In recent years, buried bellows have often had safety accidents such as pipeline bursts and ground subsidence due to the lack of adequate mechanical properties and other quality problems. In order to improve the mechanical properties of bellows, fly ash (FA) was used as a reinforced filler in high density polyethylene (HDPE) to develop composites. The FA was surface treated with a silane coupling agent and HDPE-g-maleic anhydride was used as compatibilizer. Dumbbell-shaped samples were prepared via extrusion blending and injection molding. The cross-section morphology, thermal stability and mechanical properties of the composites were studied. It was observed that when 10% modified FA and 5% compatibilizer were added to HDPE, the tensile yield strength and tensile breaking strength of the composites were nearly 30.2% and 40.4% higher than those of pure HDPE, respectively, and the Young’s modulus could reach 1451.07 MPa. In addition, the ring stiffness of the bellows was analyzed using finite element analysis. Compared with a same-diameter bellows fabricated from common commercially available materials, the ring stiffness increased by nearly 23%. The preparation method of FA/HDPE is simple, efficient, and low-cost. It is of great significance for the popularization of high-performance bellows and the high value-added utilization of FA.
The nacre has excellent impact resistance performance, and it is attracting attention in the field of aerospace composite research. Inspired by the layered structure from nacre, semi-cylindrical nacre-like composite shells of brittle silicon carbide ceramic (SiC) and aluminum (AA5083-H116) were established. Two types of tablet arrangements (regular hexagonal and Voronoi polygons) of the composites were designed, and the same size of ceramic and aluminum shell were established for the impact resistance analyzed numerically. In order to better compare the resistance performance of the four types of structures under different impact velocity, the following parameters were analyzed including energy variation, damage characteristic, bullet residual velocity, and semi-cylindrical shell displacement. The results show that the semi-cylindrical ceramic shells have higher rigidity and ballistic limit, but the severe vibration after impact causes penetrating cracks, and the whole structure failure occurred eventually. The nacre-like composites have higher ballistic limits than semi-cylindrical aluminum shells, and the impact of bullets only causes local failure. In the same conditions, the impact resistance of regular hexagons is better than Voronoi polygons. The research analyzes the resistance characteristic of nacre-like composites and single materials, and provides a reference for the design of nacre-like structures.
The mechanical behavior of buried HDPE double-wall corrugated pipes is mainly affected by the material and the structure of the pipe wall. Here we studied a peculiar material that added fly ash (FA) in high density polyethylene (HDPE) to develop composites. We have conducted research on FA/HDPE composites with different mix proportions. When 5% compatibilizer was added to the 10% FA masterbatch/HDPE composite, the Young’s Modulus of FA/HDPE composite was higher. This paper mainly studies the mechanical behavior of the structure of pipe walls for materials with this proportion of the ingredients. The mechanical behavior of double-wall corrugated pipes with different ratios of interior and exterior wall thicknesses is studied by keeping the sum of the interior and exterior wall thicknesses unchanged. Pipes with six different ratios of interior and exterior wall thicknesses are simulated; the results show that the strain of crest and liner gradually decreased and the valley strain gradually increased with the increase of the exterior wall thickness. By comparing inner and outer wall thickness ratios from 0.67 to 2.33, it is found that the structural performance and economic advantage for the double-wall corrugated pipes is best when the thickness ratio of the interior wall and the exterior wall is controlled to be from 1.3 to 1.8. This paper expounds the deformation mechanism of double-wall corrugated pipes from the perspective of mechanical behavior and structural characteristics, and provides a reference for material selection and structural design of double-wall corrugated pipes.
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