Calendar

We are pleased to invite you to attend the PME-Final MSc presentation on:

Friday 8 February 2019, 14h00
Instruction room I

Mekelweg 2
2628 CD DELFT

14h00 Richard Pleeging, specialisation: MNE
Coaches: Prof.dr. U. Staufer, Dr. D. Fan

Title: Polymer nano manufacturing of a biomimicking surface used for
kidney stone crystallization studies

Kidney stone disease is an increasing worldwide issue. There is a current lack of understanding of the exact mechanisms involved, partially due to the need for experimental instrumentation able to mimic the microenvironmental conditions present in vivo.

As crystal nucleation often initiates at liquid-solid interfaces, the interface morphology plays a significant role in the rate of nucleation. Within the nephron, the functional unit of the kidney, four distinct segments can be distinguished that contain different surface morphologies. Particularly, the cells lining these segments contain protrusions in the shape of nanopillars that vary in length, diameter and spacing.
Exploiting the opportunities provided by organ-on-chip technology, we designed and manufactured a microfluidic device proposed to increase our understanding of the exact mechanisms that drive kidney stone crystallization.
We used two-photon polymerization to fabricate surfaces that contain these morphologies in materials possessing a Young’s modulus matching the value of the biological structures. After optimizing design and process parameters like laser power and scanning speed, we manufactured nanopillars with diameters in the range of 150-250 nm and aspect ratios up to 100 with which we can mimic the protrusions in the nephron.
Pillar arrays were printed on a glass slide, and assembled with a polydimethylsiloxane (PDMS) microfluidic component (channels 150 um wide). We used high-resolution 3D printing to create master molds used for PDMS soft-lithography. After precise alignment, the two components were brought together and clamped mechanically with a 3D printed holder to ensure a watertight seal between the glass and PDMS.
This microfluidic device was used to study crystallization of the most common type of kidney stone, calcium oxalate monohydrate (COM). Because of the chip dimensions combined with a surface morphology this device closely resembles a human nephron.

The presentation will be given in English.

14h20 Debate
14h30 End

Attending colloquia is an obligatory part of the curriculum of PME.
The presence of other people who are interested will be appreciated.

We are pleased to invite you to attend the PME-Final MSc presentation on:

Friday 8 February 2019, 16h00
Instruction room J

Mekelweg 2
2628 CD DELFT

16h00 Yannick Janssens, specialisation: SOM
Coaches: Prof.dr.ir. A. van Keulen, Dr. D.P. Munro

Title: Computational efficient robustness analysis of aircraft component
distortion accounting for stochastic pre-stressed stock material
in reductive manufacturing processes

Aircraft components are manufactured from rolled plate stock material with reductive manufacturing techniques such as milling, drilling, and cutting. At the end of such a manufacturing process, the component is released from fixture and deforms. This phenomenon is called distortion and is highly undesired. Deformations are usually very small compared to the component’s dimensions. Small deviations in shape, however, are significant since aircraft components require extreme precision. This since components should fit in the final aircraft assembly without building up too much tension in bolds that could lead to fracture. In order to deal with distortion, nowadays, components are often corrected or manufactured multiple times leading to material losses costing millions of profit each year.
Distortion occurs due to the presence of residual stresses in rolled plate itself. Efforts were made to predict distortion with Finite Element tools. The idea was to find different orientations in rolled plate where components distort less. This way, significant material losses could be saved. These predictions, however, turned out to be unreliable since residual stress in rolled plate is subjected to substantial variation. Consequently, efforts were made to include the uncertainty residual stress in the distortion prediction tools, such that now the uncertainty of distortion itself could be predicted. These efforts, however, drastically worsened the computational costs of the Finite Element tools such that reliable distortion predictions simply became infeasible.
In this thesis, a methodology has been developed allowing to predict distortion along with its uncertainty in both a computational efficient and reliable manner. With this methodology, distortion and its uncertainty can be predicted for any aircraft component as a function of its three-dimensional orientation in rolled plate material.

The presentation will be given in English.

16h20 Debate
16h30 End

Attending colloquia is an obligatory part of the curriculum of PME.
The presence of other people who are interested will be appreciated.

We are pleased to invite you to attend the PME-Final MSc presentation on:

Thursday 14 February 2019, 10h00
Instruction room L

Mekelweg 2
2628 CD DELFT

10h00 Laura Dijkink, specialisation: DMN
Coaches: Prof.dr. P.G. Steeneken, Dr. F. Alijani

Title: Mechanics of wrinkled graphene membranes

The outstanding mechanical properties of graphene have made it a suitable candidate for a wide range of sensor and actuator applications in modern technology. However, before the full potential of future applications can be achieved, a proper characterisation of the fundamental properties of graphene membranes is crucial. The aim of this project was to contribute to the understanding of the mechanical response of single layered graphene nanoribbons and -cantilevers in presence of surface imperfections.

A Molecular Dynamics model have been developed of a single layer graphene ribbon to describe both the formation of wrinkles as well as the transition from the wrinkled state to the flat state. Also, a continuum model is developed to investigate the formation of wrinkles in nanoribbons. Different constitutive laws have been investigated to describe the mechanical response. It was concluded that an exponential version of Hooke's law failed to reproduce the non-linearity at small strains correctly. The non-linearity at small strains is well described by a first order compressible Ogden's law. The Ogden's law predicted a negative Poisson's ratio at small strains for wrinkled membranes, which is in agreement with previous research. Also, Ogden law predicted a decreasing shear modulus and an increasing Poisson's ratio after flattening.

Single layer graphene cantilevers show great potential, however due to the difficult manufacturing of these fragile structures they remain virtually unstudied. Herein, a Molecular Dynamics have been developed to investigate the motion of graphene nanocantilevers in presence of a curvature. We find that, depending on the aspect ratio and ratio of curvature, single layer graphene cantilevers can be (partly) stabilised by implying a curvature.

In conclusion, we showed that it is possible to tailor the mechanical properties of both single layer graphene cantilevers and ribbons by implying different surface corrugations.

The presentation will be given in English.

10h20 Debate
10h30 End

Attending colloquia is an obligatory part of the curriculum of PME.
The presence of other people who are interested will be appreciated.

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We are pleased to invite you to attend the PME-Final MSc presentation on:

Friday 15 February 2019, 13h00
Instruction room I

Mekelweg 2
2628 CD DELFT

13h00 Justin Smid, specialisation: DMN
Coaches: Prof.dr. P.G. Steeneken, Dr. F. Alijani

Title: Nonlinear damping in graphene nanodrum resonators

Mechanical resonators made from graphene are widely researched for their potential applications, such as mass sensors or pressure sensors. However, graphene resonators already show signatures of nonlinear damping at relatively low driving forces, limiting device performance. The physical mechanism that is responsible for nonlinear damping is not yet well understood. In this project, two possible sources are investigated. The first source assumes viscoelastic behavior of graphene, and is capable of producing the amplitude-dependent dissipation commonly observed in these resonators. The second source that is investigated is the optical field coming from the interferometric setup, which is used to actuate the resonator and detect its motion. Negative nonlinear damping was observed at low laser power, turning positive when the power increases. This behavior could be attributed to the equilibrium position of the resonator, which shifts with laser power.

The presentation will be given in English.

13h20 Debate
13h30 End

Attending colloquia is an obligatory part of the curriculum of PME.
The presence of other people who are interested will be appreciated.

We are pleased to invite you to attend the PME-Final MSc presentation on:

Friday 22 February 2019, 13h00
Instruction room K

Mekelweg 2
2628 CD DELFT

13h00 Koen Schreurs, specialisation: DMN
Coaches: Dr. F. Alijani, Dr. G. Radaelli

Title: The design of a compliant shape-preserving ring

Compliant shape-preserving mechanisms fill a tiny niche within the established research field of compliant mechanisms. To date no report exists on a compliant shape-preserving ring, even though such a mechanism can give rise to a multitude of practical applications: from novel sealing mechanisms and compliant grippers to medical applications.

This project presents the design of a compliant shape-preserving ring. The mechanism maintains its shape up to 99% for its full range-of-motion. A prototype was constructed from PETG using fused-filament-fabrication and an experimental evaluation of this prototype showed excellent agreement with the numerical model describing the design. Furthermore, a novel compliant scissor mechanism was obtained in the design process which can prove useful for generating other compliant shape-preserving mechanisms.

The presentation will be given in English.

13h20 Debate
13h30 End

Attending colloquia is an obligatory part of the curriculum of PME.
The presence of other people who are interested will be appreciated.