Thermal loading of short fibre composites and the induction of residual shear stresses |
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| Affiliation: | 1. MATEIS, INSA Lyon, 69621, France;2. Université de Grenoble Alpes, F-38000 Grenoble, France;3. CNRS UMR 5266, SIMaP, F-38000 Grenoble, France;4. University of Applied Science, HS Karlsruhe, 76133 Karlsruhe, Germany;1. Institute of Engineering Mechanics, China Earthquake Administration, Key Laboratory of Earthquake Engineering and Engineering Vibration of China Earthquake Administration, China;2. School of Civil Engineering, Harbin Institute of Technology, China;3. College of Civil Engineering and Architecture, Harbin University of Science and Technology, China;1. Department of Chemical and Geological Sciences, University of Cagliari, Monserrato (CA), Italy;2. Department of Biomedical Sciences, Biochemistry Unit, University of Cagliari, Monserrato (CA), Italy;3. Department of Pharmacology, College of Medicine and Health Sciences, United Arab Emirates University, Al Ain, United Arab Emirates;4. Department of Biomedical Sciences, University of Ulster, Cromore Road, Coleraine BT52 1SA, Northern Ireland, United Kingdom;1. University of Missouri, E2416 Lafferre Hall, 416S 6th St, Columbia, MO, 65201, United States;2. Thai Nguyen University of Technology, Vietnam;3. Mechanical and Aerospace Engineering, University of Missouri, Columbia, MO, USA |
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| Abstract: | A study has been undertaken to identify the effect of thermal residual stresses on the stress transfer between a short fibre and resin using the photoelastic method. As expected, it was observed that fibre fracture occurred at a higher applied load for the fibre embedded in the thermally (80 °C) cured epoxy matrix than in the room-temperature-cured epoxy. Under plane polarised light bright birefringent patterns were observed in the hot-cured epoxy matrix around the fibre-ends prior to loading. These were not present in the room-temperature-cured epoxy, indicating that thermal residual stresses had been induced during thermal-curing. On loading, the birefringent patterns in the hot-cured matrix at the fibre-ends were almost extinguished but at a particular stress reappeared as a bright region, and increased in intensity on further loading.Using a phase-stepping polariscope, four images of the fibre-ends were captured simultaneously so that detailed contour maps of fringe order could be created. To examine the micromechanical response in the matrices at the interfaces the profile of interfacial shear stress at the fibre-ends was calculated. Under a given external load the shear stress at the interface in the hot-cured matrix was significantly lower than that in the cold-cured epoxy matrix. The thermal load which is applied to a resin on cooling from manufacture requires a shear stress at the interface to put the fibre into compression. At the fibre-ends a residual shear stress of opposite sign (to that induced mechanically) leads to extension of birefringent patterns on loading. |
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