olts installed on a production line are tightened with automatic wrenches. They are to be tightened sufficiently to yield the full cross section in order to produce the highest possible initial tension. The difficulty encountered is bolt heads shearing off 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 exert a standard deviation of 2.0 Nm of LOAD. What mean value of wrench torque setting would result in only 1 bolt in 100 shearing off during assembly? What is the safety margin, and the reliability per load application (5 marks) What mean value of wrench torque setting would result in only 1 bolt in (150+YZ) bolts shearing off during assembly? What is the safety margin, and the reliability per load application (5 marks) A cheaper wrench is available, but with higher variation - standard deviation of the torque wrench setting is 5 Nm. What is the mean value of torque wrench setting corresponding to one bolt in (150+YZ) bolts shearing with this cheaper wrench?