Frequently Asked Questions about Bolt Tensile Strength Test

Frequently Asked Questions about Bolt Tensile Strength Test

Is the tensile strength test of your bolts tested by the first party or the third party? Has there ever been a mutual test result? How to judge the correct test method? This article will be based on GB/T3098.6-2014 "Fastener Machinery Performance stainless steel bolts, screws and studs" (equivalent to ISO3506- 1:2009) perspective interpretation of the tensile strength of stainless steel bolts testing method. 1. Machining sample or physical inspection? The original intention of the machined sample testing is to investigate the material's thermal processing process, whether the bolts are completely quenched, and the austenite is not The strength of stainless steel products is improved by cold working (there is no process of heat treatment to increase the strength), in the standard GB/T3098.6-2014 Clauses 7.2.2 and 7.23 clearly stipulate in the tensile test that “according to the provisions of GB/T228.

1 and GB/T3098.1, the tensile strength (Rm) should be measured on fasteners with I≥2.5d, The stress at the specified plastic elongation of 0.2% is only tested on bolts or screws. Therefore, the mechanical properties of austenitic stainless steel bolts can only be obtained through physical tensile tests. If machined specimens are tested, the tensile strength will be biased. low.

2. How to choose the cross-sectional area of half-tooth products? The nominal length of a half-tooth bolt is composed of a polished rod part and a threaded part, and their theoretical cross-sectional areas are different. Therefore, when the fracture position is in the polished rod part, which cross-sectional area should be selected for calculation? Many people take it of course to directly choose the cross-sectional area of the fracture. However, there is a special description in the standard regarding the selection of the tensile strength cross-sectional area. "Calculate according to the nominal stress cross-sectional area of the thread". Therefore, no need to consider the fracture location, just select the nominal stress cross-sectional area of the thread in Appendix A. If calculated by the cross-sectional area of the rod, the tensile strength will be low.