With ZwickRoell’s testing solution specifically designed for wedge splitting tests, the Mode I fracture toughness of common refractory materials can be tested at temperatures up to 1,500°C. For this particular purpose, ZwickRoell equipped one of MUL’s existing testing systems with a precise optical laser measuring system, a high temperature furnace and temperature controller, as well as a cooling system for the load rod. To protect the resin-bonded magnesia-carbon (MgO-C) bricks with a carbon content of 10% from oxidation, the furnace is rinsed with inert gas (e.g. argon) during the test. At elevated temperatures strain measurement can be difficult due to the convection in the furnace and the possible reaction of refractory components with the ambient atmosphere. These challenges are met with the optical strain measurement system based on the laserXtens HP from ZwickRoell. Two extensometers in accuracy class 0.5 to ISO 9513 are used, each of which have two high resolution cameras and two green laser diodes. The deformation is measured without contact on the front and back sides of the specimen. Attachment of gauge marks on the specimen is not necessary, since the measuring points are applied on the specimen via the laser light and followed in the camera image throughout the duration of the wedge splitting test.
For the determination of fracture energy and the observation of crack tendency, different fracture mechanical tests can be applied: uni-axial tensile tests, three-point flexure tests, compact tensile (CT) tests and wedge splitting tests. The principle of a wedge splitting test is based on splitting a notched prismatic specimen (e.g. with the dimensions 100x100x75mm). A wedge is inserted between two rollers attached to both sides of the specimen and impacted with a vertical force. Based on the configuration of the wedge rollers, this force is transformed into a horizontal force. The results obtained from the wedge splitting test are used for the calculation of the specific fracture energy and the nominal notch tensile strength.
With the testing solution from ZwickRoell, the fracture mechanic characterization of refractory resin-bonded magnesia-carbon bricks up to 1,500°C can be performed. K1-MET and the Chair of Ceramics at the MUL use the results from this wedge splitting test in a finite element simulation for the calculation of specific fracture energy and nominal notch tensile strength. With these values a more reliable estimation of the lifespan of refractory linings, e.g. for steel ladles in secondary metallurgy is possible.
With the development of this unique test arrangement for the “analysis of wear characteristics of refractory materials for the increase of service life” the longterm collaboration between the Chair of Ceramics at the MUL, K1-MET and ZwickRoell in Fürstenfeld continues successfully. Through the fast implementation of the project, ZwickRoell once again demonstrated its expertise in high-temperature testing and optical strain measurement, affirms Martin Stückelschweiger, former K1-MET researcher and responsible for project implementation at MUL, whose research is supported by this robust and reliable testing system.
The technical science of ceramics involves the structure, properties, production and application of mineral building materials. This includes mineral binding agents and building materials, refractories, ceramics and glass. Refractory building materials are, for example, used in the steel, glass and building materials industry. They are used as refractory linings in vessels, furnaces, ladles, etc. and withstand temperatures of more than 1,500°C. Among other things, the mechanical characterization of refractory building materials in the high temperature range by means of laboratory investigations is one of the central research priorities of the institute. In creep, compression and wedge splitting tests, as well as by measurements of the modulus of elasticity and modified shear tests, material characteristics are generated, which subsequently allow for the simulation of the mechanical and thermomechanical behavior of refractory building materials, in particular with regard to damage potential.
The K1-MET GmbH metallurgical competence center is engaged in experimental research as well as modeling and simulation of metallurgical processes, including metallurgical raw materials and refractory materials, with the overall objective of optimal process control in terms of product quality, zero waste and minimizing energy and raw material requirements. In the field of refractory technology, K1-MET GmbH conducts, among other things, finite element simulations to analyze thermically loaded refractory linings and be able to predict possible damage due to thermomechanical stress.
The K1-MET GmbH COMET Center is funded by BMVIT (Federal Ministry of Transport, Innovation and Technology), BMDW (Federal Ministry for Digital and Economic Affairs) and the federal states of Upper Austria, Styria and Tyrol as part of COMET - Competence Centers for Excellent Technologies. The COMET program is handled by the FFG (The Austrian Research Promotion Agency). In addition to grants, funding is provided by partners from industry and science.