What is the Charpy V-notch test and what does it measure?

The Charpy V-notch (CVN) test per ASTM E23 measures a steel's resistance to brittle fracture by quantifying impact toughness. A standard specimen (10 mm × 10 mm × 55 mm) with a machined 2 mm deep V-notch (45° included angle, 0.25 mm root radius) is struck by a pendulum hammer. The energy absorbed in fracturing the specimen, measured in ft-lb or Joules (1 ft-lb = 1.356 J), is the CVN value. The test determines the ductile-to-brittle transition temperature (DBTT) — the temperature below which steel transitions from ductile (high energy absorption, fibrous fracture) to brittle (low energy, cleavage fracture). This is critical for structural applications because brittle fracture can occur suddenly without warning or plastic deformation. Key test parameters include test temperature (typically +70°F to -40°F), specimen orientation (longitudinal or transverse to rolling direction), and specimen size (full-size 10×10 mm or subsize 10×7.5, 10×5, 10×2.5 mm). Subsize specimens require proportionally reduced energy acceptance criteria. Lateral expansion (mils) and percent shear fracture appearance supplement the energy measurement for toughness characterization.

What are the AISC Charpy V-notch requirements for fracture-critical members?

Per AISC 360-22 Appendix A (Alternative Methods for Fracture-Critical Members) and AISC Specification Section A3.1c, Charpy requirements depend on the service temperature zone: Zone 1 (LAST ≥ 0°F): minimum 25 ft-lb at 70°F (room temperature); Zone 2 (0°F > LAST ≥ -30°F): minimum 25 ft-lb at 40°F; Zone 3 (-30°F > LAST ≥ -50°F): minimum 25 ft-lb at 10°F; Zone 4 (-50°F > LAST ≥ -70°F): minimum 25 ft-lb at -10°F; Zone 5 (-70°F > LAST): minimum 25 ft-lb at -30°F. The zone is determined by the Lowest Anticipated Service Temperature (LAST), which accounts for the structure's geographic location and exposure. Fracture-critical members are those whose failure would result in collapse of the structure — typically main tension members in trusses, girders, and columns in critical load paths. For non-fracture-critical members, steel meeting standard ASTM requirements (A36, A992, A572) is acceptable without additional CVN testing. AISC 341 (Seismic Provisions) adds CVN requirements for members in Special and Intermediate Moment Frames: 20 ft-lb at 70°F for moderately ductile members in SMF and IMF, with higher requirements (40 ft-lb at 70°F) for demand-critical welds in SMF beam-to-column connections.

How do different steel grades compare in Charpy toughness?

At room temperature (70°F), typical CVN values show substantial variation: A36 provides 60-100 ft-lb (30-150 range) — excellent ductility, the benchmark for structural carbon steel; A992: 50-90 ft-lb (25-150 range) with good toughness from controlled chemistry and microalloying; A572 Gr 50: 50-90 ft-lb, similar to A992; A572 Gr 65: 35-70 ft-lb (15-100 range), lower due to higher strength/lower ductility trade-off; A514 (quenched and tempered, 100 ksi yield): 20-50 ft-lb (10-80 range), lowest of structural grades due to high strength and martensitic microstructure; A913 Gr 50 (QST process): 80-150+ ft-lb (50-200+ range), the best performer with excellent toughness from the quenching and self-tempering process; A500 Gr B/C (cold-formed HSS): 15-40 ft-lb with NO specification minimum, highly variable; A1085 (hot-formed HSS): 40-80 ft-lb with a guaranteed minimum of 25 ft-lb at -20°F. The key takeaway: A913 and A1085 provide guaranteed toughness for seismic and low-temperature applications; A500 should be avoided where toughness matters because it has no CVN requirement. The ductile-brittle transition is steepest for higher-strength steels like A514, which may have adequate toughness at room temperature (20-50 ft-lb) but drop to 5-15 ft-lb at -40°F.

Why does Charpy toughness matter for seismic design?

Charpy toughness is critical for seismic design because earthquakes demand ductility and energy absorption rather than strength alone. AISC 341-22 (Seismic Provisions) requires specified CVN values for members and connections in the Seismic Load Resisting System (SLRS): (1) Beam-to-column connections in Special Moment Frames (SMF) require CVN testing of the beam flange material at the welded joint region — 20 ft-lb at 70°F minimum for most applications, 40 ft-lb at 70°F for demand-critical welds; (2) Column splices in SMF and Special Concentrically Braced Frames (SCBF) where the splice is part of the protected zone require CVN verification; (3) Link beams in Eccentrically Braced Frames (EBF) require CVN testing because links undergo cyclic plastic shear and flexural yielding up to 0.08 rad rotation, demanding high toughness to prevent fracture at the link-to-brace connection; (4) Brace members in SCBF must meet CVN requirements to sustain buckling and post-buckling behavior through multiple cycles without fracture. Steels meeting AISC 341 CVN requirements are typically A992, A913, or specially ordered A572 with supplemental CVN testing. The Northridge earthquake (1994) demonstrated that low-toughness steel in welded beam-to-column connections led to brittle fracture at low drift levels (0.3-0.5% rad), motivating modern CVN requirements.

What is the ductile-to-brittle transition and how does it affect steel selection?

The ductile-to-brittle transition is the temperature range over which steel's fracture mode changes from ductile (high energy absorption, microvoid coalescence, shear fracture) to brittle (low energy absorption, cleavage fracture on crystallographic planes). The transition is characterized by: upper shelf energy (USE) — the plateau of high CVN values at warm temperatures, typically 50-150+ ft-lb for structural steels; transition temperature at a specified energy level (e.g., 15 ft-lb or 20 ft-lb); lower shelf energy (LSE) — the plateau of low CVN values at very cold temperatures, typically 2-10 ft-lb. Factors affecting the transition: (1) Steel chemistry — carbon, phosphorus, and sulfur raise the transition temperature; manganese and nickel lower it. (2) Grain size — fine grain (ASTM 7-8) lowers the transition by 20-40°F compared to coarse grain (ASTM 3-4). (3) Notch acuity — the V-notch creates triaxial stress at the root, simulating the stress state at a crack tip. (4) Loading rate — dynamic loading shifts the transition 20-50°F higher than static loading. Steel selection for cold climates: A992 with fine grain practice is adequate for Zone 1-2; for Zone 3-5 or fracture-critical applications, specify A913 or steels with nickel additions that maintain toughness at low temperatures. The DBTT for A36 is typically around -10°F to +30°F, for A992 around -20°F to +10°F, and for A913 below -50°F.

Steel Charpy Values — Impact Toughness by Grade

Toughness is steel's ability to absorb energy and deform plastically before fracturing. The Charpy V-notch (CVN) test measures impact toughness by striking a notched specimen with a pendulum hammer. Low toughness means brittle fracture, which can occur suddenly and catastrophically without warning. This page provides CVN data for structural steels.

What Is the Charpy V-Notch Test?

A standard CVN specimen (10 mm × 10 mm × 55 mm) has a 2 mm deep V-notch machined into one face. A pendulum hammer strikes the opposite face, fracturing the specimen. The energy absorbed (in ft-lb or Joules) is the Charpy impact value.

ASTM E23 governs the test procedure. Key parameters:

Specimen size: 10 × 10 × 55 mm (full-size) or subsize (e.g., 10 × 7.5, 10 × 5)
Notch: 2 mm deep, 45° included angle, 0.25 mm root radius
Test temperature: typically 70°F (room temp), 0°F, -20°F, -40°F, or per specification
Results: energy absorbed (ft-lb or J), lateral expansion (mil), percent shear fracture

Charpy Requirements by Specification

AISC Specification Requirements

AISC 360-22 requires CVN testing for:

Application	Zone	Min Energy (ft-lb)	Test Temp	Notes
Fracture-critical members (tension)	1	25	70°F	Non-critical temperature
Fracture-critical members (tension)	2	25	40°F	Moderate temperature
Fracture-critical members (tension)	3	25	10°F	Cold temperature
Fracture-critical members (tension)	4	25	-10°F	Very cold
Fracture-critical members (tension)	5	25	-30°F	Extreme cold

Zone determined by lowest anticipated service temperature (LAST) per AISC Specification Appendix A.

ASTM A709 (Bridge Steel) CVN Requirements

Grade	Zone 1 (70°F)	Zone 2 (40°F)	Zone 3 (10°F)	Zone 4 (-10°F)
36	15 ft-lb	15 ft-lb at 40°F	15 ft-lb at 10°F	15 ft-lb at -10°F
50	15 ft-lb	15 ft-lb at 40°F	15 ft-lb at 10°F	15 ft-lb at -10°F
50W	15 ft-lb	15 ft-lb at 40°F	15 ft-lb at 10°F	15 ft-lb at -10°F
HPS 50W	25 ft-lb	25 ft-lb at 40°F	25 ft-lb at 10°F	25 ft-lb at -10°F
HPS 70W	25 ft-lb	25 ft-lb at 40°F	25 ft-lb at 10°F	25 ft-lb at -10°F

HPS = High Performance Steel. Higher toughness requirements than standard grades.

A1085 (HSS) CVN Requirements

Requirement	Value
Test temperature	-20°F (-29°C)
Minimum energy (full size)	25 ft-lb (34 J)
Subsize specimens	Proportionally reduced
Frequency	Per heat, per size

This is one of the key advantages of A1085 over A500, which has no CVN requirement.

Typical CVN Values by Steel Grade

At Room Temperature (70°F / 21°C)

Steel Grade	Typical CVN (ft-lb)	Range (ft-lb)	Notes
A36	60-100	30-150	Very ductile, high toughness
A992	50-90	25-150	Good toughness standard
A572 Gr 50	50-90	25-140	Similar to A992
A572 Gr 65	35-70	15-100	Lower than Gr 50
A588	40-80	20-120	Good toughness for weathering
A514	20-50	10-80	Lower due to high strength
A913 Gr 50	80-150+	50-200+	Excellent, SEISMIC grade
A500 Gr B	15-40	5-60	Variable, no spec minimum
A500 Gr C	15-40	5-60	Variable, no spec minimum
A1085	40-80	25 min guaranteed	Minimum 25 ft-lb at -20°F

At Low Temperature (-20°F / -29°C)

Steel Grade	Typical CVN (ft-lb)	Range (ft-lb)	Notes
A36	20-60	10-80	Moderate drop from RT
A992	20-50	10-70	Moderate drop
A572 Gr 50	20-50	10-70	Moderate drop
A572 Gr 65	10-30	5-50	Significant drop
A588	15-40	8-60	Moderate drop
A514	10-25	5-40	Low toughness at cold temps
A913 Gr 50	50-120+	30-150+	Excellent cold-weather toughness

At Very Low Temperature (-40°F / -40°C)

Steel Grade	Typical CVN (ft-lb)	Ductile-Brittle Transition?
A36	10-40	Many heats show transition
A992	10-35	Transition zone for some heats
A572 Gr 50	10-35	Transition possible
A514	5-15	Likely brittle
A913 Gr 50	30-80+	Remains tough

Factors Affecting Toughness

Factor	Effect on Toughness	Design Implication
Temperature	Decreases as temperature drops	Specify CVN at service temperature
Loading rate	Impact loading reduces toughness	Fatigue and seismic checks consider this
Thickness	Thicker material has lower toughness	Constraint effect, triaxial stress state
Notch severity	Sharper notches = lower toughness	Detailing avoids notches and re-entrant corners
Grain size	Finer grains = higher toughness	Normalizing refines grain structure
Carbon content	Higher carbon = lower toughness	High-strength steels may have lower CVN
Rolling direction	Lower across rolling direction	CVN specimens oriented perpendicular to rolling

Temperature Transition Behavior

Structural steel exhibits a ductile-to-brittle transition temperature (DBTT). Above the DBTT, fracture is ductile (high energy, shear fracture appearance). Below the DBTT, fracture is brittle (low energy, cleavage fracture appearance).

Transition Indicator	Value	Description
Upper shelf energy	60-150 ft-lb	Fully ductile fracture (shear)
Transition temperature	-20°F to +40°F	50% shear fracture appearance
Lower shelf energy	5-15 ft-lb	Fully brittle fracture (cleavage)

The transition temperature varies significantly by heat, thickness, and composition. Specification minimums ensure the steel is above its transition temperature at the specified test temperature.

Frequently Asked Questions

What is a good Charpy value for structural steel? For buildings, CVN values of 25+ ft-lb at the minimum service temperature are typical minimums. For bridges, 15-25 ft-lb depending on grade and zone. Values above 40 ft-lb indicate excellent toughness.

Does every steel project need Charpy testing? No. AISC requires CVN testing only for fracture-critical members (primary tension members whose failure would cause collapse). Most building members do not require testing. Bridge projects always require it.

What is the difference between A500 and A1085 HSS? A500 has no Charpy requirement and highly variable toughness (5-60 ft-lb). A1085 requires minimum 25 ft-lb at -20°F, making it suitable for fracture-critical and seismic applications.

How does thickness affect toughness? Thicker sections have more constraint (triaxial stress state) at the notch, which reduces the apparent toughness. AISC and ASTM have different CVN requirements for different thickness ranges to account for this.

Can I use A992 without CVN testing? Yes, for non-fracture-critical building members. A992 shapes are routinely used without CVN testing. If the member is fracture-critical (primary tension), testing is required per AISC Appendix A.

Fracture Toughness — Detailed fracture mechanics
Steel Yield Strength — Fy values by grade
Steel Chemical Composition — Alloying elements
Welding Procedure — WPS and heat input effects
Steel Grades — ASTM specification overview

Disclaimer

This is a calculation tool, not a substitute for professional engineering certification. All results must be independently verified by a licensed Professional Engineer (PE) or Structural Engineer (SE) before use in construction, fabrication, or permit documents. The user is responsible for the accuracy of all inputs and the verification of all outputs.