Laminate Design of Lightweight Glass Fiber ...

Available online at www.sciencedirect.com

ScienceDirect Procedia Chemistry 19 (2016) 871 – 878

5th International Conference on Recent Advances in Materials, Minerals and Environment (RAMM) & 2nd International Postgraduate Conference on Materials, Mineral and Polymer (MAMIP), 4-6 August 2015

Laminate Design of Lightweight Glass Fiber Reinforced Epoxy Composite for Electrical Transmission Structure Haslan Fadli Ahmad Marzukia and Mariatti Jaafarb, * a

AMREC, SIRIM Berhad. Lot 34 Jalan Hi-Tech 2/3, Kulim HiTech Park, 09000 Kulim, Kedah

b

School of Material Engineering and Mineral Resources, Universiti Sains Malaysia, Engineering Campus, 14300 Nibong Tebal, Pulau Pinang

Abstract Transmission structures such as transmission towers or transmission poles were designed to endure multiple combinations of acting force. However, these current structures that were made from concrete and metal are heavyweight materials that cause difficulties in handling during assembly, maintenance and reinstallation purposes. The other problem is vandalism issues on the metallic bracing of the transmission towers. Glass fiber reinforced polymer, (GFRP) is a type of fiber reinforced composites that combine the continuous high strength reinforcing fiber material and lightweight properties of polymeric matrix, thus offers an alternative solution for those problems. In this paper, a laminate design of GFRP samples were simulated using CompositeStar© software to determine the mechanical strength and its reserve factor. The composite panels were varied in term of fiber direction and it was designed to withstand a distributed load of 5kN service load in longitudinal (x-axis) and transverse (y-axis) direction on samples with thickness range between 4.00 to 4.20 mm. From the simulated results, it shows that the panels with fiber orientation in bi-direction and quasi-direction display a balance strength and acceptable reserve factor in both x-direction and ydirection. Therefore the properties and reserve factors of laminate design simulated from this software can be used as a benchmark in designing a laminated composite. © 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license © 2016 The Authors. Published by Elsevier B.V. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia. Peer-review under responsibility of School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia KEYwords: Fiber Reinforced Polymer Composite; Laminated Composite; Mechanical Properties

* Corresponding author. Tel.: +0-000-000-0000 ; fax: +0-000-000-0000 . E-mail address: [email protected]

1876-6196 © 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia doi:10.1016/j.proche.2016.03.128

872

Haslan Fadli Ahmad Marzuki and Mariatti Jaafar / Procedia Chemistry 19 (2016) 871 – 878

1. Introduction Transmission structures were used to transmit or distribute the large amount of electrical power either in alternating current (AC) or direct current (DC) systems using an overhead power line. Currently, most of these structures were made from concrete and metal such as transmission tower that consists of a metallic lattice structure and transmission pole, some were made from concrete and others from galvanized steel structure. In general, the entire transmission structures were designed to endure a combination of service loads which includes continuous cable loads, wind resistance and seismic loading, in range of 5kN to 7.5kN for pole structure and up to 10kN for the lattice tower structure. The development in rural areas faced some difficulties in supplying electrical power due to heavyweight structures such as concrete and steel poles. The transfer and delivery activities of these heavy structure cannot be expedited due to some forest and hilly conditions which is impossible to be accessed by normal transportation i.e. truck and lorry. Moreover, if this structure is chosen to be installed at the area, it is difficult for cranes to access those areas and also, manual installation via human strength are not possible due to the heavy structures. The other problem regarding metallic transmission structures especially related to the transmission towers is vandalism. Vandals keen to steal the metal braces below the anti-climbing stage. The loss of the structural bracing will destabilize the tower lattice structure and it will tend to buckle due to loss of stability, which will lead to tower structure failure and power outages1, 2. Much effort has been taken by the maintenance unit to comprehend the vandalism problem such as welding the braces and introduce the barbed-wire below the tower. However the struggles were not sufficient enough to avoid these problems from being resolved. Fiber reinforced polymer (FRP) composite offers an alternative solution for those problems. Glass fiber reinforced polymer (GFRP) is one type of FRP that provides lightweight structures with high-strength-to-weight ratio which is comparable to steel and concrete materials3. The continuous glass fiber provides strength and stiffness while the polymeric matrices provide the lightweight requirement for the composite which offers a weight reduction of up to 80% and 40% compared to concrete and steel, respectively. Moreover the uniqueness of GFRP laminates is that it can be designed to endure the combination loads on the transmission structures (towers and pole) such as cable, wind and seismic loading which is another advantages of using GFRP to replace conventional steel and concrete structures4. In addition, vandalism issue arise due to the reprocess-ability of metallic structures. By using GFRP, the problem will be solved Laminate design is a very important procedure in designing a composite structure to ensure its capability to endure loads during service conditions without compromising its performance. Composite laminate design is an early process to determine the laminate properties by defining parameters such as fiber orientation, ply thickness, stacking sequence and volume fractions in order to obtain the optimize properties. Some researchers have been conducted to determine the laminate properties by numerical method such as genetic algorithm5 and polar-genetic method6. However, for less experienced engineer or researcher, it is difficult to familiarize with the technology, and it is time consuming for experienced engineer to keep up-to-date with the latest developments. CompositeStar© is a user-friendly software that combines a comprehensive material database and latest calculation methods regarding laminated composite technology to provide an early prediction data for the designed laminated composites. CompositeStar© also includes the calculation using latest failure criterion concept since prediction of strength is the most important factor in designing a composite structure7. The objective of the this research is to design laminate constructions of GFRP for a transmission structure such as pole and bracing for lattice structure, that able to withstand a distributed loads of up to 5kN with 2.0 reserve factor using CompositeStar® Software and following the Tsai-Wu failure criterion model. CompositeStar© is a composite database and design software composite materials. This software will calculates properties of plies and laminates in accordance to micromechanics concept, classical laminate theory (CLT), laminate load response and failure with specified failure criterion failure models. This GFRP will consist of continuous E-glass reinforcing fiber and epoxy matrix. Moreover, the simulated GFRP will be fabricated to differentiate its properties and actual reserve factor between the simulated value and the fabricated samples.


Nomenclature FRP GFRP E EX EY RF RFX RFY WF VF

Fiber Reinforced Polymer Glass Fiber Reinforced Polymer Young’s Modulus Young’s Modulus in X-axis Young’s Modulus in Y-axis Reserve Factor Reserve Factor in X-axis Reserve Factor in Y-axis Fiber Weight Fraction Fiber Volume Fraction

2. Experimental Procedure Identification of service load in service condition is a crucial step in designing a composite structure. For the purpose of transmission structure, two types of loading has been identified. One is bending load which caused by wind such as stellar or storm and the other one is compression load, caused by the overhead power cables as illustrated in Fig. 1. Moreover, the compression load for the transmission tower are also comprises of load from the upper structure. In this work, bending load has been defined to be parallel with x-axis, while compression load is defined to be parallel with y-axis and it is considered that the minimum combined load for the structure is 5kN and is assigned as distributed load for the structure.

Fig. 1. Illustration of service load on a transmission structure a) Illustrated transmission pole b) Illustrated lattice transmission tower

Materials for both reinforcing fiber and thermosetting matrix as stated in Table 1 were considered to be inserted in the material database in order to simulate the data for the laminate. For optimization using micromechanics calculations, the following parameters have been specified; 1) laminate thickness of 4.00 mm ± 0.2 mm, 2) targeted fiber weight fraction is 70% and 3) total fiber per area weight is in range of 5000 gram to 6000 gram per meter per sample. Table 1. Identified materials to be used in this study. Material

Details

Reinforcing Fiber Polymer Matrix

Unidirectional E-glass stitched fabric, 955 g/m2; roving bandwidth approximately 5 mm Epoxy ; EPOLAM 2025 from Axson Chemicals

873

874


Based on the specified parameters, six laminate constructions have been structured to simulate its properties and performance as detailed in Table 2. The stacking sequence consist of four main fiber directions, i.e. θ = 0o, +45o, 45o and 90o, that has been implemented in most composite structures for high performance application8. Next, laminates result was calculated by the software which includes the Young’s Modulus, (E) value and Reserve Factor (RF) value, in accordance to Tsai-Wu Failure Criterion. Table 2. Laminate Construction, Sequence and Code of laminates in this study. Laminate Construction Construction 01 Construction 02 Construction 03 Construction 04 Construction 05 Construction 06 Notes: 1. 2.

Stacking Sequence (0/0/0/0/0/0) (+45/-45/+45/-45/+45/-45) (0/90/0/90/0/90) (0/+45/-45/90/90/-45/+45/0) (+45/-45/90/90/90/90/-45/45) (+45/-45/90/90/-45/+45)

Laminate Code [0o]6 [45o]6 [0/90]3 [0/±45/90]S [±45/(90)2]S [(±45)2/90]S

Subscription No.: number of repeated layers (i.e. 6 for 6 repeated layers, 3 for 3 repeated layers) Subscription Alphabet: S for symmetrical, A for Antisymmetrical

In order to clarify the simulated data and the reliability of CompositeStar©, a set of composite laminate based on both materials and laminate construction in Table 1 and Table 2 were fabricated using wet-laminating technique, followed by vacuum bagging procedure and post cured up to 120oC according to Epolam2025 technical datasheet. Then, those samples were tested to determine the experimental density, fiber weight fraction (WF), Young’s Modulus (E) and the Reserve Factor (RF) of the laminate samples. The densities of fabricated samples were determined using Densimeter Model EW-300SG. The fiber weight fractions were determined in accordance to ASTM D3171 testing procedure. Value E and RF were determined in accordance to ASTM D3039 and ASTM D695 testing procedure. 3. Result and Discussion 3.1 Analysis on the Simulated Result. Table 3 shows the simulated data that consist of density, E and RF in both x-axis and y-axis loading direction. The densities of all laminate constructions are the same since the same fiber type, fiber textile weave/style and fiber weight fractions are applied in all constructions. The value of E and RF for both x-axis and y-axis directions show a different value for each fiber construction. Table 3. Simulated Modulus Young, and Reserve Factor of Laminated GFRP via CompositeStar©. Laminate Construction [Laminate Code] Construction 01 [0o]6 Construction 02 [45o]6 Construction 03 [0/90]3 Construction 04 [0/±45/90]S Construction 05 [±45/(90)2]S Construction 06 [(±45)2/90]S

Density, ρ (g/cm3)

E in-plane [GPa]

Average Reserve Factor On X-Axis Loading

Average Reserve Factor On Y-Axis Loading

10.467

7.701

0.250

13.306

12.306

0.500

0.500

1.886

24.085

24.085

1.881

1.881

1.886

21.821

21.821

1.381

1.383

1.886

12.101

31.002

0.345

3.739

1.886

13.133

22.215

0.417

1.324

(X-axis)

(Y-axis)

1.886

38.724

1.886

875


Young's modulus or modulus of elasticity indicates the stiffness of a material. In the perspective of FRP composite, it is an anisotropic material that displays different properties in different directions. Therefore Young’s Modulus of FRP depends on the direction of the reinforcing fibers. CompositeStar software focus the analysis of the designed FRP as orthotropic material, which considering three main axes that is x, y and z. In this work, based on the illustration in Fig. 1., there are two main loads that are in x-directions and y-directions, while the load acting on the direction of z-direction is equal to the load acting in x-direction. Based on the simulated data, Construction 01 shows the highest EX followed by Construction 03, 04, 02, 06 and 05 and this occurs based on the direction of the reinforcing fiber in the laminates. In Construction 01 laminate design, all fibers direction are stacked in 0O direction, that is longitudinal direction and parallel to the applied service loading in X-direction. This will allow the reinforcing fiber to endure most of the applied load during services and corresponding to the iso-strain conditions. However, in transverse direction (or Y-direction) that is perpendicular the fiber direction, this construction displays a lower E which occurs due to lack of reinforcing fiber. Decreasing the number of plies in the X-direction leads to the decreasing of EX value as simulated in Table 3. Opposite in Y direction, laminate Construction 05 displays the highest EY, followed with Construction 03, 06, 04, 02 and 01. This once again can be explained by the amount of fiber that stacked in 90o direction, that is in transverse direction and parallel to the applied service load in Ydirection. We can also observed that the laminates in bi-directional and quasi-directional with balance fiber direction and symmetrical loading show almost the same E value in both x-direction and y-direction, as simulated for construction 02, 03 and 04. For this condition, Construction 03 shows highest EX and EY value, followed by 04 and 02. Although Construction 04 has plies in ±45o direction, the laminate shows a higher EX and EY value as compared to Construction 03 which has plies in only 0o and 90o direction. According to Mathews and Al Farsakh9, 10 existence of plies in ±45o direction will create a shear mechanism effect between the reinforcement and the matrix, in which will create a resistance towards the fiber debonding failure during the loading either in 0o or 90o direction. If a laminate only compromise plies that is only perpendicular to the loading direction or iso-stress condition, the resistance towards fiber debonding failure is at the minimum level. Therefore, to strengthen a composite laminates, existence of plies that are not parallel with the loading direction is important. Moreover, since FRP is anisotropic material, it will help strengthening the laminate structure upon unexpected loads coming from various directions. Reserve Factor, RF or also known as Safety factor, SF in some countries, is the value of structural capacity of a system compared to design loads of a structure, as given in equation 1 below. Reserve Factor, RF = (Maximum Strength, TS) / (Designed Strength)

..(1)

RF is an important criteria to determine the structures’ ability to endure service load. RF is often calculated using detailed analysis because comprehensive testing is impractical and costly for large structures. Most of structural systems are constructed much stronger than the design or the working loads to avoid accidents due to unexpected loads, or overlook conditions such as degradation. However, the value of RF must be determined at a reasonable accuracy to avoid an over-engineering design which can result in excessive weight and high cost. Simulated RF value in Table 3 was calculated using the Tsai-Wu failure criterion. Tsai-Wu failure criterion is a practically simple failure criterion which takes interaction of stress in different direction of stress into account11. Therefore, since transmission structures endure multiple loads from different directions, Tsai-Wu failure criterion is suitable to be applied in order to determine the RF of the designed laminate. From the simulated data in Table 3, the RF values and trends are comparable to the EX and EY values and trends as well. Constructions with most plies stacked parallel to the loading direction shows higher RF values. As illustrated in Fig. 1., it displays that the major servicing loads are on the y-direction which caused by the permanent overhead cables, compared to service loads in x-direction that occurs occasionally due to the wind. In this conditions, it is important to emphasize major loads sustain by a structure in designing a composite laminate structure to avoid structural failure during service. For this study, in order to produce a composite transmission structure, an acceptable RFY (RF ı 2.0) must be considered first, followed by RFX. Then the designed laminate must show a balance EX and EY values. Based on this

876


requirement, simulated data from laminate design for construction 03, 04 and 05 shows an optimum value and are acceptable for this purposes. 3.2 Analysis on the Experimental Result. Based on the experimental result in Table 4, there are differences between simulated data and tested data from fabricated samples. For density and WF value, the fabricated samples displayed a lower value, which is 5% to 15% for density and 8% to 12% for WF. The difference occurs due to types of material used and various parameters involved during fabrication process. In this work, stitched unidirectional fiber fabric of 955 g/m2 with roving bandwidth of 5 mm was used. This wide bandwidth of fiber that is stitched together to form a unidirectional fiber has reduced the ability of epoxy resin to flow and impregnate between the fiber filament and piles. Resins tend to deposit at the outer-part of the fabricated sample surface due to lack of flow-ability and results in resin rich laminates. Therefore, the fiber weight fraction is lower than the simulated data from the software. Since lack of flow-ability occurs during the process, it also reduces wettability of epoxy resin towards the fibers and plies. Lack of wettability between the fibers and plies results in less efficiency of load transfer mechanism from the matrix to the fiber during loading. This is shown from the experimental data whereas the EX and EY values are too small compared to calculated value from the software, which is 80% lower from the calculated value as shown in Table 4. Table 4: Comparison between Simulated Data from CompositeStar© and Experimental Data from fabricated samples Simulated from CompositeStar© Laminate Construction [Laminate Code]

Construction 01 [0o]5 Construction 02 [45o]6 Construction 03 [0/90]3 Construction 04 [0/±45/90]S Construction 05 [±45/(90)2]S Construction 06 [(±45)2/90]S

Density

Fiber Weight Fraction, Wf (%)

Fabricated Samples

E in-plane [GPa] Density (X-axis)

(Y-axis)

Fiber Weight Fraction, Wf (%)

E in-plane [GPa] (X-axis)

(Y-axis)

1.886

70.0

38.724

10.467

1.767

59.197

5.63

1.37

1.886

70.0

13.306

12.306

1.751

60.143

1.93

1.89

1.886

70.0

24.085

24.085

1.620

58.045

3.99

3.81

1.886

70.0

21.821

21.821

1.754

60.496

3.49

3.67

1.886

70.0

12.101

31.002

1.781

62.608

1.63

5.36

1.886

70.0

13.133

22.215

1.755

60.973

1.88

3.66

The other parameter that caused huge different between the calculated and experimental value for EX and EY is lower fiber weight fraction displayed in the experimental data as compared to simulated data. Based on the Rules of Mixture, composite Young’s Modulus is inversely proportional to either fiber volume fraction, V F or fiber weight fractions, WF. Therefore the decreasing value of WF also contributes to the huge different between the simulated data and experimental data for E value. Void content is also a parameter that corresponds with lack of flow-ability and wettability. During the sample fabrication process, fabricated samples were not properly consolidated during vacuum bagging process and void between fibers and plies cannot be vented away from the laminated samples. Thus, insufficient resin flow between the fibers and plies reduce the degree of wettability which also contributed to the existence of void content. This subsequently influenced the modulus of the samples. In addition, E value for composite can also be affected by the presence of nano-filler (such as carbon nanotubes)12, 13, and types of reinforcing fiber such as glass, carbon or natural fibers14, 15. In contrast to the experimental E value, the experimental RF value resulted in more reassuring data. Overall, experimental RF for laminate construction resulted in a positive difference which is between 2 to 3 times higher than calculated value by the software, as shown in Fig. 2. Hence, laminate that have more fiber parallel to load direction

877


will display higher RF, both in x-direction and y-direction. Fig. 2. shows that Construction 05 has the highest RF in y-direction followed by 04, 03, 06, 02 and 01. Based on discussion in section 3.1, RFY must be considered first since the main service load is from Y-axis direction, followed by RFX. However, since the structure endure multiple load, a balance RFY and RFX must also be taken into account. It is observed that laminate design for Construction 03, 04 and 05 meet the requirement of RF ≥ 2.0 and the crucial consideration regarding service load on y-direction. These three laminate constructions consists of bi-directional and quasi-directional fiber orientation. Construction 04 with quasi-directional fiber orientation provides the optimize RFY and RFX followed by construction 03 and 05.

12.00

10.00

Reserve Factor, RF

8.00

6.00

4.00

2.00

0.00

Construction 01 7.701






RFX-Experiment

9.794

2.079

6.338

4.586

2.224

1.858

RFY-Simulated

0.250

0.500

1.881

1.383

3.739

1.324

RFY-Experiment

1.236

1.443

5.818

6.188

9.591

5.351

RFX-Simulated

Fig. 2: Simulated Reserve Factor vs. experimental Reserve Factor for X and Y Direction.

4. Conclusion From the simulated results, it shows that panels with fiber orientation in bi-direction and quasi-direction display a balance strength and acceptable reserve factor in both x-direction and y-direction. Therefore, the properties of laminate design simulated from this software can be used as a benchmark in designing a laminated composite. Service load direction must be properly define to ensure the fiber orientation can be appropriately determined to avoid failure during service. A large difference of E value between the simulation and the experimental data are due to parameters that need to be considered or regulated during the fabrication of sample or product. CompositeStar© simulates a laminate properties based on classical laminate theory and with assumption that an effective fabrication technique is applied during the process. Material parameters such as textile style and fiber weight per area must be properly chosen in order to allow good flow-ability and wettability during the process in order to produce an almost void free samples. Although the fabricated samples result in low modulus value as compared to simulated value due to some deficiencies, RF value simulated from the software are reliable since it shows the same trend as compared to the experimental result. Therefore, CompositeStar© is a reliable software that helps less experienced engineer or

878


researcher to familiarize with the composite technology and to gain early prediction regarding laminated composite properties and failure concepts. Acknowledgements This research was supported by School of Material and Mineral Resources Engineering, USM, Advanced Material Research Centre (AMREC) SIRIM Berhad and Tenaga Nasional Berhad.

References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.

M. Selvaraj, S.M. Kulkarni, R.R. Babu. Behavioural Analysis of Built Up Transmission Line Tower. International Journal of Emerging Technology and Advanced Engineering, Volume 2, Issue 9, 2012. Pg. 39-47. L. Di Sarno, A.S. Elnashai. Bracing Systems for Seismic Retrofitting Of Steel Frames. Journal of Constructional Steel Research, Volume 65, 2009. Pg. 452-465. B. Saboori, S.M.R. Khalili. Static Analysis of Tapered FRP Transmission Poles Using Finite Element Method. Journal of Finite Element in Analysis and Design, Volume 47, 2011. Pg. 247-255. A.C. Galeb, A.M. Khayoon. Optimum Design Of Transmission Towers Subjected To Wind And Earthquake Loading. Jordan Journal of Civil Engineering, Volume 7, No. 1, 2013. Pg. 70-92. G. Soremekun, Z. Gurdal, R.T. Haftka, L.T. Watson. Composite Laminate Design Optimization by Genetic Algorithm with Generalized Elitist Selection. Journal of Composite and Structures, 79, 2001. Pg. 131-143 M. Reza Ahmadian, Angela Vincenti, Paolo Vannucci. A General Strategy for the Optimal Design of Composite Laminates by the Polar-Genetic Method. Journal of Material and Design, 32, 2011. Pg. 2317-2327 Christian Laval. Composite Design in the real World. Reinforced Plastic, September 2003. Pg. 50-55 Thomas Jin-Chee Liu, Huang-Chieh Wub. Fiber Direction And Stacking Sequence Design For Bicycle Frame Made Of Carbon/Epoxy Composite Laminate. Journal of Material and Design, 31, 2010. Pg. 1971-1980 Mary Jacobs Mathews. Study of Delamination of Fiber Reinforced Composite Laminates. Department Of Mechanical Engineering, University of Utah 2007. Ghazi Abu-Farsak. Effect of Shear Stresses on Failure of Fibrous Composite Materials Accounting for Nonlinear Material Behavior. Jordan Journal of Civil Engineering, Volume 7, No. 4, 2013. Pg. 419-439 Pedro Ponces Camanho. Failure Criteria for Fiber-reinforced Polymer Composites. Faculty of Engineering, University of Porto 2002. Pg. 1-22 Damien M. Marquis, Éric Guillaume and Carine Chivas-Joly. Properties of Nanofillers in Polymer, In Nanocomposites and Polymers with Analytical Methods, John Cuppoletti (Editor) In Tech Publisher 2011. 261-284 L.N. Saw, M. Mariatti, A.R. Azura, A. Azizan, J.K. Kim. Transparent, Electrically Conductive, and Flexible Films Made From Multiwalled Carbon Nanotube/Epoxy Composites, Composites Part B: Engineering, Volume 43, Issue 8, 2012. Pages 2973-2979 M. R. Hossain, M. A. Islam, A. V. Vuurea, and I. Verpoest. Effect of Fiber Orientation on the Tensile Properties of Jute Epoxy Laminated Composite, Journal of Scientific Research, 2013. Pg. 43-54 Ozgur Erdal, Fazil O. Sonmez. Optimum design of composite laminates for maximum buckling load capacity using simulated annealing. Composite Structures 71, 2005. Pg. 45–52