In order to study mode Ⅱ fracture properties of ultra-high performance concrete(UHPC),compressive tests were carried out on double-notched cube(DNC)specimens of UHPC with different ratios of notch depth to specimen width(a/W).The failure characteristics and crack propagation process of DNC specimens of UHPC were analyzed based on digital image correlation(DIC)technology,the modeⅡ fracture parameters of UHPC were obtained,and the fracture properties of UHPC at different a/W were evaluated.The test shows that the failure mode of the specimens is local partial shear failure along the tip of the notch,and the main cracks of specimens include diagonal crack and left and right vertical cracks.The load-displacement curve of the specimens show the phenomenon of two peaks loads which correspond to the moment when the diagonal crack and the vertical cracks are fully expanded.The opening displacement(COD)and slip displacement(CSD)of the diagonal and vertical cracks are approximately linear with the ligament height.With the increase of a/W,the crack initiation load decreases,the fracture toughness and fracture energy first increase and then decrease,the length and starting angle of the diagonal crack decrease,the COD at the notch tip of the diagonal crack decreases,and the C SD is basically unchanged.
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