Universal tensile strength testing machine “TIRAtest 2850”
Universal tensile strength testing machine
Device designation: TIRAtest 2850
Manufacturer: TIRA GmbH
Data recording and controlling software
Device designation: EDC120
By: DOLI Elektronik GmbH
The WZR ceramic solutions GmbH is working with a universal tensile strength testing machine made by the TIRA GmbH, the model name is in 2850. Herewith strength tests can be carried for many different materials e.g. for glass, fabric, ceramics, plastics, metals, wood, and many more.
Tests can be carried out up to 50 kN tops.
Test options & Applications:
The tensile strength of brittle materials like ceramics is usually determined by bending tests. For this test prismatic specimen are laid on both edges of the lower bearing and the sample is loaded with the third edge from above until it cracks. The so called three-point bending test is carried out on silicate or refractory ceramics for example according to DIN norm EN 993-6. For the determination of tensile strength for more fine-grained and smaller samples we usually carry out the four point bending test (see picture 2). The difference between those two tests is that according to the four point bending test the sample is loaded with two upper edges instead of just one.
In this case the upper bearings distance is smaller than the lower ones; established measurements are 20 mm of distance for the upper bearings and 40 mm for the lower ones. This test for example, is standardized in DIN EN 843-1.
In addition to the applied load the deformation of the sample can be measured with a displacement transducer which is placed under the sample. By recording the load and the deflection of the sample it is possible to create a load- deflection diagramme (σ – ε diagramme)(see picture 3). Out of this diagramme the E module of the sample can be calculated. This test is carried out according to the DIN EN 843-2.
Disc compressive strength
The disc compression test of cylindrical samples also called Brazilian’s test (see picture 4) is a variation of the compressive strength test. Here, the strain is applied on the circumference of the sample resulting in tensile strain in the sample(Hierbei wird die Probe über ihren Umfang belastet, wodurch Zugspannungen im Inneren der Probe aufgebaut werden). Those cause tensile forces in a 90 °-angle to the original pressure direction leading to sample failure. With this method it is possible to determine the tensile strength of ceramic samples. The dimensions of the specimen are d=30mm and h=15mm. This procedure is not only used to check the strength of ceramic samples in new condition, but also in case of part damage when often only small samples or fragments are available.
The ball on three ball (B3B) test is a biaxial strength test especially for ceramic or brittle materials. In general the samples are thin round discs, with a diameter of some mm.
The advantages of this test in contrast to conventional bending strength tests, is a high degree of reproducibility and low expenditure for sample preparation. Furthermore it is to mention that edge effects have no influence on the test result.
Test set-up for the B3B test. (https://www.isfk.at/de/960/)
Tensile strength testing
Another possibility for measuring the indirect tensile strength of brittle materials in a compression strength measuring set-up is the testing of glasses by the ring-on-ring test (see picture 6). Here a glass plate is covered with a transparent foil and placed on a cylindrical bearing. Force is applied through a smaller cylindrical bearing on the upper side of the specimen. An increase of the force leads to sample failure with cracks arranging in a star-shaped way. This test method allows for fast and reliable testing of thin glass plates.
Metal and polymeric samples are usually tested by tensile strength measurements. For this test either cylindrical or stripe-shape test specimen are used. Standardized testing is conducted according to various norms. Picture 8 is showing the tensile strength measurement of fiber-inforced materials. By documenting the stress-strain diagram the maximum strength of the material as well as the tearing behavior of such materials can be investigated.