Page 44 - SSAB Welding Handbook Edition 2

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7.0 Aspects regarding static strength in joints Welding handbook

7.1 Issues to consider during the
tensile test Tensile Angular shrinkage
©SSAB
force
Tensile tests are normally performed for butt joints
measured transverse to the direction of the joint.
The most common purpose of this test is to measure
the tensile strength and to determine the location of Fig. 7.1: Geometric movement of a tensile specimen subjected to a
tensile test.
fracture after the test is performed.

The yield strength, determined as the stress level at Results are dependent on the exact welding situation,
0.2% elongation of the tensile test specimen, of a joint but when Strenx grades are welded using
is hard to evaluate accurately. The reasons are that: consumables with the maximum recommended
- The HAZ and the weld metal have properties that yield strength, the fracture during the tensile test
deviate from the properties of the unaffected parent typically takes place in the weld metal or the HAZ.
metal. As a consequence, during a tensile test most of For joints made with Hardox grades, the normal
the elongation can take place in the weakest zones of location of fractures is in the weld metal.
the joint. This situation makes the actual yield strength
hard to evaluate. Elongation values that are viewed transverse to the
- Measuring the yield strength transverse to the direction of the joint are often of less importance
direction of the joint may create inaccuracies since for joints in high strength steels. This is because the
there can be a movement perpendicular to the local strength transverse to the joint direction varies
direction of the joint, see fig 7.1. Straightening of and elongations and plastic deformations in joints
the specimen prior to the tensile test is not normally tend to take place in regions of reduced strength.
carried out since this could affect the mechanical Consequently, the measured elongation values are
properties of the joint. often smaller compared to the measured elongation
- There may be small sliding effects that might values for the unaffected parent metal. The tensile
occur between the specimen and the contact bars of test specimens in fig. 7.2 illustrates this phenomenon.
the tension testing machine. This sliding effect is
supported by the high levels of forces that are often
needed for joints in high strength steels. The
assessment of the tensile strength in joints is less
affected by this sliding effect and representative
values can typically be attained even if a small
amount of sliding occurs. However, it is good
procedure to make sure that there is a tight grip
between the tensile test specimen and the contact
bars.

Fig. 7.2: The upper tensile test specimen includes a joint, while the
lower specimen consists of unaffected parent metal.

44 This handbook contains general suggestions and information without any expressed or implied warranty of any kind. SSAB hereby expressly disclaims
all liability of any kind, including any damages, in connection with the use of the information and for their suitability for individual applications.
It is the responsibility of the user of this brochure to adapt the recommendations contained therein to the requirements of individual applications.