In-situ nonlinear ultrasonic technique for monitoring damage in ultra-high performance fibre reinforced concrete (UHPFRC) during direct tensile test

Abstract

This paper aims to employ the nonlinear ultrasonic technique for the in-situ monitoring of Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) structures subject to tensile loads. The UHFPRC, characterized by specific mechanical properties of high compressive and tensile strength, provides the basis for this investigation. Particularly, the nonlinear parameter β of the nonlinear ultrasonic technique is extracted by formulating a theoretical model that accounts for the interaction of contacting rough surfaces under tensile loads. The experimental findings substantiate that β provides enhanced sensitivity and feasibility for evaluating crack conditions compared to the measurements obtained through conventional Linear Variable Differential Transformers (LVDT). Furthermore, this study explores the potential application of β to estimate tensile load condition by: i) establishing an estimation equation grounded in the relationship between tensile load and displacement (kN-mm); ii) incorporating β into this estimation equation to calculate the anticipated tensile load; and iii) comparing real and estimated tensile loads. The analysis outcomes reveal that estimated tensile loads are in good agreement with the actual loads. Although the estimation equation is based on the findings of this study, it underscores the potential applicability of β for estimating the load conditions in various structures.