Download Mechanical Materials Exam: 3D - Stage 3, BEng in Mechanical Engineering and more Exams Mechanical Engineering in PDF only on Docsity!
CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Autumn Examinations 2008/
Module Title: Mechanical Materials (3D)
Module Code: MECH 8012
School: School of Mechanical and Process Engineering
Programme Title: Bachelor of Engineering in Mechanical Engineering – Stage 3
Programme Code: EMECH_8_Y
External Examiner(s): Mr. P. Clarke, Prof. R. Clarke Internal Examiner(s): Mr. S.F. O Leary
Instructions: Answer THREE questions. All questions carry equal marks.
Duration: 2 Hours Sitting: Autumn 2009
Requirements for this examination:
Note to Candidates: Please check the Programme Title and the Module Title to ensure that you have received the correct examination paper. If in doubt please contact an Invigilator.
Static Tensile Ultimate Stress σ u = 1.900MPa
Fatigue Strength Reduction Factor = K = 0.
Given:- NCR = Nf ln( )
ln( ) ,'
1
e
f
e
f b
N
f b N
cr^ σ
σ
σ
σ (^) =
(^) (34 marks)
And Table 1 Q2. Fatigue Criterion
Ductile Steels (σ≤ 1750 Mpa)
Brittle (hard) steels (σ≤ 1750 Mpa) σf Nf σe Ne σf Nf σe Ne Modified Goodman
0.9 σu 103 1/2 Kσu 106 0.9 σu 103 1/3 Kσu 108
Soderberg 0.9 σu 103 1/2 Kσu 106 0.9 σu 103 1/3 Kσu 108 Gerber 0.9 σu 103 1/2 Kσu 106 0.9 σu 103 1/3 Kσu 108 SAE σu + 350 x 10^6 1 1/2 Kσu 106 σu 1 1/3 Kσu 108
Q3. (a) The shear stress distribution, τ , in a rectangular bar of width b and depth d subjected to a shear force, V, is given by the following expression
= ^2 −^2
6 d y bd τ V
where y is distance from the centroid. Using this expression, and otherwise working from first principles, derive an expression for the strain energy stored due to this shear force. Comment on how, in practise, the strain energy due to shear force is calculated for other standard rolled steel sections. (14 marks)
(b) The curved bar, shown in Figure 1 Q3, is of rectangular cross-section of width 20mm and depth 40mm and has a radius of curvature R = 80mm. When a vertical force of P = 10 kN is applied as shown at the free end, determine the corresponding vertical deflection. If strain energy due to shear force is neglected, what percentage error is incurred? Use the result of part (a) and assume the bar is made of steel for which the Modulus of Elasticity is 210 Gpa and Poisson’s Ratio is 0.31. (20 marks)
Q4. (a) Calculate the shape factor of a T-Section beam of flange width 125mm and depth 10mm and of web depth (excluding flange) 140mm and width 10mm. (10 Marks)
(b) A beam of length 9m is constructed from the above section and is designed to carry a point load at 2m from one support. Determine the value of the point load to cause complete plastic collapse of this structure when the beam is (1) Simply supported at both ends (2) Built-in at both ends (10 marks)
(c) Find the maximum value of the point load that can be carried by the simply supported beam, if yielding is permitted over the lower part of the web to a depth of 20mm. (14 marks) Given: Yield stress of material = 250N/mm^2
