Effect of high-pressure cooling on life of SiAlON tools in machining of Inconel 718

High-pressure cooling has proven to be very effective when machining with carbide inserts. Longer tool life and improved chip breaking are among the most commonly mentioned advantages. Nevertheless, this cooling method has been reported to reduce the life of ceramic tools in machining of heat-resistant alloys. The main reason for that is said to be the accelerated notch wear. Therefore, in this study, SiAlON ceramic inserts with improved resistance to notching were tested in machining of Inconel?718 under high-pressure cooling. The results were compared to conventional cooling. It turned out that, while notch wear was still slightly increased when high-pressure cooling was applied, it was no longer critical for the tool life. Flank wear, on the other hand, was reduced, which led to significantly longer tool life. The variation of the tool life appeared to be slightly less and chip breaking was considerably improved. This shows that, when used properly, high-pressure cooling can help to increase the productivity in machining of heat-resistant alloys with ceramic tools.     

Pore structure of plain cement pastes hydrated at different temperatures

Concrete outside the laboratory cures at temperatures other than 20°C. This paper describes an investigation of the pore structure of plain cement pastes hydrated at 5°, 20°, and 50°C to reflect a range of temperatures encountered in practice. Parallel specimens of 0.50 water/cement ratio pastes were examined using mercury intrusion porosimetry and backscattered electron image analysis. Increases in curing temperature resulted in increased porosity, particularly for pores of radius 200–1000 as measured by mercury intrusion, or 2500–12,500 as measured in the backscattered electron images. The difference between the two results indicates the magnitude of the “ink bottle effect” inherent in the mercury intrusion technique. However, both methods suggest that elevated curing temperatures could have a deleterious effect on the durability of plain cement concretes.     

Literatur als Medium einer Kulturgeschichte der Mathematik

Throughout the ages writers have been concerned with contemporary problems. Their reflection became part of their literary works. By tracing and interpretating mathematical references in literature information can be obtained: on the attitude towards mathematics, on its prestige in society, its cultural recognition and its significance for education. This article analyses the implication of mathematics in some exemplary novels, essays and theoretical writings on literature of authors from the 17th to the 20th century.     

Benthic video image analysis facilitates monitoring of Dreissena populations across spatial scales

In contrast to marine systems where remote sensing methods in studies of benthic organisms have been widely used for decades, these methods have experienced limited use in studies of freshwater benthos due to the general lack of large epifauna. The situation has changed with the introduction of dreissenid bivalves capable of creating visible aggregations on lake bottoms into North American freshwaters in the 1980s and 1990s. The need for assessment of Dreissena densities prompted exploration of videography as a potentially cost-effective tool. We developed a novel sampling method that analyzes video recorded using a GoPro camera mounted to a benthic sled to estimate Dreissena coverage, density, and biomass over relatively large areas of the lake bed in the Laurentian Great Lakes compared to traditional sampling methods. Using this method, we compared quagga mussel coverage, density, and biomass estimates based on three replicate Ponar grabs vs. 500?m-long video transects across 43 stations sampled in Lake Michigan in 2015. Our results showed that analysis of images from video transects dramatically increased the bottom area surveyed compared to Ponar grabs and increased the precision of Dreissena density and biomass estimations at monitoring stations. By substantially increasing the ability to detect relatively small (<20%) changes between years within a particular station, this method could be a useful and cost-effective addition for monitoring Dreissena populations in the Great Lakes and other freshwater systems where they occur.     

Numerical Analysis of T-Bar Penetration in Soft Clay

The penetration resistance of a cylindrical T-bar penetrometer in soft clay is affected by features such as anisotropy, high strain rates, and gradual strain-softening during passage of the T-bar. In order to evaluate these effects, a detailed numerical study has been undertaken, comprising: (1) finite-element analysis; and (2) a strain path approach within the upper bound plasticity mechanism. These studies showed that the T-bar factor is relatively insensitive to the degree of strength anisotropy, provided the penetration resistance is normalized by the average shear strength. Strain rates were found to be six or seven orders of magnitude greater than typical laboratory testing rates, and about three orders of magnitude higher than in a standard vane test. However, the effect of high strain rates is partly compensated by remolding of the soil, where average strains of 400% are imposed on the soil. Charts are presented showing how the separate effects of high strain rates and partial softening may be combined to derive a T-bar factor for a given soil. The paper concludes with a discussion of the measurement of remolded shear strength using cyclic T-bar tests, and interpretation of the T-bar resistance in fully remolded soil.     

冷轧不同微量化学状态Al-Mn-Fe-Si铝合金的等温退火

通过3种不同热处理工艺使一种Al-Mn-Fe-Si合金获得了不同固溶液和不同尺寸及数量的弥散析出相,包括铸造态,一种富含高密度、细小、弥散相的状态,另外一种状态则仅有少量、相对粗大的弥散相。采用EBSD技术系统研究冷轧后退火过程中微观组织的演变以及初始组织状态对再结晶动力学、再结晶晶粒形貌和织构的影响。结果表明,再结晶动力学、最终微观组织和织构由加工条件和合金的初始组织和固溶度决定。高密度弥散析出相阻止形核,显著阻碍软化过程,最终得到粗大的狭长晶粒以及P和ND-rotated cube织构。在没有预先存在的细小、稠密的弥散相并且在退火过程中弥散相析出数量很少的时候则能更快完成再结晶并得到均匀、细小的等轴晶以及显著的立方织构。     

Through-process sensitivity analysis on the effect of process variables on strength in extruded Al-Mg-Si alloys

A concept of through-process modelling for studying the effect of process variables on the strength of extruded Al-Mg-Si alloys is presented. Five models are integrated to model casting, homogenisation, extrusion and ageing of the alloys. It is demonstrated that through-process modelling can be utilised to study isolated effects from variations in processing parameters along the value chain on the strength in the end product, which is usually difficult to obtain from experiments. In the present work it has been focused on strength after artificial ageing and the most critical parameters to follow were therefore the Mg and Si and whether these elements appear in solid solution or present in constituent phases. The as-cast and homogenised structures were predicted reasonably well by the models, and it was found that the casting parameters have a significant influence on the density of constituent particles. Chemical composition and cooling rate from extrusion temperature are the variables with the most prominent effect on the yield stress of extruded and aged sections.