can you please explain, what does " minimum 0.2 percent proof stress or yield stress, in N/mm2" explains?? in simple words to understand.High Strength Deformed bars in strength grades Fe 500, Fe 500D and Fe 500S are specified in the fourth revision of IS 1786:2008 (High strength deformed steel bars and wires for concrete reinforcement – Specification). The figures following the symbol Fe indicate the specified minimum 0.2 percent proof stress or yield stress, in N/mm2. The letters D and S following the strength grade indicates the categories with same specified minimum 0.2 percent proof stress/yield stress but with enhanced and additional requirements.
Now I am clear, thanks for your detailed answerIn some ductile materials such as Aluminium, Copper, Mild Steel, the yield point cannot be clearly defined during tension test, therefore yield stress is Unknown. For such metals design stress called PROOF stress is calculated using offset method.
Some materials like High Strength Deformed (HSD) steel, brass, duralumin etc., do not show anywell defined yield point. For these materials, proof stress serves as analogous to yield stress. Proof stress is the stress that is just sufficient to produce under load, a defined amount of permanent residual strain, which a material can have without appreciable structural damage. This arbitrary value will be different for different material or different uses of same material.
It is determined from the stress-strain curve by drawing a line parallel to initial straight part or tangent of the curve and at a distance from the origin by an amount representing the defined residual strain (normally 0.1% or 0.2%) thus determining the stress at which the line cuts the curve. In specifying proof stress, the amount of permanent strain considered, should be mentioned, i.e.,0.1% proof stress, 0.2% proof stress etc.
Good but in Tanzania we use Fy instaed of fe as per British standard.Fe415 is a grade of High Strength Deformed Steel Bar for Concrete Reinforcement. This Grade has been specified by Bureau of Indian Standards (BIS) in a documented standard IS 1786:2008.The digits denotes the minimum Yield Strength (in N/mm2) of the bar.
There are total 7 Grades specified in the standard (IS 1786), which are:
Minimum Yield Strength of the Bar should be to qualify as that Grade. Grades with “D” denotes more Ductile Grades. Where minimum Tensile Strength required should be 8% more than Yield Strength for Grades without “D”, it should be 10% more than Yield Strength to qualify as a “D” Grade.