eng analysis

8/2/2019 Eng Analysis

1/7

1

LiftLiftLiftLift----MyMyMyMy----RideRideRideRideEngineering Analysis:Engineering Analysis:Engineering Analysis:Engineering Analysis:

Lift Criteria and Assumptions:

Estimated vehicle weight: 6,000 lbs (weight of Hummer H2 or loaded LincolnNavigator)

Overestimate vehicle weight: 10,000 lbs One lift raises one wheel; 4 lifts raise 10,000 lbs Provide a single lift requirement of 2500 lbs (1.25 tons) as a conservative estimate 2500 lbs equals or exceeds full weight of most 2-seater sports cars. The scissor jackused will come pre-designed with a 2500 lb lifting capacity. The material will be designed completely using plain-carbon steel. Welding the

plain-carbon steel material will create a strength in the material greater than the

material in its undisturbed solid form when using a low alloy filler. To overestimatethe safety, we will use calculations of strength using the plain-carbon steel in its

undisturbed, solid form. Below are the likely failure points on the design which will

be discussed. Modifications to the design pictured in support of the engineering

analysis are also noted.

Possible General Failures and Design Solutions:

A. Unstable center of gravity Weighted rear support brace for balance and lengthened front floor plates

extending under car

B. Jack failure due to excess mass being lifted (> 2500 lbs) Use scissor jack designed to satisfy necessary lift requirements

C. Failure of primary bolts due to bending moments and shear stresses Solid plain-carbon steel in a U-Shaped form is used to eliminate these bolts.

D. Failure of pads at weld lines due to bending moments and shear stresses Use one part braces, molded and welded of the plain-carbon steel with a strength

exceeding the scissor jack lift specifications: no attachment of multiple parts


2/7

2

Pre-Prototype Design:

Front View

Rear View

Design in Action


3/7

3

Lift Characteristics:

Estimated weight of product:o 35-45 lbs; no counter balance necessary.

Lift height capability:o 18 inches, the maximum recommended safety for lifting one wheel at a time. Manufacturing issues:

o Maintaining material strength in critical areas, safe application of jack to otherproduct components.

Strength of materials analysis for fasteners and critical load bearing elements:o As described in analysis.

Fatigue analysis for critical load bearing elements:o Fatigue is not an issue, but load tolerance is. Jack stands are recommended tohold car once lifted as with any other jack.

Stability during of operation:o Same as stability with any traditional scissor lift. U-Shaped attachment

welded on scissor jack top platform and the floor base extensions are expected

to aid in relieving the stress caused by a side lifting jack.

Control methods and algorithms:o Traditional lock of scissor jack implemented in addition to failure-support

base platform extended under car.

Material selection:o Plain-Carbon steel parts attached to pre-designed scissor jack.

Safety:o According to jack safety requirements, a minimum factor of safety of 3 is

specified.

Human interface:o An individual must be capable of operating a traditional scissor jack.

Performance analysis and prediction:o With the support of the floor extensions and the U-shaped attachment on the

top platform of the scissor jack, the center of gravity can be stabilized duringthe lifting procedure, eliminating the threat of failure due to the lack of a top-

loading traditional lift. This in turn will allow vehicles with a very low profile

to be raised, even when immobile.


4/7

4

Material: Plain-Carbon Steel

Low - Medium Carbon steel will be usedo 0.29 % to 0.54 % Carbon - e.g. AISI 1040 steelo Medium-carbon steels can be heat treated to have a good balance of ductility

and strength. These steels are typically used in large parts, forgings, andmachined components.

Material Properties at 25 C: Low Medium Carbon Steel:

Density = 7,845 kg/m3 Young's Modulus (E) = 200 GPa Poisson's Ratio (v) ~ 0.3 Ultimate Shear Strength = 57,420 PSI = 342.4 MPa

o Approximately 66% of the UTS (87,000 PSI = 518.8 MPa) Yield Strength = 52,500 PSI = 353.4 MPa.


5/7

5

Critical Points of Failure:

1. Bending Moment on Primary Bolt: Yield Strength = 52,500 psi Dimensions: 1 Diameter Factor of Safety: 3 Load: 2,500 lbs (11121 N) Load Condition: Bending

Actual Bending Stress: 76,395 psi = Fail Possible Modification # 1: 2 Bolts (1 bolt per brace and no overlapping of braces) New Bending Stress: 19,099 psi Possible Modification # 2: Change Bolt Diameter to 1.25 New Bending Stress: 39,114 psi

2. Shear Force on Primary Bolt: Yield Strength = 52,500 psi Dimensions: 1 Diameter Factor of Safety: 3 Load: 2,500 lbs (11121 N) Load Condition: Shear Actual Shear Stress for 1 Bolt: 9,550 psi Actual Shear Stress for 2 Bolts: 4,775 psi per bolt

3. Bending Moment at Pad Weld Line: Yield Strength = 52,500 psi Dimensions: 3 x 14


6/7

6

Factor of Safety: 3 Load: 1,250 lbs (5,561 N) Load Condition: Bending Actual Bending Stress: 52,500 psi (Acceptable because FOS = 3)

4. Shear Force on Pad Weld Line: Yield Strength = 52,500 psi Dimensions: 3 Weld Line Factor of Safety: 3 Load: 1,250 lbs (5,561 N) Load Condition: Shear Actual Shear Stress: 1,250 psi

5. Bending Moment on Rotating Arm: Yield Strength = 52,500 psi Dimensions: 0.5 Thick by 3 Wide by 12 Long Factor of Safety: 3 Load: 1,250 lbs (5,561 N) Load Condition: Bending Actual Bending Stress: 60,000 psi = Fail Modification: Design Arm with Width of 3.25 New Bending Stress: 51,124 psi

Non-Critical Points of Failure:


7/7

7

References:

1. http://www.geocities.com/haimanaua/htdocs/steels/1040.html 2. http://www.efunda.com/Materials/alloys/carbon_steels/show_carbon.cfm?ID=AISI_1

040&prop=all&Page_Title=AISI%201040

3. http://en.wikipedia.org/wiki/Plain-carbon_steel

eng analysis

Documents