Question 2 8 Marks Bolts Installed On A Production Line Are Tightened With Automatic Wrenches They Are To Be Tightene 1 (70.05 KiB) Viewed 39 times
Question 2 8 Marks Bolts Installed On A Production Line Are Tightened With Automatic Wrenches They Are To Be Tightene 2 (56.81 KiB) Viewed 39 times
Question 2 (8 marks) Bolts installed on a production line are tightened with automatic wrenches. They are to be tightened sufficiently in order to produce the highest possible initial tension. The limiting condition is shearing off the bolts during assembly. Strength and load are normally distributed according to the following: The bolts have a mean shear-off strength of 20 Nm with standard deviation of 1.5 Nm. The automatic wrenches have a standard deviation of 2.0 Nm. What mean value of wrench torque setting (i.e. mean load) would result in 1 bolt in 150 shearing off? (hint- use this to reverse lookup; single cycle reliability is 99.33%) What mean value of wrench torque setting would result in an estimated 1 bolt in 250 shearing off? (same hint- single cycle reliability is 99.6%) (3 marks)
Calculate the safety margin for both torque settings. (2 marks) A cheaper wrench is available, but with higher variation - standard deviation of the torque wrench setting is 6 N m. What is the mean value of torque wrench setting corresponding to one bolt in 150 shearing with this cheaper wrench? (3)
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