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FEATURE SPRINGS & SHOCK ABSORBERS


allow for future prevention. Corrosion and wear can also lead to


damage to the surface of the wire creating an initiation point for cracks. Therefore, it is important not only to determine the failure mechanism but the root cause of failure to prevent re-occurrence. The age old saying goes ‘prevention is


What’s the cost if a spring fails?


IST (Institute of Spring Technology) is an internationally recognised and ISO 17025 accredited test house, offering a


comprehensive range of specialist mechanical tests for all types of springs and non-spring components. These vital facilities enable manufacturers, engineers and end users from across the world to understand how components fail and what


improvements can be made to make them safer and last longer. Today, we’re asking: what’s the cost if a spring fails?


T


he failure of a component can have serious consequences and cause


safety concerns, along with unnecessary costs associated with downtime. Product recalls are also a real possibility, just like Subaru’s recall back in November last


Although these stresses will be below the ultimate tensile strength of the material, they can still cause failure as the repetitive action can cause a crack initiation which then quickly propagates under the influence of its repeated use.


The main aims of our failure investigation are not just to determine the mechanism and root cause of failure, but to suggest improvements that could be made to mitigate the risk of it occurring again”


year. Understanding why a component fails and knowing how to put clear processes in place helps to minimise the risk of this happening.


Continually expanding its products and


services, IST offers


impartial consultancy, world-leading testing and research facilities, as well as spring calculation software


14


FAILURE INVESTIGATION The main aims of our failure investigation are not just to determine the mechanism and root cause of failure, but to suggest improvements that could be made to mitigate the risk of it occurring again. The most common failure mechanism for a spring is due to fatigue. Spring fatigue is due to repeated


operation between two (or more) loads, causing varying stress on the wire.


JULY/AUGUST 2019 | DESIGN SOLUTIONS However, identification of the


failure mechanism is rarely enough information to mitigate the failure occurring again – the root cause of the failure needs to be identified. A major contributing factor to the life


of the spring is the surface quality of the wire, particularly the presence of a defect that may serve as the initiation and catalyst for the failure. Surface defects, such as drawing, coiling marks or microstructural defects, can act as stress concentration points, raising the local stress and helping in the initiation of fatigue failures. Identification of these defects which lead to failure





better than the cure’, and at the Institute of Spring Technology (IST) we advise on how to identify the failure risks, so the life of the spring can be improved. Shot peening is a tried and tested method of accelerating a stream of particles (shot) at the component’s surface, putting the spring under residual compressive stress, increasing its resistance to fatigue crack formation. Another way of preventing failure is to specify a higher strength material or an improved surface quality so the life of the spring can be optimised. Finally, for springs that are too


small to shot peen, an optimised stress relief heat treatment can be applied to improve the life of springs for high duty applications. Using shaved or super clean raw material and electro polishing can be advantageous too. Failure can also be caused by


corrosion, stress corrosion cracking, hydrogen embrittlement, liquid metal embrittlement, overloading the spring, or too much relaxation of the spring and general wear and cracking of the spring. With decades of experience in


analysing springs failures and an on-site laboratory, IST will be able to identify the exact root of the failure so robust solutions can be implemented.


MORE ABOUT IST IST is an independent organisation that draws on over 70 years of knowledge and expertise to be a voice to the world’s spring industry and supply chain. Continually expanding its products


and services, IST offers impartial consultancy, world-leading testing and research facilities, as well as spring calculation software.


IST T: 0114 2760771


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