title: 3D printing of bio-inspired, multi-material structures to enhance stiffness and toughness

authors: Zhang, Xinhan

subjects: Multi-material

abstract: In nature, many biological, multi-materials have complex microstructures and excellent mechanical properties. One shellfish material called nacre has received much attention due to its unique interlocking structure of alternating calcium carbonate tablet and soft organic matter filler. It has microstructure features such as waviness which provide high strength and toughness properties. As a popular topic in the study of bio-inspired structure, it is of great significance to study the ordered microstructure and toughening mechanism of nacre.

3D printing allows for the easy manufacture of complex structures. In this project, inspired by the high strength and toughness of natural nacre, 3D printing technology was used to prepare nacre-like, multi-material structure. Tensile tests, cyclic tensile test and fracture toughness tests were carried out to investigate the relationship between multi-material structure geometry and tensile properties, fracture modes and toughness behaviour.

In the experimental part of this thesis, specimens of the tablet-filler with different dovetail angles made by polylactic acid (PLA) and thermoplastic polyurethane (TPU) inspired by the microstructure of nacre structure were prepared through Fused filament fabrication (FFF)/ Fused Deposition Modelling (FDM) type of 3D printing technology. The multi-material dovetail PLA & TPU specimens exhibited multi-stage deformation under tensile testing. By comparing the tensile performance of structure made by dovetail PLA & PLA material as well as unidirectional pure PLA specimen, it was confirmed that the incorporation of soft TPU filler gave the opportunity for tablet sliding, resulting in a complex multi-stage deformation mechanism of the structures.

Two modes of failure mechanisms, tablet pull-out and tablet break, were observed for the multi-material PLA & TPU structure under tensile testing. The combination of tablet break and pull-out modes can lead to higher strength and modulus than tablet pull-out. In the tablet pull-out mode, transverse expansion was observed in the larger angle dovetail structure, and the occurrence of negative Poisson's ratio effect was determined by calculation. In addition, there is a distinct plateau stage in the tensile curve of multi-material PLA & TPU structure, through cyclic tensile tests identified the plateau as a yield point, generated by short interface between tablets and filler broken. The cyclic tensile tests also determined that the main deformation resistance of the PLA & TPU structure was provied by the long interface broken between tablets and filler, also the interlocking and shearing between the dovetail angle tablets. 

Multi-material PLA & TPU structures with larger dovetail angles produced greater plastic deformation and absorbed more energy during tensile testing. Multi-material PLA & TPU with 5˚ dovetail showed the highest ultimate tensile strength 11.46 MPa and Young’s modulus of 495.96 MPa, but 9˚ dovetail performed poorly with 6.51 MPa and 395.48 MPa, respectively. The value even below than 1˚ dovetail (ultimate tensile strength of 9.82 MPa, modulus of 453.38 MPa). The ultimate tensile strength and Young’s modulus of the multi-material PLA & TPU structure are not as high as those of unidirectional pure PLA and dovetail PLA & PLA specimen, but energy absorption performance is improved by soft TPU filler and dovetail angles. In fracture experiments, crack extension behaviour was observed in fracture toughness specimens.

In summary, the mechanical properties of the nacre-like, multi-material structure were investigated by tensile behavior, fracture mode and energy absorption analysis in this paper. It is demonstrated that the combination of stiff tablet material and soft filler material can effectively improve the toughness of the structure. The tensile strength of the multi-material structure can be improved by increasing the dovetail angle of the tablet. However, it has not been observed that increasing the dovetail angle can significantly increase stiffness. It is confirmed that the optimized design of the 3D printed, bio-inspired, multi-material structure can change the mechanical behavior of the structure and improve its mechanical properties, can provide new ideas for the development of composite materials with excellent mechanical properties.

text: 3D printing of bio-inspired, multi-material structures to enhance stiffness and toughness In nature, many biological, multi-materials have complex microstructures and excellent mechanical properties. One shellfish material called nacre has received much attention due to its unique interlocking structure of alternating calcium carbonate tablet and soft organic matter filler. It has microstructure features such as waviness which provide high strength and toughness properties. As a popular topic in the study of bio-inspired structure, it is of great significance to study the ordered microstructure and toughening mechanism of nacre.

3D printing allows for the easy manufacture of complex structures. In this project, inspired by the high strength and toughness of natural nacre, 3D printing technology was used to prepare nacre-like, multi-material structure. Tensile tests, cyclic tensile test and fracture toughness tests were carried out to investigate the relationship between multi-material structure geometry and tensile properties, fracture modes and toughness behaviour.

In the experimental part of this thesis, specimens of the tablet-filler with different dovetail angles made by polylactic acid (PLA) and thermoplastic polyurethane (TPU) inspired by the microstructure of nacre structure were prepared through Fused filament fabrication (FFF)/ Fused Deposition Modelling (FDM) type of 3D printing technology. The multi-material dovetail PLA & TPU specimens exhibited multi-stage deformation under tensile testing. By comparing the tensile performance of structure made by dovetail PLA & PLA material as well as unidirectional pure PLA specimen, it was confirmed that the incorporation of soft TPU filler gave the opportunity for tablet sliding, resulting in a complex multi-stage deformation mechanism of the structures.

Two modes of failure mechanisms, tablet pull-out and tablet break, were observed for the multi-material PLA & TPU structure under tensile testing. The combination of tablet break and pull-out modes can lead to higher strength and modulus than tablet pull-out. In the tablet pull-out mode, transverse expansion was observed in the larger angle dovetail structure, and the occurrence of negative Poisson's ratio effect was determined by calculation. In addition, there is a distinct plateau stage in the tensile curve of multi-material PLA & TPU structure, through cyclic tensile tests identified the plateau as a yield point, generated by short interface between tablets and filler broken. The cyclic tensile tests also determined that the main deformation resistance of the PLA & TPU structure was provied by the long interface broken between tablets and filler, also the interlocking and shearing between the dovetail angle tablets. 

Multi-material PLA & TPU structures with larger dovetail angles produced greater plastic deformation and absorbed more energy during tensile testing. Multi-material PLA & TPU with 5˚ dovetail showed the highest ultimate tensile strength 11.46 MPa and Young’s modulus of 495.96 MPa, but 9˚ dovetail performed poorly with 6.51 MPa and 395.48 MPa, respectively. The value even below than 1˚ dovetail (ultimate tensile strength of 9.82 MPa, modulus of 453.38 MPa). The ultimate tensile strength and Young’s modulus of the multi-material PLA & TPU structure are not as high as those of unidirectional pure PLA and dovetail PLA & PLA specimen, but energy absorption performance is improved by soft TPU filler and dovetail angles. In fracture experiments, crack extension behaviour was observed in fracture toughness specimens.

In summary, the mechanical properties of the nacre-like, multi-material structure were investigated by tensile behavior, fracture mode and energy absorption analysis in this paper. It is demonstrated that the combination of stiff tablet material and soft filler material can effectively improve the toughness of the structure. The tensile strength of the multi-material structure can be improved by increasing the dovetail angle of the tablet. However, it has not been observed that increasing the dovetail angle can significantly increase stiffness. It is confirmed that the optimized design of the 3D printed, bio-inspired, multi-material structure can change the mechanical behavior of the structure and improve its mechanical properties, can provide new ideas for the development of composite materials with excellent mechanical properties.

year: 2021

title: A water quality model for Lake Tikitapu

authors: McBride, Chris G.

abstract: Lake Tikitapu is a small lake in the Rotorua Te Arawa Lakes region which is extensively used for recreation and sporting events, and is of cultural significance to Iwi (Te Arawa). It is an attractive and popular lake with oligotrophic-mesotrophic water quality. Tikitapu's target Trophic Level Index (TLI; Burns 1999) is 2.7, whereas a TLI of approximately 3 was observed between 2000 and 2010. An Action Plan has been established for Lake Tikitapu (BoPRC 2011) and the proposed actions have now been completed (as at 2015), including the reticulation of the lakeside wastewater systems.
This report describes the establishment of a one-dimensional hydrodynamic-ecological computer water quality model (DYRESM-CAEDYM) for Lake Tikitapu. The modelling process includes calculations for catchment and lake water balances, as well as estimation of nutrient loads to the lake. The simulation period spans from 2001 to 2010. The model has been calibrated and validated, and model performance is acceptable relative to other DYRESM-CAEDYM lake applications documented in the literature.
The established model can be used for simulating scenarios of lake management actions, and can be considered a 'decision support tool'. Initial simulations are presented for increased diffusion of silica from lake sediments (C. Hendy, pers. comm.), and for reticulation of lakeside wastewater systems. Septic systems comprise a large fraction of estimated annual nutrient loads, particularly for phosphorus. As such, simulation of the removal of septic tank nutrient loads indicated that this action alone may be sufficient to meet the TLI target for the lake.

text: A water quality model for Lake Tikitapu Lake Tikitapu is a small lake in the Rotorua Te Arawa Lakes region which is extensively used for recreation and sporting events, and is of cultural significance to Iwi (Te Arawa). It is an attractive and popular lake with oligotrophic-mesotrophic water quality. Tikitapu's target Trophic Level Index (TLI; Burns 1999) is 2.7, whereas a TLI of approximately 3 was observed between 2000 and 2010. An Action Plan has been established for Lake Tikitapu (BoPRC 2011) and the proposed actions have now been completed (as at 2015), including the reticulation of the lakeside wastewater systems.
This report describes the establishment of a one-dimensional hydrodynamic-ecological computer water quality model (DYRESM-CAEDYM) for Lake Tikitapu. The modelling process includes calculations for catchment and lake water balances, as well as estimation of nutrient loads to the lake. The simulation period spans from 2001 to 2010. The model has been calibrated and validated, and model performance is acceptable relative to other DYRESM-CAEDYM lake applications documented in the literature.
The established model can be used for simulating scenarios of lake management actions, and can be considered a 'decision support tool'. Initial simulations are presented for increased diffusion of silica from lake sediments (C. Hendy, pers. comm.), and for reticulation of lakeside wastewater systems. Septic systems comprise a large fraction of estimated annual nutrient loads, particularly for phosphorus. As such, simulation of the removal of septic tank nutrient loads indicated that this action alone may be sufficient to meet the TLI target for the lake.

year: 2014

title: Haumanu Hauora: refining public health institution policy to include Māori and climate change

authors: Masters-Awatere, Bridgette

abstract: The deepening climate crisis generates specific impacts that will exacerbate the already disproportionately negative health outcomes experienced by Indigenous people. Disparate health outcomes have not spontaneously emerged, but rather have been foreshadowed by existing inequities. This article summarizes a sample of the work from a two-year research project in Aotearoa New Zealand to understand existing policy processes and ascertain the extent to which health institutions give serious consideration to climate change impacts on Māori (Indigenous people) with health vulnerabilities. Speaking to tāngata whenua (Indigenous Māori), District Health Board (DHB) employees, and subject matter experts (SMEs), it was clear that policy processes were ad hoc and problematically silenced consistent Māori input. While research participants expressed their experiences of, and aspirations for, dealing with climate change, their voices were not evident in DHB policy development processes. The deficit within existing policy process reflects a lack of preparedness in the face of climate change. Despite clear resilience and adaptation strategies, structural change is needed to address identified disadvantages. Through a co-designed policy framework (“Haumanu Hauora”), we guide policy formation to mitigate climate change risk to Māori (and others). Central to the revised policy framework is the creation of space for both internal and external Māori voices to ensure consistent Māori input throughout the policy process. We also introduce a commissioning, refining, and monitoring stage (that includes evaluation). Haumanu Hauora considers whānau-centered healthcare knowledge, needs, resources, and aspirations, to contribute to a transformed and responsive health system. Above all, we believe that strengthening health institution responsiveness to Māori health needs is essential.

text: Haumanu Hauora: refining public health institution policy to include Māori and climate change The deepening climate crisis generates specific impacts that will exacerbate the already disproportionately negative health outcomes experienced by Indigenous people. Disparate health outcomes have not spontaneously emerged, but rather have been foreshadowed by existing inequities. This article summarizes a sample of the work from a two-year research project in Aotearoa New Zealand to understand existing policy processes and ascertain the extent to which health institutions give serious consideration to climate change impacts on Māori (Indigenous people) with health vulnerabilities. Speaking to tāngata whenua (Indigenous Māori), District Health Board (DHB) employees, and subject matter experts (SMEs), it was clear that policy processes were ad hoc and problematically silenced consistent Māori input. While research participants expressed their experiences of, and aspirations for, dealing with climate change, their voices were not evident in DHB policy development processes. The deficit within existing policy process reflects a lack of preparedness in the face of climate change. Despite clear resilience and adaptation strategies, structural change is needed to address identified disadvantages. Through a co-designed policy framework (“Haumanu Hauora”), we guide policy formation to mitigate climate change risk to Māori (and others). Central to the revised policy framework is the creation of space for both internal and external Māori voices to ensure consistent Māori input throughout the policy process. We also introduce a commissioning, refining, and monitoring stage (that includes evaluation). Haumanu Hauora considers whānau-centered healthcare knowledge, needs, resources, and aspirations, to contribute to a transformed and responsive health system. Above all, we believe that strengthening health institution responsiveness to Māori health needs is essential.

year: 2023-05-05