Experimental Evidence for the Existence of the Ti3B4 Phase

Experimental evidence for the formation of Ti₃B₄ with an orthorhombic Ta₃B₄-type structure is presented. This phase forms by a peritectic reaction between TiB₂ and liquid at ∼2200°C and is stable to temperatures at least as low as 1690°C, the lowest temperature at which samples were annealed. No evidence was found to indicate the presence of a second high-temperature form of this phase, as has been reported in the literature.     

Multifunctional design of prismatic cellular materials

Low density, prismatic cellular materials have a combination of properties that make them suitable for multifunctional or multi-physics applications such as ultralight load-bearing combined with energy absorption and heat transfer. In this work, non-uniform, graded cellular materials are designed to achieve superior thermal and structural performance. A general multifunctional design approach is presented that integrates multiobjective decision-making with multi-physics analysis tools of structural and heat transfer performance. Approximate analysis models for heat transfer and elastic stiffness are utilized to analyze designs efficiently. Search/solution algorithms are used to solve multiobjective decisions by interfacing with customized and commercial software. During the design process, cell topology is assumed to be rectangular, but aspect ratios and dimensions of cells and cell walls are varied. Two design scenarios are considered – maximum convective heat transfer and in-plane elastic stiffness in the first case and maximum convective heat transfer and elastic buckling strength in the second case. A portfolio of heat exchanger designs is generated with both periodic and functionally graded cells. Both single- and multi-objective performance are considered, and trade-offs are assessed between thermal and structural performance. Generalization of this approach is discussed for broader materials design applications in which material structures and processing paths are designed to achieve targeted properties and performance characteristics within a larger overall systems design process, and process-structure-property-performance relations are manifested on a hierarchy of length and time scales.     

TALC AS THE PRINCIPAL BODY INGREDIENT IN VITRIFIED CERAMIC BODIES1

This paper is an attempt to explain the firing behavior of pure talc as well as talc-clay, talc-lime, talc-clay lime, and some other high magnesia mixtures. Phase rule equilibrium diagrams are used. The study applies only to those mixtures where talc is present in amounts greater than 50% of the total composition.     

Effects of Microstructure Variability on Intrinsic Fatigue Resistance of Nickel-base Superalloys – A Computational Micromechanics Approach

Understanding the effects of microstructure variability on fatigue resistance is a key to selection and design of materials for fatigue applications. The traditional empirical approach rooted in experiments is being increasingly combined with systematic computational modeling. This work is concerned with demonstrating the feasibility of linking effects of microstructure variability on cyclic plasticity at the scale of intrinsic microstructure of a single crystal nickel-base superalloy. The precipitate and the matrix phases of the alloy are modeled explicitly using a physically based crystal viscoplasticity constitutive framework with appropriate scale and spacing effects to reflect dislocation–precipitate interactions. The model is implemented as a user material subroutine within a finite element code. Various realizations of different microstructures are generated using a constrained Poisson point process. Statistical volume elements (SVEs) with random-periodic boundary conditions are simulated under fully reversed cyclic loading at 650°C. Primary cooling γ′ precipitate size and volume fraction are considered in terms of their effects on the macroscopic stress–strain response and on distributed cyclic microplasticity within the SVE. To compare various microstructures in terms of probability of fatigue crack formation, an appropriate nonlocal measure of cyclic plastic shear strain range is proposed based on percolation of cyclic microplasticity at the scale of the SVE.     

An inductive design exploration method for hierarchical systems design under uncertainty

Model structure uncertainty, originating from assumptions and idealizations in modelling processes, is a form of uncertainty that is often hard to quantify. In this article, the authors propose and demonstrate a method, the inductive design exploration method (IDEM), which facilitates robust design in the presence of model structure uncertainty. The approach in this method is achieving robustness by compromising between the degree of system performance and the degree of reliability based on structure uncertainty associated with system models (i.e. models for performances and constraints). The main strategies in the IDEM include: (i) identifying feasible ranged sets of design space instead of single (or optimized) design solution, considering all types of quantifiable uncertainties and (ii) systematically compromising target achievement with provision for potential uncertainty. The IDEM is successfully demonstrated in a clay-filled polyethylene cantilever beam design example, which is a simple but representative example of integrated materials and product design problems.     

Effect of cyclic overload on the crack growth behavior during hold period at elevated temperature

Effect of tensile overload on elevated temperature crack growth behavior during the subsequent load hold period has been studied by numerical and experimental methods. Finite element analysis of compact specimens shows that when the tensile overload precedes the load hold period, C _t during the hold period is significantly smaller (i.e. retarded) compared to the case without the overload. This is due to crack tip stress relaxation associated with large crack tip plasticity generated by the overload. A modified C _t estimation scheme is proposed by introducing a new equation for t _pl. Using this scheme, the retardation behavior of C _t due to the overload is successfully modeled.Creep-fatigue crack growth data for an ex-service 1.25Cr-0.5Mo steel at 538°C (1000°F) were generated in air. The hold times are 10 seconds, 98 seconds and 10 minutes. Time-dependent crack growth rate during the load hold period, (da/dt)_avg, is correlated with (C _t )_avg estimated by the new estimation scheme. (da/dt)_avg data from all the tests with overload are higher than those from the tests without overload. The peak stress associated with the overload seems to have enhanced void nucleation and to incrase the time-dependent crack growth rate due to creep. This argument is supported by microscopic observations.     

Effect of cyclic overload on the crack growth behavior during hold period at elevated temperature

Effect of tensile overload on elevated temperature crack growth behavior during the subsequent load hold period has been studied by numerical and experimental methods. Finite element analysis of compact specimens shows that when the tensile overload precedes the load hold period,C _t during the hold period is significantly smaller (i.e. retarded) compared to the case without the overload. This is due to crack tip stress relaxation associated with large crack tip plasticity generated by the overload. A modifiedC _t estimation scheme is proposed by introducing a new equation fort _pl. Using this scheme, the retardation behavior ofC _t due to the overload is successfully modeled. Creep-fatigue crack growth data for an ex-service 1.25Cr-0.5Mo steel at 538°C (1000°F) were generated in air. The hold times are 10 seconds, 98 seconds and 10 minutes. Time-dependent crack growth rate during the load hold period, (da/dt)_avg, is correlated with (C _t )_avg estimated by the new estimation scheme. (da/dt)_avg data from all the tests with overload are higher than those from the tests without overload. The peak stress associated with the overload seems to have enhanced void nucleation and to incrase the time-dependent crack growth rate due to creep. This argument is supported by microscopic observations.     

Surface Transfer Impedance Measurements on Subminiature Coaxial Cables

The surface transfer impedances (STI) of several flexible subminiature coaxial cables, such as RG-174/U and RG-188/U, plus smaller coaxial shielded wires, were measured to determine EM shielding characteristics. The results cover the frequency range 0.1-50 MHz and correlate well with previous theoretical models and with experimental values for larger cables, such as RG-58. Copperbraided subminiature cables had STI values 2-5 times larger than those for RG-58     

THE EFFECT OF CALCINED CYANITE IN PORCELAIN BODIES1

A study was made of the physical properties of porcelain bodies containing varying amounts of calcined cyanite (mullite), feldspar, and flint with a constant content of 50% clay. All bodies were made up under uniform conditions and fired to their proper maturing temperatures which varied from cones 8 to 20. Moduli of rupture for correctly fired bars varied from 5100 to 12,100 Ibs. per square inch, those bodies high in mullite being the strongest. The coefficients of linear expansion between 30 and 844° C varied from 4.3 × 10⁻⁶ to 6.6 × 10 ×⁻⁸ 6, those bodies high in mullite having the lower expansion. Thirty per cent or more calcined cyanite (50% or more total mullite as figured from chemical composition) must be present to obtain a marked effect on either of these properties. Triaxial diagrams show the position of various typical porcelain bodies and how they might be affected by additions of this material.     

循环荷载下柔性路面路基变形的动力耦合分析(英文)

首先简要综述了循环荷载下路基变形的研究现状。然后 ,基于饱和土体的动力耦合分析理论 ,研究了平面应变条件下的柔性路面路基变形的数值分析模型和方法 ,并建立了一个简单的粘弹性动力计算模型来预测路基在循环荷载下的动力反应。该模型可以全面考虑路基材料的剪切模量、阻尼比、孔隙水压力以及永久变形。最后 ,以一个柔性路面为例 ,应用本文方法在循环荷载下的路基变形发展进行了分析。