How to Calculate the Yield Strength of a Spring

Humans have used mechanical spring action 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 stress at which the spring begins to deform plastically, that is, the stress 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 force is to subject the spring to an incremental change in tension while simultaneously finding the point of no return. However, this method of calculating the yield strength for springs of limited production is not feasible. Therefore, in such cases, the yield strength is deduced from the physical characteristics of the material and extrapolation. The most commonly used mechanical springs are coil springs, which are then classified according to the principle of spring action, as follows:

  • Extension coil springs
  • Helical compression springs
  • Twisted coil springs

Yield strength calculation is important for calculating safe load factors and ensuring long-term use of springs.

Calculation of the elastic limit of helical extension springs:

Extension coil springs are designed to exhibit elastic properties when stretched to their full length, that is, they are used to hold attached components together. A hook to secure its initial position usually characterizes these springs. The most common examples of this type of spring are trampolines and balances. To calculate the yield strength of this type of spring, a control sample of a spring is subjected to partial extension by applying force in small steps so that the spring expands by one percent of the spring’s length. By keeping the expansion of the spring constant, the strain is kept constant, making it easy to extrapolate the elastic limit. The force is applied in the form of weights, which are converted to their corresponding force equivalents by taking into account the gravitational attraction and the horizontal and vertical components of the force. After the exercise of the known force, the force is removed to check the presence of elastic properties in the spring. The point at which a complete absence of elastic properties is observed is noted and multiplied by the factor of safety. The value is an effective indicator of safe load and yield strength. Additional experimentation to determine the exact yield point is done by stressing a similar spring precisely between the points of elasticity and absence of elasticity.

Calculation of the elastic limit of helical compression springs:

This type of spring is also a type of coil springs. Unlike the operation of helical extension springs, these springs are designed to exhibit elastic properties when compressed, that is, these springs are used to keep the attached component apart. One of the most visible uses of this type of spring is shock absorbers in vehicles. Yield strength calculation on compression springs should be done a little differently than expansion springs. Unlike expansion springs, the maximum possible range of operation 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 aforementioned 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 tweezers and mousetraps. Yield strength calculation is done in a similar way to compression springs. The range of operation is limited and the force is applied in a similar way to compression springs.

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

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