厚膜电阻材料的物化特性对钌系厚膜电阻应变系数的影响

通过对厚膜电阻导电相、玻璃相的粒径控制、粒径比搭配以及在导电相、玻璃相中掺杂,研制成一种厚膜力敏电阻浆料,其应变系数GF可达15～17、工作温度可达150℃.介绍了厚膜力敏应变系数的测量方法,研究了厚膜电阻材料的物化特性对钌系厚膜电阻应变系数的影响,探讨了提高应变系数的技术途径,同时,对其导电机理作了简要的阐述.     

汽车油位传感器厚膜电阻的力学性能

通过对汽车市场应用最广的油位传感器核心部件厚膜电阻导带进行分析和样品准备,利用纳米压痕法对常用的三种油位传感器厚膜电阻导带:C4303GCD(银/钯导体浆料)、C4303M(银/钯导体浆料)和5800B(陶瓷铂金导体浆料)及其基片进行了力学性能测试,得到了厚膜电阻导带的硬度、弹性模量等力学特性参数。结果表明:C4303GSD型导带的硬度值和弹性模量最大,而且导带中银/钯含量比越低,导带硬度值越高。该研究对于油位传感器质量提高有着十分重要的意义,不但解决了目前生产厂家无法测出厚膜电阻导带力学性能的问题,也为新型油位传感器的触头导带的合理配对选型和性能改进,厚膜电阻导带的质量和耐磨性评价提供了重要的理论和试验依据。     

用于氮化铝基片的厚膜浆料研制成功

昭和电工公司研制成用于氮化铝基片的银基厚膜导电浆料-shoden,并已投放市场。氮化铝基片是混合集成电路下一代基片。这种新的厚膜浆料对于氮化基片有很强的粘着性。它与氮化铝基片粘合后所产生的电阻只有传统的玻璃浆料     

BaPbO3/Ag复合体系大功率厚膜电阻浆料的研究

提出以BaPbO3/Ag复合体系作为功能相制备低成本大功率厚膜电阻浆料的思想,研究Ag含量、峰值烧结温度对厚膜电阻电性能和热稳定性的影响,并从导电机理方面对实验结果进行了分析讨论.     

厚膜力传感器的一体化补偿

对以陶瓷双孔梁为弹性体的新型厚膜力传感器进行了零点温度漂移和零点的一体化补偿，分析了零点温度漂移和零点的补偿方法，在同一陶瓷弹性体上印刷，烧结，制备了厚膜力敏电阻，补偿厚膜热敏电阻零点补偿厚膜电阻，并较好地是实现了零点温度漂移和零点的补偿，还探讨了补偿用热敏电阻浆料性能的改进。     

厚膜pH传感器研究

用沉淀法制备pH敏感粉料，用厚膜和陶瓷技术制备pH厚膜传感器，测试了传感器的PH特性，分析了两种配方的有关物性结构，对于与敏感玻璃厚膜集成在同一基片上的加热厚膜电阻的应用亦作初步研究。     

厚膜力传感器的─体化补偿

对以陶瓷双孔梁为弹性体的新型厚膜力传感器进行了零点温度漂移和零点的─体化补偿。分析了零点温度漂移和零点的补偿方法，在同一陶瓷弹性体上印刷、烧结、制备了厚膜力敏电阻，补偿厚膜热敏电阻及零点补偿厚膜电阻，并较好地是实现了零点温度漂移和零点的补偿。还探讨了补偿用热敏电阻浆料性能的改进。     

厚膜电阻的研究现状及发展趋势

首先描述了厚膜电阻的基本结构,介绍了制作厚膜电阻的各种材料,然后详细地阐述了厚膜电阻的制备工艺,探讨了厚膜电阻的导电机理和近年来的发展趋势。     

纳米Al2O3掺杂对厚膜应变电阻性能的影响

采用粒子尺寸为８ｎｍ的纳米Ａｌ２Ｏ３作掺杂改性剂，通过选择合适粒径和配比的导电相、玻璃及烧结工艺，得到一种ＧＦ为１３、电阻温度系数小、稳定性良好的在厚膜应变电阻，并从厚膜电阻导电机理和纳米材料特性出发。     

ZnO多孔纳米固体厚膜气敏传感器的制备和性质表征

以ZnO纳米粉(平均粒径30nm)为原料,利用水热热压方法制备了多孔的ZnO体块纳米固体,测试了以多孔纳米固体为原料制成的厚膜气敏传感器对挥发性有机化合物(VOCs)乙醇、丙酮、苯、甲苯和二甲苯蒸气的气敏特性,并与用ZnO纳米粉制备的厚膜传感器进行了比较.结果发现,与ZnO纳米粉相比,用ZnO多孔纳米固体制备的厚膜传感器在空气中的电阻大大减小,最佳敏感温度降低、响应时间和恢复时间大大缩短.通过综合分析ZnO纳米粉和ZnO多孔纳米固体的XRD、TEM及厚膜传感器的SEM测试结果研究了厚膜传感器气敏特性的差异.     

Crystal plasticity-based modelling of grain size effects in dual phase steel

With decreasing grain size, the strength of steel increases due to the well-known Hall–Petch type effects, which is generally neglected in the classical crystal plasticity-based models. In the present work, the classical crystal plasticity-based model has been modified to incorporate the grain size effect. Validation of the present model was carried out with the published experimental results of a dual phase steel and, it was found to be possible to predict the grain size effects quite accurately using the model. The proposed model was used to carry out a parametric study for effects of grain size and was further used to predict the influence of grain size on cross effects during orthogonal loading.     

Buckling characteristics of nanocrystalline nano-beams

The buckling and the postbuckling characteristics of nanocrystalline nano-beams with/without surface stress residuals are investigated. A hybrid model is proposed where a non-classical beam model is incorporated with a size-dependent micromechanical model. The micromechanical model has the merit of accounting for the beam material structure effects, i.e. the grain size and the grain boundary effects. To account for the beam size effects, the couple stress theory is implemented where some measures are added to capture the grain rigid rotation effects. The proposed hybrid model is harnessed to derive the governing equations of a nano-beam subjected to an axial compressive load accounting for the mid-plane stretching according to von-Karman kinematics and the surface stress residuals. Analytical solutions for the prebuckling and postbuckling configurations and natural frequencies as functions of the applied compressive axial load are derived. The effects of the beam material structure and the beam size on the beam’s prebuckling characteristics and the postbuckling configurations and natural frequencies are studied. The obtained results reveal that both the size and the material structure of nanobeams have great impacts on their buckling characteristics.     

A constitutive model of particulate-reinforced composites taking account of particle size effects and damage evolution

This paper deals with a constitutive model of particulate-reinforced composites which can describe the evolution of debonding damage, matrix plasticity and particle size effects on deformation and damage. An incremental damage model of particulate-reinforced composites based on the Mori–Tanaka’s mean field concept has been extended to consider the particle size effects by using the Nan–Clarke’s simple method. The particle size effect on deformation is realized by introducing dislocation plasticity for stress–strain relation of in situ matrix in composites, and the particle size effect on damage is described by a critical energy criterion for particle–matrix interfacial debonding. For composites containing particles of various sizes, the effects of particle size distribution is incorporated into the model. Influence of debonding damage, particle size and particle volume fraction on overall stress–strain response of composites is discussed based on numerical results.     

Size effects in the biaxial tensile-compressive behaviour of concrete: physical mechanisms and modelling

This paper analyses failure mechanisms and apparent size effects in the biaxial tensile-compressive behaviour of concrete. To this end, a probabilistic discrete crack model is used to numerically determine failure surfaces in the tensile-tensile and tensile-compressive loading range, on account of size effects being considered as volume effects. The results (failure mechanisms, crack patterns, volume effects, etc.) are discussed in some detail with respect to the applied loading state. Size effects on the failure surface are quantified in terms of stress-invariant ratios at peak load for 8 loading paths. It is found that size effects decrease with increasing hydrostatic pressure,i.e. when passing from the tensile loading range into the tensile-compressive range. This can be explained by the activation of friction at the crack lips in a stable crack propagation, which regularises mechanical volume effects, and thus apparent size effects.     

Development of an LEFM dynamic crack criterion for correlated size and rate effects in concrete beams

The strength of concrete under severe dynamic loading depends on the specimen size and the loading rate. Although the size effect, under quasi-static loading, has been explained by the size-dependent strain energy rate, the main causes of the size and rate effects for dynamic loading cases have not been clarified. In this study, a linear elastic fracture mechanics (LEFM) dynamic crack criterion for a notched three-point bend specimen is developed to explain the size and rate effects, and the possible correlation of these effects. This was achieved by using energy balance, force equilibrium, and Griffith's crack model. From the proposed LEFM dynamic crack criterion, it was shown that (1) the kinetic energy rate seems to be the main cause of the rate effect, (2) the size and rate effects are not independent phenomena.     

颗粒粒度分布对树脂基磁致伸缩复合材料性能的影响

已有研究在Terfenol-D颗粒粒径及粒度分布对树脂基磁致伸缩复合材料性能的影响规律上存在分歧。本文中以Terfenol-D为磁致伸缩颗粒,以不饱和聚酯树脂为基体,采用5 种窄分布颗粒(30～53μm、53～150μm、150～300μm、300～450μm、450～500μm)和1种宽分布颗粒(30～500μm)制备颗粒体积分数为20 %的磁致伸缩复合材料,并测试其动静态磁致伸缩系数、磁机械耦合系数、弹性模量及抗压强度等性能参数。在窄分布颗粒制备的试样中,以53～150μm制备的复合材料的磁致伸缩性能最佳;而采用宽分布颗粒制备的试样其性能优于窄分布颗粒制备的试样。该结果表明,增大颗粒粒径同时具有积极作用与消极作用, 其对复合材料磁致伸缩性能的影响取决于哪一个居主导地位。      

铜箔抗拉强度及延伸率的尺寸效应研究

为了研究尺寸参数对金属箔材的抗拉强度和延伸率的影响规律,采用不同厚度和晶粒尺寸的铜箔进行室温单向拉伸试验.试验结果表明:铜箔的抗拉强度和延伸率同时受厚度和晶粒尺寸的影响,这种尺寸效应的描述必须引入无量纲的厚度晶粒尺寸比(T/D)作为比较参数.抗拉强度在不同厚度晶粒尺寸比区间内的变化规律不同;而延伸率在厚度晶粒尺寸比相同时都随厚度的减小而降低.拉伸断口的扫描电镜分析显示箔材的延伸率随着厚度的减小出现的突降和断裂机制的变化有关.     

Development of the Euro fracture toughness dataset

Ten European laboratories have generated the Euro fracture toughness dataset in order to provide an experimental data base sufficiently large to study specimen size and temperature effects on cleavage fracture toughness in the ductile-to-brittle fracture transition regime. The Euro fracture toughness dataset quantifies the fracture behaviour of the quenched and tempered pressure vessel steel DIN 22NiMoCr37. This material is frequently used in nuclear power plants. About 800 fracture toughness tests were performed using compact tension specimens with a size range from 1/2T to 4T.In the lower shelf temperature regime, no significant specimen size effects on cleavage fracture toughness scatter was observed. At higher temperatures, the lower tails of the toughness scatter bands are not significantly effected by the specimen size but with decreasing specimen size the toughness scatter increases due to the fact that the upper part of the scatter band is extended. The presence of a specimen size effect on fracture toughness scatter coincides with the appearance of single cleavage initiation sites at the fracture surface. At the lower shelf temperature both, cleavage initiation sites and size effects are not observed whereas at higher test temperatures both phenomena are present. The specimen size effect trends and the corresponding fracture surface morphology support a weakest-link type cleavage fracture mechanism in the ductile-to-brittle transition regime. A unique correlation between the amount of ductile tearing and cleavage fracture toughness was observed for the steel investigated. This result offers the possibility to determine cleavage fracture toughness from post-test fracture surface examinations.Due to the large number of tests and the wide range of testing conditions, the Euro fracture toughness dataset gives a comprehensive insight into specimen size effects and temperature effects on ductile-to-brittle transition fracture. The Euro fracture toughness dataset includes a large set of raw test data such as load versus load line displacement curves and raw tensile test data for deriving stress-strain curves. The Dataset can be downloaded from the internet via the address ftp://ftp.gkss.de/pub/eurodataset.     

考虑尺度依赖的平面正交各向异性功能梯度微梁的自由振动分析

基于一种新修正偶应力理论建立了微尺度平面正交各向异性功能梯度梁的自由振动模型。模型中包含两个材料尺度参数,能够分别描述两个正交方向上不同程度的尺度效应。当梁的几何尺寸远大于材料尺度参数时,本文模型亦可自动退化为相应的传统宏观模型。基于哈密顿原理推导了运动控制方程并以简支梁的自由振动为例分析了几何尺寸、功能梯度变化指数等对尺度效应产生的影响。算例结果表明:采用本文模型所预测的梁自振频率总是大于传统理论的结果,即捕捉到了尺度效应。尺度效应会随着梁几何尺寸的增大而逐渐减弱并在几何尺寸远大于尺度参数时消失;高阶自振频率所体现出的尺度效应较低阶自振频率更加明显。此外,功能梯度变化指数对尺度效应也有一定的影响。