Composite materials show excellent mechanical and chemical properties compared with conventional metal materials, such as aluminium and steel. For this reason, the use of composite materials has been drastically increased in the aerospace structures, which requires materials with high specific stren...
Composite materials show excellent mechanical and chemical properties compared with conventional metal materials, such as aluminium and steel. For this reason, the use of composite materials has been drastically increased in the aerospace structures, which requires materials with high specific strength and stiffness. Recently, as the design and manufacturing technologies of composite structures have been developed, their application areas have been widely expanding, from military aircrafts to also primary structures, such as bodies and wings of civilian aircrafts. In particular, because the cocuring method simultaneously cures the skin and the stiffener in the prepreg state without an additional adhesive, the method could reduce manufacturing time and energy consumption compared with that of secondary bonding, which separately cures the skin and the stiffener and then re-assembles them. Therefore, related studies on the cocuring method have been increased. Regardless of using the cocuring or secondary bonding, however, the bonded joint will still be vulnerable to the damage in the thickness direction compared with using a mechanical joint that uses fasteners such as bolt and rivet. Therefore, studies on how to improve the thickness-direction strength of bonded joints of composite structures have been conducted, which have mostly be on technologies, such as knitting, weaving, braiding, stitching, tufting and z-pinning. In this study, the z-pinned composite hat joints were tested to investigate the effect of z-pinning on the static and fatigue behavior of the joints under pull-off loading. The 0.3, 0.5 and 0.7 mm diameter jagged stainless pin were inserted into the bonded area with the pin areal densities of 0.5, 2.0%. The pin surface was chemically treated to increase the friction between pin and laminate. Test results showed the z-pinning significantly increase the static and fatigue strengths of hat-joints. The static strength of the joint with a 0.3 mm pin diameter and 2.0% pin density increased up to 127% compared with the unpinned joints. The z-pinning effect on fatigue strength was more evident. The fatigue strength of the joint at 1,000,000-cycle loading increased up to 140% in 0.3 mm pin diameter and 2.0% pin density.
Composite materials show excellent mechanical and chemical properties compared with conventional metal materials, such as aluminium and steel. For this reason, the use of composite materials has been drastically increased in the aerospace structures, which requires materials with high specific strength and stiffness. Recently, as the design and manufacturing technologies of composite structures have been developed, their application areas have been widely expanding, from military aircrafts to also primary structures, such as bodies and wings of civilian aircrafts. In particular, because the cocuring method simultaneously cures the skin and the stiffener in the prepreg state without an additional adhesive, the method could reduce manufacturing time and energy consumption compared with that of secondary bonding, which separately cures the skin and the stiffener and then re-assembles them. Therefore, related studies on the cocuring method have been increased. Regardless of using the cocuring or secondary bonding, however, the bonded joint will still be vulnerable to the damage in the thickness direction compared with using a mechanical joint that uses fasteners such as bolt and rivet. Therefore, studies on how to improve the thickness-direction strength of bonded joints of composite structures have been conducted, which have mostly be on technologies, such as knitting, weaving, braiding, stitching, tufting and z-pinning. In this study, the z-pinned composite hat joints were tested to investigate the effect of z-pinning on the static and fatigue behavior of the joints under pull-off loading. The 0.3, 0.5 and 0.7 mm diameter jagged stainless pin were inserted into the bonded area with the pin areal densities of 0.5, 2.0%. The pin surface was chemically treated to increase the friction between pin and laminate. Test results showed the z-pinning significantly increase the static and fatigue strengths of hat-joints. The static strength of the joint with a 0.3 mm pin diameter and 2.0% pin density increased up to 127% compared with the unpinned joints. The z-pinning effect on fatigue strength was more evident. The fatigue strength of the joint at 1,000,000-cycle loading increased up to 140% in 0.3 mm pin diameter and 2.0% pin density.
주제어
#Composite Co-curing Z-pinning Jagged pin Hat joint Fatigue
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