(root, top and wall) and base metal bending:

Bend testing is one of the mechanical tests used to evaluate the ductility of the material. This material can be plastic, fiber reinforced polymer (FRP), various metals and ceramic materials. In this article, we are going to introduce you to the bending test in the sections of the weld metal as well as the base metal.

Types of bending test

In general, the bending test can be done in three ways, which are:

One point bending test
three point bending test
four point bending test
which usually three-point and four-point bending test are used more.

In standard three-point and four-point bending tests, standard samples can have a round or rectangular cross-section and are placed in the center of the fixture. The fixed supports of the device have rolling bearings of ball bearing or roller bearing type, which are placed parallel to each other at a certain distance.

The header of the bending test machine moves downward slowly at a constant speed and loads the specimen until the specimen breaks or deforms. At this time, the maximum load applied to the sample is recorded as the bending strength of that sample.

During the test, the values of bending force and deformation are also recorded so that the obtained data can be drawn as a diagram, which is called a stress-strain curve diagram.

The three-point bending test is the most common type of bending test.

The importance of bending test of welding sections:

The bending test is one of the tests designed to determine the health of the weld and its freedom from cracks. This test is one of the most common tests in the Welding Procedure Verification (PQR) process. Usually, different methods of performing the bending test are based on whether the weld axis is transverse or parallel to the longitudinal axis of the sample and also which surface of the weld (top, root or wall of the weld) is placed on the convex or outer surface of the bent sample. It can be divided into five types.

Methods of performing the bending test of welding sections:

1. Transverse Side Bend test

In this test, the weld line is placed across the longitudinal axis of the sample and the sample is bent from the side section of the weld.

Transverse face bend test
In this type of test, the welding line is placed across the longitudinal axis of the sample and the bending is such that the welding surface is placed on the convex part or outside of the bent sample.

Transverse Root Bend test
In this test, the weld line is placed along the width of the longitudinal axis of the sample and bending occurs in such a way that the root of the weld (weld point) is located in the convex part or outside of the bent sample.

Longitudinal face bend test of the welding surface
In this test, the welding axis and the longitudinal axis of the sample are parallel to each other, and the sample is bent in such a way that the welding surface is located in the convex part or outside of the bent sample.

. Longitudinal root bend test

In this type of test, the weld axis and the longitudinal axis of the sample are parallel to each other, and the sample under test is bent in such a way that the root of the weld is placed in the convex part or outside of the bent sample.

The surface bending test (procedure) examines the quality of weld metal fusion in the walls and surface of the joint, the location of porosity, the amount of slag confinement, gas voids and other possible defects and determines the degree of weld ductility.

The root bending test examines the amount of penetration and mixing of welding metals inside the joint root.

Wall bending test or lateral bending test is used to control the health and melting rate of the weld metal.

Test Method:

The test method is as follows: First, the sample under test is placed on the gap of the device in such a way that the welding point is placed in the middle of the gap. The operation of bending the sample is done by a mandrel. Bending can occur in any of the following locations:

SIDE BEND TEST: The mandrel hits the side of the weld.
ROOT BEND TEST: The mandrel hits the weld surface.
FACE BEND TEST: The mandrel is placed on the root.
In any case, the sample is bent by the mandrel towards the matrix gap. The mandrel applies force to the sample and bends it towards the mold; To the extent that the curvature of the sample reaches such a value that a wire with a diameter of 2.3 mm does not pass through the curvature space under this mold and the test sample. Then, the entire convex surface of the sample is carefully evaluated in terms of cracks, corrosion cracks, and the appearance of other defects.

Conformity of welding bend test with welding instructions:

We performed the bending test in order to evaluate the weld ductility and strength according to the WPS welding guidelines. Strict implementation of the instructions of this standard is necessary to perform the bending test.

Basics of sample preparation for welding bending test

In the welding standard, four modes are suggested for the preparation of samples:

Face bend: The mandrel of the bending test device is placed on the root of the weld so that the weld surface is under tension.
Root Bend: The mandrel of the machine is placed on the surface of the weld so that the root of the weld is in tension.
Bending from the surface of the side wall of the weld (Side bend): The mandrel of the machine is placed on the side cut surface.
Longitudinal Bend: The sample is placed longitudinally under the bending test device, but due to the fact that the surface or root of the weld is under the beam, two situations occur:
A) Bending from the longitudinal welding surface (face longitudinal)

b) Bending from the longitudinal root