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Study on crack propagation and damage evolution process of
concrete based on fractal dimension

1 2 1 2
YIN Yajuan ，REN Qingwen ，SHEN Lei ，HAN Yan
（1. College of Hydraulic Conservation and Hydropower Engineering，Hohai University，Nanjing 210098，China；
2. Department of Engineering Mechanics，Hohai University，Nanjing 210098，China）

Abstract： The cracks evolution during the cracking process of concrete materials shows randomness. The
concrete materials are nonlinearity of themselves and the external conditions are complex. These results in
largely difficult study on the dynamic evolution law of concrete cracks. To quantitatively study the evolution
process of cracks and damage of concrete under loading，the meso-concrete mechanics model is established
assuming that the concrete is a three-phase composite composed of aggregates， mortar， and the transition
zone between them. A new calculation method of damage variable is proposed based on the crack fractal di⁃
mension， and the uniaxial tensile mechanical behavior of multiple groups of concrete specimens is studied
in numerical simulation. The concrete damage crack distribution is characterized by fractal dimension. It
shows that the results of meso-simulated crack pattern are consistent with the experimental results. The
crack fractal dimension can better reflect the damage evolution process of concrete materials， and quantita⁃
tively describe the damage evolution characteristics of concrete materials. It finds the critical point of con⁃
crete materials from "uniform" damage to local failure. The stress-strain curve， the crack fractal dimension
curve， and the damage evolution curve from meso-simulation results are all less affected by the element
size. With the increase of aggregate gradation of concrete specimens， the aggregate particles and interface
decrease， the overall energy consumption decreases， and the peak stress and crack fractal dimension de⁃
crease. In addition，it is suggested that the mutation point of the crack fractal dimension-strain curve after
the stress peak point is the critical point of the concrete materials from the "uniform" damage distribution
stage to local failure stage，which is the boundary point of damage and fracture. The corresponding damage
value is about 0.8，which can be used as the damage threshold for the occurrence of concrete macroscopic
crack. These findings in this paper deepen the understanding of the failure mechanism of concrete.
Keywords：concrete；mesoscopic；crack propagation；damage evolution；fractal dimension；mutation point

（责任编辑：王冰伟）

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