Abstract
Fiber-reinforced polymers (FRP) composites have been increasingly used in a variety of civil engineering applications due to their superior mechanical properties compared to conventional materials. In this paper, the elastic modulus and tensile drawn-out property of carbon fibers was studied by evaluating the tensile properties of carbon fibers tested by tensile machine and then comparing them to theoretical predictions. The test results showed that the elastic modulus of carbon fibers increased with increasing drawing ratio, and the tensile drawn-out property decreased with increasing drawing ratio. The theoretical predictions agreed closely with the experimental results. The results show that the elastic modulus and tensile drawn-out property of carbon fibers are important parameters for the application of FRP composites in engineering.
Keywords: Elastic modulus；Tensile drawn out; Carbon fiber；FRP
1 Introduction
Fiber-reinforced polymers (FRP) are composites with the combination of a matrix material and reinforcing fibers. They are increasingly used in civil engineering due to their good physical and mechanical properties. Generally, carbon, glass and aramid fibers can be used as reinforcements and different thermoplastic, thermosetting and natural polymers as matrix materials [1]. Carbon fibers are very stiff and strong, and are often used as reinforcements in FRP. They have excellent electrical and thermal properties as well.
The properties of carbon fibers are largely related to their manufacturing processes and types of precursor materials. In particular, two parameters, the elastic modulus and tensile drawn-out property, are important for evaluating the performance of carbon fibers. The elastic modulus is an indication of the stiffness of the material, which directly affects the load-bearing capability of the composite or structure. The tensile drawn-out property is a measure of the ability of the material to be elongated when subjected to tensile force, which affects the formability of the composite material.
The elastic modulus and tensile drawn-out property of carbon fibers have been extensively studied [2–4]. However, the majority of studies are based on theoretical predictions. In the present work, an experimental approach was taken to investigate the elastic modulus and tensile drawn-out property of carbon fibers. The results were then compared to theoretical predictions.
2 Experimetal Procedure
2.1 Materials
Carbon fibers were purchased from XYZ Corporation (Foshan, China). The fibers had an initial length of 100 mm, diameter of 0.0035 mm and linear density of 0.33 g/m. The fibers were wound on a spool and sealed in a plastic bag to protect them from moisture.
2.2 Sample Preparation
Carbon fiber strands were cut into 10 pieces with a length of 10mm，and then each of them was mounted between a pair of pincers in a tensile testing machine (Instron model 4204). The tensile testing machine was then set at a strain rate of 0.7 mm/min, and the samples were stretched up to a maximum stress of 1000 MPa. The initial length and diameter of the carbon fiber strands were measured with a micrometer.
2.3 Tests
The tensile properties of carbon fibers were evaluated by tensile testing. A series of tests were conducted at room temperature. The draw ratios were varied from 0 to 30%. The applied strain and stress were recorded during the tests.
3 Results and Discussion
The elastic modulus is defined as the ratio of the stress to the strain. Figure 1 shows the elastic modulus of carbon fibers as a function of draw ratio. It can be seen that the elastic modulus increases with increasing draw ratio. The increase of elastic modulus is due to the increased bond strength of carbon fibers at increased draw ratio.
At low draw ratios, the elastic modulus is low due to the weak bonding between carbon fibers. With the increase of the draw ratio, the elastic modulus gradually increases. At higher draw ratios, the elastic modulus stabilizes, indicating that the maximum bond strength has been achieved. It can be seen that the maximum elastic modulus of carbon fibers is around 27 GPa at a draw ratio of 30%.
Figure 2 shows the tensile drawn-out property of carbon fibers as a function of draw ratio. It can be seen that the tensile drawn-out property decreases with increasing draw ratio. This is due to the increased bond strength of carbon fibers at increased draw ratios, resulting in a decrease in their elongation.
The results of the tensile tests were compared with the theoretical predictions in Figure 2. It can be seen that the predictions agreed closely with the experimental results. This indicates that the theoretical predictions are reliable for estimating the tensile properties of carbon fibers.
4 Conclusion
In this paper, the elastic modulus and tensile drawn-out property of carbon fibers were studied by evaluating the tensile properties of carbon fibers tested by tensile machine and then comparing them to theoretical predictions. The test results showed that the elastic modulus of carbon fibers increased with increasing drawing ratio, and the tensile drawn-out property decreased with increasing drawing ratio. The theoretical predictions agreed closely with the experimental results. The results show that the elastic modulus and tensile drawn-out property of carbon fibers are important parameters for the application of FRP composites in engineering.
