Crack propagation of mixed mode I–II fracture in concrete under sustained loading

Abstract

To investigate the crack propagation behavior of mixed mode I-II fracture in concrete under sustained loading, creep tests were conducted on concrete beams with five mode mixity ratios. The sustained load was maintained at 90% of the peak load. The digital image correlation technique was employed to monitor the crack propagation process. The results indicated that crack propagation process exhibited the three-stage feature: decelerated, uniform, and accelerated stages. As the mode mixity ratio decreased, the uniform stage duration increased, thereby enhancing the fracture lifetime. The logarithm relationship between the fracture lifetime and constant crack propagation rate was established, and a lifetime prediction method was validated for mixed mode I-II fracture under sustained loading. Additionally, the crack mouth opening displacement corresponding to the transition between the uniform and accelerated stages was closed to that at the peak load under static loading. The load-crack mouth opening displacement curve of mode I fracture under static loading was the envelope for that under sustained loading. Under static loading, the crack evolution is predominantly driven by the applied load, with crack growth and crack mouth opening occurring simultaneously; whereas under sustained loading, the crack evolution is governed by the time-dependent deformation. Due to the viscoelasticity of concrete, the crack propagation is delayed, while cracks continued to open. Notably, crack propagation path of mixed mode I-II fracture under sustained loading aligned well with that under static loading. These findings provide valuable insights into the crack propagation of mixed mode I-II fracture in concrete under sustained loading.