Materials' properties play a crucial role in the selection of processes or design for manufacturingsystem components. These components should have high resistance to multiple stress factorssuch as mechanical and environmental stresses in which the component is being used. For this reason,engineers should analyze all possible scenarios and try to model for combined environmentconditions before introducing a product to the market.Polymers are specific materials with significantly high durability and resilience due to theirloosely cross-linked polymer matrix made by long interconnected polymer chains. Due to theseexcellent properties, they are among the most frequently used materials in load-transfer applicationsin adhesives, joints, sealing, bumpers, coatings, and protection shields. Due to the increasinguse of composite materials in the industry, polymers' usage, especially in polymeric adhesive,drastically increased. Since polymeric adhesives are used to join dissimilar material interfaces.However, degradation of polymeric adhesives is a menace to joints.Degradation or aging defined as the loss of properties due to environmental condition. Agingis an irreversible process that changes the network topology of the material. Polymeric adhesivesare susceptible to degradation which makes them a critical part with extreme sensitivity to temperature,moisture, and sunlight. Degradation-induced failure occurs due to damage accumulatedfrom mechanical sources and the loss of properties due to aging which cause a premature failurein system. Therefore, reliability of a system can be greatly compromised due to this degradation inducedfailure. Consequently, polymeric adhesives are a significant challenge for design reliabilityof multi-material systems. Reliable theoretical models to predict the degradation-induced failurein polymeric adhesives can substantially reduce the cost and enhance the reliability of adhesive bonding.Current approach in Original Equipment Manufacturers (OEM) companies is to use experimentalapproaches to predict the failure. However, laboratory conditions omit many factors thatare present in real-time and might not paint a clear picture of the mechanisms of failure. Mostimportantly, the time and cost needed for these tests are substantially high. To this end, developinga comprehensive software that would be able to model the real-time conditions of aging seems ofgreat value.This dissertation objective is to provide micro-mechanical constitutive models that would beable to model damage accumulation in polymers and polymeric adhesives during combined agingenvironments. These constitutive models provide the necessary modules to build a platform forcreating a Finite Element Method (FEM) based model for a 3D modeling of polymers in combinedenvironmental aging condition under mechanical stresses. To this end, the project followed fourmain steps namely, (I) performing accelerated aging tests, (II) analyzing the tests result to understandthe underlying aging phenomena, (III) developing degradation model, (IV) validating theproposed model versus the experimental data. After successfully finishing these steps, the necessarymodules to start creating an FEM platform would be ready which should be the next step forthis project.To go in further detail, this project successfully delivered five major tasks that has been definedas the necessary steps for developing the platform. These steps are as follows, (I) providing amodel for thermo-oxidative aging of polymers, (II) understanding the effects of decay functions onmodeling properties of aging, (III) developing a model for a combined thermo- and photo-oxidativeaging, (IV) developing a model that can successfully consider accumulated damage during combinedaging, (V) developing a model for cyclic environmental conditions. All of these models arethe first ones in the literature that being developed which suggests great novelty and value that thiswork can bring to the industry. The model proposed in this work can significantly enhance thedesign process by allowing pre-selection of materials and product geometries with respect to theexpected mechanical and environmental loading. Such process will allow agile design evaluation.
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