The uniform strain is often useful in estimating the formability of metals from the results of a tension test. (1) should only be used until the onset of necking. (1) assumes both constancy of volume and a homogenous distribution of strain along the gage length of the tension specimen. It may be calculated from either the specimen cross-sectional area A u or the gage length L u at maximum load.Įquation (3) may be used to convert conventional uniform strain to true uniform strain. The true stress is expressed in terms of engineering stress s by (1) The derivation of Eq. The true uniform strain e u is the true strain based only on the strain up to maximum load. However, for cylindrical tensile specimens the reduction of area q is related to the true fracture strain by the relationship (3) is not valid beyond the onset of necking, it is not possible to calculateĮ f from measured values of e f. This parameter represents the maximum true strain that the material can withstand before fracture and is analogous to the total strain to fracture of the engineering stress-strain curve. The true fracture strain e f is the true strain based on the original area A 0 and the area after fracture A f
Since the data required for this correction are often not available, true-fracture-stress values are frequently in error. This stress should be corrected for the, triaxial state of stress existing in the tensile specimen at fracture.
This therefore results in the tensile strain data going up to 2 strain then no further data is. The tensile strain data only goes up to 2 strain due to limitations of the extensometer. I am however looking for True Stress/Strain values to input in to ANSYS. The true fracture stress is the load at fracture divided by the cross-sectional area at fracture. These are Engineering Stress/Strain values provided by our testing house (raw data). The ultimate tensile strength is given by Let s u andĮ u denote the true stress and true strain at maximum load when the cross-sectional area of the specimen is Au. For most materials necking begins at maximum load at a value of strain where the true stress equals the slope of the flow curve. True strain is the natural logarithm of the ratio of the instantaneous gauge length to the original gauge length. True stress is determined by dividing the tensile load by the instantaneous area. The true stress true strain curve gives an accurate view of the stress-strain relationship, one where the stress is not dropping after exceeding the tensile strength stress level. The true stress at maximum load corresponds to the true tensile strength. At any load, the true stress is the load divided by the cross-sectional area at that instant.