( 15%) Two identical, smooth and flat steel plates are bolted together with a si
ID: 1766718 • Letter: #
Question
( 15%) Two identical, smooth and flat steel plates are bolted together with a single bolt. The assembly is subject to a separating force that fluctuates between zero and PThe bolt has a diameter (measured across the threads) of ½ in, and the head has a marking as shown in the figure below. Bolt threads extend only slightly above the nut and the bolt shank has a diameter of ½ in over its entire length. Also the bolt has been identified as having cut threads 2. a What is the minimum proof strength of the bolt? b. For a coarse thread, what would be the pitch of this bolt? c. What is the ensile stress area of the bolt? d. What is the fatigue stress concentration factor for the bolt? e. Calculate the bolt stiffness. f Calculate the clamped member stiffness. fluctuating fluctuating loed Applied loading to part 2 inExplanation / Answer
A.) Proof load is typically between 85-95% of the yield strength
SAE J429 Medium Carbon Steel, Q & T
Take the minimum yield in psi of the ASTM grade
Ymin=92 Ksi.
Proof Load=85 KSI
B)
coarse Thread Series – UNC-Basic Pitch Dia.:- 0.4500 In.
C.)
At =Tensile strength Are of Screw Therad
D=Basic Majr Dia (Thread engg Chart)
D=0.45 Coarse Thread Series – UNC.
N=No. Thread per inch.
At=8.4467 Ksi
At=0.05823 GPA
D) Clamped Stiffness
Kt=AtE/Lt
overall thread length ( LT )=2 Inch==0.0508 mtr
At = tensile-stress area of the fastener=0.05823
E = elastic modulus of the bolt material, 207 GPa
=237.275 GPA/mtr
The stiffness in the unthreaded region of a fastener is given by
Kd=AdE/Ld
Ad = major-diameter cross-sectional area of the fastener===0.1257 Inch.==8.1 * 10^-5
l = length of the unthreaded portion in the grip====NOT Given (Assumed =3/4”)
=(8.1* 10^-5*207)/(0.01875)
=0.89424 Gpa/Mtr===1.182
=1.186 Gpa/Mtr
E.) The bolt stiffness must also be considered Kb= (Ad*At*E)/(AdLt+AtLd)
=0.000976/(0.0000041+.00109)====0.89213 GPA /mtr
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