title: Effects of Gas Nitriding on Fatigue and Crack Initiation of Ti6Al4V produced by Selective Laser Melting

authors: Mukhtar, Aamir

subjects: Science & Technology

abstract: Selective laser melting (SLM) is an additive manufacturing technique which permits fabrication of three dimensional parts by selectively melting consecutive layers of metallic powder. This allows the production of parts with high geometrical complexity. Titanium alloy Ti-6Al-4V (Ti64) is widely used in industry due to its high strength-to-mass ratio, corrosion resistance and biocompatibility. SLM increases the application range of Ti64 because of its flexibility for prototyping any part and its low material waste. Nitriding is a diffusion-based thermo-chemical treatment for interstitial hardening of the surface of Ti64 alloy products. This study characterized the fatigue behaviour of SLM-produced Ti64 nitrided and annealed bars in as-built and machined surface conditions. The surface of the SLM-produced Ti64 parts after gas nitriding showed high values of micro-hardness up to 550 HV just below the surface. Fatigue testing was performed to assess the materials fatigue strength and fractographic imaging was used to examine fracture surface and nitride layer characteristics. Nitriding was found to reduce the fatigue strength of the samples to a similar level irrespective of being in the as-built or machined condition. The effect of nitriding on crack initiation and growth at various stress levels under fatigue loading was investigated.

text: Effects of Gas Nitriding on Fatigue and Crack Initiation of Ti6Al4V produced by Selective Laser Melting Selective laser melting (SLM) is an additive manufacturing technique which permits fabrication of three dimensional parts by selectively melting consecutive layers of metallic powder. This allows the production of parts with high geometrical complexity. Titanium alloy Ti-6Al-4V (Ti64) is widely used in industry due to its high strength-to-mass ratio, corrosion resistance and biocompatibility. SLM increases the application range of Ti64 because of its flexibility for prototyping any part and its low material waste. Nitriding is a diffusion-based thermo-chemical treatment for interstitial hardening of the surface of Ti64 alloy products. This study characterized the fatigue behaviour of SLM-produced Ti64 nitrided and annealed bars in as-built and machined surface conditions. The surface of the SLM-produced Ti64 parts after gas nitriding showed high values of micro-hardness up to 550 HV just below the surface. Fatigue testing was performed to assess the materials fatigue strength and fractographic imaging was used to examine fracture surface and nitride layer characteristics. Nitriding was found to reduce the fatigue strength of the samples to a similar level irrespective of being in the as-built or machined condition. The effect of nitriding on crack initiation and growth at various stress levels under fatigue loading was investigated.

year: 2019

title: Topical gradients in plant ecology

authors: Laughlin, Daniel C.

subjects: Community ecology

abstract: Plant ecology spans multiple levels of biological organization and spatio-temporal scales, and over four dozen plant ecology textbooks have been published since Warming's (1895) 'Oecology of Plants.' With increasing emphasis on specialization, students and teachers can feel paralyzed by the vast literature, and as such may lack an adequate appreciation of the history of the field. The objective of this study was to derive a comprehensive set of topics that are covered in plant ecology textbooks, and to ask (1) what are the most important topical gradients among textbooks, and (2) has the emphasis of topics changed over time? The NMS ordination determined that the first gradient represented a clear contrast in emphasis on physiological ecology versus community ecology. The second gradient represented a contrast in emphasis on abiotic environmental factors versus biotic factors. Negative interactions, growth, demography, gas exchange, mineral nutrition, stress, diversity, disturbance, herbivory, paleoecology, ecosystem ecology, pollution, and global change have increased in emphasis over time. The increasing reliance on data and the number of authors per textbook illustrates how the discipline has matured into a rigorous quantitative science that requires a diversity of specializations. These results can be used to inform the development of curricula within a single course or across several years of study, and to assist the development of new and revised textbooks. Plant ecologists need to be familiar with this core set of topics in addition to becoming an expert in a few of them.

text: Topical gradients in plant ecology Plant ecology spans multiple levels of biological organization and spatio-temporal scales, and over four dozen plant ecology textbooks have been published since Warming's (1895) 'Oecology of Plants.' With increasing emphasis on specialization, students and teachers can feel paralyzed by the vast literature, and as such may lack an adequate appreciation of the history of the field. The objective of this study was to derive a comprehensive set of topics that are covered in plant ecology textbooks, and to ask (1) what are the most important topical gradients among textbooks, and (2) has the emphasis of topics changed over time? The NMS ordination determined that the first gradient represented a clear contrast in emphasis on physiological ecology versus community ecology. The second gradient represented a contrast in emphasis on abiotic environmental factors versus biotic factors. Negative interactions, growth, demography, gas exchange, mineral nutrition, stress, diversity, disturbance, herbivory, paleoecology, ecosystem ecology, pollution, and global change have increased in emphasis over time. The increasing reliance on data and the number of authors per textbook illustrates how the discipline has matured into a rigorous quantitative science that requires a diversity of specializations. These results can be used to inform the development of curricula within a single course or across several years of study, and to assist the development of new and revised textbooks. Plant ecologists need to be familiar with this core set of topics in addition to becoming an expert in a few of them.

year: 2012

title: Te manemanerau a te kāwanatanga: A history of the confiscation of Tūhoe lands in the Bay of Plenty

authors: Melbourne, Sydney

subjects: Ngāi Tūhoe

abstract: This thesis endeavours to show that Tūhoe lands should never have been confiscated and that Tūhoe efforts to gain compensation have been totally unsuccessful to date. When certain lands within the confiscated district of the Bay of Plenty were returned to the tribes there, Tūhoe were not granted any. Furthermore, lands which actually belonged to Tūhoe were granted to other tribes.
Although the major focus is on issues specific to Tūhoe, these are viewed within the wider context of nineteenth century land acquisition in New Zealand. This study looks at Tūhoe historical claims to disputed lands included in the confiscation district of the Bay of Plenty. Chapter One traces the extent of Tūhoe territories within the confiscation district and describes how Tūhoe came to occupy them and the duration of their occupation. Information about these claims came from tribal oral sources and original manuscripts, as well as from more generally accessible sources.
The development of colonial expansion patterns is discussed in Chapter Two. The contention is that they were based on materialistic considerations and legal pretexts to justify the acquisition of Māori lands. Hostilities between Māori and Government in the Bay of Plenty are dealt with in Chapter Three. Particular attention is paid to the causes of the hostilities and the complex racial and political misunderstandings which contributed to the inevitability of war. As a result of these encounters, the New Zealand Settlements Act was imposed.
Chapter Four covers the implementation of its provisions through the Compensation Court. The failings of this Court and its commissioners and field officials are exposed.
Chapter Five examines the settlement of Tūhoe lands in Ōpouriao and Waimana, as well as the changing fortunes of some of the settlers who took advantage of the settlement scheme. After placing the experiences of Tūhoe people within the wider context of what had taken place in New Zealand, Chapter Six focuses on Tūhoe attempts to bring the wrongs they had suffered to the attention of Government. In retrospect these early Tūhoe attempts at redress show that much has to be learnt about presenting substantial submissions. It was obvious that much of what was known by the elders then, though recorded, was never used in evidence to support their petitions. Nonetheless, without the existence of these manuscripts, present attempts would not be possible.
Chapter Seven gives a basis for a proposed just settlement for the confiscation of Tūhoe lands. In order to provide a guide for monetary compensation, details of values of Tūhoe confiscated land have been sought from official records. Compensation for the denial of justice, the loss of human life, land and property, remain open for negotiation.
Finally, while certain conclusions can be and are drawn from these investigations, the end of the story remains unwritten. It will depend on the outcome of new Tūhoe attempts to gain redress from the appropriate statutory body.

text: Te manemanerau a te kāwanatanga: A history of the confiscation of Tūhoe lands in the Bay of Plenty This thesis endeavours to show that Tūhoe lands should never have been confiscated and that Tūhoe efforts to gain compensation have been totally unsuccessful to date. When certain lands within the confiscated district of the Bay of Plenty were returned to the tribes there, Tūhoe were not granted any. Furthermore, lands which actually belonged to Tūhoe were granted to other tribes.
Although the major focus is on issues specific to Tūhoe, these are viewed within the wider context of nineteenth century land acquisition in New Zealand. This study looks at Tūhoe historical claims to disputed lands included in the confiscation district of the Bay of Plenty. Chapter One traces the extent of Tūhoe territories within the confiscation district and describes how Tūhoe came to occupy them and the duration of their occupation. Information about these claims came from tribal oral sources and original manuscripts, as well as from more generally accessible sources.
The development of colonial expansion patterns is discussed in Chapter Two. The contention is that they were based on materialistic considerations and legal pretexts to justify the acquisition of Māori lands. Hostilities between Māori and Government in the Bay of Plenty are dealt with in Chapter Three. Particular attention is paid to the causes of the hostilities and the complex racial and political misunderstandings which contributed to the inevitability of war. As a result of these encounters, the New Zealand Settlements Act was imposed.
Chapter Four covers the implementation of its provisions through the Compensation Court. The failings of this Court and its commissioners and field officials are exposed.
Chapter Five examines the settlement of Tūhoe lands in Ōpouriao and Waimana, as well as the changing fortunes of some of the settlers who took advantage of the settlement scheme. After placing the experiences of Tūhoe people within the wider context of what had taken place in New Zealand, Chapter Six focuses on Tūhoe attempts to bring the wrongs they had suffered to the attention of Government. In retrospect these early Tūhoe attempts at redress show that much has to be learnt about presenting substantial submissions. It was obvious that much of what was known by the elders then, though recorded, was never used in evidence to support their petitions. Nonetheless, without the existence of these manuscripts, present attempts would not be possible.
Chapter Seven gives a basis for a proposed just settlement for the confiscation of Tūhoe lands. In order to provide a guide for monetary compensation, details of values of Tūhoe confiscated land have been sought from official records. Compensation for the denial of justice, the loss of human life, land and property, remain open for negotiation.
Finally, while certain conclusions can be and are drawn from these investigations, the end of the story remains unwritten. It will depend on the outcome of new Tūhoe attempts to gain redress from the appropriate statutory body.

year: 1987