Testing standard
ASTM E1012
Standard Practice for Verification of Testing Frame and Specimen Alignment Under Tensile and Compressive Axial Force Application
Written and technically reviewed by Dak System Inc. engineeringLast reviewed
ASTM E1012 measures how much bending a testing machine imposes on a specimen when it applies axial force. A strain-gauged alignment specimen is loaded in the elastic range through the machine's own grips, and percent bending is calculated from the differences between the gauges.
At a glance
- Test type
- Calibration & verification
- Published by
- ASTM
- Edition
- E1012-19
- Material
- Metals, alloys & welds
- Runs on
- Series 7200 and Series 9000
What the test does
A strain-gauged alignment specimen — notched or unnotched, metallic or nonmetallic — is installed exactly as a test specimen would be, through the grips and adapters actually used for testing, and loaded slowly within the elastic range to the force levels of routine work. Every gauge is read at each level. From the differences between gauges distributed around and along the specimen, the bending strain is separated from the axial strain, and the ratio of the two is reported as percent bending. The specimen is then removed, rotated and reinstalled so that its own contribution can be distinguished from the machine's.
What it measures, and why it matters
How much bending the machine puts into a specimen while applying what is supposed to be axial force — the fault that a force calibration is structurally incapable of detecting. A force certificate establishes that the machine applies the force it reports; it says nothing about where that force acts. If the load train is eccentric, the specimen carries a bending stress on top of the axial one and one side is more highly stressed than the reported stress implies. These are the two independent ways a testing machine misleads you, and each is invisible to the other's certificate.
What bending does
A misaligned load train adds a bending stress on top of the axial one, so one side of the specimen is more highly stressed than the reading suggests.
- Applies to
- Notched and unnotched specimens
- Range
- The elastic range onlyNothing may yield, or the strain differences stop describing alignment.
- Force levels
- Those used in routine tension, compression, creep and uniaxial fatigue testing
- Materials
- Valid for metallic and nonmetallic testing
- What is verified
- The frame and the specimen alignment together, as assembledGrips and adapters are part of the subject, not neutral.
- Verify in the configuration you test in
- Same grips, same adapters, same specimen typeDakAlignment is a property of the assembled load train, not of the frame alone. Changing a grip can undo it.
Acceptance limits do not come from this practice. The referencing test method sets the maximum percent bending it will tolerate, and fatigue and creep methods are usually the strictest.
Test speed
- Loading
- Slowly, within the elastic range
- Reported
- Percent bending at the stated force levels
- Positions
- Gauges distributed around and along the specimen
- Re-check after any change to the load train
- DakA new adapter, a re-seated grip or a replaced coupling can move alignment more than years of use.
Calculations
PB = (bending strain / axial strain) × 100
- bending strain
- derived from the differences between gauges around the specimen
- axial strain
- the mean strain across them
A ratio, so it is independent of the force level in principle — though in practice bending often varies with force as clearances take up.
Bending adds to the axial stress on one side of the specimen
Fatigue life is governed by the highest local stress, not the average, so a modest percent bending can shorten life substantially while the reported stress looks correct.
Set by the referencing test method, not by this practice
How the test runs
- 01Establish the configuration to be verified — the grips, adapters and specimen type used in testing.
- 02Prepare a strain-gauged alignment specimen of that geometry.
- 03Install it exactly as a test specimen would be installed.
- 04Load slowly within the elastic range to the force levels of interest.
- 05Record all gauge readings at each force level.
- 06Calculate the axial strain and the bending strain from the gauge differences.
- 07Calculate percent bending.
- 08Repeat with the specimen removed, rotated and reinstalled, to separate machine from specimen.
- 09Compare against the limit set by the referencing test method.
- 10Adjust the load train and repeat if the limit is not met.
- 11Record the configuration verified, because the result belongs to it.
What the report has to contain
- Reference to ASTM E1012 and the edition
- Machine identification and the load train as assembled — grips, adapters, couplings
- Alignment specimen geometry, material and whether notched
- Strain gauge type, number and positions
- Force levels at which bending was measured
- Axial strain, bending strain and percent bending at each level
- Results of repeat installations and rotations
- The acceptance limit applied and its source
- Any adjustment made to the load train
- Date, and the configuration to which the result applies
What the machine must be capable of
Holding its alignment once set, and being adjustable when it does not. Beyond that the requirements fall on the instrumentation rather than the frame: strain measurement fine enough to resolve the differences between gauges, and a load train whose grips, adapters and couplings can be reassembled repeatably. The practice targets the force levels of routine tension, compression, creep and uniaxial fatigue testing, so verification is done where the machine is actually worked rather than at capacity.
What goes wrong in practice
Verifying with fixtures other than the ones used for testing, which produces a number describing nothing. Verifying once and treating it as permanent, when a new adapter, a re-seated grip or a replaced coupling can move alignment more than years of ordinary use. Measuring at a single force level, when clearances take up as load rises and bending often changes with it. And reporting percent bending without the acceptance limit and its source, since this practice deliberately sets none — the referencing test method does.
ASTM E1012 or a force verification
| ASTM E1012 | ASTM E4 / ISO 7500-1 | |
|---|---|---|
| Question | Is the force axial? | Is the force correct? |
| Detects | Bending from misalignment | Error in the indicated force |
| Subject | The assembled load train | The force-measuring system |
| Substitutable | No | No |
These are the two independent ways a testing machine lies to you, and each is invisible to the other's certificate. A machine can be perfectly calibrated for force and still be bending every specimen it holds.
Questions we are asked about this test
What is ASTM E1012?
It is the ASTM practice for verifying the alignment of a testing frame and its specimen under tensile and compressive axial force. A strain-gauged alignment specimen is loaded in the elastic range through the machine's own grips, and the amount of bending imposed is calculated from the differences between the gauges. The current edition is ASTM E1012-19.
Why does alignment need verifying when the force is already calibrated?
Because they are independent faults. A force certificate says the machine applies the force it reports; it says nothing about *where* that force acts. If the load train is eccentric, the specimen carries a bending stress on top of the axial one, so one side is more highly stressed than the reported stress implies. A machine can be immaculately calibrated and still be bending every specimen it holds, and no force verification will reveal it.
What is percent bending?
The bending strain expressed as a percentage of the axial strain, derived from the differences between gauges distributed around and along the specimen. It is a ratio rather than an absolute, which makes it comparable across force levels — although in practice bending often changes with force as clearances in the load train take up, which is why it is measured at more than one level.
What is an acceptable percent bending?
This practice does not say — and that is deliberate. The acceptance limit comes from the test method that references it, and different methods tolerate very different amounts. Fatigue and creep methods are usually the strictest, because their results are governed by the highest local stress rather than the average. So the limit, and its source, both belong in the report.
Why does bending matter more in fatigue than in a tensile test?
Because fatigue life is driven by the peak local stress, not the mean. A modest bending component raises the stress on one side of the specimen, and since fatigue life falls steeply with stress, a small misalignment can shorten measured life substantially. The reported stress meanwhile looks entirely correct, so the effect appears as scatter or as a material that seems worse than it is.
Do I have to verify with my own grips?
Yes, and this is the point most easily missed. Alignment is a property of the assembled load train, not of the frame. The practice sets out to assess the bending imposed by the ordinary components of the machine as normally set up, so fitting special fixtures for the check would verify something you never test with. Change a grip or an adapter and the verification should be repeated.
Why rotate and reinstall the specimen?
To separate the machine's contribution from the specimen's. An alignment specimen is not perfectly straight or perfectly gauged either, so some of the measured bending belongs to it. Reinstalling it in different orientations and comparing results shows how much of the bending follows the specimen round and how much stays with the machine — which is the part you can actually correct.
Running ASTM E1012 on the Series 7200 and Series 9000
Dak verifies against whichever standard the method names, and where a class applies our frames sit a class tighter than it asks.
| The method asks for | Dak supplies | |
|---|---|---|
| Capacity | Whatever the machine is used at — the practice targets the force levels of routine tension, compression, creep and fatigue testing | Load cells from 1 kg to 60 ton on the Series 7200, and 0.5 to 100 kN on the Series 9000 |
| Force accuracy | Strain measurement of a resolution suited to the bending being resolved | ISO 7500-1 Class 0.5, verified to ASTM E4, DIN 51221 and BS 1610 |
| Gripping | A strain-gauged alignment specimen, loaded through the grips and adapters actually used for testing | Wedge, vice-action, pneumatic and hydraulic grips, built to the specimen |
| Environment | 23 ± 2 °C standard laboratory atmosphere | 3009 series chambers, −150 °C to +400 °C — temperature only |
This page describes the method as practised. The governing text is the current edition from the issuing body. Tell us what you are testing and we will answer with the machine, the fixture and a quotation.