Modular Car Jack Analysis for MEEN 475 by Group D

1. Modular Car Scissor Jack Analysis
MEEN 475 - 501, Group D
December 4, 2017
Brendan Cooper | Anissa Kneese | Natalie Pardivala | Miguel Rico | Ian Legg

2. Our Design

3. Scissor Jack Mechanics
• Car jacks carry ⅓ - ¼ of the
total weight of a vehicle
– Depends on the point of lift
• Weight acts on the top plate
– distributed load, bending stress
• Pins transfer load to arms
– shear stress, 2 points/pin
• Arms transfer load to screw
– compressive and bending stress
• Screw
– tensile stress

4. Merit Indices and Ashby Plots
Arms Merit Indices: E/ρ, E1/3/ρ
Derivation:
S=F/𝛅=3EI/L3, m=bhL⍴
I=bh3/12, 𝛅=12FL3/3Ebh3
b=12FL3/3Eh3 𝛅
m=12FL4⍴/3𝛅h2E
M=E/⍴
Screw: σy/ρ, Pins: 𝜏y/ρ, Plates: σy
1/2/ρ
Function Support load from plates, transfer load to screw
Constraints Must have a length of 8 in
Must have a thickness of 0.13 in
Must have a height of 3.5 in for the top plate, and 1 in for the
side plates.
Objective Maximize stiffness
Minimize buckling
Minimize mass
Free Variables Material choice

5. Scissor Jack Arm Material Properties
Material Density (g/cc) Elastic Modulus (GPa) Strength (MPa)
GFRP S Glass 2.53 89 4600
CFRP (std CF) 1.60 70 600
SiC 3.16 415 250
Alumina (Al-95) 3.65 303 137
Al 6061- T6 2.70 68.9 276
MT-17C W Alloy 17 275 517
A36 Carbon Steel 7.85 200 250
Material Families Identified:
1. GFRP
2. CFRP
3. SiC
4. Alumina - Al2O3
5. Aluminum Alloy
6. Tungsten Alloy
7. Steel

6. Results from AHP Method and FEA
Rank Arm Material
1 Silicon Carbide
2 GFRP S Glass
3 Alumina Al-95
4 MT-17C W Alloy
5 A36 Carbon Steel
6 CFRP (Std CF)
7 Al 6061-T6
Property Importance:
Elastic Modulus - 2
Density - 3
Yield Strength - 4
Cost - 5
(Eliminate ceramics for possible ultimate
failure that could result in safety issues)
FEA with GFRP S Glass:
Overall Factor of Safety: 45
1000 N bearing load applied on each top hole
Materials Chosen for all Parts:
Pins: 1080 High Carbon Steel
Screw: 1080 High Carbon Steel
Plates: Titanium Alloy Ti 6Al-4V
Weight/Unit: 9.31 lbs, Material Cost/Unit: $62.80

7. References
1. Merit Indices. Materials Selection in Mechanical Design. Accessed 3 Dec.
2017.http://mech.vub.ac.be/teaching/info/Ontwerpmethodologie/Appendix
%20les%203%20Material%20indicespdf.
2. Nucor Fastener Division. Shear Strength: Technical Data Sheet. Dec.
3,2017.https://www.nucor-
fastener.com/Files/PDFs/TechDataSheets/TDS_013_Shear_Strength.pdf
3. S, Choudhary, et al. “Development of Motorized Car Jack.” OMICS
International, OMICS International, 22 May 2016,
www.omicsonline.org/open-access/development-of-motorized-car-jack-
2168-9873-1000216.php?aid=76286&view=mobile.

8. Questions?

9. Additional Slides

10. Merit Indices and Ashby Plots
Pin Merit Index: 𝜏y/ρ
Function Connect the jack arms to the top and
base plates
Allow rotation of the jack arms
Constraints Must have a diameter of 0.5 in
Must have a length of 4.5 in
Objective Maximize strength
Minimize mass
Free
Variables
Material choice

11. Merit Indices and Ashby Plots
Plate Merit Index: σy
1/2/ρ
Function Control position of scissor jack
assembly, provide tensile strength
Constraints Must be threaded
Must be long enough to attach both
hinges of the jack
Must have a radius of 1 in
Must have a thread pitch of .15 in
Must have 7 threads per inch
Objective Maximize tensile strength
Minimize mass
Free Variables Material choice

12. Merit Indices and Ashby Plots
Screw Merit Index: σy/ρ
Function Control position of scissor jack
assembly, provide tensile strength
Constraints Must be threaded
Must be long enough to attach both
hinges of the jack
Must have a radius of 1 in
Must have a thread pitch of .15 in
Must have 7 threads per inch
Objective Maximize tensile strength
Minimize mass
Free
Variables
Material choice

13. Scissor Jack Pin Material Properties
Material Density (g/cc) Elastic Modulus (GPa) Shear Strength (MPa)
Carbon Fiber Composite 1.77 35.9 260
Ti 6Al-4V 4.43 113.8 550
Al 6061-T6 2.70 68.9 207
1080 Steel 7.85 205 520
4130 Steel 7.85 205 400
1010 Steel 7.87 200 230
Ni Alloy 8.43 207 450
Mg AZ63 1.83 50 160

14. Scissor Jack Plate Material Properties
Material Density (g/cc) Elastic Modulus (GPa) Strength (MPa)
AZ91D Magnesium Alloy 1.81 46 160
Al 6061-T6 2.70 68.9 276
Ti 6Al-4V 4.43 110 900
A36 Carbon Steel 7.88 200 250
600 Nickel Alloy 8.47 207 255
Zamak 3 Zinc Alloy 6.60 130 221
Tungsten Carbide 15.6 630 300

15. Scissor Jack Screw Material Properties
Material Density (g/cc) Elastic Modulus (GPa) Tensile Strength (MPa)
Carbon Fiber Composite 1.77 35.9 103
Ti 6Al-4V 4.43 113.8 620
Al 6061-T6 2.70 68.9 276
1080 Steel 7.85 205 585
4130 Steel 7.85 205 435
1010 Steel 7.87 200 365
Ni Alloy 600 8.43 207 552
Mg AZ63 1.83 50 97

16. Results from AHP Method
Rank Arm Material
1 Silicon Carbide
2 GFRP S Glass
3 Alumina Al-95
4 MT-17C W Alloy
5 A36 Carbon Steel
Rank Plates Material
1 Ti 6Al-4V
2 AZ91D Mg Alloy
3 6061-T6 Al
4 A36 Steel
5 ---
Rank Screw Material
1 1080 Carbon Steel
2 Ti 6Al-4V
3 Ni Alloy 600
4 6061-T6 Al
5 ---
Rank Pins Material
1 1080 Carbon Steel
2 Carbon Fiber
3 Ti 6Al-4V
4 Mg AZ63
5 ---