Copyright Goodheart-Willcox Co., Inc. 274 Gas Tungsten Arc Welding Handbook into cross sections, which are then polished, etched, and examined visually or with specialized testing equip- ment. Cross section tests include the following types: • Macrotest. Polished sections of the weld are prepared for viewing with the naked eye or a magnifying glass (low magnifi cation). Increased defi nition of the weld layers and passes can often be obtained by etching the sample with a suitable etchant. • Microtest. Very highly polished sections of the weld are prepared for viewing with high- power microscopes. This type of test is used to determine grain size, content, and structure. • Microhardness test. Very highly polished sections of the weld are tested on special machines to determine the hardness of a very small area. The results can then be evaluated to determine the hardness variations within the grain structures and the weld zones. Nick-Break Test Nick-break tests are destructive tests that are very simple to make. They are used to determine the internal quality of a weld with regard to porosity, lack of fusion, and slag. Notches are cut in the sides of a weld coupon in the weld area. The coupons are then laid across a support on each end and force is applied with a hammer to try to break the weld sideways for a simple internal inspection. A nick or groove cut into the weld helps the specimen break when force is applied. A section of the weld to be tested is removed from the weld and prepared as shown in Figure 18-17. The coupon is placed into a vise, Figure 18-18, and broken with a sharp blow to the upper section. Defects can then be observed in the broken areas. Figure 18-16. The impact test machine arm swings downward to break the coupon at impact. The results are shown on the gauge in foot-pounds. (Photo courtesy of Tinius Olsen) 1/8″ (3.2 mm) Approximately 1″ (25.4 mm) Do not remove crown and penetration Cut slot with hacksaw or oxyacetylene torch 1/8″ (3.2 mm) Figure 18-17. Nick-break test dimensions. Vise Figure 18-18. Nick-break test setup.