title: Design approaches to supercapacitor based surge resistant UPS techniques

authors: Kularatna, Nihal

subjects: Inverters

abstract: Time constants of supercapacitors are in the range of 100mS to tens of seconds compared to the time durations of power line transients, which are usually within a few hundred microseconds. Therefore supercapacitors should withstand short duration surges with energy values specified in IEEE C62-41 series and IEC 61400-4-5 and similar standards. After experimentally confirming this useful property of supercapacitors, new topologies for supercapacitor based surge-resistant uninterruptible power supplies were developed. Paper summarizes the approach to developing suitable topologies for surge-resistant UPS systems based on supercapacitor energy circulation techniques, despite the lower continuous DC voltage ratings of commercial supercapacitors.

text: Design approaches to supercapacitor based surge resistant UPS techniques Time constants of supercapacitors are in the range of 100mS to tens of seconds compared to the time durations of power line transients, which are usually within a few hundred microseconds. Therefore supercapacitors should withstand short duration surges with energy values specified in IEEE C62-41 series and IEC 61400-4-5 and similar standards. After experimentally confirming this useful property of supercapacitors, new topologies for supercapacitor based surge-resistant uninterruptible power supplies were developed. Paper summarizes the approach to developing suitable topologies for surge-resistant UPS systems based on supercapacitor energy circulation techniques, despite the lower continuous DC voltage ratings of commercial supercapacitors.

year: 2011

title: Synthesis, microstructure and mechanical properties of bulk ultrafine grained Ti-47Al-2Cr (at%) alloy

authors: Nadakuduru, Vijay Navaratna

subjects: ultrafine grained

abstract: Hot isostatic pressing (HIP) and powder compact forging of Ti/Al/Cr composite powders of composition Ti-47Al-2Cr (at%) have been carried out to synthesize bulk ultrafine grained Ti-47Al-2Cr alloy. The Ti/Al/Cr composite powders were produced using high energy mechanical milling of elemental Ti, Al, Cr powders in a retsch planetary mill. The microstructure and mechanical properties of the bulk consolidated alloy produced using different processing techniques has been investigated. The mechanical properties of the alloy were studied in tension and compression both at room and elevated temperatures especially to know the formability of the material.

The bulk alloy samples produced by HIP for 2 hours at 1000 degrees C had porosity of approximately ~ 5%, indicating that the HIP time was not sufficient to close the pores. The microstructure mainly consisted of TiAl as the major phase and Ti(Al) and Ti3Al as minors, the unreacted Ti(Al) phase in the microstructure was mainly due to the initial powder condition, in which a small fraction of powder particles were rich in Ti. Tensile testing of the alloy samples was carried out at different temperatures. At room temperature the alloy was fairly brittle, without any plastic deformation, and had a fracture strength of ~ 100 MPa. At elevated temperatures the samples became ductile, as reflected by considerable amounts of tensile elongations at 800 degrees C and above. The maximum amount of elongation was found to be between 70 - 80% at 900 degrees C. The tensile yield strength at 800 degrees C was in the range of 84-90 MPa and decreased to 55-58 MPa with the testing temperature of the samples to 900 degrees C. In compression the alloy showed plastic yielding and yield strength of ~ 1.4 GPa at room temperature. Compression testing at 900 degrees C revealed that compressive deformations equivalent to a height reduction of 50% could be easily achieved without cracking. 

 Direct powder compact forging using canned powder compacts of the Ti/Al/Cr composite powder was successfully used to produce bulk consolidated Ti-47Al-2Cr alloy samples. It has been observed that the density of the bulk consolidated alloy sample after forging varied from the centre to the periphery. XRD analysis showed that the forged samples, consisted of TiAl (as major phase) along with Ti(Al) and Ti3.3Al phases. Mechanical testing of the samples showed that the samples exhibited brittle type of fracture both in tension and compression at room temperature and the fracture strength of the samples was in the range of 115 - 130 MPa in tension and 1.38-1.4 GPa in compression without any yielding. When being tested at 900 degrees C, the samples became very ductile showing yield strength in the range of 70-90 MPa and elongation to fracture between 80-165% in tension, and a yield strength of ~ 65 MPa and 50% deformation in compression was easily achievable.

 Nearly fully dense Ti-47-2Cr alloy samples with density of ~98% were produced by using HIP at 1000 degrees C for a duration of 3 hours. TEM observations revealed equiaxed grains with grain sizes in the range of 200-500 nm. The tensile testing of the alloy samples at different temperatures revealed that the brittle to ductile transition temperature of the alloy was in the range of 700 and 750 degrees C, similar to that reported from literatures. The alloy showed significantly higher strengths both at room and at elevated temperatures, due to the low level of porosity in the sample. Elongation of  95 - 117% at 750 degrees C  and 70-100% at 800 degrees C was observed.

The ultrafine grained Ti-47Al-2Cr alloy produced using a combination of mechanical milling and HIP/powder compact forging has demonstrated good formability at elevated temperatures leaving a large space for secondary processing to improve the quality of the material.

text: Synthesis, microstructure and mechanical properties of bulk ultrafine grained Ti-47Al-2Cr (at%) alloy Hot isostatic pressing (HIP) and powder compact forging of Ti/Al/Cr composite powders of composition Ti-47Al-2Cr (at%) have been carried out to synthesize bulk ultrafine grained Ti-47Al-2Cr alloy. The Ti/Al/Cr composite powders were produced using high energy mechanical milling of elemental Ti, Al, Cr powders in a retsch planetary mill. The microstructure and mechanical properties of the bulk consolidated alloy produced using different processing techniques has been investigated. The mechanical properties of the alloy were studied in tension and compression both at room and elevated temperatures especially to know the formability of the material.

The bulk alloy samples produced by HIP for 2 hours at 1000 degrees C had porosity of approximately ~ 5%, indicating that the HIP time was not sufficient to close the pores. The microstructure mainly consisted of TiAl as the major phase and Ti(Al) and Ti3Al as minors, the unreacted Ti(Al) phase in the microstructure was mainly due to the initial powder condition, in which a small fraction of powder particles were rich in Ti. Tensile testing of the alloy samples was carried out at different temperatures. At room temperature the alloy was fairly brittle, without any plastic deformation, and had a fracture strength of ~ 100 MPa. At elevated temperatures the samples became ductile, as reflected by considerable amounts of tensile elongations at 800 degrees C and above. The maximum amount of elongation was found to be between 70 - 80% at 900 degrees C. The tensile yield strength at 800 degrees C was in the range of 84-90 MPa and decreased to 55-58 MPa with the testing temperature of the samples to 900 degrees C. In compression the alloy showed plastic yielding and yield strength of ~ 1.4 GPa at room temperature. Compression testing at 900 degrees C revealed that compressive deformations equivalent to a height reduction of 50% could be easily achieved without cracking. 

 Direct powder compact forging using canned powder compacts of the Ti/Al/Cr composite powder was successfully used to produce bulk consolidated Ti-47Al-2Cr alloy samples. It has been observed that the density of the bulk consolidated alloy sample after forging varied from the centre to the periphery. XRD analysis showed that the forged samples, consisted of TiAl (as major phase) along with Ti(Al) and Ti3.3Al phases. Mechanical testing of the samples showed that the samples exhibited brittle type of fracture both in tension and compression at room temperature and the fracture strength of the samples was in the range of 115 - 130 MPa in tension and 1.38-1.4 GPa in compression without any yielding. When being tested at 900 degrees C, the samples became very ductile showing yield strength in the range of 70-90 MPa and elongation to fracture between 80-165% in tension, and a yield strength of ~ 65 MPa and 50% deformation in compression was easily achievable.

 Nearly fully dense Ti-47-2Cr alloy samples with density of ~98% were produced by using HIP at 1000 degrees C for a duration of 3 hours. TEM observations revealed equiaxed grains with grain sizes in the range of 200-500 nm. The tensile testing of the alloy samples at different temperatures revealed that the brittle to ductile transition temperature of the alloy was in the range of 700 and 750 degrees C, similar to that reported from literatures. The alloy showed significantly higher strengths both at room and at elevated temperatures, due to the low level of porosity in the sample. Elongation of  95 - 117% at 750 degrees C  and 70-100% at 800 degrees C was observed.

The ultrafine grained Ti-47Al-2Cr alloy produced using a combination of mechanical milling and HIP/powder compact forging has demonstrated good formability at elevated temperatures leaving a large space for secondary processing to improve the quality of the material.

year: 2009

title: The Struggle For Success: A Socio-Cultural Perspective on the French Marist Priests and their Māori Mission 1838-1867

authors: Harman, Sandy Angela

subjects: missionaries

abstract: The nineteenth-century Roman Catholic missionary endeavour in New Zealand had its origins in a society of priests from Lyon, known as the Marists. The Marists’ mission has been deemed a failure due to its ongoing financial problems, its reputation for having abandoned Māori adherents, and its less visible impact compared to the Anglican Mission. This thesis examines the challenges facing the pioneer Marist priests in New Zealand and asks the question: was the Mission indeed a failure? The answer lies in the correspondence of the French Marists themselves, a largely untapped historical source which contains a different view of early New Zealand contact and religious history from that of the Church Missionary Society (CMS) evangelists. ‘The Struggle for Success’ consists of three parts examining the Mission before, during and after the pioneer phase. The first describes the Marists’ early influences and religious formation in France, which serve to elucidate the missionaries’ raison d’être and provide an historical context for the Mission. It is also an important attempt at a prosopography of men whose early lives were barely documented, and whose connection with contemporaneous and historical France, and the Lyon area in particular, would greatly affect the missions in Oceania. The subsequent comparative mission history in Part Two highlights the difficulties and conflicts that affected the progress of the Marist Māori Mission in New Zealand compared with other Christian missions in Oceania, notably the CMS in New Zealand and the early Marists in Wallis, Futuna, Tonga and New Caledonia. It describes the factors leading to the alleged failure of the Marist Māori Mission and demonstrates that hardships and struggle were the common lot of pioneer missionaries in Oceania. But the Marists on the Māori Mission had the added obstacles of being Frenchmen in a British colony, ascetics surrounded by and dependent on commerce, and dutiful religious under the authority of overburdened bishops. Irish immigration into New Zealand distorted the original aims of the French Marist missionaries, and Māori politico-religious initiatives to combat the devastating impacts of British colonialism essentially quashed Marist hopes that Māori would become a decidedly Catholic people. Having considered the obstacles to success, the thesis discusses in Part Three how the pioneer Marists understood success and conversion. In retrospect, it is clear that the missionaries underestimated the tenacity of early Māori catechists, but the CMS in New Zealand and Marists throughout Oceania were equally insensible in this respect. Finally the thesis offers an assessment of the mission’s overall success taking into account the revival of the Marist Māori Mission in the late 1870s and its continuation into the twentieth century. The social, cultural and political complexities of missionary endeavour demand a less rigid evaluation of missions than has been previously offered; and success and failure are problematic terms for the pioneer Marist Māori Mission because evangelisation was and is a work in progress.

text: The Struggle For Success: A Socio-Cultural Perspective on the French Marist Priests and their Māori Mission 1838-1867 The nineteenth-century Roman Catholic missionary endeavour in New Zealand had its origins in a society of priests from Lyon, known as the Marists. The Marists’ mission has been deemed a failure due to its ongoing financial problems, its reputation for having abandoned Māori adherents, and its less visible impact compared to the Anglican Mission. This thesis examines the challenges facing the pioneer Marist priests in New Zealand and asks the question: was the Mission indeed a failure? The answer lies in the correspondence of the French Marists themselves, a largely untapped historical source which contains a different view of early New Zealand contact and religious history from that of the Church Missionary Society (CMS) evangelists. ‘The Struggle for Success’ consists of three parts examining the Mission before, during and after the pioneer phase. The first describes the Marists’ early influences and religious formation in France, which serve to elucidate the missionaries’ raison d’être and provide an historical context for the Mission. It is also an important attempt at a prosopography of men whose early lives were barely documented, and whose connection with contemporaneous and historical France, and the Lyon area in particular, would greatly affect the missions in Oceania. The subsequent comparative mission history in Part Two highlights the difficulties and conflicts that affected the progress of the Marist Māori Mission in New Zealand compared with other Christian missions in Oceania, notably the CMS in New Zealand and the early Marists in Wallis, Futuna, Tonga and New Caledonia. It describes the factors leading to the alleged failure of the Marist Māori Mission and demonstrates that hardships and struggle were the common lot of pioneer missionaries in Oceania. But the Marists on the Māori Mission had the added obstacles of being Frenchmen in a British colony, ascetics surrounded by and dependent on commerce, and dutiful religious under the authority of overburdened bishops. Irish immigration into New Zealand distorted the original aims of the French Marist missionaries, and Māori politico-religious initiatives to combat the devastating impacts of British colonialism essentially quashed Marist hopes that Māori would become a decidedly Catholic people. Having considered the obstacles to success, the thesis discusses in Part Three how the pioneer Marists understood success and conversion. In retrospect, it is clear that the missionaries underestimated the tenacity of early Māori catechists, but the CMS in New Zealand and Marists throughout Oceania were equally insensible in this respect. Finally the thesis offers an assessment of the mission’s overall success taking into account the revival of the Marist Māori Mission in the late 1870s and its continuation into the twentieth century. The social, cultural and political complexities of missionary endeavour demand a less rigid evaluation of missions than has been previously offered; and success and failure are problematic terms for the pioneer Marist Māori Mission because evangelisation was and is a work in progress.

year: 2010