What standard governs this test?

Key testing standards: Tensile testing — ISO 6892-1 (metals at room temperature), ASTM E8/E8M; Charpy impact — ISO 148-1, ASTM E23; Hardness — ISO 6506 (Brinell), ISO 6507 (Vickers), ISO 6508 (Rockwell), ASTM E10/E18/E92; Fracture toughness — ASTM E399 (K_IC), ASTM E1820 (J-integral); Creep — ISO 204, ASTM E139. Always specify the test standard in material orders and qualification documents.

How do I interpret the test results?

Result interpretation depends on the acceptance criteria in the applicable product standard or fabrication code. Common references: structural steel — EN 10025, ASTM A572; pressure vessel plates — EN 10028, ASME SA-516; pipe — EN 10216, API 5L. Our calculators (Hardness Converter, Charpy to K_IC, Stress-Strain) help translate between test values and design parameters.

What sample size and orientation is required?

Sample orientation is critical — longitudinal (L) specimens parallel to rolling direction give higher strength and toughness than transverse (T) specimens. Charpy sub-size specimens (7.5×10mm or 5×10mm) are used when full-size (10×10mm) cannot be taken; toughness values must be corrected by the appropriate factor (typically ×1.5 or ×2 for sub-size). Specify orientation and specimen size in test certificates.

Stress-Strain Curve Calculator —

The engineering stress-strain curve is the fundamental characterisation of a material’s mechanical response to uniaxial loading. This calculator converts between engineering and true stress-strain, calculates work hardening exponent (n) and strength coefficient (K) from the Hollomon power law, and estimates key derived properties including resilience, toughness, and uniform elongation. Understanding these relationships is essential for metal forming analysis, finite element material model definition, and structural integrity assessment.

Stress-Strain Curve Parameters Calculator

Young’s Modulus — E (GPa)

Yield Strength — σ_y (MPa)

Ultimate Tensile Strength — UTS (MPa)

Engineering strain at UTS — ε_UTS (%)

Fracture elongation — ε_f (%)

Apply load point (engineering strain %)

Elastic strain at yield (ε_y = σ_y / E)—

True stress at UTS (σ_T = UTS × (1 + ε_UTS))—

True strain at UTS (ε_T = ln(1 + ε_UTS))—

Work hardening exponent — n (Hollomon)—

Strength coefficient — K (Hollomon: σ_T = K × ε_T^n)—

Engineering stress at input strain—

True stress at input strain—

Modulus of resilience (U_r = σ_y² / 2E)—

Toughness estimate (area under curve, MJ/m³)—

Engineering stress: σ_e = F/A₀ | True stress: σ_T = σ_e × (1 + ε_e)
Engineering strain: ε_e = ΔL/L₀ | True strain: ε_T = ln(1 + ε_e)
Hollomon power law: σ_T = K × ε_T^n (valid in uniform plastic deformation region)
n = strain hardening exponent: high n = better formability (304 SS n≈0.45; mild steel n≈0.20)

Figure: Engineering stress-strain curve with all key points labelled: elastic modulus E (slope), yield strength σ_y (0.2% offset), UTS (peak), necking, and fracture. © metallurgyzone.com/

Typical Hollomon n Values for Engineering Alloys

Material	n (strain hardening exponent)	σ_y (MPa)	Formability
304 Austenitic stainless	0.40–0.50	210–250	Excellent — very high n
IF (interstitial-free) steel	0.25–0.35	140–180	Excellent — deep draw quality
Low carbon mild steel (DC04)	0.20–0.25	180–240	Good — standard pressings
DP600 dual-phase steel	0.15–0.22	350–400	Good — AHSS auto panels
S355 structural steel	0.15–0.20	355–400	Moderate
S690 Q&T structural	0.05–0.10	690–750	Low — limited cold forming
Ti-6Al-4V (annealed)	0.08–0.12	880–950	Low — springback issues
Al 6061-T6	0.06–0.10	276–310	Low — limited forming after T6
Cu (annealed)	0.30–0.40	70–100	Excellent

References

Callister, W.D. and Rethwisch, D.G., Materials Science and Engineering: An Introduction. 10th ed. Wiley, 2018.
ISO 6892-1:2019 Metallic materials — Tensile testing — Part 1: Method of test at room temperature.
Hosford, W.F. and Caddell, R.M., Metal Forming: Mechanics and Metallurgy. 4th ed. Cambridge University Press, 2011.

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