Key Engineering Materials Vols. 340-341

Abstract: This paper is concerned with the geometrical similarity of heat conduction-elastioplastic structural problems. When the dimensions of a structure are geometrically scaled down/up, the similarity relations for both isolated heat conduction and elastoplastic structural problems are derived. For cases of thermo-structural coupled, it is concluded that heat conduction-static elastoplastic problems can be geometrically similarly scaled down/up and a set of similarity relations are drawn accordingly. As examples, a full-, half- and quarter-scale unilaterally-tensioned plate and internally-pressured cylindrical shell irradiated by a laser pulse are numerically analysed and the numerical results have confirmed this conclusion. However, heat conduction-dynamic elastoplastic problems are found not to comply compatibly with the geometrically similar scaling.

Abstract: The common transportation methods for the consumers of the ironwork such as the steel roll coils manufactured from the steelworks were either by the land transportation or the sea transportation. In order to transport the steel roll coil effectively and safely to the destination, the stability of the steel roll coil which induced the minimum movements during the transportation was strongly required. The basic transportation equipment for the steel roll coil such as the dunnage is made of 100% imported wood known as the apitong. However, the material characteristic such as the rigidity has caused permanent damages to the steel roll coil and the damaged steel roll coils were not easily restorable thus they were unsuitable for other purposes. Therefore, the introduction of new materials manufacturing dunnages which would have a good recovery performance and thus enable the damage prevention or reduction to the steel roll coil or any other products during the transportation is needed. This investigation was to develop the new and improved type of a dunnage from observing the current dunnage in the following areas; the array or the types of reinforcements that established the construction of the dunnage, the dunnage forming shapes of a rectangle and a trapezoid, the direct impacts to dunnage in the presence of vibration when the carrier was moving and stopping, and the critical impact to the dunnage due to the edge loading. Ultimately, the development of new type of dunnage that consisted of characteristics being soft and recoverable than the existing apitong dunnage and induces little or no damages to the steel roll coils are required.

Abstract: In this paper, a modified slab analysis has been used to determine the pressure distribution in the cylindrical compaction of aluminum powder under rotating die compaction. The analytical results are discussed to explain the pressure distribution and the interaction of the various parameters. To predict the density distribution in a powder compact under an applied pressure with torsion, the pressure function is coupled with some form of a pressure density relationship. High relative density can be realized in powder compacts by the rotating die compaction in contrast to the conventional compaction. A numerical analysis, using the DEFORM3D simulation software, is also carried out on the compaction under the rotating punch.

Abstract: The Channel Angular Extrusion (CAE) technique is a process, in which a deformable solid material is led to yielding through the intersection of inclined channels. Compared to classic plastic deformation, the process is technically simple but the material experiences, instantly, large plastic deformation. The deformation occurs locally and high internal stresses develop during the process. In most cases the process is used for grain size refinement. Equal Channel Angular Extrusion (ECAE) is a special case where the intersecting channels are of equal cross sections. In this paper, an analytical study of the internal stresses and those developed along CAE tools is presented. A deformation model is introduced for the general process of channel extrusion in which the intersecting channels are not necessarily equal. The procedure splits the material at the intersection of the channels into two zones; one causes the deformation while the other remains rigid. The analysis is also applied to the particular case of ECAE, and the results are compared with those obtained from a finite element analysis and the overall experimental pressure.

Abstract: This paper proposes a reliable and computationally efficient finite-element model (Partial Fiber Model) for the nonlinear analysis of reinforced concrete (R/C) frames under static and cyclic loading conditions that induce multiaxial bending and axial forces. The beam-column member is composed of three parts: middle elastic and two plastic regions at the two ends of beam. The plastic regions are discretized into longitudinal steel reinforcement and concrete fiber elements. The nonlinear behaviors of the elements are derived from the nonlinear stress-strain relations of the steel and concrete fibers. The global stiffness matrix of beam-column can be deduced from those of mentioned three parts. Numerical examples are calculated to prove the accuracy and efficiency of the model. The results of nonlinear analysis show the validity of the model to describe the nonlinear response of frame subjected to static and cyclic loadings.

Abstract: In ultimate asseismic design of ductile frame structures, plastic deformation and plastic hinge are generally permitted, and some preferred failure modes are often selected. It is an important problem that whether the designed structure collapses according to the designed failure mode, because of the large uncertainties included in external loads and member strength. In this paper, an identification procedure of failure modes for frame structures is developed, and the likely collapse modes of frame structures under uncertain load and member strength are investigated under assumption of normal distributed and non-normal distributed external loads and member strength. It is found that the occurrence order of likely collapse mode is much influenced by the distribution of the random variables. The occurrence order of collapse modes for column over designed structures are investigated and it is found that the increase of column over-design factor can effectively avoid the story collapse mode in probabilistic means.

Abstract: Various polygonal tubes were compressed in the axial direction under quasi-static and dynamic loading conditions. The effect of the polygonal shape and the wall thickness on the crush behavior is investigated, in which the cyclic buckling takes place. The numbers of polygonal edges were 3, 4, 5, 6 and 7 in the experiment. A circular tube was also tested for comparison. The tubes were machined from aluminum alloy A5056 bar. Crush strength is estimated as an index of the energy absorption capacity of the tube. It increases with increasing the number of polygonal edges of the tube, although it almost saturates when the number of polygonal edges is more than 6. For the wider variety of polygonal tubes than that in the experiment, numerical simulation is performed using the dynamic explicit finite element code DYNA3D. The computed crush behavior well agrees with the corresponding experimental one, however, the difference in collapse mode arises due to the slight imperfections in experiment. The deformation pattern becomes more irregular for the thinner-walled tube. Further, it is presumed that the large hardening exponent in the plastic property of the material could prevent the buckling switching from the symmetric mode to asymmetric one in the crushing of circular tube.

Abstract: Ductile frame structures are generally designed with column over-design factors (COF) to assure plastic hinges occurring in all beams and avoid unpreferable failure modes. In order to avoid story mechanisms of frame structure constructed with elastic-plastic materials, target COF has been investigated where the relative occurrence probability of most likely story mechanism is limited within a specific tolerance. In the present paper, the concept of basic and optimum column over-design factor for avoiding story mechanism are proposed and the value of them for multi-span multi-story ductile frames are presented based on a comprehensive investigation on the occurrence order of story mechanisms. The basic COF is defined as the critical value that the preferable failure mode and unpreferable failure mode are with the same failure probability, and it is the low limit assuring the entire beam-hinging pattern prior to story mechanisms. For a structure designed with a COF less than basic COF, the plastic hinges are easier to occur in partial stories to form story mechanism. The optimum COF is the most effective and economy COF to enhance the safety of structure, and it is resulted from the shift of priority of plastic hinges in different stories. The relationships between the basic and optimum COF with calculation parameters are also analyzed in this paper.

Abstract: The symmetry limit theory for 3-D continua developed by the authors, is applied to predictions of the occurrence limit of nonuniform strain in cylinders subjected to cyclic torsion. Bifurcation analysis of a steady-state path, which was defined as a continuous sequence of steady states generated under continuous increasing amplitude cyclic loading, is performed for the cylinder model. The deformation mode with very short wavelength in the circumferential direction is obtained, analogous to that in the internal buckling of a rigidly confined continuum shown by Biot. It is shown that this circumferential short-wave mode occurs at much smaller amplitude than the bifurcation under monotonic torsion.