{"id":643,"date":"2010-06-04T19:29:36","date_gmt":"2010-06-04T23:29:36","guid":{"rendered":"https:\/\/example.org\/applying-dead-loads-to-fatigue"},"modified":"2010-06-04T19:29:36","modified_gmt":"2010-06-04T23:29:36","slug":"applying-dead-loads-to-fatigue","status":"publish","type":"post","link":"https:\/\/blogs.solidworks.com\/solidworksblog\/2010\/06\/applying-dead-loads-to-fatigue.html","title":{"rendered":"Applying dead loads to fatigue"},"content":{"rendered":"

I was recently asked how to apply a dead load in a fatigue study (a none varying load that is applied to a structure all of the time, as opposed to a live or dynamic load that generates an alternating stress).<\/p>\n

The diagram below shows the definition of alternating stress (or stress amplitude) and mean stress, both of which are important in influencing the lifetime of a material.<\/p>\n

\"image\"<\/a> The normal inputs to a fatigue study are the stress amplitudes, but as you can see in the next picture, mean stresses also have an impact on the lifetime of a material. The higher the mean stress, the lower the predicted lifetime.<\/p>\n

\"image\"<\/a>Dead loads are not alternating but do contribute to the mean stress, so it is important that we can consider them in a fatigue study. But how do we do this?<\/p>\n

Alternating load only case<\/u><\/b><\/p>\n

In a normal fatigue study, the method takes the max stress, Smax<\/sub> from a static study loadcase and we use the loading ratio (R = Smin<\/sub>\/Smax<\/sub>) to define Smin<\/sub> directly. <\/p>\n

\"image\"<\/a> <\/p>\n

For example,<\/p>\n