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The propagation of hole machining defects in pin-loaded carbon/epoxy laminates subjected to uniaxial tension fatigue loading was investigated using two non-destructive examination (NDE) techniques. The KTH-method, a new method which gives defect-free1 holes, was used to machine holes in specimens. For comparison, holes were also machined using two traditional methods (DIXI and Dagger drills) causing varying extent of damage. X-ray radiography and computerised tomography were used to give two- and three-dimensional images, respectively, of defect propagation after 50,000-250,000-500,000-cycles, and after failure. Permanent hole elongation was monitored during cyclic loading. The results showed that the propagation of defects occurred in a controlled and stable phase until a sharp fatigue limit was reached (about 400,000 cycles for the DIXI specimen and about 500,000 cycles for both the KTH and Dagger specimens). During the stable phase, the global structural response of the specimens was affected very little by the damage propagation. At the fatigue limit, extensive damage development and defect propagation occurred, resulting in similar large permanent hole elongations in all specimens.

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The foundry industry is currently facing challenges to reduce the environmental impacts from application of fossil fuels. Replacing foundry coke with alternative renewable carbon sources can lead to significant decrease in fossil fuel consumption and fossil CO2 emission. The low bulk density, low energy density, low mechanical strength and the high reactivity of biocarbon materials are the main factors limiting their efficient implementation in a cupola furnace. The current study aimed at designing, optimizing and developing briquettes containing biocarbon, namely, biocarbon briquettes for an efficient use in cupola furnace. Laboratory hydraulic press with compaction pressure of about 160 MPa and stainless-steel moulds (Ø = 40 mm and 70 mm) were used for compaction. The density, heating value, energy density, mechanical strength and reactivity of biocarbon briquettes were measured and evaluated. The compressive strength and splitting tensile strength of biocarbon briquettes were measured by a compression device. The reactivity of biocarbon briquettes was measured under controlled conditions of temperature and gas atmosphere using the thermogravimetric analysis technique (TGA). Different types of binders were tested for the compaction of commercial charcoal fines with/without contribution of coke breeze. The effect of charcoal ratio, particle size, binder type, binder ratio, moisture content and compaction pressure on the quality of the biocarbon briquettes was investigated. Molasses with hydrated lime and cement were superior in enhancing the biocarbon briquettes strength and energy density among other tested binders and additives. The briquettes’ strength decreased as the biocarbon content increased. The optimum recipes consisted of 62% charcoal fines, 20% molasses, 10% hydrated lime and 8% cement. Cement is necessary to develop the tensile strength and hot mechanical strength of the briquettes. The charcoal with high ash content showed higher strength of briquettes but lower heating value compared to that with low ash content. Dispersion of silica suspension on charcoal particles during the mixing process was able to reduce the reactivity of biochar in the developed biocarbon briquettes. The biocarbon briquettes density and strength were increased by increasing the compaction pressure. Commercial powder hydrated lime was more effective in enhancing the briquettes’ strength compared to slaked burnt lime. Upscaling of biocarbon briquettes (Ø = 70 mm) and testing of hot mechanical strength under load indicated development of cracks which significantly reduced the strength of briquettes. Further development of biocarbon briquettes is needed to fulfil the requirements of a cupola furnace.

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