Conventional stress-strain curves generated in engineering units can be converted to true units for inclusion in simulation software packages.Knowing a material’s true stress-strain curve is essential for performing a nonlinear finite element analysis to solve an elastoplastic problem. Although sample dimensions are challenging to measure during a tensile test, there are equations that relate engineering units to true units. True stress and true strain provide a much better representation of how the material behaves as it is being deformed, which explains its use in computer forming and crash simulations. Stress-strain curves and associated parameters historically were based on engineering units, since starting dimensions are easily measured and incorporated into the calculations. The method by which this test is performed is covered in ISO 16808. Optical measuring systems based on the principles of Digital Image Correlation (DIC) are used to measure strains. Biaxial bulge testing has been used to determine stress-strain curves beyond uniform elongation. Inaccuracies are introduced if the true stress-true strain curve is extrapolated beyond uniform strain, and as such a different test is needed. True stress-strain curves obtained from tensile bars are valid only through uniform elongation due to the effects of necking and the associated strain state on the calculations. Where true stress = σ true strain = ε, n is the n-value (work hardening exponent or strain hardening exponent), and the K-value is the true stress at a true strain value of 1.0 (called the Strength Coefficient). True stress – true strain curves of low carbon steel can be approximated by the Holloman relationship:
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |