How to Calculate Yield Strength of a Plastic Spring Coil

Source: Ningbo Heng Yuan Wang Plastic Co., Ltd.  author:   Time: 2014-10-10

Plastic spring coil action has been used by humans since the invention of crossbow. Even though theoretical knowledge of yield strength was very rudimentary, significance of its practicality was understood. Yield strength of a plastic spring coil is described as the stress at which the spring starts deforming plastically, i.e. stress beyond which the spring stops returning to initial position. It is also known as elastic limit or yield point. This article discusses the ways of calculating the yield strength of the most commonly used mechanical springs. An accurate way to calculate the strength is subjecting the spring to an incremental stress change and at the same time looking for the point of no return. However, this means of calculation of yield strength for limited production springs is not viable. Therefore, in these cases the yield strength is deduced by physical characteristics of the material and extrapolation.

 

Calculation of yield strength of extension plastic spring coil

 

Extension plastic spring coils are designed to exhibit elastic properties when stretched across its length, i.e. they are used to hold the attached components together. the hook to secure their initial position usually characterizes these springs. Most common examples of these type of springs are the trampolines and weighing scales. To calculate the yield strength of this type of spring, the control sample of the spring is subjected to partial extension by applying force in small steps such which spring is expanded by one percent of the spring length. By keeping the expansion of spring constant, the strain is kept constant, assisting in easier extrapolation of yield point. The force is applied in the type of weights, which are converted into their relevant force equivalents by considering the gravitational pull and the horizontal and vertical components of the force. After exertion of the known force, the force is extracted to confirm the position of elastic properties in the spring. The point at which a total absence of elastic properties is observed is noted as well as multiplied with the security factor. The value is an effective indicator of safe loading and yield strength. Further experimentation to determine exact yield strength is done by subjecting the similar spring to strain in a precise manner between the points of presence and absence of elasticity.

 

Calculation of yield strength of compression coil springs

 

This spring type is actually also a type of the helical kind springs. In contrast to the working of extension coil springs, these types of springs are designed in order to exhibit elastic properties when they are compressed, i.e. these springs are used for keeping the component attached to it apart. One of this most visible uses of this type springs tend to be shock absorbers in vehicles. The calculation of yield strength in compression plastic spring coil is become done a little differently from the expansion springs. Unlike expansion springs the possible maximum range of operation is visually conceivable. In this case, the force is applied in procedures of one hundredth of the possible range of action.