Shearmatic – Automatic Shear Testing Machine

It runs direct shear tests on soil specimens automatically, from consolidation through to failure, without dead weights or lever arms.

Axial pressure is applied by a pneumatic closed loop system through a high-performance pressure regulator, which is what removes the weight hanger from the bench.

Axial pressure is applied by a pneumatic closed loop system through a high-performance pressure regulator, which is what removes the weight hanger from the bench. The test itself is the standard direct shear method covered by ASTM D3080.

A conventional machine applies normal stress by hanging dead weights on a lever arm. Every consolidation stage means an operator loading and unloading weights.

The Shearmatic applies the normal load pneumatically under closed loop control, so up to 50 consolidation steps run as a programmed sequence.

The operator's only intervention during a test is removing the clamping screws of the shear box before shearing begins. Each axial step can be applied instantly or as a linear ramp over a set time interval, which a dead weight system cannot do at all.

A bi-directional load cell of plus or minus 5 kN with nominal sensitivity 2 mV/V and accuracy of 0.003 percent, working in both compression and tension.

Two displacement transducers, 10 mm and 25 mm, each with 1 kOhm nominal resistance, 0.25 percent linearity and 0.002 mm repeatability.

A 1000 kPa pressure transducer with 0.1 kPa accuracy completes the set, so normal stress is measured rather than inferred from a hanging weight.

Yes. The pneumatic loading system requires a compressed air supply at a maximum pressure of 10 bar.

That is the one site requirement worth checking early, because a laboratory that has only run dead-weight machines may not have air at the bench.

A laboratory-model air compressor is available as an accessory: request a quote and we will include it if needed.

No. Shear box assemblies are selected and ordered separately, because the box size follows the specimen and the material being tested.

That separation is deliberate: a laboratory testing both fine soils and coarser materials needs more than one box, and bundling a single size would not serve either.

Tell us your specimen sizes and we will list the boxes with the machine: contact us.

Up to 50 pre-set consolidation steps, applied automatically in sequence.

In practice a direct shear programme uses three or four normal stresses to build the failure envelope, so 50 steps leaves room for staged consolidation within each of them.

The consolidation stage is where most of the test duration sits, which is why automating it changes the working day more than automating the shear itself. Consolidation and failure data are recorded separately, so the two phases are analysed independently.

A high-resolution stepper motor with an epicyclic reduction gear, chosen for reduced backlash.

Backlash matters here because the shear rate has to stay constant through the reversal-free travel, and any lost motion at the start of shearing shows up in the early part of the stress-displacement curve.

The shear box, drive unit and load cell are connected in a straight line so the horizontal force is transmitted along the shearing plane, rather than through the classic swan neck arrangement. Test speed is infinitely variable from 0.00001 to 11 mm/min over a maximum travel of 20 mm.

A high-resistance techno-polymeric material, chosen for resistance to corrosion, wear and the chemicals found in soil specimens.

The practical benefits are that the carriage is light to handle and easy to clean between tests, which is not a small thing in a laboratory running soils with sulphate or organic content.

It also removes the corrosion problem that metal carriages develop over years of wet specimens, and the carriage is light enough to lift and clean between tests.

From a scratchproof membrane keyboard with a large monochromatic graphic display, driven by an onboard microprocessor.

The microprocessor reads force, axial pressure and displacement, and manages the motor, the pressure valve, the safety system and the test sequence through the closed loop.

It is a stand-alone machine, so no PC is required at the bench for the test to run. Data is downloaded afterwards over an RS 232 serial port, with a choice of download protocols.

Direct shear can also be run on a digital shear testing machine, with or without data acquisition, on a large machine for 300 by 300 mm specimens, or on a Bromhead ring shear apparatus for residual strength.

The choice follows the material and the parameter. Residual strength on a clay needs the ring shear; coarse material needs the large box.

The full range is under soil mechanics testing equipment.

The direct shear test on soils under consolidated drained conditions is covered by ASTM D3080, which fixes the specimen size, the consolidation procedure and the rate of shearing.

Consolidation behaviour itself, where it is measured separately, follows ASTM D2435.

The rate of displacement is the parameter most often got wrong, because it has to be slow enough for drainage in the material actually being tested.

The compressed air supply at up to 10 bar, bench space for a stand-alone machine, and which shear box assemblies you need for your specimen sizes.

The air supply is the item that most often delays commissioning, since it is the one requirement a dead-weight machine never had.

Send your specimen range and site details and we will confirm the package: request a quote.