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Many welding codes require bend tests as part of the testing required to qualify welders and welding procedures specifications (WPSs). The concept of a bend test for welds is simple: two plates are welded together and a flat strap of metal is cut from the welded plates. Next, the flat strap of a prescribed size is bent into a U-shape, stretching the material on the outer surface of the "U," while compressing the material on the inside surface. The purpose is to make certain the weld and the base metal are properly fused, and that the weld metal and the heat-affected zone (HAZ) have appropriate mechanical properties (Figure 1).
Although bend tests appear to be simple, any number of things can cause good welding procedure specifications or good welders to fail. The person responsible for accepting or rejecting test results must understand those factors, and know how to correct for any that are causing inappropriate failure.
Bend specimens have been called "a poor man's tensile test." Although it will not show the quantitative values associated with a tensile test, a bend test will demonstrate both the quality of the weld and its overall ductility. Usually, bend tests are designed so that the outer surface of the specimen is stretched to a ductility level that approximates the minimum percent elongation required in a tensile test. When defects exist in materials strained to these limits, the material tears locally. When tearing exceeds a specific limit, the specimen fails.
Direction of rolling
Steel is not fully isotropic, and ductility is sensitive to rolling direction. When steel is strained parallel to the direction of rolling, the highest values of elongation are obtained. When it is stretched perpendicular to the rolling direction, ductility is reduced. The poorest ductility usually is measured in the through-thickness direction.
Qualification test plates can be prepared with the weld groove preparation parallel...