Journal of Materials Sciences and Applications

2015; 1(2): 65-69

Published online April 10, 2015 (http://www.aascit.org/journal/jmsa)

Keywords Experimental Study,

Kevlar/Epoxy,

Composite Materials and

Internal Pressure Loading

Received: February 28, 2015

Revised: March 18, 2015

Accepted: March 19, 2015

An Experimental Study of Hybrid/Epoxy Composite Cylinders Under Internal Pressure Loading

A. A. Ramadhan

Department of Mechanical Engineering, Al-Hawija Technical Institute, Foundation of technical

education Kirkuk, Iraq

Email address ayad_almuhndis@yahoo.com

Citation A. A. Ramadhan. An Experimental Study of Hybrid/Epoxy Composite Cylinders Under Internal

Pressure Loading. Journal of Materials Sciences and Applications. Vol. 1, No. 2, 2015, pp. 65-69.

Abstract An experimental study of Kevlar-29/epoxy composite thin wall cylinders under internal

pressure loading has been investigated in this work. Kevlar/epoxy composite specimens

have been fabricated and tested. All of these specimens were tested by using the

hydraulic pump and it were subjected to a uniformed internal pressure loading. The

results that were obtained from this work to find the (PIR) and derived the failure load

with comparison have been presented. The comparison was done and at last the more

strength material using for fabricating a thin wall composite pressure vessel was

specified. The efficient and effective composite cylinder have been presented

experimentally and provided considerable advantage for using woven roving fibers in

pressure vessels applications.

1. Introduction

The ever-increasing use of pressure vessel can been seen widely in civilian industries

such as for liquid petroleum gas tank, fire extinguisher, oxygen gas tank and the power

generation under different conditions of pressure, temperature, and environment.

Therefore, it have given special emphasis to analytical and experimental methods for

determining new materials to undergo a certain high working with an appropriate safety

factor and low maintenance cost [1-2].

The important modern materials that use in a lot of engineering applications are the

composite materials. The aim in this study to fabricate one of the composite materials

that are used for the pressure vessels to make pressure vessels that will be more safety

and more light than before. [3]

A great deal of attention is being concentrated on reducing the weight of pressure

vessels and fuel tanks by 10% to 20%. Most efforts are focused at the use of new lighter

weight to high strength materials to achieve this goal. [4].For instance, many researchers

have studied the manufacturing and designing aspects of laminated composite pressure

vessels [5-6]. Recently, a number of researchers have studied the optimal design of

laminated composite pressure vessels to reduce the weight and possible maintenance

costs and to investigate the laminate failures. But must of these studies were about

filament winding. For example, Chang R.[7] studied experimentally and theoretically the

first- ply failure of laminated composite pressure vessels, for reliability assurance, an

accurate prediction of the internal load failure process of laminated composite structures

and the maximum loads that the structures can withstand before failure occurs and the

effect of the number of layers on the ratio of increase in pressure, that has become an

66 A. A. Ramadhan: An Experimental Study of Hybrid/Epoxy Composite Cylinders Under Internal Pressure Loading

important topic of research. Hose D.R and his associates [8]

used a woven roving glass reinforced composite to made

mixed wall pipes fabricated and subjected to internal a

pressure to measure the strain in inner surface. Adali et al. [9]

gave another method on the optimization of multi-layered

composite pressure vessels using an exact elasticity solution.

A three dimensional theory for anisotropic thick composite

cylinders subjected to axis symmetrical loading conditions

was derived. The three dimensional interactive Tsai-Wu

failure criterion was employed to predict the maximum burst

pressure. The optimization of pressure vessels show that the

stacking sequence can be employed effectively to maximum

burst pressure. However Adali’s results were not compared

with experimental testing and the stiffness degradation was

not considered during analysis.

Sayman [10] studied analysis of multi-layered composite

cylinders under hygrothermal loading. Mackerle [11] gives a

bibliographical review of finite element methods applied for

the analysis of pressure vessel structures and piping from the

theoretical as well as practical points of view. Xia et al. [12]

studied multi-layered filament-wound composite pipes under

internal pressure. Xia et al. (2001) presented an exact

solution for multi-layered filament-wound composite pipes

with resin core under pure bending. Rao and Sinha [13]

studied the effects of temperature and moisture on the free

vibration and transient response of multidirectional

composites. A three-dimensional finite element analysis is

developed for the solution.

The effect of number of layers of composite pressure

vessels on the pressure increase ratio (PIR) is studied

experimentally in this work.

Experimental investigation of pressure increase ratio in

composite pressure vessel subjected to internal pressure load

in performed by using manual pump. A comparison between

test results was made to demonstrate the suitability of the

composite materials in pressure vessels fabrication.

2. Experimental Work

2.1. Materials Selection and Specimen

Fabrication

Materials selection was done after several surveys of

previous studies and thesis recommendations had make a

study about composite pressure vessels from reinforcement

and resin. Woven roving Kevlar-29 fiber with epoxy resin

(EP-A215C1) and hardener resin (EP-B215) had been

selected to fabricate the composite specimens in this paper.

All specimens have same geometry but with different

numbers of fiber layers. The length of the specimen are 320

mm and the active length that make from 2, 4, 6 layers and it

will carry the internal pressure load of the test until burst will

be in the middle of the specimen and have a length of 100

mm only, the remained inactive length will be in both

specimen sides and it will be inside the test equipment with

different geometrical shape according to the test equipment

in measurement and geometrical shape in order to make sure

that the specimens will seat fit in the test equipment without

any gap, Figure 1 shows the geometry of the specimen.

Figure 1. The geometry of the specimen (all the dimensions in mms)

For accuracy reasons, three specimens were fabricated for

each number of layers which means 9 specimens will needed,

i.e. three for each 2, 4 and 6 layers of Kevlar-29 fibers.

Comparison between the different number of layers should

be investigated, so 3(number of specimens) times 3(number

of layers) the total will be 9 specimens each tube after cutting

and finishing will produce one specimens only. Therefore,

the results were represented from the average of three

specimens under the same condition and as a result, 3 results

will be ready for analyzing and discussion, representing all

the layers and the kinds of specimens.

Hand lay-up method has been used to fabricate all the

specimens. Woven roving Kevlar-29 fiber is winding

manually in the open mold, and epoxy resin brushed over and

into the woven roving fiber. Entrapped air is removed

manually with a roller. As shown in Figure 2.

Journal of Materials Sciences and Applications 2015; 1(2): 65-69 67

Figure 2. Typical Photograph, Hand Lay-Up Process

After preparing all the materials, first step in fabrication

start with cutting woven roving fiber manually into suitable

parts. After finding circumference of each mandrel, the

length of each piece of fiber can be found by multiplying the

circumference times the number of layers. The diameter of

the mandrel is 48 mm; the circumference of the circular cross

sectional area can be obtained by multiplying the diameter (D)

by (π ).

By multiplying the circumference by the number of layers

(N) for each category of tubes 2, 4 and 6 and the length of the

piece of fiber can be obtained from equation:

The length (m) = Circumference × N

According to equation above the length of fiber can be

obtained. Till this step all the pieces of woven roving fiber

are ready to start fabricated.

Next step is preparing the mixture 20 parts by volume of

epoxy hardener from Leco Corporation USA was used for the

matrix per 100 parts by volume of epoxy resin, After the

mixture become ready, by using suitable brush the mixture

will distribute on the fiber of the active area, rolling the fiber

on the mandrel should be done in the same time to ensure the

equal distribution of the mixture between the fiber and the

layers that will produce balanced specimens and symmetrical

dimension for all parts of the specimens. The composite tube

curried out at room temperature 32 Cº and leaved behind for

72 hours to provide optimum blend.

After finishing from the fabrication processes and by using

turning machine (XL 1880) at 320 rpm in the work shop the

finishing and cutting processes should be done. The Final

specimens of Kevlar-29/epoxy composite material are shown

in Figure 3.

Figure 3. Typical Photograph of Kevlar-29/epoxy Specimens

2.2. Testing of Composite Tubes

Burst pressures were measured by applying pressurized oil

to the specimens of pressure vessels and slowly increasing

the pressure until each vessel failed. At First the specimen is

prepared via fixing among two plugs as shown in Figure4,

each plug contains three slots as a place for washers, and also

each plug must be exposed to silicon glue to make it safer

against leakage. Secondly the specimen should be fixing

from each side by the flanges, in order to ensure holding the

plugs tightly inside the specimen during pressurized process.

The third step is connecting the pump with specimen by

using a high pressure pipe between them. After that the

specimen become ready to testing and by put it above

suitable stand, pressurized oil process starting manually by

using the pump until failure done as shown in Figure 5.

68 A. A. Ramadhan: An Experimental Study of Hybrid/Epoxy Composite Cylinders Under Internal Pressure Loading

Figure 4. Typical Photograph, plugs fixing process

Figure 5. Connecting and Pressurized process until failure occurred

3. Results and Discussion

Table 1. The Burst Pressure and Average Pressure for Kevlar-29/Epoxy

Specimens

Average of Max.

Pressure (bar)

The Max.

Pressure (bar)

No. of

Specimens

No. of

Layers

96

91 Specimen 1

2 97 Specimen 2

100 Specimen 3

227

220 Specimen 1

4 236 Specimen 2

225 Specimen 3

339

331 Specimen 1

6 339 Specimen 2

348 Specimen 3

The burst pressure test applied for the three specimen sets

and the test result will discuss below and according to

average burst pressure for number of layers and by using

composite pro other relations and parameters will find and

discuss. To make a comparison for a maximum (burst)

pressure of specimens according to the number of layers a

chart include all of them has been donning and Table1 shows

the average of burst pressure for each number of layers for all

specimens

Figure 6. Average of Burst Pressure for Each Number of Layers for All

Specimens

Figure 6 illustrates the bar chart of the Pmax average for the

all specimens with different numbers of layers. From this

Figure, the value of Pmax increased gradually from the lowest

pressure in Kevlar-29/epoxy specimens depending on the

number of layers. The maximum pressure (burst pressure) is

proportional to the number of layers or the thickness of the

specimen wall. And also the specimens that have six layers

(6L) always can carry the highest Pmax and highest internal

load comparing with other specimens that made from two

layers (2L) and four layers (4L).

Pressure Increase Ratio (PIR)

The pressure increase ratio (PIR) is the ratio between the

maximum average pressures in the same type of specimens

has a different number of layers.

This can be obtained from equation:

(High No. of Layers) (Low No. of Layers)

(Low No. of Layers)

Max Max

Max

P PPIR

P

−= (1)

Where, (PMax) will be the average maximum pressure for a

different number of layers in the same type of specimens.

This parameter is very important to study the behavior of

composite materials in pressure vessels design when internal

load apply in of the specimens.

By applied (equation1) on the average maximum pressure

shown in Table 1 the pressure increase ratio for Kevlar-

29/Epoxy specimens found as schematic diagram as shown in

Figure 7 and the chart in Figure 8

Journal of Materials Sciences and Applications 2015; 1(2): 65-69 69

Figure 7. Schematic Diagram, Increase Ratio for KE specimens

Figure 8. The bar chart of Pressure Increase Ratio for KE Specimens

Figure 8 illustrates the variation of PIR in Kevlar-29/epoxy

specimens between different numbers of layers, the ratio

decrease from (137.76%) in two numbers of layers to four

numbers of layers into (49.26%) between four numbers of

layers to six numbers of layers that mean the total decrease is

(88.5%). While the PIR between the two numbers of layers

and six numbers of layers is (254.90%). That also means the

PIR for Kevlar-29/Epoxy specimens decrease as much as the

numbers of layers increase but the specimens have the best

ratio of reduce in PIR that mean in any design application it

requires less internal load.

The summery of pressure Increase Ratio of the result are

showed in figures (7 and 8) according to the number of layers.

The PIR for four layers to six layers it can clearly noticed

that the lower gain in Kevlar-29/epoxy specimens so by

increasing the number of layers in specimen it can carry more

internal load for the industrial applications. The highest PIR

for two layers to six layers can be noted during the test.

4. Conclusion

In this paper, the pressure increase ratio (PIR) of

composite cylinders were investigated and tested under

internal pressure at various numbers of the layers. The results

of the composite cylinders were presented; it was found that

PIR for Kevlar-29/Epoxy Specimens increased with

increasing number of layers from 2L to 4L. The results also

identified that the pressure increase ratio (PIR) of

Kevlar/epoxy composite cylinders was highest ratio from the

others cylinders.

References

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[2] Fukunaga H, Chou TW. Simplified design techniques for laminated cylindrical pressure vessels under stiffness and strength constraints. J Comp Mater 1988;22:1157-69.

[3] Salah M. Ali. Experimental Study of Composite Cylinders under Internal Pressure Loading. Dissertation submitted in partial fulfillment of the requirements for the degree of master of engineering, MI: University of Malaya Press, 2009.

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