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CE302 MECHANICS OF MATERIALS Chapter 7 - Tutorial Problems

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Fifth Edition

CHAPTER MECHANICS OF
MATERIALS
7 Ferdinand P. Beer
Instructors:
E. Russell Johnston, Jr.
Prof. M. J. Al-Shannag
John T. DeWolf Transformation of Stress
Dr. Ahmet
David Tuken
F. Mazurek
Dr. Hussam Alghamdi
(Tutorial Problems)
Lecture Notes:
Dr. Saleh Aldeghaither
J. Walt Oler
Texas Tech University

These lecture notes are based largely on the slides provided


by the publisher of the text-book (i.e. McGraw Hill)

© 2009 The McGraw-Hill Companies, Inc. All rights reserved.


MECHANICS OF MATERIALS
Edition
Fifth Beer • Johnston • DeWolf • Mazurek

TUTORIAL PROBLEMS

For the state of stress shown,


determine (a) the principal planes
and the principal stresses, (b) the
stress components exerted on the
element obtained by rotating the SOLUTION:
given element counterclockwise • Construct Mohr’s circle
through 30 degrees. s x + s y 100 + 60
s ave = = = 80 MPa
2 2
R= (CF )2 + (FX )2 = (20)2 + (48)2 = 52 MPa
© 2009 The McGraw-Hill Companies, Inc. All rights reserved. 7- 2
MECHANICS OF MATERIALS
Edition
Fifth Beer • Johnston • DeWolf • Mazurek

TUTORIAL PROBLEMS

• Principal planes and stresses


XF 48 s max = OA = OC + CA s min = OB = OC - BC
tan 2q p = = = 2.4
CF 20 = 80 + 52 = 80 - 52
2q p = 67.4°
s max = +132 MPa s min = +28 MPa
q p = 33.7° clockwise

© 2009 The McGraw-Hill Companies, Inc. All rights reserved. 7- 3


MECHANICS OF MATERIALS
Edition
Fifth Beer • Johnston • DeWolf • Mazurek

TUTORIAL PROBLEMS

f = 180° - 60° - 67.4° = 52.6°


• Stress components after rotation by 30o
s x¢ = OK = OC - KC = 80 - 52 cos 52.6°
Points X’ and Y’ on Mohr’s circle that s y¢ = OL = OC + CL = 80 + 52 cos 52.6°
correspond to stress components on the
t x¢y¢ = KX ¢ = 52 sin 52.6°
rotated element are obtained by rotating
XY counterclockwise through 2q = 60° s x¢ = +48.4 MPa
• Please note that s y¢ = +111.6 MPa
t x¢y¢ = 41.3 MPa

© 2009 The McGraw-Hill Companies, Inc. All rights reserved. 7- 4


MECHANICS OF MATERIALS
Edition
Fifth Beer • Johnston • DeWolf • Mazurek

TUTORIAL PROBLEMS

© 2009 The McGraw-Hill Companies, Inc. All rights reserved. 7- 5


MECHANICS OF MATERIALS
Edition
Fifth Beer • Johnston • DeWolf • Mazurek

TUTORIAL PROBLEMS

© 2009 The McGraw-Hill Companies, Inc. All rights reserved. 7- 6

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