I don't understand the nuance between yield strength and tensile strength. In my case, I have a stainless steel with a yield strength of 950 N/mm² and a tensile strength of 30 N/mm². (The tensile strength = compression limit for metals.)
In compression, I apply an imposed displacement on the material, and I observe the stresses. Does this mean that if I exceed 30 N/mm², there is deformation and below that there is no deformation? As long as the elastic limit is not exceeded, the material returns to its shape when the force is no longer there?
In my simulation, I get 54 N/mm², which means I have deformations because the compressive limit > 30 and the elastic limit not reached so we are in the elastic domain?
I found 54 N/mm² for an imposed displacement of 1mm so I should decrease this displacement to stay below < 30, right? My goal is not to break the material but to find the force exerted for the displacements so 1mm is much too big?
The elastic limit is the stress limit at which we leave the elastic domain of the material, i.e. the material will not return to its initial position after stress but will retain a residual value of deformation
Of course, you must not reach the elastic limit and you must take into account a safety factor
I don't know where you could have found such values!
As a general rule, for steels, the elastic limit is considered to correspond to the tensile or compressive limit, which is not the case, for example, for resilient materials (cast iron, concrete, etc.).
For example in compression, I apply an imposed displacement on the big cylinders at the top of 5mm and we get max stress of 43.5 N/mm² which > 30 so is there a break?
This max constraint is the whole part or just the pins?
POM large cylinder materials: tensile strength 71.5 N/mm² and elastic lim not indicated
Small cylinder stainless steel materials: tensile strength 30 N/mm² and elastic limb 950 N/mm²
If you want to be sure that your material resists, you need to take your yield strength value and divide it by a safety coefficient (2 for common cases).
If you want to "break" your material, you have to exceed your limit in traction.
I don't want to "break" my material, I want to stay in the elastic domain. My goal is to know the force exerted to make my piece move by 1mm, 2mm, etc ... without breaking my piece of course
Be careful , the tensile limit or more generally resistance does not mean rupture (excuse me) but indicates the beginning of the contraction, which means that we enter the plastic zone that will end with the rupture (breaking moment quite difficult to determine by the way, depends in particular on the tensile speed, etc...).
The Simu PEF remains in the elastic domain but says nothing about the plastic domain except to indicate that you are getting closer or that you are already at the limit of the elastic or that you are getting closer to it.
Be careful not to confuse tensile testing with compression.
The normal tensile stress (the Greek letter Sigma lowercase) equal to the force (N) by the cross-section (mm² or m²).
If we want the part to resist for sure, this stress must be smaller than the elastic resistance (Re) that we have in the graph that @A.Combier has put.
Rp = Re/s is generally used, where s is a safety factor varying from 2 to 5 for steels.
I think that the values of the custom material have been changed and there is an error, the tensile strength is very low for stainless steel and must be greater in any way than the elastic limit. Check by looking at the values of other non-customized stainless steels.
You say """ My objective is to know the force exerted to make my 1mm, 2mm piece, etc ... without of course breaking my coin"""
In your case, what matters is the distance between the fixed point of the spindle and the tangent of the big cylinder The longer the spindle, the more flexing it will be. If it's less than three mm, then you're getting into shear instead, which would be another calculation.
In your case, your pin is relatively long, so there is no chance that you will reach the yield limit, especially since for the test, your tibia is made of POM and it is the one that will go to hell well before the stainless steel (if I have followed correctly what you want to do).
POM has nothing to do with the resistance of a tibia but that's another subject.
Hello, while changing the materials of the pins, a problem appears. I get a force of 444 N for 1mm imposed, it's just impossible, put 44 Kg to move 1mm, it's incoherent. The same goes for the constraints that exceed the elastic limit of the sudden. See attached
