The mechanical action of the spring has been used by humans since the invention of the crossbow. Although the theoretical knowledge of the elastic limit was quite rudimentary, the importance of its practicality was understood. The elastic limit of a spring is defined as the tension at which the spring begins to deform plastically, that is, the tension beyond which the spring stops returning to its initial position. It is also known as elastic limit or elastic limit. This article analyzes the methods to calculate the elastic limit of the most used mechanical springs. An accurate method of calculating resistance is to subject the spring to an incremental change in tension and, at the same time, look for the point of no return. However, this method of calculating the yield strength for limited production springs is not feasible. Therefore, in such cases, the elastic limit is deduced by the physical characteristics of the material and the extrapolation. The most commonly used mechanical springs are coil springs, which are then classified according to the principle of spring action, as follows:

• Coil spring extension
• Helical compression springs
• Rotating coil springs

The calculation of the elastic limit is important for the calculation of safe load factors and to guarantee a long-lasting use of the springs.

Calculation of the elastic limit of the helical extension springs:

Extension coil springs are designed to exhibit elastic properties when stretched along their length, that is, they are used to hold attached components together. A hook to secure their initial position usually characterizes these springs. The most common examples of these types of springs are trampolines and scales. To calculate the yield strength of this type of spring, the control specimen of a spring is partially extended by applying force in small steps so that the spring expands one percent of the length of the spring. By keeping the spring expansion constant, the deformation remains constant, which facilitates extrapolation of the yield point. Force is applied in the form of weights, which are converted to their relevant force equivalents taking into account gravitational attraction and the horizontal and vertical components of the force. After exerting the known force, the force is removed to verify the presence of elastic properties in the spring. The point at which a total absence of elastic properties is observed is noted and multiplied by the safety factor. The value is an effective indicator of safe load and yield strength. Further experiments are performed to determine the exact elastic limit by subjecting a similar spring to tension precisely between the points of presence and absence of elasticity.

Calculation of the elastic limit of helical compression springs:

This type of spring is also a type of coil type springs. Unlike the operation of extension coil springs, these springs are designed to exhibit elastic properties when compressed, that is, these springs are used to keep the components attached to them separate. One of the most visible uses of this type of springs is shock absorbers in vehicles. The yield strength calculation for compression springs should be done a little differently than for expansion springs. Unlike expansion springs, the maximum possible operating range is visually conceivable. In this case, the force is applied in steps of one hundredth of the possible range of action.

Calculation of the elastic limit of helical torsion springs:

Unlike the previously mentioned types of coil springs, torsion springs employ elasticity in the axial component of the spring to exhibit elastic action. This type of spring is used in clips and mousetraps. The calculation of the elastic limit is carried out in the same way as for compression springs. The operating range is limited and the force is applied similarly to compression springs.

This type of calculation can be extended to other types of springs by evaluating the range of their performance.