According to their performance grades, high-strength bolts are categorized into grades 8. 8 and 10.9, with grade 10.9 being the only grade to use the torsional shear type of bolt. There is no use of bolts of grade 8. 8. In the marking method, the number before the decimal point represents the tensile strength after heat treatment, and the number after the decimal point represents the yield ratio, which is the ratio of the measured value of yield strength to the measured value of ultimate tensile strength. In other words, the yield ratio is the ratio of the measured value of yield strength to the measured value of ultimate tensile strength. The yield ratio can also be defined as the ratio of the measured value of the yield strength to the measured value of the ultimate tensile strength. In order for the bolt rod to receive a grade of 8. 8, its tensile strength must be at least 800 MPa, and its yield ratio must be at least 0.8. In order for it to be given the grade of 10.9, its tensile strength must be at least 1000 MPa, and its yield ratio must be at least 0.9. In structural design, the standard diameters flat head screws for high-strength bolts are M16, M20, M22, M24, M27, and M30. Other common diameters include M24 and M27. On the other hand, the M22 and M27 series are the ones that are recommended for the secondary option, while the M16, M20, M24, and M30 series are the ones that are recommended for the primary option under normal circumstances.
When assembling the high-strength bolted connection pair, the side of the nut that has the round table should face the chamfered side of the washer. This ensures that the washer is properly aligned. When making connections using high-strength bolts that have large hexagonal heads, you should position the washer so that the chamfered side that sits under the bolt head is facing the bolt head. Large hexagonal bolts made of high-strength material are used to carry the load of the pressure.
When it comes to connecting steel structures to one another, there are more than ten distinct performance grades of bolts that can be used. These grades range anywhere from 3.6 to 12.9 and include numbers such as 3.6, 4.6, 4.8, 5.6, 6.8, 8. 8, 9. 8, 10.9, and 12.9. High-strength bolts are typically defined as those that have a grade of 8. 8 or higher, are made of low-carbon alloy steel or medium-carbon steel, and have undergone heat treatment in the form of quenching and tempering. The remaining bolts are what people typically refer to as "ordinary bolts."Both the nominal tensile strength value of the bolt material as well as the yield ratio of the bolt material are both represented by separate parts of the number that are located on the performance grade label for the bolt. The nominal tensile strength value of the bolt material can be found by looking at the first part of the number on the label. For instance, a bolt with the property class 4.6 indicates the following: 1. the nominal tensile strength of the bolt material is at least 400 MPa; 2. the yield strength ratio of the bolt material is 0.6; the nominal yield strength of the bolt material is 400 minus 0.6, which equals 240 MPa; and 3. the nominal tensile strength of the bolt material is at least 240 MPa.
High-strength bolts with a performance level of 10.9 that have been subjected to heat treatment are able to accomplish the following:
1. The bolt material has a yield strength ratio of 0.9, and the nominal yield strength of the bolt material is 1000 divided by 0.9, which equals 900MPa. 2. The nominal tensile strength of the bolt material is 1000 MPa, and it has a nominal tensile strength of 1000 MPa.
When we talk about the bolt performance grade, what we're really referring to is an international standard. There is no discernible difference in performance between bolts of the same performance grade, regardless of the differences one way screws in material or origin; the performance grade is the only factor that can be selected in the design process. Grade 10 and grade 10 are the strength grades that are assigned to high-strength nuts and bolts after they have been subjected to heat treatment. Standard practice calls for grade 9 bolts to be used in conjunction with grade 10 nuts.
Because of the differences in their mechanical properties and the ways in which their strengths are calculated, standard bolts and high-strength nuts cannot be substituted for one another. While the force of an ordinary bolt directly bears the external load, the force of a high-strength nut first applies a pre-tightening force P inside it, and then generates frictional resistance on the contact surface between the connectors in order to bear the external load. In contrast, the force of an ordinary bolt directly bears the external load. The high-strength nut connection has a number of advantageous properties, including its anti-fatigue and fatigue-resistant properties, its replaceability, its good mechanical performance, and its resistance to loosening under dynamic load. The connection benefits from each of these advantages in their own unique way. This appears to be a potentially fruitful method of connection.
When high-strength nuts are tightened with a specialized wrench, a massive preload that can be controlled is applied to the bolt. This causes the nut to become more tightly secured. The amount of preload that is applied to the connecting parts is standardized by using nuts and spacers. This ensures that all of the connecting parts are stable. When the surface of the connector is subjected to the action of pre-pressure, a significant amount of frictional force will be generated on the connector's surface. As long as the axial force remains lower than the frictional force, it should not come as a surprise that the component will not slip, and the connection will not be damaged. Both of these outcomes are dependent on the same condition. This is the fundamental concept that underpins the creation of nut connections that are exceptionally sturdy.
High-strength nut connections are unable to take place because of the friction that is present between the contact surfaces of the connectors. Both the clamping force of the element and the friction coefficient of the contact surface need to be increased in order to achieve the desired level of friction at the contact surface. Only then will it be possible to achieve the desired level of friction. High-strength steel tamper proof screws is required for the bolts themselves because the clamping force between the components is achieved by applying pre-tightening force to the bolts. Because of this prerequisite, the connection in question is referred to as a high-strength bolt connection. Cause and effect
The fact that the friction coefficient has a significant impact on the bearing capacity of high-strength bolted connections should not come as much of a surprise to anyone. According to the findings, the shape of the contact surface and the material that the components are made of are the primary factors that determine the coefficient of friction. The contact surfaces of the components that are within the connection range are typically treated by sandblasting and cleaning with a wire brush. These are the typical methods that are used to treat the contact surfaces of the components. In order to increase the friction coefficient of the contact surface, this procedure is carried out.
In point of fact, there are two distinct types of high-strength nuts, and they are referred to as frictional nuts and pressure-bearing nuts, respectively. The shear force criterion for friction-type high-strength bolts states that the shear force generated by the design load must not be greater than the friction force. The construction of high-strength bolts of the bearing type is based on the principle that the plate and the body of the rod should not be crushed, and the body of the rod should not be damaged either.