应用纳米压痕技术研究表面纳米化后316L不锈钢力学性能

316L不锈钢经表面纳米化(SNC)处理后,表面形成一层纳米层。样品表面晶粒细化至纳米级大约12nm左右,随着深度的增加,晶粒尺寸逐渐增大。该文应用纳米压痕技术分析了纳米层力学性能,结果表明:纳米层的纳米硬度和弹性模量分别为6.05GPa和227GPa,是基体硬度和弹性模量的1.4倍和1.2倍。随距表面距离的增加而降低,并逐步趋近于一个稳定值。同时测得纳米层的应变硬化指数为0.44为基体的1.5倍。     

Deformation of a submicrocrystalline VT1-0 titanium alloy under static loading

Comparative deformation analysis of a VT1-0 alloy in the as-cast and submicrocrystalline states under static loading was performed. The latter was obtained by intense plastic straining through twist extrusion. It was established that the submicrocrystalline alloy exhibited higher elasticity and static strength. After plastic straining, the elastic modulus decreases, while the hardening coefficient increases.     

Effects of fiber orientation and anisotropy on tensile strength and elastic modulus of short fiber reinforced polymer composites

An experimental study was conducted to investigate anisotropy effects on tensile properties of two short glass fiber reinforced thermoplastics. Tensile tests were performed in various mold flow directions and with two thicknesses. A shell–core morphology resulting from orientation distribution of fibers influenced the degree of anisotropy. Tensile strength and elastic modulus nonlinearly decreased with specimen angle and Tsai–Hill criterion was found to correlate variation of these properties with the fiber orientation. Variation of tensile toughness with fiber orientation and strain rate was evaluated and mechanisms of failure were identified based on fracture surface microscopic analysis and crack propagation paths. Fiber length, diameter, and orientation distribution mathematical models were also used along with analytical approaches to predict tensile strength and elastic modulus form tensile properties of constituent materials. Laminate analogy and modified Tsai–Hill criteria provided satisfactory predictions of elastic modulus and tensile strength, respectively.     

Nanorheological analysis of the sphere plane contact problem with interfacial films

The contact between an elastic sphere and plane separated by an elastic interfacial thin layer is analysed under pure squeeze action. This analysis is an important step in the investigation of more realistic problem such as viscoelastic and heterogeneous squeeze problem encountered in surface force experiments. The problem is shown to be governed by two dimensionless parameters coupling the material properties of the layer (shear and bulk modulus) and the substrate (reduced young modulus) with the thinness ratio of the sphere plane distance to the sphere radius. Different regimes are obtained and described according to the value of these two parameters.     

Effective mechanical properties of layered rough surfaces

In contact mechanics of layered rough surfaces, found in various systems such as magnetic storage devices and micro/nanoelectromechanical systems, it is of interest to calculate effective elastic modulus and hardness so as to obtain contact parameters using simple analyses for homogeneous surfaces. In this study, effective elastic modulus and hardness of layered rough surfaces are defined on the basis of real area of contact. A numerical model developed by the first author to simulate the contact of layered rough surfaces is used to derive these equations. Completely nondimensionalized empirical equations for these effective mechanical properties are presented. Separate equations are developed for the contact of a single conical asperity on a flat surface, a single spherical asperity on a flat surface, and for multiple asperity contact between two rough surfaces. These equations establish the dependence of effective mechanical properties on indentation depth, layer thickness, hardness and elastic modulus ratios of layer and substrate and surface roughness/asperity geometry. Comparisons of values predicted by the equations with experimentally obtained results are presented. Contact stress contours obtained from this model are analyzed to get a better understanding of the mechanics of contact.     

The influence of the lateral filament texture on the compressive properties of PpPTA aramid filaments

A series of PpPTA aramid fibres with various degree of lateral orientation ranging from their usual radial-oriented lateral texture to a full random lateral texture were prepared by employing a series of different coagulating media in the fibre spinning process. The resulting variation in lateral texture did not lead to differences in linear tensile properties or crystallite dimensions. Raman spectroscopy measurements on embedded axially compressed filaments showed that the stresses for kink band initiation and propagation were independent of the degree of lateral texture. The kink band morphology and the final kink band density upon further straining were found to correlate with the shear modulus derived from combined mechanical and XRD data.     

新型分层模型求解非均匀土层轴对称问题

该文通过应用一种新的分层模型求解了剪切模量任意变化的非均匀土层受轴对称荷载时的表面位移沉降。根据任意曲线都可以用一系列连续的直线段来逼近,非均匀土层被分为若干个子层,在每个子层中,假设剪切模量沿厚度方向按线性变化,在子层的界面上剪切模量连续并且等于实际值。应用Hankel积分变换和传递矩阵方法,求解了剪切模量按照不同函数形式变化的表面沉降。     

The investigation of internal friction and elastic modulus in surface nanostructured materials

In this paper, 304 stainless steel and pure Fe specimens, which were processed by high-energy shot peening (HESP) and ultrasonic shot peening (USP) respectively, were studied by the internal friction method. Measurements were carried out on a vibrating reed apparatus. The change of internal friction and elastic modulus shows that the treatment duration of specimen is not accompanied by the corresponding persistent increase of internal friction and elastic modulus. There is a transition layer from the top surface to the inside of the materials. Young’s modulus of surface shows obviously a fluctuation along the depth profile. The phenomena have never been shown by other measurement methods. The microstructure change should be related to some basic mechanism of surface layer formation. It may also explain why the improvement of mechanical properties in surface nanocrystallized materials does not simply correspond to the duration time of severe deformation.     

弹性参数任意变化的非均匀土层的二维受力分析

该文利用线性分层模型模拟弹性参数按任意函数形式变化的非均匀土层,首先求解了覆有非均匀土层的半平面表面受集中线荷载的二维问题,然后以此为基本解,利用奇异积分方程技术求解了表面受刚性体作用的接触问题,计算了给定荷载下的接触表面力和沉降,讨论了弹性模量和泊松比的变化梯度对结果的影响。     

Mixture optimization of cement treated demolition waste with recycled masonry and concrete

Due to environmental reasons and the shortage of natural resources, it is greatly valuable to recycle construction and demolition waste (CDW) as much as possible. One of effective ways to reuse more CDW is to produce a cemented road base material. The recycled CDW however is a mix of recycled masonry and concrete with a wide variation in composition. This implies that the mechanical properties of cement treated demolition waste are not only determined by cement content and degree of compaction, but also by the ratio of crushed masonry content to crushed concrete content. In order to optimize its mixture proportioning, this paper explores the response surface and contour plot of the combined effect of mixture variables on the mechanical properties including the unconfined compressive strength (UCS), the elastic modulus (E) and their ratio. It has been recognized that optimizing the mixture proportioning of cement treated demolition waste should not only consider its material properties, but also needs to take into account its structural behavior as a pavement layer. Analytical results indicate that increasing the degree of compaction is an economic technique to obtain the required strength, but it is not an efficient method to enhance the admissible elastic strain (the ratio of UCS to E) and to improve the flexural rigidity of the road base layer. Obtaining a desired low flexural rigidity certainly needs adjusting of the masonry content and the cement content.     

原位自生Ti3 Al金属间化合物基复合材料的微观结构

采用原位自生（XD）法制备Ti3Al金属间化合物基复合材料,对复合材料的XRD,OM和SEM的分析结果表明,Ti-17Al-0.5C复合材料的基体为Ti3Al,增强相为Ti3AlC,且增强相在基体中按一定的方位排列,Ti-17Al-1.5(2.0)C复合材料的基体为Ti3Al,增强相由心部TiC矣包覆层Ti3AlC双层组成,随着含C量的增加,增强相由不发达的树脂晶变为等轴晶,对合金进行微力学探针测试表明,增强相TiC和Ti3AlC的显微硬度和弹性模量均大于基体Ti3Al,随着C含量的增加,合金中增强相和基体的显微硬度和弹性模量无明显变化。     

Werkstoffverhalten unter zügiger elastischer Beanspruchung

Material properties by continuous elastic straining Within the scope of a common research project of the steel and automotive industry, 20 sheet steels have been investigated to obtain input data for FE‐analysis. In detail, characteristical elastic, plastic and fatique values were determined by several testing institutes for a period of 3 years. Knowledge of dependency of Young’s modulus from temperature and orientation is important for spring back at the press shop and stiffness of parts for automotive. Young’s modulus was determined by tensile tests in delivered state, after prestraining, heat treatment at room temperature and –40 °C and 100 °C. Young’s modulus is dependent from the orientation to rolling direction and can be classified in groups. Young’s modulus of ferritic steels is decreased about 10 % by prestraining of 2 % but recovered after annealing at 170 °C. Temperature dependency well known from non destructive tests are confirmed.     

位于弹性半空间上的理想流体层动力反应—平面P波入射

根据弹性介质与理想流体交界面的边界条件以及理想流体层自由表面的边界条件,基于位移势函数,推导了平面P波从弹性半空间入射到与理想流体层的交界面时,确定交界面波的透射与反射系数的理论方程。根据该方程,通过数值算例,分析了弹性半空间的弹性模量和密度、平面P波的入射角以及入射频率对理想流体层动压力的影响。     

Stochastic FEM sensitivity analysis of nonlinear dynamic problems

This paper deals with the stochastic finite element analysis of nonlinear structural dynamic problems, consisting of a linearly elastic square plate lying on a nonlinear foundation and loaded with a deterministic uniform transverse dynamic load. The plate can be either simply-supported or fixed-all-around. The stochasticity of the problem arises from the spatial randomness of the elastic modulus of the plate and/or from the spatial randomness of a coefficient controlling the degree of nonlinearity of the foundation. Monte Carlo simulation techniques along with a finite element formulation of the problem are used in order to analyze the system. It is concluded that the maximum deflection at the center of the square plate fits to the lognormal distribution. Various conclusions are also drawn on the influence of the stochasticity of the elastic modulus and/or the stochasticity of the nonlinear foundation and the degree of nonlinearity of the foundation on the value of the coefficient of variation of the maximum deflection at the center of the plate.     

Optimum design method for double-layer thick-walled concrete cylinder with different modulus

The stress state of thick-walled cylinder will be improved when it is composed of multi-layer concrete with different Young’s modulus of elasticity. The optimum design method for double-layer concrete cylinders is discussed in this paper. When the modulus of the inner-layer concrete is less than the outer one, the stress concentration on the cylinder inner surface will be relieved and the maximum tangential stress may be transferred from the inner surface of inner-layer to the inner surface of outer-layer, where is in triaxial stress state. The elastic limit bearing capacity of double-layer concrete cylinder will be improved due to the high compressive strength of concrete in triaxial stress state. Compared with the conditional single-layer thick-walled cylinder, the thickness of the double-layer cylinder can be reduced evidently. On the basis of stress solution of double-layer cylinder and by using the mixed penalty function method, the minimum wall thickness required, the best thickness ratio and the modulus ratio of inner layer to outer layer are calculated for cases in which the external load and uniaxial compressive strength are known already. If the thickness and uniaxial compressive strength is given, the best thickness ratio and modulus ratio of inner layer to outer layer can also be proposed by using the mixed penalty function method.     

Strain mechanisms in grey cast iron

Grey cast iron exhibits a continuous stress-strain curve on which elastic and plastic strains cannot be identified. Tensile straining is analysed here in the case of a grey cast iron solidified by continuous casting. It is demonstrated that the main damaging processes are directly related to strain components which can be macroscopically identified. The amount of microcracking is evaluated by the decrease in elastic stiffness. On complete unloading, a small increase in the elastic stiffness is recorded; however, the initial value is not recovered. Deformation due to localized plastic strains is evaluated by recording the tangent modulus. For stresses inducing negligible creep strains the tangent modulus decreases linearly for increased applied stress. Under low stress amplitude, however, an elastic range is clearly observed. Both mentioned strain mechanisms are fully responsible for the non linear behaviour of the material. Furthermore, it is demonstrated that as a consequence of these strain mechanisms, the stress-strain curve of a prestrained grey cast iron is directly related to the initial stress-strain curve of the same material.     

Characterization of microstructural damage during plastic strain of a particulate-reinforced metal matrix composite at elevated temperature

The evolution of damage in a SiC-reinforced 2618 AI alloy during plastic strain has been investigated by elastic modulus reduction and direct observations of the microstructure at room temperature and temperatures up to 220 °C. Particle fracture increases as a function of strain at all temperatures but the total number of fractured particles at any given strain is lower at higher test temperatures. The dependence of fracture on particle size and aspect ratio was recorded. Normalized elastic modulus measurements decrease as a function of strain at the same rate for tests at 25,110 and 220 °C with an anomalous set of measurements at 165 °C showing a reduced damage rate. There is no universal correlation between the number of damaged particles and reduced modulus with each test temperature showing a different relation. This indicates the different temperature dependence of void nucleation and subsequent growth. The results are used to interpret different models of load sharing between reinforcement and matrix during straining.[/p]     

An analytical approach for fracture and fatigue in functionally graded materials

The problem of brittle crack propagation and fatigue crack growth in functionally graded materials (FGMs) is addressed. The proposed analytical approach can be used to estimate the variation of the stress-intensity factor as a function of the crack length in FGMs. Furthermore, according to the Paris’ law, the fatigue life and the crack-tip velocity of crack propagation can be predicted in the case of fatigue crack growth. A comparison with numerical results obtained according to the Finite Element method will show the effectiveness of the proposed approach. Detailed examples are provided in the case of three-point bending beam problems with either a FGM interlayer, or a FGM external coating. A comparison is presented between two types of grading in the elastic modulus: a continuous linear variation in the FGM layer and a discrete approximation with a multi-layered beam and a constant Young’s modulus in each layer.     

Refinement of parameters of the model for nonlocalized damage accumulation to describe deformation of the steel 20

We present a method for refining the parameters of the model for nonlocalized damage accumulation in the steel 20 under static deformation, which are determined by variation in elastic modulus and degree of homogeneity of the material, that corresponds to the scatter of hardness characteristics during mass measurements at different stages of repeated static loading.     

Mapping the elastic properties of granular Au films by contact resonance atomic force microscopy

Endowed with nanoscale spatial resolution, contact resonance atomic force microscopy (CR-AFM) provides extremely localized elastic property measurements. We advance here the applicability of CR-AFM on surfaces with nanosize features by considering the topography contribution to the CR-AFM signal. On nanosize granular Au films, the elastic modulus at the grain scale has been mapped out by considering a self-consistent deconvolution of the contact geometry effect in the CR-AFM image. Significant variation in the contact area over granular topography arises as the probe is either in single-?or multiple-asperity contact with the surface. Consequently, in extracting the elastic modulus from CR-AFM measurements on granular surfaces we considered both the normal and lateral couplings established through multiple-asperity contacts between the tip and the surface. Thus, by appropriately considering the change in the contact mechanics during CR-AFM imaging, variations in the elastic modulus have been revealed in the intergrain regions as well as across individual grains.