Approach: To reduce the weight of the vehicle, but at the same time maintaining the same structural rigidity. This is of integral importance to any BAJA Vehicle as we have a fixed power input and to gain maximum from that, a team needs to reduce its weight in other words to improve the power:weight ratio.
Areas under study: There were three areas where the material weight reduction was focused on: 1. Chassis 2. Hubs 3. Uprights
1. Chassis: Chassis is defined as the frame that supports all the required susbsystem of the vehicle and also forming an envelope for the driver, to protect him. The main materials under consideration for the chassis were: a. AISI 1018 It is a carbon steel. It finds its major use in the non-critical components of tool & die sets, tool holders, pinions, machine parts, ratchets, dowels and chain pins use AISI 1018 mild/low carbon steel. It is BAJA recommended. Chemical Composition:
Element
Content
Carbon, C
0.14 - 0.20 %
Iron, Fe
98.81 - 99.26 % (as remainder)
Manganese, Mn
0.60 - 0.90 %
Phosphorous, Phosphorou s, P
≤ 0.040 %
Sulfur, S
≤ 0.050 %
Mechanical Properties:
Mechanical Properties Hardness, Brinell
Metric
126
Tensile Strength, Ultimate
440 MPa
Tensile Strength, Yield
370 MPa
Elongation at Break (In 50 mm)
15.0 %
Reduction of Area
40.0 %
Modulus of Elasticity (Typical for steel)
205 GPa
Bulk Modulus (Typical for steel)
140 GPa
Poissons Ratio (Typical For Steel)
0.290
Machinability (Based on AISI 1212 steel. as 100% machinability)
70 %
Shear Modulus (Typical for steel)
Bending Strength: (Calc. assuming 1” OD and a wall thickness of 0.118”(3mm) which is a constraint from BAJA.) 4
4
I = π[(25.4 )-(19.4 )]/64 4
= 13748.638 mm
Bs= [365*(10^6)*13748.638*(10^-12)]/[12.7*(10^-3)] = 387.37Nm Bending Stiffness : (Calc. assuming 1” OD and a wall thickness of 0.118”(3mm) which is a constraint from BAJA.) B’s ≡ EI ≡ 205(10^9)13478.638(10^-12) 2
≡ 2763.121 Nm
Advantages: High weldability. Readily available. Good machinability.
Disadvantages: Low strength resulting in high weight of structures.
80.0 GPa
b. IS 3074 (CDS 4)
It is an Indian Standard carbon steel. It is mainly used in the automotive industry in the country. It is well suited for the purpose. Chemical Compostion:
Element
Content
Carbon, C
0.30 - 0.40 %
Iron, Fe
98.81 - 99.26 % (as remainder)
Phosphorous, P
0.040 %
Sulfur, S
0.040 %
Mechanical Properties:
Mechanical Properties Hardness, Brinell
Metric
134
Tensile Strength, Ultimate
570 MPa
Tensile Strength, Yield
460 MPa
Bending Strength: (Calc. assuming 1.125” OD and a wall thickness of 0.070”(1.8mm)) 4
4
I = π*(28.575 )-(24.975 )]/64 4
= 13629.476 mm
Bs= [460*(10^6)*13629.476*(10^-12)]/[14.2875*(10^-3)] = 438.814Nm Bending Stiffness : (Calc. assuming 1.125” OD and a wall thickness of 0.070”(1.8mm)) B’s ≡ EI ≡ 205(10^9)13629.476(10^-12) 2
≡ 2794.043 Nm
Advantages: Used for automotive purposes. Readily available. Good machinability.
Disadvantages: Requires post treatment of welds to provide good characteristics.
c. AISI 4145
It is an alloy steel. It is a variant of Chromoly. Used to build structures, tubes for supplying pressurized gas, firearms and flywheel components.
Chemical composition: Element
Content (%)
Iron, Fe
96.795-97.72
Chromium, Cr
0.800-1.10
Manganese, Mn
0.750-1.00
Carbon, C
0.430-0.480
Molybdenum, Mo
0.150-0.250
Silicon, Si
0.150-0.300
Sulfur, S
≤ 0.0400
Phosphorous, Phosphorou s, P
≤ 0.0350
Mechanical Properties: Properties
Elastic modulus Poisson's ratio Hardness, Brinell Machinability (annealed and cold drawn, based on 100 machinability for AISI 1212 steel) Yield Strength Tensile Strength
Metric
190-210 GPa 0.27-0.30 208 60 785.423 MPa 830 MPa
Bending Strength: (Calc. assuming 1” OD and a wall thickness thickness of 0.0618”(1.57mm).) 4
4
I = π*(25.4 )-(22.26 )]/64 4
= 8379.395 mm
Bs= [785.423*(10^6)*8379.395*(10^-12)]/[12.7*(10^-3)] = 518.216Nm Bending Stiffness : (Calc. assuming 1” OD and a wall thickness thickness of 0.0618”(1.57mm)) B’s ≡ EI ≡ 210*(10^9)*8379.395*(10^-12) 2
≡ 1759.673 Nm
Advantages: Used for building structures. High strength. Disadvantages: Requires post treatment of welds to provide good characteristics. Difficult to procure. d. AISI 4130 It is an alloy steel. It is a variant of chromoly. Used majorly in the aircraft industry and for fabrication of chassis of race cars. Chemical Composition: Element
Content (%)
Iron, Fe
96.795-97.72
Chromium, Cr Manganese, Mn Carbon, C
0.90-0.93 0.55 0.30-0.32
Molybdenum, Mo
0.17
Silicon, Si
0.26
Sulfur, S
0.001
Phosphorous, P
0.007
Mechanical Properties:
Properties
Metric
Elastic modulus
190-210 GPa
Poisson's ratio
0.27-0.30
Hardness, Brinell
197
Machinability (annealed and cold drawn, based on 100 machinability for AISI 1212 steel)
72
Yield Strength
690 MPa
Tensile Strength
860 MPa
Bending Strength: (Calc. assuming 1.125” OD and a wall thickness of 0.070”(1.8mm).) 4
4
I = π*(28.575 )-(24.975 )]/64 4
= 13629.468 mm
Bs= [690*(10^6)*13629.468 *(10^-12)]/[14.2875*(10^-3)] = 658.221Nm Bending Stiffness : (Calc. assuming 1” OD and a wall thickness thickness of 0.070”(1.8mm)) B’s ≡ EI ≡ 205(10^9)13629.468(10^-12) 2
≡ 2794.043 Nm
Advantages: Used for fabricating racing chassis. High strength. Does not require pre/post treatment for thin sections of tubing (below 3mm thickness). Good machinability. Good weldability.
Disadvantages: Difficult to procure.
Conclusion: We decided to go for AISI 4130 as the only real constraint with it was the procurement of the material, and hence to not compromise on the structural rigidity of the vehicle, we decided to opt for AISI 413 0. 8
6
4 Weldability Yeild Strength 2
Availability
0 AISI 1018
AISI 4145
IS 3074 CDS1
AISI 4130
2. Hubs Hub is the component which connects the wheel to the Upright/Knuckle. It is a rotating body and transmits the torque/power from the drive axle to the wheel. Hubs have a great shearing load on them due to friction between ground and tyre, and hence material selection is of paramount importance to it. As a fail ure in hub would result in the car coming to a full stop with no way to run again unless the part is replaced. The main materials under consideration for the hubs were: a. Al 6061-T6 Widely used in the construction of aircraft structures, such as wings and more commonly in homebuilt aircraft than commercial or military aircraft, remains resistant to corrosion even when the surface is abraded Chemical Composition:
Component
Weight (%)
Al
95.8 - 98.6
Cr
0.04 - 0.35
Cu
0.15 - 0.4
Fe
Max 0.7
Mg Mn Si Ti Zn
0.8-1.2 Max 0.15 0.4-0.8 Max 0.15 Max 0.25
Mechanical Properties
Properties Hardness, Vickers Ultimate Tensile Strength Tensile Yield Strength Elongation at Break(thickness) Elongation at Break(dia) Modulus of Elasticity Poisson's Ratio Fatigue Strength Machinability Shear Modulus Shear Strength
Metric 107 310 MPa 276 MPa 12 % 17 % 68.9 GPa 0.33 96.5 MPa 50 % 26 GPa 207 MPa
Inference: We were sceptical whether the Al6061-t6 would take the shear loads on the hubs, and the ANSYS of a hub made of 6061 showed us that it deforms under the loads with an FOS 2. Hence, we concluded not to go for 6061-t6. Also, the machinability of this alloy is very low. b. Al 7075-T6
It is an aluminium alloy with zinc as the main alloying element. It is mainly used in transport applications, including marine, automotive and aviation, due t o their high strength-to-density ratio.
Chemical Composition:
Component
Weight (%)
Al
87.1-91.4
Cr
0.18-0.28
Cu
1.2-2
Fe
Max 0.5
Mg Mn Si Ti Zn
2.1-2.9 Max 0.3 Max 0.4 Max 0.2 5.1-6.1
Mechanical Properties:
Properties Hardness, Vickers Ultimate Tensile Strength Tensile Yield Strength Elongation at Break(thickness) Elongation at Break(dia) Modulus of Elasticity Poisson's Ratio Fatigue Strength Machinability Shear Modulus Shear Strength
Metric 175 572 MPa 503 MPa 11 % 11% 71.7 GPa 0.33 159 MPa 70 % 26.9GPa 331 MPa
Inference: Although, the UTS and fatigue strength of this alloy is far greater in comparison to 6061, this alloy once work hardened is specifically a lot more brittle than 6061, hence resulting in the growth of a fracture. Although, this alloy passed ANSYS the FOS was not satisfactory. And, the high % elongation was also a factor. It is also extremely difficult to source out this alloy.
c. EN 8 EN8 is medium carbon steel. With good machinability. EN8 is an unalloyed medium carbon steel with good tensile strength. It is normally supplied in cold drawn or as rolled. Chemical Composition:
Material C Si Mn S P
% Composition 0.35 - 0.45 0.05 - 0.35 0.6 - 1.0 < 0.06 < 0.06
Mechanical Composition:
Properties Ultimate Tensile Strength Tensile Yield Strength Elongation at Break(thickness) Elongation at Break(dia) Modulus of Elasticity Poisson's Ratio
Metric 500-800 MPa 530MPa 7% 7% 205 GPa 0.33
Inference: It passes ANSYS with satisfactory FOS. It is easily available. And also has a low % elongation, hence making it ideal for our purposes.
3. Uprights Upright is the component that transfer the load/ reactions from the car to the road and vice versa. It is a non rotating element, fixed between the hub and the chassis. All the load from the car is directly put onto the upright.
The upright undergoes, bearing loads from the hub assembly, bending loads due to the brake caliper and tensile/compressive loads due to the wishbone travel. Any failure in upright results in complete halt of vehicle with huge down time to service the parts. The main materials under consideration for the hubs were:
a. Al 7075-T6 It is an aluminium alloy with zinc as the main alloying element. It is mainly used used in transport applications, including marine, automotive and aviation, due t o their high strength-to-density ratio.
Chemical Composition:
Component
Weight (%)
Al
87.1-91.4
Cr
0.18-0.28
Cu
1.2-2
Fe
Max 0.5
Mg Mn Si Ti Zn
2.1-2.9 Max 0.3 Max 0.4 Max 0.2 5.1-6.1
Mechanical Properties:
Properties Hardness, Vickers Ultimate Tensile Strength Tensile Yield Strength Elongation at Break(thickness) Elongation at Break(dia) Modulus of Elasticity Poisson's Ratio Fatigue Strength Machinability
Metric 175 572 MPa 503 MPa 11 % 11% 71.7 GPa 0.33 159 MPa 70 %
Shear Modulus Shear Strength
26.9GPa 331 MPa
Inference: Although, the UTS and fatigue strength of this alloy is good, this alloy comes tempered, hence it cannot be casted. And uprights are better casted than machined as they need to be not brittle. Although, this alloy passed ANSYS the FOS was not satisfactory. And, the high % elongation was also a factor. It is also extremely difficult to source out this alloy.
b. Casted S.G. Iron It is also known as ductile iron. Much of the annual production of ductile iron is in the form of ductile iron pipe, used for water and sewer lines. Ductile iron is specifically useful in many automotive components, where strength needs surpass that of aluminium but do not necessarily require steel. Chemical Properties:
Component
Weight (%)
C
3.0
Si
1.5-3
P
Max 0.08
Ni
18-22%
Cr Mn
1.75-2.75 0.70-1.25
Mechanical Properties:
Properties Ultimate Tensile Strength Tensile Yield Strength Elongation at Break(thickness) Brinell Hardness Poisson's Ratio
Metric 400 MPa 207Mpa 8% 138-202 0.33
Inference: This alloy passed the ANSYS satisfactorily and also was easily available for casting. We gave the alloy for casting and due the various factors involved in the casting procedure, we were facing repeated failures in the casting. And hence we decided to not use this material. c. EN 8 EN8 is medium carbon steel. With good machinability. EN8 is an unalloyed medium carbon steel with good tensile strength. It is normally supplied in cold drawn or as rolled.
Chemical Composition:
Material C Si Mn S P
% Composition 0.35 - 0.45 0.05 - 0.35 0.6 - 1.0 < 0.06 < 0.06
Mechanical Composition:
Properties Ultimate Tensile Strength Tensile Yield Strength Elongation at Break(thickness) Elongation at Break(dia) Modulus of Elasticity Poisson's Ratio
Metric 500-800 MPa 530MPa 7% 7% 205 GPa 0.33
Inference: It passes ANSYS with satisfactory FOS. It is easily available. And also has a low % elongation, hence making it ideal for our purposes. It did not fail during t he testing process. It is also machined and not casted.
