Hello ,
I am currently working on a project for simulation of uniaxial compression test of Impax700 engineering foam material at -40°C.I have some questions and i would really appreciate if you can help me. I use volumetric hardening model and my values for
k=1.1
kt=0.1
for elasticity young modulus=45 and poisson ratio is neglegted and equal to 0 .
Dimension of cube = 100*110*103mm
Mesh size=10mm
Deplacement=-100mm at Y direction
at simulation I have good elastic form but for plastic part , the problem is , untill 50mm it is exactly same as real result but after it starts densification part 20 mm earlier then real result. I think the problem is foam hardening input. Abaqus ask yield stress and plastic strain values. However i couldnt find clear information at documentation of Abaqus and I made some research and i found some crushable foam models from some article.
First article entered the values of true stress and volumetric logarithmic plastic strain. Here is the formules
true stress=nominal stress * (1+ nominal strain)
true strain=LN(1+nom strain)
plastic strain= true strain - (yield stress/young modulus)
volumetric logharitmic plastic strain= ln(1+plastic strain)
for this model, i put true stress values and logharitmic strain values but the results are with true stress with 2 times higher stress values and i have still this 20mm difference. But the article has been written in 2006 so i think Abaqus changed the input demande.
Second formule from another article,
true stress= nom stress / (1-poisson ratio*nom strain )^2
Plastic Strain = nom strain - (true stress/ young modulus)
Since I neglegted the poisson ratio true stress= nom stress . But plastic strain values starts to decrease after 3.5MPa stress values. And i cant enter those values to Abaqus cause since they decrease , abaqus doesnt accept logically.
So I am not sure which formule i have to use and which values i have to put for input of foam hardening.I attached the stress-strain graphe of real result with the simulation model based on second formulation.I would really apreciate for any help .
Thanks
I am currently working on a project for simulation of uniaxial compression test of Impax700 engineering foam material at -40°C.I have some questions and i would really appreciate if you can help me. I use volumetric hardening model and my values for
k=1.1
kt=0.1
for elasticity young modulus=45 and poisson ratio is neglegted and equal to 0 .
Dimension of cube = 100*110*103mm
Mesh size=10mm
Deplacement=-100mm at Y direction
at simulation I have good elastic form but for plastic part , the problem is , untill 50mm it is exactly same as real result but after it starts densification part 20 mm earlier then real result. I think the problem is foam hardening input. Abaqus ask yield stress and plastic strain values. However i couldnt find clear information at documentation of Abaqus and I made some research and i found some crushable foam models from some article.
First article entered the values of true stress and volumetric logarithmic plastic strain. Here is the formules
true stress=nominal stress * (1+ nominal strain)
true strain=LN(1+nom strain)
plastic strain= true strain - (yield stress/young modulus)
volumetric logharitmic plastic strain= ln(1+plastic strain)
for this model, i put true stress values and logharitmic strain values but the results are with true stress with 2 times higher stress values and i have still this 20mm difference. But the article has been written in 2006 so i think Abaqus changed the input demande.
Second formule from another article,
true stress= nom stress / (1-poisson ratio*nom strain )^2
Plastic Strain = nom strain - (true stress/ young modulus)
Since I neglegted the poisson ratio true stress= nom stress . But plastic strain values starts to decrease after 3.5MPa stress values. And i cant enter those values to Abaqus cause since they decrease , abaqus doesnt accept logically.
So I am not sure which formule i have to use and which values i have to put for input of foam hardening.I attached the stress-strain graphe of real result with the simulation model based on second formulation.I would really apreciate for any help .
Thanks