In this paper, the impact energy potential of hybrid fiber reinforced concrete (HFRC) was explored with different fiber mixes manufactured for comparative analyses of hybridization. The uniaxial compression and 3-point bending tests were conducted to determine the compressive strength and flexural strength. The experimental results imply that the steel fiber outperforms the polypropylene fiber and polyvinyl alcohol fiber in improving compressive and flexural strength. The sequent repeated drop weight impact tests for each mixture concrete specimens were performed to study the effect of hybrid fiber reinforcement on the impact energy. It is suggested that the steel fiber incorporation goes moderately ahead of the polypropylene or polyvinyl alcohol fiber reinforcement in terms of the impact energy improvement. Moreover, the impact toughness of steel-polypropylene hybrid fiber reinforced concrete as well as steel-polyvinyl alcohol hybrid fiber reinforced concrete was studied to relate failure and first crack strength by best fitting. The impact toughness is significantly improved due to the positive hybrid effect of steel fiber and polymer fiber incorporated in concrete. Finally, the hybrid effect index is introduced to quantitatively evaluate the hybrid fiber reinforcement effect on the impact energy improvement. When steel fiber content exceeds polyvinyl alcohol fiber content, the corresponding impact energy is found to be simply sum of steel fiber reinforced concrete and polyvinyl alcohol fiber reinforced concrete.

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This paper deals with the fracture failure analysis on plain woven laminated fabrics used in stratospheric airship structures. A series of uniaxial tensile and central slit tearing tests were carefully conducted on bias specimens, and the corresponding tensile and tearing properties, including failure mechanisms and material strengths, of a laminated fabric were discussed. Results show that laminated fabrics are typical direction-depended materials, and their failure characteristics vary greatly with the bias angles. Typical tearing stress–displacement curves of the laminated fabric could be defined as four characteristic regions: a co-deformation region, a yarn extension region (or shear deformation region), a plateau region, and a post peak region. Among bias specimens, there are many obvious differences in tearing behaviors in terms of maximum displacement, damage mode, curve slope, and number of stress peaks, which could be attributed to the material orthotropy and different failure mechanism of constituent materials. Unlike results of tensile strength, there is a W-shaped relationship between tearing strength and off-axis angle, with a local strength peak at 45° angle. Based on the Tsai-hill criterion, a new tearing strength criterion consisting of two parts, including a U-shaped and an inverted V-shaped part, is proposed for this laminated fabric. Comparisons between the experimental and calculated results for the laminated fabric are performed, and the strong agreements demonstrate that the proposed criterion is feasible and accurate.

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