Transcript Structural Requirements - Faculty of Mechanical Engineering

SMC 4133 AUTOMOTIVE STRUCTURES
MATERIAL SELECTION
This section demonstrates a method for preliminary selection of materials
• Steel is the most common material for the contemporary body structure
• Mild steel was the predominant steel grade used in the past due to
its favorable balance of strength, formability & cost
• In recent years, strict safety standards has made steel application extended
to higher-strength grades
• Increase the strength may also increase the cost
• Another significant parameter is material elongation; increased strength comes
at a reduced elongation at failure
All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design, SAE International.
SMC 4133 AUTOMOTIVE STRUCTURES
MATERIAL SELECTION
Preliminary selection of materials can be made by the following steps:
1. Determine the primary function of the structural element: stiffness, strength,
& vibration
2. Determine the objective of material selection: minimize mass etc.
3. Derive the material index corresponding to the type of structure, the function,
the objective and constrained dimensions
4. Rank materials by descending material index using a tabular form or
graphic
5. Make the final material selection after gathering information
All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design, SAE International.
SMC 4133 AUTOMOTIVE STRUCTURES
MATERIAL SELECTION
Example 1
Design requirements based on allowable deflection, delta = 20mm
and applied load, F = 6680N
1. Optimized beam thickness
2. Optimized beam mass
3. Minimum cost
Constraints: Section width = 40mm, height = 80mm, length = 1000mm
All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design, SAE International.
SMC 4133 AUTOMOTIVE STRUCTURES
MATERIAL SELECTION
Solution
Design requirements based on allowable deflection, delta = 20mm
and applied load, F = 6680N
1. Optimized beam thicknessMS
2. Optimized beam mass CFRP
3. Minimum cost MS
Constraints: Section width = 40mm, height = 80mm, length = 1000mm
material
E
A
t, m
rho
M, kg
$/kg
Cost, $
steel
2.00E+11
-6.68E-06
4.30E-03
7860
7.53
0.80
6.02
AHSS
2.00E+11
-6.68E-06
4.30E-03
7860
7.53
1.00
7.53
alu
7.00E+10
-1.91E-05
9.40E-03
2710
5.16
2.80
14.44
smc
1.00E+10
-1.34E-04
2.80E-02
2000
7.17
6.00
43.01
mg
4.50E+10
-2.97E-05
1.20E-02
1830
4.22
4.80
20.24
ti
1.20E+11
-1.11E-05
6.50E-03
4430
6.16
100.00
616.21
gfrp
2.50E+10
-5.34E-05
1.74E-02
1850
5.49
20.00
109.70
cfrp
1.60E+11
-8.35E-06
5.20E-03
1600
1.82
40.00
72.95
All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design, SAE International.
SMC 4133 AUTOMOTIVE STRUCTURES
MASS ESTIMATION
This section presents a mean to generate initial mass estimations
• Mass of vehicle subsystems is crucial in determining structural requirements
• For a new vehicle design, there are no existing subsystems to weight. Thus,
it is critical to have a method to estimate initial mass of the subsystems
Regression-based mass estimation
- to arrive at an estimate for the curb (with fluids) and gross (passenger, cargo,
and option) vehicle mass and each of the subsystems
All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design, SAE International.
SMC 4133 AUTOMOTIVE STRUCTURES
MASS ESTIMATION
Example 2
A new vehicle is in the planning stage. It is targeted at 5 passengers with a 120kg
cargo capacity. The vehicle length is 4.7m and 1.8m width. The test weight for
fuel economy is 1480 kg resulting in a 1341 kg curb mass. Determine the curb
mass for an average vehicle and to compare it to the target test weight and
mass for each subsystem.
Solution:
Mcurb =171 x 4.7 x 1.8 = 1446.6 kg
Mdiff = 1446.6 – 1341 = 105.7 kg
All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design, SAE International.
SMC 4133 AUTOMOTIVE STRUCTURES
MASS ESTIMATION
Mass-compounding model
- Unplanned mass increase in a component during vehicle design has a
uncertain effect throughout the vehicle.
- Other components need to be resizedmay increase vehicle mass even more
- A reduction of mass in a component by a new technology can result in an
even more mass reduction (secondary mass reduction) for overall vehicle
- Mass-compounding model is a way to quantify the secondary mass change.
- Each subsystem has a mass influence coefficient-as vehicle mass changes
the subsystem may also be resized.
All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design, SAE International.
SMC 4133 AUTOMOTIVE STRUCTURES
MASS ESTIMATION
Mass-compounding model
- The resulting mass for subsystem:
Ratio method
All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design, SAE International.
SMC 4133 AUTOMOTIVE STRUCTURES
MASS ESTIMATION
Mass-compounding model
Example 3
From example 2 & using mass-compounding model, estimates mass
reduction in a vehicle considering 5 hypothetical technologies.
Solution: 1446.6 – 40 – 40(1.079) = 1363.4 kg
Mdiff = 1363.4 – 1341 = 22.4 kg
All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design, SAE International.
SMC 4133 AUTOMOTIVE STRUCTURES
MASS ESTIMATION
Mass-compounding model
Example 3: Solution
From example 2 & using mass-compounding model, estimates mass
reduction in a vehicle considering 5 hypothetical technologies.
All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design, SAE International.