| name | impact-testing |
| description | Impact testing — Charpy/Izod pendulum, CVN energy, ductile-to-brittle transition (DBTT), ASTM E23, fracture appearance, instrumented impact, drop weight test (ASTM E208), Pellini test. |
| metadata | {"priority":7,"promptSignals":{"phrases":["impact testing","Charpy test","Izod test","CVN energy","ductile to brittle transition","DBTT","drop weight test"],"minScore":3}} |
Impact Testing — Complete Skill
Charpy V-Notch (CVN) Test — ASTM E23
Specimen
Standard: 10 × 10 × 55 mm; V-notch: 2 mm deep, 45° angle, 0.25 mm root radius
Sub-size specimens: 7.5 × 10, 5 × 10, 3.3 × 10, 2.5 × 10 mm (when material insufficient)
Sub-size conversions: multiply energy by (10/thickness) for rough normalization
Test Procedure
- Condition specimen to test temperature (liquid N₂ for -196°C, dry ice for -78.5°C, furnace for elevated T)
- Transfer time to anvil: ≤ 5 s (temperature change ≤ 1°C)
- Drop pendulum; measure absorbed energy CV [J] from graduated scale
- Examine fracture surface for shear fracture area fraction (%SA)
Pendulum Energy (ASTM E23)
Absorbed energy: CV = mgh₁ - mgh₂ = mg(h₁ - h₂)
Correction: friction losses, windage (<5% for good machine)
Machine capacities: 150 J, 300 J, 450 J, 815 J standard
High-energy (ESSO test): up to 3000 J for large pipe/thick sections
Reporting
- CV [J] at test temperature T [°C]
- Fracture appearance (% shear/fibrous vs. crystalline/cleavage)
- Lateral expansion [mm] (perpendicular to fracture; ductility measure)
Ductile-to-Brittle Transition (DBTT)
BCC metals (ferritic steels, Cr-Mo, etc.): exhibit transition from ductile (high CVN) to brittle (low CVN) with decreasing temperature
FCC metals (Al, Cu, austenitic SS, Ni): no transition; remain ductile to cryogenic T
HCP metals (Zn, Mg): brittle at RT
Transition Temperature Determination Methods
T_T15: temperature at which CVN = 15 ft-lb (20 J) — old criterion; reactor vessel
T_T27: temperature at which CVN = 27 J — common structural steel (ASTM A36, A572)
FATT (Fracture Appearance Transition Temperature): T at which 50% shear fracture
T_50J, T_41J, T_28J: various energy criteria depending on application
Steel example:
Low-carbon steel A36: T_T27 ≈ -30°C to +10°C depending on heat; T_FATT ≈ 0°C
High-strength low-alloy (HSLA): T_T27 ≈ -60°C
Nuclear pressure vessel SA-508: RTNDT ≤ -12°C initial; weld ≤ +10°C initial
Factors Affecting DBTT
Lower DBTT (better): smaller grain size, normalized vs. as-rolled, lower C, Mn addition, Ni addition, lower S/P
Higher DBTT (worse): larger grain size, higher C, Cr without Ni, irradiation embrittlement, strain aging, temper embrittlement
Grain size effect (Hall-Petch modified for DBTT):
ΔDBTT ≈ -11.5 × ln(d^0.5) [°C per unit decrease in ln(d); d in mm]
Smaller grain = lower DBTT ≈ 15°C per ASTM grain size number decrease
Izod Test — ASTM E23
Orientation: specimen clamped upright; cantilever; struck from front of notch
Standard specimen: 10 × 10 × 75 mm; notch at 28 mm from top; V-notch same as Charpy
Less common than Charpy (specimen clamping introduces errors; not used for structural steels)
Primary use: plastics (ASTM D256); provides impact strength per unit width [J/m]
Instrumented Impact Testing
Measures force-time and energy-time curves during impact
Key data extracted:
- P_max (maximum force) — fracture initiation
- P_A (general yield force) — onset of plastic deformation
- E_i (energy to initiation), E_p (energy to propagation)
Fracture characterization:
High P_max, high E_p → ductile fracture (high toughness)
Low P_max, low E_i → brittle cleavage fracture
Separation of E_i and E_p: determines whether specimen fails during loading or propagation
ASTM E2298: instrumented Charpy impact testing
Drop Weight Test — ASTM E208 (Pellini)
Nil-ductility transition temperature (NDTT): lowest temperature for ductile fracture under impact
Specimen: 25 × 90 × 360 mm plate; brittle weld bead on tension face; struck by falling weight
Pass criterion: no-break (SAW) = fracture does not propagate beyond 1/3 of plate
Go/No-Go test: binary result; NDTT = lowest T for no-break
RTNDT (Reference Nil-Ductility Transition Temperature):
RTNDT = max(NDTT, T[CVN ≥ 68 J] - 33°C)
RTNDT used in ASME Section XI fracture mechanics analysis for nuclear pressure vessels
Drop weight tear test (DWTT) — ASTM E436:
For pipe steels (API 5L); specimen from actual pipe; full-thickness; 85% shear area at design T
Kahn Tear Test
Used for aluminum alloys (ASTM B871)
Propagation energy (unit = in·lb/in²); tear strength, unit propagation energy
Rank alloys by toughness without K_IC testing
Impact Testing of Welds
Heat-affected zone (HAZ) impact: most critical region; grain coarsening; brittle zones
Test positions: base metal, HAZ, weld metal (centreline), WM (1/4 width)
AWS D1.1: CVN ≥ 27 J at -18°C (0°F) for bridge and building welds in Zone I (cold climate)
Temper embrittlement check:
J-factor = (Si + Mn) × (P + Sn) × 10⁴ (step-cooling test; measure Δ_FATT after embrittlement heat treatment)
J < 100 preferred for pressure vessel applications
Fracture Surface Analysis
Cleavage fracture: bright, crystalline; flat facets; BCC metals below DBTT
Shear (ductile): gray, fibrous, 45° shear lips; dimples under SEM
Intergranular: follows grain boundaries; hydrogen, sulfide, temper embrittlement
Mixed mode: mix percentage reported as %ductile
SEM fractography: identify cleavage facets, dimple size, microvoid coalescence, river patterns
Temperature–Energy Correlation for Design
Fracture safe temperature (FST) = RTNDT + margin:
ASME Section III, Appendix G: F_stress × σ × √(πa) ≤ K_IC(T) for each operating state
K_IC lower bound curve:
K_IC = 36.5 + 3.08 exp[0.036(T - RTNDT + 56)] [MPa√m; T in °C]
Applies to: ferritic steels only; austenitic stainless → no transition; use fracture mechanics directly
Output
Provide: CVN [J] at design temperature, DBTT/RTNDT [°C], transition criterion met (T27J, FATT, NDTT), fracture appearance (% shear), HAZ impact requirement for weld qualification, material condition (as-rolled/normalized/Q&T) effect on DBTT, NDTT from Pellini if required by nuclear application, applicable standard (ASTM E23, E208, E436, ASME Section XI Appendix G).
