This work examines the feasibility for estimating existing tensile stress on a stressed wire using the permeability of magnetic flux. A closed magnetic circuit has been constructed to induce magnetic flux inside a steel wire. With different tension stress levels on a wire, the permeability of magnetic flux on the wire has been measured. Two different experimental case studies have been conducted for the examination of sensitivity of permeability of magnetic flux on the stressed wire. One is a varying-length stress test, and the other is a fixed-length stress test. The results show that the permeability of magnetic flux in the varying-length stress test is inversely proportional to the applied stress, while the permeability in the fixed-length stress test is linearly proportional to the applied stress on the stressed wire. It is thus expected that the permeability of magnetic flux on a wire can be a promising indicator for the inspection of its tensile stress.

This study experimentally investigates the effects of applied stress level on the stress wave velocity of unbonded PSC tendon. A set of longitudinal impact-echo tests with respect to several applied prestress levels are conducted for both unbonded prestressed strand and steel wire. The comparison results show that the longitudinal stress wave velocity is linearly proportional to the applied stress level in the case both strand and steel wire. However, the sensitivity of the longitudinal stress wave velocity to the applied stress level is very low. Based on the result of nondimensional analysis, it is postulated that the stress wave velocity is also affected by the tensile strength level.