Bend Test
The bend test is a destructive mechanical test. A welded specimen is bent around a mandrel. This immediately reveals lack of fusion, cracks, or poor ductility of the weld.
Physicochemical mechanism of action
During bending, the specimen is severely stretched on the outside and compressed on the inside. The weld and heat-affected zone must withstand this strain without cracking. A ductile structure deforms plastically. A brittle structure cracks immediately.
Metallurgical relevance & risks in welding
The bend test reveals weld defects such as lack of fusion, slag inclusions, porosity, and cracks. These defects act as notches, concentrating stress and leading to premature fracture. A too hard, martensitic weld also fails brittle. The test also reveals defects in the heat-affected zone.
Workshop practice & instructions
The specimen is taken transverse to the weld. The surface is ground smooth. The bend angle is usually 180°. The mandrel diameter depends on the standard. According to EN ISO 5173, it is 4 times the plate thickness. Test temperature is room temperature. Bending speed must be slow. A crack over 3 mm long is considered a defect. The specimen must remain crack-free; otherwise, the weld is unacceptable.