Fracture (Break) Test

The fracture test (break test) is a destructive testing (DT) method based on forcing a welded joint specimen to rupture through the centre of the weld metal or along the fusion line, and examining the resulting fracture surface with the unaided eye or with a low-magnification lens. The physical principle of the method is simple: a sound weld metal stretches in a ductile manner under load and produces a matt, fibrous fracture surface, whereas discontinuities such as porosity, slag inclusions, lack of fusion, lack of penetration or cracks create weak regions in the cross-section and the fracture propagates through these defects. In this way, faults hidden within the weld and invisible from the surface become directly visible on the fracture surface. The fracture test is a preferred verification method particularly for evaluating root penetration and fusion quality in fillet welds, being economical compared with radiography and requiring no interpretation.

In practice the specimen is cut to defined dimensions so that it contains the weld seam. To guarantee that the fracture passes through the weld metal, a guide notch is usually machined on the root side or the face of the seam; this notch concentrates stress in the weld cross-section and initiates the fracture in the desired plane. The prepared specimen is fixed in a vice or support fixture and the weld is ruptured in a single action by applying an impact (hammer), press or bending force to its free end. In fillet welds the specimen is folded so that the root is opened up and then broken; in butt welds the weld metal is split in two by tensile or bending action. The two fractured halves are retained and reported in a way that shows the true location and distribution of the defects.

The equipment requirement of the method is simple, but critical details determine the result: a saw/plasma cutter for cutting the specimen, a milling machine or grinder for machining the notch, and a hydraulic press, jaws/vice and, where necessary, an impact arrangement for fracturing. A hand lens of at most 5–10x magnification is sufficient for evaluating the fracture surface; callipers and calibrated measuring instruments are used for measurement. In the evaluation, the type of defects (porosity, slag, lack of fusion/penetration, cracks), their size, their proportion of the fracture surface and their location are recorded. Grey-shiny, flat regions on the fracture surface indicate lack of fusion or an oxidised surface, spherical cavities indicate gas porosity and dark irregular areas indicate slag inclusions; a ductile matt region is sound weld metal.

The most common field of use of the fracture test is welding procedure qualification (WPS/WPQR) and welder qualification examinations. Where radiographic and ultrasonic testing cannot give reliable results in fillet welds because of the geometry, the fracture test is the most direct way of revealing internal defects. The method is also used in the qualification of different welding processes such as gas-shielded, covered electrode and submerged arc welding, in the periodic verification of production specimens and in failure/root cause analysis. Because it is a destructive method, it is not the component itself but a representative specimen or production test coupon that is tested.

Acceptance criteria are determined by the relevant weld quality standard and the contract specification; the assessment is generally based on the total permitted defect area along the notch length, the size of individual defects and the presence of cracks. The presence of a crack is a direct cause for rejection in most applications, while porosity and lack of fusion are limited by threshold values depending on the quality level. The report includes the specimen identification, welding process, notch location, fracturing method, the type, size and location of the observed defects and the accept/reject decision. TÜV AUSTRIA SILA KALİTE performs the fracture test under its TS EN ISO/IEC 17025 accreditation, with defined procedures and calibrated equipment; the conformity of welded fabrication with the standards is thus documented independently and traceably.