This is a national standard method for evaluating the resistance of bare wire conductors to repeated bending. It applies to measuring the bending performance of round conductors with diameters ranging from 0.3 mm to 10 mm, such as copper, aluminum, and their alloys, as well as shaped cross-section conductors with characteristic dimensions not exceeding 20 mm. The core method involves clamping one end of the sample and repeatedly bending the other end by 90° in both forward and reverse directions on a cylindrical surface with a specified radius until the specified number of cycles is reached or the sample fractures. This process tests the material's toughness and defects under repeated stress. The use of this standard must be combined with the general provisions section (GB/T 4909.1-2009). Conducting this test requires a specialized repeated bending testing machine (also known as a wire repeated bending tester), which is equipped with a fixed clamping block, a cylindrical support with a specified radius, and a bending lever to ensure the accuracy and repeatability of the bending action.