具非完美交界面多鐵性纖維複合材料之等效材料性質

Abstract

磁電材料具有磁電耦合效應，可應用於製作感測器、驅動器與記憶體上，為近代材料研究的重點之一。然而因單相磁電材料的耦合效率極低，且居禮溫度低於室溫而難以被實際應用，故發展出利用複合材料的方法來達到相同的效果。以往的文獻研究在分析壓電壓磁複合材料的問題時，多假設複合材料的交界面為完美交界面，但在現實情況中，複合材料在製作時多半會因各種因素使交界面產生瑕疵，影響複合材料的等效材料性質。 本文目的為分析具非完美交界面壓電壓磁纖維複合材料在反平面剪應變與橫向電磁場下的等效材料性質，分別以強非完美交界面與弱非完美交界面兩種情況來討論，同時運用解耦方法(Decoupling transformation)將壓電壓磁複合材料的多重物理場耦合問題轉換成各單一物理場的問題，以簡化其分析複雜度，並與其他方法得到的結果相互比對，驗證其結果的正確性。最後探討非完美交界面對等效材料性質的影響，以及非完美交界面複合材料是否符合藉由解耦所得的應變相容公式(Compatibility relation)，並藉由雙層法來解釋原因。

The magnetoelectric (ME) effect in multiferroic materials, which refers to the coupling between electric and magnetic fields, has great potential for practical device applications such as sensors, actuations and memories. However, the ME effect in single-phase multiferroic materials is too weak and cannot be observed at room temperature. On the other hand, multiferroic composites provide an alternative option for improvement. Many of the existing works about multiferroic composites assume that the interface between ferromagnetic and ferroelectric constituents are perfect. But in reality, the imperfect interfaces which can affect the ME effect may be present in many circumstance such as sliding, debonding and flaws. This research studies the effective properties of piezoelectric-piezomagnetic fibrous composites with imperfect interfaces under longitudinal shear with in-plane electromagnetic fields. We employ the decoupling transformation method to reduce the multi-field coupled problem to a set of equivalent single-field problems. Both mechanically stiff and electromagnetic highly conducting interfaces and mechanically soft and electromagnetic weakly conducting interfaces are considered. Numerical results are compared with the known solutions and are shown in good agreement. It is observed that imperfect interfaces have great influence on the ME voltage coefficient and that moduli of composites with imperfect interfaces do not satisfy the compatibility relations. Finally, we use the two-level recursive scheme to show the validity of the three-phase composite assumption in modeling the imperfect effect.