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 factors such 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 environment conditions 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 these excellent properties, they are among the most frequently used materials in load-transfer applications in adhesives, joints, sealing, bumpers, coatings, and protection shields. Due to the increasing use 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 adhesives are susceptible to degradation which makes them a critical part with extreme sensitivity to temperature, moisture, and sunlight. Degradation-induced failure occurs due to damage accumulated from mechanical sources and the loss of properties due to aging which cause a premature failure in system. Therefore, reliability of a system can be greatly compromised due to this degradation induced failure. Consequently, polymeric adhesives are a significant challenge for design reliability of multi-material systems. Reliable theoretical models to predict the degradation-induced failure in 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 that are present in real-time and might not paint a clear picture of the mechanisms of failure. Most importantly, the time and cost needed for these tests are substantially high. To this end, developing a comprehensive software that would be able to model the real-time conditions of aging seems of great 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 aging environments. These constitutive models provide the necessary modules to build a platform for creating a Finite Element Method (FEM) based model for a 3D modeling of polymers in combined environmental aging condition under mechanical stresses. To this end, the project followed four main steps namely, (I) performing accelerated aging tests, (II) analyzing the tests result to understand the underlying aging phenomena, (III) developing degradation model, (IV) validating the proposed model versus the experimental data. After successfully finishing these steps, the necessary modules to start creating an FEM platform would be ready which should be the next step for this 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 a model for thermo-oxidative aging of polymers, (II) understanding the effects of decay functions on modeling properties of aging, (III) developing a model for a combined thermo- and photo-oxidative aging, (IV) developing a model that can successfully consider accumulated damage during combined aging, (V) developing a model for cyclic environmental conditions. All of these models are the first ones in the literature that being developed which suggests great novelty and value that this work can bring to the industry. The model proposed in this work can significantly enhance the design process by allowing pre-selection of materials and product geometries with respect to the expected mechanical and environmental loading. Such process will allow agile design evaluation.
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