Model Steel for Large Deformation: Multilinear Isotropic Hardening

In summary, the conversation discusses the use of Multilinear Isotropic hardening to model steel for large deformations beyond the yield point. The speaker is unsure whether to use stress vs total strain or stress vs plastic strain, and is seeking clarification on which values to use. They clarify that they are attempting to simulate a 4 point bending test and are confused about the material modeling aspect. They also ask a question about the presence of two yield points in a stress-strain curve and the difference between engineering and true strain. The expert then explains that the difference between engineering and true strain becomes significant when phenomena like tensile necking occur, and in normal engineering structures, plastic analysis is conducted as a transition from linear-elastic to full plastic. The
  • #1
RKD89
78
1
I am trying to do a problem on Material Non-linearity , to model steel for large deformation , beyond yield point ,
I have tensile testing data for the steel ( in form of Engineering stress vs Engineering strain).

for defining the model , I chose Multilinear Isotropic hardening
now there are 2 options
stress vs total strain & stress vs Plastic strain

Which option should I choose ( I was asked to choose Stress vs Plastic strain )
Also , what values should I use ? Engineering stress , Engineering Plastic strain (engineering strain - engineering stress/youngs modulus ) ;
or True stress and true strain values ( I know how to calculate them )

can anyone clarify?

Also , to make it clear , I am trying to simulate a 4 point bending test , I know how to do contact analysis etc , I am only confused about the material modelling part
 
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  • #2


Sir, since you are concerned with the field of material science, may I ask a question in that regards??

I wanted to know why are there two yield points in a stress strain curve ?
 
  • #3


The difference between engineering strain and true strain only becomes significant when phenomena such as tensile necking occur.

In normal engineering structures plastic analyis is conducted as a transition from linear-elastic to full plastic and the resulting stress block deduced, often as the formation of a plastic hinge. In this type of analysis the strain remains small and limited by elastic engineering considerations.
 
  • #4


thnksss...but i was asking about the upper and lower yield points...the case of true engineeriing stress-strain curve and normal stress-strain curve arises only after the ultimate failure stage...
can you tell something regarding the reason as to why there are two yield points, upper and lower??
 

1. What is the purpose of using multilinear isotropic hardening in model steel for large deformation?

Multilinear isotropic hardening is used to accurately model the behavior of steel under large deformations, such as in the case of plastic deformation or structural failure. It takes into account the non-linear stress-strain relationship of steel, which is important in accurately predicting the behavior of steel structures under extreme loading conditions.

2. How does multilinear isotropic hardening differ from other hardening models?

Multilinear isotropic hardening differs from other hardening models in that it considers the isotropic hardening behavior of steel, which means that the material's strength and stiffness increase in all directions equally as it is subjected to increasing levels of stress. This is in contrast to kinematic hardening models, which only consider the increase in strength and stiffness in the direction of loading.

3. What are the key parameters used in multilinear isotropic hardening?

The key parameters used in multilinear isotropic hardening include the initial yield stress, the strain hardening coefficient, and the saturation stress. These parameters are used to define the stress-strain relationship of the material and can be determined through experimental testing or by using data from existing material databases.

4. How is multilinear isotropic hardening implemented in numerical simulations?

In numerical simulations, multilinear isotropic hardening is typically implemented through user-defined material models in finite element analysis software. The parameters of the model are defined based on the material properties of the steel being used, and the model is then applied to the structural elements in the simulation to accurately predict their behavior under large deformations.

5. What are the limitations of using multilinear isotropic hardening in modeling steel for large deformations?

One of the main limitations of using multilinear isotropic hardening is that it requires accurate and complete material data, which can be difficult to obtain for certain types of steel. In addition, the model may not be able to accurately capture the behavior of steel under extreme loading conditions, such as those encountered in high-velocity impacts or explosions. It is important for scientists and engineers to carefully select and validate their material models to ensure accurate predictions in their simulations.

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