Fracture size effect and damage properties of quasi-brittle materials

Quasi-brittle materials cover a large range of materials used in industrial practice, such as concrete, rock, ceramic, and some polymer matrix composites. A characteristic feature of quasi-brittle materials is the nonlinear fracture and damage process before failure. To describe the implications of this nonlinear process, Bazant in 1984 introduced the size effect law and subsequently made it a powerful tool for solving the problems of quasi-brittle materials.; This dissertation deals with three different ramifications and extensions of the size effect law: (1) Experimental calibration of the size effect law for some important cases: (a) Pull-out tests were conducted on specimens of different sizes involving smooth steel bars embedded in concrete cubic blocks. Based on the size effect law, the test results made it possible to determine the interface-slip parameters in formulas derived by Bazant and Desmorat in 1994. (b) Two groups of fiber/matrix composite laminate specimens were tested to determine their nonlinear fracture characteristics. Laminate lay-ups ( (0/90{dollar}sb2rbracksb{lcub}s{rcub}{dollar} and (0/{dollar}pm45/90rbracksb{lcub}s{rcub}){dollar} show nonlinear fracture behavior and confirm applicability of the size effect law. (2) Analytical characterization of the size effect in a general situation: New results are obtained by introducing second-order term of the asymptotic series expansion of the size effect law. The main parameters of the size effect law are predicted in an analytical form. This leads to a new concept of the modulus of rupture and provides its dependence on structure size. Thus a more general form of size effect law is established and its relation to these special cases is determined. Experimental proof of the generalized size effect law is obtained by statistical analysis of test data. (3) Computational simulation of the dynamic fracture process and acoustic emissions in floating sea ice plates. A random distributed particle system is adopted to simulate the fracture process in a sea ice plate. A modified Farmer-Xie model for propagating sound sources is used to simulate the individual emissions. The synthesized acoustic pressure time histories exhibit similar characteristics as the measured acoustic records. A size effect is detected in simulated root-mean-square pressure histories.