Chapter 7 Chapter 7 Conclusions and Future Scopes
4.3 Experimental Study: Optimization of Gear Materials
4.3.1 Tensile Properties
The tensile mechanical properties of the gear materials are studied by using Instron universal testing machine (ASTM D638) digitally controlled by the closed loop servo hydraulic dynamic machine (100 kN, maker, Instron, model no. 8801) with a cross head speed of 1 mm/min at room temperature. Figure 4.2(a) shows the schematic diagram of the test specimen of gear material, Figure 4.2(b), (c) and (d) are showing the various stage results after the samples are deformed while Figure 4.2(e) shows the deformed specimen with setup under testing. It is observed that with 5 % and 10 % cement filled gear materials experienced ductile failure while 15 % cement filled gear material exhibits the brittle fracture. Thus, it is observed that as the percentage of the cement fillers increases, the ductility of the composite material decreases while brittleness improved and reaches an optimal value.
(a) Final product
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(b) (c) (d)
(e)
Figure 4.2 (a) Schematic of tensile test sample (all dimensions are in mm) and (b) 5%, (c) 10% with ductile failure, (d) 15% cement filled composite gear materials undergoes brittle failure under tensile load and (e) tensile failure of the 10% cement reinforced composite specimen on the experimental
setup
After tensile failure, experimental data are collected at constant rate of elongation (CRE) of 1 mm/min and the true stress and true strain % are calculated using eqn. 4.1(a) and eqn. 4.1(b) as (Ling, 1996):
S( 1 e )
4.1(a)
ln( 1 e )
4.1(b) Where, engineering stress and strain are denoted by ‘S’ and ‘e’ respectively. Figure 4.3 shows the true stress and strain behavior of the composite materials under uniaxial tensile
Chapter 4 Design and Fabrication of Composite … load. It is observed that modulus of elasticity increases with % increase of cement particles leads to % decrease of strain value. For pure polypropylene and 5%, 10%, 15% cement filled composite gear materials, modulus of elasticity are obtained as 1325.29, 1430.56, 1540.5, 1629.48 MPa respectively.
0 5 10 15 20 25 30 35 40
0 5 10 15 20 25 30
True stress (MPa)
True strain (%)
0%
5%
10%
15%
Figure 4.3 True stress-strain behavior of polypropylene and other composite gear materials
In the Figure 4.4(a), the variation of ultimate tensile strength and elastic modulus of composite gear materials of different compositions are shown. The tensile test results are given in the Table 4.1. Figure 4.4(b) shows the change in load bearing capacity as well as 0.2% yield strength of the material with respect to the percentage of cement fillers loading. It is observed that ultimate tensile strength increases by 4% and 7% as the filler percentages changes from 5% to 10% respectively. Further increase in fillers loading decreases the tensile strength by 18% for 15% composite material. Also, the modulus of elasticity of gear materials changes remarkably with higher loading of cement particles in the polypropylene matrix. With 5%, 10% and 15% of cement fillers loading, it is observed that the elastic modulus of the composite increases by 8%, 16.24% and 23% compared to 100%
polypropylene.
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1200 1300 1400 1500 1600 1700 1800
22 24 26 28 30 32 34
0 5 10 15
Elastic modulus (MPa)
Ultimate tensile strength (MPa)
Cement content (wt%)
UTS
Elastic modulus
(a)
11 12 13 14 15 16 17
0.85 0.95 1.05 1.15 1.25 1.35 1.45
0 5 10 15
0.2% yield strength (MPa)
Max. load (kN)
Cement content (wt%)
Max. load
0.2% yield strength
(b)
Figure 4.4 (a) Ultimate tensile strength and elastic modulus, (b) variation of maximum load and yield strength at 0.2% offset with the filler % of composite materials
Table 4.1 Tensile test results of cement reinforced composite materials Filler UTS
(MPa) SD
Modulus of
elasticity (MPa) SD
Max. Load (kN) SD
0.2% Yield
Strength (MPa) SD
0% 29.44 1.40 1325.29 2.25 1.22 1.85 12.60 1.64
5% 30.65 2.02 1430.56 3.05 1.28 2.12 15.73 1.52
10% 33.52 1.58 1540.5 2.12 1.31 1.78 16.27 2.03
15% 24.07 2.11 1629.48 2.23 1.00 1.88 14.44 1.97
In comparison, Figure 4.4(b) shows the variation of maximum load and yield strength at 0.2% offset value. It is observed that for 5 % and 10 % cement particles filled gear materials,
Chapter 4 Design and Fabrication of Composite … maximum increase in load remains relatively constant to 7.35%, while further increase in fillers to 15% reduces 18% of the maximum load. Similar characteristics are also observed as the yield strength increases to 24.8% and 29% when filler loading varies from 5% to 10%
with 0.2% offset.
Thus, the results show significant improvement in mechanical properties as the filler loading percentages go up to 10%. It is anticipated that good interfacial bonding between polypropylene matrix and cement particles and better distribution of the fillers results in easy transfer of load from matrix to reinforcing element. The tensile modulus of the composite gear materials increases with an increase of cement particles loading (%wt) in polypropylene matrix. In the case of ultimate tensile strength (UTS), the trend is also increasing when the loading percentage of cement particles increased but up to a certain amount. The composite material of 10% of cement fillers is showing the highest value. Hence; further addition of loading up to 15% is showing the negative trends for ultimate tensile strength.
Materials and geometry of the composite gear significantly influence energy storage and gear performance. To imply appropriate material for the gear, specific strain energy of the cement particles filled polypropylene composite materials are considered. According to Yu and Kim, (1988), amount of specific elastic strain energy stored in a system is given as in the eqn.
(4.2).
2
2
max
se E
(4.2) where, E denotes the modulus of elasticity of the material, ρ refers the density of the material and σmax is the maximum allowable stress of the material. The above equation depicts that most appropriate material for the gear application must have maximum strength with reasonable modulus of elasticity. As shown in the Figure 4.5, the 10% cement particles filled composite gear material gives high specific elastic strain energy; make it suitable as a potential gear material for lightweight application. Hence, it is anticipated that, in dynamic loading, due to high specific strain energy of the specified material, the fatigue characteristics will be enhanced.
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0.31
0.35 0.37
0.19
0 0.1 0.2 0.3 0.4 0.5