Composites Research

The Korean Society for Composite Materials (한국복합재료학회)
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Pull-off Strength of Jagged Pin-reinforced Composite Hat Joints

요철핀으로 보강된 복합재 모자형 체결부 구조의 강도 연구

  • Kwak, Byeong-Su (School of Mechanical and Aerospace Engineering, Graduate School, Gyeongsang National University) ;
  • Kim, Dong-Gwan (Lightweight Automotive Components Development Team, LG Hausys) ;
  • Kweon, Jin-Hwe (School of Mechanical and Aerospace Engineering, Graduate School, Gyeongsang National University)
  • Received : 2018.10.12
  • Accepted : 2018.12.11
  • Published : 2018.12.31
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Abstract

The effect of stainless steel jagged-pin reinforcement on the pull-off strength of the composite hat-joint was studied by the test. The pins were physically and chemically surface-treated and inserted in the thickness direction over the interface where the skin and stiffener meet. The specimens including the jagged-pins were made by co-curing process. Diameters of the jagged-pins were 0.3, 0.5 and 0.7 mm. The pin areal densities were set to 0.5 and 2.0% based on the interface area where the skin and stiffener meet. The specimens using 0.3 mm diameter normal (un-jagged) pins with 2.0% areal density were additionally fabricated and tested to investigate the pin shape effect on the pull-off strength. The pull-off strengths of specimens reinforced with 0.5% areal density by 0.3, 0.5, and 0.7 mm diameter pins were 45, 19 and 9% higher than those of un-reinforced specimens, respectively. In case with 2.0% pin areal density, the strengths were 127, 45, and 11% higher than those of un-reinforced specimens, respectively. The test results show that the higher pin areal density results in the higher strength when the pin diameter is the same. When the pin areal density is the same, the smaller pin diameter leads to higher strength. When the joints using jagged-pins and normal pins in 2.0% areal density with 0.3 mm diameter, the joints of jagged-pins showed the 64% higher strength. From the results of this study, it was confirmed that jagged-pin reinforcement can be an effective method for improving the pull-off strength of composite hat-joint.

스테인리스 강으로 제작된 요철핀의 보강이 복합재 모자형 체결부의 풀오프 강도에 미치는 영향을 시험으로 연구하였다. 요철핀에는 물리적, 화학적 표면처리를 수행하였고, 체결부의 외피와 보강재가 만나는 영역에 두께방향으로 핀을 삽입하였다. 모자형 체결부 시편은 요철핀을 포함하여 일체성형으로 제작하였다. 사용된 요철핀의 지름은 0.3, 0.5, 0.7 mm로 세 가지이다. 핀의 삽입밀도는 외피와 보강재가 만나는 면적 기준으로 0.5, 2.0% 두 가지이다. 요철핀과 일반핀의 효과를 비교하기 위하여 0.3 mm 일반핀을 2.0% 밀도로 삽입한 시편을 추가로 제작하여 시험을 수행하였다. 0.3, 0.5, 0.7 mm의 요철핀을 0.5%의 밀도로 삽입한 시편의 강도는 보강되지 않은 시편 대비 각각 45, 19, 9% 높게 나타났고, 2.0% 밀도의 경우 강도는 각각 127, 45, 11% 높게 나타났다. 시험 결과 지름이 동일할 경우 밀도가 높을수록, 밀도가 동일할 경우 지름이 작을수록 보강효과가 더 높게 나타나는 것을 알 수 있었다. 요철핀과 일반핀의 효과를 비교한 결과 2.0% 밀도로 0.3 mm 직경의 핀을 이용하여 보강할 경우, 요철핀 보강시편이 일반핀 보강 시편보다 64% 높은 강도를 보였다. 본 연구의 결과로부터 요철핀 보강이 복합재 모자형 체결부의 풀오프 강도 향상을 위한 효과적인 방법이 될 수 있음을 확인하였다.

Keywords

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Fig. 1. Microscopic images of surface for 0.3 mm diameter Z-pin

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Fig. 2. SEM images of surface for Z-pin

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Fig. 3. Specimen configuration (unit : mm) [21]

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Fig. 4. Conceptual diagram for making specimen [21]

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Fig. 5. Typical acrylic mould for Z-pinning

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Fig. 6. Z-pins arrangement

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Fig. 7. Test set-up and fixtures

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Fig. 8. Load-deflection curves of hat joint Z-pinned with 0.5% density

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Fig. 9. Failure development of hat joint with 0.5% Z-pin density

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Fig. 10. Failure strength and bonded area between laminate and Z-pin (0.5% density)

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Fig. 11. Load-deflection curves of hat joint Z-pinned with 2.0% density

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Fig. 12. Failure development of hat joint with 2.0% Z-pin density

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Fig. 13. Failure strength and bonded area between laminate and Z-pin (2.0% density)

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Fig. 14. Load-deflection curves of hat joint Z-pinned by 0.3 mm diameter pins with 2.0% density

Table 1. Test matrix

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