Compression springs are found in various devices, their performance and lifespan can be affected by tensions. Plastic deformation, a result when a spring faces loads beyond its design capacity, plays a significant role in a spring's behavior. Think of car suspension springs that periodically support significant weight. In such a case, the design of the spring is critical to its operation; inappropriate design can lead to failures. Note that slight overload doesn't always hinder the spring's function. Plastic deformation results from several factors, including the properties of the material, the size of the load, and the duration the load is applied. This article aims to help you understand these factors and their interactions, guiding you to make informed design decisions for compression springs.

Plastic Deformation vs Elastic Deformation

Compression springs endure two distinct types of deformation: elastic and plastic. Elastic deformation is observed in the spring when a load leads to compression within its elastic limit. A notable feature of an elastic deformation is that the spring can return to its original shape after the load is removed as the energy stored during compression is completely recoverable.

The degree of elastic deformation is influenced by the kind of material and its heat treatment process. To illustrate, springs made from steel that have undergone a suitable heat treatment stage can bear larger loads and still retain their original shape due to an elevated elastic modulus.

Plastic deformation is different; it happens when a load exceeds the spring's elastic limit, leading to unchangeable deformation. In this instance, the spring's inability to entirely regain its original shape post-deformation is due to its lack of total energy recovery.

In order to limit the occurrence of plastic deformation, one takes into account the yield strength of the spring, which represents the maximum stress a spring can withstand before plastic deformation happens. Materials exhibiting high yield strengths are commonly preferred to delay the onset of plastic deformation. That said, factors such as the cost and corrosion resilience of these materials, as well as the operational environment of the spring, have to be evaluated to guarantee the best spring performance.

Why Plastic Deformation Occurs

Plastic deformation in compression springs is the result of an applied load that exceeds the proportional limit of the spring, also referred to as the elastic limit. When this limit is surpassed, the properties of the material shift, resulting in plastic deformation, which may appear as a permanent bend or fracture in the spring.

To illustrate, consider a suspension spring under a heavily loaded vehicle. If the vehicle's weight exceeds the spring's elastic limit, the spring may undergo deformation. Thus, identifying the proportional limit accurately during the design stage of a spring is crucial to its function and safety.

Besides, flaws in the material of the spring can contribute to plastic deformation. The presence of external factors like fluctuations in temperature, variation in humidity, and the rate of load application can accelerate this deformation. For instance, a spring with micro-cracks that is subjected to quick changes in load in a humid environment might deform sooner under these specific circumstances.

It should be noted that these risk factors merely set conditions that make the spring more susceptible to deformation and don't directly result in it. The main cause remains the surpassing of the spring's elastic limit by the applied load. Although factors such as material defects, environmental conditions, and rate of loading can speed up deformation, the principle factor is always the load that breaches the elastic limit. To avoid plastic deformation, the design of the spring must account for an elastic limit that accommodates the anticipated load range.

Proportionality Limit vs Elastic Limit

The proportionality limit and the elastic limit are essential concepts in understanding the deformation behavior of compression springs. The stress-strain graph indicates the proportionality limit, which establishes the boundary for Hooke's Law's relevance to compression springs. According to Hooke's Law, the necessary force for lengthening or compressing a spring by a specific distance links directly to that distance. When the spring surpasses the proportionality limit, this direct connection ceases to be valid, marking non-linear behavior initiation. For example, automotive suspension systems have springs that face varying loading conditions, possibly exceeding the springs' proportionality limit. As a result, springs could exhibit non-linear behavior, leading to unpredictable responses.

The elastic limit signifies a transition from the elastic to the plastic deformation regions. It's separate from the proportionality limit, despite common misidentification as interchangeable. When a spring surpasses its elastic limit, it enters plastic deformation, changing the spring's shape permanently. Engineers must consider this when planning a design, to ensure the machinery's effective operation. For instance, a spring continuously loaded past its elastic limit in a machine won't return to its original shape after unloading, affecting the machine's operational status. By recognizing the proportionality and elastic limits, engineers can better predict performance results and design restrictions, assisting in choosing the suitable springs for diverse applications.


Comprehending plastic deformation in compression springs is crucial for secure performance and durability. It requires a clear differentiation between plastic and elastic deformation, as well as a grasp on the principles of proportionality and elastic limit. This knowledge supports engineers in choosing suitable materials for springs and refining their designs and load applications to prevent plastic deformation. Thus, the operation of compression springs within their design limits can be assured.