Changing to polyester in airbags : A study of two test methods used for polyester fabric analyse

Abstract: This thesis is part of an on going project within Autoliv Sweden AB to develop the process in changing the material in airbags. Most airbags are today constructed of fabric in polyamide 6.6 (PA6.6) and the thesis view the possibility of changing the material to one of three different polyesters (PET1, PET2, PET3). Both materials have different properties that have been looked into by two test methods, linear testing and dynamic testing with cold gas. The two testing methods were conducted on plain fabric and on fabric with seam to see differences in the materials when subjected to different stress caused by force or pressure. During testing the seam rupture was measured by filming the test sequences, and used for visual analysis. Tensile testing was conducted using a constant-rate-of-extension machine where the material is subjected to linear force until rupture. Dynamic testing was done with a cold nitrogen gas system using vessels to build up pressure that then releases towards the material putting it under stress. Tensile testing results for elongation do not have significant differences between testing in plain fabric or fabric with seam. PET2 have highest elongation in warp and weft. Visual analysis of specimens shows difference in how materials break, where the reference material in PA6.6 breaks more even than in PET materials. Dynamic testing show that the biggest seam opening do not occur at the highest pressure. In order to understand what is happening with the fabric during testing, three different times have been chosen in the pressure-time chart. Results in dynamic testing on fabric with seam show that PET3 have the smallest seam opening while reference material in PA6.6 has the largest opening. All PET materials have similar properties even if these are not always same as reference material in PA6.6. We can neither discard nor confirm our hypothesis of seam slippage and elongation relates equally in the same material independent of test method. From these results PET2 would not be recommended due to seam opens most at maximum force and the material has the biggest elongation. PET3 would be the recommended material, since seam opening is smallest at measured pressure.