Spring Failure Explained: 5 Common Causes and Solutions
Reliable spring operation is crucial for safety-critical components in every application. For example, helical springs in an aircraft’s flight control surfaces create tension between linkages to maintain stability. In such applications, it's essential to understand standard failure modes to ensure the safe, reliable operation of safety-critical components and systems.
Springs usually operate hidden from view as a part of complex mechanisms, making it difficult to evaluate their condition. Because of this, spring failures can seemingly occur suddenly and without warning.
This article will unpack many common failure modes associated with helical coil springs. Understanding the common causes of spring failures allows you to lean on a reliable set of design and manufacturing criteria to ensure that your spring will not fail suddenly or unexpectedly. We will also highlight strategies you can take during initial spring design and material selection to ensure reliable performance in any application.
Main Types of Spring Failure
In short, the best definition of spring failure is a loss of spring functionality, up to and including a fracture of the spring coils. The following are a few of the primary causes of severe spring failure.
| Spring Failure Types |
|---|
| Plastic Deformation of the spring means that the spring does not return to its original length upon unloading. This is because the spring has deformed beyond the spring material’s elastic limit. Such deformation is sometimes called a “permanent set” of the spring. |
| Brittle Fracture of the spring occurs when it breaks suddenly, without plastically deforming. Outright brittle fracture of springs is less common but can happen more often in certain spring materials, secondary processing techniques, and environments. |
| Fatigue Fracture is a slow, progressive failure mode resulting from the cracks that initiate and propagate due to repeated spring loading and unloading cycles. This type of failure typically occurs at loads well below the spring’s maximum rated load capacity. |
| Stress Corrosion Cracking (SCC) is a type of brittle fracture failure that begins at the surface of the spring due to accumulated corrosion under prolonged periods of constant (static) applied spring load. In this way, it is an environmentally assisted failure mechanism hallmarked by visible surface damage such as rust and oxidation. |
5 Most Common Causes of Spring Failure
1. Fatigue Failure
As stated previously, fatigue failure is a fracture of the spring resulting from uncontrolled cracks that initiate and propagate from repeated cyclic loading and unloading of the spring. At many spring cycles, fatigue failure can occur at operating loads well below the maximum rated capacity of the spring.
It’s important to note that fatigue failure is a progressive failure mode that begins when small, microscopic cracks initiate on the surface of the spring at high-stress areas. After cracks initiate, they grow by small increments during each cycle of spring loading.
2. Corrosion
Corrosion is a gradual deterioration of the part's surface due to chemical or electrochemical reactions with the surrounding environment. As such, it is a visible phenomenon observed upon inspection of the spring’s surfaces for signs of oxidation manifested as rust. Corrosion is typically a concern in applications where the spring is exposed to open air and moisture, such as marine applications, or acidic chemical solutions commonly found in industrial settings.
3. Overloading
Overloading a spring occurs when it is deformed beyond its maximum rated displacement capacity or loaded beyond its maximum load rating. This results in plastic deformation of the spring, such that it does not return to its unloaded shape and length. Such plastic deformation can accumulate under repeated spring loading, seriously impeding its functionality as it loses its ductility.
Overloading can lead to a sudden fracture because the spring is repeatedly loaded beyond its elastic capability. For this reason, it is critical to ensure that a spring never exceeds the specified maximum load and displacement ratings. While this may seem straightforward, it involves selecting a strong spring to account for all possible “off-normal” loading conditions by including an appropriate safety factor in your design loads to account for such conditions.
4. Incorrect Material Selection
Specifying a material that cannot withstand your design loads and intended use environments can directly lead to one of the three failure modes delineated above.
For example, a spring’s fatigue and corrosion resistance are functions of the spring material’s atomic structure and chemical properties. Even if a spring’s wire size and outer diameter are appropriately sized for a particular load, if the underlying spring material is not strong enough, you may experience an overload failure.
Consider these common types of spring materials according to your application's load and service life requirements.
5. Improper Design and Manufacturing
Design flaws in this context refer to springs inadequately sized for a particular load, displacement, or environment. One example of this would be an extension spring with a wire that is too small to accommodate your application's load and displacement magnitudes, which would result in high spring stresses and an overload fracture or failure of the spring.
In addition, sloppy manufacturing techniques may introduce small surface imperfections such as pits or cracks that can lead to premature fatigue failure or present vulnerabilities to chemical attack and increase susceptibility to surface corrosion. During raw material processing, molecular defects can result in premature crack formation and propagation. These examples show why manufacturing precision combined with tight quality controls, from initial material procurement to final surface finish, is absolutely necessary.
Strategies to Prevent Spring Failure
If you stick to the following principles, you can prevent many of the most common helical coil spring failure modes.
However, it’s important to note that even though some of the most common strategies to prevent premature failure of your spring are detailed below, you should review your intended spring geometry, material, and use environment with a spring design and manufacturing expert to ensure the spring will not fail prematurely for the intended application.
Century Spring has a dedicated team of spring design and manufacturing engineers with expertise in all phases of product development who are available to evaluate the unique requirements of your spring design application.
Proper Material Selection
Specifying a suitable spring material will go a long way to preventing the above mentioned top three spring failure modes. For example, spring strength and fatigue life are functions of the spring material, and some spring materials have endurance limits that represent a load below which the spring can be cycled infinitely without experiencing fatigue failure.
Furthermore, corrosion can be managed by choosing a corrosion-resistant spring material or specifying a surface treatment such as passivation or electroplating.
Adhering to Design Specifications
At the design stages, you should always pay close attention to the maximum rated load capacity and the maximum rated displacement your spring will encounter in application. You should have confidence in these values so that you select a spring that will not experience an overload failure due to some load or displacement condition you did not consider.
At the spring design and selection stages, it is recommended that you clarify your spring's intended design life and use environment to the spring supplier. Such information allows our experts to tailor spring sizing calculations and evaluate whether a spring will meet your application’s life requirements.
Regular Maintenance and Inspection
As mentioned previously, your spring likely operates hidden from inspectable view. If this is the case, you should adhere to regular maintenance and inspection intervals that involve simple visual inspections of the spring. For safety-critical springs, schedule more thorough maintenance intervals involving the mechanism's disassembly, the spring's removal, and spring testing.
You should replace all affected springs and components as soon as possible if you notice any signs of damage on your spring, such as dents, cracks, or rust. If the consequences of spring failure might endanger personnel or equipment, consider replacing the spring before restarting operations.
Environmental Considerations
Numerous spring coatings and surface treatment options add excellent corrosion protection to your spring. Passivation is a commonly specified treatment that creates a protective oxide layer on the surface of the spring. Plating is an additional surface treatment option that involves adding a thin coating of dissimilar material to the spring's exposed surfaces. Compared to passivation, plating creates a thicker protective surface layer, which may be desirable for more corrosive operating environments.
Finally, if your spring operates in a highly corrosive environment or one with extreme temperature fluctuations, you should consider inspecting and replacing it at frequent intervals.
Century Spring’s Expertise in Custom Spring Solutions
Century Spring is a quality-first manufacturer with decades of experience designing and manufacturing reliable stock and custom springs for the most demanding applications across numerous industries. As the most trusted name in spring and wire form products, our dedicated customer support teams are ready to answer all your questions about spring performance, corrosion protection, and fatigue life.
We are ISO 9001-certified and produce high-quality springs that deliver unrivaled performance, engineered to resist common spring failure modes in any application or environment. Our state-of-the-art manufacturing capabilities have positioned us to offer unmatched service to industries that need large volumes of customized spring designs in accelerated development programs.
We offer rapid turnaround, shipping, and delivery on over 40,000+ stock springs available to ship today. In custom spring development programs, we are committed to minimizing the total turnaround time to pass time savings to you as reduced procurement lead times.
All our springs are always made in the USA.