The pipe bending machine holds the bending of the pipe the same as the bending of the sheet. In a pure bending environment, when a tube with an outer diameter of D and a wall thickness of t is bent under the action of an external moment M, the outer tube wall of the neutral layer is subjected to the tensile stress σ1, and the tube wall becomes thinner; the inner tube of the neutral layer The wall is subjected to tensile stress σ1, and the pipe wall becomes thicker. And the shape of the cross section changes from a circle to a similar ellipse due to the combined forces F1 and F2. When the deformation is too large, cracks will occur on the outer tube wall and wrinkles on the inner tube wall. The deformation level of the pipe depends on the relative bending radius R/D and the relative thickness t/D value. The smaller the R/D and t/D values, the greater the performance deformation level. In order to ensure the quality of pipe fittings, the deformation level must be controlled within the allowable range. The bending forming limit of pipes not only depends on the mechanical properties and bending methods of the material, but also considers the utilization requirements of the pipe fittings. The forming limit of pipe fittings should include the following contents:
1) The maximum elongation deformation in the tensile deformation zone outside the neutral layer does not exceed the plastic allowable value of the material to cause breakage;
2) In the compression deformation zone inside the neutral layer, the thin-walled layout department under the action of tangential compressive stress will not be excessively unstable and wrinkle;
3) If the pipe fitting has the requirement of ovality, control the distortion of its section;
4) If the pipe has the strength requirement to withstand the internal pressure, control the forming limit of its wall thickness reduction.
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