Damage under progressive load–unload until failure was assessed for a new woven carbon fibre/flax fibre/epoxy hybrid composite via stiffness degradation D, permanent strain [Formula: see text], and crack density [Formula: see text]. Type A configuration had woven carbon fibres and unidirectional flax fibres (i.e. [0–90C2/0F12/0–90C2]), while Type B configuration had woven carbon fibres and ±45 ° obliquely angled flax fibres (i.e. [0–90C2/(±45)F6S/0–90C2]. Results were obtained for D in tension (Type A, 0.080; Type B, 0.089) and compression (Type A, 0.178; Type B, 0.207), [Formula: see text] in tension (Type A, 0.085%; Type B, 0.075%) and compression (Type A, 0.086%; Type B, 0.086%), and [Formula: see text] in tension (Type A, range = 0.12–1.06%; Type B, range = 0.6–1.43%) and compression (Type A, range = 0.65–1.20%; Type B, range = 1.05–2.20%). Failure involved flax fibre bundle cracks and interfacial cracks in the flax fibre/epoxy region.
This is the first study on the fatigue tensile performance of a novel hybrid composite made as Type A (i.e. woven carbon fibers plus unidirectional flax fibers [WC2/0F12/WC2]) or Type B (i.e. woven carbon fibers plus oblique flax fibers [WC2/(±45)F6S/WC2]) in epoxy resin. Composite plates were examined under constant strain amplitude using conventional fatigue tests and constant stress amplitude using thermographic stress analysis at 5 Hz cycling with a constant amplitude ratio of 0.1. For conventional fatigue, the max strain εmax versus cycles to failure Nf curve for Type A was log (Nf) = 9.7–588.2εmax, while for Type B it was log (Nf) = 14.9–1000εmax; neither material had a true endurance limit since curves never became horizontal. For thermographic stress analysis, high-cycle fatigue strength for Type A was 231.7 MPa (i.e. 56% of ultimate tensile stress σut), while for Type B it was 203.2 MPa (i.e. 60% of σut).
Heat enhancement and heat removal remain important topics in engineering. Furthermore, flow in a laminar regime can reduce the cost of cooling. In the present study, flow in mini channels in a rectangular cavity is investigated with water as a circulating fluid. The height of the channel in the cavity is varied and interaction of the free flow above the channel with flow through the channel has been investigated. It is shown that a combination of these two flows can provide the optimum heat removal at a Reynolds number of 750. This finding is valid if one ignores the friction effect to the wall. The best configuration is for an aspect ratio AR = 6. If the pressure drop is taken into consideration, then the performance evaluation criterion shows that the mini-channel with aspect ratio AR = 12 is the best configuration. Different correlations have been obtained between the Nusselt number, pressure drop, friction factor, performance evaluation criterion, and the Reynolds number and the height of the channels.
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