High Strength Bolt Hsb High Load Bearing Mechanical Hardware Fatigue Resistance

High-Strength Bolt High Load-Bearing Capacity Excellent Fatigue Resistance

1. Introduction
A High-Strength Bolt (HSB) is a special type of fastener designed for critical mechanical connections. Its core characteristic is that it applies a large, controlled clamping force (preload) to generate significant friction between the connected members, thereby resisting external loads. The fundamental difference from ordinary bolts is that: ordinary bolts rely on the shear strength of the bolt shank to bear loads, while high-strength bolts rely on friction to transfer loads. This results in connections with higher stiffness, superior fatigue performance, and greater reliability. They are typically used with matching high-strength nuts and washers.

2. Advantages

• High Load-Bearing Capacity: Capable of withstanding extremely high tensile, shear, and fatigue loads, making them suitable for heavy-duty, vibrational, and impact conditions.

• Excellent Fatigue Resistance: Since load is transferred by friction, there is no clearance between the bolt shank and the hole wall, leading to a low stress amplitude and significantly improved fatigue life of the connection.

• High Connection Stiffness: The preload clamps the connected parts tightly together, resulting in high overall structural stiffness and minimal deformation.

• Safe and Reliable: Scientific methods such as the torque method, turn-of-nut method, or torque-angle method are used to control the preload, ensuring uniform and consistent force in each bolt. This makes the connection far more reliable than ordinary bolted joints.

• Good Seismic Performance: Under dynamic loads, the friction effectively absorbs and dissipates energy, preventing joint loosening.

3. Key Technical Parameters

• Property Class (Grade): This is the most important parameter. According to ISO/GB standards, common classes are Class 8.8, 10.9, and 12.9. According to ASTM standards, common grades are SAE Grade 5, Grade 8 or ASTM A325, A490. A higher number indicates higher strength.

  • Example: Class 10.9 means the nominal tensile strength is 1000 MPa, and the yield ratio is 0.9 (i.e., yield strength is 900 MPa).

• Material: Typically made from medium carbon steel or alloy steel (e.g., 35CrMo, 42CrMo) and subjected to quenching and tempering heat treatment to achieve the required property class.

• Specification: Nominal diameter (e.g., M16, M20, M24), pitch, length.

• Proof Load: The maximum axial tensile load the bolt can withstand before permanent deformation occurs.

• Torque Coefficient: A key factor used to calculate the applied torque needed to achieve the target preload.

4. Applications
High-strength bolts are widely used in fields where connection safety is paramount:

• Structural Steel Construction: Connections for beams, columns, and joints in high-rise buildings, stadiums, bridges, and airport terminals. This is their most classic application.

• Heavy Machinery: Engineering machinery (excavators, cranes), mining machinery, metallurgical equipment, pressure vessels, wind turbine tower connections.

• Transportation: Railway rail joints, bridge expansion joints, automotive chassis, and critical engine component connections.

• Aerospace: Connections in critical locations where extreme strength-to-weight ratio is required.