No. Parts Qty Description Weight (lb) Cost. 4 Wheels (E) 4 Hard Rubber Tread 4 in. dia. $38.40

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5 4 Bill Of Materials No. Parts Qt Description Weight (lb) Cost 1 Nose and back 1 0 x50 x0.16 sheet, $41.75 plates (A & B) T361 Al. Axle Bracket 8 in. 04-T361 Al. Bar, 1 in. x 0.16 in. 0.7 $ Handle (D) 0 in. 04-T361 Al. Rod, 1 in. dia..4 $ Wheels (E) 4 Hard Rubber Tread 4 in. dia. $ Nose-back plate connection 1 Box of bolts ¼ in. dia. x $5.00 (estimate) 6 Link 1 Swivel bolt $.50 Total:.8 $98.00 Note: Aluum prices approximated through Rerson. Tires and bolts taken from McMaster-Carr Catalogue. Special Acknowledgement. Note: This sample is based upon an actual project submitted in F 1997 b: Kevin Choi Marcel Gordon Michael Martini Joseph Sullivan This report is flawed b omissions (like quantit and thread size of bolts, size and description of swivel bolt ) and is more tpical of student work rather than professional work. Readers are cautioned to take this into account when reviewing it. And of course feel free to raise and discuss an questionable issues in class.

6 5 Methods To start our design, we selected a list of materials based upon strength and cost and selected aluum for the structural components because it has a good strength-toweight ratio compared to steel and it is readil available. Within the aluum famil, we chose a stronger o in order to reduce the size of members and exploit strength to weight, hence create an efficient design. We bolted the back plate to the nose plate (instead of welding them together) so that the product could be shipped in a flat box. The handle functions as an extension to the bed in cart mode and functions as usual in upright mode. The rubber wheels are gentle on floors and absorb shock. The analsis emploed strength of materials, but did not include an advanced theor for the plates. The design was given a distinctive shape to distinguish it from the competition, et not limit its function.

7 6 Assumptions 1. The shear ield stress of ASTM A36 Steel can be approximated b taking 60% of the tensile ield stress based upon comparison of data found for other steels.. The shear ield stress of Aluum 04-T361 can be approximated b taking 60% of the tensile ield stress based upon comparison of data found for other aluum os. 3. Beam theor applies to the plate structure. Warnings 1. Wheels themselves were not designed.. Weld not analzed. 3. Swivel attachment of handle not analzed.

8 7 References Corrosion Resistance (Dennis McCrosk), Simpson Strong-Tie Compan, Inc. iewed (13 Nov. 1997) Corrosion Resistance Construction Hardware (No Author), Hughes Manufacturing, Inc. iewed (17 Nov. 1997) Mechanical Properties of Some Materials iewed (4 Nov. 1997) Hibbler, R.C. (1994) Mechanics of Materials. Engle Wood Cliffs: Prentice H. Rerson Stock List and Data Book ( ) Joseph T. Rerson & Son Inc., Pittsburgh, PA

9 8 Material Properties Material σ ield (ksi) τ ield (ksi) σ ow (ksi) τ ow (ksi) Reference Al 04-T ASTM A Rerson ( ) Rerson ( ) Sample calculations: σ ow σ ield /F.S. 57/ ksi τ ow τ ield /F.S. 34./ ksi For both materials, τ ield is approximated as τ ield (0.6)σ ield Note: Shear ield not available. Taken as 60% based upon data collected for similar materials see Assumptions, pg. 6. Primar Load Data Calculation of impact force on nose plate. Conditions: 1) Specified live load: 300 lb ) Dropped from a height of 0 feet, equivalent to dropping off a curb. F impact n 1+ n 1+ F imp nf dead 1+ ( 1 h dst! 300lb 600lb ) h 0 Note: Worst case dictates that this load will be a concentrated point load in the center of the nose plate.

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11 9 Calculations Nose Plate Model: Cantilever beam. 600 lb 5 in Free-Bod Diagram: t w Cross section 600 lb 5 in. M Y Z X Calculation for nose plate. F 0 600lb M 0 z M 600lb! 5in 3000lb? in Bending analsis, detering imum thickness, t: 1M? I 3! z wt! ksi 1 I z t t 6M # w 6! 3000in " lb w 0in lb! in in 0 t in Shear analsis: Q! 6300 lb 600lb I w in x 1 I x wt 1 3 w 0in t t wt Q!! w 4 8 t / 8 w!" 1 600lb / 8 (0in /1)! 6300 lb in t in

12 10 Decision: Round thickness up to 0.16 in which is a noal value for aluum sheet. NOTE TO STUDENTS: What did the team working this example miss? Could there be another loading scenario for shear? Back Plate. Model, Free-Bod diagram and shear and bending moment diagrams: See pg.16. Cross-section: t Z w X Minimum thickness of Back Plate: max and M max taken from shear and moment diagrams. Bending: M lb? in max 5. 3lb max M I x 1 wt! in lb I x 1 t w! 15in atm M lb " in / w 15in # lb! t in 1 in max t Transverse Shear:! max I x Q w 6300 lb in t t wt Q! w! I x wt 1 3 w! 1in@ max t / 8 w " 1 5.3lb / lb! 1in in t in Decision: Thickness of back plate will be 0.16 in. as a noal value.

13 11 Axle Bracket. Model: Cantilever beam (w on left). Free-Bod Diagram: Thickness, t0.16in. into paper M F300lb Rin. Y x X Z Note: Assume tipping eent, so that wheel and axle absorb entire load. For simplification in design, setting x3.0 in. Detere dimension: F 0 ; 300lb M z 0; M 300lb! 3in 900in? lb Bending stress analsis, solving for imum : " M! I ( / ) z lb in 1 I z t 1 3 6M " t! 6! 900in " lb 0. 88in lb! 0.16in in Y Transverse Shear: Cross-section: Z! 6300 in lb Q! I t z 1 I z t 1 3 t t Q!! t 4 8 t / 8 " t 300lb! 0.5in / lb! 0.16 in /1 in in Decision: Round up to 1 in. noal. Note that - is smer than the chosen diameter for the wheels. Otherwise modifications would be necessar. Also note that x, or thickness, can be solved for instead of.

14 1 Bolts. Model (load specified near angle), Free-Bod Diagram, cross section. 600 lb. 600/ lb 300 lb Area A 1 Bolt Detering imum diameter of bolts. Bolts connect back plate, nose plate, and axle bracket, and are to be made of A-36 Steel. Four bolts between the nose plate and back plate, two bolts connected to axle bracket. Therefore, design is for axle bracket connection where two bolts must carr 600 lb load. Shear calculation:! lb 300lb A in A "! r r 300lb "! lb #! in d r in Decision: To ow for added stress from transverse shear, and for simplification, a diameter of 0.5 in will be used.

15 13 Axle Bracket (Bearing) Bearing Stress of Bolts on Axle Bracket. 600 lb Free-Bod Diagram: Thickness, t0.16 in into paper Area, A 300 lb 300 lb Note: Analzed for axle bracket, which has two bolts to carr the full 600 lbs. Checking if previousl calculated diameter (0.5 in) of bolts is acceptable. Compressive Bearing Stress: A!? R? t F / " lb!! A in R 0.15in # "! 300lb 0.15in! 0.16in lb in Since the compressive stress is much less than the owable, the bearing stress of the bolts on the axle bracket will be easil handled in the design. Also, this stress can work both was, meaning that the bearing stress ma also be on the bolts in some situations. However, the stress is also significantl smer than the owable for the bolts.

16 Axle Bracket (Tear-out Shear) Free-Bod Diagram: Thickness, t0.16in into paper F300 lb R0.085in 14 Y bolt bracket X Tear-Out Shear for plates: axle bracket Axle bracket has onl two bolts carr the 600lb where the nose plate and back plate have four bolts, so the axle bracket calculation will govern design. F 0; F F 300 lb : 150lb! A t!" 6300 lb in A! t 150lb 0.16in! 6300 lb in 0.037in Therefore, the center of the bolts must be at least inches from the bottom of the axle bracket or the plates. Checking with previous calculations: d bracket bolts 1.0in 0.5in 0.037in bracket! d? bolt 1.0! 0.5? Decision: Design for axle bracket is suitable, and bolts will be placed in the center of the bracket.

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