Engineering robust extension springs requires knowledge of the factors that cause their failure. Common problems such as fatigue, deformation, and corrosion are typically symptoms of deeper underlying conditions, rather than isolated issues. For example, corrosion might occur not because of simple surface oxidation, but due to an inappropriate operating environment combined with lack of suitable coatings. This article will examine each cause, emphasizing the link between different contributing factors. It will also provide guidance on often neglected aspects like appropriate material selection and environment suitability, to help prolong the life cycle of extension springs.

Fatigue Stress

Fatigue stress is a reduction in the strength of a material due to repetitive loading. It is a common reason extension springs fail. The constant cycle of extension and compression leads to a decrease in the ability of the springs to bear load, which can eventually cause complete failure in extreme circumstances.

Extension springs used in applications with high frequencies or heavy loads are more susceptible to fatigue stress. For example, springs used in industrial assembly lines are subjected to continuous stretching and releasing. This ongoing action greatly contributes to fatigue stress. As a result, engineers modify the design by changing parameters such as the diameters of the wire and the material selection. Using a wider wire diameter usually improves the resilience of the spring when subjected to heavy loads, thus reducing fatigue stress.

Modifying the design can help to delay, but not completely eliminate, fatigue stress. It is important for engineers to understand the context of the extension spring's application, its load, and frequency of use. This awareness aids in the creation of a spring that is better equipped to resist fatigue stress, thereby extending its lifespan.

Permanent Deformation

Permanent deformation refers to the phenomenon whereby an extension spring does not return to its initial form post-extension. This typically transpires when the extension spring is exposed to strain exceeding its elastic limit or yield point. The process of accurately determining this yield point is a crucial phase in the design procedure of the spring.

Take, for instance, if an engineer is tasked with designing a spring for the lid of a car's boot. Over-stretching the spring means it might not be able to bring the boot lid back to its complete position, leading to operational complications. To avoid this, the engineer takes into consideration elements such as the load and the most allowable lid extension during the design phase. These parameters aid in setting the yield point of the spring and directing the choice of a spring with an appropriate limit.

However, identifying the yield point does not solely revolve around performing force calculations. External factors, for example elevated temperature, can affect a spring's yield point. A case in point is a spring operating under a car engine's heat which might touch its yield point earlier than anticipated, triggering permanent deformation. Hence, it is vital for engineers to factor in the operational conditions and revise the yield point where necessary. In addition, the selection of a spring material with superior heat resistance may offer advantages.


Corrosion occurs due to chemical reactions that take place when the spring material comes in contact with elements from the environment, which results in the failure of extension springs. This most commonly takes the form of rust, a process that slowly reduces the mechanical strength of the spring and can eventually lead to its malfunction.

Take, for example, an extension spring used in a marine environment. This particular environment increases the rate of corrosion because of the high salt concentration in the air. The continuous exposure to salt accelerates the rust formation on the spring, which affects its performance and reduces its operational period.

A practical method of preventing rust formation on springs is the use of materials that are resistant to corrosion for their manufacturing. If it's not possible to use corrosion-resistant materials, surface coatings can be applied to the springs. Powder or galvanized coatings represent examples of such protective interventions, as they create protective layers that help delay corrosion. In environments with high levels of wear, where these coatings can easily be worn down, corrosion-resistant materials might be more beneficial. Therefore, different measures can be taken to manage corrosion, and the choice between them should be based on the respective conditions in which the extension spring is to operate.


Knowing the reasons behind the failure of extension springs is needed for sound engineering. The main causes of spring failure are fatigue stress, permanent deformation, and corrosion. All of these must be factored into the design and selection processes of springs. Factors like the type of materials used, environmental conditions, load bearing, and usage frequency also participate in spring failure.

Proper balancing of these factors can reduce the likelihood of these failures and extend the lifespan of your spring. A well-designed and selected spring can help maintain the operation of your projects and ward off potential issues. Gaining proficient understanding of the principles of spring design and selection paves the way to minimizing spring failures.