w11-hw2-dim-tol-stat-mat

w11-hw2-dim-tol-stat-mat - ME250 Design and Manufacturing I...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: ME250 Design and Manufacturing I Winter 2011 Lecture HW #2 Name: ___________________________ UMID: _________________ Lab Section #: _______ Note: You must indicate name, UMID, and Lab Section # otherwise the homework will not be returned. 1. Draw orthographic views of the following object and dimension them. [25 pts] Front view 2. Fill the table with MMC and LMC values corresponding to features A—F. [15 pts] 3. The flange joint assembly for a pressure vessel is shown in the figure below. A No. 370 O ring is to be installed in the gland in order to avoid the leakage. The gland dimensions are G = 7.24 ± 0.13 [mm], F = 4.32 ± 0.13 [mm], and Y = 218.48 ± 1.10 [mm]. The outside diameter of No. 370 O ring is 219.58 ± 0.34 [mm] and the cross‐ sectional diameter is 5.33 ± 0.13 [mm]. [30 pts] end plate Y O ring G G gland F (a) When the end plate is bolted in position, the O ring is compressed. Assuming absolute tolerance, what is the amount of the minimum compression (squeeze) [mm] of the O ring? (10 pts) (b) Assuming statistical tolerances, what is the probability that the O ring is circumferentially compressed when the O ring is placed in the gland prior to assembly of the end plate? Note that this is a desired situation since adequate compression can help sealing. (10 pts) (c) Assuming statistical tolerances, what is the probability that the O ring is circumferentially stretched when the O ring is placed in the gland prior to assembly of the end plate? Assume the cross‐sectional diameter of the O ring at one location is independent of the cross‐sectional diameter at another location. Assume the same for the width G of the gland. Note that this is an undesired situation since stretching an O ring can cause poor sealing. (10 pts) 4. Global bending of a vehicle chassis can be approximately modeled as bending of a simply supported plate under distributed load. In the figure below, b, h, and l are the width, the thickness, and the length between supports of a plate, respectively, and w is a load per unit length that is applied on the plate. w h l b The plate is made of a material with the density and Young’s modulus E. The maximum allowable displacement of the plate is 0 and we are interested in minimizing the mass of the plate, m, for given l and b which are specified by the overall vehicle size. The 2nd moment of area of the cross section of the plate is given by I bh3 /12 and the maximum displacement (occurs at a half of the length) is given by: 5wl 4 384 EI Answer the following. [30pts] (a) Express m with respect to the given quantities. [5pts] (b) For given b, l, w and 0, show that material index (to be maximized) for selecting the material minimizing m is E1/3/Note that h is a free variable that should be eliminated in your calculation. [5pts] (c) Using the line selection method with bubble chart in CES EduPack software, select three materials for the chassis that maximize the material index in (b) with 0.5×106 psi ≤ E ≤ 10×106 psi. Use the “Edu Level 2: Materials” data. Attach the printout of the bubble chart with the selection line. [10pts] (d) Consider now the material used for the semester project, PVC (E = 421000 psi and Sy = 7500 psi). What is the minimum value of h so that the displacement can be kept below 0? Use b = 2.0 in, l = 5.0 in, w = 0.30 lb/in, and 0 = 0.10 in. [5pts]. (e) The maximum stress (occurs on the top and bottom surfaces at a half of the length) is given by: wl 2 h 16 I Using the same values for b, l, w, and 0 as in (d) and the minimum thickness obtained in (d), calculate the factor of safety of the chassis. [5pts] ...
View Full Document

This note was uploaded on 09/12/2011 for the course MECHENG 250 taught by Professor Stevis during the Winter '09 term at University of Michigan.

Ask a homework question - tutors are online