Plane Stress Steady Crack Growth in a Power-Law Hardening Material

The paper reports the results from an asymptotic analysis for a crack growing quasistatically under Mode I, plane stress conditions for a power-law hardening material. The asymptotic stress and deformation velocity fields near the growing crack tip are determined, comparisons to related work are discussed and some numerical results for aluminum are included. This revised version was published online in August 2006 with corrections to the Cover Date.     

Improved fatigue crack growth resistance by retrogression and re‐aging heat treatment in 7010 aluminum alloy

Aircraft grade 7010 aluminum alloy was heat treated to two different conditions: (1) standard peak aging (T6) and (2) retrogression and re‐aging (RRA). The microstructures of these alloys were characterized by using transmission electron microscope. Fatigue crack growth rate (FCGR) tests were conducted using standard compact tension specimens, following ASTM standards. Tests were conducted at various stress ratios, R ranging from 0.1 to 0.7. The RRA‐treated alloy was observed to contain coarsened η′ (MgZn₂) precipitates with higher inter‐particle spacing when compared with T6‐treated alloy. The grain boundary precipitates (GBPs) were also coarsened and discontinuous in RRA‐treated alloy as compared with continuous GBPs in T6 condition. The FCGR was lower and ΔK_th was higher in RRA‐treated alloy compared with T6‐treated alloy at all the stress ratios investigated. Improved fatigue crack growth resistance in RRA‐treated alloy was correlated to the modified microstructure and enhanced crack closure levels.     

Research,development and growth in state-owned enterprises: empirical evidence from Ecuador

ABSTRACT

Investment in R&D is essential for the survival and growth of organizations. Recent literature has focused on the study of effects of R&D on the growth of private companies. However, there is no research studying the effects of R&D on the growth of Latin American public companies. This paper estimates, using an endogenous growth model, the effect of investments in R&D on sales growth in public enterprises of Ecuador. Data corresponding to a sample of 86 public companies have been taken from the Survey of Activities of Science and Technology (ACTI) of Ecuador for the period 2012 to 2014. These data are estimated by OLS. The results show that there is a statistically significant positive relation between investment in research and development and the growth of sales in public companies.     

Key Aspects of Lithium Metal Anodes for Lithium Metal Batteries

Rechargeable batteries are considered promising replacements for environmentally hazardous fossil fuel‐based energy technologies. High‐energy lithium‐metal batteries have received tremendous attention for use in portable electronic devices and electric vehicles. However, the low Coulombic efficiency, short life cycle, huge volume expansion, uncontrolled dendrite growth, and endless interfacial reactions of the metallic lithium anode are major obstacles in their commercialization. Extensive research efforts have been devoted to address these issues and significant progress has been made by tuning electrolyte chemistry, designing electrode frameworks, discovering nanotechnology‐based solutions, etc. This Review aims to provide a conceptual understanding of the current issues involved in using a lithium metal anode and to unveil its electrochemistry. The most recent advancements in lithium metal battery technology are outlined and suggestions for future research to develop a safe and stable lithium anode are presented.     

Measurement of Local Si‐Nanowire Growth Kinetics Using In situ Transmission Electron Microscopy of Heated Cantilevers

A technique to study nanowire growth processes on locally heated microcantilevers in situ in a transmission electron microscope has been developed. The in situ observations allow the characterization of the nucleation process of silicon wires, as well as the measurement of growth rates of individual nanowires and the ability to observe the formation of nanowire bridges between separate cantilevers to form a complete nanowire device. How well the nanowires can be nucleated controllably on typical cantilever sidewalls is examined, and the measurements of nanowire growth rates are used to calibrate the cantilever‐heater parameters used in finite‐element models of cantilever heating profiles, useful for optimization of the design of devices requiring local growth.     

Crystal growth and characterization of CuI single crystals by solvent evaporation technique

Cuprous iodide (CuI) crystals are grown by slow evaporation technique in three different solvents. Large CuI single crystals with dimensions of 7.5 mm × 5 mm × 3 mm are obtained in pure acetonitrile solvent at 40 °C. The as-grown crystals are analyzed by X-ray diffraction, energy-dispersive X-ray analysis, differential scanning calorimetry, current-voltage characteristic and photoluminescence spectrum. The results show that the CuI crystal has the zinc-blende structure with no secondary phase. The elemental Cu/I ratio is 1.09:1. The melting point of the crystal is 875 K and two phase transitions occur from room temperature to its melting point. The electrical conductivity of CuI platelet crystal is in the range of 1.11-2.38 Ω⁻¹ cm⁻¹. Under ultraviolet excitation, the CuI crystals exhibit three emission bands with peak positions at 426, 529 and 671 nm. The nature of the luminescence is discussed.     

Microhardness studies on calcium hydrogen phosphate (brushite) crystals

Vicker's and Knoop microhardness studies were carried out on grown calcium hydrogen phosphate dihydrate (CaHPO₄·2H₂O) crystals over a load range of 10-50 g. The Vickers (H_V) and Knoop (H_K) microhardness numbers for the above loads were found to be in the range of 94-170 kg/mm² and 28-35 kg/mm² respectively. It was also found that these numbers increased with increase in load. The Mayer's index (n) was found to be greater than 1.6 showing soft-material characteristics. The fracture toughness values (K_c), determined from measurements of crack length, were estimated to be 6 ± 0.5 × 10³ kg m^−3/2 and 4.5 ± 0.5 × 10³ kg m^−3/2 at 25 g and 50 g respectively. The brittleness indices (B_i) were found as 2.3 ± 0.1 × 10⁴ m^−1/2 for 25 g and 3.7 ± 0.1 × 10⁴ m^−1/2 for 50 g. Using Wooster's empirical relation, the elastic stiffness coefficient (c₁₁) has been calculated from Vicker's hardness values as 4.8 ± 0.5 × 10¹⁵ Pa for 10 g, 9.7 ± 0.5 × 10¹⁵ Pa for 25 g and 13.3 ± 0.5 × 10¹⁵ Pa for 50 g. The Young's modulus was calculated as 1.5 ± 0.1 × 10¹⁰ N m⁻² from Knoop microhardness values.     

An angular distribution function for the sputter-depositing atoms and general equations describing the initial thickness profile of a thin film deposited inside a via and trench by sputtering

We developed an angular distribution function that describes the distribution of directional sputter-depositing atoms: g(θ) = (k sin²θ + k⁻¹cos²θ)⁻², where k is a directionality factor that determines the directionality of depositing atoms and θ is the incident angle of a depositing atom. The thickness profiles of the sputtered films deposited inside a vertical trench were simulated using the ballistic transport reaction model in conjunction with the angular distribution function, g(θ). The simulated thickness profile agreed well with the experimentally measured thickness profile. General equations that describe the thickness profile of sputter-deposited films inside vias and trenches were derived. The initial film thickness profile could be predicted by substituting the directionality factor, k, and the geometric parameters of the via or trench in the general equations. An optimum directionality factor, defined as the directionality factor that maximizes the sidewall coverage of a vertical pattern, was obtained by solving the general equations. An ideally-tapered via that maximizes sidewall coverage was identified by optimizing the directionality factors and aspect ratios of the vias.     

植物叶片厚度日变化及其与生态因子相关性的研究

多数植物的叶片很薄、很软、充满水分,对其组织结构的研究主要集中在显微结构和亚显微结构方面.利用自主研发的YI-20010A型植物叶片厚度精密测量仪,对几种温室栽培的植物叶片进行监测,可以直接获得叶片厚度的实时变化情况.供试的5种植物叶片都在正午前后出现叶片厚度一天中的最低值.对番茄和高羊茅叶片厚度与相同时段的叶片附近的光照强度、空气温度、相对湿度三个周期性变化的生态因子的相关性进行分析,得出叶片厚度变化与光照强度有显著的负相关,与相对湿度呈显著的正相关.     

Fracture mechanics approach for a partially debonded cylindrical fibre

The mechanical behaviour of the fibre-reinforced composites depends on the properties of the matrix, the fibres and their reciprocal bonding. Degrading effects occurring in such materials under service – such as matrix–fibre detaching (debonding), fibre breaking, matrix cracking – must be taken into account in the safety assessments. In the present paper, the fibre–matrix debonding phenomenon at the fibre–matrix interface is examined through fracture mechanics concepts, since a geometric discontinuity arises at the edge of the debonded zone (between two dissimilar materials) producing a stress singularity. The mixed mode stress-intensity factors are determined, and the effects of the geometrical and mechanical parameters related to matrix and fibres are discussed.