ISO 148-3 Charpy V-notch test pieces for indirect verification of pendulum impact machines

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ISO 148-3 — Metallic materials — Charpy pendulum impact test — Part 3: Preparation and characterization of Charpy V‑notch test pieces for indirect verification of pendulum impact machines

ISO 148-3 core focus is to establish unified rules for manufacturing, qualification, certification and proper use of Charpy V-notch reference test pieces, which are essential for the indirect verification of Charpy impact machines as required by ISO 148-2. It is a critical supporting document in the complete ISO 148 series, working alongside ISO 148-1 (test method) and ISO 148-2 (machine verification).

It covers the full lifecycle of reference specimens: raw material selection, machining requirements, batch qualification, statistical characterization, certification rules and on-site usage guidelines. The nominal dimensions of reference specimens follow ISO 148-1, but their dimensional, surface and material tolerances are far stricter to maintain high uniformity. It only applies to steel reference materials for Charpy impact machines and does not cover U-notch specimens, Izod test specimens or reference materials for other impact equipment.

Core Principle

Indirect verification (stipulated in ISO 148-2) relies on comparing test results of certified reference pieces against their known certified energy values. The principle behind ISO 148-3 is:

Produce batches of highly homogeneous steel specimens with stable microstructure and impact performance under unified material and processing rules.

Test these specimens on qualified reference impact machines to determine their certified absorbed energy (KV) and associated uncertainty.

Issue formal certificates for each set of reference pieces.

End-users test these certified specimens on routine industrial impact machines; deviations between measured values and certified values are used to judge machine accuracy, repeatability and overall performance.

This eliminates discrepancies caused by machine differences and unifies test results across laboratories worldwide.

Reference Test Specimen (Reference Test Piece)

1, Basic Dimensions & Geometry

The nominal size is identical to the standard Charpy V-notch specimen in ISO 148-1: 55 mm (length) × 10 mm (width) × 10 mm (thickness).

A standard 45° V-notch (2 mm depth, 0.25 mm root radius) is machined at the midpoint. All geometric tolerances are tightened compared with routine test specimens.

2, Surface Requirements

Notched surface roughness: Ra ≤ 1.6um

Other surfaces roughness: Ra ≤ 3.2um

The notch root must be smooth with no machining defects or scratches to ensure consistent crack initiation.

ISO 148-3 Charpy V-notch test pieces for indirect verification of pendulum impact machines

3, Material & Heat Treatment Rules

All specimens in one batch must come from a single ingot/melt of steel to guarantee chemical consistency.

The entire batch undergoes the identical heat treatment process to stabilize microstructure and impact performance.

Reference specimens are classified into four energy grades based on certified absorbed energy:

Low energy: < 30 J

Medium energy: 30 J ~ 110 J

High energy: 110 J ~ 200 J

Ultra-high energy: ≥ 200 J

4, Marking Rules

Each specimen must have a permanent, unique mark. Markings can only be made on surfaces that do not contact anvils or the striker, and must not cause plastic deformation or affect impact energy.

5, Batch Homogeneity Requirement

For a qualified batch:

If certified energy < 40 J: Standard deviation of test results ≤ 2 J

If certified energy ≥ 40 J: Standard deviation ≤ 5% of the certified K_V value.

Key Test Parameters & Mandatory Stipulations

1 Regular Periodic Verification

Full direct + indirect verification must be conducted at least once every 12 months.

2 Unscheduled Mandatory Re-Verification

Re-verification is required immediately in the following cases:

The machine is moved, re-installed or repaired.

Key components (striker, anvils, pendulum, bearings) are replaced.

Test data is obviously abnormal or disputed between laboratories.

Long-term shutdown (more than 3 months) before re-use.

Test Parameters & Stipulations

1, Striker Specifications

Two standard strikers (2 mm and 8 mm edge radii) are allowed. The striker type used for certification is clearly marked on reference piece certificates, and end-users must use the matching striker during machine verification.

2, Usage Stipulations for Reference Sets

A standard reference set contains 5 randomly selected specimens from a qualified batch. No replacement or mixing of specimens from different sets is permitted.

During machine indirect verification, all 5 pieces in one set must be tested in random order, and all results are used to calculate the average for evaluation.

Reference pieces are destructive after testing and cannot be reused.

3, Uncertainty Stipulations

The standard defines a complete uncertainty assessment system, including uncertainty from material homogeneity, short/long-term stability, and inter-machine deviation. The expanded uncertainty (95% confidence level) of the certified value must be listed on the certificate.

Standard Qualification Procedures

The procedures are divided into two main phases: batch characterization (certification by producers) and machine indirect verification (application by end-users).

Phase 1: Batch Characterization & Certification (Producer Side)

Raw material confirmation: Verify all specimens originate from one melt and have uniform heat treatment.

Dimensional & surface inspection: Screen unqualified specimens with out-of-tolerance size or surface defects.

Sampling: Randomly pick no fewer than 25 specimens from the batch.

Performance testing: Test the samples on fully verified reference machines, record each K_V value.

Statistical analysis: Calculate the average energy, standard deviation and combined measurement uncertainty. Check if homogeneity meets requirements.

Batch grouping: Divide the qualified batch into standard sets (5 pieces per set).

Certificate issuance: Issue a formal certificate for each set with certified energy, uncertainty, striker type, test temperature, storage conditions and shelf life.

Phase 2: Indirect Verification (End-User Side, per ISO 148-2)

Preparation: Take a complete reference set and check the certificate information. Ensure the impact machine uses the matching striker.

Testing: Test 5 reference pieces one by one in random order under specified temperature.

Data comparison: Calculate the average measured energy, compare with the certified value to obtain machine bias and repeatability.

Result judgment: If bias and repeatability meet ISO 148-2 limits, the machine passes indirect verification.

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
ASTM E2298	Standard for instrumented impact testing, matching conventional impact tests in ASTM E23 to collect force-displacement curves.
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
GB/T 19748	Metallic materials—Charpy V-notch pendulum impact test—Instrumented test method
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

Charpy impact test verification specimens are physical standards with stable, uniform, and certified impact energy values determined by authoritative organizations. They are mainly used to check and verify the accuracy of impact testing machines

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.

Instrumented impact tester is adopts advanced foreign technology and cooperate with China National Engineering & Physical research institute to developed a new products. Instrumented impact tester is measuring the impact value, collect and analysis the impact process data, figure energy curve.

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 148-3?

A: ISO 148-3:2016 is Part 3 of the ISO 148 series for metallic Charpy pendulum impact tests. It specifies the full requirements for the preparation, machining, batch qualification, characterization and certification of Charpy V-notch reference test pieces. These reference specimens are exclusively used for the indirect verification of Charpy impact machines as required by ISO 148-2.

Q2: What is the core role of ISO 148-3 in the ISO 148 system?

A: ISO 148 forms a complete testing system: ISO 148-1 (test method), ISO 148-2 (machine verification), and ISO 148-3 (reference specimens for indirect verification). ISO 148-3 provides qualified reference materials, which are the essential carrier to implement the indirect verification required by ISO 148-2. Without compliant reference pieces, machine verification and data traceability cannot be realized.

Q3: Why is ISO 148-3 extremely important for Charpy impact testing?

A:It ensures reference specimens have excellent homogeneity and stable impact performance, which is the premise for accurate machine verification.

It unifies global rules for reference specimen production and certification, making Charpy test results from different laboratories and countries comparable and mutually recognized.

It builds a complete metrological traceability chain for impact tests, supporting laboratory accreditation and industrial quality supervision.

It solves the problem that machines passing direct inspection may still output inconsistent test data, effectively eliminating machine-induced measurement errors.

It guarantees the reliability of material toughness assessment, especially for low-temperature steel, pipeline steel and structural steel used in critical engineering.

Q4: What types of specimens does ISO 148-3 cover?

A: It only applies to Charpy V-notch steel reference test pieces. It does not include U-notch specimens, Izod specimens, miniature impact specimens or reference materials for other impact testing equipment.

Q5: What is the difference between reference specimens (ISO 148-3) and routine test specimens (ISO 148-1)?

A: They share the same nominal dimensions, but reference specimens have far stricter dimensional tolerances, surface roughness and material uniformity. Besides, reference pieces are produced from a single melt and unified heat treatment to ensure batch consistency, while routine specimens follow general machining rules.

Q6: What are the standard dimensions of the Charpy V-notch reference specimen?

A: The nominal size is identical to ISO 148-1: 55 mm (length) × 10 mm (width) × 10 mm (thickness). It has a 45° V-notch with 2 mm depth and 0.25 mm root radius. All geometric tolerances are tightened for reference pieces.

Q7: What are the surface roughness requirements for reference specimens?

A: The notched surface shall have a roughness of Ra ≤ 1.6 μm; other surfaces shall be Ra ≤ 3.2 μm. No machining scratches or defects are allowed at the notch root.

Q8: What material and heat treatment rules apply to a batch of reference pieces?

A:All specimens in one batch must be manufactured from a single steel ingot/melt to ensure consistent chemical composition.

The entire batch must undergo the identical heat treatment process to stabilize microstructure and impact energy.

Q9: What is a reference testing machine?

A: A high-precision pendulum impact machine specially used to characterize and certify reference specimens. It must comply with ISO 148-2 plus additional stricter technical rules specified in ISO 148-3.

Q10: How many specimens are required for batch qualification sampling?

A: To qualify a batch, randomly select at least 25 specimens for testing on one or multiple reference machines. The average of all test results is taken as the batch’s certified reference energy (K_VR).

Q11: What is a reference set?

A: After a batch is qualified, specimens are divided into standard sets, with 5 pieces per set. One complete set must be used for a single indirect verification; specimen replacement or mixing between different sets is prohibited.

Q12: Can reference specimens be reused after testing?

A: No. Charpy impact is a destructive test. Once fractured, the reference piece loses its effectiveness and cannot be reused.

Q13: Can I mix specimens from different reference sets during verification?

A: Strictly prohibited. Each verification must use an intact set of 5 pieces from the same batch.

Q14: What is the expanded uncertainty?

A: It is the total uncertainty at a 95% confidence level, calculated by combining all uncertainty components. It must be clearly marked on the reference piece certificate for data evaluation.

Q15: What is the rule for transferring certified values between primary and secondary batches?

A: A primary batch (PB) with known certified values can be used to calibrate a new secondary batch (SB). The two batches must have similar performance, and the deviation between test results shall not exceed the specified limit.

Q16: What is the difference between ISO 148-3 and ASTM related reference specimen standards?

A: ISO 148-3 follows ISO series rules for material selection, tolerance and uncertainty calculation, while ASTM uses NIST reference specimens with independent certification criteria. Their reference pieces and test results are not interchangeable.

Q17: Why do test results of reference pieces have large dispersion?

A: Possible reasons: 1) The reference batch fails the homogeneity requirement; 2) The impact machine has excessive friction or unstable vibration; 3) Improper specimen placement. Recheck the machine first, then confirm the reference piece status.

Q18: Can subsize reference specimens be used per ISO 148-3?

A: No. ISO 148-3 only standardizes full-size 10 mm × 10 mm Charpy V-notch reference specimens. Subsize specimens are not covered.

Q19: Is U-notch reference specimen specified in ISO 148-3?

A: No. This standard only applies to V-notch reference pieces. U-notch reference materials follow other relevant regulations.

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