Browsing by Subject "Size effect"
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Item Low-temperature fracture behavior of asphalt concrete in semi-circular bend test.(2012-06) Zegeye Teshale, EyoabAsphalt concrete mixtures behave as quasi-brittle materials at temperatures close to the glass transition of the component asphalt binder. A salient feature of structures that consists of quasi-brittle materials is that there exists an intricate size effect on the structural strength. The existence of such size effect is mainly attributed to the presence and the stable growth of a relatively large fracture process zone (FPZ) that develops ahead of the crack tip prior to failure (maximum load) of the structure. This inelastic region is characterized by non-linear material deformation and fracture energy dissipation that ultimately generate stress redistribution and govern the strain-softening of the material. Understanding this size effect is crucial for two purposes: a) extrapolation of small-scale laboratory testing results to full-scale design, and b) identification of material fracture properties. In this research work, laboratory experiments and numerical simulations were conducted to investigate the size effect of asphalt concrete tested in semi-circular bend (SCB) test at low temperature. Geometrically similar specimens of different sizes and with different notch lengths were tested. The experimental results were analyzed with the energetic-size effect theory, and were used to develop type I and II strength scaling laws, respectively, for the notchless and deep notched specimens. The validity of the scaling laws at large sizes was evaluated through finite element simulations of mode I crack growth in the SCB test. A cohesive zone model (CZM) was successfully calibrated by experimental data, and implemented to predict the nominal strength in large SCB specimens. The strengths predicted from the numerical models were in good agreement with the scaling laws' strength prediction. Based on the analyses of the strength scaling laws derived, important conclusions on the fracture behavior of asphalt concrete at low temperature, as well as size of FPZ were drawn.Item Size effect on fatigue crack growth of a quasibrittle material(2013-01) Manning, JonathanThe Paris-Erdogan law describes the rate of fatigue crack growth as a function of the amplitude of the applied stress intensity factor. This equation, however, does not include a dependence of the crack growth on the structure size, which has been observed experimentally for concrete. The size effect on the fatigue crack growth is derived based on two hypotheses: (1) the scaling of the critical energy dissipation for fatigue crack growth has the same form as that of fracture energy for monotonic loading; (2) the difference in transitional sizes between the fatigue and monotonic loading is purely due to the difference in the fracture process zone (FPZ) size. The size-dependent fatigue crack growth law is verified experimentally through size effect tests on Berea sandstone. Using digital image correlation, it is shown that the FPZ length is approximately 7 mm and 11 mm for monotonic and cyclic loading, respectively. Optimal fitting resulted in transitional sizes of 34 mm and 54 mm for monotonic loading and cyclic loading, respectively, which shows a proportional relationship between the FPZ length and the transitional size.Item Strength size effect in asphalt binders and mixtures at low temperature(2013-01) Cannone Falchetto, AugustoLow temperature cracking is the prevailing failure mode in asphalt pavements built in cold regions. This phenomenon manifests as a set of surface-initiated transverse cracks which can lead to further damage due to water penetration. Good strength properties of asphalt binders and asphalt mixtures are, therefore, critical for building durable pavements. The current testing methods used to characterize asphalt binder and mixture strength require the use of very expensive and sensitive testing devices and present limitations in the extrapolation of results from laboratory specimens to larger structures such as full scale pavements. In this thesis the strength size effect of asphalt materials is investigated with the aim of addressing the possibility of using a simple laboratory device, called Bending Beam Rheometer (BBR), for performing strength tests on small beam specimens of asphalt binders and asphalt mixtures. Using three-point bending experimental data and size effect theory for quasibrittle materials, the failure distribution of the Representative Volume Element (RVE) of asphalt binders and asphalt mixtures is evaluated, and a RVE substructure model for asphalt mixture is proposed to analyze the strength measurements obtained on small BBR beams. Forward and back calculation procedures are implemented to directly link the statistic parameters of failure distribution of one RVE to the mean size effect curve of structural strength and vice versa. The effect on strength of different cooling media used in BBR is also evaluated.