Determination of the Temperature-Dependent Fracture and Damage Properties of Ceramic Filter Materials from Small Scale Specimens

AbstractOpen cell ceramic foam filters are used to improve the quality of metallic cast products. They play a major role on reducing the number of inclusions within the microstructure of the cast product and restraining the liquid flow inside the mold. The newly developed carbon-bonded alumina ceramics are investigated considering the mechanical and thermal loads of the filtration process. The aim of this project is to assess the strength, the fracture mechanical behavior, and the damage properties of the filter material. Since the tiny struts of the foam have different properties than the common bulk material specimen, small specimens of millimeter size are needed. Within this work, a combination of experiments and numerical simulations are conducted for various mechanical tests at temperatures up to 1500 $${}^{\circ }\text {C}$$ ∘ C . The first test is the small punch test (SPT), where a small disk-like specimen is supported on a circular die and loaded with a spherical tipped punch until failure of the disk occurs. The small punch fracture stress is obtained from the experiments, as well as the corresponding parameters of the Weibull distribution necessary for the evaluation of the cold modulus of rupture (CMOR). Furthermore, a modified version of the SPT, the so called ball on three ball test (B3B), is carried out. In the B3B test, miniaturized disk-shaped specimens are supported with three spherical balls and loaded with a spherical tipped punch until failure. Hereby, the fracture mechanical parameters, such as the fracture toughness, are identified with the help of numerical simulations. Moreover, the Chevron notched beam test (CNB) is used to determine the fracture toughness of the ceramics. The final test is the Brazilian disc test (BDT), where compressive loads are exerted on the specimen leading to tensile stresses along the specimen diameter, perpendicular to the applied load direction. This test is employed to determine the Young’s modulus, the yield stress and the fracture toughness. In general the simplicity of all these tests, their setup, application, and results evaluation, in addition to the ease of specimens production, make them very attractive. The size of these specimens is about one order of magnitude smaller than that of common standard tests. The accompanying numerical simulations are inevitable to extract from the measurements the wanted mechanical properties.