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Fatigue Tests on PE Pipelines to ISO 18489

Today, fatigue tests on thermoplastics are often performed to ISO 18489 since the specified Cracked Round Bar Test delivers results extremely quickly. The TGM Institute of Technology in Vienna employs an electrodynamic testing machine from ZwickRoell for these tests. 

A fatigue life of at least 50 years is expected of pipelines made from thermoplastic materials such as polyethylene (PE). To determine the life expectancy of materials, the resistance to long-term failure (slow crack growth, SCG) is often measured. The tear strength of modern PE materials is high however. Thus, the previously used test methods such as the Full Notch Creep Test (FNCT) or the Pennsylvania Edge Notch Tensile (PENT) Test are reaching their limits and are usually discontinued after one year, without any quantitative results. Therefore, the Cracked Round Bar (CRB) Test to ISO 18489, which delivers results within 48 hours, is a popular choice for determining slow crack growth. TGM in Vienna relies on an LTM series testing machine from ZwickRoell for determining slow crack growth.

Previous tests were extremely time consuming and often required the use of thermal or physical/chemical aging methods. These can influence the polymer structure of the specimen and distort the test results. On the other hand, the new test method reduces the test duration to a minimum and can be performed at room temperature. ZwickRoell developed the LTM testing machine with patented linear drive technology and force-controlled pneumatic grips that reliably prevent specimen overloading during the gripping process specifically for testing to ISO 18489. The coaxial and specimen-related travel measuring system mounted in the piston rod not only deliver high precision measurements, but the wear-free drive and low power 

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