Until recently, multi-stable mechanical metamaterials have been primarily used in passive energy absorption systems. However, the ability to actively program these structures has gained significant interest, expanding their functionality to enable on-demand adaptive deformation. While existing active programming methods effectively induce global state transitions, localized actuation remains largely unexplored. This study introduces a novel approach to actively programming multi-stable metamaterials via local thermal stiffness modulation at boundary conditions. Using a polymer bi-material design with distinct glass transition temperatures between the beam and boundary supports, the system can transition from a bi-stable to a mono-stable state, enabling controlled snap-back behaviour after deformation. An analytical model is developed to characterize the snap-through behaviour of the unit cell, providing insight into the geometric interactions and sensitivities associated with various design parameters. Experimental implementation, using multiple additive manufacturing techniques, revealed key limitations and design considerations. In particular, the importance of constraining the second buckling mode and careful material selection emerged as fundamental design requirements for ensuring functionality. This work contributes to the growing field of actively programmable mechanical metamaterials, with implications for compact motion systems in future work.

This research successfully establishes a proof of concept for the hot forming of PEEK sheets using resin-printed polymer molds.
Mechanical metamaterials, through their architected inner structures, offer unique properties that enable unparalleled functionalities. In the MECOMOS project, a novel manufacturing method is proposed to fabricate a multi-stable 3-DoF PEEK metamaterial that enables tip, tilt, and z-translation. The method involves forming PEEK layers to create the geometries of the unit cells, followed by joining these formed layers to produce a monolithic metamaterial.
In this research, a new forming method, hot forming, is developed and analyzed for shaping these layers. This method creates microscale features in PEEK sheets by implementing the process steps of hot embossing into matched die thermoforming.
Polymer molds with various geometries, including rounded cylinders, blocks and trapezoids, are successfully resin printed. Key variables influencing the mold output in resin printing include the cleaning procedure, post-curing, and layer thickness. The smallest printable features measure 400x400x100 µm, and the printing errors range from 40 to 150 µm and are predominantly independent of feature size.
The proof of concept for the hot forming process reveals its strong potential as a manufacturing method.The forming parameters are highly forgiving, with a broad range of process parameters still yielding high replication quality. The suitable forming temperature spans from 100 to 150°C, and pressing forces between 750 and 3000 N prove effective.

This study establishes an adhesive bonding strategy for the micro-assembly of optical components using UV-curable adhesives. The focus is on factors influencing adhesive shrinkage and alignment accuracy. Key findings reveal that higher UV intensity reduces both volumetric and linear shrinkage, while curing from below the substrate minimizes horizontal shifts on the to-be bonded optical components, eliminating the need for horizontal offset adjustments. The study highlights how variations in the distance between the substrate and component affect vertical shrinkage displacements and stresses the importance of precise adhesive volume control to enhance accurate shrinkage prediction. The developed shrinkage prediction model forecasts sub-micrometer accurate vertical component shrinkage compensations, validated through comprehensive parameter testing. To advance research toward more accurate shrinkage predictions and a deeper understanding of adhesive shrinkage behavior, future studies propose integrating multi-angle observation systems and expanding parameter testing. These efforts aim to refine prediction models and validate strategies in real-world applications, thereby enhancing the reliability and precision of optical systems across industrial and scientific domains.

For the design of new manufacturing methods for mechanical metamaterials in compact motion systems, a new bonding technique has been developed. The manufacturing technique requires thermoformed PEEK films to be bonded together. Literature review has shown that laser welding, and specifically laser transmission welding, is a valuable method for this manufacturing technique, particularly for bonding materials that are tens of microns thick, such as thermoformed and PEEK films. This research demonstrates how to define a viable process and how to optimize laser parameters to achieve maximum joint strength and identifies factors that can diminish the quality of the bond, thereby affecting optimal speed.

Further investigation of the PEEK and absorptive coating spectral curves has revealed that absorption coating is effective in increasing the absorbance used in this research. Welding with an infrared laser around one µm wavelength can rapidly produce strong welds, where the tensile strength of the welds exceeds that of the material. A fluence of around 20 to 30 mJ/mm^2 results in optimal weld peel strengths.

The optimal parameters for 125 µm lap welding include a speed between 10 and 15 millimeters per second and a defocussing distance between 4 and 7 millimeters. The thickness of the welded films range from 25 to 125 microns. It has also been observed that thicknesses of 25 and 50 micrometers can produce welds with 125 thick thermoformed PEEK films, allowing for 2.5D film welding capabilities.

Reliable assembly methods are needed to translate new endoscopic probes from the research phase to clinical testing. Design variation complicates standardized assembly and leads to a lengthy process creating inaccurate prototypes, preventing repeatable research. This thesis proposes a strategy for selecting the most effective assembly method by examining alignment and bonding relations among parts. Considering the manufacturing tolerances of the optical parts leading to a loss of image quality, an approach for testing is selected to align the gradient index (GRIN) lens and fibre. This approach implements an active alignment procedure and reaches a sensitivity of 3𝜇𝑚 for the concentricity, 0.4 deg for the colinearity and 40𝜇𝑚 for the separation distance. These results validate a better result than reachable with passive alignment. An optimization algorithm could replace the manual comparison of the ideal beam profile for increased repeatability. To advance the research to the assembly of complete prototypes, more components of the probes should be added to the investigation and a method for fixing the components to the housing should be introduced.

This study explores the design and implementation of an electrowetting-on-dielectric (EWOD) system for precise die positioning in a chip assembly environment, utilizing a millimeter-scale ”chip-on-droplet” approach. Two methodologies were investigated: coarse positioning using digital signals, a method well-documented in prior research, and fine positioning using analog signals, which, to the best of our knowledge, had not been applied to droplet positioning at the time of writing. The primary advantage of the fine positioning approach lies in its independence from feature size, allowing for significantly smaller step sizes. Experimental results demonstrated that the analog system achieved step sizes as small as 3.5 μm in a ”droplet only” setup, outperforming the ”traditional” coarse positioning system. Performance limitations were found to arise primarily from the tracking setup rather than the EWOD system itself.
The study also evaluated various surface layers, confirming prior findings that a smooth, thin, and homogeneous surface layer is critical for achieving consistent and precise movement. Attempts to en- hance droplet guidance through modified surface structures were unsuccessful due to pinning forces exceeding the generated EWOD forces. These findings highlight the potential of analog signal-driven EWOD systems for fine positioning applications, with important implications for chip assembly tech- nologies.

In this thesis report, the potential for high-throughput fabrication of micromechanical metamaterials is studied. Metamaterials are structures typically consisting of repetitive micrometre-sized features that introduce new and extraordinary ‘material’ properties. However, up to now these structures are predominantly fabricated with slow 3D-print fabrication techniques. In this work, a range of micromechanical metamaterial designs are closely studied for their design aspects, alongside an investigation towards the high-throughput opportunities of mechanical contact-based fabrication techniques like nano imprint lithography and microtransfer moulding. What is missing from current research, is the connection between the design attributes of micromechanical metamaterials and the capabilities of high-throughput micrometre-level fabrication techniques.

Here I showthat micromechanical metamaterials can be broken down into geometric elements and eventually elementary material transformations that can be directly linked to fabrication techniques with high-throughput potential. These material transformations can be used to form several fabrication process flows. During this breakdown, stencil printing emerged as a compelling fabrication technique for high-throughput fabrication of thin intricate 2½D features. At this moment little is known about the prospects for stencil printing with polymeric materials because stencil printing has its origins in printed circuit board (PCB) fabrication. By performing experiments on the most influential parameters of ordinary PCB stencil printing found in literature and applying these parameters to polymer stencil printing, an understanding of the operating mechanisms is obtained. It is exhibited that by tweaking parameters such as viscosity, wettability,
stencil design and substrate temperature, stencil printing with polymers like polydimethylsiloxane (PDMS) can be transformed from an ill-defined mess to a successful replication of the designed laser-cut stencil. The achieved stencil print shows good replication with a mean line width of 638 &m with a standard deviation of 20.8 &m against a 585 &m line width of the laser-cut stencil. The key to this rewarding transformation is the mixing of polytetrafluoroethylene (PTFE) into the PDMS matrix in a 50/50 wt% mixing ratio.

This thesis aims to solve the problems and fabricate fully inkjet-printed dielectric elastomer actuators with silver electrodes and a PDMS middle layer. First, a conductive silver electrode is printed on a coated PET substrate, followed by a printing of the dielectric elastomer middle layer to cover the bottom electrode. Then, the top silver layer is printed on the PDMS to achieve the top electrode. The problems intended to be solved in this work include printing the dielectric elastomer middle layer, treating
the PDMS layer, the significant surface cracking, and the non-conductivity of the top electrode. During the fabrication process, different concentrations of PDMS solution are tested printing. Observations on these printed samples are made to validate the most suitable printing solution and printing process/settings. Different surface treatment cycles for the PDMS layer are also adopted to determine the most suitable one, what effect is brought to the PDMS layer surface, and how they influence the top electrode. For the fabrication of the top electrodes, experiments are accomplished and repeated, coming with failures, which will be presented and discussed later. Lastly, displacement and frequency response measurements are essential to check the performance of the DEAs, being critical sections of the thesis.

Capillary self-alignment shows the potential to keep small components aligned using soft liquid contact when disturbed by external forces. Whilst this concept has been promising, mostly static situations have been investigated, making it unclear how a receptor-droplet-chip (RDC) configuration behaves dynamically and where its stability limits are.

The primary aim of this research was to determine the stability limits of such a configuration and explore its failure modes. Two non-linear analytical models simulate the situation and investigate the parameters exposed to the system. These models predict the relative lateral displacement of the chip and its tilt, which can predict when failure should occur. Results from Surface Evolver, a computational software, and experimental data from a laboratory setup validate these models. A shaker induced one DOF linear accelerations, and high-speed cameras observed these tests. The validated model was then used to investigate the effects of variables such as lubricant height, chip dimensions and acceleration magnitudes.

This project gives an insight into how a chip behaves dynamically on a liquid meniscus and was the first to investigate the tilt of the component during accelerations. The key finding is a stable region showing what amount of liquid results in reaching the highest possible acceleration without failure. Secondly, the models and experiments showed that smaller liquid volumes and chip sizes increase the attainable acceleration. Chips of L = 2mm were able to be accelerated up to a = 27g without failure, parts of L = 1mm even reached an acceleration of a = 35g at which the RDC configuration remained intact. Moreover, possible eigenfrequencies were observed, and the system could re-align at specific frequencies from a tilted pose. Therefore, this research has demonstrated that, under the right conditions, capillary interfaces can be useful to transport components under high accelerations.

The research investigates the creation of an end-effector capable of pick-and-placing thin laminates of various materials. The chosen end-effector design induces a pressure differential with a membrane, and is capable to achieve a large switching force for various delicate and geometric complex laminates. The concept utilizes an array of holes, over which a membrane is suspended, hereafter called suction cups. By applying pressure upon the suction cups, the membrane deforms, resulting in a vacuum capable of generating large switching forces. During contact the vacuum is created, and during release the membranes are expanded to release the laminate.
The design variables (radius, membrane height, membrane thickness, Young's modulus of membrane) of the concept are numerically investigated to analyze their influence on the suction pressure, the deformation of the membrane and the corresponding stresses in membrane and laminate. The numerical results indicated that the membrane thickness and material are vital. As an increase in thickness and young's modulus results in an exponential increase in switching force. These numerical results and the end-effector production method determine the final dimensions. The prototype is then used to perform a set of experiments to validate the numerical model.
The measurement results on the deformation of the end-effector membrane confirm model results. However, production inaccuracies and the application method of the membrane resulted in inconsistencies in the dimensions and its performance. The force measurement results indicate that the force created by the end-effector is heavily impeded by the sealing performance of the suction-cups. Improving the sealing performance resulted in values in accordance with the numerical model. The pick-and-place experiment indicates that a substantial force is created by the suction cups, capable of pick-and-placing rigid laminates. For the transportation of flexible laminates (thinner and/or smaller young's modulus), smaller forces are created due to the compliance of the laminate, therefore more accurate production and a thinner and more flexible membrane is required. Depending on the laminate material and shape, certain design guidelines are in place. A larger force can be created on more rigid laminates, allowing for the application of a less flexible membrane. For thinner laminates the switching force is reduced, and therefore the membrane needs to be very flexible and thin. For a more complex shape, smaller and more suction cups are required, impacting the other variables. Additional guidelines for various laminate materials and shapes are found at the end of this report.
In conclusion, an end-effector based on the membrane induced pressure differential is a design path which is worth investigating further for pick-and-placing thin laminates. Depending on the application and thus the target laminates, certain design guidelines are set up at the end of this report. These can be used for further research to pick-and-place geometric intricate laminates of various materials.

Multi-stable beam-type metastructures exhibiting snap-through behavior have been extensively studied in recent years , as their stable states can be maintained without the need of external power supply. By arranging a series of beams exhibiting bi-stability, multi-stable metastructures can be constructed. However, current designs of multi-stable metastructures are limited in terms of structural kinematics and the associated functionalities are not fully explored. This thesis aims to present design strategies that can facilitate new kinematic behavior and functionalities for multi-stable metastructures (i.e., energy absorption and shape reconfiguration). Specifically, we investigate the additional rotational degrees of freedom by incorporating rotational compliance in both 2D and 3D designs. In doing so, multi-stable metastructures are capable of realizing both translational and rotational motion, facilitating their applicability in soft robotics and deployable structures. Moreover, the energy dissipation of multi-stable metastructures are studied, where we have proposed design strategies that can enhance the energy absorption without using more materials. In addition, it is demonstrated that multi-stable metastructures can also be designed to realize shape reconfiguration of a morphing surface, where the stability requirement and accessible configurations have been presented. Such multi-stable metastructures exhibiting translational and rotational degrees of freedoms hold great potential for developing reconfigurable structures and energy absorbers.@en

Dielectric elastomer actuators (DEAs) are a type of soft actuators that consist of a dielectric elastomer membrane, covered with an electrode on the top and the bottom. When applying a potential, the opposite charges on the electrodes induce an electrostatic force which squeezes the elastomer, causing it to expand. This expansion can be used as an actuation mechanism, in a wide variety of applications. A specific field of interest are low actuation voltage DEAs. These DEAs require low stiffness and thin elastomer layers, but are easier and cheaper to implement due to the lower voltage requirements. The goal of this research is to develop a manufacturing process for an inkjet-printed low actuation voltage DEA while achieving insights into the requirements and limitations of the steps involved with this process. By using the PiXDRO LP50 inkjet printer in combination with the Dimatix DMC printhead, the bottom electrode is printed on a Novele substrate with Mitsubishi NBSIJ-MU01 AgNP ink. A dielectric elastomer ink has been formulated consisting of polydimethylsiloxane (PDMS) and octyl acetate (OA) in 1:4 and 1:3 ratios. These inks have been characterised on several printability parameters, placing both formulations in the jettable range based on their Z-value. Although theoretically jettable, both formulations showed difficult jetting behaviour. To resume the research, the PDMS layer is instead applied by spin coating. The PDMS surface is hydrophobic, requiring surface treatment before the electrode can be printed on top. Several methods have been investigated, of which O2 plasma treatment showed the best results. The top electrode is printed using NovaCentrix Metalon JS-B25P AgNP ink. Several different sintering methods have been explored to cure the printed silver. Next to the experimental work, a finite element analysis model has been built to provide a basis for designing low actuation voltage DEAs.

Multi­-material 3D inkjet printing has great potential for rapid prototyping and manufacturing of functional mesoscale structures when novel inks are combined into a fully integrated AM-process. This process can be faster and cheaper than conventional methods to produce functional structures. Research is conducted on a large range of potentially inkjet­-printable materials to extend current possibilities with 3D inkjet printing. Material incompatibility together with strict fluid properties limit the range of multifunctional inks available for an integrated print process. This raises challenges such as printing with three or more materials, and finding inkjet printable materials that can be cured simultaneously using the same curing method. The aim of this research is to print functional structures using at least three materials consisting of a structural, support, and conductive material, requiring only one curing technique involving UV light exposure. An experimental setup of PiXDRO LP50 inkjet printers and various printhead assemblies are used to conduct experiments. Suitable off the shelf available inks are selected after a state of the art literature review. Stratasys Vero­series and Stratasys SUP706B are industry standard, compatible materials and cure using UV induced photopolymerisation. They are chosen as structural and support material, respectively. Novacentrix Metalon JS­B25P and Mitsubishi NBSIJ­MU01 silver nanoparticle inks are chosen as conductive inks. First, multi­material printing is set up and extended to 3D printing using the structural and support material inks only. Afterwards, conductive inks are tested for resistivity and behaviour on different substrates before integrating with the structural and support material ink into a multi­material 3D print. Conductive nanoparticle inks show good conductivity on photopaper substrate, but not when printed on top of structural material. Several experiments are performed to document ink behaviour and optimise performance. A workflow is designed allowing the conversion of complex CAD models to inkjet ­printable files. Custom support material density for stronger supports can be generated using an in-­house developed conversion application. Proof­ of ­concept multi­-material functional structures are printed showcasing success of the proposed methodology.

Freeform overhanging microstructures are used for various applications, for example in micro metamaterials. To create these structures industry uses a variety of manufacturing methods. There is a gap in manufacturing methods that can produce a microstructure at a high resolution and use multiple materials at individual locations. Inkjet printing can fill this research gap because multiple materials can be printed at individual points in structures by using multiple ink reservoirs. The goal of the research is to develop a method to produce overhanging microstructures using inkjet printing.

Using inkjet printing structures are produced bottom-up therefore a (sacrificial) support material is needed to support building material during the production. This material is later removed resulting in an overhanging structure. To allow removal of the sacrificial material both materials must cure differently. After considering different candidate materials, one building material (mr¬UVCur26SF) and one sacrificial material (KL5315) were used during the manufacturing process. The sacrificial material is a positive photoresist and can be removed in a NaOH (1w%) solution after UV curing as opposed to the building material that solidifies after UV curing.

Two methods were used to increase the height of inkjet-printed structures. The first method is to print multiple layers of material on top of each other while curing the material between each layer, this is used to print the building material. This first method led to poor alignment between layers of sacrificial support material, therefore a new method is proposed to print the sacrificial material. Using the second method multiple lines of sacrificial material are printed next to each other without intermediate curing using a high cross-scan resolution of 4800[dpi] increasing the height of the structure.

Printing both materials close to each other to create an overhanging structure led to a loss of shape because the materials were attracted to each other. To solve this issue a new method is proposed using sacrificial dikes to prevent the building material from losing its shape. The first step of this method is to print and cure a grid of sacrificial support material. After that, the building material is printed in the free space between and on top of the dikes resulting in a microbridge once the sacrificial support material is removed. Using this method a microbridge with an overhanging part of approximately 50 micrometers is created.

The demand for nanoparticles in various applications is increasing. These applications can only be realised if nanoparticles can be specifically arranged and patterned on a substrate. This thesis considers a direct write method that uses an aerodynamic focusing nozzle to deposit these particles. A major challenge arises when the nanoparticles are decreased in size. This research studies the control of the deposition resolution of small sized nanoparticles (≤10 nm) in an aerosol flow. A FEM model was developed to describe the particle’s path. These models were made for a converging and converging sheath gas nozzle. Due to the small particle sizes considered, it was found that only the Stokes (drag) force needs to be accounted for during modelling. The effect of different nozzle exit throat, working distance, angle and flow rate configurations are studied. Nozzle designs were evaluated using three performance criteria, namely the contraction factor, focusing ratio and line width. These describe the contraction of the particles within the nozzle system, the focusing after the nozzle system and the width of the line, respectively.
It was found that smaller angles, longer converging sections and higher velocities resulted in smaller line widths. Also, the contraction factor hardly depends on the particle size. Smaller nozzle exit throats have significantly higher focusing ratios for particles smaller than 10 nm. The working distance does not effect the contraction factor directly, indicating capabilities of deposition on non-flat surfaces. The converging nozzles can only deposit ≤10 nm particles if the nozzle exits are sufficiently small. This can cause clogging. The focusing ratios, in these nozzles, never exceeds the value of one, indicating always a larger line width than the nozzle exit diameter.
In the sheath gas nozzle system, high sheath gas ratios are essential for increasing the contraction factor and particle velocity. This prevents clogging. Introducing the sheath gas earlier in the nozzle system is more effective than at the end. The best modelled contraction factor, focusing ratio and line width achieved, using 10 nm particles, with a converging nozzle are 1.0, 0.4 and 874 microns, respectively. This nozzle has a nozzle exit throat of 400 microns and an angle of 10 degrees. However, a modelled contraction factor of 9.3, focusing ratio of 3.8 and line width of 104 microns are achieved using a converging sheath gas nozzle with a nozzle throat of 400 microns and an angle of 5 degrees. Narrower line widths are expected if the throat diameters are reduced.
For the experiments, a setup was used in which nanoparticles are generated using a spark ablation method. During these experiments it was seen that the maximum flow rate is mainly dependent on the nozzle exit throat of the aerosol channel. The line widths, during experimenting, were found to be wider due to inaccuracies in the stage and the differences in settings between the model and setup.

The purpose of this study is to investigate how metamaterials with a negative Poisson ratio, so-called auxetic metamaterials, can be used for conversion of pressure from a fluid to strain in a solid for application in a medical pressure sensor. As a first step, a literature review was carried out to identify the potential of auxetic metamaterials as a solution direction for pressure to strain conversion. From considering three optimal case scenarios for solution directions to create strain in a fiber, the approach of auxetic metamaterials stood out. High axial strains and a linear straining behavior, which is important for the read-out of the sensor, were expected. Auxetic Chiral structures were designed and fabricated and their effective Poisson ratios were experimentally evaluated. It was found that the boundary effects that are introduced during experiments influence the behavior of the auxetic structure, especially on the unit cells close to the boundaries. A region was found where the unit-cells behave as theory describes and the boundary effects are dissipated. Additionally, it was found that for the an-isotropic Meta Tetra Chiral structure the Poisson ratio is influenced by applied strain. The isotropic Anti Tetra Chiral structure did not show strain dependent behavior. The relation between pressure to strain conversion and the effective properties of auxetic structures indicated that an-isotropic effective properties are preferred. Using this finding Re-entrant Honeycomb structures were designed for high pressure to strain conversion. From measuring the force input and output while deforming the structure, the expectations were verified. In this research it was found that auxetic metamaterials with an-isotropic effective properties, such as Re-entrant Honeycomb structures, are an effective intermediate for converting pressure from the fluid domain to strain in a fiber.

Administration of drugs can help in the recovery of the brain for example after a stroke. There are many available delivery routes such as intravenous injection or local injection in the brain. Whereas, the former encounters problems with systemic side effects, the latter requires multiple invasive brain surgery. Local drug administration could be achieved with a drug delivery implant to reduce the amount of invasive procedures and to include useful features such as electrodes for monitoring neural activity. In this study an advancement is made towards spatial control of permeability in a membrane. Porous PDMS membranes were fabricated by replica molding in a 3D-printed mold. The smallest pore diameter was 100 μm and the thinnest membrane thickness was 160 μm. The permeability of such a membrane is tested by a dye which must go through the membrane in order to observe staining in 0.6% agarose gel to simulate diffusion of brain tissue. No staining was detected using pristine PDMS membranes. However, a fast flow from hydrophobic to hydrophilic side was observed in a PDMS membrane recently treated with plasma on a single side. Furthermore, slow diffusion of the dye was present in a less hydrophilic, dextran-modified membrane that received plasma treatment on one side as well. Thus, the permeability was controlled by the wettability of the membrane surface without modification of the entire inner pore. The same experiments were performed on a mouse brain to be compared to the results on agarose gel. The use of agar as a brain phantom material is useful for further investigation of a local drug delivery device, but a few improvements are required to better correspond to the brain.

Nanoparticles have unique properties that are sought after for the development and improvement of applications. Prerequisite to achieve these applications, methods are required to put the nanoparticles in different patterns and arrangement on a target substrate.
In the course of developing an aerosol-based nanoparticle printing system, this work explores the results of different aerosol deposition configurations.
The work is based on a spark ablation process that generates an aerosol of argon and copper nanoparticle agglomerates. The deposition configuration deposits the aerosol on a target substrate. Three configurations are explored, one which deposits at subsonic velocities, and two which deposit at sonic velocities. The aim is to find the most favourable deposition conditions for the direct writing of nanoparticle patterns.
It is found that a sonic deposition configuration with a low pressure ratio at small substrate distances has the smallest deposit diameter. The configuration allows for the patterning of narrow lines, that consist of two deposition regions: a micro-aggregate region and a nanoparticle region. It was found that the density of these regions is mainly influenced by the process variables of the spark ablation process, and can thus be used to gain a high consistency and well-defined edges.

This work introduces a new method to deal with design dependent pressure loads in Topology Optimisation (TO) using the SIMP material model. A pronounced focus is on optimising pressure actuated compliant mechanisms. The difficulty herein is the interpretation of the pressure boundary in a TO design. In TO the boundaries are blurry, because of the filtering of the design variables, which is necessary to prevent checkerboarding. Another reason why the boundary is poorly defined is that the optimisation starts from an equally distributed grey, where black and white respectively are solid and void, so the boundary is either the domain boundary or not defined in early iterations of the optimisation.
The methods proposed in literature often try to find the void-solid interface exposed to the pressure source to apply the loading from a pressure line directly. The method proposed in this work, appropriately called the Darcy method, first calculates the pressure field by using Darcy's law governing the flow through porous media and the associated pressure drop. A flow coefficient is introduced that decreases if the virtual element density increases. This results in a design dependent pressure field that can be solved using the Finite Element Method (FEM), which can then be translated to consistent nodal forces that are applied to the TO problem. A drainage coefficient has also been introduced to make sure that the pressure is drained entirely to the environment pressure over the first encountered void-solid interface exposed to the pressure source. The Darcy method has proven to function well in several test cases. The method has been thoroughly tested using several parameter sweeps on a clamping problem objective. The parameters whose influence is examined are: the initial condition, the density threshold value, flow coefficient gradient at the threshold, output spring stiffness and the volume fraction.
Subsequently, some alternative TO problems are solved showing the diversity of the method. In perspective of future research, the Darcy method can function as a great tool to research load sensitivities by tuning the pressure field control parameters. The extension of the Darcy method to 3D or to several load cases comes naturally but has not been tested in this work, this is also recommended for future research.