Abstract:

Objective Owning to the advantages in terms of low-density, low-cost, recyclability, and excellent mechanical properties, the natural fiber reinforced thermoplastic composites have broad application prospects in fields such as transportation and construction. However, natural fiber reinforced thermoplastic composites are still limited in engineering design and application, partly due to a lack of in-depth and comprehensive understanding of its mechanical properties and failure mechanisms under complex loading conditions. Therefore, the paper proposed to investigate the influence of cyclic loading paths on the deformation characteristics and mechanism of jute fabric/polyethylene composites.

Method Jute fabric/polyethylene composite prepared by hot press method based on jute woven fabric as reinforcement and polyethylene film as matrix, the mechanical properties of the composite were tested under cyclic loading paths of constant-amplitude cyclic loading, stepwise increasing cyclic loading and decreasing cyclic loading. The accumulated strain, strain of each cycle and strain recovery factor were analyzed, and the deformation mechanism was also discussed.

Results The jute fabric/polyethylene composite exhibited cyclic softening characteristic at all loading stages under constant-amplitude cyclic loading, and stepwise increasing cyclic loading and in first loading stage under stepwise decreasing cyclic loading led to cyclic hardening in the subsequent loading stages under stepwise decreasing cyclic loading (Fig. 3). Under constant-amplitude cyclic loading and stepwise increasing cyclic loading, the jute fabric/polyethylene composite demonstrated similar deformation mechanism; and with the increase of cyclic peak stress and cycle number, the accumulative strain (accumulative maximum and residual strain) of each loading stage was increase (Fig. 5), and the loading strain, elastic strain and residual strain of each loading stage were decrease (Fig. 6). Under stepwise decreasing cyclic loading, the variation of accumulative strain, loading strain, elastic strain and residual strain with cycle number in the first loading stage was similar to that under constant-amplitude cyclic loading and stepwise increasing cyclic loading, and was opposite in the subsequent loading stages (Fig. 5, Fig. 6). Meanwhile, the strain recovery coefficient gradually approached 100% with increase with cycle number under different cyclic loading paths, and the strain recovery coefficient gradually increase close to 100% in all loading stages under constant-amplitude and stepwise increasing cyclic loading and in first loading stage under stepwise decreasing cyclic loading, however, decreased close to 100% in the subsequent loading stages under stepwise decreasing cyclic loading (Fig. 7).

Conclusion The results show that deformation characteristics and mechanism of jute fabric/polyethylene composite are affected by cyclic peak stress, which is also closely related to cyclic loading paths. Hence, the influence of cyclic loading path was investigated on the deformation characteristics of the natural fiber reinforced thermoplastic composites, which better reflect the long-term mechanical performance under actual use conditions, and thus make more practical conclusions. In order to comprehensively study the mechanical behavior of these materials under complex loading histories, in-depth investigation on deformation and energy dissipation under different cyclic loading rates, random cyclic peak stresses was proposed for future research.

Key words: jute fabric, polyethylene, thermoplastic composite, cyclic loading, loading path, deformation characteristic