Determining the critical stress range of compression springs is not just about design. It's also about factoring in how these components withstand operational strains. One misstep in estimating a spring's stress handling capacity can lead to early failure, potentially disrupting industrial processes. This calls for accurate calculation of these stresses.
The focus here is on the process of calculating compression spring stress. We'll familiarize you with pertinent spring stress equations, focusing on the significant parameters that primarily include the type and intensity of the force that the spring must endure. Nevertheless, these equations serve only as a general guide, and you may encounter deviations due to a range of variables in realworld applications. We will provide pointers on how to effectively tackle such deviations.
The information provided here will aid in your understanding, designing, and selecting the best compression springs for your specific needs.
Spring Stress Equation
The equation for calculating the stress experienced by compression springs due to applied force is as follows:
σ = (8FDm)/(πd^3)
In this equation:
σ is the shear stress
F is the force acting on the spring
Dm is the mean diameter of the spring
d is the wire diameter
In terms of the relationship between these variables, the shear stress (σ) increases with the applied force (F) and the mean diameter (Dm). Conversely, an increase in the wire diameter (d) reduces the shear stress.
We can illustrate this equation with a simple example. Let's consider a spring with constant force and mean diameter. If you were to increase the wire diameter in this scenario, the spring's stress would decrease. This practical example emphasizes the importance of wire diameter in reducing stress for loadbearing applications.
However, this equation doesn't account for certain factors that can affect the actual stress experienced by the spring. Elements such as the material properties of the spring, temperature fluctuations, and variations in manufacturing processes can all directly influence the stress levels. It's important to account for these elements, typically by applying a factor of safety between 1.11.6 depending on the criticality and fatigue expectation of the application. Our Spring Calculator automatically applies a factor of safety of 1.5 for custom springs and 1.1 for vendor springs.
Key Assumptions
In the calculation of spring stress, the underlying assumptions include:

Linear Elastic Deformation Curve : The material of the spring is presumed to follow Hooke's law up to its yield point, resulting in a linear deformation curve under shear stress. This is relevant to all metallic materials, whereas the traditional calculation of stress does NOT apply to springs made from composites or plastics.

Constant Pitch : The spring is coiled with a consistent pitch, which affects stress distribution and, in turn, impacts the spring's durability.

Perfectly Cylindrical Wire : The spring wire is assumed to be perfectly cylindrical. While deviations in wire diameter may occur in actual manufacturing processes, these are typically minimal and don't greatly influence stress calculations.

Equally Distributed Load : The load on the spring is evenly distributed across the coils. This means an axial load is applied and is common in multiple practical applications.

Homogeneous Material : The spring is made of material with consistent mechanical properties. While minor inconsistencies can exist in reality, highgrade spring wire often minimizes such discrepancies.
While these assumptions provide a basis for spring stress calculations, it is important for the engineer to account for deviations in actual scenarios. For example, in situations where the spring material goes beyond its elastic limit due to extreme stress, spring failure might occur if not properly considered. Therefore, while these assumptions simplify calculations, they must be weighed against the realworld application of the spring design.
Conclusion
The calculation of compression spring stress is a straightforward process rooted in understanding the fundamental principles and variables involved. The stress equation sheds light on the impact of elements like force, mean diameter, and wire diameter on spring stress. In your future design projects involving compression springs, these parameters play a vital role in tailoring a spring resistant to the loads experienced during application. Knowledge of the applied force magnitude and usage over time enable engineers to predict and adjust their spring designs, bolstering the durability and efficiency of the machinery it serves.