Laser-welded ”wind turbine steel” behaves as it ought to during tensile testing.
LWT has begun to look into heavy section welding of steel, and has been involved in hybrid laser welding of 20 mm thick and 40 mm thick steel samples. The picture series below shows an advancing tensile strength test of a laser-welded specimen with a color distribution as a function of the mechanical stresses.
The colder the color (blue is coldest), the less the stress, and the hotter the color (red is hottest), the higher the stress. The stress distribution in the test specimen is shown at various stages during the tensile test, clearly showing, that the weld (and near weld) material is stronger than the bulk material. The shown strain distribution is representative for all test specimens.
Stress distribution during various stages of uniaxial tensile testing of a laser-welded S355NL test specimen, which is 20 mm thick. The colors in the pictures show the real-time stress distribution during tensile testing, load increasing left to right. The technique used to measure these stresses is referred to as digital image correlation (DIC). It works by tracking multiple tiny points, superimposed on the test specimen. The position of each point is tracked during testing, and the relative movements of the points are followed. This allows real time measurement of the stresses acting (locally) in the test specimen. Using designated software, the stress distribution can be visualized by different colors. S355NL is the typical steel grade used for wind turbine towers and foundations. In these real-life applications the steel is applied in thicknesses, ranging from 8 to 150 mm. Image: LWT