ASTM E8 & ASTM E8M: Tensile tests on metallic materials
The ASTM E8 and ASTM E8M standards govern the performance of tensile tests on metallic materials and are among the most important standards in materials testing worldwide. Laboratories, materials testers, engineers, and technical buyers regularly face the challenge of selecting or procuring testing machines that reliably meet the requirements of the ASTM E8 and ASTM E8M standards – whether for incoming goods inspection, quality assurance, or materials and development projects.
Key facts at a glance
ASTM E8 / E8M is a globally recognized American standard for tensile testing of metallic materials.
It is not only valid in North America, but also forms the normative basis of numerous international product and material standards, including ASTM A370 (steel), API standards for pipe materials, ASME regulations for pressure vessels, and SAE specifications.
Standardized testing provides key parameters such as yield strength, tensile strength, modulus of elasticity, and elongation at break, thus forming the basis for material approval, quality assurance, and component design. This results in reproducible test results that support technical decisions and ensure international comparability.
Typical key figures:
- E-modulus (“spring constant” – auxiliary quantity for determining yield strengths)
- Yield Point (yield limit, first damage)
- yield strength Rp0,2
- UTS (Ultimate Tensile Strength) / Tensile strength Rm
- uniform stretching
- elongation at break
- constriction
What are ASTM E8 and ASTM E8M?
ASTM E8 is a American standard, which is also used internationally for Tensile tests on metallic materials, published by ASTM International (American Society for Testing and Materials). It defines Method for determining tensile strength, yield strength, elongation at break and other mechanical properties when metallic samples are subjected to stress. The standard is used worldwide in materials testing and is applied in quality assurance, product development and material release.
ASTM E8M is the metric version of this standard. While ASTM E8 uses units of measurement such as inches and pounds, ASTM E8M is based on the International System of Units (SI) with millimeters and newtons. Both versions contain identical technical requirements and differ only in the units of measurement used.
Tensile tests according to ASTM E8 or E8M enable precise and reproducible characterization of metallic materials and are a standard procedure in many industries.
Differences between ASTM E8 and ASTM E8M
The only difference between ASTM E8 and ASTM E8M lies in the units of measurement used. ASTM E8 uses the imperial system of inches and pounds, while ASTM E8M is based on the metric system of millimeters and newtons. Both versions are equivalent in content and allow for identical test results, provided the respective units of measurement are used correctly.
For testing machines, this means that they must be equipped with software and measurement technology that support both systems in order to comply with the respective standard requirements.
| Criterion | ASTM E8 | ASTM E8M |
| System of units | Imperial (US) | Metric (SI) |
| units | Inch, pound (lbf) | Millimeter, Newton (N) |
| Application | North America, international industry | Europe, international industry |
| technical requirements | Identical to ASTM E8M | Identical to ASTM E8 |
| Test procedure and evaluation | Just like with E8M | Just like with E8 |
| Standard setter | ASTM International | ASTM International |
Relevance for European testing environments
In Europe, the majority of the Use the metric variant ASTM E8M. European industrial companies must therefore ensure that their testing machines and software support ASTM E8M-compliant settings and evaluations. This applies to both the calibration of force measurements and the configuration of specimen geometry and strain measurement in metric units.
In internationally operating companies, it is important to use machines that can flexibly switch between E8 and E8M be able to switch between different testing requirements to meet standards-compliant testing requirements from different markets.
Modern testing software such as LabTest by GALDABINI Enables the parallel processing of metric and imperial units as well as the switching of display units in real time – without affecting the standard-compliant evaluation of the test results.
Contents and requirements of ASTM E8 and ASTM E8M
The aim of the ASTM E8 and ASTM E8M standards is to comparable determination of mechanical properties such as tensile strength, yield strength and elongation at break. They contain clear specifications regarding sample geometry, test conditions, test speed and evaluation – for both round and flat sample shapes.
They apply to a wide variety of metallic materials, including Steel, aluminium, copper alloys and nickel-based materials. The application is not limited to a specific product field, but is found in numerous industries such as mechanical engineering, aviation, automotive industry or materials development.
Testing methods for metallic materials
The standard describes the execution of tensile tests under quasi-static conditions. A standardized specimen is stretched at a constant rate until it breaks. Force and strain values are recorded and used to calculate the following characteristic values:
- Ultimate Tensile Strength (UTS)
- Yield strength
- elastic modulus
- elongation at break
- fracture constriction
The test procedures are defined in such a way as to ensure reproducible and comparable results – regardless of the testing equipment used, provided it meets the standard.
Key figures determined at a glance:
- Tensile strength (UTS)
- Yield strength (ReH) or 0,2% proof strength (Rp0,2)
- Yield strength elongation (Lüders elongation), if applicable
- Elongation at break (A)
- Fracture reduction (reduction of cross-sectional area, Z or RA)
- Elastic modulus (E)
- Optional: material-specific additional properties according to product standard
Sample shapes and dimensions according to ASTM E8 and ASTM E8M
The standards ASTM E8 and ASTM E8M define precise requirements for the shape, dimensions, and fabrication of tensile test specimens to ensure the comparability of test results. They describe different specimen shapes for various material types and product geometries – including flat specimens, round specimens, and specimens made from tubes or castings.
Typical sample forms are:
- Flat samples (e.g. for sheets, strips, foils)
- Round samples (e.g. for rods, wires, solid semi-finished products)
- Samples with threaded heads or shoulder heads for special sample holders
The initial gauge length (ISO = L0 initial gauge length) is a key criterion for strain measurement. There is a normative difference between ASTM E8 and ASTM E8M in this regard:
- ASTM E8: Initial gauge length = 4D (four times the diameter for round specimens)
- ASTM E8M: Initial gauge length = 5D (five times the diameter for round specimens)
This difference directly affects the calculated parameters such as elongation at break (they differ from each other). Therefore, a clear assignment of the standard version used is necessary to avoid misinterpretations.
In addition, the standard specifies minimum dimensions and permissible tolerances for the sample geometry. During sample preparation, care must be taken to ensure that no changes occur to the microstructure or surface finish that could influence the test result. Areas affected by cold working due to punching or cutting may require post-processing. Materials with a constant cross-section (e.g., wires, tubes, or profiles) may be tested without post-processing.
Sample preparation and boundary conditions:
- Cold-worked areas from punching or shearing must be removed or reworked if they may affect the results.
- Thermal cutting processes (laser cutting) should be avoided, as heat can alter the material properties. If unavoidable, appropriate post-processing is required.
- Transition radii and shoulder areas must be designed in such a way as to avoid stress peaks.
- Materials with a constant cross-section (e.g., wire, tubes, profiles, rods) and cast specimens may often be tested without rework.
Sample holders and clamping devices:
The selection depends on the sample shape and material.
(For pressures above 1000 MPa, force-actuated (mostly hydraulic) clamps are usually required)
- Flat specimens: mostly wedge clamping devices with linear or planar force application
- Round samples: Threaded heads or shoulder pieces for higher forces
Crucial is the reproducible and aligned clamping (to avoid bending influence) with a constant clamping length.
Specifications for samples, experimental setup and evaluation
ASTM E8/E8M specifies exactly:
- the geometry of the samples (e.g. diameter, parallel length, transitions),
- the permissible surface preparation,
- the clamping conditions in the testing machine,
- the permissible test speeds depending on the yield strength behavior,
- as well as the calculation methods for all mechanical properties.
Particular importance is attached to the measurement of strain. The standard permits various methods (contact or non-contact), but requires defined initial gauge lengths (Le, Lc). The failure of the specimen is also documented (e.g., fracture location, fracture type).
For the precise, standard-compliant determination of the Young's modulus and the yield strength Rp, an extensometer is indispensable. Simple, inexpensive extensometers are typically removed after approximately 2 mm. If these extensometers are used, the tensile specimen must first be marked with measuring marks, and the elongation of the specimen pieces folded together after fracture must be measured manually.
Comparison with ISO 6892-1
The ISO 6892-1 is the European and international equivalent to ASTM E8/E8M. It also regulates the tensile testing of metallic materials, but is based entirely on the metric system and differs in some aspects, e.g.:
| Aspect | ASTM E8 / E8M | ISO 6892-1 |
|---|---|---|
| units | Imperial (E8) and metric (E8M) | Metric (SI) |
| Types of regulation (Key performance indicator) |
|
|
| Regulatory principle (Measurement traceability) |
|
|
| Sample forms | Defined in inches or mm, depending on E8 or E8M. | Defined in mm, with partially differing shape specifications. |
| International application | Global, with a focus on North America, a frequent reference in product standards | Global, with a focus on Europe and Asia |
In practice, both standards are often considered in parallel. Modern testing software makes it possible to create test plans according to both ASTM and ISO standards and to evaluate them in accordance with the standards.
Technical requirements for testing machines
For the proper execution of tensile tests according to ASTM E8 or ASTM E8M, a precisely designed and calibrated testing machine is required. The standard does not specify the machine type itself, however clear requirements regarding its performance, measurement accuracy and calibrationOnly if all technical requirements are met can the test results be recognized as valid and comparable.
Calibration according to ASTM E4 as a basis
The ASTM E4 standard specifies the requirements for the calibration of force measurement systems in tensile testing machines. A testing machine may only be used for tensile tests according to ASTM E8 if its force measurement technology has been validated according to ASTM E4.
This means:
- Traceable calibration with certified reference device
- Documented repeatability and reproducibility
- Calibration across the entire force measurement range
Tensile testing machines such as the GALDABINI QUASAR series fully meet these requirements.
Key parameters: force measurement, strain, speed
In addition to force measurement, other technical properties are crucial for compliance with the standard:
- Measurement resolution and linearity: High resolution (e.g. >3 million digits at GALDABINI) ensures precise values even at low forces.
- Strain measurement: Various measuring systems are supported, including extensometers (contact or optical), laser or video technology.
- Truss control: Precise control of the testing speed is necessary, especially when determining the yield strength.
- Frame stiffness: Minimal deformation under load prevents measurement deviations and is essential for compliance with the standard.
Importance of software for standards-compliant testing procedures
Not all suppliers fully meet the normative requirements for metal tensile testing according to ISO 6892-1 or ASTM E8/E8M – in particular, the correct integration of the extensometer is not always guaranteed. At the same time, the testing software has become a crucial differentiating factor. Although almost all manufacturers advertise it as "easy to use," in practice there are significant differences in structure, clarity, and user interface. Today, clearly structured, intuitively operable testing software should be the central main argument for investment decisions.
- Creation of standards-based test plans with defined measuring length, fracture criteria, etc.
- Real-time acquisition and visualization of force-strain curves
- Automatic calculation of all standard-relevant parameters
- Documentation and export of results according to test report specifications
Test speeds and control methods according to ASTM E8 and ASTM E8M
The ASTM E8 and ASTM E8M standards place particular emphasis on the testing speed during tensile testing, as properties such as yield strength and proof strength are strongly influenced by the selected strain rate. To ensure reproducible results, the standard defines several permissible methods for determining and controlling the testing speed.
ASTM E8/E8M allows the following approaches:
- Strain rate or strain rate on the sample
- Voltage rate (increase in voltage per unit of time)
- Traverse velocity (movement of the traverse or crosshead)
Control methods according to ASTM E8/E8M
The standard describes three approved control methods for controlling the test speed:
| Method | Description | Advantage | Disadvantage |
| Method A: Voltage rate | Speed is controlled by the increase in voltage. | Easy to set up | High dependence on sample and machine properties |
| Method B: Strain rate control (closed loop) | The extension rate is kept constant, controlled via an extensometer. | Highest accuracy and reproducibility | Higher technical effort |
| Method C: Traverse speed | The speed of the traverse is kept constant. | Simple, also possible without an extensometer | Less precise with discontinuous deformation |
Practical tolerance specifications according to ASTM E8/E8M:
- Method A (stress rate): In the linear elastic range, the stress increase should lie within a tolerance band of approximately 6 to 60 MPa per second.
- Method B (strain rate control, closed loop): The strain rate is typically set to 0,005 – 0,051/min. This method is considered preferred because it provides the most reliable accuracy with an extensometer in the control loop.
- Method C (crossbeam speed): The crossbeam must be adjusted so that the initial gauge length experiences a strain of 0,015 ± 0,003 mm/mm/min.
Note: ASTM E8 / E8M defines speed in minutes (ISO 6892 in seconds).
Important: The standard requires that these tolerances be maintained during the relevant test phases and documented in the test report. Modern systems ensure this through software-based control and complete data recording.
Suitable products that meet all requirements
Other relevant standards in the context of ASTM E8
In addition to ASTM E8 and ASTM E8M, there are other standards frequently used in the field of tensile testing of metallic materials. These standards expand the test conditions, specialize in specific materials, or regulate tests at different temperatures. For internationally oriented companies, it is important to keep these standards in mind as well.
- ISO 6892-1: International standard for tensile testing at room temperature. Content-wise comparable to ASTM E8/E8M, fully metric.
- ISO 6892-2: Governs tensile tests at elevated temperatures. Important supplement for applications in energy and high-temperature engineering.
- ASTM E21: American standard for hot tensile testing of metals. Comparable to ISO 6892-2, but with a focus on the US market.
- ISO 10113 (r-value): Defines the determination of the plasticity ratio r of sheet metal specimens. Relevant in sheet metal forming, especially for automotive applications.
- ISO 10275 (n-value): Describes the determination of the hardening exponent n, also important in sheet metal forming technology.
Frequently Asked Questions about ASTM E8 and ASTM E8M
What is the purpose of the ASTM E8 and ASTM E8M standards?
These standards define standardized procedures for tensile tests on metallic materials to reproducibly determine mechanical properties such as tensile strength, yield strength, and elongation at break. They are the American equivalent of the ISO standard ISO 6892 ff.
What is the difference between ASTM E8 and ASTM E8M?
ASTM E8 uses the US system of units with inches and pounds, while ASTM E8M is based on the SI metric system with millimeters and newtons. Both standards are technically identical in content, but differ in their units of measurement and the definition of the initial gauge length (4D in E8, 5D in E8M). For internationally operating companies, it is important to be able to consider both versions.
Which materials can be tested according to ASTM E8/E8M?
The standard applies to a wide range of metallic materials, including steel, aluminum, copper alloys, and nickel-based alloys. Tensile tests according to ASTM E8/E8M are well-established in both research and industrial quality control. Castings or semi-finished products with a constant cross-section can also be tested according to these specifications.
What requirements does ASTM E8 place on testing machines?
A tensile testing machine must be calibrated according to ASTM E4 and enable precise force and strain measurements. Additionally, the machine must be capable of adhering to defined testing speeds and control methods (A, B, or C). Modern systems such as the GALDABINI QUASAR series meet these requirements and are prepared for standards-compliant testing.
Where are tensile tests according to ASTM E8/E8M used?
In quality assurance, materials testing, research, development and incoming goods inspection — especially in the metal industry, aerospace, automotive industry and mechanical engineering, provided the supply chain concerns the American market or if testing is to be carried out according to the product standards ASTM A 370 (steel), API (pipes), ASME (pressure vessels), SAE (formerly automotive).
What testing speed does ASTM E8/E8M specify?
The standard permits various control methods (A–C) based on strain, stress, crosshead speed, time control, or free-running crosshead speed without load. Method B (strain rate control) is recommended for reproducible results.
What does the initial measurement length 4D or 5D mean?
The initial length is set to four times (4D) or five times (5D) the diameter for round specimens (4D). This affects the calculated elongation at break. (D4 and D5 are not directly comparable and must be converted.)
- For ASTM E8: Gauge Length (initial gauge length L0) = 4 × diameter
- For ASTM E8M: Gauge Length (initial gauge length L0) = 5 × diameter
How does ASTM E8/E8M differ from ISO 6892-1?
Both test metallic materials at room temperature, but ISO 6892-1 is fully metric and defines test speeds via stress rates (Methods A/B).
Which supplementary standards are relevant?
- ASTM E4: Calibration of force measurement systems
- ASTM E21 / ISO 6892-2: Tensile tests at elevated temperature
- ISO 10113 / ISO 10275: r and n values for sheet metal forming
