Carbon-fiber Reinforced Concrete with Short Aramid-fiber Interfacial Toughening

Transcription

1 2016 International Conference on Electronic Information Technology and Intellectualization (ICEITI 2016) ISBN: Carbon-fiber Reinforced Concrete with Short Aramid-fiber Interfacial Toughening Shun Wang, Xiaofei Zhang* and Songyan Jiang ABSTRACT The interfacial fracture and delamination mechanism of a concrete beam reinforced by carbon-fiber reinforced plastic was investigated in this study. Short aramid fiber mats were applied between the carbon-fiber cloth and concrete to improve the interfacial toughness. Four-point bending tests (FPB) were carried out to determine measure the critical strain energy release rate. By testing specimen with different amount of carbon-fiber cloth and aramid-fiber mat, the thickness influence was also investigated. SEM image of the splitting fibers explains the enhancement of the critical energy release rate the enhancement of the critical energy release rate was studied by EM image of the splitting fibers. The critical energy release rate of the interfacial delamination was also evaluated through the Finite element analysis (FEA) simulation and was used to verify the experimental result. INTRODUCTION Carbon fiber reinforced plastic/polymer (CFRP) has been routinely used as structural material due to its high specific stiffness and strength in axial direction, low density and easy fabrication [1-3]. Exist studies confirmed that, the long term structural performance of structures reinforced by the carbon-fiber plastic is influenced by potential interfacial fatigue and delamination. Recently, a new method to improve the interfacial toughness and strength of sandwich structures was proposed by applying short aramid-fiber mat between aluminum foam and carbon-fiber cloth[4, 5]. Improvement in both Mode-I and II interfacial toughness and strength under quasi-static and impacting load were observed [6-9] due to the bridging effects Shun Wang, Xiaofei Zhang*, School of Architecture and Engineering, Shenyang University, No. 21 Wanghuanan St., Shenyang Liaoning , P.R. China Songyan Jiang, Liaoning Building Science Research Institute, Shenyang Liaoning , P.R. China 546

2 of those short aramid fibers. The experimental findings were further confirmed through analytical modelling of the short aramid fiber inter-laminar toughening [6, 7, 10]. In this study, the short aramid-fiber mat will be used to improve the concrete reinforced by the carbon-fiber polymer/plastic. The four-point bending test (4 PB) will be used to determine the interfacial toughness and the interfacial fracture pattern will be examined using the Scanning Electric Microscopy (SEM). Specimens with different amount of carbon-fiber cloth will also be examined so that the thickness influence is also investigated. Commercial Finite Element Analysis (FEA) simulation software (ABAQUS v ) will be used to numerically verify the experimental result. By using the xfea function, which allows pre-defined fracture propagates according to the selected criterion, the critical energy release rate can be determined. Specimen Design, Material Selection and Experiment. Figure 1. Scheme of a standard 4 PB test concrete specimen reinforced by carbon-fiber cloth. The short aramid-fiber mat is applied on the interface. Testing specimen are prepared according to the ASTM standard [11]. As shown in Fig. 1, for the concrete beam reinforced by the carbon-fiber fabric, the aramid-fiber mat is applied on the interface. When more carbon-fiber layer/cloths are used, the short aramid-fiber mats will be applied between the carbon-fiber layer/cloths. Instead of using the commercial carbon-fiber prepregs, the carbon-fiber fabric is used and will be cured together with the short aramid fiber interleave. Epoxy resin is mixed with slow hardener using the recommended ratio of 2:3. Thermal treatment will be given for the epoxy curing and the specimen will be cooled down to the room temperature for 24 hours to release the pre-stress in the carbon-fiber/epoxy matrix. Twill weave (3K, 200g/m2) carbon-fiber cloth was used as the face sheet material. Thickness of single layer of carbon-fiber cloth is about 12 μm. The length of the aramid fiber is 6 mm ± 0.5 mm and its density is controlled as 12 g/m2. 547

3 Important mechanical properties of the carbon-fiber/epoxy and aramid fiber mat are summarized in Table 1. TABLE 1. MATERIAL PROPERTIES INVOLVE IN THE EXPERIMENT. Properties (units) carbon fiber/epoxy aramid fiber Density (g/m 2 ) Young s modulus (GPa) Tensile strength (MPa) Poisson s ratio (υ/υ 12) Pre-crack on the interface is made by inserting 2 tinfoil layers at the interface. For each testing conditions, 9 tests are repeated and the experimental result is shown in Fig. 1 comparing with experimental result of the specimens without using short aramid-fiber mat. Figure 2. Critical energy release rate G (N/m) of the concrete specimens reinforced by carbon-fiber cloth and short aramid-fiber mats (1 to 3 layers) comparing with the control group. The average energy release rate and standard deviations of GC of carbon-fiber concrete sandwich samples. As shown in Fig. 2, it is obviously that, when the short aramid-fiber mats is applied, the energy release rate increases nearly 50%. It has to note that, for all specimen, the critical energy release rate is consistent regardless the number of carbon-fiber cloth and short aramid-fiber mats. This founding implies the interfacial delamination mechanism is that the interfacial delamination only occurs at the interface between the carbon-fiber cloth and the concrete. 548

4 Figure 3. Resin-rich section on the carbon-fiber face-sheet of the carbon-fiber concrete with aramid fibers. To fully understand the interfacial delamination and the fracture of the aramid fiber, a detailed Scanning Electron Microscope (SEM) analysis of the fracture surface is given. Fig. 3 shows good interface bonding between the aramid fibers and epoxy matrix, and extensive splitting at the aramid fiber ends. These are the typical features of fiber-bridging and subsequent tensile failure during crack extension, which contribute to the energy absorption and enhancement in the critical energy release rate. Finite Element Analysis (FEA) Simulation of the Four-point Bending (FPB) Test The interfacial delamination and fracture are also investigated through the FEA simulation. In the 2-D (cross-sectional) elastic-plastic model, the pre-crack at the interface is assumed and is expected to propagate by using the extended Finite Element Analysis (xfea) function. The meshing grid is refined until the simulation converges independent to the meshing method. The simulation result of the critical energy release rate is plotted in Fig. 4 comparing with the experimental result. The difference between the experimental and numerical results are all less than 5% which could be attributed to the elastic assumption so that the experimental result is numerically validated. CONCLUSION A new interfacial strengthen method using short aramid-fiber mats for the concrete reinforced with carbon-fiber epoxy/plastic composite has been investigated in this study. Four-point bending tests was were used carried out to measure the energy release rate of the specimens under loading. It was found that, for the specimen without using the short aramid-fiber mat, even using more carbon-fiber cloth, the energy release rate of the interfacial delamination has rarely change. The short aramid-fiber mat can improve the interfacial toughness, 50% at least for a single short aramid-fiber mat. The SEM image of the interface bonding between the aramid fibers and epoxy matrix shown the 549

5 mechanism of such the energy release rate enhancement. The SEM image also verified the bridging effect of short aramid fibers. By using the xfea function, the pre-crack was defined at the interface in the model and the energy release rate of the crack propagation was measured. As shown in Fig. 4, the simulation results well agreed with the experimental results. Figure 4. Simulation result of energy release rate comparing with the experimental result. ACKNOWLEDGEMENTS The authors are grateful to the financial supports of Shenyang Science and Technology Bureau (Grant No. F ) and Liaoning Building Science Research Institute for the technical support to the specimen fabrication. REFERENCES 1. Gueribiz, D., et al., Homogenization of moisture diffusing behavior of composite materials with impermeable or permeable fibers application to porous composite materials. Journal of Composite Materials, (12): p Sohn, M.-S. and X.-Z. Hu, Mode II delamination toughness of carbon-fibre/epoxy composites with chopped Kevlar fibre reinforcement. Composites Science and Technology, (3): p Sohn, M., et al., Impact damage characterisation of carbon fibre/epoxy composites with multi-layer reinforcement. Composites Part B: Engineering, (8): p Sun, Z., et al., Adhesive joints between carbon fiber and aluminum foam reinforced by surface treated aramid fibers. Polymer Composites, (1): p Sun, Z., et al., Short-aramid-fiber toughening of epoxy adhesive joint between carbon fiber composites and metal substrates with different surface morphology. Composites Part B: Engineering, : p Huang, B. and X. Hu, Modelling toughening of composites with interleaved chopped fibres. Plastics, Rubber and Composites, (4): p Huang, B.-Z., X.-Z. Hu, and J. Liu, Modelling of inter-laminar toughening from chopped Kevlar fibers. Composites Science and Technology, (13): p Kuwata, M. and P.J. Hogg, Interlaminar toughness of interleaved CFRP using non-woven veils: Part 1. Mode-I testing. Composites Part A: Applied Science and Manufacturing, (10): p

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