ISO 148-1 Metal Charpy pendulum impact test methods

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ISO 148-1 — Metallic materials – Charpy pendulum impact test – Part 1: Test method

ISO 148-1 defines the method for the Charpy (V-notch & U-notch) pendulum impact test to determine the absorbed energy when a notched metallic specimen is broken by a single swinging pendulum blow. It does not cover instrumented impact testing (that belongs to ISO 14556).

This test measures notch toughness / impact energy absorption, which captures how a material behaves under high strain-rate, dynamic loading with a stress concentration (the notch). It is especially valued for revealing the ductile-to-brittle transition: many metals lose toughness dramatically as temperature drops, something static tensile tests alone will not expose.

That matters because brittle fracture can initiate at flaws, notches, or low temperature and propagate with essentially no plastic warning, leading to catastrophic failures in pressure equipment, pipelines, ships, bridges, cranes, offshore structures, rail, and vehicle chassis. The Charpy absorbed energy (KV/KU) is therefore a mandatory acceptance/rejection gate in many product specs and QA programs.

Test Principle

A standardized notched test piece is placed horizontally on two anvil supports (span = 40 mm per ISO machine geometry).

A raised pendulum hammer is released; its striker delivers a single blow on the face opposite the notch, centered on the notch plane.

The tester reads the energy loss (after friction/air-resistance corrections), reported as absorbed energy K (J).

Optionally (informative): lateral expansion and shear fracture appearance (%) are also evaluated.

Key physical note: because pendulum velocity decreases during the swing, the measured absorbed energy should remain within a valid range—ISO 148-1 requires K ≤ 80 % of the machine's initial potential energy Kₚ (otherwise the value is flagged as approximate / beyond valid capacity).

ISO 148-1 Metal Charpy pendulum impact test methods

Test Specimen Requirements

Standard Specimen

Basic dimensions: Length 55 mm, square cross-section 10 mm × 10 mm. A V-notch or U-notch is precisely machined at the longitudinal midpoint of the specimen.

V-notch specifications: Included angle 45°, notch depth 2 mm, root radius 0.25 mm.

U-notch specifications: Notch depth 5 mm (default), root radius 1 mm.

Dimensional tolerances: Strict machining tolerances are defined for overall size, notch geometry and notch centering position.

The surface roughness of the specimen (except end faces) shall be better than Ra 5 μm to avoid affecting test results.

ISO 148-1 Metal Charpy pendulum impact test methods

Subsize Specimens

When standard full-size specimens cannot be sampled from materials, subsize specimens with thicknesses of 7.5 mm, 5 mm or 2.5 mm are allowed.

Test results of different-sized specimens are not directly comparable, which must be clearly stated in reports.

Specimen Preparation Rules

Notches shall be machined after final heat treatment of heat-treated materials (unless proven that pre-machining has no impact on results).

Machining marks at the notch root are prohibited, as they will distort absorbed energy data.

Markings on specimens can only be made on surfaces that do not contact supports, anvils or the striker, and shall not be located in deformation zones.

Test Equipment of ISO 148-1 Metal Charpy pendulum impact test methods

Charpy Pendulum Impact Testing Machine	The UnitedTest Impact Testing machine consists of a pendulum hammer, fixed anvils/supports, scale/indicator, shielding cover and temperature conditioning accessories. It must be installed and verified in accordance with ISO 148-2 before use. Defined support span = 40 mm between anvils. Anvil radius & taper per standard geometry.
Striker	Two standard striker radii are specified: 2 mm and 8 mm. Test results from different strikers differ significantly, so the striker size must be marked in the result symbol (e.g., KV₂) for 2 mm striker + V-notch)
Anvils and Supports	The specimen is placed squarely on the anvils; the notch’s symmetry plane shall be within 0.5 mm of the mid-plane between the two anvils.
Temperature Conditioning Devices	Liquid or gaseous medium containers for heating/cooling specimens, and insulated transfer tongs for rapid specimen handling.

Key Test Parameters:

Test Temperature: Ambient test temperature: 23 °C ±5 °C.

For specified temperatures: Specimen temperature shall be controlled within ±2 °C. For liquid medium conditioning, the medium temperature is stabilized within ±1 °C for at least 5 minutes; for gaseous medium, stabilization lasts at least 30 minutes.

Specimen Transfer Time: For non-ambient tests, the time from removing the specimen from the conditioning medium to impact shall not exceed 5 seconds. If the temperature difference between the specimen and environment is less than 25 °C, the limit extends to 10 seconds.

Energy Range Limit: The measured absorbed energy shall not exceed 80% of the pendulum’s initial potential energy. Exceeding this limit will lead to inaccurate data and must be noted in reports.

Friction Loss: Total friction loss of the machine ≤ 0.5% of nominal energy K_N.

Main Test Stipulations & Operational Procedures of ISO 148-1 Charpy Impact Test

1, Pre-Test Preparation

Inspect and verify the impact machine following ISO 148-2, then measure daily friction loss as required.

Check specimen dimensions, notch quality and surface condition to eliminate unqualified samples.

Condition specimens to the required test temperature using liquid or gaseous media as applicable.

2, Formal Test Steps

Place the conditioned specimen steadily on the anvils, ensuring accurate centering. Use self-centering tongs for low-temperature tests if needed to avoid specimen rebound interference.

Lift the pendulum to the designated initial position and lock it.

Release the pendulum to strike the specimen; record the indicated absorbed energy after fracture.

Observe the fracture state: record incomplete fracture, specimen jamming or abnormal impacts. If the specimen jams between machine parts, discard the result and inspect the machine for damage.

3, Test Report Requirements

Reference to ISO 148-1:2016; specimen identification and size; test temperature; absorbed energy (marked with notch type and striker radius); fracture status; all abnormal conditions affecting results.

Industrial Application Fields

As a universal mechanical performance test standard for metals, ISO 148-1 is widely applied in quality control, material R&D and product certification across industries:

Steel & Iron Industry: Routine inspection for carbon steel, alloy steel, high-strength steel plates, bars and steel pipes; core test for steel product delivery acceptance.

Petroleum & Chemical Industry: Impact toughness testing for pressure vessels, pipeline steel and low-temperature service equipment (to evaluate low-temperature brittle failure resistance).

Automotive Industry: Testing for chassis parts, engine components and body structural metals to ensure resistance to shock loads during driving.

Construction & Infrastructure: Inspection for building steel structures, bridge steel and reinforcing steel to guarantee structural safety under impact or earthquake loads.

Machinery & Equipment Manufacturing: Quality verification for gears, shafts, castings and forgings subjected to dynamic impact.

Aerospace & Defense: Auxiliary toughness evaluation for structural metals (often combined with subsize specimen tests for limited sampling space).

Scientific Research & Material Development: Studying the ductile-brittle transition characteristics of new metal materials, optimizing heat treatment and processing techniques.

Related Test Standard:

ISO 148-1	Metallic materials - Charpy pendulum impact test - Part 1: Test method
ASTM E23	Standard Test Methods for Notched Bar Impact Testing of Metallic Materials
AASHTO T 266	Standard Method of Test for Notched Bar Impact Testing of Metallic Materials (CVN)
JIS Z 2242	Method for Charpy pendulum impact test of metallic materials
KS B 0810	Method of impact test for metallic materials
GB/T 229	Metallic materials—Charpy pendulum impact test method
ASTM E2298	Instrumented impact test standard, matching E23 to collect force-displacement curves.
ISO 14556	Metallic materials — Charpy V-notch pendulum impact test — Instrumented test method
EN 10045-1	Charpy Impact Test for Metallic Materials - Test Method
ISO 148-2	Metallic materials - Charpy pendulum impact test - Part 2: Verification of testing machines
ISO 148-3	Metallic materials. Charpy pendulum impact test. Preparation and characterization of Charpy V-notch test pieces for indirect verification of pendulum impact machines
ISO 148-4	Metallic materials. Charpy pendulum impact test - Testing of miniature Charpy-type V-notch test pieces
ASTM E2248	Standard Test Method for Impact Testing of Miniaturized Charpy V-Notch Specimens

Impact Tester is mainly used to determine the anti-impact capability of ferrous metal materials with high toughness, especially for steel and iron and their alloy, under dynamic load. This series tester is operated semi-automatically.

Electric impact specimen U/V notching machine is a specialized specimen preparation device for metal Charpy pendulum impact tests. It is driven by a motor and lead screw, and uses forming cutting tools to cut a V-shaped or U-shaped notch in a single pass, meeting standards such as GB/T 229, ISO 148,

CST-50 projector is a supplemental equipment for impact test, mainly used to check the accuracy of impact specimen U/V notch. Put the notched specimen on projector working table, multiple 50* and compare the projection image with standard plate, then identify the quality of impact specimen notch.

DWC low temperature chamber is a supplemental equipment for impact test under low temperature. Use imported high quality compressor to refrigerate, single-chip micro processor control, auto control temperature, timing, alarm etc.; Refrigeration fast, big volume.

Q1: What is ISO 148-1:2016?

A: It is the primary international standard for Charpy pendulum impact tests on metallic materials. It specifies the uniform test method to measure the energy absorbed by notched metal specimens when fractured by a swinging pendulum. This standard only applies to conventional energy measurement and excludes instrumented impact testing (governed by ISO 14556)

Q2. Why is the Charpy impact test (ISO 148-1) so important for metals?

A: Unlike a slow tensile test, the Charpy test measures a metal’s toughness under high-strain-rate (dynamic) loading. Its primary importance lies in identifying the ductile-to-brittle transition temperature (DBTT). Many metals (like structural steel) behave ductile at room temperature but become dangerously brittle in cold environments. This test helps prevent catastrophic failures in bridges, ships, and pressure vessels by ensuring materials can withstand sudden impacts and low temperatures without fracturing.

Q3. What is the main difference between a "V-notch" and a "U-notch" test piece?

A: The difference lies in the notch geometry, which significantly affects stress concentration:

V-notch: Has a sharp, 45° angle with a very tight 0.25 mm root radius. It is more sensitive to brittle fracture and is the global standard for most structural steel specifications.

U-notch: Has a rounded 1 mm root radius and a depth of 5 mm. It is less severe than the V-notch and is typically used for cast irons, non-ferrous metals, or specific legacy specifications.

Note:You cannot directly compare KV (V-notch) and KU (U-notch) results.

Q4. What did ISO 148-1:2016 change regarding the dimensions of the test piece?

A: The 2016 revision updated terminology to align with other fracture mechanics standards:

The dimension previously called "Height" is now officially "Width (W)" (the distance between the notched face and the opposite face).

The dimension previously called "Width" is now "Thickness (B)" (the dimension parallel to the notch).

Note:While the names changed, the physical 10x10 mm dimensions of the standard specimen remain the same.

Q5. Why is the 80% machine capacity rule so critical?

A: The test requires the absorbed energy (K) to be ≤ 80% of the machine’s initial potential energy (K_p). If the energy absorbed is too high, the pendulum slows down excessively during the fracture. Since the test relies on a constant impact velocity to be accurate, exceeding 80% capacity leads to erroneous energy readings. If exceeded, the result must be reported as "approximate."

Q6. How strictly must the test temperature be controlled?

A: Temperature control is vital because impact energy varies drastically with temperature.

Standard Ambient: 23^∘C±5^∘C.

Specified Temperature: The specimen must reach ±2^∘C of the target.

Transfer Time: Once removed from the bath/oven, you have a maximum of 5 seconds to strike the specimen (extended to 10 seconds only if the temperature difference is less than 25^∘C).

Warning:In liquid baths near boiling points, evaporative cooling can drop the specimen temperature instantly, leading to invalid tests.

Q7. What happens if the specimen doesn't break into two pieces?

A: It depends on the purpose of the test:

Material Acceptance Testing: It is generally not required to report incomplete fractures; the energy value is used as-is if the machine indicates it.

Research or Design: Unbroken specimens must be reported. However, if the two halves are "hinged" and can be pushed apart by hand without tools, they are often considered "broken" for reporting purposes.

Q8. Can I use a 2 mm striker and an 8 mm striker interchangeably?

A: No. The standard explicitly warns that tests carried out with 2 mm and 8 mm striker radii can yield different results. You must specify the striker radius in your report (e.g., KV₂ for a V-notch with a 2 mm striker).

Q9. How does ISO 148-1 relate to ISO 148-2 and ISO 14556?

A: ISO 148-2: This covers the verification and calibration of the machine itself. You cannot perform a valid ISO 148-1 test on a machine that hasn't been verified to ISO 148-2.

ISO 14556: This covers Instrumented Impact Testing. If you need to measure the force-time curve or ductile crack initiation (rather than just the total energy), you must refer to ISO 14556, as it is outside the scope of ISO 148-1.

Q10. Are sub-size specimens allowed, and are they comparable to standard ones?

A: Yes, if the material is too thin for a standard 10 mm specimen, you may use 7.5 mm, 5 mm, or 2.5 mm thick sub-size pieces. However, results are not directly comparable to standard 10 mm specimens. The standard warns that direct comparison is only significant when made between test pieces of the same form and dimensions.

Q11: How to handle incomplete fracture of specimens?

A: 1. For routine material acceptance tests: No extra record is required.

2. For research, design or third-party testing: Incomplete fracture must be clearly recorded.

3. A specimen is defined as "broken" if the two fractured halves can be separated manually without tools.

Q12: What to do if the specimen jams in the machine after impact?

A: The test result must be discarded immediately. The entire machine shall be thoroughly inspected for damage that may affect calibration before continuing tests. Jammed specimens will cause extra energy absorption and completely invalidate data.

Q13: Can test results from ISO 148-1 and ASTM E23 be directly converted?

A: Generally not recommended for direct conversion. The two standards differ in striker size, specimen tolerance, support geometry and test details. Cross-standard result comparison must be verified through a large number of comparative tests.

Q14: Is a higher absorbed energy value always better?

A: In most engineering scenarios, yes. Higher absorbed energy means better toughness and stronger impact resistance. But for individual components that require high hardness and rigidity, appropriately low toughness may meet design requirements. Data shall be evaluated combined with actual service conditions.

Q15: Can I ignore the notch quality of specimens?

A: Absolutely not. Tiny machining scratches at the notch root will become stress concentration points, leading to lower measured absorbed energy and distorted evaluation of material toughness. The notch is the core part of the Charpy test.

Q16: Is the Charpy test the same as the Izod impact test?

A: No. ISO 148-1 is for Charpy (simply supported beam) test; Izod is a cantilever beam impact method. ISO 148-1 does not cover Izod tests, while ASTM E23 includes both methods. The two test principles and specimen clamping methods are different, and results cannot be equated.

Q17: When is low-temperature Charpy testing required?

A: It is mandatory for metals serving in cold regions, cryogenic equipment, liquefied gas storage tanks and low-temperature pipeline steel, to verify that materials will not suffer brittle fracture under low-temperature working conditions.

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