The BEND TEST!

One of the tests used to determine the soundness of weld metal is a bend test. A bend test can take a few forms and may have to meet different requirements. For the purpose of this short piece of information, we will talk about the “Guided Bend Test” as opposed to the “Free Bend Test”. Here is a closeup video of a students GMAW Side bend. https://www.youtube.com/watch?v=q6b0Lp-pqbM

A bend tests can provide information on both the soundness and ductility of a weld. This type of test is a “Destructive Test” so it is not used on welds that you want to put into use later. The test is done by bending a strip of the material to a certain radius which stretches the outer  surface of the material to a point where it “yields”. This will cause opening such as cracks to occur in material that isn’t very ductile or if there is a discontinuity present in the material already. it may stretch and grow to a size that doesn’t meet the requirements of the test.

Discontinuities such a such as porosity and lack of fusion become readily visible.  Where there are areas of varying hardness and tensile strength, the material may fail because of the stronger/harder area not stretching and the remainder of the bend must stretch more.

• Bend Tests are used for evaluating welds for welder performance qualification testing, welding procedure qualification, and product sampling.
• Bend tests may bend the weld towards the face, towards the root, or sideways.
• The most common is a guided bend test as opposed to a free bend test.
• Some materials are required by certain codes to be bent at specific radii. The property that dictates this is often the required “elongation” in the specimen.
• changing the diameter of the plunger on a testing jig or the thickness of the specimen will affect the amount of elongation.
• a bend test does not “measure” anything but it does show the result of “elongating” a specimen and allow any resulting openings to be measured and evaluated.

Links to better information

• https://www.twi-global.com/technical-knowledge/job-knowledge/bend-testing-073/ 
• http://www.esabna.com/euweb/awtc/lesson10_15.htm