Tomi Lindroos

Dynamic compression testing of a tunable spring element consisting of a magnetorheological elastomer

Magnetorheological elastomers (MRE) are interesting candidates for active vibration control of structural systems. In this study, spring elements consisting of magnetorheological elastomer were prepared and tested in dynamic compression to study the changes in their stiffness and vibration damping characteristics under the influence of a magnetic field. Aligned and isotropic magnetorheological elastomer composites were prepared using room temperature vulcanizing silicone elastomer as the matrix material and carbonyl iron as the magnetizable filler. Aligned MREs were prepared by curing the material under an external magnetic field. Aligned MREs were tested and the results were compared with isotropic composites with no preferred orientation. The mechanical properties of the MREs were tested in cyclic compression passively and with increasing magnetic flux density. The influence of the testing frequency and strain amplitude on the dynamic stiffness and damping properties was studied. It was noted that when measured in a magnetic field both the dynamic spring constants and the loss factor values of aligned MREs were increased compared to the zero-field values. The dynamic stiffness of aligned MREs increased with increasing testing frequency and it was tunable with magnetic flux density in the studied frequency range. The loss factor of aligned MREs was also tunable with the magnetic flux density but the absolute values also depend on the testing frequency. The dynamic stiffness of the aligned MREs measured in compression decreased with increasing strain amplitude, but the damping properties were not affected similarly. On the basis of these results, MREs are applicable as tunable spring elements for active vibration control.

Microstructure analysis and damage patterns of thermally cycled Ti?49.7Ni (at.%) wires

Long-term behaviour and fatigue endurance are the key issues in the utilization of SMA actuators, but systematic research work is still needed in this field. This study concentrates on the effects of three major design parameters on the long-term behaviour of binary Ti?49.7Ni-based actuators: the effect of the temperature interval used on thermal cycling, the effect of the stress level used and the effect of the heat-treatment state of the wire used. The long-term behaviour of the wires was studied in a custom-built fatigue test frame in which the wires were thermally cycled under a constant stress level. Before the fatigue testing, a series of heat treatments was carried out to generate optimal actuator properties for the wires. This paper concentrates on the systematic fractographic analysis of the fatigue fractured Ti?49.7Ni wires. The aim was to discover the relationships between the macro-scale behaviour and the microstructural changes of the material. During thermal cycling the surfaces of the Ti?49.7Ni wires were examined with an optical microscope. Clear connections between the detected surface defects and fracture nucleation sites were not established. Multiple cracks were initiated and grew during thermal cycling. SEM examinations showed that the fracture surfaces can be divided into different and separate zones: a smooth surface region with radial marks indicating the fatigue crack propagation area, a rougher ductile fracture surface region area and the roughest surface region on the interface of these two surfaces. It was detected that the size of the crack propagation area is related to the fatigue lives of the thermally cycled wires. Surface cracking and subsequent crack growth proved to be responsible for the accumulation of fatigue damage in the studied wires. It was detected from the fracture surface cross-sections that cracks were not initiated at the oxide layer. The major factor for nucleating the surface cracking and then shortening the fatigue endurance of the binary SMA actuator wires seems to be the accumulated plastic strain.

Baltic Energy Technology Scenarios 2018

Baltic Energy Technology Scenarios 2018 (BENTE) is a scenario-based energy system analysis that explores the changes in the Baltic countries’ energy systems. What are the drivers and their impacts ...

Alueellinen metsähaketase vuonna 2030

Anttila P., Nivala V., Salminen O., Hurskainen M., Kärki J., Lindroos T.J., Asikainen A. (2018). Alueellinen metsähaketase vuonna 2030. Metsätieteen aikakauskirja 2018-9999. Tutkimusseloste. 3 s. https://doi.org/10.14214/ma.9999 Yhteystiedot 1Luonnonvarakeskus (Luke), Tuotantojärjestelmät, Joensuu; 2 Luonnonvarakeskus (Luke), Biotalous ja ympäristö, Rovaniemi; 3 Luonnonvarakeskus (Luke), Biotalous ja ympäristö, Helsinki; 4 Teknologian tutkimuskeskus VTT Oy, Luonnonvaraja ympäristöratkaisut, Jyväskylä; 5 Teknologian tutkimuskeskus VTT Oy, Älykäs teollisuus ja energiajärjestelmät, Espoo Sähköposti perttu.anttila@luke.fi Hyväksytty 04.05.2018 Seloste artikkelista Anttila P., Nivala V., Salminen O., Hurskainen M., Kärki J., Lindroos T.J., Asikainen A. (2018). Regional balance of forest chip supply and demand in Finland in 2030. Silva Fennica vol. 52 no. 2 article id 9902. https://doi.org/10.14214/sf.9902

A risk hedging strategy for the 2°C target and the Copenhagen Accord

This report presents the results from a research project ”Long term impact of the Copenhagen accord regarding the 2 degree target”, done at VTT Technical Research Centre of Finland during autumn 20 ...