Comparing Rigidising Methods Using Re Enforced Material - Coursework Example

Comparing rigidising methods using re enforced material Comparing rigidising methods using re enforced material Introduction A fiber-reinforced polymer (FPR) is a material containing high-strength fibers made of either glass or carbon implanted in a polymer matrix. FPRs are of great benefit in repair and construction works because of their enhanced strength, resistance to corrosion and ability to use with ease as opposed to steel materials. Carbon fibers are the best to use in the reinforcement because they induce higher stiffness, general strength and effective fatigue and durability properties [8]. Glass fibers are more effective in achieving shear strengthening. Various methods can be used in the reinforcement of polymers using carbon or glass fibers. Some of the methods include curing pressure increase and filler incorporation and vacuum infusion. This paper outlines a comparison among the various rigidising methods using reinforced material to increase the general strength of the materials. The electrical conductivity of the materials has also been analyzed [8]. Curing pressure increase and filler incorporation This ridigising method enhances the through-thickness thermal conductivity of carbon fiber polymer-matrix. This method is used to increase heat dissipation by enhancing the low through-thickness thermal conductivity of carbon fiber polymers. The conductivity is normally raised by 60 percent by enhancing the curing pressure from 0.1 to 2.0 MPa and almost by 35 percent by incorporation of a filler. This was reported in an experiment conducted at Composite Materials Research Laboratory in the University of Buffalo [4]. The experiments were conducted to determine the effect of curing pressure and filler incorporation on the mechanical and conductivity properties on a material. The mechanical test was conducted on a 15-lamina crossply composite plate under flexure using a hydraulic mechanical testing procedure. The thermal resistivity (m2 K/W) and the thermal resistant (K/W) were used to report the increase in thermal conductivity of the resultant material after this treatment. The thermal resistivity increased after a raise of the curing pressure from 0.1 to 2 MPa. This resistivity further increased after the filler incorporation [4]. This implies that the thermal conductivity of the material increased after subjecting the material to the two treatments. It was also noted that increasing curing pressure increases the through-thickness thermal conductivity more that the filler incorporation. The experiment revealed that the optimum through-thickness thermal conductivity achieved through the process was 1.5 W/m K. The highest ever recorded value for this form of rigidness enhancement technique is 3.3 W/m K. this does not imply that the process is ineffective or inconsistent. The difference could have aroused due to the process prepreg. The material resistivity and intralaminar fiber-fiber interfacial resistivity are lowered by close to 56 Percent by enhancing the curing pressure and by around 36 percent though the filler incorporation [4]. This further proves that curing pressure increase is more useful in increasing thermal conductivity compared to filler incorporation. Vacuum infusion Vacuum infusion of vinyl ester resin into biaxial knitted glass and carbon fiber complexes enhances the strengths of the materials under tensile and indentation forces. The carbon fiber complexes after this vacuum infusion are mechanically stronger when subjected to loading pressures [7]. The strengths of the carbon fiber material can be proved by carrying out various tests including tensile strength test, compression strength test, open hole tensile (OHT) strength test and Open hole compression (OHC) strength test. An experiment conducted at the department of mechanical engineering in Lehigh University proved that in deed the mechanical properties of carbon fiber complexes is enhanced through vacuum infusion using vinyl ester resins. In the experiment, the tensile strength test was conducted using ASTM standard D3039. The tests were conducted on a Baldwin 270 kN hydraulic technique [9]. The compression strength test was carried out using the Wyoming Test Fixtures WTF-EL-29 technique on a 44 kN screw driven scale. The open hole tensile strength test was conducted using a 270 kN Baldwin machine while the OHC strength test was conducted via the Northrop Grumman standard scale. The results of the experiment indicate that vacuum infusion enhances the strength of both glass and carbon fiber materials. The tensile strength of the carbon fibers increases by twice compared to that of the glass material. This rigidising technique is thus effective in enhancing the mechanical properties of the carbon and glass material. This implies that the material is more resistant to indentation, bending, and compression forces after this treatment. The glass and carbon reinforced material has been found useful in construction of Naval vessels due to its enhanced strength [9]. The increases in strength after this treatment are represented by the graph below. In another experiment conducted at the University of Limerick’s department of Mechanical and Aeronautical engineering to investigate the open hole tension properties between high strength glass and CFRP, the S2-glass FRP showed lower OHT strengths compared to CFRP. The experiment revealed that CFRP OHT materials had a powerful stiffness and strength while the GFRP OHT materials showed higher strain to failure and a noteworthy greater toughness. The two materials had a similar trend concerning damage and failure progression [9]. Thermal activation and impacts of moisture These processes reduce the structural and tensile properties of carbon fiber materials. Thermal activation is not an effective method in enhancing the mechanical strength of carbon fiber-polymer composite materials because it reduces the tensile strength of such materials. Thermal activation weakens the carbon fibers and affects the tensile properties of the material [6]. An experiment at the Royal Melbourne Institute of Technology revealed that the rate of tensile strength decrease is directly proportional to the increase in temperature. The softening of the material results from surface composition induced by high temperatures. The fiber strength of such material also lowers because of the thermally activated damage [2]. The mechanical properties of CFRP also reduce when the material is subject to water. This was revealed by an experiment conducted at the Institute of Composite Materials in University of Kaiserslautern. The effect of moisture on the material was investigated by subjecting the material to distilled water. The experiment revealed that moisture has a negative effect on the epoxy-based composites. This is due to a raise in interface failure on the material resulting from the moisture [2]. Retrofitting Retrofitting is another technique used in the strengthening of glass fiber reinforced polymers. Retrofitting enhances the structural properties of such material to prevent collapsing of walls constructed using the materials when subjected to seismic pressure. Retrofitting prevents either the in-plane and out-of-plane failure mechanisms of such constructions. An experiment conducted to investigate the cyclic trends of perforated masonry walls enhanced with glass fiber conducted at the department of civil engineering in the Amirkabir University of technology reveled that retrofitting enhances the strength of such material [5]. The experiment was conducted to investigate the in-plane performance of unreinforced brick walls after retrofitting by applying the Glass Fiber Reinforced Polymers (GFRPs). The various techniques that can be used in the retrofitting process include ferrocement, grout injection, external reinforcement and post tensioning procedures. The experiment revealed the cyclic shear-compression of such walls is increased by 1.68 times through retrofitting. The walls resistance to deformation was also increased by a similar margin. GFRP is thus an effective technique in enhancing the seismic resistance of unreinforced brick walls [5]. The S2 glass woven roving technique and the 5-harness satin weave technique These techniques represent GRP architectures used to enhance the mechanical properties of rigidised glass fiber polymer complexes. A report of an experiment conducted at the Western Reserve University in Cleveland revealed that the two techniques are effective in increasing the spall strength of such polymer composites. The two experiment to determine the spall strength were conducted separately in which the S2 glass woven roving technique was applied in the first experiment while the 5-harness satin weave technique was used in the second experiment. The first experiment was conducted at impact stress ranging between 0 and 175 MPa while the second impact sress ranged between 175 and 600 MPa [10]. It was revealed that the range of the impact stress in the first experiment was too low to cause any spallation. High levels of impact stress were not effective in measuring spall resistance because the magnitude of the deformation caused too much damage on the material to record any spall resistance. Under a combination of compression and shear loading, the measure of the spall strength in the two experiments was found to lower with rising levels of subjected normal and shear-stress. At a normal stress of 975 MPa and a shear-strain of 1.056 percent, the E-glass GRP recorded zero spall strength while the S2 glass GRP had a higher spall strength. The recorded spall strengths are however higher for the two materials than those observed in other materials such as monolithic metals, ceramics and polymers [10]. Electrical properties of the polymers It is significant to note that most of the composites are non-conductors of electricity. It is however possible to get some levels of electrical conductivity by inclusion of a conductor such as a metal and carbon particles. The composites containing the carbon fibers will thus have a small percentage as opposed to the glass fiber reinforced ones. Electromagnetic interference shielding in the polymers can also be induces by incorporating conductive materials [1]. Summary and comparison of the methods Among the various methods discussed, Curing pressure increase and filler incorporation, vacuum infusion and retrofitting are the most effective in enhancing the structural properties of composite materials. Vacuum infusion is the best method among those discussed in the paper because it enhances virtually all the significant properties of the composites. Vacuum infusion of vinyl ester resin into biaxial knitted glass and carbon fiber complexes increases the strengths of the composites especially when tested against tensile and indentation forces [3]. The materials after vacuum infusion treatment are mechanically stronger as evidenced by subjecting it to loading pressures. Various tests including tensile strength test, OHT and OHC tests indicate a positive increment after vacuum infusion of the material. The tensile strength of the carbon fibers increases by twice compared to that of the glass material. This shows that this method is more effective with the carbon fibers. Retrofitting comes second among these methods because it can only be used with the glass fiber reinforcements. This method is owever superior to the other in that several techniques are available for the application of the method. Some of these methods include ferrocement, grout injection, external reinforcement and post tensioning procedures. Retrofitting strengthens composite materials to be able to absorb in-plane and out-of-plane pressures resulting from seismic forces [1]. The cyclic shear-compression of unreinforced walls is increased by 1.68 times through retrofitting [5]. The walls resistance to deformation was also increased by a similar margin. The S2 glass woven roving technique and the 5-harness satin weave technique are not very effective because they can only be used with the glass fiber polymer complexes. Thus the rigidising methods discussed are effective in the following order: Curing pressure increase and filler incorporation vacuum infusion and retrofitting S2 glass woven roving technique and the 5-harness satin weave technique Conclusion This paper has provided a comparison among the various rigidised materials using reinforced materials. Some of the methods that have been discussed include Curing pressure increase and filler incorporation, vacuum, infusion and retrofitting and S2 glass woven roving technique and the 5-harness satin weave techniques [4]. Other methods such as thermal-activation of the material and subjecting the material to moisture have also been discussed although they do not increase the strength properties of composite material. These have been discussed because they are very critical in determining the effectiveness of application of reinforced composite material. The mechanical properties of such material are negatively affected by the exposure to extreme temperatures and/or moisture. Another issue discussed in the paper is the electrical conductivity of reinforced material. Composites are generally non-conductors of electricity. They however conduct electricity with the addition of a conducting material such as a metal or a carbon element. Some of the composites containing the carbon fiber will thus conduct electricity while those having pure glass material will not conduct electricity. References [1] ACI 440.2R-08, Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures, American Concrete Institute, Farmington Hills, MI, USA, 2008. [2] Bisby, L.A., Green, M.F., and Kodur, V.K.R., Response to fire of concrete structures that incorporate FRP, Progress in Structural Engineering and Materials, 7, 3, 2005, pp. 136-149 [3] Feih, S. and Mouritz, A. P. Tensile properties of carbon fibers and carbon fibre-polymer composites in fire, Composites: Part A 43, 765-772, (2012). [4] Han, S. and Chung, D.D. Increasing the through-thickness thermal conductivity of carbon fiber polymer-matrix composite by curing pressure increase and filler incorporation, Composites Science and Technology 71, 1944-1952, (2011) [5] Kalali, A. and Kabir, M. Z. Cyclic behavior of perforated masonry walls Strengthened with glass fiber reinforced polymers, Scientia Iranica A 19(2), 151-165, (2012). [6] Katz, A., Berman, N., and Bank, L.C., Effect of high temperature on the bond strength of FRP rebars, Journal of Composites for Construction, 3, 2, 1999, pp. 73-81 [7] Kaw, Autar K., 1997, Mechanics of Composites Materials, CRC Press, New York, NY. Miller, Tara, 1998, Introduction to Composites, 4th Edition, Composites Institute, Society of the Plastics Industry, New York, NY. [8] Saadatmanesh, H., and Ehsani, M. R., RC Beams Strengthened with GFRP Plates, Experimental Study, Journal of Structural Engineering, ASCE, Vol. 117, No. 11, pp. 3417-3433, (2001) [9] Wonderly, C. et al. Comparison of mechanical properties of glass fiber/vinyl ester and carbon fiber/vinyl ester composites, Composites: Part B 36, 417-426, (2005). [10] Yuan, F. et al. Spall strength of glass fiber reinforced polymer composites. International Journal of Solids and Structures 44, 7731-7747, (2007). Read More