title: Investigation into strain propagation to determine preserve regions for compliant mechanisms

authors: Venter, Christoff

subjects: compliant mechanisms

abstract: This thesis aims to improve the theoretical modelling of compliant mechanisms. The
conclusions drawn from this work will help designers understand sources of error associated
with strain propagation when designing with lumped compliance. Compliant mechanisms
have increased in popularity as they allow for designs that feature lower part counts,
increased precision and reduced manufacturing costs. Although using theoretical models
to design compliant mechanisms is a useful tool, there is an assumption that only the
nodes in a compliant mechanism undergo strain. This is not the case. There is strain
occurring outside of the node in a region called the preserve region. The preserve region’s
impact on the theory is greatly under-explored in the literature.
The preserve region’s size, shape, and impact were found and quantified for a range
of critical node types. This was done through the use of FEA software by altering the
model of a simple, compliant mechanism. The size of the preserve region changed based
on the thickness and the fillet used, with an increase of thickness from 4mm to 8mm,
causing the radius of the arc that encompasses the preserve region to grow from 8.5mm to
13mm. The shape was also found to be an ellipse, irrespective of the node’s geometry. The
preserve region’s impact on the theoretical models was also quantified. It was found that
the thickness has the most drastic effect on the compliance values of the node, increasing
the error from 20.53% to 102.18% when the thickness was increased from 4mm to 8mm.
This work shows the importance of considering the preserve region when creating
theoretical models of compliant mechanisms. When properly considered, this research
shows that the error between the theoretical and the FEA values can be greatly reduced.

text: Investigation into strain propagation to determine preserve regions for compliant mechanisms This thesis aims to improve the theoretical modelling of compliant mechanisms. The
conclusions drawn from this work will help designers understand sources of error associated
with strain propagation when designing with lumped compliance. Compliant mechanisms
have increased in popularity as they allow for designs that feature lower part counts,
increased precision and reduced manufacturing costs. Although using theoretical models
to design compliant mechanisms is a useful tool, there is an assumption that only the
nodes in a compliant mechanism undergo strain. This is not the case. There is strain
occurring outside of the node in a region called the preserve region. The preserve region’s
impact on the theory is greatly under-explored in the literature.
The preserve region’s size, shape, and impact were found and quantified for a range
of critical node types. This was done through the use of FEA software by altering the
model of a simple, compliant mechanism. The size of the preserve region changed based
on the thickness and the fillet used, with an increase of thickness from 4mm to 8mm,
causing the radius of the arc that encompasses the preserve region to grow from 8.5mm to
13mm. The shape was also found to be an ellipse, irrespective of the node’s geometry. The
preserve region’s impact on the theoretical models was also quantified. It was found that
the thickness has the most drastic effect on the compliance values of the node, increasing
the error from 20.53% to 102.18% when the thickness was increased from 4mm to 8mm.
This work shows the importance of considering the preserve region when creating
theoretical models of compliant mechanisms. When properly considered, this research
shows that the error between the theoretical and the FEA values can be greatly reduced.

year: 2024

title: Is there a salty solution to sensitive soil sliding in the Bay of Plenty, New Zealand?

authors: Robertson, Thomas Paul

subjects: Sensitive Soils

abstract: Found globally, sensitive soils are widely regarded as a key cause of slope instability. These sensitive soils often contribute to the production of large retrogressive landslides that pose significant danger to a people and infrastructure. Within the Bay of Plenty region, sensitive soil based landslides are widespread and numerous Moum et al (1970) successfully trialled remediation of a sensitive soil landslide in Scandinavia by application of potassium chloride via leaching columns. The aim of this study is to determine whether salt treatment of sensitive soils formed in halloysite rich soils of the Bay of Plenty provides a viable means of improving soil behaviour.
Soil collected from the base of the landslide at Bramley Drive, Omokoroa, was treated with 3 differing potassium based salts (KCl, KOH and K₂CO₃) to observe which would produce the greatest positive rheological effect. Results indicated that treatment with KCL and KOH had a negative rheological effect on the soil reducing the liquid limit of the soil from a baseline of 92.3 to 79.3 and 83.5 respectively. Only K₂CO₃ did not have a negative effect on the soil, maintaining the liquid limit at 92.6. Soil kept within soil cores was then soaked in K₂CO₃ solution for a period of three weeks before being subjected to tri-axial testing at three confining pressures of 205 kPa, 280 kPa and 355 kPa; untreated soil cores were tested at the same stress conditions
Tri-axial testing of the soil showed a significant increase in the peak deviator stress measured when comparing the untreated and treated soils at its point of failure, with increases in peak deviator stress measured for the treated soils in the order of 227% at 205 kPa, 187% at 280 kPa and 124% increase at 355 kPa. Strain softening for treated soil was also measured to be less than that of the untreated soil at all confining pressures, a trait reflected in pore pressures measured at point of failure also. Stress path plots indicated that untreated samples underwent contraction rapidly as deviator stress increased, with no clear failure point observed as would be expected from an over consolidated clay. In contrast, stress paths for the treated samples showed the soils dilating before reaching point of failure and undergoing contraction following failure. Differences in friction angle and cohesion were also measured between treated and untreated samples, with untreated soil indicating friction angle and cohesion of Φ’=19.3o, C’=26.6 kPa. These results were consistent with those given in literature and fell within the range expected for halloysite rich clays (Mills, 2016; Moon, 2016). Both friction angle and coheion values increased in treated soils (Φ’=28.2 and C’=58.4).
Based upon the results gathered during this study I infer that stabilisation of the sensitive layer of soil found within Omokoroa is possible, in particular when treated with K₂CO₃. It is my belief that this occurs due to the successful intercalation of the K₂CO₃ ion into the halloysite basal space, displacing the water found in the space originally, and causing an expansion of the crystal lattice. The expansion of the halloysite crystal lattices in turn increases the particle contact areas, which as a result causes a rise in the cohesion and friction angle as a result of increased energy required to overcome the grain to grain friction when stress is applied. Increased basal spacing in the halloysite crystals accommodates pore fluid and thus allows for reduced pore water pressure during stress application.
Though further research is warranted, results produced from this study show that treatment increases the effective strength of the soil to a significant and noticeable degree, and provides the impetus to warrant further research into the subject in the near future, as the potential engineering impacts in being able to effectively stabilise soil rich in halloysite holds significant value both in New Zealand and on a global scale.

text: Is there a salty solution to sensitive soil sliding in the Bay of Plenty, New Zealand? Found globally, sensitive soils are widely regarded as a key cause of slope instability. These sensitive soils often contribute to the production of large retrogressive landslides that pose significant danger to a people and infrastructure. Within the Bay of Plenty region, sensitive soil based landslides are widespread and numerous Moum et al (1970) successfully trialled remediation of a sensitive soil landslide in Scandinavia by application of potassium chloride via leaching columns. The aim of this study is to determine whether salt treatment of sensitive soils formed in halloysite rich soils of the Bay of Plenty provides a viable means of improving soil behaviour.
Soil collected from the base of the landslide at Bramley Drive, Omokoroa, was treated with 3 differing potassium based salts (KCl, KOH and K₂CO₃) to observe which would produce the greatest positive rheological effect. Results indicated that treatment with KCL and KOH had a negative rheological effect on the soil reducing the liquid limit of the soil from a baseline of 92.3 to 79.3 and 83.5 respectively. Only K₂CO₃ did not have a negative effect on the soil, maintaining the liquid limit at 92.6. Soil kept within soil cores was then soaked in K₂CO₃ solution for a period of three weeks before being subjected to tri-axial testing at three confining pressures of 205 kPa, 280 kPa and 355 kPa; untreated soil cores were tested at the same stress conditions
Tri-axial testing of the soil showed a significant increase in the peak deviator stress measured when comparing the untreated and treated soils at its point of failure, with increases in peak deviator stress measured for the treated soils in the order of 227% at 205 kPa, 187% at 280 kPa and 124% increase at 355 kPa. Strain softening for treated soil was also measured to be less than that of the untreated soil at all confining pressures, a trait reflected in pore pressures measured at point of failure also. Stress path plots indicated that untreated samples underwent contraction rapidly as deviator stress increased, with no clear failure point observed as would be expected from an over consolidated clay. In contrast, stress paths for the treated samples showed the soils dilating before reaching point of failure and undergoing contraction following failure. Differences in friction angle and cohesion were also measured between treated and untreated samples, with untreated soil indicating friction angle and cohesion of Φ’=19.3o, C’=26.6 kPa. These results were consistent with those given in literature and fell within the range expected for halloysite rich clays (Mills, 2016; Moon, 2016). Both friction angle and coheion values increased in treated soils (Φ’=28.2 and C’=58.4).
Based upon the results gathered during this study I infer that stabilisation of the sensitive layer of soil found within Omokoroa is possible, in particular when treated with K₂CO₃. It is my belief that this occurs due to the successful intercalation of the K₂CO₃ ion into the halloysite basal space, displacing the water found in the space originally, and causing an expansion of the crystal lattice. The expansion of the halloysite crystal lattices in turn increases the particle contact areas, which as a result causes a rise in the cohesion and friction angle as a result of increased energy required to overcome the grain to grain friction when stress is applied. Increased basal spacing in the halloysite crystals accommodates pore fluid and thus allows for reduced pore water pressure during stress application.
Though further research is warranted, results produced from this study show that treatment increases the effective strength of the soil to a significant and noticeable degree, and provides the impetus to warrant further research into the subject in the near future, as the potential engineering impacts in being able to effectively stabilise soil rich in halloysite holds significant value both in New Zealand and on a global scale.

year: 2017

title: Contemporary attitudes to traditional facial ta moko: A working paper

authors: Rua, Mohi

subjects: Maori

abstract: Until it came under serious attack from nineteenth century missionaries, ta moko was an
integral part of traditional Maori society. Facial moko conveyed important information about
identity, whakapapa and status. The process of receiving a moko was tapu and highly regulated.
Recent years have seen an increase in the number of Maori receiving ta moko. Moko have been
seen as a symbol of Maori pride and identity and have often been associated with political
activism. This study set out to investigate the contemporary meaning of ta moko, the reactions
wearers encounter from others and the ways wearers cope with those reactions.
Three case studies are presented. These show that the issues of personal identity and
whakapapa were central to the meaning wearers attached to their moko. Receiving a moko was
often associated with significant personal changes and an increased political commitment to
Maori self determination. On the whole, positive reactions were more common than negative
reactions but wearers did find themselves subjected to racist and antagonistic responses.
Wearing moko was also reported to mean that others, particularly other Maori, placed certain
expectations on the wearer, notably to be fluent in te reo and to be able to exercise leadership.
Participants considered that there was a need for education about the significance of ta moko
and recommended that those contemplating receiving a moko ensure that they are reasonably
fluent in te reo.

text: Contemporary attitudes to traditional facial ta moko: A working paper Until it came under serious attack from nineteenth century missionaries, ta moko was an
integral part of traditional Maori society. Facial moko conveyed important information about
identity, whakapapa and status. The process of receiving a moko was tapu and highly regulated.
Recent years have seen an increase in the number of Maori receiving ta moko. Moko have been
seen as a symbol of Maori pride and identity and have often been associated with political
activism. This study set out to investigate the contemporary meaning of ta moko, the reactions
wearers encounter from others and the ways wearers cope with those reactions.
Three case studies are presented. These show that the issues of personal identity and
whakapapa were central to the meaning wearers attached to their moko. Receiving a moko was
often associated with significant personal changes and an increased political commitment to
Maori self determination. On the whole, positive reactions were more common than negative
reactions but wearers did find themselves subjected to racist and antagonistic responses.
Wearing moko was also reported to mean that others, particularly other Maori, placed certain
expectations on the wearer, notably to be fluent in te reo and to be able to exercise leadership.
Participants considered that there was a need for education about the significance of ta moko
and recommended that those contemplating receiving a moko ensure that they are reasonably
fluent in te reo.

year: 1999