This discussion focuses on determining whether a shaft subjected to fluctuating loads has finite or infinite life, emphasizing the role of material properties in this assessment. It is established that steel can exhibit infinite life below a specific stress amplitude, while other materials may behave differently. The concept of damage tolerance is introduced, where initial crack lengths are considered to calculate cycles to failure using appropriate crack growth laws. The discussion clarifies that "infinite life" in engineering refers to the absence of microscopic cracking under certain stress conditions, rather than an absolute absence of failure.
PREREQUISITESMechanical engineers, materials scientists, and anyone involved in the design and analysis of components subjected to cyclic loading will benefit from this discussion.
Yea, infinite life has a specific meaning in engineering when the term is used in relation to stresses in materials. Imagine putting stress on a beam by supporting the two ends and putting a weight in the middle. Imagine the stress being much less than yield so when you remove the weight, the beam springs back to where it originally was. Now imagine putting that weight on and taking it off millions of time. You might think the beam would bend a little and spring back just like it did originally, and that it would do that no matter how many times you applied the weight. But that isn't what necessarily happens. If the weight puts more stress on the beam than a given amount, microscopic cracks can develop, and after many millions of cycles, the beam could break all the way through. If the weight isn't enough to cause this microscopic cracking, you can essentially apply the weight as many times as you want and it won't break (ie: it has infinite life).Danger said:
Q_Goest said:
