Copyright Goodheart-Willcox Co., Inc. 272 Gas Tungsten Arc Welding Handbook weldment has been in service. This comparison can help engineers identify areas of the weldment that are stressed by service. Destructive Tests Destructive tests are used for welder qualifi cation and certifi cation, as well as welding procedure qualifi - cations. In large production runs, destructive tests are often made by pulling apart sample units. It is often less expensive to scrap a part to make a destructive quality test than to test the parts using more expen- sive nondestructive tests. Bend Test Bend tests are used to determine internal weld quality. As shown in Figure 18-12, there are three different types of bend tests: • Face bend (face of the weld is tested) • Root bend (root of the weld is tested) • Side bend (sides of the weld are tested) In bend tests, a weldment is sliced into test strips, called coupons. The weld is then bent around a die of a specifi c size, creating a horseshoe of the coupon. This process stretches the weld to test the weld’s integrity. Figure 18-13 shows a radius bend testing machine. This machine bends the prepared test coupon into a U form over a specifi ed radius, which is dependent on the thickness and strength of the material. After bending, the outer surface and the inner surface of the U are checked for cracks and other indications as required by the weld inspection criteria. The outer face of the bend may be examined by a visual, pene- trant, or magnetic particle test to detect defects such as cracks, lack of fusion, and lack of penetration. Tensile Test Tensile tests are used to compare the weldment to the base metal mechanical values and specifi cation requirements. The weldment is sliced into coupons, and then each end of the coupon is pulled in oppo- site directions until the coupon fails (breaks). A tensile test machine is shown in Figure 18-14. Tensile tests are made to determine the following: • Ultimate strength of the weld. This is the point at which the weld fails under tension. • Yield strength of the weld. This is the point at which the weld yields or stretches under tension and will not return to its original dimensions. • Elongation. This is the amount of stretch that occurs during the tensile test. It is measured by placing gauge marks on the sample or coupon before testing and comparing the after-break distance with the original gauge marks. Root bend Male die Female die Face bend Side bend Figure 18-12. The three types of bend tests are shown here. The root bend test places the greatest amount of stress on the weld root. The face bend test places the greatest amount of stress on the weld face. The side bend places the greatest amount of stress along the weld axis. Completed test samples Figure 18-13. A radius bend testing machine. (Mark Prosser)