![]() One of the key responsibilities of an engineer is to understand the limitations of the method of analysis he has selected. Let’s begin with a brief refresher on how to properly perform basic fatigue calculation using a single widely applicable method. In a short series of articles starting with this one, I will cover the basics of fatigue analysis in several categories. Luckily, the process of performing proper fatigue calculations can be at least partially automated allowing for ease of use and reducing calculation errors. This, in fact, is a requirement, not an option, in guarding against the possibility of a fatigue failure.” “As noted previously, it is always good engineering practice to conduct a testing program on the materials to be employed in design and manufacture. The bottom line is that fatigue calculations performed on a preliminary basis can provide a good estimate of expected product life but physical testing is the only way to precisely determine a cycle life. Standard methods of calculation have been developed in an attempt to simplify the situation but these simplifications come at the expense of precision. Fatigue life has been found to depend on manufacturing methods, shape, loading style, cycles count, and many other conditions. For example, a surface defect on a shaft may act as a fatigue initiation site under high-cycle loading but would make no difference under static loading. The manner in which fatigue initiates and propagates is sensitive to more variables than that of static failure. There is more than ample motivation to take the time to complete proper fatigue calculations in design.įatigue calculations are more nuanced than static structural analysis and less precise. ![]() Further, the manner in which fatigue failures occur is typically sudden and without warning, making them often more dangerous than static failures. However, this is unfortunate as many people estimate that as much as 90% of all mechanical failures occur due to fatigue. This may be due to a number of factors but I think it’s mostly due to the less precise nature of fatigue and the sometimes-messy calculations required to predict it. Many engineers will shy away from fatigue calculations if they can, opting to do simple static analysis and making what is presumably a large enough static factor of safety to “cover” fatigue. Mechanical structures can fail for a variety of reasons, one of which is by “fatiguing” which is what happens when a structure fails from repeated loading even though it was strong enough to handle a singular load of the same magnitude. Engineering calculations come in many flavors and must be carried out in a way that accurately describes the real-world situation.
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