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In this paper, the mechanical damage behavior is investigated based on the characteristic roughness on the surface and the orientation of superficial structures. The main goal is to explore the surface roughness on mechanically loaded copper conductors as a lifetime indicator. For this purpose, copper conductors are mechanically stressed in accordance with EN 50,396 and then examined metallographically and microscopically. The microstructure examination shows that the roughness is caused by material extrusion and cracks due to work hardening in the surface area. Using confocal microscopy, it is shown for the first time that significant formation of surface roughness takes place over the service life of copper conductors. The roughness increases monotonically, but not linearly with number of cycles, due to internal microstructural processes and can be divided into three sections. First inspections of the conductor surface over lifetime show a correlation between the intensity of structures orientated 45° to the loading direction and the roughness. This phenomenon, already known from microscopic slip lines, is thus also evident in macroscopic roughness formation and is well founded by the research theory on material extrusion along dislocation lines. In summary, a lifetime determination is possible based on its developing roughness which enables the utilization as a sensor element. Graphical abstract

In this paper, a methodical approach for the in-situ monitoring of the mechanical wear of electrical conductors is presented. The state of life can be assessed by means of the characteristic attenuation of an applied high-frequency alternating current. The advantages of this approach include its non-destructive nature and the applicability to installed and otherwise inaccessible conductors.

In this paper, the radio frequency (RF) behavior of mechanically stressed coaxial and for the first time also twisted-pair transmission lines is investigated over their service life. The main goal is to enable predictive maintenance for cables in moving applications and avoid preventive replacement. This also reduces the use of high-cost resources. For this purpose, stranded and solid-core variants of coaxial and twisted-pair type cables are mechanically loaded on the two-pulley apparatus according to EN 50396. Their RF transmission (S21) behavior is measured using a vector network analyzer and presented over bending cycles. For the first time, the phase response of mechanically loaded transmission lines is evaluated with respect to their service life. Two significant causes for the increasing attenuation and altered phase response are identified: breakage in foil screen and increasing surface roughness on the copper conductors. The identified causes are supported with literature evidence. Through measurements and theoretical calculations, it is proven that the phase is much more suitable for an assessment of the remaining service life than the amplitude. The findings can be used to implement a cable monitoring system in industrial environments which monitors the lines in-situ and reminds the user to replace them, whenever a certain wear-level is reached.

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