Tensile Testing — Complete Guide: SOP Procedure, Rp0.2% Calculation, and Comparative Data Sheet

Tensile Testing — Complete Guide

This guide brings together the three pillars of mastering tensile testing on special steels: SOP 300 kN | Rp0.2% Offset Calculation | Comparative Technical Data Sheet for 6 Grades

PART 1 — SOP: 300 kN Standard Operating Procedure

ISO 6892-1 (Method B) | ASTM A370 (Method A) | ASTM E8/E8M | ASTM E1012

Section 00 — Grip Alignment & Verification (ASTM E1012)

⚠️ Improper alignment generates parasitic bending stress which distorts the Young's modulus and underestimates Rp0.2%.
# Action Detail / Criterion
1 Clean grips Brush prisms with a wire brush
2 Upper grip tightening Lock hydraulic/mechanical pressure
3 Lower grip tightening Lock when machine displays ± 100 N
4 Witness preload 1 mm/min up to 10 kN — linear elastic slope

Section 01 — System Characteristics

Parameter Value
Machine capacity 300 kN
Specimen geometry Cylindrical — d₀ = 10 mm
Initial cross-section S₀ 78.54 mm²
Extensometer gauge length Lₑ 25 mm

Section 02 — Control Speeds

Zone Speed Normative range
Elastic 0.2 mm/min 6 to 60 MPa/s
Transitional Rp0.2% 0.37 mm/min < 0.0025 s⁻¹
Plastic & fracture 12 mm/min < 0.008 s⁻¹

Section 03 — Thresholds by Grade

Grade Expected limit Software threshold
ASTM A193 B7 ≥ 720 MPa ≥ 28 kN
ASTM A453 Gr.660 Cl.A ≥ 585 MPa ≥ 23 kN
AISI 904L ≥ 220 MPa ≥ 8.5 kN
ASTM B8/B8M Cl.1 ≥ 205 MPa ≥ 8.0 kN
ASTM B16 H02 (brass) ≥ 170 MPa ≥ 6.5 kN
Universal plastic threshold: elongation ≥ 0.25 mm → 12 mm/min + extensometer disengagement
Fracture: force drop ≥ 80% of Fmax → immediate motor cutoff

Section 04 — Corrective Actions

Symptom Cause Action
Unstable elastic slope Insufficient clamping Increase hydraulic pressure
Extensometer slips Polished stainless steel surface Clean knife edges with IPA
Fracture in grips Alignment defect ASTM E1012 Calibration

PART 2 — Rp0.2% Calculation — Segment Method (Offset Method)

ISO 6892-1 | ASTM E8/E8M | ASTM A370

1 — Force → Stress Conversion

σ = F / S₀

S₀ = 78.54 mm² | Example: F = 40 kN → σ = 509.3 MPa

2 — Strain (ε)

ε = ΔL / Lₑ

Lₑ = 25 mm | Example: ΔL = 0.125 mm → ε = 0.005 (0.5%)

3 — Offset Method Algorithm

Step A — Young's Modulus E
Linear regression on elastic zone: σ = E × ε → E = 190,000 to 210,000 MPa
Step B — Offset line (0.2% Offset)
σ = E × (ε − 0.002)
Step C — Intersection
The intersection point between the actual curve and the offset line gives Rp0.2%.

PART 3 — Comparative Technical Data Sheet — 6 Grades

Machine: Tinius Olsen IMD STAF | Extensometer: MF IMD 1123401 | Laboratory: APAVE Lyon

Normative Framework

⚠️ Key difference ISO vs ASTM: ISO 6892-1 controls the elastoplastic zone (≤ 0.0025 s⁻¹) ; ASTM A370 does not specify this. Both are equivalent for heat-treated alloy steels.

Results by Grade

35NCD6 — ISO 6892-1 method B (Oct-23) | Specimen no. 46

Quantity Result Min. requirement Status
Rp0.2% 980 MPa ≥ 862 MPa ✅
Rm 1,090 MPa ≥ 965 MPa ✅
A% 17% ≥ 13% ✅
Z% 58% ≥ 50% ✅

Rp0.2%/Rm = 0.899 | ✅ COMPLIANT

A320-L7 — ASTM A370 method A (Jun-24) | Specimen no. 1905 ⚠️ Lot at low limit

Quantity Result Min. requirement Status
Rp0.2% 725 MPa ≥ 724 MPa ✅ (+1 MPa)
Rm 870 MPa ≥ 862 MPa ✅ (+8 MPa)
A% 18% ≥ 16% ✅
Z% 52% ≥ 50% ✅ (+2%)

Rp0.2%/Rm = 0.833 | ✅ COMPLIANT ⚠️ narrow margins — Require 3.1 certificate

Comparative Summary — 6 Grades

Grade Standard Rp0.2% Rm A% Z% Rp/Rm Status
35NCD6 Oct-23 ISO 6892-1 B 980 MPa 1,090 MPa 17% 58% 0.899 ✅
A320-L7 Jun-24 ASTM A370 A 725 MPa 870 MPa 18% 52% 0.833 ✅ ⚠️
A193-B8 Cl.2 ASTM A370 A — — — — — ⏳
AISI 904L ASTM A370 A — — — — — ⏳
Grade 660 Cl.B ASTM A370 A — — — — — ⏳
35NCD6 Jun-24 ASTM A370 A — — — — — ⏳

⏳ Data currently being integrated.

References: NF EN ISO 6892-1:2019 | ASTM E8/E8M-22 | ASTM A370-22 | ASTM E1012-14

Authored by: A. Talal — Mechanical Metrology Laboratory — June 2026