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The main reason for the definition of leaf springs as safety parts is that even the smallest mistake in its functioning can cause severe accidents. It is imperative to ensure the endurance of leaf springs under high deformation and stress. In this reference study, we examine deviations resulting from production and design variations known as” noise factor” which can affect the fatigue life of a parabolic leaf spring. It will be a mistake to evaluate the design roughly with the stress levels on the layer. It has been described in this study with relevant examples that the leaf spring with 1550 N/mm2 tensile strength may be broken under much lower stress levels if it is exposed to dynamic loads.

Parabolic leaf springs are used as safety parts in heavy/ light commercial vehicles. When designing leaf springs, one must complete the evaluation from the perspectives of fatigue life and durability in order to ensure optimization of the design. After the initial design, rather than trying to establish optimization by producing prototypes by trial and error method, using the virtual prototype process to achieve design optimization, thereby reducing the costs will offer competitive advantage for both suppliers and original equipment manufacturers in the global market. In a reference study carried out in a partnership with Ford Otosan, the finite element methodology was used to verify the design of a 4- layered parabolic leaf spring and a multi-parabolic spring designed as its alternative. The stress distribution on layers during vertical, loaded and windup moment was examined.

Leaf springs are mainly used for absorbing energy associated with road outputs and they release energy coming from the road. If the complete leaf stiffness and each leaf stress distribution can be calculated carefully, while ensuring safety, required ride comfort will also be maintained. The desired vehicle ride height (attitude) under load must be taken into consideration during calculations of leaf spring design. In addition to providing the loads coming from the vehicle, leaf springs are significantly controllers of windup effects. Braking windup causes rotation at the lateral axis. When vertical F jounce load and braking moment are applied to the leaf spring simultaneously, von misses stress value on leafs will increase to a higher level which is very close to and sometimes higher than the tensile strength. The designers must ensure safety and endurance for any case during working conditions. The most critical point is front axle windup stopper position.

Parabolic leaf springs are safety components on the suspension system. They provide ride comfort due to calculated stiffness characteristics and they absorb and release energy associated with the road outputs of a fully loaded vehicle. Leaf springs determine the desired vehicle ride height from the ground. As a critical safety part, leaf spring endurance must be ensured. Conventional leaf springs, multi-parabolic leaf springs and parabolic leaf springs are the general types in use. The most commonly used type of leaf spring is the parabolic leaf spring. The main advantages of parabolic leaf springs are that they are lighter, cheaper, with fatigue advantages, and they isolate more noise. Classical leaf spring design and prototype process methodology consists of fatigue tests repeated for each case considering different geometry alternatives, leaf layer additions, material and suspension hard points improvements. This methodology takes a long time and requires a significant budget.