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ASTM E8 - Metal Tensile Testing Equipment

ASTM E8 round tensile specimen strain simulation
Tensile Testing Machine for ASTM E8
ASTM E8 Tensile Grips
Universal Grip ASTM E8 tensile fixture for universal testing machines

Downloads: Standard Test Methods for Tension Testing of Metallic Materials - PDF · ASTM E8 Tensile Fixture – Universal Grip Data Sheet (PDF)

Cutting dies for ASTM E8: Sheet-type specimen · Subsize specimen (hardened or ribbon steel, with data sheets)

Non-contact strain measurement: UGC-VE-2106 ASTM video extensometer · all UGC-VE models

Written by Chris Thomas, Universal Grip Company · Reviewed by Frank Bertini · Updated October 17, 2026

ASTM E8 / E8M is the standard test method for tension testing of metallic materials at room temperature. A machined round or flat specimen is pulled to fracture at a controlled rate while load and extension are recorded, giving yield strength, tensile strength, elongation and reduction of area. It is the foundation test of metals certification: mill certificates, aerospace and automotive material qualification, forging and casting acceptance, heat-treatment verification and failure investigations all rest on it, and most product standards (A370 for steel products, B557 for aluminum, A615 for rebar, F606 for fasteners) refer back to it for the method.

The method is short on words and long on details that decide whether a result is valid: the specimen proportions and the 4D versus 5D gauge length, the three rate-control methods and their numerical limits, the extensometer class required for each property, the alignment requirements, where the fracture must fall, and how to measure elongation and reduction of area after the test. This guide collects all of it with the current E8/E8M-25 figures, works an example from load to reported values, maps the method to ISO 6892-1, and describes the grips, extensometers and machines Universal Grip supplies for the test.

In this guide: What ASTM E8/E8M Measures · Specimen Types and Dimensions · Test Speed: Control Methods A, B and C · Extensometers: Classes and Gauge Lengths · Grips and Alignment · Step-by-Step Procedure · Calculations and Worked Example · Precision: What to Expect · ASTM E8/E8M vs ISO 6892-1 · Common Errors · Equipment for ASTM E8/E8M · FAQ

What ASTM E8/E8M Measures

E8 (inch-pound) and E8M (SI) are published together as one document; the two differ in units and in one substantive point, the gauge length of round specimens (4D in E8, 5D in E8M), which is why the designation must be reported with the result. The method determines:

  • Yield strength: by the 0.2 % offset method (the most common), by extension under load (EUL), or as the upper or lower yield point for materials with a yield point elongation, such as low-carbon steels.

  • Yield point elongation: the strain over which a discontinuous-yielding material stretches at or near constant load.

  • Tensile strength (ultimate tensile strength): maximum load divided by original cross-section.

  • Elongation after fracture: the permanent extension of the gauge length, as a percentage, measured by fitting the pieces together.

  • Reduction of area: the percentage decrease in cross-section at the fracture.

  • Uniform elongation and elongation at fracture from the extensometer, where required.

The test runs at 10 to 38 °C (50 to 100 °F); elevated-temperature tension testing is ASTM E21. Related methods on the same machine include ASTM E290 bend, E23 Charpy impact on a separate pendulum machine, and A370, the mechanical-testing umbrella for steel products that adopts E8 for tension. Our metals testing page covers the lab as a whole.

Specimen Types and Dimensions

E8 defines round, flat (sheet and plate), subsize, tube, wire, and powder-metallurgy specimens. The ones below cover the large majority of tests.

Round specimens

The standard round specimen has a reduced-section diameter D of 12.5 mm (0.500 ± 0.010 in) with a gauge length G of 50 mm (2.000 ± 0.005 in) in E8, which is 4D, or 62.5 mm in E8M, which is 5D. The fillet radius R is at least 10 mm (3/8 in) and the reduced section A is at least 56 mm (2 1/4 in) long in E8, 75 mm in E8M. Proportional small-size rounds keep the same ratios: in E8M, D 9 mm with G 45 mm, D 6 mm with G 30 mm, D 4 mm with G 20 mm and D 2.5 mm with G 12.5 mm (5D); in E8, D 0.350 in with G 1.400 in, 0.250 in with 1.000 in, 0.160 in with 0.640 in and 0.113 in with 0.450 in (4D). The famous 0.505 in diameter is the inch-pound alternative because its area is 0.2003 in², so stress in psi is load in pounds divided by 0.2.

The ends may be plain (for wedge or V-jaw grips), threaded, shouldered (button-head) or pin-loaded; the end form is chosen to suit the grips and the material, and the reduced section may taper by up to 1 % from the ends to the centre so that fracture favours the middle.

Flat specimens

  • Sheet type: gauge length 50 mm (2.000 ± 0.005 in), width 12.5 mm (0.500 ± 0.010 in), fillet radius 12.5 mm (1/2 in), reduced section at least 57 mm (2 1/4 in), grip section at least 50 mm, overall length at least 200 mm (8 in). For thickness from 0.13 to 19 mm; foil under 0.15 mm goes to ASTM E345.

  • Plate type: gauge length 200 mm (8.00 ± 0.01 in), width 40 mm (1 1/2 in), fillet radius 25 mm (1 in), overall length at least 450 mm (18 in). For plate 5 mm and thicker.

  • Subsize: gauge length 25 mm (1.000 ± 0.003 in), width 6.0 mm (0.250 ± 0.005 in), fillet radius 6 mm (1/4 in). For thin or narrow material and small castings; thickness up to 6 mm.

Width tolerances along the reduced section are tight (the ends may be at most 1 % wider than the centre), and the edges must be machined, not sheared, with a surface finish that leaves no notches; sheared edges on high-strength sheet lower both strength and elongation. The standard specifies the measurement resolution by size: dimensions of 5 mm (0.200 in) and over to 0.025 mm (0.001 in), 2.5 to 5 mm to 0.0125 mm, and 0.5 to 2.5 mm to 0.0025 mm. Cross-section errors go straight into the stress: a 0.1 mm error on a 12.5 mm round is a 1.6 % error in every strength value.

Full-section and other forms

Tubes may be tested full-section with plugs in the grips, or as longitudinal strips or rounds; wire and rod are tested full-section with the gauge length taken as a multiple of the diameter; powder-metallurgy specimens have their own flat and round forms and are exempt from the 4D/5D rule; and for products such as rebar, bolts and welded wire the product standard sets the specimen and E8 supplies the method.

Test Speed: Control Methods A, B and C

Since the 2009 revision E8 defines three ways to control the rate through the yield region, and the chosen method must be reported. All three are applied up to and through yield; after yield the crosshead speed is set between 0.05 and 0.5 mm/mm of reduced-section length per minute to fracture, unless the material specification says otherwise.

  • Method A, stress rate control: 1.15 to 11.5 MPa/s (10,000 to 100,000 psi/min) in the elastic region, run as load control, or as a crosshead speed that produces that stress rate on the specimen in its elastic range. The traditional method and the one most mill labs use.

  • Method B, closed-loop strain rate control: 0.015 ± 0.006 mm/mm/min (in/in/min) of strain measured by the extensometer, held through yield. The most reproducible method for rate-sensitive materials, and the one ZwickRoell and ISO 6892-1 recommend, but it requires a machine that can close the loop on extensometer strain.

  • Method C, crosshead speed control: 0.015 ± 0.003 mm/mm/min of the reduced-section length, so on a specimen with a 60 mm reduced section the crosshead runs at 0.9 ± 0.18 mm/min. Simple and common on electromechanical machines, but the actual strain rate on the specimen is lower than the nominal value before yield because the machine and grips also stretch.

Two cautions. The rate matters: yield and tensile strength of most steels rise a few percent for a ten-fold rise in strain rate, and the material specification may override E8 (titanium and high-temperature alloys often require a specific strain rate). And one conservative speed for everything is not compliant; an audit of certification labs found that a single fixed crosshead speed used for all specimen sizes fell outside the Method C limits for many of them, because the limit scales with the reduced-section length. Set the speed per specimen, and record the method and the rate.

Extensometers: Classes and Gauge Lengths

An extensometer per ASTM E83 is required for yield strength by offset or EUL and for any extensometer-based elongation. The class requirement depends on the property:

  • Yield strength (offset or EUL): Class B2 or better (error not more than 0.0002 mm/mm or 0.5 % of reading, whichever is greater).

  • Uniform elongation and elongation at fracture from the extensometer: Class B2 for strains under 5 %, Class C for 5 % to under 50 %, Class D for 50 % and over.

  • Gauge length: should match the specimen gauge length (50 mm on the standard specimens) and, on specimens without a reduced section, must not exceed 80 % of the free length between the grips.

A clip-on extensometer with a 50 mm gauge is the workhorse for yield; it is usually removed after yield to protect it, so elongation after fracture is then measured by fitting the pieces together. Automatic contacting extensometers and video extensometers stay on to fracture and give uniform elongation and elongation at fracture directly, which is required by some aerospace and automotive specifications and is simply faster for high-throughput labs. For materials that neck late, a video system also records the strain field and the fracture location. Our guide to extensometer types compares clip-on, automatic, long-travel and video systems for E8.

Grips and Alignment

E8 requires that the load be applied axially, with the specimen held so that it is not bent, and in the current edition refers to ASTM E1012 for verifying alignment. Bending is the hidden error of tension testing: for a 12.5 mm round, each 0.025 mm (0.001 in) of eccentricity between the load axis and the specimen axis adds about 1.5 % to the surface stress; on a 6 mm round the same eccentricity adds about 3 %. The error shows up as low and scattered yield strengths and elongations, because one side of the specimen yields first.

Grip selection by specimen

  • Hydraulic wedge grips: the standard for production metals testing from 100 kN upward. Constant hydraulic clamping (typically 210 bar / 3,000 psi and up) holds flat and round specimens without slippage through yield and fracture; side-loading jaws with serrated flat faces for sheet and plate and V-faces for rounds; the specimen is centred by the jaw geometry. Available for floor-standing universal testing machines from 200 to 2,000 kN.

  • Mechanical wedge grips: self-tightening by the wedge angle; the usual choice on benchtop machines up to 100 kN. Flat serrated faces for sheet and subsize specimens, V-faces for small rounds. The initial clamping must be firm enough that the specimen does not slip and re-seat during the elastic region, which shows as steps in the stress-strain curve.

  • Threaded and shouldered (button-head) holders: for round specimens with threaded or shouldered ends, load is transferred through the end form rather than friction, so there is no slippage and no jaw damage; split inserts hold the shoulder. Used for high-strength alloys, hard materials that wedge jaws cannot bite, and specimens for elevated-temperature testing. Mount them on spherical-seat or universal couplings so the specimen self-aligns.

  • Pneumatic grips: thin sheet, foil and wire at low force, where hydraulic clamping would crush the specimen.

  • Bollard and wire grips: wire and strand, which cannot be gripped by jaws without a jaw break.

Alignment is set in the grips and the couplings, not in the specimen: use grips whose jaws centre the specimen automatically, mount them with concentric adapters, and verify with a strain-gauged alignment specimen per E1012 when the quality system (Nadcap, ISO 17025 scopes for aerospace) requires it. All of our metals grips are built in adapters that match the load string of Instron, MTS, ZwickRoell, Shimadzu, Tinius Olsen and other machines; the tensile grips page lists capacities and jaw faces.

Step-by-Step Procedure

  • 1. Measure the reduced-section diameter or width and thickness at three places and compute the original area A0 from the minimum. Mark the gauge length on the specimen (punch marks or scribed lines, light enough not to start a fracture) if elongation will be measured after fracture.

  • 2. Grip the specimen centrally with equal engagement at each end, the gauge length centred between the grips. Apply no more than a small preload (the standard limits preloads to 20 % of nominal yield for dynamic alignment checks and 10 % for static, and in a normal test the preload is just enough to seat the grips).

  • 3. Attach the extensometer on the gauge length, centred, and zero it.

  • 4. Select the control method (A, B or C), set the rate for this specimen's dimensions, and set the post-yield crosshead speed.

  • 5. Run through yield; remove a clip-on extensometer after the yield region if it is not rated to fracture, then continue at the post-yield speed to fracture.

  • 6. Check the fracture location. For reduction of area the fracture must be in the middle half of the reduced section. For elongation after fracture, if the fracture is within 25 % of the gauge length from a gauge mark the elongation may be invalid and the standard allows a retest (or the fitted measurement to be reported with a note).

  • 7. Fit the pieces together and measure the final gauge length to 0.1 mm (0.01 in on gauge lengths up to 50 mm) and the minimum diameter or width and thickness at the fracture.

  • 8. Calculate and round: strengths to 1 MPa (100 psi below 50 ksi, 500 psi from 50 to 100 ksi, 1 ksi above), elongation to 0.5 % (or 1 % above 10 %), reduction of area to 0.5 % up to 10 % and 1 % above.

Calculations and Worked Example

  • Tensile strength: TS = P max ÷ A0.

  • 0.2 % offset yield: draw a line parallel to the elastic portion of the stress-strain curve offset by 0.002 mm/mm; the stress where it crosses the curve is the yield strength. Software does this by fitting the modulus line over a defined elastic window; make sure the window excludes the seating region at the start.

  • EUL yield: the stress at a specified total extension, commonly 0.5 % (0.005 mm/mm), used for materials without a well-defined linear region.

  • Elongation after fracture: EL = (L f − L 0) ÷ L 0 × 100, from the fitted pieces.

  • Reduction of area: RA = (A 0 − A f) ÷ A 0 × 100, with A f from the minimum fracture dimensions.

Worked example (E8M, 12.5 mm round, 5D). Measured diameter 12.48 mm, so A0 = π × 6.24² = 122.3 mm². Gauge length 62.5 mm. Under Method C with a 75 mm reduced section, the crosshead speed through yield is 0.015 × 75 = 1.125 mm/min (limits 0.9 to 1.35 mm/min); after yield, 0.1 × 75 = 7.5 mm/min. The 0.2 % offset line crosses the curve at 51.3 kN, and the maximum load is 70.6 kN. Yield strength = 51,300 ÷ 122.3 = 419 MPa (round to 420 MPa); tensile strength = 70,600 ÷ 122.3 = 577 MPa. The fracture falls 28 mm from one gauge mark (inside the middle half of the reduced section and more than 25 % of the gauge length from the mark). Fitted gauge length 78.1 mm, so elongation = (78.1 − 62.5) ÷ 62.5 × 100 = 25 %. Minimum fracture diameter 8.42 mm, A f = 55.7 mm², reduction of area = (122.3 − 55.7) ÷ 122.3 × 100 = 54.5 %, rounded to 54 %. Reported: 420 MPa yield (0.2 % offset), 577 MPa tensile, 25 % elongation on 5D (62.5 mm), 54 % reduction of area, Method C.

Note the elongation would be higher on a 4D gauge length, because the necked region is a larger share of a shorter gauge length; that is why E8 and E8M elongations are not directly comparable and why the gauge length (4D, 5D, or 50 mm on a flat) is always reported with the value. Conversion formulas between gauge lengths exist (ASTM E8 refers to the Oliver relation and ISO 2566) but they are approximations.

Precision: What to Expect

The interlaboratory study in E8 gives coefficients of variation of roughly 0.9 % within a lab and 1.3 % between labs for tensile strength, 1.4 % and 2.3 % for 0.2 % offset yield, 2.8 % and 5.4 % for elongation, and 2.8 % and 4.6 % for reduction of area. Strengths are therefore very reproducible when the cross-section is measured correctly and the rate is controlled; elongation and reduction of area are operator-sensitive, and most of their scatter comes from gauge marking, fitting the pieces together and the fracture location. A lab whose yield strength scatter exceeds 2 % on one heat should look at alignment and rate control first.

ASTM E8/E8M vs ISO 6892-1

  • Control methods: ISO 6892-1 Method A1 (closed-loop strain rate 0.00025 s⁻¹, which is 0.015/min) corresponds to E8 Method B; A2 (crosshead speed) to E8 Method C; ISO Method B (stress rate 2 to 20 MPa/s for steel-modulus materials, 6 to 60 for higher modulus) is close to E8 Method A but with different limits.

  • Gauge length: ISO uses proportional specimens with 5.65√S0, which is 5D on rounds, the same as E8M; E8 uses 4D.

  • Extensometer: ISO requires Class 1 for yield and Class 0.5 for elongation-based properties; E8 uses E83 classes B2, C and D.

  • Yield: both use 0.2 % offset (Rp0.2) and upper/lower yield (ReH, ReL); ISO defines Rt for total extension in place of EUL.

  • Rounding and reporting conventions differ, as does the handling of specimens that fracture near a gauge mark.

A lab serving both markets normally runs Method B / A1 with a long-travel or video extensometer, which satisfies both standards with one setup, and reports the gauge length and method with every result.

Common Errors

  • Reporting E8 when E8M was followed, or mixing 4D and 5D elongations in one comparison.

  • One crosshead speed for all specimens, outside the Method C band for some reduced-section lengths.

  • Rate too fast through yield, raising yield and tensile strength.

  • Area from nominal instead of measured dimensions, or measured at one place only.

  • Clip-on extensometer left on to fracture and damaged, or removed before yield is complete.

  • Extensometer class too low for the property (Class C used for offset yield).

  • Misalignment from worn jaws, mismatched adapters or offset couplings, giving low scattered yields.

  • Jaw slippage during the elastic region, producing steps and a false modulus line for the offset.

  • Fracture at a gauge mark or outside the middle half, reported without a note.

  • Sheared or notched edges on flat specimens, lowering elongation.

  • Stale edition: the current standard is E8/E8M-25; rate methods and extensometer rules changed in 2009 and later.

Equipment for ASTM E8/E8M

See our article on how to run ASTM E8 for a lab-floor checklist, and the metals testing page for complete system configurations.

ASTM E8 FAQ

What is the difference between ASTM E8 and E8M?

E8 is the inch-pound version and E8M the SI version of the same test method. The substantive difference is the gauge length of round specimens: 4 times the diameter (4D) in E8 and 5 times (5D) in E8M, so elongation values differ and the designation must be reported.

What are the standard ASTM E8 specimen dimensions?

The standard round has a 12.5 mm (0.500 in) diameter with a 50 mm (2 in) gauge length in E8 or 62.5 mm in E8M. The standard sheet specimen has a 12.5 mm (0.5 in) width and 50 mm (2 in) gauge length; the plate specimen 40 mm (1.5 in) by 200 mm (8 in); the subsize 6 mm (0.25 in) by 25 mm (1 in).

Why is the ASTM E8 round specimen 0.505 inches in diameter?

Because a 0.505 in diameter has an area of 0.2003 in², so stress in psi equals load in pounds divided by 0.2, which made hand calculation easy. The metric equivalent is 12.5 mm (122.7 mm²).

What is the test speed for ASTM E8?

It depends on the control method. Method A: stress rate 1.15 to 11.5 MPa/s (10,000 to 100,000 psi/min). Method B: closed-loop strain rate 0.015 ± 0.006 mm/mm/min. Method C: crosshead speed 0.015 ± 0.003 mm/mm/min of the reduced-section length. After yield, 0.05 to 0.5 mm/mm/min of the reduced section.

How is yield strength determined in ASTM E8?

Usually by the 0.2 % offset method: a line parallel to the elastic slope, offset by 0.002 strain, intersects the stress-strain curve at the yield strength. The extension-under-load method (stress at a specified total extension, often 0.5 %) and upper and lower yield points for discontinuous yielding are also defined.

What extensometer class does ASTM E8 require?

Class B2 or better per ASTM E83 for yield strength by offset or EUL. For extensometer-based elongation, Class B2 below 5 % strain, Class C from 5 to under 50 %, and Class D at 50 % and above.

How is elongation measured in ASTM E8?

After fracture, the two pieces are fitted together and the distance between the gauge marks is measured; elongation is the increase as a percentage of the original gauge length. If the fracture is within 25 % of the gauge length from a gauge mark, the result may be invalid and a retest is allowed.

How is reduction of area calculated?

RA = (A0 − Af) ÷ A0 × 100, where A0 is the original cross-section and Af the minimum cross-section at the fracture, measured after fitting the pieces together. The fracture must be in the middle half of the reduced section.

What grips are used for ASTM E8?

Hydraulic wedge grips for production testing of flat and round specimens, mechanical wedge grips on benchtop machines, threaded or button-head holders for round specimens with machined ends, pneumatic grips for thin sheet and foil, and bollard grips for wire. Alignment is verified per ASTM E1012.

What is the difference between ASTM E8 and ISO 6892-1?

The methods are similar but not identical. ISO Method A1 corresponds to E8 Method B and A2 to Method C, ISO uses 5D proportional specimens like E8M, extensometer classes and rounding rules differ, and the stress-rate limits in ISO Method B differ from E8 Method A.

What temperature range does ASTM E8 cover?

Room temperature, defined as 10 to 38 °C (50 to 100 °F). Elevated-temperature tension testing is ASTM E21.

How repeatable is ASTM E8?

The standard's interlaboratory data give coefficients of variation of about 0.9 % (within lab) and 1.3 % (between labs) for tensile strength, 1.4 % and 2.3 % for 0.2 % offset yield, 2.8 % and 5.4 % for elongation, and 2.8 % and 4.6 % for reduction of area.

Need a fixture, grips or a complete system for ASTM E8? Contact Universal Grip with your specimen details, capacity and machine connection and we will quote the right setup.

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