Strenght testing methods

The strength of advanced ceramics is measured by uniaxial bending tests for common. The 3- and 4-point bending tests can be performed at the ISFK with different support sizes (e.g. 4-point bending test: 80/40 mm, 40/20 mm, 30/10 mm, 20/10 mm; special designs if required).


In the biaxial ring-on-ring test, the specimen is loaded between two rings of different sizes and the strength is calculated from the fracture forces.


The B3B test can be used for biaxial strenght testing of disc and plate shaped specimens.



The notched ball test is used to determine the strength of ceramic balls (e.g. ball bearing balls) made of brittle materials. The notched ball test can also be used for characterization of fatigue strength (of damage caused in service).

The notched roller test is used for testing cylindrical specimens.



Strenght data are analysed by use of the Weibull theory.



Slow crack growth

EN843-3, ASTM C1368, ASTM C1576

There are cases where ceramic materials fail after a certain time, although the load is far below the characteristic strength of the ceramic, i.e. the strength decreases as a function of time. In these cases, slow ("subcritical") crack growth occurs. Cracks already present in the ceramic grow over time until they reach a critical size and the component breaks under loads that are below the characteristic strength of the material. At the ISFK, tests on slow crack growth are carried out using both bending tests and the ball-on-three-balls test.

Determination of fracture toughness

EN 1425-1, EN 14425-3, EN ISO15732, ISO 18756, ISO 21618, ISO24370, ASTM C1421

The SEVNB method is suitable for simple, accurate and reliable determination of the fracture toughness of ceramic materials. The method provides well reproducible values. A specimen provided with a sharp notch is loaded in bending until fracture occurs.


Other methods (e.g. IF, SCF, CNB, ) can be performed on request.

Determination of hardness

EN 843-4, ISO 14705, ASTM C1326, ASTM C1327

The following methods are used at the ISFK:

  1.     Vickers hardness measurements
  2.     Knoop hardness measurements
  3.     Brinell hardness measurements


Determination of the modulus of elasticity (Young’s) modulus

EN 843-2, ISO 17561

Young’s modulus can be seen as the resistance of a material to elastic deformation. It describes the stiffness of the material. At the ISFK, the Young's modulus of ceramics is determined using static methods (3 or 4-point bending). Thereby, the deflection of a bending specimen is measured as a function of the applied force.




Determination of toughness

CEN/TS 843-9

Edge chipping is frequently observed when using brittle materials (e.g. paper machine linings or drills). In edge toughness tests, a Rockwell C indenter is pressed into the surface at a constant speed at defined distances from the edge. The load increases until breakage occurs and a chip detaches. The peak load is registered and the distance of the indentation from the edge and the chip geometry are measured microscopically.




Determination of thermophysical properties

EN 820-3, ASTM C1525

In order to make statements about the thermal shock resistance of ceramics, quenching tests are carried out under conditions that are as defined as possible. One standardized method is the water quench test, in which heated specimens are thermally shocked by rapid immersion in water. Thereby, the "critical" temperature difference between initial specimen temperature and water temperature, at which a significant drop in specimen strength occurs after the test, is sought.


Thereby, a sample is heated up in a dilatometer at a certain uniform rate or under defined temperature increments and subsequently cooled down. The changes in length and temperature are measured continuously during the experiment and the percentage expansion or contraction is calculated as a function of temperature. The results are reported as the average coefficient of thermal expansion over the temperature range.



In thermography, the intensity of infrared radiation emitting from a body is interpreted as a measure of its temperature. A thermal imaging camera converts the infrared radiation, which is invisible to the human eye, into electrical signals and generates an image in wrong colours. This measurement technique is used at the ISFKto examine, among other things,electroceramic components such as varistors or PTCs.


Ceramographic (EN 623-3, EN 623-5, ASTM E112, ASTM E1382) and fractographic investigations (EN 843-6, ISO CD13383-1, ISO CD1383-2, ASTM C1678):

Quantitative ceramography is the quantitative description of the microstructure of ceramic materials (fraction, arrangement and size distribution of phases, grain size distribution, grain morphology, determination of porosity). The evaluation is carried out using the image analysis system OLYMPUS Stream.



Fractographic investigations are used to identify fracture origins in specimens and components. Fractographic examinations are a fundamental part of failure analysis.