Abstract
A comprehensive experimental study has been performed on the damage sensing capabilities of (a) carbon/glass fiber intraply hybrid composites under mode-I and mode-II loading conditions and (b) jute/flax fiber hybrid composites reinforced with carbon fibers under flexural loading. A novel conductive network capable of damage sensing is established by embedding multi-walled carbon nanotubes in the epoxy matrix for each study, while the jute/flax fiber composites also were reinforced with short carbon fibers by electro-flocking them to the laminates. The composites are then made using a vacuum infusion process. A four circumferential probe measuring technique is used to measure the electrical response under mechanical loading. A parametric study was performed to understand damage detection capabilities of intra-ply glass/carbon composites embedded with carbon nanotubes under mode-I and mode-II fracture. Novel modified four circumferential probes were employed on fracture test specimens to capture piezo-electrical response. The effect of three different laminate orientations (G-0-C-90, C-0-G-90, and G-45-C-45) on both mode-I and mode-II fracture initiation toughness and the electrical-fracture response were discussed. Glass fibers were found to have rougher fracture surfaces, which correlates well with the result of the largest GIC value of 308 J/m2 for the C-0-G-90 composites. When the glass fiber was in the direction of crack growth, the G-0-C-90 composite had the largest GIIC value of 541 J/m2. All three types of composites demonstrated different electrical response for mode-I and mode-II fracture loading conditions. Another parametric study was performed to investigate the electro-flexure response of conductive natural fiber hybrid laminate composites. The composites were composed of laminates of jute and flax fibers, and the composites were subjected to flexural loading for the electrical and bending response. Short carbon fibers were reinforced in-between the laminates using “wet flocking” technique. To measure the electrical response under flexural loading, a four-point circumferential probe method was used. A parametric study was conducted to investigate flexural performance and damage sensing by varying carbon fiber lengths (150 and 350 μm) and the carbon fiber densities (500, 1000, 1500, and 2000 fibers/mm2). The addition of carbon fibers decreased the flexural strength for most of the cases, the addition of carbon fibers reduced flexural strength in most cases, aside from composites of 150 μm carbon fibers and 2000 fibers/mm2 fiber density and composites of 350 μm carbon fibers and 1500 fibers/mm2. However, the carbon fibers increased the flexural strain at break for all composites of carbon fiber length of 150 μm. During the nonlinear deformation, the composites of carbon fiber length of 150 μm demonstrated a linear increase in resistance, however that of carbon fiber length of 350 μm showed increasing slope of resistance. Overall, the composites of carbon fiber length of 350 μm showed lower resistance change at break compared to that of carbon fiber length of 150 μm.