Numeričko modeliranje procesa deformiranja poroznog kućišta konektora

master's thesis

• Title (english): Numerical modelling of deformation processes of porous connector housing
• Author: Zoran Tomić
• Mentor: Zdenko Tonković (mentor)
• Granter: University of Zagreb; Faculty of Mechanical Engineering and Naval Architecture; Zagreb
• Defense date and country: 2019-12-06, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Mechanical Engineering; General Mechanical Engineering (Construction)

Abstract

Cilj rada bio je istražiti utjecaj poroznosti na mehaničko ponašanje polimernog materijala polibutilen tereftalata (PBT-a) koji spada u grupu (polu-) kristalnih polimera, odnosno poliester termoplastika. PBT se najčešće koristi u električnoj industriji za proizvodnju konektora i prekidača te ostalih komponenata električne industrije gdje je potrebno zadovoljiti stroge norme i propise. Kada govorimo o automobilskoj industriji, PBT se može pronaći na gotovo svim mjestima automobila, od odbojnika, ručica vrata pa sve do električnih konektora kao što je slučaj u tvrtki Yazaki Europe Ltd. Iako PBT posjeduje zavidna mehanička svojstva, nerijetko se dodatno poboljšava ojačanjem u vidu staklenih vlakana.
U ovom radu provedeno je numeričko modeliranje i računalna simulacija procesa deformiranja PBT-a ojačanog staklenim vlaknima kao i čistog PBT-a bez ojačanja vlaknima.
Za modeliranje mikrostrukture primijenjena je direktna numerička simulacija (engl. Direct Numerical Simulation; u daljnjem tekstu DNS) s modelima dobivenim primjenom 3D mikroračunalne tomografije X-zrakama (3D X-ray micro-Computed tomography (μ-CT)). Prije provedbe analiza dana je teorijska pozadina vezana za tehnologiju računalne tomografije, kratki opis korištenih materijala te DNS metoda. Pojam DNS odnosi se na provođenje detaljnim numeričkih simulacija ponašanja materijala pri čemu se eksplicitno modelira mikrostruktura materijala bez upotrebe višerazinskih simulacija koje uključuju homogenizacijske procedure i definiranje reprezentativnog volumenskog elementa (RVE) materijala. Pritom treba identificirati minimalno potrebnu veličinu modela te istražiti utjecaj rubnih uvjeta na vanjskim plohama modela na deformiranje uzorka materijala.
Prvi dio rada bavi se istraživanjem utjecaja veličine RVE modela na mehaničko ponašanje PBT-a. Istraživanje je provedeno na 3D modelima akademskih primjera materijala i modelima dobivenim preko mikro CT tehnologije. Također, analizirane su različite veličine RVE modela čistog PBT materijala i vlaknima ojačanog PBT-a. Nakon što su numeričke analize provedene na akademskim modelima, istražen je utjecaj veličine RVE modela s CT snimki. Numeričke analize validirane su koristeći odgovarajuće eksperimentalne testove. U tu svrhu, izvršeni su jednoosni testovi na kidalici i to na uzorcima sa i bez staklenih vlakana.
U drugom dijelu rada provedena je numerička analiza naprezanja u standardnom električnom konektoru za automobilsku industriju. Numeričke analize provedene su na CT modelu osigurača konektora, poznatijem kao CPA (engl. Connector Positioning Assurance) a rezultati su validirani eksperimentalnim testom. Također, istražen je utjecaj poroznosti na mehaničko ponašanje CPA komponente konektora. Na modelima s mikro CT-a isprovocirane su pore te su uspoređeni rezultati s različitim udjelom poroznosti.
Na kraju rada izrađena je diskusija gdje su prokomentirani svi rezultati. Isto tako, potencijalna poboljšanja numeričkih modela a i budući rad prikazan je na kraju rada.

Abstract (english)

The main goal was to investigate porosity influence on mechanical behaviour of the polymer material, the polybutylene terephthalate (PBT) which belongs to the group of (semi-) crystal polymers, or polyester thermoplastics. PBT is often used in electrical industry for connector and plug switches and other components of electrical industry where strict regulations and standards are present. When dealing with automotive industry, PBT can be founded in all sections of the car, from bumpers, handles to electrical connectors, like the one company Yazaki designs and produces. Even thought PBT has envious mechanical properties, very often PBT is additionally glass fibre reinforced.
In this thesis, numerical modelling and computer simulations of deformation process are carried out with the glass fibre reinforced and the unreinforced PBT samples.
For the microstructure modelling, direct numerical simulation (DNS) is applied on the models based on micro X-ray computed tomography (μ-CT, or CT). Before the analyses, theoretical background of the CT technology is given, along with mechanics of used material and DNS method. The term DNS is usually referred to detail numerical simulations of the heterogeneous materials during which microstructure is directly modelled without multilevel simulations including homogenisation procedures and defining representative volume element (RVE) of a material. During this process, RVE size must be determined and boundary conditions on external surfaces must be investigated for appropriate model deformation.
The first part of the thesis is dealing with research on different RVE sizes and their connection with mechanical behaviour. The research is conducted on academic based RVE models and CT gained models. Different sizes of pure PBT samples, along with glass fibre reinforced samples are simulated, respectively. After the research on academic-based models, CT based RVEs are also analysed. Numerical results are validated using appropriate experimental tests. For these purposes, uniaxial experimental tests are conducted on pure and glass-fibre reinforced PBT testing samples.
The second part of the thesis deals with investigation of the stress analysis in standard electrical connector for automotive industry. Numerical simulations are conducted on a CT based model of the connector position assurance (CPA) component. Numerical results are then compared with experimental tests. Influence of porosities on CPA mechanical behaviour is investigated. On the CT based models, pores are modelled in different percentages and results are compared afterwards.
At the end of the thesis, results are discussed. Potential improvements and future work are given.

• Keywords: polibutilen tereftalat (PBT); metoda konačnih elemenata; direktna numerička simulacija (DNS); mikroračunalna tomografija X-zrakama (mikro CT); reprezentativni volumenski element (RVE); električni konektor
• Keywords (english): Polybutylene terephthalate (PBT); finite element method; direct numerical simulation (DNS); micro X-ray computed tomography; representative volume element (RVE); electrical connector
• Language: english
• URN:NBN: urn:nbn:hr:235:504882
• Study programme: Title: Mechanical Engineering; Study programme type: university; Study level: graduate; Academic / professional title: magistar/magistra inženjer/inženjerka strojarstva (magistar/magistra inženjer/inženjerka strojarstva)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Embargoed access; Embargo expiration date: 2024-11-28
• Created on: 2019-11-28 09:11:49