In order to clarify mechanical phenomena in civil engineering, it is necessary to improve computational theory and technique in consideration of the particularity of objects to be analyzed and to update computational mechanics focusing on practical use. In addition to the analysis of infrastructure, for damage prediction of natural disasters such as earthquake, tsunami and flood, since it is essential to reflect broad ranges in space and time inherent to fields of civil engineering as well as material properties, it is important to newly develop computational method in view of the particularity of fields of civil engineering. In this context, research trend of methods of computational mechanics which is noteworthy for resolving the complex mechanics problems in civil engineering is reviewed in this paper.
The conventional discrete element model without the rotational stiffness between the spherical elements can't at all describe the damping of the rotational motion of the sphere. In order to overcome the limits of the conventional discrete element model, this study presents the generalized discrete element model that is developed by formulating the rotational stiffness and the fracture criterion based on the Hertz-Mindlin contact mechanics. The new model is applied in the rotational motion of a sphere on the horizontal surface, and it is shown that the damping effect of the rotational motion is realistically described according to the physical properties of the spherical element.
Dynamic crack propagation is one of the unsolved problems in the field of continuum solid mechanics. Especially, lack of governing mechanism of dynamic crack propagation velocity makes the problem difficult. Most of the existing numerical analysis methods for dynamic crack propagation introduce rate dependent material parameters. A numerical analysis method for dynamic crack propagation without rate dependent material parameters is proposed in this paper. All the material parameters used in the proposed method can be experimentally determined. The major technical elements in the proposed method are PDS-FEM (Particle Discretization Scheme Finite Element Method) and newly proposed "working hypothesis on the governing mechanism of dynamic crack propagation." These technical elements introduce (i) simple treatment of fracture and corresponding discontinuity in displacement field, (ii) mechanism for re-distribution of residual nodal force, and (iii) governing mechanism for crack propagation velocity without rate dependent artificial material parameters.
In order to evaluate the effects of sample preparation method on the shear behavior of granular assemblies, three types of specimens were prepared: FC-specimens compacted by controlling inter-particle friction angle, TC-specimens compacted by controlling compaction time, and CC-specimens compacted by cyclic simple shear loading, respectively. A series of simple shear simulations by DEM on these specimens showed that the relationship between the void ratio and friction angle obtained in simple shear computed for the peak strength was unique irrespectively of the sample preparation methods. However, the shear moduli in small strain range were different for FC-, TC- and CC-specimens. To identify the reason for this difference, the micro-mechanical information such as coordination number, distribution of inter-particle forces were quantitatively evaluated. As a result, the granular packing structures were found to be different between three types of specimens, which might affects the deformation behavior in small strain range.
In this study, firstly in order to make a verification of appropriateness of an advanced buckling analysis program based on the elasto-plastic and finite displacement analysis which the authors have developed, the results obtained by this program were compared with the results from CWERRI and CWR-BUCKLE which have been developed in Europe and in U.S.A. respectively, and also compared with the results of actual track buckling tests. Secondarily the authors carried out a buckling analysis of a ballasted track equipped with continuous welded rails, using parameters such as lateral resistance of ballast, initial track misalignments, track curvature, etc., and clarified the influence of these parameters on the rail temperature increase from the neutral temperature corresponding to the minimum possible buckling resisting strength which is the important index in evaluating the track buckling. Thirdly the authors proposed the lower critical value of lateral peak resistance of ballast to prevent track buckling according to the track curvature, on the condition that the rail temperature increase from the neutral temperature is set to 35°C and also to 42°C (considering the margin of 20% for 35°C which is the sum of the critical temperature rise and the rail neutral temperature).
The shear behavior of binary granular mixtures was studied using the 2D discrete element method (DEM). Various specimens were prepared using different volume fractions and shapes i.e., disk and peanut, of small particles. The analyses showed that the average particle rotation of both small and large particles is equivalent to the continuum rotation field. However, when a specimen contains small disks of volume fractions in the range 5% - 15%, the average particle rotation is found to be much larger than the continuum rotation that accompanies the reduction in both shear resistance and thickness of the shear band. In such specimens, it was observed that many small particles were sandwiched by two large particles and underwent considerable rotation. In this paper, this irregul ar phenomenon is referred to as the "ball-bearing effect."
This paper studies the stability of dynamic crack growth in a homogeneous body, carrying out a numerical experiment of a plate with two anti-symmetric cracks. PDS-FEM proposed by the authors is extended to dynamic state and used in the numerical experiment. It is shown that while a common process is not found for the crack growth, there are two dominant patterns for the final crack configuration. The first pattern is anti-symmetric, indicating the stability of the homogeneous body solution, and the second pattern is not anti-symmetric, suggesting that the solution becomes unstable. It is also shown that higher loading rate tends to shift the crack configuration to the second pattern, losing the stability of the solution.