There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

The American Society for Testing and Materials (ASTM) is an independent organization devoted to the development of standards.

American Society for Testing and Materials

1. Introduction 2. The physical metallurgy of nickel and its alloys 3. Single crystal superalloys for blade applications 4. Superalloys for turbine disc applications 5. Environmental degradation: the role of coatings 6. Summary and future trends.

The Superalloys: Fundamentals and Applications

The natural initiation and growth of short cracks in Inconel®718 U-notch specimens has been studied at 600 °C in air. U notches were introduced through broaching, and hardness traces and optical microscopy on cross-sections through the U notch broaching showed that the broaching process had introduced a deformed, work hardened layer. Fatigue tests were conducted under load control using a 1-1-1-1 trapezoidal waveform, on specimens with as-broached and polished U-notches. Multi-site crack initiation occurred in the notch root. Many of the cracks initiated at bulge-like features formed by volume expansion of oxidising (Nb,Ti)C particles. In unstressed samples, oxidation of (Nb,Ti)C particles occurred readily, producing characteristic surface eruptions. Scanning electron microscopy on metallographic sections revealed some sub-surface (Nb,Ti)C oxidation and localised matrix deformation around oxidised particles. A mechanism for crack initiation by carbide expansion during oxidation is discussed. Surface short crack growth rates in the notch root of polished specimens were measured using an acetate replica technique. Observed short-crack growth rates were approximately constant across a wide range of crack lengths. However, there was a transition to rapid, accelerating crack growth once cracks reached several hundred micrometers in length. This rapid propagation in the latter stages of the fatigue life was assisted by crack coalescence. Polishing the U-notch to remove broaching marks resulted in a pronounced increase in fatigue life.

/pdf/short-crack-initiation-and-growth-at-600-c-in-notched-11ggpqvr68.pdf

Short crack initiation and growth at 600 °C in notched specimens of Inconel718

Tribological coatings with low coefficients of friction are in high demand by various industries since they can improve machine efficiency and have an environmental impact. A self-lubricating Ni-P-MoS2 composite coating has been successfully deposited on a mild steel substrate by electrodeposition. The effects of MoS2 on the tribological coatings have been investigated. Compared to a pure Ni-P coating, the Ni-P-MoS2 composite coating exhibited a dramatic reduction in friction coefficient against a bearing steel ball from 0.45 to 0.05. Examination and analysis of the worn surfaces and wear debris, the composite coating showed minimum wear and oxidation compared to the severe wear and oxidation observed in the pure Ni-P coating. The evolution of MoS2 particles in sliding wear has been elucidated.

/pdf/self-lubricating-ni-p-mos2-composite-coatings-1z6rlell6x.pdf

Self-lubricating Ni-P-MoS2 composite coatings

Fatigue crack initiation and short crack growth in nickel-base turbine disc alloys: the effects of microstructure and operating parameters

Synchrotron radiation computed tomography has been used to analyse fibre break accumulation in unidirectional composites loaded in tension. The data are compared to model predictions. The model only slightly overestimated the composite failure strain, but predictions of fibre break density were too high, which can be mainly attributed to errors in the Weibull distribution. Both the number and percentage of interacting fibre break clusters were under-predicted by the model. This was attributed to an underestimation of stress concentrations in the model. While the experimental observations revealed mainly co-planar clusters, the model predicted mainly diffuse clusters. The experiments showed that the clusters did grow any further after their formation, while the model predicted a gradual development. Both local and dynamic stress concentrations were hypothesised to be key features for further exploration. The discrepancies identified, inform suggestions for directions advancing the state-of-the-art strength models of UD composites.

/pdf/synchrotron-radiation-computed-tomography-for-experimental-3aw27j0ku1.pdf

Synchrotron radiation computed tomography for experimental validation of a tensile strength model for unidirectional fibre-reinforced composites

An assessment of the effects of microstructure on fatigue crack initiation and short crack growth in a turbine disc nickel-base superalloy at 650 °C in air is presented. U720Li and microstructural variants of U720Li, i.e. U720Li-LG (large grain variant) and U720Li-LP (large intragranular coherent γ′ precipitate variant) have been assessed by uninterrupted and replicated short crack tests in polished U-notch specimens using a 1-1-1-1 trapezoidal loading cycle at nominal stress levels ranging between 700 and 850 MPa (calculated in the uncracked ligament). Crack initiation was primarily due to porosity on or near the surface but also due to grain boundary oxidation. Initial transgranular crack growth across four to six grains in air was noted at short crack lengths before oxidation-assisted intergranular crack growth modes were established at larger crack lengths. At a nominal applied stress of 840 MPa, U720Li and U720Li-LP show similar fatigue lifetimes while U720Li-LG demonstrates a significantly improved fatigue lifetime, particularly when lifetimes are compared on a local strain range basis. A larger grain size gave the most significant performance benefits in terms of overall fatigue lifetime under these test conditions.

Philippa Reed

Papers

Short crack initiation and growth at 600 °C in notched specimens of Inconel718

Self-lubricating Ni-P-MoS2 composite coatings

Fatigue crack initiation and short crack growth in nickel-base turbine disc alloys: the effects of microstructure and operating parameters

Synchrotron radiation computed tomography for experimental validation of a tensile strength model for unidirectional fibre-reinforced composites

Microstructure effects on high temperature fatigue crack initiation and short crack growth in turbine disc nickel-base superalloy Udimet 720Li