Abstract
This paper investigates the mechanical performance and electrical resistivity of a structural adhesive epoxy enhanced using milled carbon fibre (MCF) as well as the bond performance of carbon fibre reinforced polymers (CFRP) and steel adhesively bonded joints using the enhanced epoxy. The epoxy was enhanced using such MCFs with different weight ratios of 1.5%, 3% and 5%. Tensile experiments were performed on the original and enhanced epoxy specimens according to ASTM D638. More ductile process failure was found for the epoxy after modification and significant improvements of E-modulus and tensile strength were evidenced when the MCF weight ratio was larger than 1.5%. Scanning electron microscopy (SEM) revealed that the failure mechanism of short MCFs pulled out from the epoxy matrix contributed to the enhancement of the mechanical performance of the epoxy. The electrical resistivity of the epoxy with MCF weight ratio of 5% was reduced by at least four orders of magnitude compared to the original epoxy, due to the conductive network formed by MCFs. Steel/CFRP double strap joints (with either CFRP sheets or CFRP laminates) were prepared using the enhanced epoxy and then tested in tension, however no obvious increase in joint stiffness or strength was observed.
Highlights
Steel structures are susceptible to corrosion and fatigue damages and there is an urgent need to repair and retrofit such deteriorated steel structures
The stress and strain curves of typical EP specimens with different weight ratios of milled carbon fibre are summarized in Figure 3, where the stress values were calculated using the measured loads divided by the sectional area at the failure position
These joints failed through the delamination of the carbon fibre sheet at the centre of the joints, regardless of the different milled carbon fibre (MCF) weight ratios used in the epoxy adhesive
Summary
Steel structures are susceptible to corrosion and fatigue damages and there is an urgent need to repair and retrofit such deteriorated steel structures. The use of adhesively bonded carbon fibre reinforced polymer (CFRP) composites in strengthening of steel structures may be an advantageous solution, because of the excellent mechanical properties of CFRP such as high strength to weight ratios (with an E-modulus of 240 GPa and nominal tensile strength of 3800 MPa) and excellent resistance to corrosion and fatigue. Recent studies indicated that combining FRP and steel in different configurations, such as adhesively bonding [3,4] and confining [5,6] may form a reliable load-carrying system and can be utilized in steel structure strengthening in a safe and economic manner. Investigations on enhancement of epoxy using chopped carbon fibres indicated an improvement of its toughness up to a fibre volume fraction of 36% [21], studies on the mechanical performance of modified epoxy using MCFs are limited. The electrical resistivity of the MCF modified epoxy was tested as a preliminary study for its potential application in health monitoring of a FRP/steel bonding system
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