Direct Tensile Properties of Fiber-Reinforced Cement Based Composites according to the Length and Volume Fraction of Amorphous Metallic Fiber

비정질 강섬유의 길이 및 혼입률에 따른 섬유보강 시멘트복합체의 직접인장특성

Abstract

In this study, the direct tensile properties of amorphous metallic fiber-reinforced cement based composites according to the strain was evaluated. A thin plate-shape amorphous metallic fiber with 15mm and 30mm in length was used. And fiber-reinforced cement based composites were prepared with contents of 1.0, 1.5, 2.0%. The direct tensile test was conducted under the conditions of $10^{-6}/s(static)$ and $10^1/s(dynamic)$ strain rate. As a results, amorphous metallic fiber with a length of 15mm was observed in pull-out behavior from the cement matrix because of the short fiber length and large portion of mixed fiber. On the other hand, amorphous metallic fiber with a length of 30mm were not pulled out from matrix because the bonding force between the fiber and matrix was large due to rough surface and large specific surface area. However, fracture occurred because thin plate shape fibers were vulnerable to shear force. Tensile strength, strain capacity and toughness were improved due to the increase in the fiber length. The dynamic increase factor of L15 was larger that of L30 because the bonding performance of the fiber-matrix interface is significantly affected by the strain rate.

본 연구에서는 변형속도에 따른 비정질 강섬유보강 시멘트복합체의 직접인장특성에 대하여 평가하였다. 길이 15, 30mm의 박판형 비정질 강섬유를 각각 1.0, 1.5, 2.0% 혼입한 섬유보강 시멘트복합체를 제작하였으며, 변형속도 $10^{-6}/s$(정적), $10^1/s$(동적)의 조건에서 직접인장시험을 수행하였다. 그 결과, 길이 15mm의 비정질 강섬유는 섬유의 섬유의 길이가 짧고 혼입개체수가 많기 때문에 섬유가 매트릭스로부터 인발되었다. 반면, 길이 30mm의 비정질 강섬유는 섬유의 표면이 거칠고 비표면적이 크기 때문에 매트릭스와의 부착성능이 우수하지만, 박판형의 섬유 형상이 전단력에 약하기 때문에 섬유가 인발되지 않고 파단 되었다. 섬유의 길이가 길수록 인장강도, 변형능력 및 인성이 큰 것으로 나타났다. 반면, 길이 30mm의 비정질 강섬유는 매트릭스로부터 인발되지 않고 파단 되지만 길이 15mm의 비정질 강섬유는 매트릭스로부터 인발되기 때문에 변형속도의 영향을 받는 섬유-매트릭스 계면의 부착효율이 크게 되어, 인장강도, 변형능력 및 인성에 대한 동적증가계수가 큰 것으로 나타났다.

Figure 1. Shape of amorphous metallic fiber

Figure 2. Dumbbell shape tensile test specimen

Figure 3. Static direct-tensile test equipment

Figure 5. Direct tensile stress-strain curve according to the strain rate

Figure 6. Fiber fracture properties

Figure 8. DIF of tensile properties according to the fiber length

Figure 7. Tensile properties according to the strain rate and fiber length

Figure 4. Dynamic direct-tensile test equipment

Table 1. Mechanical properties of the amorphous fibers

Table 2. Details of specimen and compressive strength

Table 3. Mix proportions of AFRCC

Table 4. Mechanical properties of used materials