Modelling of adhesive bonding for aircraft structures applying the insertion squeeze flow method

A numerical model for simulating the flow of an adhesive during an insertion squeeze flow (ISF) bonding process for joining composite structures is presented. The model is developed using the commercial CFD code FLUENT®. The numerical model is validated for a Newtonian fluid by comparing the predicted insertion forces that act during the insertion process with those obtained both from experiments and calculated using a simplified analytical model. Very good agreement is obtained. The model is then used to investigate the effect of insertion speed and adhesive viscosity on the ISF bonding process. The findings, and the further application of the numerical and analytical models, are valuable to ensure the quality of Pi-slot joints.     

Polishing of paramagnetic materials using atomized magnetic abrasive powder

This paper reports on the polishing of paramagnetic materials in the magnetic abrasive finishing (MAF) process by using atomized-type magnetic abrasive powder (MAP). After atomization process, a spherical MAP with captured Al₂O₃ hard particles was obtained. The MAF process was experimented on two plane workpieces with different hardnesses. An orthogonal array containing five factors with three levels was applied in the experiment. Based on analysis results, the model of surface roughness was obtained, and the rotational speed of the MAPs played the most dominant role in the surface quality of both finished experimental materials. By comparing the value of the finished surface roughness at different process parameters, the influence of single process parameter on processing quality was analyzed. Furthermore, the minimum surface roughness of both materials was obtained at the best combination of process parameters. Finally, the experiment of the material removal and the produced surface morphology was examined in order to understand the finishing characteristics of the atomized MAPs during the MAF process.     

SDC99钢淬火过程中应力和组织演变的有限元模拟

为了研究钢铁材料在淬火过程中内部组织和应力的变化,以自主研发的SDC99钢为研究对象,考虑相变潜热的影响,采用有限元方法对偏心圆环的淬火过程进行模拟仿真,并对淬火过程中模型的温度场、应力场和组织场的变化进行分析和研究.结果表明:经实验测定淬火过程中温度场及残余应力的分布与模拟结果吻合较好,偏心圆环上最大残余应力出现在45°及315°位置;模型硬度的分布与其马氏体含量分布趋势一致,模拟的硬度值略小于实测值.     

A statistical model for fatigue crack growth under random loads including retardation effects

A model for the statistical analysis of crack growth under random loading that includes the loading sequence effect is presented. The model defines and incorporates an equivalent closure stress that is included in the fatigue crack growth law via the effective stress intensity factor. The equivalent closure stress for each loading process is obtained from the probability density function of peaks p(S) in the random loading process, the properties of the material and the specimen geometry. The model was applied to the analysis of crack growth life under random loading on sheets of two different aluminum alloys: 2024-T351 and 2219-T851. The crack-growth lifetimes thus obtained were consistent with experimental data and with the results obtained by using a cycle-by-cycle simulation scheme.     

Mathematical modeling of scroll compressors — part II: overall scroll compressor modeling

This paper presents the development of a comprehensive simulation model of a horizontal scroll compressor, which combines a detailed compression process model (Chen Y., Halm N., Groll E., Braun J. Mathematical modelling of scroll compressors — part I: compression process modeling, International Journal of Refrigeration 2002;25(6):731–750) and an overall compressor model. In the overall model, compressor components are analyzed in terms of nine different elements. Steady state energy balance equations are established applying the lumped capacitance method. In combination with the detailed compression process model, these equations were implemented into computer code and solved recursively. In this way, the temperature and pressure of the refrigerant in different compressor chambers, the temperature distributions in the scroll wraps, and the temperatures of the other compressor elements can be obtained. Thereafter, power consumption and efficiency of the compressor can be calculated. Tests were used to verify the overall model on a macroscopic basis. Using the simulation program based on the overall compressor model, a parametric study of the scroll compressor was performed, and the effects of internal leakage and heat transfer losses were investigated and some preliminary results were obtained. These results indicate that the comprehensive scroll compressor model is capable of predicting real compressor behavior and useful to the design and optimization of scroll compressors.     

A comprehensive study on variability of relative density in selective laser melting of Ti-6Al-4V

ABSTRACT

In this research, the effects of Selective Laser Melting (SLM) process parameters comprising laser power, scan speed, hatch space and scan pattern angle on the formation of porosity and subsequently density have been analysed. To improve the mechanical properties, post-processes (heat treatment) must be performed. Therefore, heat treatment was added to the design of experiment to analyse the effect of this process coupling with SLM process parameters on the value of density. A comprehensive design set with five levels for each parameter was selected so Taguchi L25 was used as the design of experiment. The significance of each parameter on obtained results was examined using statistical analysis (F-Test) and numerical model (interrogator analysis). The correlation between two process parameters was discussed by using 3D analytical and contour plots and the mechanisms behind these were discussed in depth. The contribution of this paper is a deep investigation of the relation of process parameters and heat treatment on density based on the Artificial Neural Network model. Results showed that better density is obtained with lower scan speed, laser power and scanning pattern angle. Meanwhile, for heat treatment and hatch space, the best density was obtained in their optimum range.     

Mathematical modeling of the lysis of clots in blood vessels

A mathematical model of the lysis of clots in blood vessels has been constructed on the basis of convectiondiffusion equations. The fibrin clot is considered as an immobile solid phase, and the plasminogen, plasmin, and plasminogen activators — as dissolved liquid phases. As a result of the numerical solution of the model, dependences predicting the development of the lysis process have been obtained. An important role of clot swelling in the process of lysis has been revealed.     

Development of response surface model for tensile shear strength of weld-bonds of aluminium alloy 6061 T651

The development of a response surface model to study the influence of process parameters of weld-bonding on tensile shear strength of the weld-bond of 2 mm thick aluminium alloy 6061 T651 sheets has been reported. Significant and controllable process parameters of the weld-bonding (surface roughness, curing time, welding current, welding time and electrode pressure) and their ranges were identified by conducting pilot experiments. Welding current, welding time and welding pressure were identified as significant and controllable parameters. Influence of the significant process parameters and their interaction on the tensile shear strength of the weld-bonds was studied using response surface methodology (RSM). Using model, the optimal combination of weld bonding process parameters for maximum tensile shear strength of the weld bond was obtained. The validity of the model was evaluated on weld bonds developed using different levels of process parameters and testing their tensile shear strength. The model error was found to be in a range of 3–7%.     

大厚度复合材料曲面典型构件的工艺优化

大厚度复合材料的数值仿真存在缺乏实尺度验证、数值模型待优化等问题。本文针对真空辅助树脂传递模塑成型的大厚度复合材料曲面构件,通过大型风电叶片主梁的工艺仿真与实尺度实验验证,进行了工艺设计与工艺参数模型预测。首先对比研究了不同的工艺仿真方案;然后利用所选优化方案对树脂灌注方案进行工艺设计,并进行了实验验证;最后,提出了不同厚度制件的工艺参数预测模型。结果表明:所选优化方案可同时得到理想的计算效率和流动模拟结果;所设计工艺方案与实验吻合性良好;工艺参数预测模型所得结果与模拟结果基本一致。      

A New Model for Repairable Systems with Nonmonotone Intensity Function

In this study, a new model based on the mixture of bounded Burr XII failure intensity and bounded intensity process is proposed to describe the failure intensity of minimally repaired systems with approximate bathtub behavior. The estimates of the model parameters are easily obtained using the maximum likelihood estimation method. The confidence intervals for the model parameters are also provided. Other existing models, such as superposed power law process, log‐linear process–power law process, and bounded bathtub intensity process are used to compare with our proposed model. Through numerical examples, the results show that our proposed model performs well regarding the Akaike information criterion value and the mean of square errors. Copyright © 2014 John Wiley & Sons, Ltd.     

Characterization of Carbonated Beverages Associated to Corrosion of Aluminium Packaging

The objectives of this study were to evaluate the characteristics of commercial soft drinks related with the corrosion process of the aluminium packaging and based on that, propose model solutions for future studies of beverage/package interaction and corrosion process of metal packages. Therefore, the pH, acidity, concentration of chlorides and copper in six types of soft drinks were determined, as well as the corrosion potential of the aluminium and the current density corrosion obtained in polarization curves using the beverages as electrolyte. Based on the results obtained, a solution of citric acid (pH = 3) containing chloride (250 mg/kg) and copper ions (250 µg/kg) is proposed. The obtained results are potentially useful for the industry and future studies regarding the interaction process between soft drinks and aluminium cans. Copyright © 2015 John Wiley & Sons, Ltd.     

A kinetic study of the thermal decomposition of ammoniojarosite

Polycrystalline powdered ammoniojarosite was obtained by hydrolysis from bio-oxidized sulphuric pickling waste water. The kinetic parameters of the thermal decomposition process of ammoniojarosite were calculated by means of thermogravimetric measurements. Analyses were performed in non-isothermal conditions at different heating rates. The three stages of the thermal decomposition process (dehydration, dehydroxylation and deammoniation, and sulphate decomposition) are best described by the Avrami–Erofeev Am model. The kinetic exponent m increases, in general, with the heating rate. Apparent activation energies of 54, 244 and 130 kJ mol–1, respectively, were obtained for each decomposition stage.     

A Non-markovian Model of Photodetection of Cavity Radiation

A non-markovian model of the detection of cavity photons is proposed. The cavity photons interact with the atoms of the detector in a two-stage process, while the evolution of the cavity photons is modelled, as usual, as a population process with constant rate parameters. The joint distribution of the cavity photons and the number of detected photoelectrons is studied. The results corresponding to the markovian model proposed by Shepherd are recovered by an appropriate limiting procedure. Some simple characteristics of the twofold counting statistics are also obtained. In particular, the memory effects of two-stage detection are shown to result in a depletion of bunching; the shape of the spectrum (in the time domain), while similar to that obtained using the Shepherd model, is depressed pointwise by a memory-dependent factor.     

基于响应面法的大型锥筒件内凸缘缩口成形工艺参数优化

目的 探究大型锥筒件内凸缘缩口成形的最佳工艺参数。方法 首先,根据内凸缘缩口成形的工艺原理,使用三维软件构建内凸缘缩口成形的仿真模型,并用Deform进行仿真成形。在此基础上,以缩口件高度和成形载荷作为内凸缘成形质量的判断依据,基于响应面法得到关于缩口件高度和成形载荷的回归预测模型。分析不同的摩擦因数、挤压速度和凹模锥度对内凸缘成形质量的影响,优化得到最佳的成形工艺参数,最后进行物理试验验证。结果 通过响应面法拟合得到了缩口件高度和成形载荷关于3因素的多元非线性模型,模型通过F检验得出的显著性概率P值均小于0.000 1,失拟项值均大于0.05,且模型预测值与试验模拟值的关系接近直线,充分说明了该数学模型的合理性。当摩擦因数为0.3、挤压速度为3 mm/s、凹模锥度为9°时,毛坯的成形载荷最小,为90 k N,缩口件高度最低,为1 350 mm,与模型预测相比,误差均小于10%。结论 优化后的工艺参数使内凸缘成形质量高、表面光滑无缺陷、成形载荷小,为大型锥筒的内凸缘成形工艺提供了参考。     

Verification and prediction of residual strength of C/SiC composites under non-stress oxidation

This article describes the strength behavior of C/SiC composites under non-stress oxidation. The oxidation kinetics model of a ceramic matrix composite contains both a reaction-controlled process and a diffusion-controlled process. The oxidation process has an effect on the fiber volume fraction, radius, and the composite interface shear stress. We obtained the residual strength of unidirectional C/SiC composites under 400–900 °C oxidation with non-stress environments by combining the mass loss rate model with the strength failure model at room temperature. This model considers the different components of the system to be subject to oxidation at different temperature ranges. Then, the influence of oxidation temperature, oxidation time, and fiber volume fraction on residual strength was studied. Experiments on C/SiC composites at 650 and 800 °C in an air environment with non-stress conditions were then performed, and the theoretical results of C/SiC composites were in good agreement with the experimental data.     

Handling of Non-Sink Conditions: In-Vitro Dissolution Rates of Some Common Pharmaceutical Calcium Salts

Abstract

A model is developed for convenient treatment of data obtained from non-sink dissolution. To demonstrate its utility, the dissolution profiles of calcium sulfate, calcium carbonate and three calcium phosphates were determined by USP dissolution in pH 1. 2 buffer. A model is developed taking into account both the decreasing size (surface area) and the changing concentration gradient during the dissolution process. All the salts adhere well to the proposed model.     

Semi-Markov modeling of dependability of VoIP network in the presence of resource degradation and security attacks

Nowadays VoIP has become an evolutionary technology in telecommunications. Hence it is very important to study and enhance its dependability attributes. In this paper, an analytical dependability model for VoIP is proposed. The study is focused on analyzing the combined effects of resource degradation and security breaches on the Quality of Service (QoS) of VoIP, to enhance its overall dependability. As a preventive maintenance policy to prevent or postpone software failures which cause resource degradation, software rejuvenation is adopted. The dependability model is analyzed using semi-Markov process which captures the effects of non-Markovian nature of the time spent at various states of the system. The steady-state as well as the time-dependent analysis of the dependability model is presented. The steady-state results are obtained analytically, whereas the time-dependent results are obtained from simulation. Also, the analytical model is validated via simulation. The model analysis using a numerical example indicates the feasibility of our approach. Various dependability attributes such as availability, reliability and confidentiality are also obtained. A comparative study is also done between our proposed model and the existing models.     

Optimization of nuclear demagnetization process

On the basis of a relatively simple thermal model of an adiabatic nuclear demagnetization apparatus a system of differential equations has been obtained. A numerical solution of this system describes the demagnetization process and a subsequent warming-up process. These results are confirmed by comparison with experimental data. The model suggested allows an optimal law of magnetic field decrease in demagnetization to be obtained.     

Identifying the time of polynomial drift in the mean of autocorrelated processes

Control charts are used to detect changes in a process. Once a change is detected, knowledge of the change point would simplify the search for and identification of the special ause. Consequently, having an estimate of the process change point following a control chart signal would be useful to process engineers. This paper addresses change point estimation for covariance‐stationary autocorrelated processes where the mean drifts deterministically with time. For example, the mean of a chemical process might drift linearly over time as a result of a constant pressure leak. The goal of this paper is to derive and evaluate an MLE for the time of polynomial drift in the mean of autocorrelated processes. It is assumed that the behavior in the process mean over time is adequately modeled by the kth‐order polynomial trend model. Further, it is assumed that the autocorrelation structure is adequately modeled by the general (stationary and invertible) mixed autoregressive‐moving‐average model. The estimator is intended to be applied to data obtained following a genuine control chart signal in efforts to help pinpoint the root cause of process change. Application of the estimator is demonstrated using a simulated data set. The performance of the estimator is evaluated through Monte Carlo simulation studies for the k=1 case and across several processes yielding various levels of positive autocorrelation. Results suggest that the proposed estimator provides process engineers with an accurate and useful estimate for the last sample obtained from the unchanged process. Copyright © 2009 John Wiley & Sons, Ltd.     

Gaussian Process Model – An Exploratory Study in the Response Surface Methodology

This paper explores the benefits of Gaussian process model as an alternative modeling technique for problems developed in the Response Surface Methodology framework. Three case studies with different type and number of responses were investigated, and the compromise solutions obtained with three modeling techniques were evaluated. Results provide evidences of the Gaussian process model usefulness for stochastic responses, namely, when responses are correlated. Copyright © 2015 John Wiley & Sons, Ltd.