双轴光纤光栅及其传感应用

简要介绍和分析了保偏光纤及双轴光栅的性质，研究了双轴光栅用作传感器的基本原理，介绍了它在三维应变测量、横向负载测量及双折射光纤拍长测量方面的应用。     

Fatigue-Resistant Conducting Polymer Hydrogels as Strain Sensor for Underwater Robotics

Conducting polymer hydrogels are widely used as strain sensors in light of their distinct skin-like softness, strain sensitivity, and environmental adaptiveness in the fields of wearable devices, soft robots, and human-machine interface. However, the mechanical and electrical properties of existing conducting polymer hydrogels, especially fatigue-resistance and sensing robustness during long-term application, are unsatisfactory, which severely hamper their practical utilities. Herein, a strategy to fabricate conducting polymer hydrogels with anisotropic structures and mechanics is presented through a combined freeze-casting and salting-out process. The as-fabricated conducting polymer hydrogels exhibit high fatigue threshold (>300 J m⁻²), low Young's modulus (≈100 kPa), as well as long-term strain sensing robustness (over 10 000 cycles). Such superior performance enables their application as strain sensors to monitor the real-time movement of underwater robotics. The design and fabrication strategy for conducting polymer hydrogels reported in this study may open up an enticing avenue for functional soft materials in soft electronics and robotics.     

不同围压下混凝土受压弹塑性损伤本构模型的研究

在ＭＴＳ公司８１５０２型电液伺服系统上，完成了围压由０～４０ＭＰａ范围内混凝土受压试验，发现随着围压的增大，应力应变全曲线的峰值应力与峰值应变均有所提高，但弹性模量基本不变在此基础上，根据等效应变假定和内变量理论，建立了考虑不可逆应变影响的弹塑性损伤本构模型只要计及峰值应力和峰值应变的变化，该模型可以统一地描述不同围压下混凝土的力学性能     

应变花的平差计算及其在工程中的应用

根据自由网平差理论，提出了一种处理应变网络数据以确定该点应力状态的方法，推导出更符合实际、适应性更广泛的计算主应力公式结果表明，该方法能够充分利用所有的测试信息，大大地提高了处理实测应变数据的精度，效果良好因此，在验算金属支架强度、高层钢结构网架的可靠度等方面具有一定的应用价值     

无铅焊点的电阻应变温度迟滞回线特性

在焊点热可靠性研究过程中,发现无铅焊点在313.15～398.15K循环热载荷条件下电阻应变与温度存在滞后效应,以力学分析方法对该效应的迟滞回线进行了分析讨论。结果表明:塑性电阻应变是引起迟滞回线变化的主要原因;稳定期内一个循环的最大塑性电阻应变量是0.00158,电阻应变滞后于温度变化18.31s;高温迟滞回线变化较低温更明显,二者相差0.0036749,反映了高温下焊点内部损伤程度更快。随着循环次数的增多,迟滞回线从不稳定趋向稳定,最后趋向不闭合,且斜率降低。     

包层变化型光纤光栅传输特性研究

运用传输矩阵理论分析了一种包层半径变化的光栅结构。对包层形状变化取不同形式的光栅传输特性进行了模拟。研究发现,包层半径沿z轴非单调变化将比单调变化时具有更好的方波形反射谱;当半径变化因子g取0．1,包层形状为sin型及外加应力F为1．0N时,可以得到带宽为0．9nm,中心波长为1．55685μm的方波形反射谱。对光栅施加外力时的应变响应进行了研究,发现其对应力也是非常敏感的。     

High quality relaxed Ge layers grown directly on a Si(0 0 1) substrate

After a long period of developing integrated circuit technology through simple scaling of silicon devices, the semiconductor industry is now embracing technology boosters such as strain for higher mobility channel material. Germanium is the logical supplement to enhance existing technologies, as its material behaviour is very close to silicon, and to create new functional devices that cannot be fabricated from silicon alone (Hartmann et al. (2004) [1]). Germanium wafers are, however, both expensive and less durable than their silicon counterparts. Hence it is highly desirable to create a relaxed high quality Ge layer on a Si substrate, with the provision that this does not unduly compromise the planarity of the system. The two temperature method, proposed by Colace et al. (1997) [2], can give smooth (RMS surface roughness below 1 nm) and low threading dislocation density (TDD <10⁸ cm⁻²) Ge layers directly on a Si(0 0 1) wafer (Halbwax et al. (2005) [3]), but these are currently of the order of 1-2 μm thick (Hartmann et al. (2009) [4]).We present an in depth study of two temperature Ge layers, grown by reduced pressure chemical vapour deposition (RP-CVD), in an effort to reduce the thickness. We report the effect of changing the thickness, of both the low temperature (LT) and the high temperature (HT) layers, emphasising the variation of TDD, surface morphology and relaxation.Within this study, the LT Ge layer is deposited directly on a Si(0 0 1) substrate at a low temperature of 400 °C. This low temperature is known to generate monolayer islands (Park et al. (2006) [5]), but is sufficiently high to maintain crystallinity whilst keeping the epitaxial surface as smooth as possible by suppressing further island growth and proceeding in a Frank-van der Merwe growth mode. This LT growth also generates a vast number of dislocations, of the order of 10⁸-10⁹ cm⁻², that enable the next HT step to relax the maximum amount of strain possible. The effect of varying the HT layer thickness is studied by depositing on a LT layer of fixed thickness (100 nm) at a higher growth temperature of 670 °C. We find that the HT layer allows Ge-on-Ge adatom transport to minimise the surface energy and smooth the layer. The final step to the technique is annealing at a high temperature that allows the dislocations generated to glide, increasing the degree of relaxation, and annihilate. We find that annealing can reduce the TDD to the order of 10⁷ cm⁻², but at a cost of a significantly roughened surface.     

Engineered Elastomer Substrates for Guided Assembly of Complex 3D Mesostructures by Spatially Nonuniform Compressive Buckling

Approaches capable of creating 3D mesostructures in advanced materials (device‐grade semiconductors, electroactive polymers, etc.) are of increasing interest in modern materials research. A versatile set of approaches exploits transformation of planar precursors into 3D architectures through the action of compressive forces associated with release of prestrain in a supporting elastomer substrate. Although a diverse set of 3D structures can be realized in nearly any class of material in this way, all previously reported demonstrations lack the ability to vary the degree of compression imparted to different regions of the 2D precursor, thus constraining the diversity of 3D geometries. This paper presents a set of ideas in materials and mechanics in which elastomeric substrates with engineered distributions of thickness yield desired strain distributions for targeted control over resultant 3D mesostructures geometries. This approach is compatible with a broad range of advanced functional materials from device‐grade semiconductors to commercially available thin films, over length scales from tens of micrometers to several millimeters. A wide range of 3D structures can be produced in this way, some of which have direct relevance to applications in tunable optics and stretchable electronics.     

Highly Stretchable and Sensitive Strain Sensors Using Fragmentized Graphene Foam

Stretchable electronics have recently been extensively investigated for the development of highly advanced human‐interactive devices. Here, a highly stretchable and sensitive strain sensor is fabricated based on the composite of fragmentized graphene foam (FGF) and polydimethylsiloxane (PDMS). A graphene foam (GF) is disintegrated into 200–300 μm sized fragments while maintaining its 3D structure by using a vortex mixer, forming a percolation network of the FGFs. The strain sensor shows high sensitivity with a gauge factor of 15 to 29, which is much higher compared to the GF/PDMS strain sensor with a gauge factor of 2.2. It is attributed to the great change in the contact resistance between FGFs over the large contact area, when stretched. In addition to the high sensitivity, the FGF/PDMS strain sensor exhibits high stretchability over 70% and high durability over 10 000 stretching‐releasing cycles. When the sensor is attached to the human body, it functions as a health‐monitoring device by detecting various human motions such as the bending of elbows and fingers in addition to the pulse of radial artery. Finally, by using the FGF, PDMS, and μ‐LEDs, a stretchable touch sensor array is fabricated, thus demonstrating its potential application as an artificial skin.     

Stress relaxation behavior of composite and eutectic Sn-Ag solder joints

Stress relaxation experiments were carried out at 25 C and 150 C on 96.5Sn-3.5Ag eutectic solder and Sn-Ag composite solder joints (Sn-Ag eutectic solder with 20 vol.% Cu₆Sn₅ reinforcements incorporated by in-situ methods). The magnitude of the stress drop during relaxation depends primarily upon the plastic shear strain imposed prior to the stress relaxation process. For sequential stress relaxation experiments that include unloading, the stress drop is nearly independent of the accumulated plastic shear strain. However, for sequential stress relaxation that does not include unloading, the stress relaxation is more dependent upon the cumulative plastic shear strain history. The stress in single shear lap joints does not relax to zero stress, as is observed in stress relaxation of bulk tension specimens, even at 150 C. Creep strain rates extracted from the relaxation data were much lower with smaller pre-strains in both eutectic Sn-Ag and composite solder joints. The stress exponent values (n) calculated from the stress relaxation test data ranged from 7 to 15 for both eutectic and composite solder joints, which were consistent with conventional creep data. These stress-relaxation behaviors can be explained on the basis of dislocation recovery processes that occur during relaxation and when specimens are unloaded.