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Mechanical Engineering


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  1. Good morning to all, I have some questions regarding car chassis. Reading the articles I seem to have understood that the design requires that the normal use strain always remain well below the frame fatigue limit. Could someone explain me how this fatigue limit is calculated? I mean, are spot welds taken into account in addition to the plates? on the web I didn't find much about it, just some tests on heavy vehicles and kerbs/ potholes. Thanks
  2. Thanks for the answer, i have another questions please, about stress relaxation and fatigue limit: What about stress relaxation? Is also an ambient temperature phenomenon that can affect a car chassis or is nothing like that? from what I've read, there is a stress value below which the steel does not record damage and can therefore be folded indefinitly. from some tests performed with modern test machines that are able to overcome the "old" cycle threshold it has been discovered that in reality the fatigue limit does not exist, exceeded a certain number of cycles the piece will begin to have fractures even if it has always worked below the fatigue limit. What do you think about it? Does this fatigue limit for steel exist or not? thanks
  3. Speaking of cars, in particular of the chassis, if we keep a car stopped for years, will the weight of the engine and all the components form cracks in the crystalline microstructure of the iron? if we think about a spring, if we leave it compressed for so long it will lose its ability to flex, it will not come back as before (i guess), isn't it the same for a frame that has to hold up an engine for years? perhaps there is a load limit below which the piece will return as before also being compressed for many years? What happens to the metal microstructure in these cases? Correct me if I'm wrong. if the weight of the motor has been designed to keep the deformation of the underlying frame always in the "elastic" and not "plastic" area, how can it damage the metal in the absence of external environmental attacks? thanks
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