Presentation by Andreas Schleicher Tackling the School Absenteeism Crisis 30 ...
Lecture 05 som 27.02.2021
1. BIBIN CHIDAMBARANATHAN
STRESS ANALYSIS OF
BARS OF VARYING
SECTIONS
BIBIN.C / ASSOCIATE PROFESSOR / MECHANICAL ENGINEERING / RMK COLLEGE OF ENGINEERING AND TECHNOLOGY
2. STRESS ANALYSIS OF BARS OF VARYING SECTIONS
❖ Consider the following non uniform cross sections of a
member AB, BC, and CD is subjected with an axial load P
as shown in figure.
❖ The length and cross-sectional areas of each section of
bar is different and therefore stress induced, strain and
change in length too will be different for each section of
bar.
❖ Young’s modulus of elasticity of each section might be
same or different depending on the material of the each
section of bar.
❖ Axial load for each section will be same i.e. P.
❖ Determine the total change in length of the bar of
varying sections, by adding change in length of each
section of bar.
BIBIN.C / ASSOCIATE PROFESSOR / MECHANICAL ENGINEERING / RMK COLLEGE OF ENGINEERING AND TECHNOLOGY
3. STRESS ANALYSIS OF BARS OF VARYING SECTIONS
❖ P = Axial Load applied on the bar
❖ 𝐴1, 𝐴2 𝑎𝑛𝑑 𝐴3 = Area of cross section of section
1, section 2 and section 3 respectively
❖ 𝑙1, 𝑙2 𝑎𝑛𝑑 𝑙3 = Length of section 1, section 2 and
section 3 respectively
❖ 𝜎1, 𝜎2 𝑎𝑛𝑑 𝜎3 = Stress induced for the section 1,
section 2 and section 3 respectively
❖ 𝑒1, 𝑒2 𝑎𝑛𝑑 𝑒3= Strain developed for the section
1, section 2 and section 3 respectively
❖ E = Young’s Modulus of the bar
BIBIN.C / ASSOCIATE PROFESSOR / MECHANICAL ENGINEERING / RMK COLLEGE OF ENGINEERING AND TECHNOLOGY
5. 𝑇𝑜𝑡𝑎𝑙 𝐸𝑙𝑜𝑛𝑔𝑎𝑡𝑖𝑜𝑛 𝛿𝑙 = 𝛿𝑙1 + 𝛿𝑙2 + 𝛿𝑙3
𝛿𝑙 =
𝑃 𝑙1
𝐴1𝐸
+
𝑃 𝑙2
𝐴2𝐸
+
𝑃 𝑙3
𝐴3𝐸
𝛿𝑙 =
𝑃
𝐸
𝑙1
𝐴1
+
𝑙2
𝐴2
+
𝑙3
𝐴3
Let us consider that Young’s modulus of elasticity of each section is different, then the
total change in length of the bar.
𝛿𝑙 = 𝑃
𝑙1
𝐴1𝐸1
+
𝑙2
𝐴2𝐸2
+
𝑙3
𝐴3𝐸3
BIBIN.C / ASSOCIATE PROFESSOR / MECHANICAL ENGINEERING / RMK COLLEGE OF ENGINEERING AND TECHNOLOGY
6. Problem 06
A straight bar of 450 mm long is 20 mm in diameter for the first 250 mm length and
10mm diameter for the remaining length. If the bar is subjected to an axial pull of 10KN
find the extension of the bar. Take 𝐸 = 2 × 105 𝑁/𝑚𝑚2.
𝑮𝒊𝒗𝒆𝒏 𝒅𝒂𝒕𝒂:
𝑻𝒐 𝒇𝒊𝒏𝒅:
𝑙 = 450 𝑚𝑚
𝑃 = 10 𝑘𝑁 = 10 × 103 𝑁 𝐸 = 2 × 105 Τ
𝑁 𝑚 𝑚2
𝐸𝑥𝑡𝑒𝑛𝑠𝑖𝑜𝑛 𝑜𝑓 𝑡ℎ𝑒 𝑏𝑎𝑟 𝛿𝑙 =?
250 mm 200 mm
𝜑 20 𝑚𝑚 𝜑 10 𝑚𝑚
𝑃 𝑃
𝑑1 = 20 𝑚𝑚
𝑑2 = 10 𝑚𝑚
𝑙1 = 250 𝑚𝑚
𝑙2 = 200 𝑚𝑚
BIBIN.C / ASSOCIATE PROFESSOR / MECHANICAL ENGINEERING / RMK COLLEGE OF ENGINEERING AND TECHNOLOGY
7. 𝑭𝒐𝒓𝒎𝒖𝒍𝒂 ∶
𝐴𝑟𝑒𝑎 of section 1 𝐴1 =
𝜋
4
× 𝑑1
2
𝐸𝑥𝑡𝑒𝑛𝑠𝑖𝑜𝑛 𝑜𝑓 𝑡ℎ𝑒 𝑏𝑎𝑟 (𝛿𝑙) =
𝑃
𝐸
𝑙1
𝐴1
+
𝑙2
𝐴2
𝐴𝑟𝑒𝑎 of section 2 𝐴2 =
𝜋
4
× 𝑑2
2
BIBIN.C / ASSOCIATE PROFESSOR / MECHANICAL ENGINEERING / RMK COLLEGE OF ENGINEERING AND TECHNOLOGY
15. Problem 08
A member formed by connecting a steel bar to an aluminium bar shown in the figure.
Assuming that the bars are presented from buckling sideways. Calculate the magnitude of
the force ’P’ that will cause total length of the member to decrease 0.25mm. The values of
elastic modulus for steel and Al are 2.1 × 105 𝑁/𝑚𝑚2 𝑎𝑛𝑑 7 × 104 𝑁/𝑚𝑚2.
𝑮𝒊𝒗𝒆𝒏 𝒅𝒂𝒕𝒂:
𝑻𝒐 𝒇𝒊𝒏𝒅:
𝛿𝑙 = 0.25 𝑚𝑚 𝐸1 = 2.1 × 105 Τ
𝑁 𝑚 𝑚2
M𝑎𝑔𝑛𝑖𝑡𝑢𝑑𝑒 𝑜𝑓 𝑡ℎ𝑒 𝑓𝑜𝑟𝑐𝑒 𝑃 =?
𝐴1 = 5 𝑐𝑚 × 5 𝑐𝑚
𝑙1 = 30 𝑐𝑚 = 300 𝑚𝑚
𝐸2 = 7 × 104 Τ
𝑁 𝑚 𝑚2
𝑙2 = 38 𝑐𝑚 = 380 𝑚𝑚
𝐴2 = 10 𝑐𝑚 × 10 𝑐𝑚
BIBIN.C / ASSOCIATE PROFESSOR / MECHANICAL ENGINEERING / RMK COLLEGE OF ENGINEERING AND TECHNOLOGY
18. Problem 09
The bar shown in the figure subjected to a tensile load of 160 kN. If the stress in the
middle section is limited to 150 𝑁/𝑚𝑚2
, determine the diameter of the middle portion.
Find the length of the middle portion if the total elongation of the bar is to be 0.2mm.
Youngs modulus of the materials is 2.5 × 105 𝑁/𝑚𝑚2.
𝑮𝒊𝒗𝒆𝒏 𝒅𝒂𝒕𝒂:
𝑃 = 160 𝑘𝑁 = 160 × 103
𝑁
𝐸 = 2.5 × 105 Τ
𝑁 𝑚 𝑚2
𝑙 = 40 𝑐𝑚 = 400 𝑚𝑚
𝑑1 = 𝑑3 = 6 𝑐𝑚 = 60 𝑚𝑚
𝜎2 = 150 𝑁/𝑚𝑚2
𝛿𝑙 = 0.2 𝑚𝑚
𝑻𝒐 𝒇𝒊𝒏𝒅:
Diameter of the middle portion 𝑑2 =?
Length of the middle portion 𝑙2 =?
𝑙 = 𝑙1 + 𝑙2 + 𝑙3
BIBIN.C / ASSOCIATE PROFESSOR / MECHANICAL ENGINEERING / RMK COLLEGE OF ENGINEERING AND TECHNOLOGY
19. 𝑆𝑡𝑟𝑒𝑠𝑠 at section 2 𝜎2 =
𝑃
𝐴2
𝑭𝒐𝒓𝒎𝒖𝒍𝒂 ∶
𝑇𝑜𝑡𝑎𝑙 𝐸𝑥𝑡𝑒𝑛𝑠𝑖𝑜𝑛 𝑜𝑓 𝑡ℎ𝑒 𝑏𝑎𝑟 (𝛿𝑙) =
𝑃
𝐸
𝑙1
𝐴1
+
𝑙2
𝐴2
+
𝑙3
𝐴3
𝐴𝑟𝑒𝑎 of section 1 𝐴1 =
𝜋
4
× 𝑑1
2
𝐴𝑟𝑒𝑎 of section 2 𝐴2 =
𝜋
4
× 𝑑2
2
𝐴𝑟𝑒𝑎 of section 3 𝐴3 =
𝜋
4
× 𝑑3
2
BIBIN.C / ASSOCIATE PROFESSOR / MECHANICAL ENGINEERING / RMK COLLEGE OF ENGINEERING AND TECHNOLOGY