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A study was conducted to examine the integrations of the magneto-electro-elastic Eschelby tensors for a piezoelectric-piezomagnetic composite reinforced by ellipsoidal inclusions. The tensors provided the basis for evaluating magneto-electro-elastic response of composites. The tensors were also correlated with elastic response owing to eigenstrains. Results showed that the magneto-electro-elastic Eshelby tensors were obtained in closed forms when the constituents of the composite were transversely isotropic and the shapes of the inclusion were elliptic.

Creep behavior is very important to reliability of micromechanical components. Therefore, there are some emerging research efforts that focus on creep of silicon. However, few have focused on interaction among microscale dimension effect, temperature, and applied stress, which are more crucial to microelectrical mechanical system components compared with regular size components. This paper presents investigation of creep of single crystal silicon cantilever microbeams with a specific focus on the length effect. Results are presented characterizing the creep behavior in the length range of 300–700 µm, the temperature range of 600–700℃, and the stress range of 235–501 MPa. As the temperature or stress increases, the creep rate of silicon increases and duration of the steady-state creep decreases. Creep rate decreases with the increase of microbeam length. At 600℃, creep rupture lifetime approximately increases with the increase of microbeam length. At 700℃, maximum lifetime shifts to medium length of 400 µm. Factors that influence rupture lifetime include short beam effect, defect distribution, stress, temperature, and brittleness caused by oxidation. To summarize, creep failure modes for short beam and long beam are, respectively, dislocation motion by multiple slip systems and single slip system. [ABSTRACT FROM AUTHOR]

This study reports the fracture evolution of thick cross-plied composites under static compression loading. The prepreg employed was TC-35 carbon fiber/EHM-63 epoxy, and the composite was laminated using a pressure rolling machine. Six types of symmetric stacking were adopted: [0m/902m/0m] n (m = 40, 20, 10, 5, 2, 1 and n = 1, 2, 4, 8, 20, 40, respectively). All specimens contain a total of 160 layers, and the numbers of 0° and 90° layers are both 80. The nominal thickness specimen is 24 mm. For different pairs of m and n, the number of 0°/90° interfaces varies. To apply the compressive load, an end-supported, end-loaded fixture was used. The growth of cracks was monitored and recorded in real-time by picture and video cameras. The relationships among the stacking sequence, the support conditions, the resulting properties, the induced failure modes, and the fracture evolution are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Fatigue behavior is very important to reliability of micromechanical components. Therefore, there are some emerging research efforts that focus on fatigue of silicon. However, few have looked across the interacting spectrum of several material systems, which is more crucial in MEMS components. This paper presents investigation of fatigue of Si3N4/SiO2 coated single crystal silicon (CSCS) cantilever microbeams. The composite microbeams were tested using a bending mode under cyclic strain. A micro-force testing machine with a micro-probe was used to load the beams. In the fatigue testing, various percentages of failure strain obtained from static testing were adopted as the maximum cyclic strain, and their strain ratios were set as zero. The fatigue strain-life curves were achieved. Furthermore, the enhancement of fatigue performance by coatings was investigated by scratch tests and microscopic examination of the scratch surface. In order to determine the fatigue failure modes, SEM was employed to carefully observe the failed CSCS beams. Interface bonding, surface roughness, residual stress, and mechanical properties that influence the contribution of the coating were discussed. The results demonstrate that very thin ceramic coating can significantly improve the fatigue performance of silicon. [Copyright &y& Elsevier]