement (CMOD), for asphalt concrete overpredicts its magnitude. Therefore, the δ 25 parameter, which was inspired by the δ 5 concept of Schwalbe and co-workers, is proposed as an operational definition of a crack tip opening displacement (CTOD). The δ 25 measurement is incorporated into an experimental study of validation of its usefulness with asphalt concrete, and is utilized to estimate fracture energy. The work presented herein validates the δ 25 parameter for asphalt concrete, describes the experimental techniques for utilizing the δ 25 parameter, and presents three-dimensional (3D) CZM simulations with a specially tailored cohesive relation. The integration of the δ 25 parameter and new cohesive model has provided further insight into the fracture process of asphalt concrete with relatively good agreement between experimental results and numerical simulations.

Rate- and Temperature-Dependent Fracture Characteristics of Asphaltic Paving Mixtures

“…At À10 C, the fracture energy from force-NTOD curves was about 30 % less than that from force-NMOD curves, whereas the level of deviation increased to 37 % at 0 C and up to 50 % at 21 C and 30 C depending on the loading rate. A similar finding was also observed in other studies [10,23]. This clearly indicates that, although it has been widely adopted because of its simple and practical aspects, the use of NMOD measurements in the fracture characterization of asphaltic materials needs great care and is even more cautious at elevated temperatures when the materials present several sources of energy dissipation, such as material viscoelasticity/plasticity and crack growth.…”

“…However, the true fracture properties of asphalt mixtures could be misled by as much as an order of magnitude because the material responses captured by the extensometers or clip-on gauges are limited to accurately represent material behavior at the actual FPZ. This discrepancy can become worse if the material is highly heterogeneous and inelastic [9,10], which is typical in asphaltic paving materials. In addition, most of the studies have adopted low-temperature testing conditions in which the type of fracture is much more brittle than it should be to accurately characterize fracture behavior such as fatigue cracking observed at intermediate service temperatures.…”

“…There were several methods [10,18,[23][24][25] found in the open literature to calculate the fracture energy. Among them, this study attempted two approaches: one is based on the concept of the critical energy release rate and the other is by modeling the SCB fracture tests with cohesive-zone elements.…”

“…However, such careful efforts to characterize the FPZ in asphalt concrete mixtures have not yet sufficiently been made. To the authors' best knowledge, only limited attempts [10][11][12][13] have been carried out because of many experimental-analytical complexities.…”

IlliTC – low-temperature cracking model for asphalt pavements

“…The relationship between displacement jump and traction capacity across crack can be defined by different geometric shapes. Various shapes have been proposed for use with asphalt concrete, such as bilinear (Song et al, 2006), power law (Song, Wagoner, Paulino, & Buttlar, 2008), and exponential (Dave & Buttlar, 2010).…”