Washers serve a critical function in bolting systems by distributing the concentrated loads exerted by bolt heads and nuts. This load distribution is achieved by increasing the contact area between the fastener and the material being joined. Without washers, the high bearing stress at the bolt head or nut could exceed the bearing strength of the connected materials. This can result in several detrimental effects, including:
Loss of Preload: The preload, which is the initial tension applied to the bolt during tightening, is essential for maintaining a secure and reliable joint. Excessive bearing stress can cause the bolt to elongate or the material to deform, leading to a loss of preload and a weaker connection.
Creeping: Creeping refers to the gradual deformation of materials under sustained load. When the bearing stress is too high, the connected materials may creep, leading to loosening of the joint over time and potential failure.
To address these issues, washers are inserted between the bolt head or nut and the connected materials. They act as a buffer, spreading the load over a larger area and reducing the bearing stress to a safe level. This ensures that the preload is maintained, and the joint remains secure and stable.
Alternatively, flanged fasteners can be used instead of washers. These fasteners have a built-in flange or enlarged head that serves the same purpose as a washer, distributing the load over a wider area and reducing bearing stress.
In conclusion, washers or flanged fasteners are essential components in bolting systems. They play a crucial role in distributing loads, preventing loss of preload, and mitigating the risk of creeping. By incorporating these elements into the design, engineers can ensure the long-term integrity and reliability of bolted connections.