Key Engineering Materials Vols. 306-308

Abstract: Using rigid-plastic finite element DEFORMTM 2D software, this study simulates the plastic deformation of complex sheets at the roll gap during the sheet rolling process. Specifically, the study addresses the deformation of complex sheets containing inclusion defects. Under various rolling conditions, the present numerical analysis investigates the damage factor distributions, the void length at the front and rear of the inclusion, the deformation mechanisms, and the stress-strain distributions around the inclusion. The relative influences of the thickness reduction, the roll radii, and the friction factors on the void length at the front and rear of the inclusion, respectively, are systematically examined. Additionally, the correlation between the front and rear void lengths and a series of damage factors is explored. The simulation results appear to verify the suitability of the DEFORMTM 2D software for modeling the rolling of complex sheets containing inclusions.

Abstract: 3D FE (finite element) simulations of the deformation and damage evolution of particle reinforced composites are carried out for different microstructures of the composites. Several new methods and programs for the automatic reconstruction of 3D microstructures of composites on the basis of the geometrical description of microstructures as well as on the basis of the voxel array data have been developed and tested. Different methods of reconstruction and generation of finite element models of 3D microstructures of composite materials (geometry-based and voxel array based) are discussed and compared. It was shown that FE analyses of the elasto-plastic deformation and damage of composite materials using the microstructural models of materials generated with these methods yield very close results. Numerical testing of composites with random, regular, clustered and gradient arrangements of spherical particles is carried out. The fraction of failed particles and the tensile stress-strain curves were determined numerically for each of the microstructures. It was found that the rate of damage growth as well as the critical applied strain, at which the damage growth in particles begins, depend on the particle arrangement, and increase in the following order: gradient < random < regular < clustered microstructure.

Abstract: This paper describes the numerical modeling based on combination of finite element method (FEM) and discrete element method (DEM) has been employed to simulate crack propagation under mixed mode loading. The work demonstrates the ability of combination finitediscrete element method to simulate the crack propagation that is usually performed through, what is termed, transition from continua to discontinua process. Crack propagation trajectory under selected loading angles (30o & 60o) are presented. The result obtained using the proposed model compare well with experimental result.

Abstract: Applications of above-coercive electric fields lead to domain switching of a large or global scale. Large scale switching model is proposed to deal with load-induced domains witching in experiment. Both a discussion of crack initiation via the stress intensity factor and a discussion of crack path stability via T-stress are presented. The theoretical predictions and the experimental data roughly coincide for crack initiation, propagation and stability phenomena. Attention is also extended to consider the effect of non-uniform ferro-elastic domain switching in the vicinity of a crack. The domain switching zone is divided into a saturated inner core and an active surrounding annulus. Toughening for ferroelectrics with different poling states is estimated via Reuss type approximation. Solutions obtained according to spherical and cylindrical inclusions cover the range of experimental data.

Abstract: A numerical technique based on using manifold elements in finite element method, for modeling propagation of arbitrary cracks in solids, is described. When the region with crack(s)is subjected to external loading and the crack(s) starts to extend, the crack growth may intersect boundaries of nearby finite elements. Those intersected finite elements are replaced by manifold elements. The technique, by which the initial finite element mesh can be kept unchanged during the processes of crack propagation, is called manifold elements in finite element method. The crack growth is governed by the theories of linear elastic fracture mechanics. The stress intensity factors are computed by a contour integral technique and crack trajectory is determined by applying the maximum tangential stress criterion. Finally, test examples are given to verify the new method and the predicted trajectories are compared to experimentally obtained crack growth paths with good agreements

Abstract: The structural design problems are acknowledged to be commonly multicriteria in nature. The various multicriteria optimization methods are reviewed and the most efficient and easy-to-use Pareto optimal solution methods are applied to structural optimization of grillages under lateral uniform load. The result of the study shows that Pareto optimal solution methods can easily be applied to structural optimization with multiple objectives, and the designer can have a choice from those Pareto optimal solutions to meet an appropriate design environment.

Abstract: In the displacement measurement inside a specimen by speckle photography, it is not easy to get clear Young's fringes images. Stress-intensity factors of mixed mode can be estimated by embedded speckle photography. However, the error of the stress intensity factor inside a specimen was considerably large. To evaluate the 3-D stress field inside the specimen from displacement data on the free surface obtained from the 2-D intelligent hybrid method, we developed the 3-D local hybrid method based on an inverse problem analysis. The accuracy of the 3-D local hybrid method varies depending on the depth of the plane of error assessment, hybrid domain size, and specimen thickness. Hence the optimal analysis conditions were discussed.

Abstract: The optimum midship section design of container ship belongs to the nonlinear constrained optimization problem. The determination of scantlings for the midship region is a very crucial matter out of whole structural design process of a ship. This determination may be a process of satisfying a lot of complicated design constraints empirically, rather than optimizing some objective function. However, in order to realize optimum or rational design for midship region with complicated design constraints, it is necessary to model the design problem as strictly as possible and to accomplish more highly numerical optimization. Real-coded micro-Genetic lgorithm (RμGA) is proposed to find the optimum midship section arrangement of an actual hatchcoverless container ship without handling any of penalty functions.

Abstract: The response analysis of reinforced concrete (RC) structures subjected to strong earthquake motions require realistic conceptual models. The special models, such as Clough and Takeda, which describe the non-linear section characteristic of reinforced concrete beam and column. In the earthquake motions, the deforming is sensitive to the response of structures intensively. The traditional lumped plastic model inevitably induces inaccuracy. Hence, meshing the members or distributing stiffness along the whole member is employed to simulate the seismic response of the structures. In this paper, Takeda elastic-plastic beam element model has been developed, which is based on general FEM code ABAQUS in order to simulate the response of RC. The influence is discussed due to the different lengths of plastic zone and element sizes.

Abstract: A general helicopter uses rotary power produced from the installed engine in order to get the directional thrust. In the case of a tip-jet rotor helicopter, the compressed air or the combustion gas passes through a duct system inside rotors and is ejected out of the nozzle at the blade tips to produce torque enough for rotation of the rotor system. The generated torque makes the rotor system rotate, so that it can create the directional thrust. Since the anti-torque does not occur in this tip-jet rotorcraft, the tail rotor can be removed, which can be very attractive. In this paper, a power system for a reduced-scale tip-jet rotor by using a small turbo-jet engine is designed and tested for feasibility study. The in-plane thrust that the power system can produce is measured and compared with the calculated one. Finally, the finite element analysis of a conceptually designed tip-jet rotor is performed to ensure structural safety.