Proceedings of International Conference on Mechanical Engineering and Industrial Automation Held on 21-22, Nov, 2015, in Dubai, ISBN:9788193137321

EFFECTS OF CURING PRESSURE ON TENSILE AND FATIGUE STRENGTH OF GLASS FIBER REINFORCED EPOXY COMPOSITES EMPLOYED Fırat Durmus

Mursel Ekrem

Omer SOYKASAP

Department of Engineering, Selçuk

Department of Engineering,

Materials Science and Engineering

University, Alaaddin Keykubat

Necmettin Erbakan University,

Department, Afyon Kocatepe

Campus 42100 Selçuklu, Konya,

Köyceğiz Campus 42090 Meram,

University, Afyon/Türkiye

TURKEY

Konya, TURKEY

Abstract— In this study, effects of the tensile and fatigue

the developments of the science. Hence the studies to manufacture both durable and economic and very light material are already concentrated. And so, composite materials obtained through the physical merging of several materials with different properties by specific methods are employed in place of many materials due to physical, mechanical and chemical features [1]. The fatigue of the machinery parts, which are under dynamic tension, generally results in cracks and damages over the materials. The continuous progress of such cracks eventually ends up with severe damages over the machine parts. Thus, the crack and damage behaviors of composite materials is an essential topic since it helps machinery designers to reduce the negative effects of the fractures, which occur as a consequence of fatigue of the materials, at the design time of the machinery parts [2]. Hence, there are several studies in the literature that aim to examine the effects of the tensile and fatigue behaviors of composite materials [3, 4]. Composites are the materials, adaptable to engineering and improvable. Durability of composite materials relies on volume/weight ratio of reinforcement material, angle of oriententation and the other factors [5]. Singh et al. have focused on defining mechanical properties of pristine epoxy and glass fibers in the weight of 10 % and 20 % and composite materials reinforced with randomly [6] managed glass fiber. Experimental results have revealed the durability of tensile increases as the weight at reinforced ratio increases. Compared to the pristine epoxy, the tensile and bending durabilities of 20 % glass fiberreinforced composites have exhibited 45.5 %and 123.5 % increase.

characteristics on glass fiber composites produced under various pressures have been investigated. For this intention, 8 laminate glass fiber composite plates are manufactured under 3 different curing pressures (15 inhg, 20 inhg , 25 inhg ) by manual (layup) spreading method. Tensile properties of laminated composites have been detected at 2mm / min jaw speed according to the ASTMD 3039-08 and fatigue experiments have been realized by the load control at f = 5 Hz in the frequency of sinusoidal and the tensile fatigue is determined with 8801 Universal Tensile Utensil, the capacity of 50 kN Maximum tensile resistance at 325 Pa under 20 inhg curing pressure and fatigue behavior under 20 inhg have been obtained better from the manufactured sample.

Keywords— Polymer matrix composites, fatigue, glass fiber, effect of curing pressure. I.

INTRODUCTION

In our century where productions of the spacecraft have been launched, it has been preferred to produce both technically and economically convenient materials depending on the available materials to meet the need of the current state in parallel with innovations of the age and 72

Proceedings of International Conference on Mechanical Engineering and Industrial Automation Held on 21-22, Nov, 2015, in Dubai, ISBN:9788193137321 absorbed, already manages to cure itself at the room

Vacuum assisted resin transfer molding (VARTM) is a composite manufacturing process [7-9] that involves the lay-up of dry reinforcing fibers in fabric form as a preform in a mold and impregnation of the preform with liquid resin under vacuum pressure, followed by cure. The advantages of the VARTM process include the use of a single-sided mold, which reduces tooling costs and other capital investments. Addition, large parts can be infused rapidly by applying a highly permeable distribution media as a surface layer into the preform [10, 11]. Upon opening of an inlet, the resin flows preferentially across the surface and simultaneously through the preform thickness. In large structures, numerous inlets and vacuum ports are required and flow fronts become quite complex and are highly dependent on the sequence that inlets are opened [12, 13].

temperature in about a week. In this experiment, the parts manufactured from glass textile through the layup method were produced being cut at the angles of 0 and 45, as shown in Fig. 1a.

(a)

II.

METHOD

(b)

Fig. 1 Glass fiber composite materials a) cutting according to the desired angle of the glass fiber cloth and b) fiber orientation

A. Materials In our study, BMS 8-301 CLASS 1EA 9390 epoxy adhesive with low viscosity and curing in temperatures, used by Boeing was applied. As the reinforcement material, BMS 9-3 7781 glass fiber was used. Materials in this experiment were manufactured at The Composite Workshop of Turkish Airlines

Depending on the dimension of the part to be manufactured at the bottom, nylon should be evenly spread. “Nylon should be glued to make sure the stretch.” Over the spread nylon, the compound obtained from the reaction should be evenly spread over the whole surface. On the compound/mixture spread on the bottom surface, glass textile is spread with no creases at the angle of 0. Again the resin with the help of a plastic spatula is evenly absorbed on the 0 glass textile. 90 glass textile is put on the top of the surface with resin. One of the problems encountered here is that the textiles of +45 are placed on the bottom surface. Because 45 textiles have an opposite angle with 0 textiles, they overlap each other with difficulty, but after a while when the contact with the resin underneath it is made sure with hands, the textile fits well. Similarly -45 textiles is also absorbed in resin with the even distribution of the absorption. These phases continue for 8 layers(e.g. Fig.1b). After the absorption at resin process is completed, as with the bottom section, the layup procedure is performed with the placement of the nylon over the top.

B. Production of Glass fiber-Reinforced Composite Material through manual spreading method This method is a technique employed in the production of modern composite materials. In this method, fibers are spread on a prepared mould and absorbed with resin. Thus, following the provision of the desired thickness spreading the other layers on the initial layer and then absorbing in resin, the layers are left alone to solidify. This process called the curing takes place at 121 for 150 for our adhesive. This method is often employed for glass fiber and epoxy composite parts used by Boeing. Prior to the manufacture of glass fiber composite materials, the material should be prepared being cut into rolls of textile in advance depending on the purpose of the manufacture because in half an hour after the production

Following the vacuum process of composite materials, they are cured under the effect of certain temperature and pressure. The matrix of the curing solidifies forming a

process starts, the resin should be absorbed and taken into the room temperature. The material, after the resin is 73

Proceedings of International Conference on Mechanical Engineering and Industrial Automation Held on 21-22, Nov, 2015, in Dubai, ISBN:9788193137321 chemical bond. After the absorption of the resin and obtaining a smooth edged surface, vacuum process should be followed right away. The point to be paid attention here is that the particular parts should be vacuumed and cured presently. As the parts may cure themselves even at the room temperature upon the absorption of resin, the curing time tends to prolong. The durability of the part is adversely affected by this situation. In this experiment, glass composite materials were vacuumed at 15, 20, 25 inhg pressure values and cured at 121 C (e.g. Fig. 2 a and b)

(a)

obtained from the experimental samples, as shown in Table I, Table II and Table III. Since the tensile resistance of the samples which came off from the points around the jaws was considerably low, the experiments are not regarded as a success and the average volume is not combined in the calculations.

(b)

Fig. 4 Dimensions of glass fiber reinforced composite material

Fig. 2 Glass fiber composite materials a) vacuumed different pressures and b) curing process

TABLE I RESULT FROM THE TENSILE TEST OF GLASS FIBER REINFORCED COMPOSITE MATERIALS UNDER 15 INHG CURE PRESSURE

Once the curing process is accomplished, the parts are laid to rest at room temperatures and the parts are taken out cutting the vacuum nylon without causing any damage, as shown in Fig. 3.

Fig. 3 Peeling off the cured parts of glass fiber fabrics by hand scattering method III.

Samples

Max. load (kN)

Tensile strength (Mpa)

Max. strain (%)

Modulus of elasticity (Gpa)

1

15.88

313.08

1.70

188.48

2

15.28

305.64

1.70

179.78

3

16.07

306.01

1.75

174.91

4

16.64

316.98

1.73

181.56

Average

15.72

310.43

1.72

180.68

RESULTS AND DISCUSSION

TABLE II

A. Tensile Test

RESULT FROM THE TENSILE TEST OF GLASS FIBER REINFORCED COMPOSITE MATERIALS UNDER 20 INHG CURE PRESSURE

Each of the 5 experimental samples was prepared under the pressures of 15, 20, 25 inhg for the tensile test. During the tensile check, the speed of tensile jaws was adjusted at 2 mm/min according to ASTM D 3039-08 standarts. The dimensions of experimental samples are defined in Fig. 4. Experimental results were compaired in accordance with the types of the materials, and the experiment pressures 74

Samples

Max. Load (kN)

Tensile strength (Mpa)

Max. strain (%)

Modulus of elasticity (Gpa)

1

16.56

339.75

1.75

194.14

2

15.67

318.88

1.71

186.50

Proceedings of International Conference on Mechanical Engineering and Industrial Automation Held on 21-22, Nov, 2015, in Dubai, ISBN:9788193137321 3

15.92

316.35

1.75

187.65

B. Fatigue Test

4

15.70

315.76

1.93

173.62

Average

15.96

322.69

1.79

185.48

Tests have been carried out with load checks and under 5 Hz sinuzoidal frequencies in which the loads are applied. The samples were put into tensile-tensile fatigue applications. To this aim, tensile ratios 90-80-70-60-50 % were taken for calculations. Up to the 90-80-70-60-50 % of the maximum resistance values figured out from the tensile test were respectively employed and as a result of the fatigue, the conversion figures were discovered.

TABLE III RESULT FROM THE TENSILE TEST OF GLASS FIBER REINFORCED COMPOSITE MATERIALS UNDER 25 INHG CURE PRESSURE Samples

Max. Load (kN)

Tensile strength (Mpa)

Max. strain (%)

Modulus of elasticity (Gpa)

1

15.60

315.82

1.80

175.46

2

15.02

300.87

1.68

179.08

3

16.06

337.81

1.75

193.04

4

15.07

312.30

1.62

192.78

5

15.16

313.97

1.60

196.21

Average

15.38

316.15

1.69

187.31

Fatigue experiments/test of the samples with better mechanical properties under the 15 and 20 inhg curing pressures, obtained from the tensile test of glass fiber reinforced composite materials under different curing pressures were carried out. The obtained results are seen in Fig. 6 a and b. In the figure, the maximum exerted loads and their converted figures are presented. As well the second best polynomial approaches, crossections through the experiment points are presented. According to this, the fatigue behavior of the composite cured under 15 inhg is considerably lower than the one cured under 20 inhg. This shows the cure pressure has effects on fatigue. (a)

Load (kN)

Compared to the tensile strength of the composite materials manufactured under 20 inhg cure pressure, the tensile strength of glass fiber reinforced composite materials under 15 inhg showed an increase of 4 % from 310 MPa to 323 MPa. Moreover modulus of elasticity under 20 inhg curing pressure is observed with an increase of 3 %. When tensile test results of glass fiber reinforced composites under different curing pressures are closely studied, it is apparent that 20 inhg curing pressure has better results. After loading of glass fiber reinforced composite material, as seen in Fig. 5 shows a broken state.

Load (kN)

(b)

Fig. 6 Fatigue behaviors of the glass fiber reinforced composite materials a) 15 inhg and b) 20 inhg curing pressures

Fig. 5 The appearance of the glass fiber reinforced composite material broken

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Proceedings of International Conference on Mechanical Engineering and Industrial Automation Held on 21-22, Nov, 2015, in Dubai, ISBN:9788193137321 After loading of glass fiber reinforced composite material, as seen in Fig. 7 shows a broken state.

composites for wind turbine blades", J Reinf Plast Comp, 33 (2014) 2287-99. [6] Taha I., Abdin Y.F., "Modeling of strength and stiffness of short randomly oriented glass fiberpolypropylene composites", J Compos Mater, 45 (2011) 1805-21. [7] Durmuş F., "Material failures in aircraft fuselage and mechanic tests of a repaired composite structure", Graduate School of Natural and Applied Sciences, Afyon Kocatepe University, Afyon, 2006, p. 132.

Fig. 7 The appearance of the glass fiber reinforced composite material broken IV.

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CONCLUSIONS

Tensile and fatigue tests have been carried out to determine the mechanical performance of the glass fiberreinforced composite materials. The effect of the different curing pressure on the behaviors of tensile and fatigue has been evaluated. The best result in both the resistance of tensile and the fatigue has been gained from the composites manufactured under the curing pressure of 20 inhg.

[9] Arulappan C., Duraisamy A., Adhikari D., Gururaja S., "Investigations on pressure and thickness profiles in carbon fiber-reinforced polymers during vacuum assisted resin transfer molding", J Reinf Plast Comp, 34 (2015) 318.

REFERENCES [10] Zhang K.M., Gu Y.Z., Li M., Zhang Z.G., "Effect of rapid curing process on the properties of carbon fiber/epoxy composite fabricated using vacuum assisted resin infusion molding", Mater Design, 54 (2014) 624-31.

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