A methodology for numerical prototyping of inflatable dunnage bags

Venter, Martin Philip (2015-03)

Thesis (PhD)--Stellenbosch University, 2015.


ENGLISH ABSTRACT: Dunnage bags are an inflatable dunnage variant, positioned and inflated between goods in multi-modal containers to restrain and protect the goods while in transit. This project endeavours to develop a simple method of generating new numerical prototypes for dunnage bags suitable for simulating operational loading of the bags. Previous research has produced a model that simulates the inflation of a paper dunnage bag using a simple pressure load. A dunnage bag reinforced with plain-woven polypropylene was chosen as the test case. Woven polypropylene is a highly non-linear, non-continuous, non-homogeneous material that requires specialised material models to simulate. A key aspect of this project was to develop a simple method for characterising woven-polypropylene and replicating it's response with material models native to LS-DYNA. The mechanical response of the plain-woven polypropylene was tested using a bi-axial tensile test device. The material response from physical testing was then mapped to two material models using the numerical optimiser LS-OPT. The response of the calibrated material models was found to correlate well with the measured response of the woven material. Dunnage bags are subjected to cyclic loading in operation. In order to capture the effects of compressing the contained gas, a gas inflation model was added to the model that calculates the pressure in the bag based on the Ideal Gas Law. A full bag model making use of the calibrated material models and the inflation model was subjected to a cycled boundary condition simulating loading and unloading of an inflated dunnage bag. The two prototype models captured the pressure drop in the bag due to material plastic deformation and the restraining force produced by the bag to within 10 %. The prototype models were also found suitable for predicting burst pressure in voids of arbitrary size and shape.

AFRIKAANSE OPSOMMING: Stusakke is 'n opblaasbare soort stumateriaal wat tussen goedere in multimodale vraghouers geposisioneer en opgeblaas word om sodoende die goedere vas te druk en te beskerm tydens vervoer. Hierdie projek poog om 'n eenvoudige manier te ontwikkel om nuwe numeriese prototipes vir stusakke, geskik om operasionele lading van die sakke te simuleer, te ontwikkel. Vorige navorsing het 'n model ontwikkel wat die opblaas van 'n papier stusak met eenvoudige drukkrag simlueer. 'n Hoë-vlak stusak versterk met plein-geweefde polipropileen, is gekies om getoets te word. Geweefde polipropoleen is 'n hoogs nie-lineêre, onderbroke, nie-homogene materiaal wat gespesialiseerde materiaalmodelle nodig het vir simulasie. Een van die fokuspunte van hierdie projek is om 'n eenvoudige metode te ontwikkel om die karaktereienskappe van polipropoleen te identifiseer en die gedrag daarvan na te maak met die materiaalmodelle van LSDYNA. Die meganiese reaksie van die plein-geweefde polipropoleen is getoets met 'n biaksiale/tweeassige trektoets-toestel. Die materiaal se reaksie op die fisiese toets is ingevoer op 'n numeriese optimiseerder, LS-OPT, om op die materiaalmodelle te toets. Die reaksie van die gekalibreerde materiaalmodelle het goed gekorelleer met die gemete reaksie van die geweefde materiaal. Stusakke word tydens diens onderwerp aan sikliese lading. Om die effek van die saamgepersde gas vas te stel is 'n gas-opblaasbare model bygevoeg by die model wat die druk in die sak bereken, soos gebaseer op die Ideale Gas Wet. 'n Volskaalse sakmodel wat gebruik maak van die gekalibreerde materiaalmodelle en die opblaas-model is onderwerp aan sikliese grensvoorwaardes wat die lading en ontlading van 'n opblaasbare stusak simuleer. Die twee prototipe modelle het die drukverlies in die sak a.g.v. die materiaal-plastiek vervorming en die bedwingingskrag van die sak beperk tot 10 %. Die protoyipe modelle is ook geskik bevind om barsdruk in arbitrêre leemtes te voorspel.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/97124
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