Flatness Improvement of Double-Sided Magnetic Film for Narrow Gap Electromagnetic Energy Harvester

This paper reports the design, modeling and preliminary fabrication result of the flatness improved magnetic film on a silicon structure for narrow-gap electromagnetic (EMG) vibration energy harvester (VEH). The harvester has double-sided corrugated shape silicon vibration mass with 15 µm-thick NdFeB permanent magnet. The narrower air-gap between the magnetic film and a counter coil electrode the higher output power. While the sputtered magnetic film shows good characteristics equivalent to a bulk magnet, it hinders to reduce the air-gap because the silicon structure was curved by its high residual stress. Applying the double-sided magnet to our previous device, the curvature radius of moving mass with 15 µm-thick NdFeB film was improved from 5.3 m to 40.1 m because of the stress compensation. With the narrowed 2 µm air-gap device, the resulting simulated output power is 48 µW that is 190 times as large as previous device.

Two-Scale Analysis of Thermal Behavior of CFRP Laminates Based on a Thermoelastoviscoplastic Homogenization Theory

In this study, a two-scale thermoelastoviscoplastic analysis method for carbon fiber-reinforced plastic (CFRP) laminates is proposed based on a homogenization theory for time-dependent composites. For this, macroscopic and microscopic boundary value problems for CFRP laminates are derived to discuss the relation between the two problems. Using the relation, a two-scale thermoelastoviscoplastic analysis method is constructed, and then applied to the analysis of thermal behavior of an unsymmetric cross-ply carbon fiber/epoxy laminate. The laminate is subjected to a macroscopic temperature change from 180°C to 20°C. It is shown that quite high residual stress and strain occur both macroscopically and microscopically in the laminate, resulting in large macroscopic warpage of the laminate.

Factor Affecting Corrosion Behavior of Weldment of S30400 Stainless Steel in Cold Region

The influence of residual stress and sensitizing on the electrochemical and corrosion behavior of type SUS304 stainless steels weldment has been studied in the Freeze-Thaw condition. After immersion test at Freeze-Thaw cyclic condition the severe corrosion damage was detected in the vicinity of weld boundary more than isothermal condition. The corrosion damaged zone corresponds to the location in which there are high residual stress and sensitization. The influence of residual stress and sensitization was distinguished and its magnitude was evaluated by voltammetry method.

Mechanical Proprieties and Residual Stress Evaluation on Heteroepitaxial 3C-SiC/Si for MEMS Application

SiC is a candidate material for micro- and nano-electromechanical systems (MEMS and NEMS). The hetero-epitaxial growth of 3C-SiC on silicon substrates allows one to overcome the traditional limitations of SiC micro-fabrication, but the high residual stress created during the film grow limits the development of the material for these applications. In this work, in order to evaluate the amount of residual stress released from the epi-film, different micro-machined structures were developed. Through the measurement of natural resonant frequencies and Raman shift analysis, a strong relationship between the mechanical proprieties of the material (Young’s modulus) and the film crystal quality (defect density) was observed.

Advanced Stress Analysis by Micro-Structures Realization on High Quality Hetero-Epitaxial 3C-SiC for MEMS Application

SiC is a candidate material for micro- and nano-electromechanical systems (MEMS and NEMS). The fabrication of SiC MEMS-based sensors requires new processes able to realize microstructures on either bulk material or on the SiC surface. The hetero-epitaxial growth of 3C-SiC on silicon substrates allows one to overcome the traditional limitations of SiC micro-fabrication, but the high residual stress created during the film grow limits the development of the material for these applications. In order to evaluate the amount of residual stress released from the epi-film, different micro-machined structures were developed. Finite elements simulations of the micro-machined structures have also been carried out in order to evaluate, in detail, the stress field inside the structures and to test the analytical model used. With finite element modeling a exponential approximation of the stress relationship was studied, yielding a better fit with the experimental data. This study shows that this new approximation of the total residual stress function reduces the disagreement between experimental and simulated data.

Overview on the Corrosion Behavior of Ultra-Fine Grained Materials Fabricated by Equal-Channel Angular Pressing

With the development of the ECAP technology, the corrosion behavior of the UFG materials has been investigated in some degree. Two categories of corrosion behaviors of UFG material were discussed in this paper. The large proportion of the non-equilibrium grain boundaries and high residual stress inside of the grain were regarded as the key to affect the corrosion behavior of the UFG materials. The corrosion behavior was also affected by the ECAP factors especially the press pass number and the pressing temperature. Finally some prospects of making UFG materials combined with high mechanical property and good corrosion resistance by ECAP technology were expounded.

Finite Element Analysis of Residual Stress in Diamond/Steel Brazed Joint

In the application of brazed diamond tools, residual stress caused by differences in materials properties is an important factor in obtaining good brazing quality. The residual stress in diamond/steel brazed joint is studied by means of finite element method and Raman spectroscopy in this paper. The comparison between the results from the simulations and the measurements shows that a good agreement has been reached. Tensile stress concentration at the diamond edge near interface was observed. High residual stress concentration may cause cracks in diamond. Actually, cracks in diamond caused by brazing residual stress after were observed. The stress concentration of the joint must be reduced to obtain good brazed joint. The change of brazing atmosphere or to adopt the soft brazing alloy will reduce the stress concentration.

3C-SiC Films on Si for MEMS Applications: Mechanical Properties

Single crystal 3C-SiC films were grown on (100) and (111) Si substrate orientations in order to study the resulting mechanical properties of this material. In addition, poly-crystalline 3C-SiC was also grown on (100)Si so that a comparison with monocrystaline 3C-SiC, also grown on (100)Si, could be made. The mechanical properties of single crystal and polycrystalline 3C-SiC films grown on Si substrates were measured by means of nanoindentation using a Berkovich diamond tip. These results indicate that polycrystalline SiC thin films are attractive for MEMS applications when compared with the single crystal 3C-SiC, which is promising since growing single crystal 3C-SiC films is more challenging. MEMS cantilevers and membranes fabricated from a 2 µm thick single crystal 3C-SiC grown on (100)Si under similar conditions resulted in a small degree of bow with only 9 µm of deflection for a cantilever of 700 µm length with an estimated tensile film stress of 300 MPa. Single crystal 3C-SiC films on (111)Si substrates have the highest elastic and plastic properties, although due to high residual stress they tend to crack and delaminate.

High Residual Stress Between Zirconia Grains Observed With Laue Micro-Diffraction

Highly focused synchrotron X-rays were used to measure residual stresses in dental grade yttria stabilized zirconia. The technique uses a sub-micron polychromatic beam to produce Laue diffraction spots. Diffraction spots from individual grains of zirconia provide the deviatoric stress tensor of the residual stress. Significant local grain-grain stresses were observed nearly 10–15% of the 1500 grains examined exhibiting stresses above 500 MPa. These residual stresses influence crack propagation and fracture.