This study aims to evaluate the effectiveness of Ultrasonic-assisted drilling (UAD) of Glass laminate aluminium reinforced epoxy (GLARE) at high cutting speeds (Spindle speeds: 3000–7500 rpm; feed rates 300–750 mm/min) by analysing the thrust force and hole quality metrics (surface roughness, hole size, and burr formations. The research also presents numerical modelling of FMLs under conventional and UAD regimes to predict thrust force using ABAQUS/SIMULIA. The thrust force and exit burrs were reduced by up to 40.83 % and 80 %, respectively. The surface roughness metrics (R_a and R_z) were slightly higher using UAD but remained within the desirable limits of surface roughness for machined aeronautical structures. The discrepancy between the simulation and experimental results was adequate and did not exceed 15 %. The current study shows that it is feasible to drill holes in GLARE using higher cutting parameters and maintain excellent hole quality, which means increased productivity and reduced costs.

GLARE laminates are multi-layered metal-composite materials created from bonding sheets of metallic alloys with carbon or glass fibre layers. The application of hybrid-conventional machining processes such as ultrasonic-assisted drilling (UAD) is becoming of great interest to the aerospace industry due to its capability in reducing the cutting forces and tool wear which are directly responsible for drilling-induced delamination. There is rich literature on the conventional drilling (CD) of GLARE, but no work reported using UAD process. This study will fill this gap and investigate the UAD of GLARE laminates using an indigenously developed UAD system. The influence of spindle speed and feed rate on thrust force and surface roughness metrics (R_a and R_z) were investigated under CD and UAD regimes. The quality of the borehole and damage mechanisms in the laminate constituents was examined using scanning electron microscopy (SEM). The contribution of the drilling parameters on the measured outputs was further evaluated using the analysis of variance (ANOVA) statistical analysis. It was found that UAD resulted in a significant reduction in thrust force by up to 65% while surface roughness metrics R_a and R_z were unaffected by the type of drilling process used. SEM analysis showed irregular and fuzzier surfaces in glass fibre layers in holes machined using UAD due to the longitudinal vibration of the tool.

In this study, the pore structure of alkali-activated fly ash (AAFA) pastes characterized by different techniques, including mercury intrusion porosimetry (MIP), nitrogen adsorption and image analysis (based on backscattered electron images), was evaluated and compared critically. The degree of reaction of fly ash in AAFA pastes was derived from image analysis. It was found that due to a significant “ink-bottle” effect, the pore diameter of capillary pores derived from MIP was two orders of magnitude smaller than the size determined by image analysis. MIP and nitrogen adsorption results showed different peaks corresponding to the gel pores of AAFA pastes. Based on the experimental results, image analysis is regarded as a reliable technique for the characterization of large pores (> 1 μm) in AAFA pastes. Nitrogen adsorption is more suitable to characterize small pores (< 0.1 μm) in AAFA than MIP, and MIP data should be carefully interpreted, preferably in combination with other characterization techniques.