The thesis deals with the design, modelling and simulation of two testing micro-machines adopted to study the fracture behaviour of a single stopper. This structural component is used inside MEMS to limit the motion of the movable masses when accidental events occur. Understanding its failure mechanism is essential to well design it, and therefore to provide an higher level of robustness for the entire MEMS. In the two testing micro-machines proposed in this work, the principal component is a movable mass, called shuttle, which is pushed toward the stopper. The actuation is provided by a series of parallel plates and comb fingers capacitors with the aim of generating load able to break the specimen. Due to the high computational cost requested to perform a complete 3D analysis of the testing micro-machine and the stopper, the simulations are subdivided in two different steps. In the first phase a 2D model in the plane of the device is considered, and the goal is to evaluate the pressure profile along the contact surface between the specimen and the movable mass; in the second step, instead, only the stopper is modelled, and the attention is focused on the fracture behaviour. The main drawback of this two phase simulation is the necessity to assume a pressure distribution along the height of the stopper, which is not provided by the 2D model. In order to consider different load distributions, three cases are analysed. The two commercial software adopted in this work are ANSYS and ABAQUS. The first one is used to study the electro-mechanical behaviour of the micro-devices, while the second one is selected to simulate the fracture propagation.
La presente tesi tratta la progettazione, la modellazione e la simulazione di due micro-dispositivi utilizzati per la caratterizzazione a frattura di uno stopper. Questo elemento strutturale viene utilizzato all’interno dei MEMS per limitare lo spostamento delle parti mobili dovuto ad azioni accidentali. Studiarne il comportamento a frattura risulta essenziale per poterne eseguire una corretta progettazione, incrementando così anche il margine di robustezza dell’intero MEMS. I due micro dispositivi presentati in questo elaborato sono essenzialmente costituiti da una massa mobile, chiamata shuttle, che viene spinta verso lo stopper. L’attuazione è prodotta da una serie di condensatori con l’obiettivo di generare una forza sufficiente ad indurre un processo di frattura nel campione. Data la difficoltà in termini computazionali di gestire l’intero dispositivo test e lo stopper in un ambiente tridimensionale, la simulazione viene suddivisa in due fasi differenti. Nella prima parte viene modellato il micro-dispositivo nel proprio piano attraverso elementi bidimensionali, con l’obiettivo di determinare il profilo di pressione nell’interfaccia tra il provino e la massa mobile; nella seconda fase, viene invece studiato unicamente lo stopper con un modello 3D e l’implementazione della frattura. Il problema principale legato a questa analisi in due fasi risiede nella necessità di assumere una distribuzione di pressione lungo l’altezza dello stopper, che non è determinabile attraverso il modello 2D. A tale fine, vengono considerati diversi profili di carico analizzandone nello specifico tre casi. I due software commerciali utilizzati in questa tesi sono ANSYS e ABAQUS. Il primo è stato impiegato per studiare il comportamento elettro meccanico dei micro-dispositivi, il secondo è stato scelto per simulare la propagazione di frattura.
Modelling simulation and design of micro-testing machines for microsystem fracture characterization
FURLAN, MATTEO
2019/2020
Abstract
The thesis deals with the design, modelling and simulation of two testing micro-machines adopted to study the fracture behaviour of a single stopper. This structural component is used inside MEMS to limit the motion of the movable masses when accidental events occur. Understanding its failure mechanism is essential to well design it, and therefore to provide an higher level of robustness for the entire MEMS. In the two testing micro-machines proposed in this work, the principal component is a movable mass, called shuttle, which is pushed toward the stopper. The actuation is provided by a series of parallel plates and comb fingers capacitors with the aim of generating load able to break the specimen. Due to the high computational cost requested to perform a complete 3D analysis of the testing micro-machine and the stopper, the simulations are subdivided in two different steps. In the first phase a 2D model in the plane of the device is considered, and the goal is to evaluate the pressure profile along the contact surface between the specimen and the movable mass; in the second step, instead, only the stopper is modelled, and the attention is focused on the fracture behaviour. The main drawback of this two phase simulation is the necessity to assume a pressure distribution along the height of the stopper, which is not provided by the 2D model. In order to consider different load distributions, three cases are analysed. The two commercial software adopted in this work are ANSYS and ABAQUS. The first one is used to study the electro-mechanical behaviour of the micro-devices, while the second one is selected to simulate the fracture propagation.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/173812