VT - visual methods

Visual testing is an NDT method that involves an examination with the unaided eye to detect, locate and evaluate a discontinuity or defect present on the surface of the material being tested. It is the oldest NDT method and considered one of the most important. The method is applicable at all stages of construction and/or production of a component or process installation.

Visual inspection is usually performed using unaided eyes. The effectiveness of the method can be improved by using special tools such as mirrors, magnifying glasses (magnifiers, telescopes) and boroscopes, fiberscopes, videoendoscopes.

However, with the use of more sophisticated equipment (i.e. videoendoscope), visual inspection can be extended to remote areas (remote examination) that are normally inaccessible to the operator. The use of specialised equipment allows the detection of defects, corrosion changes that cannot be seen with the unaided eye.

Magnetic-powder method MT

Magnetic-powder testing (MT) is an NDT method that uses the principle of magnetism. The material being tested is magnetised. Magnetic powder (finely ground iron particles coated with a colour pigment) is then applied to the component. A magnetic field is dispersed at the location of the discontinuity. The powder particles, attracted by the dispersed magnetic field, collect to form an indication located directly above the discontinuity. The method provides a visual representation of the defect.

Magnetic-powder testing (MT) is used to locate small surface and subsurface discontinuities or defects. MT is only applicable to magnetic materials (ferromagnetics). Therefore, it can only be used on metallic parts and industrial structures.

Eddy current method ET

Eddy current (ET) testing involves the use of an alternating current (AC) coil that induces a current (the so-called eddy current) on the surface of the component. By measuring the changes in eddy current, it is possible to detect the presence of defects and material discontinuities in the sample. The ET method can be used to verify the quality of metal tubular components of technological installations.

Nanoindentation

Nanoindentation is an advanced technique for measuring the mechanical properties of materials on a very small scale. In brief, it involves the controlled pressing of an indenter of known geometry into the surface of the material under test and then measuring the response of the material to this stress. This allows hardness, modulus of elasticity and other mechanical parameters to be determined at the nanometre level.

The method is particularly useful for testing nanocrystalline materials, thin films, or nanocomposites and implanted materials, where traditional measurement methods may be insufficient.

Impact testing

Impact testing is a key element of materials testing that assesses the resistance of a material to dynamic loads. The Materials Research Laboratory is equipped with two Charpy pendulum-type hammers with initial energies of 450 and 25 J. We perform tests at room temperature, elevated temperature (up to 200 °C) and reduced temperature (down to -90 °C). The purpose of low-temperature impact testing can be to determine the risk of a material becoming brittle under operating conditions. Importantly, hardness testing enables the inspection of welded or heat-treated materials, allowing verification of the correctness of the processes carried out. Test results are compared with the requirements set out in specific specifications or subject standards. We carry out impact tests on selected specimen geometries in an instrumented manner, i.e. by measuring the fracture force as a function of time or distance.

Fracture toughness testing

Assessing the strength of materials in traditional analyses assumes that they are flawless. Such a perspective does not take into account possible discontinuities that may affect the strength of the structure and consequently lead to failure earlier than predicted by standard strength calculations. Fracture mechanics makes it possible to determine the highest load at which a material with existing cracks of known size will still retain integrity, or to determine the largest fractures that will not lead to material failure under a given load. The fracture toughness tests we carry out in the Materials Research Laboratory include the determination of the stress intensity factor (K_Q, K_IC), the fracture opening value (δ, δ_c) and the fatigue fracture growth rate (da/dN). Test specimen geometries include a single-notch specimen for three-point bending SENB and a compact specimen for tensile testing CT. Most of the fracture toughness measurements are carried out using a 100 kN universal testing machine equipped with a temperature chamber.

The transmission electron microscopy (TEM) laboratory is equipped with a high-resolution JEOL JEM F-200 microscope equipped with a Schottky Field Emission Gun. The microscope allows observations to be made in both TEM mode (resolution: 0.06 nm) and STEM scanning-transmission mode (resolution: 0.16 nm). In addition, the microscope is equipped with a dual-detector energy-dispersive X-ray spectroscopy (EDS) microanalysis system that allows chemical composition analysis in point, line or chemical element distribution mapping mode. Studies are carried out on samples less than 100 nm thick by electrolytic or ion beam polishing methods. The laboratory also has holders for in-situ high-temperature observations (up to 1000°C) and material deformation studies.