• Advances in Computational Design
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• 제5권4호
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• pp.349-362
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• 2020

Dynamic characteristics of a scale-dependent porous metal foam cylindrical shell under a traveling load have been explored within this article based on a numerical approach. Within the material texture of the metal foams, uniform and non-uniform porosities may be dispersed. Based upon differential quadrature method (DQM) and Laplace transforms, the equations of motion for a shear deformable scale-dependent shell may be solved numerically. Scale-dependent shell modeling has been provided based upon strain gradient elasticity. Solving the equations will give the shell deflection as a function of load speed. Also, it is reported that shell deflection relies on the porosity dispersion and strain gradient influences.

• 대한기계학회논문집A
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• 제25권2호
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• pp.220-227
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• 2001

The fatigue crack initiation life is studied on automotive tensile-shear spot weldment made from cold rolled carbon steel(SPC) sheet by using DCPDM and local strain approach. It can be found that the fatigue crack initiation behavior in spot weldment can be definitely detected by DCPDM system. To predict the fatigue life of spot weldment, the local stresses and strains at the potential critical region are estimated by approximate method based on Neubers rule and elastic-plastic FEM analysis. A satisfactory correlation between the predicted life obtained from Local strain approach based on Neubers rule and experimental life can be found in spot weldment within a factor of 2.

• Journal of Welding and Joining
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• 제28권2호
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• pp.39-46
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• 2010

IIn this study, used is the equivalent loading method based on the inherent strain to predict the welding deformation of panel members. Equivalent loads are computed from the inherent strain distribution around weld line, and then applied for the linear finite element analysis. Thermal deformation of panel members can be, of course, carried out through the rigorous thermal elasto-plastic analysis procedure but it is not practical in applying to predicting the welding deformation of large structures such as blocks found in a ship structure from view of computing time. The present equivalent load approach has been applied to flat plate model to verify the present approach, and to several curved plate models having the curvature in the welding direction to investigate the effect of the longitudinal curvature upon the weld-induced deformation. The results are compared with those by thermal elasto-plastic analysis. As far as the present results are concerned, it can be said that the present approach shows good agreement with the results by welding experiment and the rigorous thermal elasto-plastic analysis. The present approach has been also applied to predict the welding deformation of panel block as for application illustration to practical model.

• Geomechanics and Engineering
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• 제22권6호
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• pp.553-564
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• 2020

In this study, a simple numerical approach for a circular tunnel opening in strain-softening surrounding rock is proposed considering out-of-plane stress and seepage force based on Biot's effective stress principle. The plastic region of strain-softening surrounding rock was divided into a finite number of concentric rings, of which the thickness was determined by the internal equilibrium equation. The increments of stress and strain for each ring, starting from the elastic-plastic interface, were obtained by successively incorporating the effect of out-of-plane stress and Biot's effective stress principle. The initial value of the outmost ring was determined using equilibrium and compatibility equations. Based on the Mohr-Coulomb (M-C) and generalized Hoek-Brown (H-B) failure criteria, the stress-increment approach for solving stress, displacement, and plastic radius was improved by considering the effects of Biot's effective stress principle and the nonlinear degradation of strength and deformation parameters in plastic zone incorporating out-of-plane stress. The correctness of the proposed approach is validated by numerical simulation.

• 세라미스트
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• 제23권1호
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• pp.89-100
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• 2020

Abnormally large electromechanical strain properties have been reported in bismuth-based piezoelectric ceramics, which cast a promise for replacing the market-dominating PZT-based piezoelectric ceramics in actuator applications. In spite of these large strains in bismuth-based piezoelectric ceramics, there still remains a critical issue for its safe transfer to practical applications, representatively, a relatively high operating field required to obtain the large strain properties. To overcome the challenge, much attention has been paid to so-called 0-3(or 3-0) type ceramic/ceramic composite approach to better tailoring the strain properties of bismuth-based piezoelectric ceramics. The approach turns out to be highly effective, leading to a drastic decrease in the operating electric field for these materials. Besides, both extensive and intensive search for the related mechanism revealed that the reduction in the operating electric field is largely due to the contribution from polarization coupling or strain coupling model between two different ceramics. This article reviews the status of the art in the development of novel ceramic/ceramic composites to make large incipient piezostrains in bismuth-based lead-free piezoelectric ceramics practical.

• Geomechanics and Engineering
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• 제12권3호
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• pp.347-360
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• 2017

The problem of cylindrical cavity expansion incorporating deformation dependent of intermediate principal stress in rock or soil mass is investigated in the paper. Assumptions that the initial axial total strain is a non-zero constant and the axial plastic strain is not zero are defined to obtain the numerical solution of strain which incorporates deformation-dependent intermediate principal stress. The numerical solution of plastic strains are achieved by the 3-D plastic potential functions based on the M-C and generalized H-B failure criteria, respectively. The intermediate principal stress is derived with the Hook's law and plastic strains. Solution of limited expansion pressure, stress and strain during cylindrical cavity expanding are given and the corresponding calculation approaches are also presented, which the axial stress and strain are incorporated. Validation of the proposed approach is conducted by the published results.

• Geomechanics and Engineering
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• 제5권5호
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• pp.379-399
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• 2013

In practice, analysis of laterally loaded piles is carried out using beams on non-linear Winkler springs model (often known as p-y method) due to its simplicity, low computational cost and the ability to model layered soils. In this approach, soil-pile interaction along the depth is characterized by a set of discrete non-linear springs represented by p-y curves where p is the pressure on the soil that causes a relative deformation of y. p-y curves are usually constructed based on semi-empirical correlations. In order to construct API/DNV proposed p-y curve for clay, one needs two values from the monotonic stress-strain test results i.e., undrained strength ($s_u$) and the strain at 50% yield stress (${\varepsilon}_{50}$). This approach may ignore various features for a particular soil which may lead to un-conservative or over-conservative design as not all the data points in the stress-strain relation are used. However, with the increasing ability to simulate soil-structure interaction problems using highly developed computers, the trend has shifted towards a more theoretically sound basis. In this paper, principles of Mobilized Strength Design (MSD) concept is used to construct a continuous p-y curves from experimentally obtained stress-strain relationship of the soil. In the method, the stress-strain graph is scaled by two coefficient $N_C$ (for stress) and $M_C$ (for strain) to obtain the p-y curves. $M_C$ and $N_C$ are derived based on Semi-Analytical Finite Element approach exploiting the axial symmetry where a pile is modelled as a series of embedded discs. An example is considered to show the application of the methodology.

• Structural Engineering and Mechanics
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• 제90권1호
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• pp.1-18
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• 2024

The present study conducts a thorough analysis of thermal vibrations in functionally graded porous nanocomposite beams within a thermal setting. Investigating the temperature-dependent material properties of these beams, which continuously vary across their thickness in accordance with a power-law function, a finite element approach is developed. This approach utilizes a nonlocal strain gradient theory and accounts for a linear temperature rise. The analysis employs four different patterns of porosity distribution to characterize the functionally graded porous materials. A novel two-variable shear deformation beam nonlocal strain gradient theory, based on trigonometric functions, is introduced to examine the combined effects of nonlocal stress and strain gradient on these beams. The derived governing equations are solved through a 3-nodes beam element. A comprehensive parametric study delves into the influence of structural parameters, such as thicknessratio, beam length, nonlocal scale parameter, and strain gradient parameter. Furthermore, the study explores the impact of thermal effects, porosity distribution forms, and material distribution profiles on the free vibration of temperature-dependent FG nanobeams. The results reveal the substantial influence of these effects on the vibration behavior of functionally graded nanobeams under thermal conditions. This research presents a finite element approach to examine the thermo-mechanical behavior of nonlocal temperature-dependent FG nanobeams, filling the gap where analytical results are unavailable.

• Journal of Welding and Joining
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• 제31권6호
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• pp.37-43
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• 2013

This study targets to make clear the connection between MS (Martensite start) point and welding shrinkage. We approved that a Martensite-transformed weldment may not yield state under low MS point, but also admitted the limitation of numerical calculation by inherent strain approach or thermal strain approach. Therefore, new thermal strain formulae during cooling stages were made. As a thermal strain is obtained by integrating thermal extension coefficient, a constant of integration should be decided. In our suggested formulae, the origin was based on totally remained austenite, and added strain from volume changes in Martensite transformation was based on totally transformed ferrite. Through the suggested methodology, It is verified that an MS point under a critical temperature can let weld shrinkage relax and the critical value can be obtained. For supporting this process, 15 weld-consumables were made, were tested by fillet type and were measured. As a result, a positive correlation between MS point and level of weld-distortion was obtained, but it was rather weak.

• Geomechanics and Engineering
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• 제13권4호
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• pp.585-600
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• 2017

This study deals with simple solutions for a spherical or circular opening excavated in elastic-brittle plastic rock mass compatible with a linear Mohr-Coulomb (M-C) or a nonlinear Hoek-Brown (H-B) yield criterion. Based on total strain approach, the closed-form solutions of stresses and displacement are derived simultaneously for circular and spherical openings using original H-B and M-C yield criteria. Two simple numerical procedures are proposed for the solution of generalized H-B and M-C yield criteria. Based on incremental approach, the similarity solution is derived for circular and spherical openings using generalized H-B and M-C yield criteria. The classical Runge-Kutta method is used to integrate the first-order ordinary differential equations. Using three data sets for M-C and H-B models, the results of the radial displacements, the spreading of the plastic radius with decreasing pressure, and the radial and circumferential stresses in the plastic region are compared. Excellent agreement among the solutions is obtained for all cases of spherical and circular openings. The importance of the use of proper initial values in the similarity solution is discussed.