• Steel and Composite Structures
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• v.26 no.4
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• pp.421-437
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• 2018

Free vibration analysis of a three-layered microbeam including an elastic micro-core and two piezo-magnetic face-sheets resting on Pasternak's foundation are studied in this paper. Strain gradient theory is used for size-dependent modeling of microbeam. In addition, three-unknown shear and normal deformations theory is employed for description of displacement field. Hamilton's principle is used for derivation of the governing equations of motion in electro-magneto-mechanical loads. Three micro-length-scale parameters based on strain gradient theory are employed for prediction of vibrational characteristics of structure in micro-scale. The results show that increase of three micro-length-scale parameters leads to significant increase of three natural frequencies especially for increase of second micro-length-scale parameter. This result is according to this fact that stiffness of a micro-scale structure is increased with increase of micro-length-scale parameters.

• Structural Engineering and Mechanics
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• v.53 no.3
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• pp.429-442
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• 2015

The measurement from the indentation process depends on the amount of pile-up or sink-in around the contact impressions. In this paper, finite element concept is utilized to study the pile-up and sink-in behaviour for the wide range of materials with different young's modulus, yield stresses, strain-hardening exponents and coefficient of friction values. The exact indentation model is created by using the two dimensional axisymmetrical model for simulating the spherical indentation process on the lines of Taljat and Pharr (2004) work. The result shows that during spherical indentation process the amount of pile-up is greatly influenced by the strain hardening exponents in addition to other material properties and depth of penetration. The numerical results from the finite element analysis are also validated using the exact multilinear material properties obtained from the tensile testing for the materials like mild steel, brass and aluminium.

• Interaction and multiscale mechanics
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• v.4 no.2
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• pp.155-164
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• 2011

The lattice strain evolution within polycrystalline solids is influenced by the crystal orientation and grain interaction. For multi-phase polycrystals, due to potential large differences in properties of each phase, lattice strains are even more strongly influenced by grain interaction compared with single phase polycrystals. In this research, the effects of the grain interaction and crystal orientation on the lattice strain evolution in a two-phase polycrystals are investigated. Duplex steel of austenite and ferrite phases with equal volume fraction is selected for the analysis, of which grain arrangement sensitivity is confirmed in the literature through both experiment and simulation (Hedstr$\ddot{o}$m et al. 2010). Analysis on the grain interaction is performed using the results obtained from the finite element calculation based on the model of restricted slip within crystallographic planes. The dependence of lattice strain on grain interactions as well as crystal orientation is confirmed and motivated the need for more in-depth analysis.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.687-691
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• 2001

Al alloy matrix composite with TiNi shape memory fiber as reinforcement has been fabricated by hot pressing to investigate mechanical properties. The stress-strain behavior of the composites was evaluated at temperatures between 363K and room temperature as a function of pre-strain by using experimental and finite element analysis, and both cases showed that the tensile stress at 363K was higher than that of the room temperature. Especially, the tensile stress of this composite increases with increasing the amount of pre-strain, and it also depends on the volume fraction of fiber and heat treatment. The smartness of the composite is given due to the shape memory effect of the TiNi fiber which generates compressive residual stress in the matrix material when heated after being pre-strained.

• Structural Engineering and Mechanics
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• v.5 no.3
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• pp.221-237
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• 1997

This paper presents a new uniaxial material model for rate-sensitive analysis addressing both the transient and steady-state responses. The new model adopts visco-plastic theory for the rate-sensitive response, and employs a three-parameter representation of the overstress as a function of the strain-rate. The third parameter is introduced in the new model to control its transient response characteristics, and to provide flexibility in fitting test data on the variation of overstress with strain-rate. Since the governing visco-plastic differential equation cannot be integrated analytically due to its inherent nonlinearity, a new single-step numerical integration procedure is proposed, which leads to high levels of accuracy almost independent of the size of the integration time-step. The new model is implemented within the nonlinear analysis program ADAPTIC, which is used to provide several verification examples and comparison with other experimental and numerical results. The companion paper extends the three-parameter model to trilinear static stress-strain relationships for steel and concrete, and presents application examples of the proposed models.

• Computers and Concrete
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• v.22 no.1
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• pp.11-25
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• 2018

A numerical approach for the evaluation of the flexural response of Steel Fibrous Concrete (SFC) cross-sections with arbitrary geometry, with or without conventional steel longitudinal reinforcing bars is proposed. Resisting bending moment versus curvature curves are calculated using verified non-linear constitutive stress-strain relationships for the SFC under compression and tension which include post-peak and post-cracking softening parts. A new compressive stress-strain model for SFC is employed that has been derived from test data of 125 stress-strain curves and 257 strength values providing the overall compressive behaviour of various SFC mixtures. The proposed sectional analysis is verified using existing experimental data of 42 SFC beams, and it predicts the flexural capacity and the curvature ductility of SFC members reasonably well. The developed approach also provides rational and more accurate compressive and tensile stress-strain curves along with bending moment versus curvature curves with regards to the predictions of relevant existing models.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.445-450
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• 2003

The moment-curvature envelope describes the changes in the flexural capacity with deformation during a nonlinear analysis. Therefore, the moment-curvature analysis for reinforced concrete columns, indicating the available flexural strength and ductility, can be conducted providing the stress-strain relation for the concrete and steel are known. The moments and curvatures associated with increasing flexural deformations of the column may be computed for various column axial loads by incrementing the curvature and satisfying the requirements of strain compatibility and equilibrium of forces. Clearly it is important to have accurate information concerning the complete stress-strain curve of confined high-strength concrete in order to conduct reliable moment-curvature analysis to assess the ductility available from high-strength columns. However, it is not easy to explicitly characterize the mechanical behavior of confined high-strength concrete because of various parameter values, such as the confinement type of rectilinear ties, the compressive strength of concrete, the volumetric ratio and strength of rectangular ties, etc. So a stress-strain confinement model is developed which can simulate a complete inelastic moment-curvature relations of a high-strength reinforced concrete column

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1996.10a
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• pp.38-47
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• 1996

Sectional analysis program for plane strain or axisymmetric geometry of aluminum alloy sheet metals was developed. For modeling the anomalous behavior of aluminum alloy, Barlat's strain rate potential and Hill's 1990 non-quadratic yield theory arranged under the plane stress assumption were employed. 2-D rigid-viscoplastic FEM formulation based on the bending-augmented membrane theory was derived, solving simultaneously force equilibrium as well as non-penetration condition. Isotropic hardening law was also assumed for yielding behavior. To verify the validity and availability of the developed program, 2-D stretch/draw forming process for plane strain geometry and cylindrical cup deep drawing process for axisymmetric geometry were simulated.

• Journal of Ocean Engineering and Technology
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• v.13 no.2 s.32
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• pp.41-50
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• 1999

As for the properties on both the aluminum and the CFRP which are used to make A17075/CFRP multi-layered hybrid composites, CRALL(carbon reinforced aluminum laminate). In the CRALL specimen for rule of mixture, we were analyzed notched strength by finite element method. The results obtained from FEM analysis are as follows; In the unnotch CRALL specimen, the stresses CFRP, epoxy, Al 7075 obtained by finite element method strength solution for A/C0001, when strain is 0.28%, are 1400MPa, 38MPa, 411MPa. respectively and for A/C9991, when strain 0.48%, are 392MPa, 26MPa and 321Mpa, respectively. the solpe of the stress-strain curve by FEM increases in keeping with the hole size and the yield strain decrease to 36% and 55% for A/C9993 and A/C9991 respectively.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.10a
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• pp.85-89
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• 2002

This paper used the Laser Speckle Interferometry to present the strain analysis of Nd:YAG Laser welding zone. Previous TIG welding to sheet plate, which welds only high-skilled engineer, produces residual stress nearby welding zone due to thermal effect. However, Laser welding makes sheet pate welding easy and thermal effect minimum. Thermal effect zone is measured by strain analysis of the laser-welding zone by ESPI under tensile testing of sheet plate welded by Nd:YAG laser. The ESPI results, which compared with strain gage method, are agreed within error 3 %.