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

The Charpy V-Notch (CVN) impact test measures the energy absorbed (in ft-lb or Joules) when a standard specimen (10×10×55 mm bar with a 2 mm deep 45° V-notch) is fractured by a pendulum striker at a specified test temperature. The notch creates a triaxial stress state at the root, simulating the most severe condition: an existing crack or stress concentration combined with rapid loading and low temperature. The test temperature is critical because steel undergoes a ductile-to-brittle transition (DBTT): above the transition temperature range, the fracture surface is fibrous and shear-dominated with energy absorption > 40 ft-lb (upper shelf); below the transition, fracture surfaces are flat and crystalline cleavage with energy < 15 ft-lb (lower shelf). Within the transition zone (15-40 ft-lb), fracture is mixed-mode and unreliable for design. The CVN value is NOT a direct material property like yield stress — it's a comparative index used to qualify material for service conditions. Structural steels are specified with a minimum CVN at a given temperature: 20 ft-lb at 70°F is a common requirement (AISC 341 heavy shapes); 20 ft-lb at −20°F is required for demand-critical weld filler metal per AWS D1.8. The 20 ft-lb threshold comes from correlation studies (Barsom and Rolfe, 1970s-1980s) showing that bridges and buildings fabricated from steel with CVN > 15-20 ft-lb at the minimum service temperature have negligible risk of brittle fracture under normal design and fabrication conditions. Three specimens are tested per condition; the average must meet the minimum and no single specimen may be below 2/3 of the minimum.

What CVN requirements does AISC 341-22 impose for seismic applications?

AISC 341-22 imposes two main categories of CVN requirements. (1) Heavy shapes (Section A3.3): W-shapes with flange thickness tf ≥ 1.5 inches used in the seismic force-resisting system must demonstrate CVN ≥ 20 ft-lb at 70°F (21°C). Testing is at the flange core (the slowest-cooling, lowest-toughness region) per ASTM A6 Supplementary Requirement S30. This applies because thick flanges cool slowly after hot rolling, developing coarser grain structure and lower toughness at the core than at the surface. Common heavy shapes in SMF columns: W14×283 and larger (tf > 1.5"), W14×398 (tf = 2.845"), W14×730 (tf = 4.91") — all require CVN testing. Lighter columns like W14×132 (tf = 1.025") do not trigger the requirement. (2) Demand-critical welds (Section A3.4): Filler metal for complete-joint-penetration groove welds in demand-critical locations must achieve CVN ≥ 20 ft-lb at −20°F (−29°C) per AWS D1.8 Annex A (Supplemental Welding Provisions for Seismic Applications). This applies to: CJP welds at beam-to-column moment connections in SMF and IMF; CJP welds at column splices when the splice is in the protected zone or within the middle third of the column clear height; and CJP welds at brace-to-gusset connections in SCBF. The −20°F test temperature (vs +70°F for base metal) is much more stringent because the weld metal's microstructure (rapidly solidified cast structure) and the higher constraint at the weld joint demand higher toughness at lower temperatures. Filler metals that typically meet this requirement include E71T-8Ni1 (FCAW with 1% Ni), E81T1-Ni1, and ER80S-Ni1 (GMAW with Ni). E70T-7 (standard FCAW without nickel) typically does NOT meet the requirement.

How does the ductile-to-brittle transition temperature affect material selection?

The ductile-to-brittle transition temperature (DBTT) is the temperature range where steel's fracture mode shifts from ductile microvoid coalescence (high energy, safe, gives warning through deformation) to brittle cleavage (low energy, sudden, no warning). The DBTT is not a single temperature but a range of 30-80°F where CVN energy drops from the upper shelf to the lower shelf. The 20 ft-lb threshold is typically used as the index temperature for transition. Material selection must ensure that the steel's DBTT is below the minimum anticipated service temperature (MAST) for the structure: for an indoor heated building in a cold climate, MAST ≈ 35-40°F (interior steel never reaches the −20°F outside temperature during occupancy); for an exposed unheated structure (parking garage, bridge, outdoor stadium canopy), MAST = lowest 1-day mean temperature per ASCE 7 climate data (typically −10°F to −30°F in northern US, −30°F to −50°F in northern Canada). Factors that shift DBTT UP (worse toughness): thicker sections (slower cooling during rolling → larger grain size → higher DBTT), higher carbon content (0.02% C increase can shift DBTT +10°F), higher phosphorus and sulfur content, cold working (cold straightening of flanges shifts DBTT 20-40°F higher), and triaxial constraint at connections (thick CJP welds with backing bars). Factors that shift DBTT DOWN (better toughness): fine grain practice (ASTM A6 S30 requires fine austenitic grain size #5 or finer), nickel addition ( 1-3.5% Ni in ASTM A203/A553 for cryogenic service), quenched and tempered processing (A913, A514), low carbon content (< 0.10%), and vacuum degassing (removes hydrogen and oxygen). For a W14×398 in an SMF in Minneapolis (MAST ≈ −15°F for indoor heated): A913 Gr 65 (QST process, fine grain, low C) is specified over A992. For exposed bridge girders in northern Alberta (MAST = −40°F): specify ASTM A709 HPS 70W with CVN 35 ft-lb at −10°F per AASHTO Zone III requirements.

What is the k-area embrittlement problem in W-shape columns?

The k-area (the region of the web within approximately 1-2 inches of the flange, including the fillet) in hot-rolled W-shapes can have reduced fracture toughness due to residual stresses from the rotary straightening process. During production, W-shapes are cold-straightened by passing through rotary straighteners that apply bending at the flanges to correct camber and sweep. The straightening concentrates plastic strain at the web-to-flange junction (k-area), work-hardening the steel and elevating the DBTT in that local zone. For a W14×398 column in an SMF connection, the k-area is directly adjacent to the beam flange CJP welds where the highest strain demand occurs during seismic drift — creating a stress concentration at the worst-toughness location. The Northridge earthquake (1994) revealed k-area cracking as one of several contributors to moment connection fractures. AISC 341-22 addresses this through: (1) the protected zone concept — no welding, cutting, or tacking is permitted within the protected zone of the beam (typically the region within one beam depth of the column face), preventing additional stress concentrations from erection aids; (2) requiring CVN testing at the flange core (the lowest-toughness position) for heavy shapes; (3) prohibiting cold straightening of flanges in the protected zone of moment frame beams; (4) recommending the use of A913 shapes (which are straightened by the QST process rather than cold rotary straightening) for heavy seismic columns. For rehabilitation of existing Northridge-era moment frames: supplemental fillet welds at the beam web-to-column flange k-area and horizontal stiffener plates (continuity plates) are retrofit strategies.

How is plane-strain fracture toughness KIc estimated from CVN data?

The Barsom-Rolfe correlation provides an empirical relationship between CVN impact energy and the plane-strain fracture toughness KIc for structural steels on the upper shelf (ductile region): KIc² = 5 × E × CVN (upper-shelf correlation), where KIc is in ksi·√in, E is the elastic modulus (29,000 ksi for steel), and CVN is in ft-lb. For CVN = 40 ft-lb (upper shelf): KIc² = 5 × 29,000 × 40 = 5,800,000, KIc = √5,800,000 = 2,408 ksi·√in ≈ 2,648 MPa·√m (standard engineering approximation). This is high toughness — indicative of the upper shelf where extensive plastic deformation precedes fracture. In the transition region (lower shelf), the dynamic fracture toughness KId (for loading rates equivalent to the CVN test) is: KId ≈ 15.5 × √(CVN) ksi·√in. For CVN = 15 ft-lb (near the lower bound of the transition): KId = 15.5 × √15 = 60 ksi·√in. For comparison with KIc: at low loading rates, KIc ≈ KId × (1 + 0.1 × T_shift) approximately. Application: for fitness-for-service assessment of a 50-year-old bridge girder with an 0.25" deep fatigue crack discovered during inspection, and material test gives CVN = 25 ft-lb at the minimum service temperature (meets the 20 ft-lb threshold). KIc ≈ √(5 × 29,000 × 25) ≈ 1,902 ksi·√in. The stress intensity at the crack tip: KI = 1.12 × σ × √(π × a) where a = crack depth. For σ = 18 ksi (service dead + live load stress): KI = 1.12 × 18 × √(π × 0.25) = 1.12 × 18 × 0.886 = 17.9 ksi·√in. KIc >> KI (factor of 100), so the crack is stable from a fracture mechanics standpoint — repair by drilling a crack-arrest hole (~1" diameter) at the crack tip and monitoring.

Steel Fracture Toughness — Charpy V-Notch Testing, CVN Requirements & Brittle Fracture Prevention

Q: What is the k-area embrittlement problem in W-shape columns?

The k-area (the region of the web within approximately 1-2 inches of the flange, including the fillet) in hot-rolled W-shapes can have reduced fracture toughness due to residual stresses from the rotary straightening process. During production, W-shapes are cold-straightened by passing through rotary straighteners that apply bending at the flanges to correct camber and sweep. The straightening concentrates plastic strain at the web-to-flange junction (k-area), work-hardening the steel and elevating the DBTT in that local zone. For a W14×398 column in an SMF connection, the k-area is directly adjacent to the beam flange CJP welds where the highest strain demand occurs during seismic drift — creating a stress concentration at the worst-toughness location. The Northridge earthquake (1994) revealed k-area cracking as one of several contributors to moment connection fractures. AISC 341-22 addresses this through: (1) the protected zone concept — no welding, cutting, or tacking is permitted within the protected zone of the beam (typically the region within one beam depth of the column face), preventing additional stress concentrations from erection aids; (2) requiring CVN testing at the flange core (the lowest-toughness position) for heavy shapes; (3) prohibiting cold straightening of flanges in the protected zone of moment frame beams; (4) recommending the use of A913 shapes (which are straightened by the QST process rather than cold rotary straightening) for heavy seismic columns. For rehabilitation of existing Northridge-era moment frames: supplemental fillet welds at the beam web-to-column flange k-area and horizontal stiffener plates (continuity plates) are retrofit strategies.

Q: How is plane-strain fracture toughness KIc estimated from CVN data?

The Barsom-Rolfe correlation provides an empirical relationship between CVN impact energy and the plane-strain fracture toughness KIc for structural steels on the upper shelf (ductile region): KIc² = 5 × E × CVN (upper-shelf correlation), where KIc is in ksi·√in, E is the elastic modulus (29,000 ksi for steel), and CVN is in ft-lb. For CVN = 40 ft-lb (upper shelf): KIc² = 5 × 29,000 × 40 = 5,800,000, KIc = √5,800,000 = 2,408 ksi·√in ≈ 2,648 MPa·√m (standard engineering approximation). This is high toughness — indicative of the upper shelf where extensive plastic deformation precedes fracture. In the transition region (lower shelf), the dynamic fracture toughness KId (for loading rates equivalent to the CVN test) is: KId ≈ 15.5 × √(CVN) ksi·√in. For CVN = 15 ft-lb (near the lower bound of the transition): KId = 15.5 × √15 = 60 ksi·√in. For comparison with KIc: at low loading rates, KIc ≈ KId × (1 + 0.1 × T_shift) approximately. Application: for fitness-for-service assessment of a 50-year-old bridge girder with an 0.25" deep fatigue crack discovered during inspection, and material test gives CVN = 25 ft-lb at the minimum service temperature (meets the 20 ft-lb threshold). KIc ≈ √(5 × 29,000 × 25) ≈ 1,902 ksi·√in. The stress intensity at the crack tip: KI = 1.12 × σ × √(π × a) where a = crack depth. For σ = 18 ksi (service dead + live load stress): KI = 1.12 × 18 × √(π × 0.25) = 1.12 × 18 × 0.886 = 17.9 ksi·√in. KIc >> KI (factor of 100), so the crack is stable from a fracture mechanics standpoint — repair by drilling a crack-arrest hole (~1" diameter) at the crack tip and monitoring.

Fracture toughness measures a material's resistance to crack propagation. In structural steel, low fracture toughness at service temperatures can cause sudden brittle fracture — catastrophic failure without warning or yielding. The Charpy V-Notch (CVN) impact test is the primary quality metric. AISC 341-22 mandates CVN testing for seismic connections, heavy shapes, and demand-critical welds because these locations experience high strain rates, constraint, and triaxial stress states that promote brittle behavior.

The Charpy V-Notch test

A standard CVN specimen (10 × 10 × 55 mm bar with a 2 mm deep 45-degree V-notch) is struck by a pendulum at a specified temperature. The energy absorbed before fracture, measured in foot-pounds (ft-lb) or Joules, indicates the material's toughness at that temperature.

Ductile-to-brittle transition temperature (DBTT): Steel transitions from ductile (high energy absorption, shear-type fracture surface) to brittle (low energy, cleavage fracture) over a temperature range. The goal is to ensure the DBTT falls well below the lowest anticipated service temperature.

Fracture behavior	CVN energy	Fracture surface
Fully ductile	> 40 ft-lb	Fibrous, shear lips
Transition zone	15–40 ft-lb	Mixed shear + cleavage
Brittle	< 15 ft-lb	Flat, crystalline cleavage

AISC 341-22 CVN requirements

AISC 341-22 Section A3.3 specifies CVN testing requirements for seismic applications:

Heavy shapes (AISC 341-22 Section A3.3): Shapes with flange thickness tf ≥ 1.5 in used in seismic force-resisting systems must demonstrate CVN toughness of 20 ft-lb at 70 degrees F. Testing is performed at the core of the flange (the slowest-cooling region with the worst toughness) per ASTM A6 Supplementary Requirement S30.

Demand-critical welds (AISC 341-22 Section A3.4): Weld filler metal must achieve 20 ft-lb at -20 degrees F per AWS D1.8 Annex A. This is far more stringent than the heavy shape requirement because weld metal cools rapidly and develops more constrained microstructures.

Beam-to-column connections in SMF/IMF: Both base metal and weld metal must meet the CVN requirements. The column flange material in the k-area (where rolling-induced residual stresses are highest) is particularly vulnerable.

Factors affecting fracture toughness

Factor	Effect on toughness	Design implication
Temperature	Lower T → lower toughness	Specify CVN test temperature at or below minimum service temperature
Strain rate	Higher rate → lower toughness	Seismic loading has high strain rates at plastic hinges
Constraint (triaxiality)	Higher constraint → lower toughness	Thick flanges, CJP welds with backing bars, k-area
Material grade	A913 > A992 > A572 > A36 (generally)	Use A913 Gr 65 for heavy seismic columns
Prior cold work	Reduces toughness	Avoid cold-straightened flanges in seismic zones

Worked example — specifying CVN for a seismic column

Given: W14x398 column (tf = 2.845 in) in an SMF, SDC D, minimum service temperature = 0 degrees F.

Step 1 — Check heavy shape threshold: tf = 2.845 in > 1.5 in — heavy shape provisions apply per AISC 341-22 Section A3.3.

Step 2 — Required CVN for base metal: 20 ft-lb at 70 degrees F, tested at the core of the flange per ASTM A6 S30. Specify this in the structural steel material specification on the drawings.

Step 3 — Weld filler metal: Demand-critical CJP groove welds at beam-to-column connections require filler metal with CVN = 20 ft-lb at -20 degrees F per AWS D1.8.

Step 4 — Material selection: A913 Gr 65 is preferred over A992 for heavy W14 columns in seismic applications. A913 is produced by quenching and self-tempering (QST process), which provides superior CVN toughness in thick sections. A992 produced by traditional hot-rolling may have marginal toughness at the flange core of shapes with tf > 2 in.

Specification note on drawings: "W14x398: ASTM A913 Gr 65, Supplementary Requirement S30 (CVN 20 ft-lb at 70F at flange core). CJP welds at moment connections: AWS D1.8, demand-critical filler metal E71T-8Ni1 (CVN 20 ft-lb at -20F)."

KIc correlation from CVN

For fitness-for-service assessments (e.g., evaluating existing structures with discovered cracks), the plane-strain fracture toughness KIc can be estimated from CVN data using the Barsom-Rolfe correlation:

KIc² / E = 5 × CVN    (upper-shelf, in ksi²·in / ksi = ksi·in units)

For the transition region (lower shelf):

KId = 15.5 × (CVN)^0.5    (dynamic fracture toughness, ksi·sqrt(in))

These correlations are approximate and should be used for screening only. Actual KIc testing per ASTM E399 is required for critical fracture mechanics assessments.

Code comparison

AISC 341-22 (USA): Requires CVN testing per Section A3.3 for heavy shapes (tf ≥ 1.5 in) and demand-critical welds. Test temperatures: 70 degrees F for base metal, -20 degrees F for weld metal. AWS D1.8 governs welding procedure qualification for seismic connections.

AS 4100-2020 Section 2.5 (Australia): Specifies minimum impact properties by reference to AS/NZS 3678 and AS/NZS 3679.1. Steel grade designations include toughness subgrades (e.g., Grade 300L15 requires 40 J at -15 degrees C). The designer selects the appropriate subgrade based on the minimum design service temperature from AS 4100 Table 2.5.1. For thicknesses above 40 mm, L0 or L15 subgrades are typically required.

EN 1993-1-10 (Eurocode 3): Uses a maximum permissible thickness approach based on steel toughness subgrade (JR, J0, J2, K2), reference temperature TEd, and stress level. Table 2.1 of EN 1993-1-10 cross-references charpy temperature, member thickness, and reference temperature to determine whether a given subgrade is acceptable. The reference temperature TEd = Tmd + DTsigma + DTR + DTcf, accounting for minimum air temperature, stress level, strain rate, and cold forming effects.

Common mistakes engineers make

Specifying CVN for the wrong test temperature. The AISC 341 base metal requirement is 20 ft-lb at 70 degrees F (room temperature) — this is not a cold-weather test. The -20 degrees F requirement applies only to weld filler metal. Confusing these leads to either unnecessarily expensive base metal procurement or non-compliant weld metal.
Assuming all A992 steel has adequate toughness. ASTM A992 does not include a mandatory CVN requirement. Unless Supplementary Requirement S30 is specified on the purchase order, no CVN testing is performed. For heavy seismic columns, S30 must be explicitly called out on the drawings and purchase order.
Ignoring the k-area problem in heavy W-shapes. The k-area (the web-to-flange fillet region) of heavy W-shapes produced by rotary straightening can have reduced toughness due to cold work. AISC 341-22 Commentary Section A3.3 warns against welding in this region. Column stiffeners and continuity plates should be clipped to avoid welding in the k-area.
Using lamellar tearing-susceptible material for through-thickness loading. When tensile forces act through the thickness of a plate or flange (e.g., at column continuity plates), lamellar tearing can initiate along non-metallic inclusions. Specifying ASTM A770 (through-thickness tensile testing) or using Z-quality steel per EN 10164 prevents this failure mode.

Charpy V-Notch requirements per AISC 360-22

AISC 360-22 does not mandate CVN testing for standard building structures (it relies on the steel specifications ASTM A992, A36, etc. to provide minimum toughness). However, AISC 360-22 Appendix X and the Commentary discuss fracture control for special applications. The primary CVN requirements come from AISC 341-22 for seismic applications and from project specifications for cold-temperature or fatigue service.

Summary of CVN requirements by specification

Specification	Application	Test temperature	Required CVN energy	Test location
AISC 341-22 A3.3	Heavy shapes (tf >= 1.5 in) in SFRS	70F (21C)	20 ft-lb (27 J)	Flange core (ASTM A6 S30)
AISC 341-22 A3.4	Demand-critical weld filler metal	-20F (-29C)	20 ft-lb (27 J)	Weld metal per AWS D1.8
AWS D1.8 Clause 5.3	Demand-critical CJP welds	-20F (-29C)	20 ft-lb (27 J)	Weld metal deposit
AASHTO (bridges)	Fracture-critical members	Zone 1 (0F), Zone 2 (-30F), Zone 3 (-60F)	25 ft-lb (34 J) minimum	Per AASHTO Table 6.6.2-2
ASTM A992 (base spec)	General structural	Not specified	Not specified	N/A
ASTM A992 S30 (supplement)	When specified by engineer	70F (21C)	20 ft-lb (27 J)	Flange core
ASTM A913	Quenched and self-tempered	Varies by grade	20-30 ft-lb at specified temp	Per ASTM A913 Table 4

Temperature transition curve explanation

The ductile-to-brittle transition is the fundamental concept in fracture toughness. A single CVN test temperature does not fully characterize a steel's toughness -- the entire transition curve must be understood:

Transition curve regions

Region	Temperature range (typical for A992)	CVN energy	Fracture appearance	Engineering significance
Upper shelf	Above 50F (10C)	80-200+ ft-lb	100% shear (fibrous)	Fully ductile, no fracture risk
Transition zone	-20F to 50F (-29C to 10C)	15-80 ft-lb	Mixed shear and cleavage	Risk depends on specific temperature
Lower shelf	Below -40F (-40C)	5-15 ft-lb	100% cleavage (crystalline)	Brittle, high fracture risk

The width and position of the transition zone varies by steel grade, thickness, and production method. Modern A992 from EAF mills typically has a transition zone centered around 0-30F (-18 to -1C), while A913 Gr 65 has a transition zone centered around -20 to 10F (-29 to -12C), providing better low-temperature performance.

Factors that shift the transition curve

Factor	Effect on transition curve	Practical implication
Increasing thickness	Shifts curve to the right (more brittle)	Heavy shapes require more careful CVN specification
Higher strain rate	Shifts curve to the right	Seismic loading is effectively a high strain rate event
Higher constraint (triaxial stress)	Shifts curve to the right	CJP welds with backing bars are highly constrained
Higher carbon content	Shifts curve to the right	A514 has higher CE and worse toughness than A992
QST process (A913)	Shifts curve to the left (more ductile)	A913 has better toughness than A992 at same strength
Cold working (straightening)	Shifts curve to the right	k-area of rotary-straightened heavy shapes

CVN values by steel grade

Steel grade	Typical upper shelf CVN (ft-lb)	Transition temperature (15 ft-lb)	CVN at 70F	CVN at -20F	Notes
A36 (modern, EAF)	80-150	-10 to 20F	60-120	20-60	Lower strength generally means better toughness
A992 (standard)	80-200+	-20 to 30F	60-180	15-80	Wide scatter; S30 specification recommended for heavy shapes
A992 (heavy W-shapes, tf > 2 in.)	40-100	10 to 60F	20-60	5-30	Core location may have significantly lower toughness
A572 Gr 50	80-180	-10 to 30F	50-150	15-60	Similar to A992
A913 Gr 50	120-250+	-40 to 0F	100-200	40-120	QST process provides excellent toughness
A913 Gr 65	100-200+	-30 to 10F	80-180	30-100	Best choice for heavy seismic columns
A514 (Q&T, 100 ksi)	40-80	0 to 50F	20-50	5-25	Higher strength reduces toughness; careful welding required
A588 (weathering)	80-150	-10 to 30F	50-130	15-60	Similar to A572 Gr 50

Note: These are typical ranges from mill data and published test results. Actual values vary by heat, thickness, and mill. Always specify CVN requirements on the purchase order.

Thickness effects on toughness

Thicker steel sections have lower fracture toughness than thinner sections of the same grade due to two effects:

Triaxial constraint: Thicker sections develop higher triaxial stress states at crack tips, which suppress plastic deformation and promote brittle cleavage fracture.
Cooling rate: The core of a thick section cools slower than the surface during rolling, producing a coarser grain structure with lower toughness.

Maximum thickness guidelines without supplemental CVN testing

Steel grade	Minimum service temperature 0F	Minimum service temperature -20F	Minimum service temperature -40F
A36	No limit (typical)	4 in.	2 in.
A992 (no S30)	6 in. (typical availability)	4 in.	2 in.
A992 (with S30)	No limit (if CVN met)	6 in. (if CVN met)	4 in. (if CVN met)
A913 Gr 65	No limit	6 in.	4 in.
EN 10025 S355 J2	6 in. (150 mm)	4 in. (100 mm)	2.5 in. (63 mm)

These are approximate guidelines. The EN 1993-1-10 maximum thickness table provides a more rigorous approach combining steel grade, subgrade, reference temperature, and stress utilization ratio.

Brittle fracture case studies

Historical failures that shaped modern practice

Incident	Year	Location	Cause	Lesson learned
Hasselt Bridge	1938	Belgium	Brittle fracture of welded I-girder at low temperature, stress concentration at weld defect	Welded construction requires attention to toughness and defect control
Duplessis Bridge	1951	Quebec, Canada	Brittle fracture at -30F in non-toughness-rated steel at welded connection	Cold-climate structures need toughness-rated steel
Liberty Ships	1942-1945	Various (WWII)	1,500+ ships developed cracks; 230+ seriously damaged; 19 broke in half	Welded connections, stress concentrations, and cold temperatures combine to cause brittle fracture
Point Pleasant Bridge	1967	West Virginia, USA	Fatigue crack growth to critical size followed by brittle fracture of a single eyebar	Fracture mechanics approach needed for critical members
Northridge earthquake weld fractures	1994	California, USA	Brittle fracture of beam flange CJP welds in 150+ steel moment frame buildings	Demand-critical welds need CVN-rated filler metal and proper detailing
Kobe earthquake column fractures	1995	Japan	Brittle fracture of thick box column sections in moment frames	Thick sections need enhanced toughness requirements

These failures collectively drove the development of modern fracture toughness requirements in AISC 341, AWS D1.8, and international codes.

Material selection for low-temperature service

For structures serving in cold climates, select steel grades with appropriate toughness ratings:

Minimum service temperature	Recommended steel grade (North America)	Recommended steel grade (Europe)	CVN specification
32F (0C) and above	A992 or A572 Gr 50	S355 JR	Standard grade, no supplemental testing
0F (-18C)	A992 with S30, or A913 Gr 50	S355 J0 or J2	20 ft-lb at 70F (base metal)
-20F (-29C)	A913 Gr 50 or Gr 65	S355 J2 or K2	20 ft-lb at 0F to -20F
-40F (-40C)	A913 Gr 50 or Gr 65	S355 K2 or S460 NL	20 ft-lb at -40F
-60F (-51C) and below	Special order with project-specific CVN specification	S500 QL1 or special	Consult with steel producer; consider A516 Gr 70 (pressure vessel quality)

Design strategies for cold-temperature service

Specify the CVN test temperature at least 10F below the lowest anticipated service temperature.
Avoid thick welded joints where possible. Use bolted connections for critical tension members.
Detail connections to minimize stress concentrations. Use generous radii at re-entrant corners.
Specify low-hydrogen welding consumables with CVN ratings below the minimum service temperature.
For extreme cold (-60F and below), consider stainless steel (ASTM A240 Type 304L or 316L) for exposed connections, as austenitic stainless steel does not exhibit a ductile-to-brittle transition.

ASTM E23 test procedure

The Charpy V-Notch test is standardized by ASTM E23 ("Standard Test Methods for Notched Bar Impact Testing of Metallic Materials"). Key aspects of the test procedure:

Parameter	Specification
Specimen dimensions	10 mm x 10 mm x 55 mm (standard full-size)
Notch type	V-notch, 2 mm deep, 45 degree included angle, 0.25 mm root radius
Sub-size specimens	Permitted when material thickness < 10 mm (e.g., 10x7.5, 10x5)
Striker energy	264-325 ft-lb (standard pendulum)
Impact velocity	16-19 ft/sec
Test temperature	As specified by the referencing code or specification
Temperature control	+/- 2F (+/- 1C) at the specimen
Transfer time	Less than 5 seconds from bath/furnace to fracture
Number of specimens	Minimum 3 per test temperature per lot
Reporting	Individual and average CVN energy, fracture appearance (% shear), lateral expansion

Sub-size specimen correlation

When testing thin material that cannot produce a full-size 10 mm specimen, sub-size specimens are used. The CVN energy from a sub-size specimen cannot be directly compared to full-size requirements without conversion:

Specimen size	CVN energy relative to full-size	Conversion factor (approximate)
Full (10 x 10 mm)	1.00	None needed
3/4 size (10 x 7.5 mm)	0.75	Multiply by 4/3 for equivalent full-size
1/2 size (10 x 5.0 mm)	0.50	Multiply by 2 for equivalent full-size

However, ASTM E23 notes that energy conversion is approximate because the stress state differs between specimen sizes. For code compliance, the specification should state whether the requirement applies to full-size or sub-size specimens.

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Related references

Disclaimer

This page is for educational and reference use only. It does not constitute professional engineering advice. All design values must be verified against the applicable standard and project specification before use. The site operator disclaims liability for any loss arising from the use of this information.

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Frequently Asked Questions

What is the recommended design procedure for this structural element?

The standard design procedure follows: (1) establish design criteria including applicable code, material grade, and loading; (2) determine loads and applicable load combinations; (3) analyze the structure for internal forces; (4) check member strength for all applicable limit states; (5) verify serviceability requirements; and (6) detail connections. Computer analysis is recommended for complex structures, but hand calculations should be used for verification of critical elements.

How do different design codes compare for this calculation?

AISC 360 (US), EN 1993 (Eurocode), AS 4100 (Australia), and CSA S16 (Canada) follow similar limit states design philosophy but differ in specific resistance factors, slenderness limits, and partial safety factors. Generally, EN 1993 uses partial factors on both load and resistance sides (γM0 = 1.0, γM1 = 1.0, γM2 = 1.25), while AISC 360 uses a single resistance factor (φ). Engineers should verify which code is adopted in their jurisdiction.