Michal Švantner

Frictionally Excited Thermoelastic Instability and the Suppression of Its Exponential Rise in Disc Brakes

This paper deals with processes of thermoelastic instability occurring on brake systems that become evident as a non-uniform distribution of temperature with hot spots on contact surfaces. Thermoelastic instability is accompanied by the exponential rising of temperature amplitudes of hot spots during its initial linear phase. The authors discuss different mechanisms of interruption of the growth, based on experimental and computational results. An example of experimental data is presented for the case of a disc brake.

Thermal effects of laser marking on microstructure and corrosion properties of stainless steel

Laser marking is an advanced technique used for modification of surface optical properties. This paper presents research on the influence of laser marking on the corrosion properties of stainless steel. Processes during the laser beam-surface interaction cause structure and color changes and can also be responsible for reduction of corrosion resistance of the surface. Corrosion tests, roughness, microscopic, energy dispersive x-ray, grazing incidence x-ray diffraction, and ferrite content analyses were carried out. It was found that increasing heat input is the most crucial parameter regarding the degradation of corrosion resistance of stainless steel. Other relevant parameters include the pulse length and pulse frequency. The authors found a correlation between laser processing parameters, grazing incidence x-ray measurement, ferrite content, and corrosion resistance of the affected surface. Possibilities and limitations of laser marking of stainless steel in the context of the reduction of its corrosion resistance are discussed.

Uncertainties of the Evaluation of the Hole Drilling Residual Stress Measurement According to the ASTM E837 Standard

The paper deals in hole drilling residual stress measurement method. The basic principles of measurement and evaluation by the uniform stress and Integral methods are described. The uncertainties of the residual stress evaluation procedure based on the ASTM E837 standard are analyzed. Examples of residual stress evaluation and comparison of different ASTM E837 standard editions are presented.

Active thermography inspection of protective glass contamination on laser scanning heads

Industrial lasers are an expanding technology of welding and other materials processing. Lasers with optical scanning heads are often used, as these provide more versatility, accuracy, and speed. The output part of the scanning head is covered by a protective glass, which might get contaminated by various particles from the laser processing. This decreases the transmissivity of the glass, and it can affect the production quality. The contamination needs to be checked regularly, but a visual inspection might not always be effective. This paper proposes two alternative methods of inspecting the protective glass: flash-pulse active thermography, and laser active thermography. They are based on the thermal excitation of the glass and measuring the response with an infrared camera. The experimental setup and practical results are described and the advantages and disadvantages are discussed. The presented methods are proven to be effective in detecting the contamination of the glass.