When referring to mechanical fatigue, we are concerned with the long-term performance and service life of rubber components subjected to repeated mechanical loading and unloading cycles. Conveyor, synchronous conveyor belt, different tire components, AV base in the work need repeated mechanical cycle.
Rubber mechanical fatigue begins with homogenous fracture (precursor to fracture) in the rubber composite. Then cracks in the rubber body grow, leading to catastrophic failures as the loading cycle progresses. According to this failure mechanism, we need to consider two aspects, one is rupture nucleation (i.e. the homogeneity of the complex) and the inherent fatigue crack propagation resistance.
The challenge often faced by composite developers is how to extend the fatigue life of components without affecting other performance, or how to improve dynamic performance without affecting the service life of components. Fortunately, in the face of such challenges, we have a rich and well-developed scientific framework to address them, as well as some basic material selection guidelines that can help us.
Deformation control mode
First, we need to understand the loop running conditions of the component. Is rubber deformation controlled by the cyclic load or displacement applied? This is crucial because it helps us to adjust the stiffness of the complex to ensure that storage capacity is minimized in the event of possible deflection of cracks. For example, under deflection control, we can select a soft compound that minimizes the energy stored in the complex under deflection and inhibits crack propagation. Instead, for load control situations, the complex can be hardened to minimize component deflection.
Selection of rubber
The selection of suitable rubber is the most important for mechanical fatigue properties. Natural rubber is an excellent choice for crack and tear resistant compounds. Its ability to crystallize under strain results in automatic strengthening of the crack tip. This mechanism prevents and passivates cracks during cyclic relaxation and non-relaxation deformation. Of course, natural rubber is not suitable for every application. High temperature operations or harsh chemical conditions require the use of specific synthetic rubber. Compared with natural rubber, the strain crystallization properties of most synthetic rubber are not outstanding. Instead, synthetic rubber relies entirely on particle strengthening operations to achieve the desired crack growth and tear resistance.
Selection of reinforcing agent
Reinforcing agents such as carbon black play an important role in determining the crack growth and tear resistance of rubber components. The key is to select the right load grade, surface area and structural layer of carbon black. The selected carbon black is required to exhibit good dispersion properties and minimal physical impurities during the complex mixing process to achieve further improvement. The same considerations should be taken into account when selecting other granular preparations. Filler polymers and raw material impurities lead to an increase in the size and number of cracks in the composite, both of which have adverse effects on fatigue life.
Carbon black in natural rubber can reduce the displacement required by strain crystallization by enlarging the local strain in the rubber matrix. This essentially enhances the self-reinforcing power of natural rubber. Carbon black incorporates the excess energy consumption mechanism into the rubber complex, which is one of the main reasons for the increased tear strength and crack resistance of rubber with carbon black compared to rubber without carbon black. To break the packed rubber, additional external forces are required to compensate for the energy consumed by the carbon black in the viscoelastic processing area before reaching the crack tip. This is particularly important for amorphous rubber.
We need to be careful because excessive energy consumption can lead to the accumulation of harmful heat in the complex under cyclic load, affecting dynamic mechanical properties (e.g. rolling resistance). The same is true of rubber technology, which requires a careful balance.

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