The effect of factors on the flexural of the composite leaf spring

Materials Today: Proceedings xxx (xxxx) xxx

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The effect of factors on the flexural of the composite leaf spring Anwer J. Al-Obaidi a, Shaymaa Jumaah Ahmed b, Hussain M. Sukar c a

University of Wasit, Baghdad, Iraq University of Technology, Baghdad, Iraq c Alrookal Company, Baghdad, Iraq b

a r t i c l e

i n f o

Article history: Received 6 July 2019 Received in revised form 2 September 2019 Accepted 29 September 2019 Available online xxxx Keywords: Leaf spring Composite materials Epoxy Polyester E-glass fiber Flexural

a b s t r a c t The modern automobile industry is heading into reducing the weight of vehicles in-order to reduce the fuel consumption of the modern vehicles, for that reason composite materials have gain special position when developing vehicles. This paper studied leaf spring, which is one of car part that can be manufactured from composite material, the material used at this research was E-glass fiber with polyester and epoxy matrices. experimental work showed the relation between load capability and the fiber distribution within the composite, having a better load bearing capability for material made from woven fiber. Additionally, the increase of fiber fraction in composite will improve its mechanical properties. Moreover, the type of matrix used in manufacturing the composite had a significant factor on material stiffness, where the mechanical properties of composite with epoxy matrix improved and increased the weightlifting ability more than a matrix made from polyester. Furthermore, the composite leaf spring has nearly the same stiffness of steel when its thickness 11 mm, while the thickness of steel spring is 5 mm. The reduction of weight in composite spring is 84% lower than steel spring. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 2nd International Conference on Materials Engineering & Science.

1. Introduction As the automobile industry developed and with the introduction of electrical cars commercially, the need for lightweight vehicles increased. The reasons for using lightweight material in the automobile industry are weight reduction, and energy economizing. Composite materials have these required characteristics. The use of composite material involved in different parts of the car body. One of these car parts is the suspension leaf spring, which it can be manufactured from composite materials. The Suspension leaf spring makes about ten to twenty percent of the total weight for the damping system in any vehicle. The word composite signifies to combine two or more materials in a structural unit. Generally, the composite materials can be used when desirable properties can be achieved. These desirable properties cannot be achieved when the constituent materials used alone. The fibrous composite made of reinforcing fibres embedded in a matrix material is the most common example of the composite materials [1]. Composite material can be classified into three main categories depending on the matrix used for its manufacturing, such as Cera-

mic Matrix Composites (CMCs), Metal Matrix Composites (MMCs) and Polymer Matrix Composites (PMCs). In the current research, the category that used is Polymer Matrix Composites (PMCs), and this category use polymer as the base for its matrices, and with combination of fibers as glass or carbon. PMCs have low strength and stiffness [2]. Use of the fiber reinforced polymer materials (FRP) is widely increasing in different applications due to offer important benefits over the traditional materials, such as high strength to weight ratio (lightweight materials), low maintenance, corrosion resistance, stable in dimensions, and high dielectric strength [3]. Composite leaf spring are made from fiberglass, carbon fiber, and epoxy formed into one large semi-elliptical leaf with steel re-enforced contact points. Composite springs over a large weigh reduction in comparison with the traditional steel ones, the weight reduction up to 75% [4]. Leaf spring was first introduced in the seventeenth century to support the body of hours drawn coaches. Today, leaf springs are manufactured from carbon steel alloys (low, medium to high alloy), which it has very high yield strength, allowing the spring to return to its original shape after it has been deflected without

https://doi.org/10.1016/j.matpr.2019.09.190 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 2nd International Conference on Materials Engineering & Science.

Please cite this article as: A. J. Al-Obaidi, S. J. Ahmed and H. M. Sukar, The effect of factors on the flexural of the composite leaf spring, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.190

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deformation. Leaf spring leaves are short peened in manufacturing to reduce surface stress and lessen the possibility of a stress riser that could lead to cracked or broken spring. A mulitleaf spring pack is a stack of spring steel leaves held together with a center bolt. The spring pack may have several spring alignment clips to keep the leaves parallel to each other. The top leaf or plate, of the spring usually have an eye formed at the ends for attachment purpose. Each subsequent leaf in the stack will be shorter than the one above so the spring pack will have a shape of half diamond. A multileaf spring that are tightly clamped together have a selfdamping characteristic, as the spring is deflected, the leaves straightens out, causing each leaf to move against each other that leads to interleaf friction. The interleaf friction absorbs the energy from the spring oscillation. Using interleaf friction solely as a shock absorbance method leads to rough ride [4]. Kumar [5] found that the leaf spring, which it made from composite materials had 67.35% lesser stress, 64.95% higher stiffness and 126.98% higher natural frequency comparing with the existing steel leaf spring. Gulur et al. [6] in his paper stated that composite spring compared with spring made from steel has much lower stress, contrarily the natural frequency is higher, and with weight reduction up to 85%. Mohammad and Goudarzi [7] concluded that composite leaf spring has better durability from the ones made from steel. Shivashankar et al. [8] studied using of composite materials for manufacturing the leaf spring and the consented fuel efficiency. The design criteria involved using generic logarithm for optimal design. Ahmad Refngah [9] studied the fatigue life of parabolic spring made from composite material, the researcher used a fatigue life predication depended on the FEA with variable amplitude loading. Through the defection of spring, leaf spring reduces the automobile vibration, which means that the leaf spring stored energy and it will be released gradually [10]. For more convenient ride the stain energy absorbed by the leaf spring needs to be maximized. The strain energy follows the equation below:

U¼

r2 qE

ð1Þ

where: U = Strain energy, r = Strength, q = Density E = Leaf spring’s young’s modulus. Based on the above equation, it can be concluded that the highest value of strain energy can be produced when the materials have the lowest values of both density and Young’s modulus. The composite materials have a lower Young’s modulus and density than the metals. In addition, higher strength to weight ratio makes composite materials as one of the best alternative materials for manufacturing leaf spring [11]. Based on above, this research aims to determine the flexural stiffness of composite leaf spring and studying the factors that affect the stiffness such as (thickness, width, type of matrix and type of filler) of composite leaf spring and comparing with the existing steel leaf spring.

Fig. 1. Schematic of flat spring.

materials, for analysis let consider flat plate fixed from one edge and loaded from the other end as illustrated in Fig. 1. Where, T = plate’s thickness, b = plate’s width, L = plate’s length, and W = load. Maximum bending moment at the cantilever will be at point A according to equation:

M ¼W L

ð2Þ

and section modulus,

I bt3 =12 1 2 ¼ ¼ bt Y t=2 6

Z¼

ð3Þ

Bending stress:

M WL ¼ 2 Z bt

r¼

ð4Þ

Maximum deflection at the free end with concentrated load:

d¼

WL3 4WL3 2rL2 ¼ ¼ 3EI 3Et Ebt 2

ð5Þ

The stress distribution of layers due to the bending moment will be in tension at the top layer, while it will be in compression at the bottom layer. The shear stress will be zero at both ends, while the maximum shear stress will be in the center, as illustrated in Fig. 2. For analysis, only the bending stress will be considered. A simply supported beam can be adopted to analyse the leaf spring, then the maximum bending moment in the center:

M ¼W L

ð6Þ

Section modulus, 2

bt 6

Z¼

ð7Þ

Bending stress,

6WL

r¼

bt

2

ð8Þ

Maximum deflection in the center:

d¼

WL3 3EI

ð9Þ

Based on 3-point bending, the flexural strain is:

ef ¼

6dt L2

ð10Þ

2. Theory

2.1. Determination of fiber volume fraction

Based on the purpose of this study, a single leaf spring was investigated. In general leaf spring are made from plate shaped

The fiber volume fraction is used in the design of composite materials in order to calculate the composite properties and nor-

Please cite this article as: A. J. Al-Obaidi, S. J. Ahmed and H. M. Sukar, The effect of factors on the flexural of the composite leaf spring, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.190

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Fig. 2. Stress distribution of layers.

mally calculated as the ratio of the reinforcement’s volume to the total volume of the composite. Fiber volume fraction can be calculated exploratory through weighing the lamina, after that the matrix must be removed and weighing the fibers. For the analytical calculations of fiber volume fraction, fiber arrangement and the form of the fiber reinforcement in the lamina should be known. For the calculations of loading in the material contents of composite material expressed in volume, but during manufacturing, the measurement of the volume is difficult, as a result, the weight fraction is used [1]. The calculation of the volume fraction can be used the following equations:

Vf ¼

Vf ¼

qc  qm ðAssuming zero void contentÞ qf  qm

1 þ qqmf

1 

1 wf

1



ð10Þ

ð11Þ

Let, V f = Fiber Volume Fraction wf = Fiber Weight Fraction qc = Composite’s Density (g/cm3) qm = Density of Cured Resin/Hardener Matrix (g/cm3) qf = Fiber’s Density (g/cm3)

3. Methodology and experimental work The materials and equipment, that are used in the current research, are Epoxy resin, Polyester resin, E-Glass fiber, Polyvinyl Acetone as a release agent for the mold and Ethanol for cleaning off the leftover of resin from the apparatus. Additionally, the balance is used to weigh the resin and fiber. The silicon rubber mold is cleaned and coated by wax to serve as a release agent for the mold. Then, a weighed coat of resin containing curing additives is brushed evenly over the surface of the mold. After that, a weighed layers of fiberglass reinforcement are applied and made sure that these layers are fully wetted with resin. This technique is called hand-layup technique. The produced samples in the current research are had a varying fiber content 35 ± 5%. Fig. 3 shows the actual pictures of composite leaf spring samples.

3.1. Mechanical tests Instron device is used to perform the tensile test for the samples according to ASTM D412 with crosshead speed 5 mm/min. Moreover, it is used to perform the 3-point bending test following the recommended standard procedure (ASTM D790). Table 1 shows the mechanical properties of steel used for leaf spring and the proposed composites. 3.2. Sample dimensions All samples have the same total length 1000 mm, while the thickness and width are varied as illustrated in Table 2. 4. Results and discussion The experimental work provided a clear insight into the relationship between the load and the deflection linked to each type of composite used. Fig. 4 describes the relation between load and the deflection for composite leaf spring made from (Random fiber) and (polyester matrix), width = 60 mm. It can be clearly shown that the deflection of the leaf spring decreases with the increase of the composite thickness. Additionally, the deflection of steel leaf-spring is almost the same when the composite spring is made with thickness as double as the thickness of steel spring. The relation between load and the deflection for composite leaf spring made from (Random fiber) and (polyester matrix), width = 70 mm is shown in Fig. 5. The relation between load and deflection has the same pattern before, with one significant difference that the deflection in composite leaf with 11 mm thickness as lower than the one made from steel as a result for the increase size of the composite spring, as shown in Fig. 6. Load versus deflection for composite leaf spring filler (Woven) and matrix (polyester) at width = 60 mm (Fig. 6), the deflection increased with the increase of load, and the deflection decrease when the thickness increased under the same load. Load versus deflection for composite leaf spring filler (Woven) and matrix (polyester) at width = 70 mm (Fig. 7), the deflection increased with the increase of load, and the deflection decrease when the thickness increased under the same load. Load versus deflection for composite leaf spring filler (Woven) and matrix (epoxy) at width = 60 mm (Fig. 8), the deflection increased with the increase of load, and the deflection decrease when the thickness increased under the same load.

Please cite this article as: A. J. Al-Obaidi, S. J. Ahmed and H. M. Sukar, The effect of factors on the flexural of the composite leaf spring, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.190

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Fig. 3. Composite leaf spring.

Table 1 The mechanical properties of steel and composites.

Tensile strength (MPa) Yield strength (MPa) E Modulus (MPa)

Steel

E glass/epoxy

E glass/polyester

1967 1504 2.2  105

906 765 38600

679 565 21146

Table 2 Sample dimensions. Material

Length (mm)

Width (mm)

Thickness (mm)

Steel Random fiber + Polyester (matrix) Woven fiber + Polyester (matrix) Woven fiber + Epoxy (matrix)

1000 1000 1000 1000

60 60 and 70 60 and 70 60 and 70

5 5, 8 and 11 5, 8 and 11 5, 8 and 11

Fig. 5. The relation between load and the deflection for composite leaf spring made from (Random fiber) and (polyester matrix) – width = 70 mm.

Fig. 6. The relation between load and the deflection for composite leaf spring made from (woven fiber) and (polyester matrix) – width = 60 mm. Fig. 4. The relation between load and the deflection for composite leaf spring made from (Random fiber) and (polyester matrix) – width = 60 mm.

Load versus deflection for composite leaf spring filler (Woven) and matrix (epoxy) at width = 70 mm (Fig. 9), the deflection increased with the increase of load, and the deflection decrease when the thickness increased under the same load.

In the Figs. 3–8, the increase load resistance from composite materials is the result of increased mechanical properties of composite, as the mechanical properties increased with the increasing in the glass fiber contents [2]. From Fig. 10, shows the relation between random and woven fiber with polyester matrices having the same width. From the graph, it can be clearly indicated that the load bearing capability

Please cite this article as: A. J. Al-Obaidi, S. J. Ahmed and H. M. Sukar, The effect of factors on the flexural of the composite leaf spring, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.190

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Fig. 7. The relation between load and the deflection for composite leaf spring made from (woven fiber) and (polyester matrix) – width = 70 mm.

Fig. 8. The relation between load and the deflection for composite leaf spring made from (woven fiber) and (epoxy matrix) – width = 60 mm.

Fig. 9. The relation between load and the deflection for composite leaf spring made from (woven fiber) and (epoxy matrix) – width = 70 mm.

Fig. 10. Relationship between load and deflection of woven and random fiber with polyester matrices at the same width against steel leaf spring.

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for composite leaf spring made from woven fibers is higher than the ones made for random fiber. This can be related to the fact that the stiffens in composite with woven fiber is higher than the random, and the orientation of fiber along the leaf spring body results in better loading resistance ability. Fig. 11 shows the relation between the composite leaf spring with polyester matrix with woven and random fiber against the leaf spring made from steel. The dimension for composite leaf is the same (11 mm thick, 60, 70 mm width). From graph it can be shown that the maximum deflection in composite leaf is less by 1.5% percent for random fiber and by 12% percentage for woven composite in comparison to the maximum deflection for steel this for 60 mm width spring. Furthermore, this percent reached 16% percentage for woven fiber made spring having width of 70 mm. Both Figs. 12 and 13 present the relation between the load and deflection, samples were made from woven fiber with two type of matrix (epoxy and polyester), the main feature in both graphs is the clear advantage when using epoxy as the matrix in the spring

Fig. 11. Relationship between load and deflection of woven and random fiber with polyester matrices against steel leaf spring.

Fig. 12. Relationship between load and deflection of woven and random fiber with polyester matrices at the same width = 60 mm against steel leaf spring.

Fig. 13. Relationship between load and deflection of woven and random fiber with polyester matrices at the same width = 70 mm against steel leaf spring.

Please cite this article as: A. J. Al-Obaidi, S. J. Ahmed and H. M. Sukar, The effect of factors on the flexural of the composite leaf spring, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.190

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leaf as the deflection in springs with epoxy matrix is less at any load or thickness. 5. Conclusions The most important observation from the tests is relation between the deflection and the load in composite leaf spring. The experimental result showed a better load bearing capability for material made from woven fiber, additionally, the increase of fiber fraction in composite will improve its mechanical properties. Secondly, the mechanical properties of the composite leaf spring improved when using epoxy as a matrix compared with the polyester matrix and increase the weightlifting ability as it can be seen in the results. These two factors are the two main reason that effect on the stiffness of the leaf spring that led to the use of composite instead of steel. Acknowledgment The authors would like to thank the Composite Research Group at the Wasit university for their assistance during the bench work of the current research. It is self funded and CRG at the University of Wasit support us by provide us some materials therefore, we thank them.

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Please cite this article as: A. J. Al-Obaidi, S. J. Ahmed and H. M. Sukar, The effect of factors on the flexural of the composite leaf spring, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.190