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주기하중을 받고 있는 금속의 시간의존적 소성 모델 비교
Dongkeon Kim,Gary Dargush 한국복합신소재구조학회 2013 복합신소재구조학회논문집 Vol.4 No.1
In real world applications, the response of structures may be dependent on the rate of loading and thus can be affected by transient loading, especially when the rate of loading is significant. In such situations, the rate of loading may become a major issue to understand structures during earthquake excitation or under blast or high velocity impact. In some cases, the rate effect on structures under strong earthquake excitation cannot be ignored when attempting to understand inelastic behavior of structures. M any researchers developed the constitutive theories in cyclic plasticity and viscoplasticity. In this study, numerical simulation by cyclic visocoplasticity models is introduced and analyzed. Finally, the analytical results are compared with experimental results as a means to evaluate and verify the model.
Unified Space-Time Finite Element Methods for Dissipative Continua Dynamics
Kim, Jinkyu,Dargush, Gary F.,Roh, Hwasung,Ryu, Jaeho,Kim, Dongkeon World Scientific Publishing Company 2017 International journal of applied mechanics Vol.9 No.2
<P>Based upon the extended framework of Hamilton’s principle, unified space-time finite element methods for viscoelastic and viscoplastic continuum dynamics are presented, respectively. For numerical efficiency, mixed time-step algorithm in time- and displacement-based algorithm in space are adopted. Through analytical investigation, we demonstrate that the Newmark’s constant average acceleration method and the present method are the same for viscoelasticity. With spatial eight-node brick elements, some numerical simulations are undertaken to validate and investigate the performance of the present non-iterative space-time finite element method for viscoplasticity.</P>
Preliminary study on a composite steel slit damper
Jinkyu Kim,김민철,Dongkeon Kim 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.9
A steel slit damper has been used to enhance the seismic performance of structures with several advantages. The damper can be easily manufactured at a low cost. Furthermore, it can dissipate a significant amount of seismic energy through the stable hysteretic behavior of steel. This study presents a preliminary investigation of the development of a composite steel slit damper that can respond effectively at multiple levels of seismic loading. The performance of the prototype composite steel slit damper is investigated in both experimental and analytical ways. In the experiments, the specimen shows the stable hysteretic response with sufficient ductility, where the multi-phased response is observed in the incremental-amplitude cyclic loading case. Furthermore, a nonlinear numerical analysis that combines both kinematic hardening and isotropic hardening models can reliably describe such characteristics.
Jinkyu Kim,Dongkeon Kim 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.9
A common approach for dynamic analysis in current practice is based on a discrete time-integration scheme. This approach can be largely attributed to the absence of a true variational framework for initial value problems. To resolve this problem, a new stationary variational principle was recently established for single-degree-of-freedom oscillating systems using mixed variables, fractional derivatives and convolutions of convolutions. In this mixed convolved action, all the governing differential equations and initial conditions are recovered from the stationarity of a single functional action. Thus, the entire description of linear elastic dynamical systems is encapsulated. For its practical application to structural dynamics, this variational formalism is systemically extended to linear elastic multidegree-of-freedom systems in this study, and a corresponding weak form is numerically implemented via a quadratic temporal finite element method. The developed numerical method is symplectic and unconditionally stable with respect to a time step for the underlying conservative system. For the forced-damped vibration, a three-story shear building is used as an example to investigate the performance of the developed numerical method, which provides accurate results with good convergence characteristics.