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July 20, 2023 at 10:07 am
Andrei Ancuta
SubscriberHello,
I am playing with a parametrical optimisation. The objective function is reducing the mass, and all the contraints are regarding the lifetime. The min lifetime that i want is 25.000. This optimisation is about a structural steel component.
The model have geometrical singularities (witch are also making a contact), so, from this point of view i decided that i should estimate the lifetime using strain-life parameters ( and i think is not very bad because 25.000 is aproximative in the limits of low cycle fatigue).
I am using the default strain-life parameters of structural steel.Â
It is clear that i need to define the plasticity of the material. I had choose the multilinear isotropic hardening approach, but it does not have default values, so i needed to chose them from literature.
So, the problem is that i do not have any ideea if the strain stress curve should be the engineering one or the real one. (or even a mixture, the engineering strain and the real stress).
I think the FEM approach should have the real curves and characteristics of the material...but i am not sure if the default values for strain-life parameters are real or engineering ones.Â
It is also for the first time when i see how is defined in ansys the low cycle fatigue behaviour.
I tried a lot of combinations on a cube model but i did not saw anything realistic.
I think the strain-life parameters are not defined in accordance with the real curve that i found in literature, maybe this is the problem and it can be for choosing a wrong material to read about(i searched for S275)
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July 24, 2023 at 11:16 am
Lydia
Ansys EmployeeHello Andrei,
If I understand correctly your problem is how to define the strain stress curve for the plasticity model. You can have a look at this course Defining a Multilinear Hardening Plasticity Model | Ansys Courses which explains all the steps that need to be followed. Â
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July 25, 2023 at 10:04 am
Oak Mound
Subscriber[quote]
Hello Andrei,
If I understand correctly your problem is how to define the strain stress curve for the plasticity model. You can have a look at this course Defining a Multilinear Hardening Plasticity Model | Ansys Coursesrocket bot royale which explains all the steps that need to be followed. Â
[/quote]
This means the material deforms irreversibly and does not return to its original shape and size, even when the load is removed, right?
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July 26, 2023 at 8:30 am
Lydia
Ansys EmployeeYes, this is the definition of plasticity
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July 24, 2023 at 12:28 pm
danielshaw
Ansys EmployeeAndrei:
If you are using the Mechanical Fatigue Tool (FT) you should not use an elastic-plastic material model. The FT performs StrainLife (EN) fatigue using elastically calculated stresses and the Neuber elastic-plastic correction method. It does not use FE calculated plastic strains.
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July 26, 2023 at 8:31 am
Lydia
Ansys EmployeeYou can also have a look at this thread /forum/forums/topic/elasto-plastic-curve-and-multilinear-isotropic-hardening/ -
July 27, 2023 at 7:59 am
Andrei Ancuta
SubscriberThank you very much for all this informations, is more than enought!
Thank you very much again!
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- The topic ‘Component fatigue behaviour’ is closed to new replies.
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