Side bend test specimen
The side bend test is a destructive test specimen taken from a weld joint. It is taken transverse to the weld and bent to 180° with the cut cross-section facing outward. This immediately reveals internal lack of fusion, porosity, or cracks at the bend edge.
Physical-Chemical Mechanism of Action
When bending, the outside of the specimen is heavily stretched. The cross-section of the weld shows all internal irregularities like lack of fusion, pores, and slag lines. These act as notches and concentrate the bending stress. Once the local strain exceeds the material's elongation at break, the specimen tears at the weakest point. This checks the formability of the entire weld cross-section.
Metallurgical Relevance & Welding Risks
Side bend specimens reveal lack of penetration, lack of fusion at the weld face, pores, and slag inclusions. Brittle microstructures like martensite or coarse grain also fail before reaching the required bend angle. This points to too fast cooling of the weld (t8/5 under 5 seconds for hardenable steels) or wrong heat control. The specimen then doesn't just crack at the defect, but through the whole brittle material.
Workshop Practice & Action Steps
Take the specimen transverse to the weld, weld centered. Specimen thickness 10 mm, width equal to full weld thickness (max 40 mm), length at least 150 mm. Bend angle 180°. Bend former diameter 4 × specimen thickness for steels with elongation over 20 %, otherwise 6 × specimen thickness. When clamping, put the cut cross-section facing out on the tension side. After bending, check both bend edges: any crack length over 3 mm means a defect.