Suppose that the fatigue data for the steel alloy in Problem 9.12 were taken for bending-rotating tests, and that a rod of this alloy is to be used for an automobile axle that rotates at an average rotational velocity of 600 revolutions per minute. Give the maximum lifetimes of continuous driving that are allowable for the following stress levels: (a) 450 MPa (65,000 psi), (b) 380 MPa (55,000 psi), (c) 310 MPa (45,000 psi), and (d) 275 MPa (40,000 psi). Reference: Problem 9.12 is listed below (only use for reference but does not need to be solved). The tensile strength of brittle materials may be determined using a variation of Equation 9.1. Compute the critical crack tip radius for an Al2O3 specimen that experiences tensile fracture at an applied stress of 275 MPa (40,000 psi). Assume the acritical surface crack length of 2 x 10-3 mm and theoretical fracture strength of E/10, where E is the modulus of elasticity.
Design Against Fluctuating Loads
Machine elements are subjected to varieties of loads, some components are subjected to static loads, while some machine components are subjected to fluctuating loads, whose load magnitude tends to fluctuate. The components of a machine, when rotating at a high speed, are subjected to a high degree of load, which fluctuates from a high value to a low value. For the machine elements under the action of static loads, static failure theories are applied to know the safe and hazardous working conditions and regions. However, most of the machine elements are subjected to variable or fluctuating stresses, due to the nature of load that fluctuates from high magnitude to low magnitude. Also, the nature of the loads is repetitive. For instance, shafts, bearings, cams and followers, and so on.
Design Against Fluctuating Load
Stress is defined as force per unit area. When there is localization of huge stresses in mechanical components, due to irregularities present in components and sudden changes in cross-section is known as stress concentration. For example, groves, keyways, screw threads, oil holes, splines etc. are irregularities.
Question:
Suppose that the fatigue data for the steel alloy in Problem 9.12 were taken for bending-rotating tests, and that a rod of this alloy is to be used for an automobile axle that rotates at an average rotational velocity of 600 revolutions per minute. Give the maximum lifetimes of continuous driving that are allowable for the following stress levels: (a) 450 MPa (65,000 psi), (b) 380 MPa (55,000 psi), (c) 310 MPa (45,000 psi), and (d) 275 MPa (40,000 psi).
Reference:
Problem 9.12 is listed below (only use for reference but does not need to be solved).
The tensile strength of brittle materials may be determined using a variation of Equation 9.1. Compute the critical crack tip radius for an Al2O3 specimen that experiences tensile fracture at an applied stress of 275 MPa (40,000 psi). Assume the acritical surface crack length of 2 x 10-3 mm and theoretical fracture strength of E/10, where E is the modulus of elasticity.
Trending now
This is a popular solution!
Step by step
Solved in 3 steps
