Ingenieurwissenschaften und zugeordnete Tätigkeiten
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Organisationseinheit der BAM
A self-restraint hot cracking test (free edge test) was used in combination with a novel optical measurement technique to determine the critical straining conditions for solidification cracking for the stainless steel grade 1.4828 (AISI 309). The Lucas-Kanade algorithm for the optical flow (OF) calculation was implemented to obtain the full-field displacement and then the full-field strain.
The use of external laser illumination with appropriate filters allows to obtain good image quality with good contrast. The critical straining conditions required for solidification cracking can be obtained by means the proposed technique in the immediate vicinity of the solidification front. A very good repeatability was demonstrated for the used measurement technique. The critical straining conditions for solidification cracking for the tested steel und under this welding conditions has been detected
Using a novel optical measurement technique together with the optical flow algorithm, a two-dimensional deformation analysis during welding was conducted. The presented technique is the first to provide a measurement of the full strain field locally in the immediate vicinity of the solidification front.
Additionally, the described procedure of the optical measurement allows the real material-dependent values of critical strain and strain rate characterizing the transition to hot cracking during laser welding processes to be determined. Furthermore, the above-mentioned technique is independet on the welding process, which means, it can be also used for arc welding processes. Dependency between the external strain rate and the critical local strain and strain rate has been observed. That is to say, the critical local strain and strain rate is increased with an increase of the strain rate.Moreover, this technique allows automatic identification of the cases that can be critical for the solidification crack formation by monitoring the state of strain on the crack-sensitive region within the mushy zone.
This paper represents the results for proposed optical flow method based on the Lucas-Kanade (LK) algorithm applied to two different problems. The following observations can be made:
- The estimated strain and displacement for conducted tensile test are generally very close to those measured with conventional DIC-technique.
- The LK technique allows measurement of strain or displacement without special selection of a region of interest.
Using a novel optical measurement technique together with the optical flow algorithm, a twodimensional deformation analysis during welding was conducted. This technique is the first to provide a measurement of the full strain field locally in the immediate vicinity of the solidification front. Additionally, the described procedure of the optical measurement allows the real material-dependent values of critical strain characterizing the transition to hot cracking during laser welding processes to be determined.