Graduate Thesis Or Dissertation
 

Fatigue Testing and Analysis of Polymer and Composite Materials Used in Heavy-Duty Trucks

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/5d86p6060

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  • As structural durability analysis is increasingly trusted during the design processes of the automotive industry, more complete and sophisticated modeling of material behavior under both static and dynamic loading conditions is paramount. This is especially true regarding the application of heavy-duty trucks, where modern designs contain large parts such as body panels, splash shields and hoods that are made of polymers or polymer-composite materials rather than metal as found in small passenger vehicles or historical truck designs. While the use of these more advanced materials provides a significant reduction in the total weight of a truck, there is a severe lack of research-backed knowledge regarding their mechanical behavior when subjected to static and dynamic loads. Data that is necessary input information for achieving accurate analysis results for truck models containing such materials is often replaced by generic properties, or taken from third-party testing reports that can be easily misinterpreted. Thus, there are multiple opportunities for improvement in this area of work. The research presented in this thesis is focused on obtaining the above-mentioned data for three materials that are commonly used on large trucks: polydicyclopentadiene (pDCPD), 40% wt. chopped-glass-fiber-reinforced polypropylene (40% GF-PP) and 35-40% wt. vinyl ester Sheet-Molding Compound (SMC), though the results for SMC are not presented in this thesis. This is done by adapting practices from several standard testing procedures for both monotonic and strain-controlled uniaxial fully-reversed fatigue testing. The validity of applying the strain-based fatigue approach to these types of materials is then questioned and studied. In addition, a procedure is suggested for obtaining a stress-life fatigue definition from strain-controlled fatigue test data, and the results are compared to the stress-life definition obtained from load-controlled fatigue testing of the same material. Lastly, the finalized material property information is applied to improve the durability simulations of a pre-existing model of a truck part; the significant increase in calculated damage due to the integration of the new data is discussed. The conclusions of this research can thus be divided into two categories. The primary outcome is the procurement of new, more accurate material data that will be directly used to improve design and analysis processes for heavy-duty trucks. The secondary outcome is the investigation and improvement of test methods that can be used to evaluate the monotonic and fatigue characteristics of polymers and polymer-composite materials. Specifically, if the strain-life fatigue definition is perused for a polymer or polymer-composite material, it is suggested that this data should only be applied to analysis simulations if there exists a fatigue transition point on the strain-life curve. Otherwise, the simpler stress-life definition will suffice.
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