柔性电子器件有着广泛的应用前景，目前研究主要集中于柔性可穿戴设备，而在传统工业方面则涉足较少。岛桥结构是柔性电子器件的一个典型结构，既可以集成功能元件，又可以实现可拉伸变形能力，在高铁等具有复杂曲面的大型交通设备方面有着广泛的应用空间，值得深入探索。本文首先对多层岛桥结构中桥结构的刚度问题进行了理论研究，为岛桥结构变形定量分析和设计提供了依据，之后采用多层岛桥结构设计，分别制备了用于高铁车头表面压力监测和车轴超声无损检测的柔性电子器件。

多层岛桥结构中的桥结构作为一种多层复合条带结构，其拉伸/弯曲刚度作为重要的力学参数被广泛应用于岛桥结构的力学分析。研究者一般都是采用平面应变模型去计算多层复合条带结构的拉伸/弯曲刚度，但实际结构更接近于零合力条件。鉴于此，本文建立了零合力理论模型，用于精确计算多层复合条带结构的拉伸/弯曲刚度。研究发现，零合力模型介于平面应变模型和平面应力模型之间，并且更接近于平面应力模型，同时有更精确的解答。本文还解释了平面应变/平面应力/零合力这三种理论模型在计算拉伸刚度时产生差异的原因。零合力模型为岛桥结构变形定量分析和设计提供了依据。

目前，高铁表面压力监测一般都是采用测压孔技术，该技术很难实现小范围复杂表面压力分布的监测，而且会对高铁车身造成一定的破坏，同时，测压系统的安装也较为繁琐。为此，本文基于柔性电子技术，采用多层曲桥互联岛桥结构设计，制备了一种大面积可拉伸气压传感器阵列，用于高铁车头表面压力场的监测。有限元模拟和拉伸实验表明，该气压传感器阵列具有良好的力学拉伸性能（50%）；高铁动模型实验和数值模拟也证实了该气压传感器阵列可以实现表面压力场监测。

传统超声探头（单晶探头、相控阵探头等）都是刚性的，很难用于高铁车轴的无损检测。本文基于柔性电子技术，采用多层直桥互联岛桥结构设计，制备了一种柔性超声相控阵换能器（12*12），用于高铁车轴无损检测。1-3压电复合材料阵元之间通过硅橡胶粘接形成柔性压电阵列；每个压电阵元有着独立背衬和匹配层；采用多层柔性电路板实现12*12路独立信号通道的电路连接。脉冲回波实验、缺陷回波实验和缺陷检测成像实验表明，该柔性超声相控阵换能器可以准确地实现曲面工件的无损检测。

Flexible electronics have extensive application prospects; however, most related researches focus on flexible wearable devices, while little attention has been paid to conventional industries. As a typical structure of flexible electronics, the island-bridge structure can not only integrate various functional components but also achieve stretchability, which results in wide potential applications in large-scale transportation equipments with complex surfaces such as high-speed trains. Therefore, it is worth researching on the island-bridge structure of flexible electronics in those equipments. First, this dissertation develops some mechanics researches on the stiffnesses of laminated bridges of island-bridge structures in order to guide quantitative analysis and design of the deformation of island-bridge structures. Then, laminated island-bridge structures are applied to the fabrication of two flexible electronics, which aim for surface pressure monitoring of the high-speed train locomotive and ultrasonic nondestructive detection of the high-speed train axles, respectively.

Laminated structures have been widely adopted in the stretchable interconnects of island-bridge structures, and both their tensile and bending stiffnesses, which act as key mechanical parameters, have been widely applied to the mechanical analyses for the island-bridge mesh structures. Nowadays, researchers usually get the tensile or bending stiffness with the plane-strain assumption. However, it is found that the practical condition is usually closer to the traction-free condition. Here, a traction-free model is proposed to analytically obtain the effective tensile and bending stiffnesses of laminated structures. According to this dissertation, the tensile/bending stiffnesses of the traction-free model are between the plane-strain model and the plane-stress model, and are closer to those of the plane-stress model. Besides, the traction-free model is found to be more accurate than both plane-strain and plane-stress models. Meanwhile, this work has also explored the mechanism why there are some differences among these three analytical models when calculating the tensile stiffnesses of laminated structures. The traction-free model can provide valuable guidance to quantitative deformation analyses and design of the island-bridge structures.

At present, the pressure tap technique is usually adopted for the measurement of surface pressure for high-speed train. However, it is very difficult or even impossible for this technique to measure the surface pressure field in local small area with complex surface such as the locomotive, and this technique could cause some damage to high-speed train body, and it is difficult to install or replace its pressure measurement system. This work reports a kind of large-scale and stretchable pressure sensor array with the design of laminated island-bridge structures connected by curved bridges, which aims for the measurement of surface pressure field for high-speed train locomotive. The results of the finite element modeling and tensile experiment show an excellent stretchability (50%) of this pressure sensor array. Besides, the moving high-speed train model test and numerical simulation validate the accuracy and reliability of this pressure array in measuring surface pressure fields.

Conventional ultrasonic probes such as single crystal probe and phased array probe are usually rigid, and it is difficult to apply them to the nondestructive detection of curved workpieces. In this work, a flexible ultrasonic phased array transducer with the design of laminated island-bridge structures connected by linear bridges is designed and fabricated, which aims for the nondestructive detection of high-speed train axles. All array elements made from 1-3 piezo-composite were bonded together with silicon rubber to form a flexible array; each array element owns its individual backing layer and matching layer; the flexibility and the electrical connection of 12*12 autonomous signal channels are achieved with laminated flexible printed circuit board. The experimental results of pulse echo experiment, defect echo experiment and defect imaging experiment indicated that this flexible ultrasonic phased array can achieve the nondestructive testing for curved workpieces accurately.