Integrated strain sensing in CFRP using piezoresistive carbon fiber sensors (CFS) is hindered by leakage currents and signal interference caused by laminate conductivity, while thermoset-compatible insulation concepts validated in tensile tests remain scarce. This work introduces an insulated carbon fiber sensor (iCFS) concept intended to provide an approximately linear strain-dependent resistance response in CFRP. The iCFS are fabricated by twisting and pretensioning 1 K carbon rovings, epoxy impregnation, dip coating, and four-wire contacting. Insulation quality is assessed in liquid gallium, and the sensors are embedded in autoclave-processed unidirectional (UD) CFRP and GFRP laminates and characterized by cyclic tensile tests using video-extensometer reference strains. Fully insulated iCFS retain >99.8% of their initial resistance in gallium. For three specimens per material system, five measurements of five load–unload cycles each were performed at target strains of 0.2% and 0.6%. A single fit was applied to each five-cycle measurement, yielding specimen-specific mean gauge factors of 1.64–2.12. In one exploratory increasing-load test per material system, a more pronounced nonlinear response emerged at approximately 0.7% strain in the investigated specimens. The results provide proof-of-concept evidence for electrical insulation and iCFS integration in UD CFRP for strain-sensitive resistance measurements under controlled room-temperature axial tensile loading.     «

Integrated strain sensing in CFRP using piezoresistive carbon fiber sensors (CFS) is hindered by leakage currents and signal interference caused by laminate conductivity, while thermoset-compatible insulation concepts validated in tensile tests remain scarce. This work introduces an insulated carbon fiber sensor (iCFS) concept intended to provide an approximately linear strain-dependent resistance response in CFRP. The iCFS are fabricated by twisting and pretensioning 1 K carbon rovings, epoxy i...     »