title: Preparation, microstructure and properties of Ti-6Al-4V rods by powder compact extrusion of powder mixture

authors: Yang, Fei

subjects: Extrusion

abstract: Ti-6Al-4V (wt%) alloy rods were prepared successfully using a low-cost method that combines mixing elemental and master alloy powders and powder compact extrusion. The microstructure and mechanical properties of the rods and the effects of extrusion temperature on them were investigated. The results showed that the microstructure and mechanical properties of the extruded rods were strongly affected by the extrusion temperature. With increasing extrusion temperature from 1200°C to 1300°C and keeping the powder compact holding time unchanged at 2 minutes, the fraction of undissolved V rich particles in the microstructure of the extruded rod decreased substantially to zero, the level of composition homogenization increased dramatically to the highest level, and the UTS and elongation of the extruded rods increased significantly from 886MPa and 1.2% to 1300MPa and 7.1%, respectively. The tensile properties of the Ti-6Al-4V alloy rods produced by powder compact extrusion of the powder mixture are comparable to those of Ti-6Al-4V alloy produced by ingot metallurgy and thermomechanical processing.

text: Preparation, microstructure and properties of Ti-6Al-4V rods by powder compact extrusion of powder mixture Ti-6Al-4V (wt%) alloy rods were prepared successfully using a low-cost method that combines mixing elemental and master alloy powders and powder compact extrusion. The microstructure and mechanical properties of the rods and the effects of extrusion temperature on them were investigated. The results showed that the microstructure and mechanical properties of the extruded rods were strongly affected by the extrusion temperature. With increasing extrusion temperature from 1200°C to 1300°C and keeping the powder compact holding time unchanged at 2 minutes, the fraction of undissolved V rich particles in the microstructure of the extruded rod decreased substantially to zero, the level of composition homogenization increased dramatically to the highest level, and the UTS and elongation of the extruded rods increased significantly from 886MPa and 1.2% to 1300MPa and 7.1%, respectively. The tensile properties of the Ti-6Al-4V alloy rods produced by powder compact extrusion of the powder mixture are comparable to those of Ti-6Al-4V alloy produced by ingot metallurgy and thermomechanical processing.

year: 2012

title: Kinematics of Usain Bolt’s maximal sprint velocity

authors: Čoh, Milan

subjects: Science & Technology

abstract: This study investigated the maximal sprint velocity kinematics of the fastest 100 m sprinter, Usain Bolt. Two high-speed video cameras recorded kinematics from 60 to 90 m during the men 100 m final at the IAAF World Challenge Zagreb 2011, Croatia. Despite a relatively slow reaction time (194 ms), Bolt won in 9.85 s (mean velocity:10.15 m/s). His fastest 20-m section velocity was 12.14 m/s, reached between 70 and 90 m, by 2.70-m long strides and 4.36 strides/s frequency. At the maximal velocity, his contact and flight times were 86 and 145 ms, respectively, and vertical ground reaction force generated equalled 4.2 times his body weight (3932 N). The braking and propulsion phase represented 37% and 63% of ground contact, respectively, with his centre of mass (CoM) exhibiting minor reductions in horizontal velocity (2.7%) and minimal vertical displacement (4.9 cm). Emerged Bolt’s maximal sprint velocity and international predominance from coordinated motor abilities, power generation capacities, and effective technique. This study confirms that his maximal velocity was achieved by means of relatively long strides, minimal braking phase, high vertical ground reaction force, and minimal vertical displacement of CoM. This study is the first in-depth biomechanical analysis of Bolt’s maximal sprinting velocity with the segmental reconstruction.

text: Kinematics of Usain Bolt’s maximal sprint velocity This study investigated the maximal sprint velocity kinematics of the fastest 100 m sprinter, Usain Bolt. Two high-speed video cameras recorded kinematics from 60 to 90 m during the men 100 m final at the IAAF World Challenge Zagreb 2011, Croatia. Despite a relatively slow reaction time (194 ms), Bolt won in 9.85 s (mean velocity:10.15 m/s). His fastest 20-m section velocity was 12.14 m/s, reached between 70 and 90 m, by 2.70-m long strides and 4.36 strides/s frequency. At the maximal velocity, his contact and flight times were 86 and 145 ms, respectively, and vertical ground reaction force generated equalled 4.2 times his body weight (3932 N). The braking and propulsion phase represented 37% and 63% of ground contact, respectively, with his centre of mass (CoM) exhibiting minor reductions in horizontal velocity (2.7%) and minimal vertical displacement (4.9 cm). Emerged Bolt’s maximal sprint velocity and international predominance from coordinated motor abilities, power generation capacities, and effective technique. This study confirms that his maximal velocity was achieved by means of relatively long strides, minimal braking phase, high vertical ground reaction force, and minimal vertical displacement of CoM. This study is the first in-depth biomechanical analysis of Bolt’s maximal sprinting velocity with the segmental reconstruction.

year: 2018

title: Mokena Hou and his wife Rina

authors: Hart, Philip

abstract: Mokena Hou had a distinguished whakapapa, but as nephew to Hou was subordinate to the latter’s son, Karauna Hou. He was born near the Te Aroha hot pools, and his future wife, Rina, who also had illustrious ancestors, including some Ngati Haua, was born in the same area. Both were affiliated to several hapu. After the Hauraki tribes fled from Ngapuhi in 1821, he would be present at the battle of Taumatawiwi in 1830 (though he did not fight) and participated in a later siege of the Ngati Haua pa at Matamata. During the 1830s and later, he mostly cultivated land and dug gum in the lower Waihou region and as well as cultivating at Te Aroha. 
 After living at Kaitawa before the Thames goldfield opened, nearby, in 1867, he moved to Te Aroha, where he would live continuously, warding off the ambitions of Ngati Haua. When the land court investigated the ownership of blocks of land in Hauraki, he sought to obtain as many interests as possible, not always successfully, and tried to get more than his fair share of both land and revenue. 
A devoted Anglican, he assisted the early missionaries to the Waihou region. Wanting peaceful relations with Pakeha, he assisted both the surveying and the settlement of the Aroha Block. When gold was discovered at Te Aroha in 1880, he assisted the prospectors, opened his land for mining and for a township, and invested in some claims, expecting and obtaining a good financial reward. He may have assisted in making the hot pools a public reserve, and certainly gave sections of land within the settlement for public and religious purposes. When he and his wife died a month apart, they were fondly remembered.

text: Mokena Hou and his wife Rina Mokena Hou had a distinguished whakapapa, but as nephew to Hou was subordinate to the latter’s son, Karauna Hou. He was born near the Te Aroha hot pools, and his future wife, Rina, who also had illustrious ancestors, including some Ngati Haua, was born in the same area. Both were affiliated to several hapu. After the Hauraki tribes fled from Ngapuhi in 1821, he would be present at the battle of Taumatawiwi in 1830 (though he did not fight) and participated in a later siege of the Ngati Haua pa at Matamata. During the 1830s and later, he mostly cultivated land and dug gum in the lower Waihou region and as well as cultivating at Te Aroha. 
 After living at Kaitawa before the Thames goldfield opened, nearby, in 1867, he moved to Te Aroha, where he would live continuously, warding off the ambitions of Ngati Haua. When the land court investigated the ownership of blocks of land in Hauraki, he sought to obtain as many interests as possible, not always successfully, and tried to get more than his fair share of both land and revenue. 
A devoted Anglican, he assisted the early missionaries to the Waihou region. Wanting peaceful relations with Pakeha, he assisted both the surveying and the settlement of the Aroha Block. When gold was discovered at Te Aroha in 1880, he assisted the prospectors, opened his land for mining and for a township, and invested in some claims, expecting and obtaining a good financial reward. He may have assisted in making the hot pools a public reserve, and certainly gave sections of land within the settlement for public and religious purposes. When he and his wife died a month apart, they were fondly remembered.

year: 2016