Volume 14.5
See You At
Simulation Tip
Interpreting Tensile Strength in the True Stress-Strain Environment
Most finite element analyses (FEA) use true (Cauchy) stress-strain for
presentation of material data to the simulation. On the other hand, testing
of materials traditionally uses an engineering stress-strain basis. 
This tradition is rigidly enforced via the use of test standards from
international bodies such as ASTM and ISO. Care must be taken in the use of reportable's such as tensile strength at yield and break, and their
corresponding strain values in the true stress-strain environment. These
properties continue to be reported in an engineering stress-strain basis, as
required by the standards. Unless otherwise noted, all such data available
from databases, handbooks, the internet or other sources will be based on
this tradition. FEA users of such properties may wish to convert these data
to true form prior to using them to describe the von Mises stress or other
analogous FEA yield criteria. The equations for conversion are the same as those used to convert stress-strain data. Obviously, variation between the two are most noticeable with non-metals such as plastics where significant strain is incurred prior to yield. Modulus calculations are not affected because these take place in the initial linear region of the stress-strain curves, thus producing a one to one relation between true modulus and engineering modulus.
Partner Show Case: Abaqus
  • FeFp material model, True modeling of plastics behavior is possible with the FeFp material model by Abaqus . This material model is able to capture the non-linear elastic behavior of the plastic as well as the development of plastic strain as the material goes beyond its elastic limit. The FeFp model can be calibrated by performing the tests described in the following TestPak available from DatapointLabs. For details read the Paper.
  • Validated visco-elastic material model, Visco-elastic material models give powerful predictive capability to FEA. The models must be implemented carefully because there are so many ways in which to present the data to the Abaqus simulation. The manner of presentation is dependent on the use case, among other things. 
    To ensure that the model is working properly and does indeed represent the raw material master curve DatapointLabs now offers a closed loop validation of the material model. A simulation of the actual experiment is carried out and the results of the simulation are compared to the tests data. A close correlation indicates a higher degree of confidence that the material model indeed reflects the experimental material data. 
  • Non-linear NVH modeling, a newly showcased feature of 
    Abaqus FEA from SIMULIA, allows for more precise simulation of systems that contain rubber bushings, gaskets and other hyper elastic elements. These components, though small in size relative to the entire structure, can have a large damping effect in NVH simulations. Modeling these materials requires their non-linear visco-elastic properties. These properties can be tested at DatapointLabs with the following TestPak. Data are provided in Abaqus-ready digital format.
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