Abstract
Affected by physical properties of various components, characteristics and stress states of junction surface and other multiple factors, concrete, as a kind of multi-phase composite material, has complicated failure mechanism, thus making its fracture mechanism research difficult. But concrete has been widely used in engineering construction, so research on concrete fracture theory is of important realistic significance and construction value. This study discusses influence rule of specimen size and crack-depth ratio (?0/h) on doubleK fracture parameters (initial fracture toughness ini ICK and unstable fracture toughness un ICK ) and its size effects by using fracture test. Different sizes of concretes and roller compacted concrete (RCC) specimens are adopted to explore influence of specimen size on concrete double-K fracture parameters. Results reveal that initial fracture toughness ini ICK and unstable fracture toughness un ICK increase as specimen size enlarges, showing a size effect; besides, subcritical crack extends with the increase of specimen size. With regard to specimens with different crack-depth ratios, its unstable fracture toughness un ICK is unrelated to initial crack-depth ratio when crack-depth ratio is more than or equal to 0.4, while initial fracture toughness ini ICK is correlated with initial crack-depth ratio, which indicate that double-K fracture parameters can be considered as material constants describing concrete initial fracture, stable expansion and whole process of stability failure.
Highlights
As some problems may exist in part of specimen making and maintenance, here, the quantity of several effective specimens with good surface, basically complete trial curve, small deviation and calculative in double-K fracture parameter is listed in Tab. 3
I t is summarized from analysis of fracture test results of roller compacted concrete (RCC) and ordinary concrete wedge-splitting specimens that double-K fracture criterion may have some differences it is simple, practical and without human distractions
Change rules of unstable fracture toughness of ordinary concrete and RCC are basically the same, and crack-depth ratio plays a role in fracture toughness of ordinary concrete and RCC, but not identical
Summary
Two-parameter model considers actual crack in combination with micro-crack zone as an effective crack, obtains results using theory of linear elastic fracture mechanics and combines it with numerical computation method. Xu Shilang [3], a scholar from China, put forward a simple and applicable fracture criterion in 1999, namely, double-K fracture criterion. This criterion, belonging to the first type, corrects linear elastic fracture mechanics model based on a complete theory, and decides its fracture parameters with the help of simple test methods, which is expected to be popularized and applied in practical engineering. Two fracture parameters are introduced into this criterion, initial fracture toughness
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