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Mechanical characterisation for simplified response modelling of woven polypropylene

Ellis, David Rostin (2017-03)

Thesis (MEng)--Stellenbosch University, 2017.

Thesis

Methods of modelling woven polymer textiles within the Finite Element (FE) environment result in a compromise between level of detail captured, computational resources required and simplicity in its implementation. This research has attempted to develop a methodology that simpli es this process starting from the physical mechanical testing of the material. A biaxial and shear test rig was developed capable of testing for material response at various biaxial load ratios. Tests were performed at the fabric level using a single cycle load path to the maximum desired load before gradually being reduced to zero whilst the material deformation was captured using Digital Image Correlation. Time-dependent material response was not tested for speci cally. The response of the material was calculated as the instantaneous sti ness and modelled as a function of strain using a combination of power law and linear regression ts. An equation was derived that allows for the unload response to be modelled using data for a full-load test, but be applied to loads intermediate thereof, all whilst being implementable within the FE environment. This material law was implemented as a user-de ned subroutine for MSC.Marc as demonstration of its intended use and application. The methodology proved accurate at determining the load and unload paths for loads intermediate to those physically tested for.

AFRIKAANSE OPSOMMING: Metodes om geweefde polimeer-tekstiele te modeleer binne die Eindige Element (EE) omgewing is grotendeels 'n kompromie tussen die breedvoerigheid van die besonderhede wat vasgelê kan word, die vereiste rekenaarberekeningsvermoë en die moeilikheidsgraad wat gepaard gaan met die implementering daarvan. Hierdie navorsing het gepoog om 'n metode te ontwikkel wat die proses vereenvoudig vanaf die fisies-meganiese toetsproses. 'n Biaksiale skuifwerking-toetstuig met die vermoë om materiaal-reaksies by verskeie biaksiale ladingsverhoudings te meet is ontwikkel. Toetse is op materiaalvlak uitgevoer deur middel van 'n enkel-siklus ladingspad tot by die maksimum gewenste lading, waarna die lading geleidelik verminder is tot nul en die materiaal-vervorming tegelykertyd vasgevang is met gebruik van Digitale Beeld Korrelasie. Daar is nie spesifiek getoets vir tyd-afhanklike materiaalreaksie nie. Materiaal-reaksie is bereken as oombliklike styfheid en gemodelleer as 'n funksie van vervorming met behulp van 'n kombinasie van logaritmiese en lineêre funksiepassings. 'n Vergelyking is afgelei wat dit moontlik maak om die materiaal-reaksie te modelleer soos dit vervorm vanaf die maksimum aangewende krag terug na nul, gegewe die data vir 'n vol-las siklus, maar toegepas op intermedie^ere-las aangeleenthede. Hierdie vergelyking is van toepassing in die EE omgewing. Materiaal-reaskie is as 'n subroetine geïmplementeer in MSC.Marc om die uiteindelike toepassing en gebruik daarvan te demonstreer. Die metode is getoets en as akuraat bevind om die volle siklus van materiaal vervorming vir intermedieêre lasprofiele te bepaal.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/101280
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