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Figure 1: The tire industry has used Metravib’s automated DMA since 1999. Image: Michelin

Figure 2: Metravib believes the DMA+2000 set a new standard for tire industry testing laboratories

Automated DMAA new fully automated dynamic mechanical analyzer is designed to boost material testing productivityby Hugues Baurier, Metravib, ACOEM group, France

Involved in development and marketing of innovative instruments for measuring the viscoelastic properties of materials since 1972, Metravib identified the

increasing need for dynamic mechanical analysis (DMA) in the tire industry in the mid-1990s.

This led Metravib to market a first fully automated DMA dedicated to shear testing in 1998. Since 1999, tire manufacturers and their materials suppliers have been using Metravib’s automated DMA around the clock.

The intensive use of DMA testing by the tire industry revealed new expectations in terms of the performance and capabilities of DMA instruments.

Major improvements were expected in three main areas: data accuracy, instrument flexibility and testing productivity.

Improved data accuracy includes better data repeatability, improved measurement ability at small strain amplitude and low temperature, capabilities for measuring stiffer compounds, capabilities to analyze very small or large specimens, improved correlation of data between multiple DMA units, and a reduction in the influence of the operator on results.

Improved flexibility means automated solutions for various test modes (shear, compression, tension), the flexibility to switch between various automated testing modes on one single DMA instrument, and the flexibility to switch from automated mode (routine test) to a ‘manual mode’ to cover research testing needs.

Finally, improved productivity measures include easy specimen preparation, high testing throughput, and easy instrument operation requiring no specific qualifications for the operator.

DMA developmentsIn 2012, Metravib took a first step to meeting these expectations in introducing the new DMA+series with an extended force range up

to 2,000N, a frequency range up to 1kHz, a temperature domain from -150°C up to 500°C, and a displacement range of 12mm.

Featuring a new mechanical frame, new electronics, and new software, the DMA+series uses the latest technologies to achieve extremely accurate dynamic testing.

The heart of the DMA+series is the common mechanical test frame: a massive single block molded in die-cast aluminum.

The main purpose of this unique, in-house design is to give the mechanical test frame high stiffness (low compliance), which is essential to ensure an accurate measurement of the specimen stiffness variations while temperature changes, and during measurement out of resonances. A rubber specimen that is soft at room temperature becomes very stiff below the glass transition temperature, as its Young modulus can be multiplied by a factor of 1,000.

Highly accurate data can be obtained because of the accurate temperature control of the thermal chamber combined with new 16bit electronics and the advanced control algorithms of Dynatest software that ensures an accurate strain amplitude control over the whole test, whatever the mechanical response of the material might be.

As a consequence, resolution up to 10E-5 on tan δ can be obtained in both the rubbery region and the glassy region, and five decades of strain sweep can be easily achieved in one single test.

Now Metravib is further meeting the tire industry’s expectations in introducing Xpander, a new automated specimen handling system dedicated to the DMA+series.

Xpander descriptionXpander fully automates DMA testing including specimen uploads and downloads. It comprises a six-axis robot arm (collaborative robot technology), a Smart Robotic Toolbox for specimen gripping and clamping (SRT), and a magazine composed of a carousel including up to 12 removable racks containing specimens to test.

The SRT is fixed at the extremity of the robot arm and includes three tools to accomplish all functions of the automation: a finger for rotating of the carousel and opening and closing the thermal chamber; a suction grip to upload and download specimen; and a pinch for clamp and release of the specimen holder.

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Figure 3: Metravib Xpander coupled to DMA+1000: fully automated DMA in tension, compression and shear

Figure 4: Metravib Xpander: the three steps of gripping and clamping a specimen in the DMA+ are unique to Metravib

The carousel may be equipped with three types of racks, one each for the three modes suitable for testing rubber compounds: tension, compression and shear.

The racks can individually contain 9, 34 and 37 specimens respectively in tension, compression and shear.

In tension mode, for HWT specimen geometry up to 60 x 30 x 3mm, the minimum specimen storage is 108 specimens.

In compression mode, for H/D specimen geometry of up to 26mm/18mm, the minimum specimen storage is 408 specimens.

In shear mode, for D/T specimen geometry of up to 10mm/2mm, the minimum specimen storage is 444 specimens.

Xpander is located on the left side of the DMA+ and occupies a reduced floor surface similar to the DMA+ footprint, which represents in total roughly 1.5m2.

Xpander may be coupled to a DMA+ already in place without requiring any changes to the DMA+, nor any expensive waste.

The robot armThe Xpander’s robot arm is a Universal Robot UR3, a compact, collaborative industrial table-top robot that can work side-by-side with employees. The UR3 is the perfect robotic solution for DMA+ in offering high accuracy, high reliability, cost-effectiveness and safety. UR3 features 0.1mm repeatability and can be set to stop if it encounters a force as low as 50N in its route.

With typical current DMA test average durations of 30 minutes to 2 hours, the UR3 will easily last the

life of an Xpander system compared with its other industrial applications in the medical field and electronics components, for which UR3 has been designed to work intensively.

In the Xpander application, the six-axis robot arm takes the specimen out of the carousel and into the test station; loads the specimen into the DMA+ holders, clamps the holders (for tension and shear modes only, compression mode doesn’t require any specimen clamping); closes the thermal chamber; and launches the test under the controlled dynamic excitation, static load and thermal conditions previously programmed.

While compression specimens are simply placed in-between parallel plates, for shear and tension testing, material specimens are attached to small, light metallic supports.

The gripping of the specimen is done by a suction extractor positioned on one of the faces of the SRT. The extractor grips the specimen or its supports at three or four points depending on the test mode.

This functionality is essential to guarantee that the test process can be performed entirely, even if one specimen breaks during a dynamic test and splits into two or three separated parts. In such cases, all separated specimen parts can be taken out of the thermal chamber, making it possible to continue to conduct the test program.

After putting the specimen inside the DMA specimen holder, the SRT

rotates and operates the clamp with a dedicated plier on a second face into the specimen holder of the DMA.

The specimen clamping system uses a proprietary Metravib patented system. This system features a pin-assembly spring combining small mass and a high level of rigidity.

This clamping technology has proven for 17 years to be highly reliable and easy to maintain, having been used in earlier robotic solutions for Metravib’s DMA, the Viscopilot and ROB100.

Flexibility and reliabilityWhile the earlier Metravib automated DMA systems were dedicated to dynamic shear testing, Xpander makes it possible to run fully automated tests for shear, compression and tension on a single DMA+ unit.

The carousel may then be equipped with a combination of racks dedicated respectively to tension, compression, and shear specimens.

In case specific tests are required with different test modes and/or specimen geometries requiring specific DMA configuration, the switch from the Xpander configuration to a manual configuration requires only a few minutes. The same DMA+ unit can then be easily used for routine industrial tests as for answering R&D needs.

The overall DMA+ and Xpander design has also been designed to offer operational testing solutions in all modes both for characterizing new compounds (molding of a specimen using limited material volume) and for characterizing a specimen taken from the tread or sidewall of a commercial tire.

The specimen transportation and clamping operation performed by the Xpander definitively eliminates any effect on test results by the human operator and brings total repeatability to the specimen handling process.

Advanced algorithms of the Metravib Dynatest software enable 4

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Figure 5: Metravib Xpander robot arm opens DMA+ thermal chamber

Figure 6: Three specimens of the same compound were tested with Metravib Xpander

the excitation amplitude setting value (strain or stress) to be reached rapidly without any overshoot, to guarantee a well-handled excitation profile for each datapoint. This is especially important for materials like rubber compounds, which often exhibit highly non-linear behavior.

Figure 6 shows the data issued from a DMA+2000 equipped with Xpander. Three different specimens of the same rubber compound were tested in the same conditions of frequency, strain and temperature.

In the glass transition region, the tan δ dispersion observed is better than ±0.006.

The new one-piece DMA+ mechanical test frame minimizes machine response variability from one test unit to another. The number of mechanical parts and associated assembly that may induce variable machine compliance from one unit to another are minimized.

Comparisons between various testing units, various laboratories, and various companies are then easier and much more efficient.

Positioning calibration by the robot is made when the test mode and associated specimen holder are selected.

The design of the rack makes the positioning in the carousel easy, without requiring any position recalibration by the robot.

Positioning the specimens in the racks is also an easy operation and can be done with racks in the testing position, or with racks outside of the system.

If specimens are loaded into the removable racks outside of the system, then uninterrupted testing is possible.

The Xpander test definition program in the Dynatest software has been designed to be efficient for totally different uses.

The same test definition may be applied to all specimens by a few clicks for a routine test sequence, while totally different tests sequences can be chained together independently for each specimen. For instance, a TG test (temperature ramp at 10Hz) can be chained with a Payne/Mullins effect test for specimen one, while a frequency sweep can be applied to specimen two, etc.

Depending on the testing conditions (low or high frequency, different strain sweeps or number

of cycles, temperature program), a DMA test can take a couple of minutes up to few hours. The new Metravib DMA software suite includes an innovative productivity tool called Operator Alert. When a lengthy test is over or if, for any reason, the test finishes earlier than expected, the operator is notified by text message, email or phone, meaning that a new test can be begun as soon as the machine is available without any testing time being lost.

Data files are exported as CSV files in order to be collected by the customer’s data exploitation program.

ConclusionMetravib’s Xpander eliminates repetitive tasks and considerably limits the operator time required for analysis. It makes it possible to use the DMA+ full-time, even during weekends, days off and laboratory shutdown periods.

Suitable for both research work and for routine industrial testing, the DMA+1000 and DMA+2000 testing machines bring extended capabilities, smart innovative testing solutions and enhanced performance.

In Metravib’s view, the main benefits of the DMA+ series, now boosted by Xpander, are the ability to distinguish mechanical behavior of compounds in a way that no other mechanical or rheological instruments can, and to offer unique flexibility and high testing throughput. tire

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Specimen Universal tension jaws

Dim. (mm) : H = 15, W = 10.75, T = 201/23/2017

Temperature (°C)