**4. Well-accepted myth**

*Adhesives and Adhesive Joints in Industry Applications*

detail on each fastener in this article.

**3. Structure of bolt and nut assembly**

control during assembly.

should be able to be disassembled by tool anytime. Does this sound logical to meet both requirements at the same time to you? In reality, design engineers have spent a lot of time to design mechanical fasteners that can achieve those two functions. Consequently, various mechanical fasteners have been introduced, and they will be reviewed more in

In order for fasteners to do their job ideally, they should resist to external vibrations, shock, and impact, withstand shock and impact, tolerate differences in thermal expansions, protect against corrosion, and provide a consistent torque

Bolt is not a bolt; it is a spring. When tightening a bolt in the assembly, it means

Clamp load is the force that holds a joint together. In a threaded assembly, the clamp

tensioning or slackening a spring. Bolt is pulling the flanges together as a "bolt spring." "Bolt spring" force must pull the flanges together more than the forces acting to push them apart. If "bolt spring" is too loose, the pressure stretches the bolt, and the flange opens and leaks. Therefore, "bolt spring" should prevent the flanges

load is equal in magnitude to the tension of the bolt but opposite in direction. Bolt tension is achieved after some friction loss at bolt head and thread. This clamp load is very critical as a bolted joint is designed so that the external forces never overcome the

clamp load, and this is the major reason fasteners are used (see **Figure 1**) [1].

from separating; therefore, bolts are preloaded (stretched).

**118**

**Figure 2.**

**Figure 1.**

*Forces acting on a "bolt spring."*

*Typical stress-strain curve of steel.*

For such a long history of mechanical fasteners, those people related to designing, assembly, and repair have built some mindset on their own for a long time, it has become a conviction, then belief, and then it has become a myth to them. Here in this chapter, some of their "truth" will be shared to see if they are true.


#### **5. Conventional thread locking fasteners**

There are various conventional fasteners available in the market, in this article, eight different frequently used fasteners are explained on how each one works and what is the area of improvement regarding performance and cost.

#### **5.1 Spring washer**

Spring washer creates mechanical force against the nut and substrate surface which means mechanically "pushes the surface." What does this mechanical etching of the surfaces or how does this affect areas prone to corrosion? It may maintain the bolt tension in the beginning of assembly, but as time goes by, it loses its spring form and becomes flat due to the empty space between threads, and then, the bolt tension is reduced, and the assembly pressure is reduced, too, which results in the loosening of bolt and nut, and additional cost of spring washer is required (see **Figure 3**) [1].

#### **5.2 Star washer**

The star washer uses friction of the raised metal portions to mechanically "grip" the surface. This method allows an initial loosening as the washer rotates and grips into the substrate, and then bolt tension is already reduced, but it can prevent a further

#### *Adhesives and Adhesive Joints in Industry Applications*

**Figure 3.** *Conventional thread locking fasteners.*

loosening. This also does not seal, can damage the surface of softer or coated metals, and is not reusable, and additional cost of star washer is required (see **Figure 3**) [1].
