Kenichi Masuda

Crushing Behavior of Thin-Walled Hexagonal Tubes with Partition Plates

The crushing behaviour of hexagonal thin-walled tube with partition plates subjected to axial compression is studied by using finite element method. It is found that, in the crushing process, the folds, which generate along the full length of the tube, come to be crushed simultaneously and the compressive load will not descend, since the compressive load produced in the central part does not descend with the folds forming on outer walls. Therefore, in order to suppress a fluctuation of the compression load in crushing of the tube and to raise its average compression load, it is an effective method to introduce corner parts, especially corner parts where three plates intersect, in the geometry of the thin-walled tube.

Numerical Study on the Strength of Pipe Joints

With respect to the collapse behavior of joints in a steel pipe truss structure, in the present study, we carry out numerical analyses using a general-purpose FEM software package on the yield strength and the stress distribution near the connection in order to obtain information on the collapse behavior and the yield strength of joints. 𝑇-joint and 𝑌-joint are investigated. It is found that the joint strength is proportional to the 𝜆th power of thickness 𝑇 of a main tube for various joints with a fixed branch-to-chord diameter ratio 𝑑/𝐷. The index 𝜆 changes with 𝑑/𝐷 and in the range of 𝑑/𝐷=0.1 to 0.91, 𝜆≅1.93 to 1.55 holds with smaller values corresponding to larger 𝑑/𝐷. A compressive axial force along the main tube will reduce the joint strength, and it is also found that the strength-reduction ratio for 𝑌-joint is almost the same as that for 𝑇-joint having the same 𝑇 and 𝑑/𝐷. Also, the joint strength is influenced by the span length of the main tube. The joint strength decreases as the span length increases. However, the influence is small for small 𝑑/𝐷.

Equivalent Elastic Modulus of Asymmetrical Honeycomb

The equivalent elastic moduli of asymmetrical hexagonal honeycomb are studied by using a theoretical approach. The deformation of honeycomb consists of two types of deformations. The first is deformation inside the unit, which is caused by bending, stretching, and shearing of cell walls and rigid rotation of the unit; the second is relative displacement between units. The equivalent elastic modulus related to a direction parallel to one cell wall of the honeycomb is determined from the relative deformation between units. In addition, a method for calculating other elastic moduli by coordinate transformation is described, and the elastic moduli for various shapes of hexagon, which are obtained by systematically altering the regular hexagon, are investigated. It is found that the maximum compliance 𝐶𝑦𝑦|max and the minimum compliance 𝐶𝑦𝑦|min of elastic modulus 𝐶𝑦𝑦 in one rotation of the (𝑥,𝑦) coordinate system vary as the shape of the hexagon is changed. However, 𝐶𝑦𝑦|max takes a minimum and 𝐶𝑦𝑦|min takes a maximum when the honeycomb cell is a regular hexagon, for which the equivalent elastic moduli are unrelated to the selected coordinate system, and are constant with 𝐶11=𝐶22.

PREDICTION OF MAXIMUM MOMENT OF CIRCULAR TUBES SUBJECTED TO PURE BENDING IN CONSIDERATION OF THE LENGTH EFFECT

In the present study, the bending collapse of an elastoplastic cylindrical tube subjected to static pure bending is investigated using the finite element method (FEM). The moment of the elastoplastic cylindrical tube is controlled by the flattening rate of the tube cross-section. For a long tube, the flattening rate can be expressed in terms of the axial and circumferential stresses that, in turn, depend on the material and geometrical properties and the curvature of the tube. On the other hand, for a short tube, the boundary condition of the fixed walls prevents the flattening rate. In order to account for the length effect of tubes, we propose a new method in which flattening is considered as a deflection problem of a fixed curved beam. The proposed method was able to predict the change in the flattening rate as the curvature was increased. A rational prediction method is proposed for estimating the maximum bending moment of cylindrical tubes that accounts for the length effect. Its validity is demonstrated by comparing it predictions with numerical results obtained using the finite element method.