Bend Testing

Bend testing is an easy qualitative test mostly and mainly used for the evaluation of both the material soundness and the ductility. At Applied Technical Services, we frequently assess butt-welded joints used as a quality control. The bend test is performed by using a sample coupon that is bent in three point bending to a specified angle.

A premature failure of a sample coupon is revealed on the external part of the bend when it is plastically distorted showing any defects in, or embrittlement of the material. A bend test is performed by wrapping a coupon around a former of a specified diameter into a specified angle and is the kind of test identified in a welding qualification specification and/or welder procedure. The bend angle may be from 90° to 180° depending on the requirements specified.

The diameter of the former is identified in the test specification or standard and it differs with the material ductility and strength. When testing for welder qualification or for butt weld procedure, sample may be oriented parallel or transverse to the welding direction. The transverse face bend specimen will disclose any defects on the face such as the lack of sidewall fusion or the excessive undercut close to the cap, opposite to the root bend in which it identifies the lack of penetration or root fusion. There is also a side bent test. Premature failure happens when extensive deformation occurs in the weaker section of two materials coming together.

Bend Testing mechanical properties:

All of the following are mechanical properties that aid to define the anticipated tensile strength performance of a precise fastener and can be calculated in units of force. The force is reported in Newtons (N) and/or pound-force (lbf). Because the strength of fasteners is normally great, it is habitually to report these forces in kilonewton (kN) and kilopound-force (klbf). The difference is that one is used for standard measurements (inches) and the other is mostly use for metric measurements (mm).

Applying maximum tensile force to a fastener that the outcome will not show plastic deformation is known as proof load. Proof load yield strength is between 85% - 95% normally. That is to say, the fastener must stay in its elastic area when force is applied up to its proof load. We can define Yield Strength as the tensile force that will produce permanent distortion (most commonly 0.2%) to a specified fastener. The maximum force a fastener must tolerate before rupture is defined as Ultimate Tensile Strength.

Bend Testing is perform for:

  • Welder Qualifications
  • Procedure Qualification Requirements
  • Material qualification or identification

Bend Testing is perform per:

  • ASTM E190-92
  • AWS
  • BS EN 910
  • ISO 9606 and 15614 Part 1
  • ASME IX
  • Other specifications

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