Magnetic Stress Monitoring Using a Directional Potential Drop Technique

Abstract

An alternating current potential drop technique is presented that exploits anisotropic magnetostriction to monitor changes in applied stress in steel. The background to the technique is provided together with an ad hoc approximation that describes the sensitivity of the sensor to the underlying properties. A uniaxial loading experiment has been conducted on duplex and mild steel specimens showing that changes in stress are measureable. Saturation and hysteresis afflict the measurement, which, in addition to sensitivity to temperature and magnetisation, may undermine inversion. With the capabilities and limitations of the proposed technique introduced, guidance on possible suitable applications are given, concluding that use for monitoring the number and relative size of fatigue stress cycles may be a suitable and attractive opportunity.

A Quasi-DC Potential Drop Measurement System for Material Testing

“…Interested readers are referred to [45] for more information on the influence of elastic stresses on PD measurements. It is worth reemphasising the compromise in the selection of the measurement frequency.…”

Four-point transient potential drop measurements on metal plates

“…The resulting surface voltage is (10) which decays to zero for t → ∞ reflecting the fact that the current density tends to zero as the total current is distributed throughout the half-space. Note that we implicitly assume zero fields for t 0 and therefore omit the unit step function u(t) in the expressions for H and V.…”

“…Although (15) can be made accurate at short times by including enough summation terms, an exact expression for the thin-skin approximation is found by noting that the halfspace result in (10), with similar reasoning as in the previous section, can be used to write the four-point potential drop as…”

“…As a model for variation of material properties with depth the theory of four-point ACPD on a layered halfspace [8] has also been given. In other applications to NDE, Sposito et al used ACPD for measurement of material loss [9] and recently the application to stress monitoring by means of directional four-point probes was studied by Corcoran and Nagy [10].…”

Multisensor Inspection of Laser-Brazed Joints in the Automotive Industry

“…Current is injected with two excitation electrodes/contacts while two sensing instances are used to read current distribution modifications, forming a so-called four-point probe. Application examples include the inspection of electronic cabling [14] and connectors [15], monitoring cracks under fatigue loading [16][17][18][19], the estimation of geometrical dimensions as thickness [20] and weld nugget [21], and the mapping of local conductivity [22] and mechanical stress [23]. Provided an available access to the part conductive surface, CPD methods are a simple, reliable, and inexpensive NDT option.…”