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    An Experimental-Cohesive Zone Model Approach to Predict Fatigue Life of Adhesive Joints with Varying Modes of Loading and Joint Configurations for Automotive Applications
    (Taylor & Francis, 2024-10-03) Ibrahim, Ahmed Hanafy; Watson, Brock; Jahed, Hamid; Rezaee, Saeid; Cronin, Duane
    Predictive fatigue life models of adhesive joints are necessary to enable the assessment of automotive bonded structures while reducing costly experimental testing. However, contemporary models have typically been calibrated for specific joint configurations and modes of loading, limiting their applicability to large-scale structures. Additionally, available models are based on simulation of cumulative fatigue cycling, making them computationally prohibitive. In the current study, fatigue experimental tests were undertaken on adhesive joints in cross-tension (CT) (load angles of 0°, 45°, and 90°) and single-lap shear joint (SLJ) configurations. A total of nine joint configurations, having symmetrical (same material and thickness) and asymmetrical (dissimilar material or unequal thickness) joints, were tested. Fatigue tests at load levels between 25-75% of the static peak load were performed until joint failure or to runout (two million load cycles). The static tests of the joints were simulated to failure using finite element (FE) models with the cohesive zone method (CZM). The maximum fracture energy release rates (Gmax) were calculated within the adhesive bond line at static loads corresponding to the peak loads of the fatigue tests. The Gmax values, computed from single cycle, specimen-specific FE simulations, were correlated with the measured fatigue life (Nf) of the adhesive joints with varying modes of loading and joint configurations. The fatigue life prediction model, based on Gmax − Nf correlation, predicted the cycles to failure for 85% of the fatigue tests, and 81% of the independent validation tests. The proposed fatigue life prediction approach provides computational efficiency and large-scale compatibility.
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    Characterization of the Structural Response of Adhesively Bonded Ultra-High Strength Steel Tubes under a Range of Loading Conditions and Assessment of a Rate Dependent Cohesive Zone Model
    (Springer, 2024-02-27) Liu, Brian; Watson, Brock; Worswick, Michael; Cronin, Duane
    Weight reduction through the use of adhesive joining in multi-material lightweight structures requires material characterization and substructure level model validation to support CAE design. In this study, automotive-scale structural tubes were created by adhesively joining tailored hot stamped (THS) ultra-high strength steel (UHSS) hat sections using a two-part toughened epoxy adhesive applied to the flanges. A custom fixturing method was developed to achieve consistent bond line thickness for the adhesive joint. The physical tubes were tested in three-point bend, axial crush, and Mode I loading at quasi-static and dynamic loading rates, from which the structural response and failure characteristics were established. The experiments were modeled numerically using a previously developed cohesive zone method (CZM) that had been validated for coupon level tests. In the current work, the CZM model is assessed under structural loading conditions, based on predictions of load-displacement response, peak load, energy absorption, displacement-to-failure, and deformation pattern. In addition, crack extension along the adhesive joint was assessed for the Mode I loading condition. The novel bonding procedure developed for this study resulted in consistent experimental loading response. Generally, the predicted results agreed with experimental results, particularly for the Mode I loading and crack extension behavior. However, the CZM model was not able to accurately predict displacement-to-failure for the three-point bend tests, owing to out-of-plane buckling observed in the experiments. With a few exceptions, the CZM adhesive model based on coupon-level data was able to predict the peak force, displacement-to-failure, and energy absorption of the bonded structural assemblies to within 16% of the average experimental responses.
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    Integration of Muscle Pre-tension and Activation to Evaluate Neck Muscle Strain Injury Risk during Simulated Rear Impacts Using a Finite Element Neck Model
    (SAE International, 2025-02-06) Correia, Matheus; McLachlin, Stewart; Cronin, Duane
    Prevention of rear-impact neck injuries remains challenging for safety designers due to a lack of understanding of the tissue-level response and injury risk. Soft tissue injuries have been inferred from clinical, cadaveric, and numerical studies; however, there is a paucity of data for neck muscle injury, commonly reported as muscle pain. The goal of this study was to investigate the effect of muscle pre-tension and activation on muscle strain and injury risk resulting from low-severity rear impacts using a detailed finite element head and neck model (HNM). The HNM was extracted from the GHBMC average stature male model and re-postured to match a volunteer study, with measured T1 kinematics applied as boundary conditions to the HNM. Three cases were simulated for three impact severities: the baseline repostured HNM, the HNM including muscle pre-tension, and the HNM with muscle pre-tension and muscle activation. The head kinematics, vertebral kinematics, muscle strains, and three neck injury criteria were calculated to assess injury risk. The kinematic response of the neck model demonstrated an S-shaped pattern, followed by extension in the rear impact cases. The maximum kinetics, kinematics, and muscle strains occurred later in the impact during the extension phase. The distribution and magnitude of muscle strain depended on muscle pre-tension and activation, and the largest predicted strains occurred at locations associated with muscle injury reported in the literature. The HNM with muscle pre-tension and muscle activation provides a tool to assess rear impact response and could inform injury mitigation strategies in the future.
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    Impact Location Dependence of Behind Armor Blunt Trauma Injury Assessed using a Human Body Finite Element Model
    (American Society of Mechanical Engineers (ASME), 2024-01-29) Bustamante, Michael C.; Cronin, Duane S.
    Behind Armor Blunt Trauma (BABT), resulting from dynamic deformation of protective ballistic armor into the thorax, is currently assessed assuming a constant threshold of maximum backface deformation (44 mm). Although assessed for multiple impacts on the same armor, testing is focused on armor performance (shot-to-edge and shot-to-shot) without consideration of the underlying location on the thorax. Previous studies identified the importance of impacts over organs of animal surrogates wearing soft armor. However, the effect of impact location was not quantified outside the threshold of 44 mm. In the present study, a validated biofidelic advanced human thorax model (50th percentile male) was utilized to assess the BABT outcome from varying impact location. The thorax model was dynamically loaded using a method developed for re-creating BABT impacts, and BABT events within the range of real-world impact severities and locations were simulated. It was found that thorax injury depended on impact location for the same BFDs. Generally, impacts over high compliance locations (anterolateral rib cage) yielded increased thoracic compression and loading on the lungs leading to pulmonary lung contusion. Impacts at low compliance locations (top of sternum) yielded hard tissue fractures. Injuries to the sternum, ribs, and lungs were predicted at BFDs lower than 44 mm for low compliance locations. Location-based injury risk curves demonstrated greater accuracy in injury prediction. This study quantifies the importance of impact location on BABT injury severity and demonstrates the need for consideration of location in future armor design and assessment.
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    Making Political Party Leaders: The Practice of Political Leadership in Canadian Party Leadership Races
    (University of Waterloo, 2025-12-04) Columb, Conor Donnie
    Party leaders are central to the Canadian party system because they represent their political parties at the national level, hold significant power within them over policy and messaging, and they often go on to form government following elections. Although scholars have studied leadership selection methods, party organization, and political campaigning, less attention has been paid to how aspiring party leaders develop political leadership in their respective campaigns. This gap invites the following questions: (1) how is political leadership constructed and communicated by aspiring leaders in Canadian political party leadership races; and (2) what campaign strategies do they most commonly use to present themselves as viable party leaders to party members? This study examined 16 candidates across three federal leadership races: the Liberal Party (2013); the New Democratic Party (NDP) (2017); and the Conservative Party of Canada (CPC) (2022). Through a qualitative content analysis of the campaign materials of each candidate in these races, such as media coverage, debate performances, and websites, this study identified the ways that candidates construct and communicate political leadership through their campaigns to persuade party members to vote for them as the party leader. Overall, this study further contextualized how leadership is marketed and performed in party politics.