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Stress during continuous elongation of seamless steel tubes
The seamless steel pipe is a metal material with a yield phenomenon. The stress at which the specimen can continue to stretch without increasing the force during the tensile process (keep constant) is called the yield point. If the force decreases, the upper and lower yields should be distinguished The unit of yield point is N / mm2 (MPa).
Upper yield point (σsu) of the seamless steel tube: the maximum stress before the first drop of the sample when the yield occurs; lower yield point (σsl): the minimum stress in the yield phase when the initial transient effect is not taken into account.
The formula for calculating the yield point of seamless steel pipes is:
In the formula: Fs--yield force (constant) in the tensile process of the sample, N (Newton) So--the original cross-sectional area of the sample, mm2.
Elongation after fracture of seamless steel pipe (σ)
In the tensile test, the percentage of the length of the gauge that is increased after the sample is broken is the percentage of the original gauge length. It is called elongation. It is expressed by σ and the unit is%. The calculation formula is:
In the formula: L1-gauge length after the sample is broken, mm; L0-original gauge length of the sample, mm.
Sectional shrinkage of seamless steel pipe (ψ)
In the tensile test, the maximum reduction of the cross-sectional area at the reduced diameter of the sample after the sample is broken and the percentage of the original cross-sectional area is called the reduction of area. It is expressed by ψ and the unit is%.
In the formula: S0--the original cross-sectional area of the specimen, mm2; S1--the minimum cross-sectional area at the reduced diameter of the specimen after breaking, mm2.