Damage and life assessment of materials undergoing concurrent fatigue and cyclic plastic strain accumulation over asymmetric multiaxial stress cycles with various loading spectra

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The accumulated plastic strain over asymmetric stress cycles, referred as ratcheting, and gradual damage progress over fatigue cycles are the principal causes of failure in many engineering components and structures. The reported cost of catastrophic failure in engineering structures annually exceeds $150 billion due to the complexity in geometry of components/ structures and the severe loads they experience in service. Both fatigue and ratcheting phenomena progressively cause damage when they are coupled. Safety issues and expenses associated with failure of engineering materials, necessitate implementing a high degree of reliability in design and analysis against failure of materials by developing a robust fatigue-ratcheting damage approach.***The proposed research offers a novel fatigue-ratcheting model to assess overall damage of engineering materials subjected to asymmetric multiaxial stress cycles. The proposed research will develop an algorithm to concurrently assess fatigue damage and plastic strain accumulation over asymmetric cycles of various multiaxial loading spectra by means of the Varvani-Topper fatigue damage model and the modified Ahmadzadeh-Varvani hardening rule. The proposed model will address shortcomings of earlier developed constitutive models by modifying cyclic plasticity parameters to account for non-proportional loading paths, and loading sequences which are influential parameters in assessing overall damage of components in-service.***The ultimate objective of the proposed research over the next five years is to develop a simple, accurate, and reliable damage framework to predict the life of engineering components under various multiaxial step-loading histories. The proposed research is geared to developing the model based on fatigue damage and plastic strain accumulation to reliably predict lives of engineering components. Using the applicant's NSERC funded equipment, multiaxial tests will be conducted to evaluate the capability of the proposed methodology. ***The applicant's long-term objective and future outlook will be to comprehensively expand research on the damage assessment of materials at various complex loadings, hostile environments, and elevated temperatures with viscoplastic nature where there is a shortage of rigorous scientific literature.***The applicant believes that the outcomes of the proposed research will largely contribute in developing design guidelines and codes of safety leading professionals in the field toward a safer and more reliable design of load-bearing components against failure. The involvement of students over steps of research under the applicant's supervision will train HQP capable of serving in Canadian and world-wide industries including automotive, aerospace, pressure vessel, and pipeline. This will benefit Canadian society employing safe and reliable manufactured goods and components.