While Asian monsoon (AM) changes have been clearly captured in Chinese speleothem oxygen isotope (δ18O) records, the lack of glacial-interglacial variability in the records remains puzzling. Here, we report speleothem δ18O records from three locations along the trajectory of the Indian summer monsoon (ISM), a major branch of the AM, and characterize AM rainfall over the past 180,000 years. We have found that the records close to the monsoon moisture source show large glacial-interglacial variability, which then decreases landward. These changes likely reflect a stronger oxygen isotope fractionation associated with progressive rainout of AM moisture during glacial periods, possibly due to a larger temperature gradient and suppressed plant transpiration. We term this effect, which counteracts the forcing of glacial boundary conditions, the moisture transport pathway effect.

A study was undertaken to investigate the wear characteristics of polycrystalline cubic boron nitride (PCBN) cutting tools and surface integrity during machining of STAVAX (specialised stainless steel) with and without coolant. Plastic deformation and formation of overtempered martensite and white layer (untempered martensite) were the dominant subsurface and surface defects. It was found that decreasing the hardness of the STAVAX from 55 HRC to 40 HRC could result in fracture on the flank face, leading to a deterioration of the surface finish. It was observed that low CBN content tools (60%CBN/40%TiN) exhibited greater fracture resistance than high CBN content tools (85%CBN/15%TiN, 90%CBN/10%Co). Although coolant could not bring about a reduction in the flank wear, it was effective in reducing the subsurface and surface defects, and in preventing chipping of the tool edge, leading to an improved surface finish. A superior surface finish (Ra<0.3 μm) was obtained with cutting fluid using a tool with a radius of 0.8 mm, depth of cut of 0.05 mm and feed rate of 0.05 mm/rev.

Ultra-precision machines are widely used to turn aspherical or spherical profiles on mould inserts for the injection moulding of optical lenses. During the turning of a profile on a stainless steel mould insert, the cutting speed reduces significantly to 0 as the cutting tool is fed towards the centre of the machined profile. This paper reports experiments carried out to study the wear of uncoated and PVD-coated carbide tools (carbide tool coated with 2000 alternate layers of AlN and TiN, each layer 1.5 nm and carbide tool coated with 0.5 lm TiN, 5.5 lm TiCN and 0.5 lm TiN) in the ultra-precision machining of STAVAX (modified AISI 420 stainless steel) at low speeds with and without lubricant. A sprayed mixture of compressed air, liquid paraffin oil and cyclomethicone was used as lubricant. Examination of the wear at the rake face of the tool suggests that during machining of the alloy with a hardness of 55 HRC without lubricant, the cutting edge is subjected to high compressive stress, resulting in fracture. Reducing the hardness of the alloy would therefore result in a lower stress acting on the cutting edge, thus rendering the tool less susceptible to fracture. Both the rake and the flank faces of the coated tools exhibited lower wear than the uncoated tools. This was due to the former tools possessing higher fracture resistance owing to the presence of the coating. The lubricant was effective in improving surface finish, preventing surface fracture and reducing flank wear.

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