Machine Design test on “Eccentric Loaded Perpendicular to axis of Bolt”.
For questions 1-7.
The following data is given for bracket
P=20kN, e=100mm, S(yt)=400N/mm², FS=3
1. Find the direct shear stress in bolts if diameter =18mm
a) 16.9N/mm²
b) 19.6 N/mm²
c) 78.6 N/mm²
d) 76.8 N/mm²
Answer: b
Clarification: Direct shear stress=one fourth of P/A.
2. If distance between the bolts from the axis of tilting is 125mm and 25mm, then find the effective tensile force acting on the bolts lying at 125mm from tilting axis.
a) 6765.2N
b) 8798.2N
c) 7692.3N
d) 7962.11N
Answer: c
Clarification: Tensile force=Pe x 125/2(125²+25²).
3. If distance between the bolts from the axis of tilting is 125mm and 25mm, then find the effective tensile force acting on the bolts lying at 25mm from tilting axis.
a) None of the listed
b) 7692.3N
c) 2345.2N
d) 1538.46N
Answer: d
Clarification: Tensile force=Pe x 25/2(125²+25²).
4. Which bolt can be used as criteria for designing?
a) Left top bolt
b) Both top bolts
c) Left bottom bolt
d) Both bottom bolt
Answer: b
Clarification: The bolts farthest from the tilting axis are under the maximum tensile force.
5. Find the principal shear stress in the top bolts in terms of area A?
a) None of the listed
b) 5309.2/A
c) 6308.2/A
d) 6980.4/A
Answer: c
Clarification: Shear Stress in one bolt=5000/A and tensile stress in upper bolt=7692.3/A. τ(max)=√[(σ/2)²+ τ²].
6. Find the size of the bolt using maximum shear stress theory.
a) 11mm
b) 12mm
c) 13mm
d) 14mm
Answer: a
Clarification: 400 x 0.5/3 =6308.2 x 4 /πd².
7. Find the size of the bolt using maximum principal stress theory.
a) None of the listed
b) 19.2mm
c) 15.3mm
d) 21.2mm
Answer: b
Clarification: σ(max)=σ/2 + √[(σ/2)²+ τ²]=10154.35/A = 35N/mm².
For questions 8-13
A wall bracket is attached to the wall by means of 2 identical bolts, one at A and one at B. The force of 20kN acts at a distance of 400mm. Bolt A lies at a distance of 50mm from axis of tilt and bolt B 500mm.
Allowable shear stress in the bolts is 100N/mm² and tensile is 40N/mm².
8. Which bolt is used a criterion for designing?
a) A
b) B
c) A or B
d) None of the listed
Answer: b
Clarification: The bolt lying farthest from the axis of tilt experience the maximum stress.
9. Find the effective tensile force acting in the two bolts.
a) Bolt B=792.07N & Bolt A=792.07N
b) Bolt B=792.07N & Bolt A=7920.8N
c) Bolt B=7920.8N & Bolt A= 792.07N
d) Bolt B=7920.8N & Bolt A=7920.8N
Answer: c
Clarification: F₁=Pel₁/2(l₁² + l₂²) and F₂= Pel₂/2(l₁² + l₂²).
10. Find the radius of Mohr circle which can be made from the shear stress and tensile stress acting on bolts.(Consider bolt under max stress and area of bolt is A)
a) 10000/A N/mm²
b) 6378.5/A N/mm²
c) 10755.7/A N/mm²
d) None of the listed
Answer: b
Clarification: r=√(σ/2)²+ τ² where σ=7920.8/A and τ=20000/4A.
11. Find the ratio of the effective tensile load to which the two bolts are subjected.
a) 1
b) 10
c) 12
d) 8