Page 183 - Marine Structural Design

Chapter 9 Buckling and Local Buckling of Tubular Members 159

availability for the pipe of these sizes, the test specimens were fabricated by cold forming
from pipe of 3.2 mm wall-thickness. Due to the Bauschinger‘s effect introduced in the cold
fabrication process, the ultimate tensile stress is much higher than the ultimate compressive
stress. Tensile test specimens were fabricated by cutting from the circular pipe along the
longitudinal direction. The cross-section of the material test specimens was fabricated to
rectangular cross-section, according to the industry standard for material tensile testing. In the
2 sides of the central cross-section, strain gauges were attached for the purpose of measuring
the strain. The nominal stress-strain relations for the specimens of A, B, C and D series are
shown in Figure 9.3 in solid lines. Due to the cold fabrication process, the ductility of the
material was reduced. Tensile failure occurred when the strain was in the order of 6 - 14 %.

0 0.2 0.4 0.6 0.8 1 .o
E Yo

Figure 9.2 Tensile Stress-Strain Curve for Large Scale Test Specimens
The measured cross-section areas for the specimens, the measured Young’s modules and yield
stress are listed in Table 9.3. Two types yield stresses were defined: yield strength
corresponding to 0.2 % offset plastic strainoo,2, and yield strength corresponding to 0.5 %
total strain CF~,~.

Table 9.3 Dimensions and Results of Material Tests for Small Scale Test Specimens
Specimen Tensile Tensile Compressive Compressive Compressive Compressive
Wall- Test Yield Test Yield
Specimen Thickness D/t Cross- Test Yield Test Yield Test Yield Test Yield Stress Force
ratio Sectional Stress
Force
Stress
Force
Number t
(-1 (-) Area 00.2 p0.2 00.2 po.2 00.5 4.5
A(m2) (kpf/mm2) (kgf) (kgfl-’) (kgWm2) (kgf)
A 1.0 97.0 301.59 45.00 13751.55 35.25 10631.05 40.00 12063.60
B 1.2 81.2 362.67 58.00 21034.86 37.50 13600.13 44.50 16138.82
C 1.6 61.4 485.56 54.23 26341.63 37.00 17965.72 42.75 20757.69
D 2.5 40.0 765.76 46.75 35799.28 33.00 25270.08 38.25 29290.32