title: Modeling and simulation of the dynamic process in high energy ball milling of metal powders

authors: Wang, Wei

abstract: Mechanical alloying/mechanical grounding by using high-energy ball milling has been considered as a promising materials processing technique to synthesize materials. In this study, modeling simulation has been carried out to investigate the impacts, which are basic events in milling, as well as the milling dynamics in order to control and optimize this process. 

A 3-dimensional model has been developed to simulate the head-on impact process between two balls or between a ball and the vial wall with powder in between by considering the elastic deformation of impact objects, and the visco-plastic flow and elastic deformation of the powder compact. The comparison between the experimental results published in literature and the simulation outcome demonstrates that this model is the best to simulate the head-on impact process, which involves powder. Application of the model in high-energy ball milling shows that the ball-ball and ball-wall impacts do have some difference. It was also observed that the ball size, impact velocity and powder thickness all affect the impact pressure, and that the deformation of balls is substantial comparing to the powder thickness involved in an impact. 

3-dimensional models have also been developed to simulate the movement of balls considering the effects of powder, ball spinning and oblique impact of balls. The multi-ball impacts, which have been proved to occupy a substantial fraction among impacts, were also considered. Having realised the importance of knowing the volume of the powder involved in each impact, a model was also developed to estimate this volume. The prediction of the weight of powder involved in each impact made based on this model was in good agreement with the observation reported. 

A 3-dimensional global model has been developed for the SPEX-8000 Mixer/Mill based on the mechanics of the machine. By using this model, the motion of the vial was numerically determined. Then the global model was coupled with the models for the impacts in order to predict the dynamics of milling process. The simulation results revealed that the movement of balls after milling starts can be separated into two stages. The first stage is the unstable stage, which lasts for less than 0.3 second and involves mostly rolling and slipping of balls on the vial wall. The second stage is the stable stage, when the impact frequency, the mean impact velocity and mean spinning velocity of balls do not change significantly over time. Numerical experiments indicate that the frequency of impacts between balls and the vial wall is linearly proportional to the number of balls and the frequency of impacts between balls is nearly proportional to the square of the number of balls and the square of radius of balls. It is also shown that the majority of the impacts occur at low velocities of less than 4 m/s and with impact angles in the range of 15∼75°. The prediction of the impact frequency and impact angle distribution made from the simulation agrees well with the probability analysis. 

An effective model has been developed for the first time to calculate the time needed for mechanical milling based on probability analysis. This model can be used once the effective impact frequency and the fraction of powder effectively mechanically milled powder are known. The latter can be achieved through modeling. The milling efficiency corresponding to various ball numbers and sizes have been evaluated. The results show that there is an optimum number for the best milling efficiency for a given size of balls. 

Global models for the milling process in a planetary mill and an attritor mill have also been developed. Preliminary simulation experiments have been conducted.

text: Modeling and simulation of the dynamic process in high energy ball milling of metal powders Mechanical alloying/mechanical grounding by using high-energy ball milling has been considered as a promising materials processing technique to synthesize materials. In this study, modeling simulation has been carried out to investigate the impacts, which are basic events in milling, as well as the milling dynamics in order to control and optimize this process. 

A 3-dimensional model has been developed to simulate the head-on impact process between two balls or between a ball and the vial wall with powder in between by considering the elastic deformation of impact objects, and the visco-plastic flow and elastic deformation of the powder compact. The comparison between the experimental results published in literature and the simulation outcome demonstrates that this model is the best to simulate the head-on impact process, which involves powder. Application of the model in high-energy ball milling shows that the ball-ball and ball-wall impacts do have some difference. It was also observed that the ball size, impact velocity and powder thickness all affect the impact pressure, and that the deformation of balls is substantial comparing to the powder thickness involved in an impact. 

3-dimensional models have also been developed to simulate the movement of balls considering the effects of powder, ball spinning and oblique impact of balls. The multi-ball impacts, which have been proved to occupy a substantial fraction among impacts, were also considered. Having realised the importance of knowing the volume of the powder involved in each impact, a model was also developed to estimate this volume. The prediction of the weight of powder involved in each impact made based on this model was in good agreement with the observation reported. 

A 3-dimensional global model has been developed for the SPEX-8000 Mixer/Mill based on the mechanics of the machine. By using this model, the motion of the vial was numerically determined. Then the global model was coupled with the models for the impacts in order to predict the dynamics of milling process. The simulation results revealed that the movement of balls after milling starts can be separated into two stages. The first stage is the unstable stage, which lasts for less than 0.3 second and involves mostly rolling and slipping of balls on the vial wall. The second stage is the stable stage, when the impact frequency, the mean impact velocity and mean spinning velocity of balls do not change significantly over time. Numerical experiments indicate that the frequency of impacts between balls and the vial wall is linearly proportional to the number of balls and the frequency of impacts between balls is nearly proportional to the square of the number of balls and the square of radius of balls. It is also shown that the majority of the impacts occur at low velocities of less than 4 m/s and with impact angles in the range of 15∼75°. The prediction of the impact frequency and impact angle distribution made from the simulation agrees well with the probability analysis. 

An effective model has been developed for the first time to calculate the time needed for mechanical milling based on probability analysis. This model can be used once the effective impact frequency and the fraction of powder effectively mechanically milled powder are known. The latter can be achieved through modeling. The milling efficiency corresponding to various ball numbers and sizes have been evaluated. The results show that there is an optimum number for the best milling efficiency for a given size of balls. 

Global models for the milling process in a planetary mill and an attritor mill have also been developed. Preliminary simulation experiments have been conducted.

year: 2000

title: Climate swings and roundabouts – paleoclimatic fluctuations across Zealandia. Publication date 01 Nov 2015]

authors: Lowe, David J.

abstract: Zealandia’s sedimentary deposits, rocks and their fossil record provide an outstanding archive of mid-latitude climate change for the past 66 million years, including details of the c. 50 major, worldwide, glacial–interglacial cycles that occurred during Quaternary time (the past 2.6 million years).

text: Climate swings and roundabouts – paleoclimatic fluctuations across Zealandia. Publication date 01 Nov 2015] Zealandia’s sedimentary deposits, rocks and their fossil record provide an outstanding archive of mid-latitude climate change for the past 66 million years, including details of the c. 50 major, worldwide, glacial–interglacial cycles that occurred during Quaternary time (the past 2.6 million years).

year: 2015

title: Reclaiming the Māori language for future generations: Flax root perspectives. Tīkina te mana o te reo Māori: Te pūtaketanga o te pā harakeke

authors: Peters, Murray Hamaka

subjects: te reo Māori

abstract: Using a combination of semi-structured interviews, focus group discussion and questionnaires (designed to elicit as many comments as possible), this thesis explores, through their own voices, the attitudes and practices of a group of people, mainly Māori but including a few Pākehā (non-Māori) who are attempting to reclaim te reo Māori (the Māori language), for themselves, their families and, above all, their children and grandchildren. Many of them were brought up in a context in which one or more parents, caregivers or relatives spoke te reo Māori fluently but few were given the opportunity to acquire the language naturally in infancy, generally because of a desire to protect them from the discrimination suffered by their elders. Those who were brought up to speak te reo Māori often suffered from language attrition at a time when the English language began to feature prominently in their lives. A few have attended kōhanga reo and kura kaupapa Māori. Many have attended courses in the Māori language and culture, often at considerable personal cost. Some have achieved their dream of becoming fluent speakers of the language; some have suffered frustration and disappointment. Whatever their own experiences, almost all of them want their children and grandchildren to be fluent speakers of the language, believing that this will give them confidence and a genuine sense of identity and belonging. Although the majority are committed to using te reo Māori as much as possible at home, especially when speaking to their children and grandchildren, most experience difficulties in doing so. These difficulties relate, in general, to their own lack of confidence and/or limited competence in the language, the fact that some of their friends and/or members of their immediate or extended family are monolingual in English, and resistance from some of the children, particularly as they grow older and are increasingly influenced by the dominant language and culture. Among those involved in this research project, there was widespread awareness of the importance of inter-generational transmission of te reo Māori and evidence of considerable commitment to learning the language and/or improving their existing competence in it. However, although the attempts of these adults to use te reo Māori in the home are clearly of considerable importance, they often, where they lacked a high level of oral proficiency, met with confusion, frustration, tension and resistance as their children grew older. This, combined with the fact that there are currently so few domains in society at large in which the language can be used naturally, has led many of them to develop strategies aimed at ensuring that their children and grandchildren, as they grow towards adulthood (a) appreciate the sacrifices made by so many in order to give them the opportunity to learn the language and the responsibilities associated with these sacrifices, (b) are recognised and rewarded for their linguistic achievements, and (c) are encouraged and assisted to involve themselves in contexts where they can use the language. This includes encouraging them to become involved in kapa haka and other culturally significant activities in which the language plays a prominent part, promoting as much engagement as possible with friends and whānau who have a high level of proficiency in the language (including involving them and their friends in marae-based activities), and inviting into their homes people who are fluent speakers (which sometimes involves a conscious effort on the part of the adults to cement friendships with fluent speakers and to encourage them to interact with their children). These are things which all parents and caregivers can do, irrespective of their own language competence. 

In doing these things, those who currently feel that they have little to offer in relation to the revitalization of the language can experience a genuine sense of involvement and empowerment. Accepting that there are currently many parents and caregivers who cannot realistically become involved in genuine inter-generational transmission of the language in the home does not mean accepting that they have nothing to offer. 

Mā te kōwhiringa o ngā uiuitanga hangā ngāwari, te whiriwhiri ā rōpū kanohi, me te puka patapātai (hei tōngia mai ngā kōrero whānui kē atu o tēnā, o tēnā), ka whakatewhatewha te tuhinga nei i ngā waiaro me ngā ritenga o tētehi rōpū e ngana ana ki te haumanu i te reo Māori hei taonga mō rātou ko ō rātou whānau, ā, mō ā rātou tamariki, mokopuna hoki. Te nuinga o te hunga nei he Māori; he tokoiti anō he Pākehā. He tokomaha o rātou i tipu ake i roto i te horopaki o te reo Māori, arā, kotahi neke atu o ō rātou mātua rānei, kaitiaki rānei, whanaunga rānei he matatau ki te reo Māori. Ahakoa rā, kāore te nuinga i whāngaihia ki te reo i ā rātou e pēpi ana, kei whakapai kanohitia pērā i ō rātou tūpuna. Ko rātou te hunga i tipu reo Māori mai, ka memeha haere tō rātou reo nō te tino putanga ake o te reo Pākehā ki ō rātou ao. He tokoiti o tēnei rōpu i kuraina ki te kōhanga reo me te kura kaupapa Māori; he tokomaha anō i whai wāhi ki ngā akoranga reo Māori me ōna tikanga, hāunga rā te nui o te nama. Ko ētehi, kua ea ngā wawata, kua matatau ki te reo; ko ētehi atu anō, kua pāngia kētia e te hōhā me te hēmanawatanga. Heoi, ahakoa ngā wheako ake o tēnā, o tēnā, he hiahia nō te nuinga kia matatau ā rātou tamariki me ā rātou mokopuna ki te reo, kia tū pakari ai, kia tū Māori ai ki tēnei ao. Te nuinga o tēnei rōpū he manawanui ki te kōrero Māori i te kāinga i te nuinga o te wā, koia anō rā i ā rātou e kōrero ana ki ā rātou tamariki me ā rātou mokopuna. Heoi anō, kei reira anō ngā papatoieketanga, e pā ana ki ō rātou ake tītengi rānei, ki te takarepatanga o tō rātou reo rānei, me te mōhio anō ko ētahi o ō rātou hoa, whānau, whānau whānui anō hoki, he reo tahi kē, arā, ko te reo Pākehā te reo kawe. Anō hoki, ko ētahi o ngā tamariki, i ā rātou e pakeke haere ana ka kaha papare i te reo Māori, ka whakawaia kētia rātou e te reo Pākehā me ōna tikanga. I waenganui i te hunga i whai wāhi ki tēnei kaupapa rangahau kua kitea he mārama pū te nuinga ki te tino hiranga o te tuku ihotanga o te reo; kua kitea hoki tō rātou kaingākau nui ki te ako i te reo, ki te whakapakari rānei i tō rātou reo. Hāunga tērā, me ō rātou ngana anō ki te kawe i te reo Māori i te kāinga, ko ngā mātua kāore anō kia tino eke te reo ā-waha ka mate i te pōraruraru, te pōkaikaha, te āwangawanga, me te kaha papare a ngā tamariki e pakeke haere ana. Nā runga i tērā, me te take anō hoki he ruarua noa iho ngā wāhi o te hapori whānui i ēnei rā kia taea te reo Māori te rere noa, kua whakapuāwaitia e te tokomaha o tēnei rōpū ētahi rautaki hei ārahi i ngā tamariki me ngā mokopuna i ā rātou e pakeke haere ana, kia mārama rātou ki ngā whakahere tinana a te marea kia whai wāhi ai rātou ki te ako i te reo, me ngā here e haere kōtui ana ki ērā āhuatanga, kia whakanuia, kia utua hoki ngā tamariki i runga anō i ngā whakatutukitanga reo, kia manaakitia hoki rātou ki te whai wāhi anō ki ngā horopaki reo Māori. Hei konei ka ākina rātou ki te uru ki ngā kapa haka me ngā tino kaupapa anō o te ao Māori e whakatairanga nei i te reo. Anō hoki, ka whakahauhautia kia piritata ki ā rātou hoa me ō rātou whanaunga e tino mōhio ki te reo, me te whakauru hoki ki ngā mahinga marae. Waihoki, ka pōwhiritia te hunga matatau ki te reo ki te toro mai ki ō rātou kāinga (nā reira, me whakapau kaha anō ngā mātua ki te whakahoahoa, ki te patipati, ērā tāngata kia whakaae mai ki te noho ki te taha o ngā tamariki whakaputa kōrero ai). Koinei ngā mea ka taea ai e ngā mātua katoa, e ngā kaitiaki katoa, ahakoa kei hea te tohungatanga o tō rātou reo.  Mā reira, ka whai wāhi tonu, ka whakamanahia tonu tēnei hunga e pōhēhē nei pea he iti noa iho tā rātou hei koha atu ki te whakarauoratanga o te reo. Nō reira, hāunga rā te whakaaro he nui ngā mātua me ngā kaitiaki tamariki i tēnei wā e kore e tino whai wāhi ki te tukunga iho o te reo i te kāinga, ehara i te mea he kore noa iho tā rātou hei koha atu ki tēnei kaupapa whakahirahira.

text: Reclaiming the Māori language for future generations: Flax root perspectives. Tīkina te mana o te reo Māori: Te pūtaketanga o te pā harakeke Using a combination of semi-structured interviews, focus group discussion and questionnaires (designed to elicit as many comments as possible), this thesis explores, through their own voices, the attitudes and practices of a group of people, mainly Māori but including a few Pākehā (non-Māori) who are attempting to reclaim te reo Māori (the Māori language), for themselves, their families and, above all, their children and grandchildren. Many of them were brought up in a context in which one or more parents, caregivers or relatives spoke te reo Māori fluently but few were given the opportunity to acquire the language naturally in infancy, generally because of a desire to protect them from the discrimination suffered by their elders. Those who were brought up to speak te reo Māori often suffered from language attrition at a time when the English language began to feature prominently in their lives. A few have attended kōhanga reo and kura kaupapa Māori. Many have attended courses in the Māori language and culture, often at considerable personal cost. Some have achieved their dream of becoming fluent speakers of the language; some have suffered frustration and disappointment. Whatever their own experiences, almost all of them want their children and grandchildren to be fluent speakers of the language, believing that this will give them confidence and a genuine sense of identity and belonging. Although the majority are committed to using te reo Māori as much as possible at home, especially when speaking to their children and grandchildren, most experience difficulties in doing so. These difficulties relate, in general, to their own lack of confidence and/or limited competence in the language, the fact that some of their friends and/or members of their immediate or extended family are monolingual in English, and resistance from some of the children, particularly as they grow older and are increasingly influenced by the dominant language and culture. Among those involved in this research project, there was widespread awareness of the importance of inter-generational transmission of te reo Māori and evidence of considerable commitment to learning the language and/or improving their existing competence in it. However, although the attempts of these adults to use te reo Māori in the home are clearly of considerable importance, they often, where they lacked a high level of oral proficiency, met with confusion, frustration, tension and resistance as their children grew older. This, combined with the fact that there are currently so few domains in society at large in which the language can be used naturally, has led many of them to develop strategies aimed at ensuring that their children and grandchildren, as they grow towards adulthood (a) appreciate the sacrifices made by so many in order to give them the opportunity to learn the language and the responsibilities associated with these sacrifices, (b) are recognised and rewarded for their linguistic achievements, and (c) are encouraged and assisted to involve themselves in contexts where they can use the language. This includes encouraging them to become involved in kapa haka and other culturally significant activities in which the language plays a prominent part, promoting as much engagement as possible with friends and whānau who have a high level of proficiency in the language (including involving them and their friends in marae-based activities), and inviting into their homes people who are fluent speakers (which sometimes involves a conscious effort on the part of the adults to cement friendships with fluent speakers and to encourage them to interact with their children). These are things which all parents and caregivers can do, irrespective of their own language competence. 

In doing these things, those who currently feel that they have little to offer in relation to the revitalization of the language can experience a genuine sense of involvement and empowerment. Accepting that there are currently many parents and caregivers who cannot realistically become involved in genuine inter-generational transmission of the language in the home does not mean accepting that they have nothing to offer. 

Mā te kōwhiringa o ngā uiuitanga hangā ngāwari, te whiriwhiri ā rōpū kanohi, me te puka patapātai (hei tōngia mai ngā kōrero whānui kē atu o tēnā, o tēnā), ka whakatewhatewha te tuhinga nei i ngā waiaro me ngā ritenga o tētehi rōpū e ngana ana ki te haumanu i te reo Māori hei taonga mō rātou ko ō rātou whānau, ā, mō ā rātou tamariki, mokopuna hoki. Te nuinga o te hunga nei he Māori; he tokoiti anō he Pākehā. He tokomaha o rātou i tipu ake i roto i te horopaki o te reo Māori, arā, kotahi neke atu o ō rātou mātua rānei, kaitiaki rānei, whanaunga rānei he matatau ki te reo Māori. Ahakoa rā, kāore te nuinga i whāngaihia ki te reo i ā rātou e pēpi ana, kei whakapai kanohitia pērā i ō rātou tūpuna. Ko rātou te hunga i tipu reo Māori mai, ka memeha haere tō rātou reo nō te tino putanga ake o te reo Pākehā ki ō rātou ao. He tokoiti o tēnei rōpu i kuraina ki te kōhanga reo me te kura kaupapa Māori; he tokomaha anō i whai wāhi ki ngā akoranga reo Māori me ōna tikanga, hāunga rā te nui o te nama. Ko ētehi, kua ea ngā wawata, kua matatau ki te reo; ko ētehi atu anō, kua pāngia kētia e te hōhā me te hēmanawatanga. Heoi, ahakoa ngā wheako ake o tēnā, o tēnā, he hiahia nō te nuinga kia matatau ā rātou tamariki me ā rātou mokopuna ki te reo, kia tū pakari ai, kia tū Māori ai ki tēnei ao. Te nuinga o tēnei rōpū he manawanui ki te kōrero Māori i te kāinga i te nuinga o te wā, koia anō rā i ā rātou e kōrero ana ki ā rātou tamariki me ā rātou mokopuna. Heoi anō, kei reira anō ngā papatoieketanga, e pā ana ki ō rātou ake tītengi rānei, ki te takarepatanga o tō rātou reo rānei, me te mōhio anō ko ētahi o ō rātou hoa, whānau, whānau whānui anō hoki, he reo tahi kē, arā, ko te reo Pākehā te reo kawe. Anō hoki, ko ētahi o ngā tamariki, i ā rātou e pakeke haere ana ka kaha papare i te reo Māori, ka whakawaia kētia rātou e te reo Pākehā me ōna tikanga. I waenganui i te hunga i whai wāhi ki tēnei kaupapa rangahau kua kitea he mārama pū te nuinga ki te tino hiranga o te tuku ihotanga o te reo; kua kitea hoki tō rātou kaingākau nui ki te ako i te reo, ki te whakapakari rānei i tō rātou reo. Hāunga tērā, me ō rātou ngana anō ki te kawe i te reo Māori i te kāinga, ko ngā mātua kāore anō kia tino eke te reo ā-waha ka mate i te pōraruraru, te pōkaikaha, te āwangawanga, me te kaha papare a ngā tamariki e pakeke haere ana. Nā runga i tērā, me te take anō hoki he ruarua noa iho ngā wāhi o te hapori whānui i ēnei rā kia taea te reo Māori te rere noa, kua whakapuāwaitia e te tokomaha o tēnei rōpū ētahi rautaki hei ārahi i ngā tamariki me ngā mokopuna i ā rātou e pakeke haere ana, kia mārama rātou ki ngā whakahere tinana a te marea kia whai wāhi ai rātou ki te ako i te reo, me ngā here e haere kōtui ana ki ērā āhuatanga, kia whakanuia, kia utua hoki ngā tamariki i runga anō i ngā whakatutukitanga reo, kia manaakitia hoki rātou ki te whai wāhi anō ki ngā horopaki reo Māori. Hei konei ka ākina rātou ki te uru ki ngā kapa haka me ngā tino kaupapa anō o te ao Māori e whakatairanga nei i te reo. Anō hoki, ka whakahauhautia kia piritata ki ā rātou hoa me ō rātou whanaunga e tino mōhio ki te reo, me te whakauru hoki ki ngā mahinga marae. Waihoki, ka pōwhiritia te hunga matatau ki te reo ki te toro mai ki ō rātou kāinga (nā reira, me whakapau kaha anō ngā mātua ki te whakahoahoa, ki te patipati, ērā tāngata kia whakaae mai ki te noho ki te taha o ngā tamariki whakaputa kōrero ai). Koinei ngā mea ka taea ai e ngā mātua katoa, e ngā kaitiaki katoa, ahakoa kei hea te tohungatanga o tō rātou reo.  Mā reira, ka whai wāhi tonu, ka whakamanahia tonu tēnei hunga e pōhēhē nei pea he iti noa iho tā rātou hei koha atu ki te whakarauoratanga o te reo. Nō reira, hāunga rā te whakaaro he nui ngā mātua me ngā kaitiaki tamariki i tēnei wā e kore e tino whai wāhi ki te tukunga iho o te reo i te kāinga, ehara i te mea he kore noa iho tā rātou hei koha atu ki tēnei kaupapa whakahirahira.

year: 2014