PSI - Issue 79

Karolina Głowacka et al. / Procedia Structural Integrity 79 (2026) 155– 160

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1. Introduction Rubber materials, including fiber-reinforced rubbers, are widely used in the automotive, construction, and technical equipment industries due to their ability to damp vibrations, durability, and elasticity under variable loading conditions [1 – 3]. In automotive applications, they are commonly employed in suspension components, engine mounts, and pneumatic bellows, where they are subjected to long-term cyclic loading [1]. The fatigue durability of such materials is complex due to their hyperelasticity, viscoelastic behavior, and intricate interactions between the rubber matrix and the reinforcement [3]. In the literature, studies on rubber fatigue generally follow two main approaches: crack initiation and crack propagation, both of which are strongly influenced by the conditions of cyclic loading, temperature, and the type and amount of fillers (e.g., carbon black, silica, nanoparticles) [4]. Commonly used methods for evaluating the durability of rubber composites are derived from classical materials testing techniques and include Wöhler (S– N) curve analysis [5, 6] and fracture mechanics approaches such as the Paris – Erdogan relationship [7]. Reinforcements in rubber composites — whether in the form of short fibers or cords — not only enhance strength and fatigue life but also significantly affect crack propagation behavior [8]. The interfacial region between the individual phases is often the weakest part of the material, which is why various surface treatments are employed to improve fiber – matrix adhesion [9]. Several studies have indicated that the application of pre-tension (pre-loading) can significantly influence the fatigue behavior of rubber materials. Drozdov and Dorfmann [10] investigated filled elastomers under finite viscoelastic loading and showed that pre-loading alters the stress relaxation behavior, which may affect fatigue life. Le Cam et al. [11] demonstrated that pre-strain modifies the strain-induced crystallization process and the interface structure in elastomer composites, thereby impacting crack initiation and propagation. Similarly, Ruellan et al. [12] highlighted that strain-induced crystallization in natural rubber improves fatigue resistance by forming reinforcing crystalline domains, suggesting that pre-strain can alter the microstructural response to cyclic loading. These findings underline the potential importance of pre-tension in fatigue performance; however, systematic studies on composite rubber systems under bending conditions remain limited. Most available research is restricted to uniaxial tension – compression tests and does not account for the characteristic geometries of composite elements operating under real service conditions (e.g., bending). Comprehensive experimental data concerning the effect of pre-tension on the fatigue life of rubber-based composites are still lacking [13]. The aim of the present study is to address this gap by experimentally investigating the influence of pre-strain (~10%) on the fatigue life of a rubber –nylon composite with a 0/90° reinforceme nt configuration, subjected to cyclic three-point bending. Although the employed test is a modified version of the classical three-point bending method — resulting primarily in tensile loading — it provides a broader insight than pure tension tests. The obtained results are analyzed in terms of the relationship between the maximum strain in the specimen and the number of cycles to failure. These findings not only contribute to the understanding of the fatigue behavior of rubber composites but also have practical implications for the design of rubber components operating under cyclic loading and initial strain. 2. Materials and methods The tested material consisted of a composite composed of a flexible rubber matrix and a single reinforcement layer made of interwove n nylon cords arranged in a 0/90° configuration, forming a woven structure. Under cyclic loading, this material is subjected to self-heating caused by internal energy dissipation. The accumulated heat affects not only the mechanical properties of the rubber matrix itself but also the structure of the reinforcing fibers and the interfacial region between the rubber and the cords. These changes may alter the fatigue process of the composite, making the analysis of loading frequency effects an important aspect of the present study. 2.1. Specimen preparation The specimens were cut from composite sheets with a uniform thickness of 3 mm. Each sheet contained a single reinforcement layer positioned in the mid-plane. The composite sheets were produced at the University of Maribor. Strips with a width of 45 mm were first cut, ensuring consistent fiber orientation so that the 0/90° configuration was identical across all specimens. The strips were then trimmed to a length of 300 mm, following the requirements of the