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).
Figure 1: In a bend test, a flat strap of metal is bent into a U-shape,stretching the material on the outer surface of the "U," while
compressing the material on the inside surface.
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
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.