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仪器分析设计性实验是培养大学生创新能力的重要手段和途径。根据仪器分析实验课的特点,开设“维生素C的3种分光光度法测量比较”设计性实验项目,通过文献调研、原理阐述、方案制定、性能测试、SPSS数据处理分析软件应用等实验环节,培养学生的综合能力和创新能力。分别建立了每种方法的标准曲线,比较相关系数、回收率和相对标准偏差,并对3种方法进行精密度与准确度实验。实践表明,通过设计性实验的实践,学生的实践能力、创新能力、基本科学素养和综合素质得到明显提高。 相似文献
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利用岩石力学试验系统(RMT)对负温下钢纤维混凝土进行了单轴压缩实验,测得了-5℃、-10℃、-15℃、-20℃下钢纤维混凝土的应力-应变曲线、杨氏模量、极限应力、泊松比等。实验结果表明材料的强度、杨氏模量随温度的下降而上升,尤其是当温度由-10℃下降至-15℃时,这些物理量变化特别显著,之后它们将逐渐趋于某一稳定值。本文对钢纤维混凝土力学性能的温度效应进行了分析并对实验结果进行了细观上的讨论。最后针对负温钢纤维混凝土应力-应变曲线的特点,基于塑性力学和损伤力学理论,建立了负温钢纤维混凝土的含损伤本构方程。该方程物理概念清晰,形式简单,具有一定的应用参考价值。 相似文献
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We analyze a field experiment where ambient air is injected into the soil during the summer and extracted again during the winter. A multiphase model accounting for the conductive transport as well as the convective transport with the moving liquid and gas phases is used along with a more simplified single-phase model where the convective transport is due to the gas alone. The latter model also accounts for subzero wintertime temperatures. The multiphase model captures well both the seasonal variations and the actual test sequence, the main calibration being in the adjustment of medium permeabilities based on the observed pressure responses. The effect of the injection pump on the temperature and humidity of the injection air needs to be known accurately. Taking into account the humidity of the injection air explicitly instead of using humidity-corrected enthalpy values also has an effect. The effect of various humidity and specific enthalpy assumptions is of the order of 1–1.5°C, while ignoring the wintertime subzero temperatures has an effect of 1–2°C. These differences are of the same order of magnitude as the heterogeneity-introduced differences in field data. Using the simplified single-phase model typically appears to cause a difference of 1–2°C, but can yield an even higher deviation of the order of 3–4°C. 相似文献
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Residual stress is the stress present in the unloaded equilibrium configuration of a body. Because residual stresses can significantly affect the mechanical behavior of a component, the measurement of these stresses and the prediction of their effect on mechanical behavior are important objectives in many engineering problems. Common methods for the measurement of residual stresses include various destructive experiments in which the body is cut to relieve the residual stress. The resulting strain is measured and used to approximate the original residual stress in the intact body. In order to predict the mechanical behavior of a residually stressed body, a constitutive model is required that includes the influence of the residual stress.In this paper we present a method by which the data obtained from standard destructive experiments can be used to derive constitutive equations that describe the mechanical behavior of elastic residually stressed bodies. The derivation is based on the idea that for each infinitesimal neighborhood in a residually stressed body, there exists a corresponding stress free configuration. We refer to this stress free configuration as the virtual configuration of the infinitesimal neighborhood. The derivation requires that the constitutive equation for the stress free material be known and invertible; it is used to relate the residual stress to the deformation of the virtual configuration into the residually stressed configuration. Although the concept of the virtual configuration is central to the derivation, the geometry of this configuration need not be determined explicitly, and it need not be achievable experimentally, in order to construct the constitutive equation for the residually stressed body.The general mathematical forms of constitutive equations valid for residually stressed elastic materials have been derived previously for a number of cases. These general forms contain numerous unknown material-response functions or material constants that must be determined experimentally. In contrast, the method presented here results in a constitutive equation that is an explicit function of residual stress and includes only the material parameters required to describe the stress free material.After presenting the method for the derivation of constitutive equations, we explore the relationship between destructive experiments and the theory used in the derivation. Specifically, we discuss the use of the theory to improve the design of destructive experiments, and the use of destructive experiments to obtain the data required to construct the constitutive equation for a particular material. 相似文献
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The probability distributions of sand particles' lift-off and incident velocities in a wind-blown sand flux play very important
roles in the simulation of the wind-blown sand movement. In this paper, the vertical and the horizontal speeds of sand particles
located at 1.0 mm above a sand-bed in a wind-blown sand flux are observed with the aid of Phase Doppler Anemometry (PDA) in
a wind tunnel. Based on the experimental data, the probability distributions of not only the vertical lift-off speed but also
the lift-off velocity as well as its horizontal component and the incident velocity as well as its vertical and horizontal
components can be obtained by the equal distance histogram method. It is found, according to the results of the χ2-test for these probability distributions, that the probability density functions (pdf's) of the sand particles' lift-off
and incident velocities as well as their vertical components are described by the Gamma density function with different peak
values and shapes and the downwind incident and lift-off horizontal speeds, respectively, can be described by the lognormal
and the Gamma density functions. These pdf's depend on not only the sand particle diameter but also the wind speed.
The project supported by the National Natural Science Foundation of China (10532040) and the Hundred Talents Project, the
Knowledge Innovation Project of Chinese Academy of Sciences (KZCX2-304). The English text was polished by Keren Wang. 相似文献
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轮胎钢丝帘线拉伸力学性能的实验研究 总被引:2,自引:0,他引:2
对两种结构类型的钢丝帘线在单向拉伸和循环加载下的力学性能进行了实验研究。结果表明:帘线的结构形式对拉伸力学性能(包括摩擦能量损耗)有显著影响。不考虑载荷很小的情况时,普通结构帘线可近似为弹脆性材料,高伸长结构帘线却可以产生较大的塑性变形;循环载荷下,普通结构帘线几乎没有摩擦能量损耗,而高伸长结构帘线不仅有明显的摩擦能量损耗,而且随着循环应力幅值的增加,摩擦能量损耗呈加速增加的趋势;在循环应力幅值较大时高伸长结构帘线还出现了类似于高温下循环硬化金属材料的循环蠕变现象。文章还讨论了高伸长结构帘线由于塑性变形而引起循环蠕变现象的机理。 相似文献