Comparison between simultaneously performed measurements of electrochemical noise and mechanical parameters during stress-corrosion processes

Namen našega dela je bil določiti značilnosti elektrokemijskega šuma, povzročenega z napetostno-korozijskim pokanjem. Želeli smo predvsem ugotoviti poveznanost značilnih elektrokemijskih fluktuacij z mehanskimi spremembami zaradi procesov pokanja ter tako posredno tudi oceniti primernost te metode za detekcijo in študij različnih oblik pokanja. Elektrokemijski šum smo merili med počasnim enakomernim nateznim obremenjevanjem delovne elektrode (modificiran Slow Strain Rate Test), izdelane iz nerjavnega avstenitnega jekla tipa AISI 304 v žarjenem ter toplotno neobdelanem stanju. Izrazite nenadne fluktuacije napetostnega in tokovnega šuma smo opazili po preseženi napetosti tečenja. Vse se časovno popolnoma ujemajo z nenadnimi spremembami raztezka natezno obremenjene elektrode, kar dokazuje zanesljivo možnost detekcije pokanja. Iz izmerjenih sprememb raztezka smo določili hitrost rasti razpok ter jih primerjali z amplitudami fluktuacij elektrokemijskega šuma. Dokazali smo, da obstaja med vrednostmi teh dveh količin linearna odvisnost. Poudariti je treba, da samo poznanje elektrokemijskih razmer ter spremljanje mehanskih sprememb, povzročenih s pokanjem, še ni dovolj za ovrednotenje mehanizmov napetostno-korozijskega pokanja, pač pa bo za to v prihodnosti treba vključiti še fraktografsko analizo prelomnih površin.The main aim of the research work was to asses basic characteristics of electrochemical noise generated by stress-corrosion cracking, and especially to find a correlation between the electrochemical and mehanical quantities. Electrochemical noise was measured during slow constant increasing of stress (modified Slow Strain Rate Test) on tensile tube made from austenitic stainless steel of the type AISI 304, in sensitized and nonsensitized condition. One of the objectives of this research was to investigate the possibility of electrochemical noise method for studying stress-corrosion processes. After the reaching yielding point, voltage and current spikes, as well as elongation transients, all appearing at the same time, were detected. Afterwards, the cracking velocities were determined from the time series of elongation, and compared to characteristic parameters of the measured electrochemical noise. The results of the comparision indicated that the amplitudes of the electrochemical noise spikes are lineary dependent upon cracking velocity. It has to be pointed out, that the knowledge of elecrochemical conditions and mechanical changes generated by cracking processes by themselves, cannot form revalant information concering the cracking mechanisms. In order to get better overview to this problem additional fractographic inspections of cracking surfaces has to be performed

An assessment of the damage to ropeway clips and an analysis of the source of the damage

Vrvna prižemka je nosilni, dinamično obremenjen konstrukcijski element, ki povezuje sedežno obešalo s transportno vrvjo sedežnice. V lanskem letu smo sistematično vizuelno in defektoskopsko pregledali večje število prižemk in ostalih vitalnih konstrukcijskih elementov sedežnic. Osnovni cilj preiskav je bil oceniti njihovo stanje, detektirati obstoječe razpoke in ostale poškodbe, ki bi lahko vodile do nenadnih lomov ter določili obseg teh poškodb. Ultrazvočna metoda s posebej prirejeno površinsko sondo se je pokazala kot najprimernejša in izredno zanesljiva metoda za določanje razpok na prižemkah. Rezultati preiskav so pokazali, da ima material prižemk in nekaterih drugih konstrukcijskih elementov zelo nizko žilavost in grobo zrnato feritno - perlitno mikrostrukturo, ki je posledica neustrezne toplotne obdelave. Konstrukcijski elementi iz materiala s tako strukturo ne zagotavljajo zadostne odpornosti proti krhkemu lomu.A ropeway clip is an important dynamically loaded construction element that fastens together the hanger bar and the rope. During the last year, we were involved in systematic non-destructive testing of a range of ropeway clips and some other important construction elements. The main goal of the research was to detect the existance of cracks and other types of the damage that can lead to unexpected fracture, and an evaluation of the condition of the ropeway clips. The ultrasound method, accompanied by a specially arranged ultrasound surface beam-probe proved to be the most suitable, precise and reliable method for the cracks detection on the clips. In addition, several laboratory investigations were carried out in order to find causes for the initiation and propagation of cracks in the clips. Results of laboratory examinations revealed that the material of the clips, and also of the other construction elements, had very low toughness and a coarse-grain pearlite-ferritic microstructure, which is a result of improper heat treatment. It was concluded that the construction elements made from material with this kind of structure and mechanical properties would not ensure sufficient resistance to brittle fracture

Development of an Electrical Resistance Sensor from High Strength Steel for Automotive Applications

This work focuses on a demonstration of the monitoring of corrosion processes taking place in high strength steel in automotive applications. This is performed by means of a corrosion sensor, which operates as an electrical resistance sensor. It was developed from the same type of material that is used for the high-strength steel parts produced in the automotive industry. Using the sensor, real time corrosion processes can be measured. It is attached to a location inside the vehicle’s engine and is equipped with a data logger, which enables wireless transfer of the measured data. In this study the development, operation, and evaluation of the monitoring process are presented. Corrosion estimation is verified by means of electrochemical methods. A metallographic investigation was included in order to verify the similarity between the microstructural properties of the sensor and those of the as-received high-strength steel sheet