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<\/p>\nI have an issue that lets me loose hope on fatigue calculation.<\/p>\n
I have an SN Curve (Figure1) and implied it to ANSYS (figure2).<\/p>\n
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Now the calculated equivalent stress of 105MPa<\/strong> is way higher than infinite life (that starts at 80Mpa).It results in a stress maximum<\/strong> spot as can be seen in figure below.<\/p>\n <\/p>\n <\/p>\n In fatigue tool, i applied 4sec of history Data, consisting of approx5000 loadsteps, as can be seen in figure below.<\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n Since the variation is in between ~0.8-1.2*Equivalent stress, which is above<\/span><\/strong> infinite life, it should calculate valid failure but. Result always looks as below: Whole body is red, showing same number for everything. Now i noticed that i can change infinite live (red circle in 2 Pictures above) blocks and read in ANSYS help:<\/p>\n <\/p>\n “For Stress Life, another available option when cond<\/span>ucting a variable amplitude fatigue analysis is <\/span>the ability to set the value used for infinite life<\/span><\/strong><\/span>. In constant amplitude loading, if the alternating<\/span>stress is lower than the lowest alternating stress <\/span>on the fatigue curve, the fatigue tool will use the<\/span>life at the last point. This provides for an added <\/span>level of safety because many materials do not <\/span>exhibit an endurance limit. However, in non-consta<\/strong><\/span>nt amplitude loading, cycles with very small <\/span>alternating stresses may be present and may incorre<\/span>ctly predict too much damage if the number <\/span>of the small stress cycles is high enough. To help <\/span>control this, the user can set the infinite life <\/span>value that will be used if the alternating stress i<\/span>s beyond the limit of the SN curve. Setting a <\/span>higher value will make small stress cycles less dam<\/span>aging if they occur many times. The Rainflow <\/span>and damage matrix results can be helpful in determi<\/span>ning the effects of small stress cycles in your <\/span>loading history.”<\/span><\/strong><\/em><\/p>\n <\/p>\n i figured, that i can play along with that value, however, if i change it what exactly does happen? I get lower result but the min life is calculated and shown on the whole blade instead of highest stress region?<\/p>\n I have no further idea on that, since my load is above infinite load, every help is welcome!!![\"\"](\"https:\/\/us.v-cdn.net\/6032193\/uploads\/attachments\/aed83d50-43a7-4349-a233-aa1700cd6b2a\/dde9cbfd-0d10-43ab-a08e-aa5b011e6439_105mpa.jpg?width=690&upscale=false\")
<\/p>\n![\"\"](\"https:\/\/us.v-cdn.net\/6032193\/uploads\/attachments\/aed83d50-43a7-4349-a233-aa1700cd6b2a\/8a8c1ea2-254a-4c41-9a48-aa5b011edebe_signal.jpg?width=690&upscale=false\")
<\/p>\n![\"\"](\"https:\/\/us.v-cdn.net\/6032193\/uploads\/attachments\/aed83d50-43a7-4349-a233-aa1700cd6b2a\/485660d1-6e7a-4310-bd7c-aa5b011e976e_red.jpg?width=690&upscale=false\")
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