The Yield Strength (YS) of a material is the stress required to permanently deform a material to a discernible extent ( in the case of ductile materials, it is o.2% proof stress, while, the Ultimate Tensile Stength (UTS) is the maximum stress load capacity the material can take up in uniform elongation.
Ductile materials with low yield strength can have high tensile strength (eg., AISI 304 steel for which yield strength is around 170 MPa while ultimate tensile strength id 580 to 620 MPa).
Brittle materials may have tensile strength nearly equal to to yield strength (like polymer and ceramic materials which have low ductility).
Therefore, the ratio of the UTS to the YS is a function of ductility of a material or the work hardening exponent.Materials with high work hardening exponent will have the UTS which is much higher the YS. When the work hardening exponent is 0. 29, the UTS is double that of the YS.
When the work hardening exponent is zero, the UTS is equal to the YS. In other words, the material behaves in an elastic- rigidly plastic way.
In short, there is no relation between YS and UTS without linking work hardening exponent.
Please do not hesitate to ask for any clarification.
The work hardening is major factor which affects the UTS after YS. The work hardening totally depends on phase transformation during deformation such as austenite to martensite transformation, matrix or presence of hard phase/constituents in the alloy matrix, such as Ti, V, or Intermetallic phases which pins the dislocation movement during deformation. Therefore, it may be difficult to directly correlate the UTS to YS.
I think through hardness (Vicker's and Brinell's) Measurements we could arrive easily at Yield Strength and Ultimate Tensile Strength.
Tensile strength can be roughly estimated by multiplying 3.45 and Brinell hardness.
Yield strength can be roughly estimated by dividing 3.00 with Vickers hardness.
thanks & regards,
G. Sudhakar,phd(materials engg),hcu.
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