Randomly Dispersed Coated Composites Study by Statistical Approach and Numerical Homogenization Method

The aim of this work is the computation of effective elastic properties of 3D 3-phase random heterogeneous coated materials. For that, a new expression of the integral range for 3-phase random coated heterogeneous materials is used. The computation is achieved using a representative microstructure with non-overlapping inclusions. Numerical simulations is used under periodic boundary conditions (PBC) and kinematic uniform boundary conditions (KUBC) prescribed over Representative Volume Element (RVE). The obtained effective elastic properties are compared with different analytical models as Hashin and Shtrikman bounds and the n+1 phase model. Using the statistical methods, a new extension of the integral range for 3-phase coated materials is proposed.

Экспресс-оценка пространственных и временных возможностей вертолетов при выполнении задач пожаротушения и аварийно-спасательных работ

В статье рассмотрен графоаналитический метод, позволяющий оперативно осуществлять оценку пространственных и временных возможностей вертолетов при выполнении задач авиационного пожаротушения и аварийно-спасательных работ, связанных с доставкой сил и средств противодействия чрезвычайным ситуациям. Актуальность материалов статьи обусловлена следующим: выполнение большого объема расчетов по нескольким вариантам действий требует значительных затрат времени при использовании традиционных методов, изложенных в Руководствах по летной эксплуатации вертолетов. По мнению авторов, представленный в статье графоаналитический метод экспресс-оценки успешно применяется в частях и подразделениях военной авиации и позволяет проводить расчеты оперативно.The article describes the grapho-analytical method for quick assessment of spatial and temporal capabilities of helicopters when solving tasks of aviation fire fighting as well as rescue and emergency operations. The relevance of the article is caused by the following: performing a large amount of calculations for several action options requires significant time when using traditional methods from the helicopter flight Manuals. The presented in the article grapho-analytical method of express-evaluation is successfully used by military aviation units and allows performing calculations quickly. When solving problems related to the delivery of forces and means of emergency response, helicopter crews have to fly again to places for loading additional equipment or replenishment of the onboard water supply (fire-extinguishing composition). In such situation it is extremely important for crews to be aware of the possible number of flights to the wrecking area without refuelling. For assessment of helicopter capabilities it is not always possible and operational to use traditional methods of engineering and navigation calculation. One of the easiest ways to solve such problems, which do not require a lot of time, is a graphical method using a set of integral range lines. In the article the set of lines is presented in the form of nomogram to make the task solving process easier. The nomogram is constructed based on the information from the helicopter flight Manual concerning the hourly and kilometre fuel consumption. There are given algorithms for operative task solution with use of this nomogram. The use of nomograms while decision-making for emergency and rescue tasks performance provides an operational assessment of helicopter capabilities to reach objects of impact without computationally intensive traditional engineering and navigation calculations.

Estimation of Crack Growth Rate by J-Integral Range for Type SUS304 Stainless Steel Plate in Creep-Fatigue Tests at High Temperature

In structures having stress concentration under cyclic loading, a small crack initiates and it grows and propagates. Evaluating crack growth is important to estimate the remaining life of cracked components. The present paper shows the estimation of crack growth rate under creep-fatigue loading with some patterns of strain holding times. Creep-fatigue tests of the perforated plate having initial crack were conducted with the different strain holding time under strain-controlled loading at 550°C. The crack growth was observed from the photographs taken at each cycle. The crack growth per one cycle of creep-fatigue loading was evaluated by the creep-fatigue crack propagation law which used increment J-integral range. Comparing the crack growth rates of experimental with those of predicted, the crack growth rates were predicted by using increment J-integral range with the accuracy was factor of 2.

J-Integral Approach to Creep-Fatigue Crack Propagation in Lead-Free Solder under Various Loading Waveforms

Crack propagation tests of lead-free solder were conducted at room temperature in air using center-notched plates under load-controlled conditions with three waveforms: triangular pp waveform having fast loading and unloading rates, cp-h waveform having a hold time under tension, and cc-h waveform having a hold time under tension and compression. The J integral was evaluated from load-displacement curves. For fatigue loading of pp waveform, the crack propagation rate was expressed as a power function of the fatigue J-integral range. The creep component due to the hold time greatly accelerated the crack propagation rate. The creep crack propagation rate was found to be a power function of the creep J integral range for each case of cp-h and cc-h waveforms. The creep crack propagation rate for cp-h waveform was higher than that for cc-h waveform. Displacement-controlled tests were also performed under four triangular strain waveforms: pp, cp, cc and pc. For the case of pp waveform, the crack propagation rate was also expressed as the same power function of the fatigue J integral range as in the case of load-controlled tests. The creep crack propagation rate was expressed as a power function of the creep J integral range for each case of cp, pc and cc waveforms. Microscopic observations were conducted to clarify micromechanisms of creep-fatigue crack propagation.

Statistical properties of supersonic turbulence in the Lagrangian and Eulerian frameworks

We present a systematic study of the influence of different forcing types on the statistical properties of supersonic, isothermal turbulence in both the Lagrangian and Eulerian frameworks. We analyse a series of high-resolution, hydrodynamical grid simulations with Lagrangian tracer particles and examine the effects of solenoidal (divergence-free) and compressive (curl-free) forcing on structure functions, their scaling exponents, and the probability density functions of the gas density and velocity increments. Compressively driven simulations show significantly larger density contrast, more intermittent behaviour, and larger fractal dimension of the most dissipative structures at the same root mean square Mach number. We show that the absolute values of Lagrangian and Eulerian structure functions of all orders in the integral range are only a function of the root mean square Mach number, but independent of the forcing. With the assumption of a Gaussian distribution for the probability density function of the velocity increments for large scales, we derive a model that describes this behaviour.

Crack Propagation Behavior at Sn37Pb-Copper Interface in Low Cycle Fatigue

This paper studies the crack propagation at Sn37Pb-copper interface in push-pull low cycle fatigue. Bonded specimens of Sn37Pb and copper having notch holes with different distances from the interface were fatigued at 313K and the crack propagation paths were observed. Cracks propagated at the interface when the notch hole was near the interface but propagated in the solder when the notch hole was away from the interface. The propagation rate of the interfacial crack was faster than that of non-interface crack. The crack path and crack propagation rate of the two types of cracks were discussed in relation to J integral range calculated by finite element method.

Development of Flaw Evaluation System for Creep-Fatigue Crack Propagation of High-Temperature

Central Research Institute of Electric Power Industry (CRIEPI) has been conducting a research project on the verification of evaluation method for structural integrity of high-temperature components. As a part of the framework, we developed a flaw evaluation system on PC to predict creep-fatigue crack propagation, which was considered to be an essential crack driving force at high temperature especially in case where stresses caused by thermal loading were significant. The system is featured by easy and dialogical operation with graphical user interface. Fatigue and creep crack propagation behavior can be predicted using fatigue J-integral range and creep J-integral, respectively, which are the variations of the non-linear fracture mechanics parameter, J-integral. Both fatigue J-integral range and creep J-integral are calculated by the reference stress method with revised solutions developed by detailed finite element analysis.