Mechanical Property requirements of a Leaf Spring Steel

In this brief article, we will discuss the type of steel used for manufacturing leaf spring suspensions. We will also discuss alternate materials used in leaf spring manufacturing.

Mechanical Property requirements of a Leaf Spring Steel

• The Basic mechanical property requirement for any spring is high tensile strength and stiffness. 
• The other important property is the ‘Resilience’ of the spring. The resilience of spring steel is influenced by its elastic deformability. It is the property of Resilience that enables a leaf spring to sustain loading within its designated range without undergoing any permanent bending or deformation. Once the load is removed, the leaf spring “Springs Back” to its original shape and dimension.
• The material needs to have endurance or resistance to ‘Fatigue’. This means that the material must be able to withstand the maximum number of cycles of loading and unloading without breaking or permanently deforming

In order to achieve these material properties, the steel composition would have to be an alloy that includes chromium, molybdenum and vanadium, apart from carbon content, silicon and manganese.

Steel used to manufacture leaf springs

The common practice, therefore, is to utilize high-strength steel containing 0.9–1 wt.% carbon has been used for leaf spring applications. The general term to describe steels used for the manufacturer of springs is “Spring Steel”.

The most common Grade spring steel used for Leaf Spring is the 

51CrV4 (50CrV4), manufactured by Arcelor-Mittal. This grade is in use by large European OEMs like Daimler, Volkswagen group and Volvo Commercial vehicles.

Alternate Leaf spring Materials

• The Volvo XC90’s rear suspension features a composite transversely-mounted leaf spring. The composite leaf is produced by process of resin transfer molding (RTM). The adoption of the new transverse leaf arrangement results in a weight saving of 4.5 kg as compared to a similar leaf spring made from steel.
• In order to achieve a high flexibility and tolerance to high fatigue, the polyurethane (PUR) matrix resin has been used. Moreover, the PUR matrix resin cures much faster than epoxy resin for the RTM process.
• The Corvette uses a transverse-mounted rear leaf spring suspension that is made from fiber reinforced plastic (FRP) instead of steel. Apparently, FRP can sustain approximately five times as much deformation as compared to a conventional spring steel setup. The FRP composite leaf also happens to weigh only 1/3 of the weight of the equivalent steel spring. The FRP monoleaf system has a fatigue life that is 10 times that of the steel spring.

Conclusion

In this brief article, we have discussed the type of steel used for manufacturing leaf spring suspensions. We have also discussed alternate materials used in leaf spring manufacturing.

In case of any queries or comments, please feel free to ask.

References