The main goal is to develop leaf chain that lasts longer, costs less to maintain and uses fewer materials and energy to produce. You can read more about the project by clicking here.
Early work has focused on setting performance benchmarks to serve as reference points as we explore different approaches. It has become clear that treating leaf chain as a complete mechanical system, rather than just a small component, has significantly improved its lifespan.
Understanding the mechanical properties of materials is crucial to ensuring the safety and longevity of the leaf chain. Two fundamental concepts often need to be considered: fatigue strength and tensile strength. While both relate to how materials respond to stress, they describe distinctly different phenomena that can significantly influence the performance and durability of the leaf chain. Tensile strength refers to the maximum stress a material can withstand when being stretched or pulled before breaking. It is a measure of the material’s resistance to a single, static load and is typically determined through standardised tests. On the other hand, fatigue strength describes the ability of a material to resist failure when subjected to repeated or fluctuating loads over time. Even if the applied stresses are well below the material’s tensile strength, repeated cycles can initiate cracks and ultimately cause catastrophic failure.
Over the years, there has been a focus on a leaf chain’s tensile strength as an indicator of its quality. This has been partly driven by machinery standards, which set safety factors from tensile strength to working load. It was not until 2015 that the ISO leaf chain standard was updated to include a minimum fatigue value, and the ANSI leaf chain standard still only sets out tensile and dimensional requirements for a chain that meets a minimum tensile strength. Most manufacturers publish figures that exceed the main chain standards. Most leaf manufacturers now publish tensile strengths that are 20% above the standard, and the chain will likely fail in excess of this figure.
It is relatively easy to increase the tensile strength of a leaf chain by increasing the hardness of the chain components; higher surface hardness of the pin can improve its wear resistance. In doing so, you reduce the ability of the chain to handle dynamic loads or shock loads. So, a stronger chain isn’t always a better one, there’s a balance between hardness and flexibility that directly impacts fatigue performance. To demonstrate this, we produced a BL834 leaf chain, and we increased the hardness of the components by 10% and 15%, which translated into a chain with an increased tensile strength of 9% and 17%. All versions of the chain exceeded ISO 4347 tensile strength.
Tensile Strength vs. Hardness
Using the staircase fatigue test method to estimate the fatigue limit of the leaf chain with increased HRC components, we found that the increased strength does not transfer into increased fatigue resistance; the chain with the mid-strength and plate hardness achieved the highest fatigue performance overall.
Fatigue Strength vs. Hardness
The increased strength does not translate into increased fatigue resistance; the chain with the mid-strength and plate hardness achieved the highest fatigue resistance. This reinforces that achieving balance is more effective than just aiming for higher hardness, too much hardness leads to brittleness while too little reduces wear resistance.
The shape of the stress-strain curve provides valuable insight into the material properties of leaf chain components. When materials have been made excessively hard, the curve tends to show a steep rise followed by an abrupt drop at the failure point, indicating a lack of ductility and increased brittleness. Such materials absorb less energy before fracturing, which means they are more susceptible to sudden breakage under dynamic or shock loads. This brittle behaviour can compromise the reliability and longevity of the leaf chain, as it may fail without warning rather than deforming gradually, making the curve a key indicator of over-hardening in the manufacturing process. By aiming for a balance, we can design chains that combine strength, flexibility and durability, ensuring longer service life and greater sustainability in manufacturing.
For further advice on choosing the right Leaf Chain solution for your application, feel free to get in touch.
