1. Tensile strength: Tensile strength is the maximum force applied to a fastener on it finished before failure or simultaneously with the start of the destruction, the load can withstand a "nominal thread stress area" value. Tensile strength is generally expressed as a "stress" value. Fastener system in the United States, its units: lb / inch 2 (ksi). If you need to know the tensile load value that a fastener product can withstand, multiply the tensile strength value (stress value) by the nominal cross-sectional area of ​​the thread. In US fasteners, the tensile load is expressed in pounds ( lbf ). The relationship between tensile strength and tensile load can be expressed by formula: Tensile load = tensile strength  X thread nominal stress cross section        The bolt wedge load test is the most common and important application method for testing the tensile strength of bolts. The wedge load test was carried out on the physical bolt, and the minimum tensile strength was measured, and the plasticity of the bolt: "head joint strength" was also evaluated. 2. Yield strength, specified non-proportional elongation stress: Yield strength is the stress value under a tensile load when a fastener product produces a permanent deformation of a specified size. When the fastener reaches the yield strength, it has entered the plastic deformation range. It should be pointed out here that the low-strength product can exhibit yielding when subjected to tensile loads and can measure the yield strength. High-strength products cannot measure the yield strength because there is no physical yielding phenomenon, but should measure the “specified non-proportional elongation stressâ€. 3. Guaranteed load: The guaranteed load is the tensile load that the fastener must bear and does not undergo permanent deformation. The guaranteed load is a toughness indicator and is an assessment of the hardenability index in the pad treatment process. It is an absolute value and cannot be a maximum or minimum. The stress value corresponding to the guaranteed load is the guaranteed stress. For most strength grade fasteners, the guaranteed load is typically 90% to 93% of its minimum yield strength , ie guaranteed load = ( 0.9 to 0.93 ) x minimum yield strength (or specified non-proportional elongation stress). 4. Elongation after fracture and reduction of section: The elongation after fracture and the shrinkage of the section reflect and measure the deformation ability of the fastener product before it is destroyed. Elongation after fracture and reduction of section are indicators of the plasticity of the material used in fasteners. The larger the elongation training field, the stronger the uniform deformation ability and the better the plasticity. The section shrinkage ratio refers to the ratio of the maximum reduction of the cross-sectional area at the reduced diameter to the original cross-sectional area after the sample is broken. The greater the shrinkage rate, the stronger the uneven deformation ability and the better the plasticity. The post-break elongation training field and the section shrinkage rate can only be measured by a tensile test on the "machined test piece". 5. Impact toughness: Impact toughness is a measure of the ability of a fastener to withstand an impact. 6. Shear strength: The shear strength is the maximum load that the fastener bears perpendicular to the axis before it breaks. Ability. It is also a stress value. In general, carbon steel fasteners have a shear strength of 60% of their minimum tensile strength . 7. Torsional strength: Torsional strength is generally expressed by the minimum breaking torque. It is a supplementary test item for bolts and screws that are small in size and short and cannot be subjected to tensile testing. It is also a very important test item for self-tapping screws and locking fasteners. 8. Fatigue strength: Fatigue strength is a measure of the ability of a fastener to withstand the specified, repeated maximum load before it is destroyed . Again it is also a stress value. 9. Hardness: Hardness is a measure of the ability of a fastener to resist wear and external force. Due to the limitations of various hardness test methods and hardness testers, the hardness of materials and products ranges from low to high. Therefore, a hardness test method cannot be used to detect fasteners of various performance levels from low to high. Therefore, in the fastener performance standards, three hardness test methods of Rockwell hardness ( HRC , HRB ), Brinell hardness and Vickers hardness are specified. The surface hardness of the US fasteners is based on the HR30N Vickers hardness tester.  In summary, the mechanical performance indicators and testing items of externally threaded fasteners can be divided into the following categories: 1. Strength index: tensile strength, specified non-proportional elongation stress or yield strength, guaranteed stress, shear strength, torsional strength, fatigue strength, etc. 2. Plasticity and toughness index: elongation after fracture, reduction of section, wedge load strength, head joint strength, impact toughness, etc. 3. Hardness: The hardness here refers to the general hardness. It is divided into three hardness values : Rockwell hardness ( HRC , HRB ), Brinell hardness (HB) and Vickers hardness ( HV ). 4, other testing items: the highest surface hardness, thread decarburization layer, impact absorption work, return to the hardness reduction value (measured by re-tempering test), according to the specific provisions of the performance standards. Guangzhou Quanxu Technology Co Ltd , https://www.skychema.com