A micromechanical method for predicting the precipitation hardening response of particle strengthened alloys hardened by ordered precipitates

Summary A micromechanical method was developed for predicting the precipitation hardening response of particle strengthened alloys hardened by ordered precipitates based on the microstructure, composition, and heat treatment, and utilizing a minimum number of experimental tests to evaluate the microstructural constants of the overall model. The overall approach was based on incorporating the dislocation particle interaction mechanics, particle growth and coarsening theory, thermodynamics, and particle strengthening mechanisms applicable to precipitation hardened alloys as part of the overall micromechanical method. The method/model evaluates, from a minimum number of experimental tensile tests, microstructural constants necessary in determining the precipitation srengthening response of a particle strengthened alloy. The materials that were used as vehicles to demonstrate and evaluate the model were precipitation hardenable aluminium-lithium-zirconium and nickel-aluminum alloys. Utilizing these demonstration alloys, the method used a total of four tensile tests to evaluate the necessary microstructural constants and thus predict the variation in strength as a function of aging time, aging temperature, and composition, for the underaged, the peak-aged, and the overaged conditions. Predictions of the precipitation strengthening response were made incorporating the Wagner particle distribution model to evaluate the size distributions of particles in the microstructures. The predicted variation of strength with aging practice and composition using the Wagner distribution model compared well with the corresponding experimental yield strength results.Notation b Burgers vector - average particle size diameter for a particle distribution - d _loop particle looping diameter for dislocation bypassing by Orowan looping - f _v volume fraction of precipitates - h() Wagner particle size distribution function - n _total total number of precipitate particles per unit area on a given microstructural plane - average particle size radius for a particle distribution - average planar particle size radius on a given microstructural plane - t aging time, in hours - average planar particle cross sectional area - G _t total shear modulus of the material - K _c particle growth rate constant - texture or Taylor grain orientation factor - N _v total number of precipitate particles per unit volume - Q _A activation energy for diffusion - R universal gas constant - T aging temperature - the interparticle separation or spacing - _y yield strength - _q as-quenched strength - _i intrinsic lattice strength - _c critical resolved shear strength - _loop critical resolved shear strength for dislocation particle bypassing via. Orowan looping - _particle total critical resolved shear strength for particle strengthening - _shear critical resolved shear strength for dislocation particle shearing, in underaged state     

A semi-empirical correlation for predicting the frost density on hydrophilic and hydrophobic substrates

A new semi-empirical correlation for the prediction of frost density on hydrophilic and hydrophobic surfaces is proposed. The proposed correlation is a function of the modified Jakob number and contains two correction terms, one for surface contact angle and another for relative humidity. Whereas most frost correlations exclude surface wettability as a parameter, our research has shown that the surface contact angle can be important when trying to accurately predict the properties of a growing frost layer. The correlation was developed using data from three different surfaces. On each surface, the frost was grown for three hours and then defrosted. The proposed correlation predicted more than 93% of the data to within a ±20% error band and is proposed for use on surfaces with contact angles 45° < θ < 160°, relative humidity 0.40 < ϕ < 0.80, and plate temperatures −13 °C < T_w < −5 °C under natural convection conditions.     

A numerical method for treating indentation problems

Summary Abel transforms are used to simplify the equations describing the deformation of an elastic medium by a rigid indentor with a circular cross-section. The equations derived constitute a convenient starting point for the numerical solution of such problems. As a particular example the case of a parabolic rough punch is treated.     

A semi-empirical correlation for the frost density

A first-principles model for predicting the evolution of the porosity of a frost layer over time was advanced. The theoretical model was used together with experimental data obtained elsewhere to put forward a semi-empirical correlation for the frost density as a function of the time, and the modified Jakob number, which carries information about the thermodynamic conditions of the air stream and the chilled surface. When compared to experimental data, the proposed correlation showed errors within ±10% bounds. Comparisons with other frost density correlations available in the open literature are also reported.     

一种基于极大团的蛋白质相互作用预测方法

针对大规模、高通量方法识别出的蛋白质相互作用数据集包含噪声较高的问题,根据蛋白质相互作用网络中噪声数据的特点和网络拓扑属性,提出了一种基于极大团的相互作用预测方法以提高识别出的这种数据集的可靠性.该方法通过蛋白质与蛋白质团之间的关联程度来预测蛋白质间是否存在相互作用,同时结合噪声数据在网络中的特点将预测结果放大并将伪相互作用分离出来,最后可获得可靠性较高的预测数据集.实验结果显示,所提出的方法不仅可以预测更多相互作用而且具有更高的可靠性.     

A method for predicting crack growth in nonhomogeneous viscoelastic media

Equations are developed for predicting crack growth in the opening mode for quite general situations, including many quasi-static and dynamic problems involving moisture and temperature gradients in monolithic and composite materials. Except for the small zone of failing material at the crack tip, the body is assumed to be linearly viscoelastic. A method for obtaining viscoelastic stresses and displacements from elastic solutions is first described. The traction boundary condition for the crack faces is not in general satisfied by these results. However, it is shown by modifying the failure zone in the elastic problem this condition can be met, and an integral equation for the stress in the modified failure zone is derived. Approximate analysis similar to that used previously by the author in stress analysis is then employed to solve the integral equation and develop relatively simple equations for predicting crack speed; these equations relate crack speed in the viscoelastic material to stress intensity factors in a suitably defined elastic body.

---

Résumé Des équations ont été développées pour prédire la croissance de la fissure suivant un mode d'ouverture pour des situations tout à fait générales incluant plusieurs problèmes quasi-statiques et dynamiques comportant de l'humidité et des gradients de tempèrature dans des matériaux monolitiques et dans des matériaux composites. A l'exception de la petite zône de matière située à la pointe de la fissure, le corps est supposé être linéairement visco-élastique. Une méthode pour obtenir les contraintes et les déplacements visco-élastiques à partir des équations élastiques est en premier lieu décrite. La condition de frontière à la traction pour les faces de la fissure n'est en général pas satisfaite par ces résultats. Toutefois, on montre qu'en modifiant la zône de rupture dans le problème élastique, cette condition peut être atteinte et une équation intégrale pour la contrainte dans la zône de rupture modifiée est dérivée. Une analyse approximative similaire à celle utilisée précédemment par l'auteur dans l'analyse des tensions est ensuite utilisée pour résoudre l'équation intégrale et développer des équations relativement simples pour prédire la vitesse de fissuration. Ces équations mettent en relation la vitesse de fissuration dans le matériau visco-élastique aux facteurs d'intensité des contraintes dans uns corps élastique défini de manière appropriée.

---

---

Sponsored by the Air Force Office of Scientific Research, Office of Aerospace Research, grant No. 74-2697. Presented at the Environmental Degradation of Engineering Materials conference, October 10–12, 1977. Virginia Polytechnic Institute, Blacksburg, Va.     

A nonstationary method for measuring heat fluxes

A nonstationary method for measuring heat fluxes using a hollow cylindrical probe placed in the critical cross section of a nozzle is proposed. The temperature at a fixed distance from the inner surface of the probe is measured as a function of time. The time variation of the heat flux is determined by solving the one-dimensional nonlinear heat-conduction equation.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 29, No. 1, pp. 51–55, July, 1975.     

A semi-theoretical model for predicting refrigerant/lubricant mixture pool boiling heat transfer

This paper outlines the framework of a semi-theoretical model for predicting the pool boiling heat transfer of refrigerant/lubricant mixtures on a roughened, horizontal, flat pool-boiling surface. The predictive model is based on the mechanisms involved in the formation of the lubricant excess layer that exists on the heat transfer surface. The lubricant accumulates on the surface in excess of the bulk concentration via preferential evaporation of the refrigerant from the bulk refrigerant/lubricant mixture. As a result, excess lubricant resides in a thin layer on the surface and influences the boiling performance, giving either an enhancement or degradation in heat transfer. A dimensionless excess layer parameter and a thermal boundary layer constant were derived and fitted to data in an attempt to generalize the model to other refrigerant/lubricant mixtures. The model inputs include transport and thermodynamic refrigerant properties and the lubricant composition, viscosity, and critical solution temperature with the refrigerant. The model predicts the boiling heat transfer coefficient of three different mixtures of R123 and lubricant to within ±10%. Comparisons of heat transfer predictions to measurements for 13 different refrigerant/lubricant mixtures were made, including two different refrigerants and three different lubricants.     

A meshless method for conjugate heat transfer problems

Mesh reduction methods such as boundary element methods, method of fundamental solutions, and spectral methods all lead to fully populated matrices. This poses serious challenges for large-scale three-dimensional problems due to storage requirements and iterative solution of a large set of non-symmetric equations. Researchers have developed several approaches to address this issue including the class of fast-multipole techniques, use of wavelet transforms, and matrix decomposition. In this paper, we develop a domain decomposition, or the artificial sub-sectioning technique, along with a region-by-region iteration algorithm particularly tailored for parallel computation to address the coefficient matrix issue. The meshless method we employ is based on expansions using radial-basis functions (RBFs).An efficient physically based procedure provides an effective initial guess of the temperatures along the sub-domain interfaces. The iteration process converges very efficiently, offers substantial savings in memory, and features superior computational efficiency. The meshless iterative domain decomposition technique is ideally suited for parallel computation. We discuss its implementation under MPI standards on a small Windows XP PC cluster. Numerical results reveal the domain decomposition meshless methods produce accurate temperature predictions while requiring a much-reduced effort in problem preparation in comparison to other traditional numerical methods.     

A study of the heat capacity of coated metal materials by the laser flash method

Results of laser-flash measurements of the specific heat capacity of samples of metallic materials (12Kh18N9T stainless steel, VZhM-4 nickel superalloy) coated with heat-resistant silicate enamel in a temperature range of 20–1300°C are described. In this temperature range, the coating is characterized by a high emissivity factor with a constant magnitude of 0.9. Analysis of the measurement results for the specific heat capacity of the steel samples and comparison of these results with the reference data and the most reliable literature data reveal that a decrease in the apparent specific heat capacity in a temperature range of 850–1100°C is attributed to an exothermic heat effect. The deviation of the measurement results from the reference data is no more than 3%. New data on the heat capacity of the VZhM-4 nickel alloy are derived. The temperature dependences of the apparent (with allowance for the heat effect of dissolution of the γ' phase) and true specific heat capacities are described. The discrepancy between the calculated and measured values does not exceed 2%.     

A study of the CEN test method for measurement of the carbonation depth of hardened concrete

This paper reports on the effect of an enhanced test method for the recently drafted CEN method for measuring the depth of carbonation of hardened concrete which was aimed at reducing the known variability of the test. Variations in environmental factors that may have led to a poor precision have been identified, for example the assumption that natural ventilation will provide the required level of carbon dioxide and relative humidity has been shown to be incorrect. This lead to the development of an environmental control system the actively controls the storage atmosphere. In addition to this, a two stage normalisation process of test data is proposed comprising the use of two additional mixes along with the mix being tested. Results from the assessment of the repeatability of a limited series of 10 mixes carried out by one operator of a 37 N/mm² PC/30% PFA concrete mix indicated that a significant improvement could be achieved following this type of control and normalisation.     

一种预测反应性树脂体系黏度随时间变化关系的新方法

为了预测在固化度、温度和固化放热共同作用下, 树脂体系的黏度随时间的变化, 提出了一种确定反应性树脂体系黏度随时间变化关系的新方法。该方法从等温黏度-时间曲线和固化度-时间曲线出发, 分别得到黏度-固化度关系和黏度-温度关系, 从而将影响反应性流体黏度变化的两个主要因素温度和固化程度分离开来。基于反应性树脂体系的局部绝热假设, 将反应性树脂体系的固化放热引入到黏度变化关系中, 得到反应性树脂体系黏度在固化度、温度和固化放热共同作用下的黏度-时间关系。黏度预测值与用旋转黏度计测量值的黏度变化趋势具有高度的一致性, 可以应用此方法实现对实际环境中考虑固化反应热效应的反应性树脂体系黏度的预测。      

A simple method for predicting the chloride diffusivity of cement paste

A simple method for predicting the chloride diffusivity of cement paste is presented. In this method, cement paste is modeled as a two-phase composite material, consisting of solid matrix and pore space. By incorporating the classical percolation theory into the effective medium approach, an explicit solution is formulated for the chloride diffusivity of cement paste. Two parameters involved in the solution are determined by fitting the solution to experimental data. After the validity of the simple method is verified with experimental results obtained from the literature, the effects of the water/cement ratio and the degree of hydration on the chloride diffusivity of cement paste are evaluated in a quantitative manner. The paper concludes that the proposed simple method can predict the chloride diffusivity of cement paste with reasonable accuracy.     

A hybrid regularization method for inverse heat conduction problems

This paper presents a hybrid regularization method for solving inverse heat conduction problems. The method uses future temperatures and past fluxes to reduce the sensitivity to temperature noise. A straightforward comparison technique is suggested to find the optimal number of the future temperatures. Also, an eigenvalue reduction technique is used to further improve the accuracy of the inverse solution. The method provides a physical insight into the inverse problems under study. The insight indicates that the inverse algorithm is a general purpose algorithm and applicable to various numerical methods (although our development was based on FEM), and that the inverse solutions can be obtained by directly extending Stolz's equation in the least‐squares error (LSE) sense. Direct extension of the present method to the inverse internal heat generation problems is made. Four numerical examples are given to validate the method. The effects of the future temperatures, the past fluxes, the eigenvalue reduction, the varying number of future temperatures and local iterations for non‐linear problems are studied. Copyright © 2005 John Wiley & Sons, Ltd.     

A proposed method of predicting ship collision damage

In the past, research on ship collision strength has centered on nuclear ship structures, but now emphasis is shifting to low-energy collisions of ordinary ships carrying hazardous cargoes including crude oil.A ship collision is too complex to study using theoretical methods alone, yet tests with small-scale models of thin steel plate fail to duplicate actual ship collision damage for the following reasons:

1. (1) The fracture of actual ship shell plate and model shell plate defies the law of similarity;

2. (2) Some structural members are usually omitted for ease of fabrication in relatively small models.

Accordingly, the authors propose a method for predicting ship collision damage that resorts to three combined experiments:

1. (1) A fundamental test determining the initiation of plate fracture;

2. (2) A local structure model test evaluating the effects of structural details;

3. (3) A structural model test investigating the deformation of a ship hull.

This paper reviews, by way of example, some results of the experimental studies which the authors have performed.The laws of similarity proved very important in the study of plate fracture.The authors believe that the proposed method will prove useful especially in dealing with low-energy ship collisions.