The image above shows a hydraulic cylinder that pushes a heavy tool during the o
ID: 2996059 • Letter: T
Question
The image above shows a hydraulic cylinder that pushes a heavy tool during the outward stroke, placing a compressive load of 400 lb in the piston rod. During the return stroke, the rod pulls on the tool with a force of 1500 lb.
a) Compute the resulting design factor of safety for the 0.60-in-diameter rod when subjected to this pattern of forces for many cycles. The material is SAE 4130 WQT 1300 steel.
b) If the resulting design factor is much different from 4.0, determine the size of rod that would produce N = 4.0.
Explanation / Answer
a) SAE 4130 upon cyclic loading for >1000 cycles has a maximum allowable stress of ~300MPa.
Maximum stress generated here = 1500 lb /(pi * 0.3*0.3 in2) = 36.58 MPa
Hence, factor of safety = Max allowable stress/ max stress generated = 8.2
b) For a factor of safety of 4, max stress generated = 300MPa/4 = 75MPa
Thus, 1500 lb /(pi * r2) = 75MPa
Hence, r = 0.00532m = 0.2094 inches
Hence diameter = 0.4192 inches ~ 0.42 inches
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