Destructive tests aim to examine the mechanical, chemical, and metallurgical properties of a weldment by breaking, deforming, or chemically processing test specimens removed from a welded joint. These tests are considered to be a direct method of examining the qualities of the weldment.
The destructive tests can be classified into mechanical tests, chemical tests, and structure tests.
The destructive tests are often used to confirm whether or not specific welding procedures can produce the required qualities of the weldment. The following sections outline the major destructive tests.
Destructive tests are as follow –
Tension tests examine yield strength, tensile strength, elongation and reduction in area by stretching a tension test specimen until it ruptures. The tension tests of a weld metal and a welded joint are conducted according to the specification to be followed.
For fillet welds, the shearing strength of fillet joints is examined, using a tension test machine.
Bend tests examine the ductility of welds and whether they contain welding defects or not.
Bend test specimens are usually removed from butt weld joints so that the weld is perpendicular to the longitudinal axis of the specimen.
In bend tests, three different types of specimens are used, depending on the surface to be tested:
- Face-bend specimens,
- Root-bend specimens, and
- Side-bend specimens.
The bend tests include the roller bend test, guide bend test, and free bend test.
Metals may be fractured in the ductile mode or brittle mode depending on the environment where the metals are loaded. The fracture of a metal with plastic deformation in standard tensile testing and slow bend testing is considered ductile fracture.
Ductile metals (as judged by tensile or bend tests), however, may fracture with little or no plastic deformation, when subjected to critical testing or service conditions.
This type of fracture is considered brittle fracture. The critical conditions depend on the fracture toughness of the metal. The brittle fracture is considered more dangerous because a high-velocity failure takes place in steel structures.
Three factors markedly influence the brittle fracture behavior of a metal; namely,
- the presence of a notch in the metal,
- the temperature of the metal, and
- the residual
The hardness of a weld is the ability to resist indentation or penetration by the point of a material that is harder than the weld being tested.
The hardness test is required to confirm whether or not the weld is hard enough to resist mechanical wearing, or whether or not the weld is ductile enough to stresses, depending on the usage of the weldment.
Four different methods of measuring hardness are in use depending upon the requirement: Brinell, Rockwell, Vickers, and Shore hardness.
In particular, Vickers hardness is most suitable to measure the hardness distribution in a weld.