Key Engineering Materials Vol. 741

Abstract: The paper summarizes capabilities of the small punch tests on miniature disc specimens from metallic materials. Results obtained by small punch tests can be correlated with mechanical properties determined by conventional or other miniature tests. Three basic types of small punch test setup: i) static/fracture, ii) creep and iii) stress relaxation are described and the basic quantities that can be obtained are shown. Relations for an assessment of conventional mechanical properties from quantities obtained by small punch test are presented.

Abstract: The knowledge of classical mechanics gives deeper insight into the Herbert hardness tester applicability for material testing. Elastic materials with low friction presence between contact surfaces are supposed to be investigated in this study. Firstly the dynamics approach is used to obtain simplified solution of swing angle. Then a new solution of the problem is gained by means of an energy approach. Slight decrease of the swing angle is predicted by the new solution as also shown in experiments. After comparison of both solutions a new formulae useful for evaluation of rolling resistance coefficient is applied for measurements performed on some metallic materials and artificial sapphire. Rolling resistance coefficients obtained by the way are always less than maximal estimated value.

Abstract: The paper deals with microstructure characterization of a full-scale X14CrMoVNbN 10 1/ 27NiCrMoV 15-6 heterogeneous weld intended for IP/LP welded rotors. The welded rotors are being developed for modern turbines of coal fired power plants operating above 570 °C. The full–scale weld has been shown to be of good internal quality. Hardness surveys revealed the effects of post weld heat treatment parameters on weld metals and parent steels. Microstructure and precipitation of minor phases in parent materials, heat affected zones and weld metals in the state after the final stress relief annealing have been studied.

Abstract: Indications were detected on dissimilar metal welds (DMW) of steam generators (SG) after 20 years of operation during NDT inspections. Indications started slowly growth every year. DMW on SGs had to be repaired. Paper describes experimental analysis and degradation mechanism of SG weld joints failures.

Abstract: Digital image correlation (DIC) method is a convenient strain analysis method calculating strain from the difference of images between before and after deformation and shows an advantage to apply to any deformation mode or materials as long as significant contrast. We reviewed basic principles of DIC method and then demonstrated strain distribution in tensile deformed ferritic steel and cyclic deformed tempered martensitic steel. Strain distribution in tensile deformed ferritic steel becomes inhomogeneous with lowering temperature due to restriction of slip systems at low temperature. Strain distribution around a fatigue crack in cyclic deformed tempered martensitic steel was visualized by DIC analysis for replica film and strain concentrated on crack tip same as previous report in DIC analysis for specimen surface, which suggests that strain distribution obtained from replica film has an enough reliability. From these results, it can be concluded that DIC analysis is effective method to investigate local deformation and relation between local deformation and fracture behavior in metal materials.

Abstract: Power module is a system consisting electronic components to perform the power conversion. Power module is a significant impact on the operation of the equipment and its reliability evaluation is very important. Especially, intermittent electric current flowing in the power module causes repeating the heat generation and cooling. It produces a large thermal stress and cause thermal fatigue failure in the solder part. Car makers usually use the power cycle test to measure the thermal fatigue life. But, it is difficult to simulate the field conditions by this test method. Because, in the actual use environment, the irregular current flows with an irregular cycle. In this research, analysis in the conditions near real usage environment was conducted. It aims at establishment of the reliability assessment method of the power module near a real operating condition.