Microscopic Mechanical Analysis of Interface Deformation During Pull-Out of Single Polypropylene Fiber

To investigate the bonding mechanical properties between polypropylene fiber and concrete interface, this study analyzed the debonding process of the interface through single fiber pull-out microscopic mechanical experiments and numerical simulations. An in-situ scanning observation system was established using micro CT and a self-developed single fiber drawing device to observe the process of pulling out a single polypropylene fiber with indentation from the mortar matrix. The deformation fields of the interface between fiber and matrix was obtained with mechanically regularized global digital volume correlation, and the interface debonding was quantified by calculating the relative displacement of the shared nodes between the fiber and the matrix. A 3D microscopic numerical model reflecting the true shape of fibers and matrix was established based on CT images, and the single fiber drawing process was simulated and analyzed. The results show that the force-displacement curves display multi-peak fluctuations corresponding to the fiber geometry after the peak. The strain fields at interfaces measured by digital volume correlation and numerical simulation show a strain concentration phenomenon related to the geometric shape of the indentation fiber, indicating that the periodic indentation of the fiber increases mechanical interlocking and friction forces between the fiber and the matrix during pullout. The relative displacement at the interface is greatest and decreases along the fiber's axial direction. In the horizontal direction, the variation of relative displacement was correlated with the geometric shape of the fiber. The relative displacement in the vertical direction reflected that the fiber and matrix have completely debonded before the pullout force reaches the peak load.