Demattia Flex Cracking Tester

Choose by the specimen your method calls for, because the two models are built around two specimen shapes. The GenFlex-B1 takes a long strip of 154 × 25 × 6.3 mm, and the GenFlex-B2 takes a wider piece of 108 × 70 mm.

Tolerances are tight on both. The B1 strip is held to ±1 mm on the width and ±0.15 mm on the thickness, and the B2 piece to ±0.5 mm on both sides. Specimens cut to these limits bend the same way in every run, which keeps one result comparable with the next.

The models also differ in motion: the B1 runs a longer stroke, while the B2 moves a shorter distance and cycles faster. Both share the same cabinet and power options, so the specimen decides.

Tell us the specimen you flex and the cycle count it has to reach, and a short quote request is all we need to confirm the model for you.

The GenFlex-B1 moves its specimen through a reciprocating stroke of 57 mm at 300 ±10 cycles per minute. The fixtures open to a maximum distance of 75 mm, which suits the long 154 mm strip this model takes.

Holding the rate within ±10 cycles per minute matters because rubber warms as it flexes. Part of the work in every bend turns into heat inside the compound, and a faster or drifting rate changes the specimen temperature and with it the point at which a crack starts. A fixed rate keeps that variable out of the comparison.

The B1 is the model for methods built around a long strip flexed through the longer stroke at a steady rate. Strips for it are cut from molded sheet, and our rubber specimen preparation equipment covers the cutting presses for that work.

The GenFlex-B2 flexes a 108 × 70 mm piece over a stroke of 44 mm, with the fixtures opening to a maximum distance of 57 mm. Its rate runs from 340 to 400 cycles per minute, held within ±10, which makes it the faster of the two models.

The shorter stroke and higher rate suit a wider specimen that is cycled quickly over a smaller travel. As on the B1, the rate is held within ±10 cycles per minute, so every specimen in one comparison sees the same speed and the same warming from repeated bending.

The faster cycling also adds flexes more quickly, which shortens each run when a development program has many formulations waiting. Other machines for flex fatigue and crack growth are grouped in our rubber flex testing range.

Each specimen is fixed into the movable grips and watched for the first crack while an LCD counter records every flex from 0 to 999,999. An intelligent failure system stops the run when the specimen gives way, so the counter holds the number of cycles the specimen survived.

That automatic stop protects the result. Without it, the machine would keep cycling a failed specimen and the count would run past the real point of failure, which overstates the life of the compound.

The six-digit counter covers runs of several hundred thousand flexes, the range in which a compound that passes a tensile test can still split. A single reading at the end of a long run therefore carries the whole result, with no need to log the count by hand while the machine works.

Run time is the cycle count you need divided by the cycle rate. On the GenFlex-B1 at 300 cycles per minute, 100,000 flexes take about 5.5 hours. On the GenFlex-B2 at its top rate of 400 cycles per minute, the same count takes a little over 4 hours.

Flex cracking often appears only after a few hundred thousand flexes, so long runs are common. At 300 cycles per minute, 300,000 flexes take close to 17 hours, and at 400 cycles per minute about 12.5 hours.

Because the tester stops itself when the specimen fails and the counter keeps the figure, long runs can continue outside working hours. A laboratory can load specimens at the end of the day and read the counts in the morning, which keeps the machine productive through the night.

The tester reproduces flexing under fixed conditions of speed, mode and degree of bend, so a result from one run can be compared with the next. Crack initiation in rubber is sensitive to how far and how fast the specimen bends, and changing either one moves the cycle count.

With those conditions locked, the remaining difference between two runs comes from the material. That lets a laboratory compare a new compound against a proven one, check each production batch against its own history, or qualify a second supplier of the same part.

The comparison holds within one model and one specimen shape. A count from the GenFlex-B1 strip and a count from the GenFlex-B2 piece come from different strokes and rates, so a laboratory keeps each compound on the same model when it builds up a record of results.

Both GenFlex models use the same cabinet of 35 × 60 × 75 cm (13.8 × 23.6 × 29.5 in), width by depth by height, and weigh 78 kg (172 lbs).

The power supply is 110 V / 60 Hz or 220 V / 50 Hz, chosen at order to suit the local mains. The 110 V / 60 Hz version matches the standard supply in North America, and the 220 V / 50 Hz version fits laboratories on that grid.

A solid bench or stand that carries the weight without flexing keeps the machine steady while it cycles at 300 to 400 flexes per minute. Leave room in front of the grips for loading specimens and for reading the counter, since the operator returns to it to note the first crack.

Our team handles installation, training and calibration, and supports the tester for its working life.

Flex cracking is one part of a rubber quality control laboratory, and the other tests often run on the same compound. We equip the rest of the laboratory as well, from rheometers and viscometers to hardness and rebound testers.

Ageing is the closest partner. Many programs flex specimens before and after heat ageing to see how much crack resistance the compound keeps over time, and our aging oven prepares the aged set for that comparison.

Footwear and soling laboratories often add a Ross flex test, which bends a pierced specimen to follow how a cut grows. Our Ross flex tester covers that method, and abrasion testers, salt spray chambers and specimen cutting presses complete the line.

We coordinate the full set as one project, with one partner for installation, training and support.

The following industry standards are typically followed when testing with the DeMattia Flex Cracking tester:
ISO 132, ISO 6943, ASTM D813, ASTM D430-B and JIS K_6260

Most commonly, rubber sole material is used in a DeMattia Flex tester. Due to the fact that the rubber soles are being used daily and coming into contact with roads, dirt and other elements, they endure the maximum level of flexing. It is the friction from all the flexing that can lead to a surface crack which can lead to failure of the rubber compound.

While rubber has an extremely high strength rating, it also exhibits some faulty characteristics after being exposed to heat, cold weather and humidity/temperature changes. After being exposed to these elements, it is common for a crack to develop on the surface and these cracks have a tendency to continue to grow. DeMattia Flex Cracking can help to estimate the rubbers lifespan after a crack has formed in the materials surface.

Up to 6 specimens can be tested at one time after setting the frequency per your industry standard.

The specimen must first be created in the size required per the industry standard. NextGen can supply the ASTM D430, Method B cutting dies along with the D813 mold required to perform these tests. ISO moulds can also be provided as a custom order.

The DeMattia test allows the operators to analyze the fatigue-cracking properties of the material in question. It provides a picture of the potential lifespan of the material when being used in its service application.

The DeMattia Flex Tester provides a representation of the ability for a punctured rubber specimen to resist crack growth while enduring bending and flexing. Because of the large number of variables, there is no exact correlation to draw between the test results and the ability of the rubber to perform in its intended application.