In Situ DIC Study on LCF Behavior of Retired Weld Joint Subjected to Prolonged Service at Elevated Temperature

The thermal effects at elevated temperatures mostly exist for pressure vessel and pipe (PVP) applications. The technologies for diagnosis and prognosis of PVP systems need to take the thermal effect into account and compensate it on sensing and monitoring of PVP structures. One of the extensively employed sensor technologies has been permanently installed piezoelectric wafer active sensor (PWAS) for in-situ continuous structural health monitoring (SHM). Using the transduction of ultrasonic elastic waves into voltage and vice versa, PWAS has been emerged as one of the major SHM sensing technologies. However, the dynamic characteristics of PWAS need to be explored prior its installation for in-situ SHM. Electro-mechanical impedance spectroscopy (EMIS) method has been utilized as a dynamic descriptor of PWAS and as a high frequency local modal sensing technique by applying standing waves to indicate the response of the PWAS resonator by determining the resonance and anti-resonance frequencies. Another SHM technology utilizing PWAS is guided wave propagation (GWP) as a far-field transient sensing technique by transducing the traveling guided ultrasonic waves (GUW) into substrate structure. The paper first presents EMIS method that qualifies and quantifies circular PWAS resonators under traction-free boundary condition and in an ambience with increasing temperature. The piezoelectric material degradation was investigated by introducing the temperature effects on the material parameters that are obtained from experimental observations as well as from related work in literature. GWP technique is also presented by inclusion of the thermal effects on the substrate material. The MATLAB GUI under the name of Wave Form Revealer (WFR) was adapted for prediction of the thermal effects on coupled guided waves and dynamic structural change in the substrate material at elevated temperature. The WFR software allows for the analysis of multimodal guided waves in the structure with affected material parameters in an ambience with elevated temperature.

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Observations of Magnetic Domain Structure Change in Nd2Fe14B Magnets at Elevated Temperature with External Magnetic Field by Lorentz Microscopy

MRS Proceedings ◽

10.1557/opl.2015.585 ◽

2015 ◽

Vol 1754 ◽

pp. 31-36 ◽

Cited By ~ 1

Author(s):

Toshimasa Suzuki ◽

Koichi Kawahara ◽

Haruka Tanaka ◽

Kimihiro Ozaki

Keyword(s):

Elevated Temperature ◽

Domain Wall ◽

Wall Motion ◽

Magnetic Domain ◽

Domain Wall Motion ◽

Magnetic Domain Wall ◽

Lorentz Microscopy ◽

Pinning Effect ◽

In Situ Observations

ABSTRACTIn this study, we conducted the in-situ observations of the magnetic domain structure change in Nd2Fe14B magnets at elevated temperature by transmission electron microscopy (TEM) / Lorentz microscopy. The in-situ observations in Nd2Fe14B magnets revealed that the magnetization reversal easily occurred at the elevated temperature. At more than 180°C, the magnetic domain wall motion could be observed by applying the magnetic field of less than 20 mT. The motion of the magnetic domain wall was discontinuous and the domain wall jumped to one grain boundary to the neighboring grain boundary at 180°C. On the other hand, the continuous domain wall motion within grain interior as well as discontinuous domain wall motion was observed at 225°C, and some grain boundaries showed still strong pinning effect even at 225°C. The temperature dependence of the pinning effect of grain boundaries would not uniform.

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A Comparative Study on the Tribological Properties of a Cobalt-Free Superaustenitic Stainless Steel at Elevated Temperature

Metals ◽

10.3390/met10091123 ◽

2020 ◽

Vol 10 (9) ◽

pp. 1123

Author(s):

Frederic van gen Hassend ◽

Sebastian Weber

Keyword(s):

Stainless Steel ◽

Wear Resistance ◽

Elevated Temperature ◽

Superaustenitic Stainless Steel ◽

Material Loss ◽

Hardness Tests ◽

Alternative Material ◽

Wear Tests ◽

Hot Hardness

The properties of a cobalt-free cast superaustenitic stainless steel (SASS) is investigated comparatively to the commercial high-cobalt alloyed GX15CrNiCo21-20-20 (1.4957, N-155) steel regarding its global hardness and wear resistance at elevated temperature by means of in situ hot hardness tests and cyclic abrasive sliding wear tests against an Al2O3 (corundum) counter-body at 600 °C. In the aged condition, results show that the 1.4957 steel suffers a higher material loss due to brittle failure initiated by coarse eutectic Cr-rich carbides which are incorporated into a mechanically mixed layer during abrasive loading. In contrast, within the Co-free steel eutectic M6(C,N) carbonitrides are distributed more homogeneously showing less tendency to form network structures. Due to the combination of primary Nb-rich globular-blocky MX-type carbonitrides and eutectic M6(C,N) carbonitrides dispersed within an Laves phase strengthened austenitic matrix, this steel provides comparable hardness and significantly improved wear resistance at elevated temperature. Thus, it may be an adequate alternative material to commercial SASS and offers the possibility to save cobalt for future applications.

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