• Smart Structures and Systems
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• v.28 no.6
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• pp.745-760
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• 2021

Dynamic buckling of structure is one of the failure modes that needs to be considered since it may result in catastrophic failure of the structure in a short period of time. For a thin fiber-reinforced polymer (FRP) plate under compression, buckling is an inherent hazard which will be intensified by the existence of defects like holes, cracks, and delamination. On the other hand, the growth of the delamination is another prime concern for thin FRP plates. In the current paper, reinforcing the plates against buckling is realized by using SMA wires in the form of stitches. A numerical framework is proposed to simulate the dynamic instability emphasizing the effect of the SMA stitches in suppressing delamination growth. The suggested algorithm is more accurate than the other methods when considering the transformation point of the SMA wires and the modeling of the cohesive zone using simple and yet reliable technique. The computational design of the method by producing the line by line orders leads to a simple algorithm for simulating the super-elastic behavior. The Lagoudas constitutive model of the SMA material is implemented in the form of user material subroutines (VUMAT). The normal bilinear spring model is used to reproduce the cohesive zone behavior. The nonlinear finite element formulation is programmed into FORTRAN using the Newmark-beta numerical time-integration approach. The obtained results are compared with the results obtained by the finite element method using ABAQUS/Explicit solver. The obtained results by the proposed algorithm and those by ABAQUS are in good agreement.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.7 s.112
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• pp.754-761
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• 2006

This paper presents the dynamic characteristics of MR impact damper for vehicle collision system. Various types of mechanism have been proposed to reduce force transmitted to the vehicle chassis and finally to protect occupants from injury. In the case of head-on collision, the bumper makes main role of isolation material for collision attenuation. In this study, the proposed bumper system consists of MR impact damper and structures. The MR impact damper utilizes MR fluid which has reversible properties with applied magnetic field. The MR fluid operates under flow mode. The bellows is used for generation of fluid flow. A mathematical model of the MR impact damper is derived incorporating with Bingham model of the MR fluid. Field dependent damping force is investigated with time and frequency domain. The MR impact damper is then incorporated with vehicle crash system. The governing equation of motion of vehicle model is formulated considering occupant model. Dynamic characteristics of vehicle collision system investigated with computer simulation.

• Steel and Composite Structures
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• v.43 no.1
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• pp.79-90
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• 2022

In this study, the dynamic behavior of functionally graded layered deep beams with viscoelastic core is investigated including the porosity effect. The material properties of functionally graded layers are assumed to vary continuously through thickness direction according to the power-law function. To investigate porosity effect in functionally graded layers, three different distribution models are considered. The viscoelastically cored deep beam is exposed to harmonic sinusoidal load. The composite beam is modeled based on plane stress assumption. The dynamic equations of motion of the composite beam are derived based on the Hamilton principle. Within the framework of the finite element method (FEM), 2D twelve -node plane element is exploited to discretize the space domain. The discretized finite element model is solved using the Newmark average acceleration technique. The validity of the developed procedure is demonstrated by comparing the obtained results and good agreement is detected. Parametric studies are conducted to demonstrate the applicability of the developed methodology to study and analyze the dynamic response of viscoelastically cored porous functionally graded deep beams. Effects of viscoelastic parameter, porosity parameter, graduation index on the dynamic behavior of porous functionally graded deep beams with viscoelastic core are investigated and discussed. Material damping and porosity have a significant effect on the forced vibration response under harmonic excitation force. Increasing the material viscosity parameters results in decreasing the vibrational amplitudes and increasing the vibration time period due to increasing damping effect. Obtained results are supportive for the design and manufacturing of such type of composite beam structures.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.9 no.3
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• pp.56-61
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• 2010

Recently, UV pulse laser is widely used in micro machining of the research, development and industry field of IT, NT and BT products because the laser short wavelength provides not only micro drilling, micro cutting and micro grooving which has a very fine line width, but also high absorption coefficient which allows a lot of type of materials to be machined more easily. To analyze the dynamic deformation during a very short processing time, which is nearly about several tens nanoseconds, the commercial Finite Element Analysis (FEA) code, LS-DYNA 3D, was employed for the computitional simulation of the UV laser micro machining behavior for thin copper material in this paper. A finite element model considering high strain rate effect is especially suggested to investigate the micro phenomena which are only dominated by mechanically pressure impact in disregard of thermally heat transfer. From these computational results, some of dynamic deformation behaviors such as dent deformation shapes, strains and stresses distributions were observed and compared with previous experimental works. These will help us to understand micro interaction between UV laser beam and material.

• Structural Engineering and Mechanics
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• v.15 no.4
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• pp.477-493
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• 2003

Masonry is not a simple material, the influence of mortar joints as a plane of weakness is a significant feature and this makes the numerical modelling of masonry very difficult especially when dynamic (seismic) analysis is involved. In order to develop a simple numerical model for masonry under earthquake load, an analytical model based on Distinct Element Method (DEM) is being developed. At the first stage, the model is applied to simulate the in-plane shear behaviour of an unreinforced masonry wall with and without opening where the testing results are available for comparison. In DEM, a solid is represented as an assembly of discrete blocks. Joints are modelled as interface between distinct bodies. It is a dynamic process and specially designed to model the behaviour of discontinuities. The numerical solutions obtained from the distinct element analysis are validated by comparing the results with those obtained from existing experiments and finite element modelling.

• Coupled systems mechanics
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• v.6 no.4
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• pp.501-522
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• 2017

This paper introduces a numerical procedure to incorporate elasto-plastic local deformation effects in the dynamic analysis of beams. The appealing feature is that simple beam type finite elements can be used for the global model which needs not to be altered by the localized elasto-plastic deformations. An overlapping local sophisticated 2D membrane model replaces the internal forces of the beam elements in the predefined region where the localized deformations take place. An iterative coupling technique is used to perform this replacement. Comparisons with full membrane analysis are provided in order to illustrate the accuracy and efficiency of the method developed herein. In this study, the membrane formulation is able to capture the elasto-plastic material behaviour based on the von Misses yield criterion and the associated flow rule for plane stress. The Newmark time integration method is adopted for the step-by-step dynamic analysis.

• Earthquakes and Structures
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• v.13 no.2
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• pp.211-220
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• 2017

Observations from past strong earthquakes revealed that near-fault ground motions could lead to the failure, or even collapse of electricity transmission towers which are vital components of an overhead electric power delivery system. For assessing the performance and robustness, a high-fidelity three-dimension finite element model of a long span transmission tower-line system is established with the consideration of geometric nonlinearity and material nonlinearity. In the numerical model, the Tian-Ma-Qu material model is utilized to capture the nonlinear behaviours of structural members, and the cumulative damage D is defined as an index to identify the failure of members. Consequently, incremental dynamic analyses (IDAs) are conducted to study the collapse fragility, damage positions, collapse margin ratio (CMR) and dynamic robustness of the transmission towers by using twenty near-fault ground motions selected from PEER. Based on the bending and shear deformation of structures, the collapse mechanism of electricity transmission towers subjected to Chi-Chi earthquake is investigated. This research can serve as a reference for the performance of large span transmission tower line system subjected to near-fault ground motions.

• Structural Engineering and Mechanics
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• v.86 no.4
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• pp.519-533
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• 2023

This work focuses on the dynamic analysis of thermal barrier coated straight and curved turbine blades modelled as functionally graded sandwich panel under thermal environment. The pre- twisted straight/curved blade model is considered to be fixed to the hub and, the complete assembly of the hub and blade are assumed to be rotating. The functionally graded sandwich composite blade is comprised of functionally graded face-sheet material and metal alloy core. The constituents' material properties are assumed to be temperature-dependent, however, the overall properties are evaluated using Voigt's micromechanical scheme in conjunction with the modified power-law functions. The blade model kinematics is based on the equivalent single-layer shear deformation theory. The equations of motion are derived using the extended Hamilton's principle by including the effect of centrifugal forces, and further solved via 2D- isoparametric finite element approximations. The mesh refinement and validation tests are performed to illustrate the stability and accurateness of the present model. In addition, frequency characteristics of the pre-twisted rotating sandwich blades are computed under thermal environment at various sets of parametric conditions such as twist angles, thickness ratios, aspect ratios, layer thickness ratios, volume fractions, rotational velocity and blade curvatures which can be further useful for designing the blade type structures under turbine operating conditions.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.5
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• pp.204-209
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• 2003

An elastomeric bushing is a device used in automotive suspension systems to reduce the load transmitted from the wheel to the frame of the vehicle. A bushing is an elastomeric hollow cylinder which is bonded to a solid steel shaft at its inner surface and a steel sleeve at its outer surface. The relation between the load applied to the shaft or sleeve and the relative deformation of elastomeric bushing is nonlinear and exhibits features of viscoelasticity. A load-displacement relation for elastomeric bushing is important for dynamic numerical simulations. A boundary value problem for the bushing response leads to the load-displacement relation which requires complex calculations. Therefore, by modifying the constitutive equation fur a nonlinear viscoelastic incompressible material developed by Lianis, the data fur the elastomeric bushing material was obtained and this data was used to derive the new load-displacement relation for radial response of the bushing. After the load relaxation function for the bushing is obtained from the step displacement control test, Pipkin-Rogers model was developed, Solutions were allowed fur comparison between the results of Modified Lianis model and those of the proposed model. It is shown that the proposed Pipkin-Rogers model is in very good agreement with Modified Lianis model.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.415-419
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• 2003

An elastomeric bushing is a device used in automotive suspension systems to reduce the load transmitted from the wheel to the frame of the vehicle. A bushing is an elastomeric hollow cylinder which is bonded to a solid steel shaft at its inner surface and a steel sleeve at its outer surface. The relation between the load applied to the shaft or sleeve and the relative deformation of elastomeric bushing is nonlinear and exhibits features of viscoelasticity. A load-displacement relation for elastomeric bushing is important for dynamic numerical simulations. A boundary value problem for the bushing response leads to the load-displacement relation which requires complex calculations. Therefore, by modifying the constitutive equation for a nonlinear viscoelastic incompressible material developed by Lianis, the data for the elastomeric bushing material was obtained and this data was used to derive the new load-displacement for radial response of the bushing. After the load relaxation function for the bushing is obtained from the step displacement control test, Pipkin-Rogers model was developed. Solutions were allowed for comparison between the results of Modified Lianis model and those of the proposed model. It is shown that the proposed Pipkin-Rogers model is in very good agreement with Modified Lianis model.