Elevated thermal conditioning effect on flexural strength of GFRP laminates: An experimental and statistical approach

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This study aims to investigate the flexural strength and damage formation in glass fibre reinforced polymer (GFRP) laminates for different thicknesses (2, 3 and 4 mm), small span length variations (50.8 and 56 mm), crosshead speeds (1 and 10 mm/min), thermal conditioning duration (3 and 6 h) and thermal conditioning temperatures (27 °C (room temperature), 50 °C, 100 °C and 150 °C). A closed muffle furnace used for thermal conditioning of GFRP specimens. A quasi-static transverse load applied using four-point bend method. GFRP plates are translucent; hence high-intensity background light is used to observe the formed damage and its extent after four-point bend test. The most effectively influencing parameters among GFRP laminate thickness, span length, thermal conditioning temperature, thermal conditioning time and crosshead speeds on the flexure strength of GFRP plates analysed by adopting the two-parameter Weibull distribution statistical method. Flexural strength of the GFRP laminates severely degraded when the exposed elevated temperature approached the glass transition temperature (Tg) 100 °C. Exposure duration affected the flexural strength. GFRP composites exposed for 6 h showed comparatively better flexural strength regain than those GFRP specimens exposed for 3 h. GFRP laminate thickness showed a more significant influence on the flexural strength compared to small span length variation. GFRP laminate with 2 mm thickness showed highest flexural strength compared to 3 mm and 4 mm thick GFRP specimens while the span length 50.8 mm showed higher flexural strength compared to GFRP laminates with 56 mm span length. Crosshead speed also affected the flexural strength and GFRP specimens tested at 10 mm/min showed higher flexural strength compared to specimens tested at 1 mm/min. For specimens tested at room temperature the cumulative failure probability curves agglomerated at a single region in the graph. However, as the temperature and laminate thickness increased these curves dispersed over the entire graph. Experimental flexural strength showed good agreement with the theoretical flexural strength calculated from gamma function.