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Influence of dynamic loading on failure behavior of spot welded automotive steel sheets
Noh, Wooram,Koh, Youngwoo,Chung, Kwansoo,Song, Jung-Han,Lee, Myoung-Gyu Elsevier 2018 International journal of mechanical sciences Vol.144 No.-
<P><B>Abstract</B></P> <P>Dynamic failure of the spot welded automotive steel sheets, similar and dissimilar combinations of TRIP980 and GMW2 sheets, was analyzed with finite element (FE) simulations. The strain rate-sensitivity of the base sheets was considered to investigate the influence of dynamic loading on failure behavior of the welded sheets. Mechanical properties were first identified under the quasi-static loading as the reference condition. Hardening behavior and fracture criterion were identified by numerical inverse method applied to the standard tensile test and a miniature tensile test for the base sheet and the weld nugget, respectively. Moreover, strain rate-sensitivities of the base sheets were inversely characterized as a function of strain and strain rate. Dynamic lap-shear and coach-peel coupon tests were performed to evaluate the dynamic failure behavior of the welded sheets. Peak strength, failure mode and load-displacement curves of the coupon tests were predicted with the FE simulations. The combined experimental and numerical approach showed that the strain rate-sensitivity of the base sheet played a key role on determination of failure characteristics in coupon tests.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Dynamic failure behavior of the spot welded automotive sheets was modeled based on coupled experiment and FE simulations. </LI> <LI> Strain rate-sensitive mechanical properties of the constituent zones in the welded joints were characterized and modeled. </LI> <LI> An in-depth FE analysis was provided to predict and to analyze the effect of the rate-sensitivity on failure behavior of welds. </LI> <LI> The proposed modeling approach could provide good predictions for the performance of welded coupons and fracture modes. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Dongjoon Myung,Wooram Noh,김지훈,Jinhak Kong,Sung‑Tae Hong,Myoung‑Gyu Lee 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.4
In this study, a simulation-based examination on the deformation mechanism in the friction stir welding (FSW) process isconducted, which may not be efficiently feasible by experiment due to severe deformation and rotation of material flow neara tool pin. To overcome the severity of distortion of plastically deforming finite element meshes in the Lagrange formulation,and an over-simplified elastic-plasticity constitutive law and contact assumption in the Eulerian formulation, the arbitraryLagrangian–Eulerian (ALE) formulation is employed for the finite element simulations. Superior accuracy in predictingthe temperature profiles and distributions of the friction stir welded aluminum alloy workpiece could be obtained comparedto the results of Eulerian based simulations. In particular, the ALE based simulations could predict the sharper gradient oftemperature decrease as the distance from the welding zone increases, while the Eulerian based model gives more uniformprofiles. The second objective of the study is to investigate the coupling of simulation-based temperature histories into thestrength prediction model, which is formulated on the basis of precipitation kinetics and precipitate-dislocation interaction. The calculated yield strength distribution is also in better agreement with experiment than that by the Eulerian based model. Finally, the mechanism of the FSW process is studied by thoroughly examining the frictional and material flow behaviorof the aluminum alloy in the welded zone. It is suggested that the initially high rate of temperature increase is attributedto frictional heat due to slipping of material on the tool surface, and the subsequent saturated temperature is the result ofsequential repetitive activations of the sticking and slipping modes of the softened material. The sticking mode is the mainsource of plastically dissipated heat by the large plastic deformation around the rotating tool pin. The present integratedfinite element simulation and microstructure-based strength prediction model may provide an efficient tool for the designof the FSW process.
Jeongmin Lee,Sangwook Lee,Wooram Jung,Guk Bae Kim,Taehun Kim,Jiwon Seong,장혜민,Young Noh,Na Kyung Lee,Boo Rak Lee,Jung-Il Lee,Soo Jin Choi,Wonil Oh,Namkug Kim,Seunghoon Lee,Duk L. Na 대한의학회 2022 Journal of Korean medical science Vol.37 No.31
Background: To deliver therapeutics into the brain, it is imperative to overcome the issue of the blood-brain-barrier (BBB). One of the ways to circumvent the BBB is to administer therapeutics directly into the brain parenchyma. To enhance the treatment efficacy for chronic neurodegenerative disorders, repeated administration to the target location is required. However, this increases the number of operations that must be performed. In this study, we developed the IntraBrain Injector (IBI), a new implantable device to repeatedly deliver therapeutics into the brain parenchyma. Methods: We designed and fabricated IBI with medical grade materials, and evaluated the efficacy and safety of IBI in 9 beagles. The trajectory of IBI to the hippocampus was simulated prior to surgery and the device was implanted using 3D-printed adaptor and surgical guides. Ferumoxytol-labeled mesenchymal stem cells (MSCs) were injected into the hippocampus via IBI, and magnetic resonance images were taken before and after the administration to analyze the accuracy of repeated injection. Results: We compared the planned vs. insertion trajectory of IBI to the hippocampus. With a similarity of 0.990 ± 0.001 (mean ± standard deviation), precise targeting of IBI was confirmed by comparing planned vs. insertion trajectories of IBI. Multiple administrations of ferumoxytol-labeled MSCs into the hippocampus using IBI were both feasible and successful (success rate of 76.7%). Safety of initial IBI implantation, repeated administration of therapeutics, and long-term implantation have all been evaluated in this study. Conclusion: Precise and repeated delivery of therapeutics into the brain parenchyma can be done without performing additional surgeries via IBI implantation.