Experimental study of thickness reduction effects on mechanical properties and spinning accuracy of aluminum 7075-O, during flow forming

Flow forming technology is widely used in the production of the axisymmetric industrial parts. The advantage of flow forming process over other manufacturing methods such as press forming is use of simple tooling, reduced forming loads due to localized deformation, and enhanced mechanical and surface quality of finished parts. In this study, the effects of thickness reduction on the mechanical properties and spinning accuracy are experimentally investigated on 7075-O aluminum tube. A prototype spinning machine has been designed and manufactured. The effects of spinning accuracy, surface roughness, percentage of elongation, yield strength, and the ultimate strength as a function of thickness reduction are experimentally examined. The experimental results show that with increment of thickness reduction, the yield strength, ultimate strength, surface hardness, and crystal refining increase, and on the other hand, it has adverse effect on diameter growth, geometrical accuracy, surface roughness, and percentage elongation of spun tube.     

Numerical study on the dynamics of an electrical discharge generated vapor bubble in EDM with different shapes of the tool and the workpiece

In this paper, the effect of the shapes of the tool and the workpiece on the dynamic behavior of an electrical discharge generated vapor bubble in the process of EDM (Electrical Discharge Machining) is investigated. The boundary integral equation method is employed for numerical simulation of the problem. Results show that in the case of the concave tool and workpiece the lifetime of the electrical discharge generated vapor bubble is longer than the case of the flat tool and workpiece. By increasing the concavity of the shapes of the tool and the workpiece, the lifetime of the bubble increases. Results also show that in the case of the convex tool and workpiece, the lifetime of the electrical discharge generated vapor bubble is shorter than the lifetime of the bubble in the case of the flat tool and workpiece. In this case also, by increasing the convexity of the shapes of the tool and the workpiece, the lifetime of the bubble decreases. Numerical results show that in the case of the concave tool and workpiece the rate of pressure drop on the surface of the workpiece is higher than the rate of pressure drop on the workpiece in the cases of the flat and convex tool and workpiece. The high rate of pressure drop on the surface of the workpiece leads to the ejection of more molten material from the crater and consequently leads to more material removal rate.     

A consecutive modal pushover procedure for nonlinear static analysis of one-way unsymmetric-plan tall building structures

Seismic responses of unsymmetric-plan tall buildings are substantially influenced by the effects of higher modes and torsion. Considering these effects, in this article, the consecutive modal pushover (CMP) procedure is extended to estimate the seismic demands of one-way unsymmetric-plan tall buildings. The procedure uses multi-stage and classical single-stage pushover analyses and benefits from the elastic modal properties of the structure. Both lateral forces and torsional moments obtained from modal analysis are used in the multi-stage pushover analysis. The seismic demands are obtained by enveloping the peak inelastic responses resulting from the multi-stage and single-stage pushover analyses. To verify and appraise the procedure, it is applied to the 10, 15, and 20-storey one-way unsymmetric-plan buildings including systems with different degrees of coupling between the lateral displacements and torsional rotations, i.e. torsionally-stiff (TS), torsionally-similarly-stiff (TSS) and torsionally-flexible (TF) systems. The modal pushover analysis (MPA) procedure is implemented for the purpose of comparison as well. The results from the approximate pushover procedures are compared with the results obtained by the nonlinear response history analysis (NL-RHA). It is demonstrated that the CMP procedure is able to take into account the higher mode influences as well as amplification or de-amplification of seismic displacements at the flexible and stiff edges of unsymmetric-plan tall buildings. The extended procedure can predict to a reasonable accuracy the peak inelastic responses, such as displacements and storey drifts. The CMP procedure represents an important improvement in estimating the plastic rotations of hinges at both flexible and stiff sides of unsymmetric-plan tall buildings in comparison with the MPA procedure.     

Liquid crystalline thermosets as binder for powder coatings: Thermoanalytical study of the cure characteristics of a carboxylated main chain liquid crystalline oligoester

The curing behavior of a liquid crystalline oligoester (LCO), based on 4,4′-diacetoxybiphenyl and dodecanedioic acid, as a model resin for powder coatings, in presence of triglycidyl isocyanurate (TGIC), as a curing agent, was studied by isothermal differential scanning calorimetry (DSC). The analysis of isothermal data was performed using the model-free isoconversional method. Activation energy as a function of extent of conversion, , has been calculated by the Friedman technique. It showed an ascending trend from about 133.7 kJ/mol, at =0.1 to 177.2 kJ/mol, at =0.4, then it reached approximately a constant value of about 150±5% kJ/mol in the range of 50–90%.

The results indicated that the kinetic process does not follow a single-step curing reaction model. To verify the isothermal analysis result, we carried out further, non-isothermal differential scanning calorimetry and depolarizing transmittance measurements on the stoichiometric mixture of LCO/TGIC, at different heating rates. The results of these experiments exhibited that the kinetic process of the investigated system is strongly influenced by curing condition which alters the liquid crystalline state of the sample.     

Research into a Management System for Diagnosis, Maintenance, and Repair of Concrete Structures

The choice of an appropriate repair material and method requires a systematic observation of the symptoms and their probable cause together with a source of available information relating to durability. In response to a growing awareness of durability problems, a repair of concrete (REPCON) database has been developed, which deals with the diagnosis, evaluation, maintenance, and repair of concrete structures. The REPCON Management System is designed to be an effective support tool for experts whose data can be evaluated and tested to ensure that the evolving database retains its integrity. By providing a quantitative and consistent means for evaluating both new data and the person contributing it, the confidence level (CL) allows new knowledge and experience to be gathered and monitored over time. The paper explains how a computerized database management system can allow an initial database to evolve and become a forum for exchanging ideas in the field of concrete repair, and how the new methodology of data/user evaluation could have wider implication in many knowledge-rich areas of expertise.     

Evaluation of ground motion scaling methods in soil–structure interaction analysis

Dynamic analysis of structures deals with scaling of ground motions, which is vital for estimation of seismic responses. A major source of variability in seismic responses of structures arises from scaling of ground motions. In this paper, the accuracy of six conventional scaling methods on estimation of engineering demand parameters of soil–structure interacting systems is investigated. Two‐dimensional structural models of 5, 10, and 20 stories shear buildings are studied by using stick models, whereas the underlying soil is modeled using the cone model concept. This research attempts to elucidate the accuracy of considered methods for the evaluation of responses. The results show that a suitable scaling method for a response may differ from one to another in terms of accuracy and efficiency. Copyright © 2012 John Wiley & Sons, Ltd.     

Efficiency of active systems in controlling base‐isolated buildings subjected to near‐fault earthquakes

It has been pointed out that base‐isolated structures may be vulnerable during near‐fault earthquakes and special considerations are required in the design of isolated structures in near‐fault areas. This paper investigates the efficiency of active control systems in reducing the responses of base‐isolated structures with various isolation parameters. The design of hybrid control systems using base isolation and active systems are optimized in order to accomplish different design purposes. Also for some cases, equivalent passive control systems are introduced which result in comparable responses with respect to hybrid control systems. Copyright © 2009 John Wiley & Sons, Ltd.     

Optimization of phthalic/maleic anhydride‐endcapped PET oligomers using response surface method

Poly(ethylene terephthalate) (PET) from off‐grades of industrial manufacturers was partially and thoroughly depolymerized in order to synthesize PET oligomers and bis(hydroxyethyl) terephthalate (BHET), respectively. Design of experiments and analysis of variance (ANOVA) were applied for optimization of samples. Effects of reaction time, volume of glycol, catalyst concentrations, and particle size of off‐grade PET were investigated. The optimal conditions to synthesize PET oligomers (3–8 repeating units) were glycol/PET molar ratio of 1, a weight ratio (catalyst to PET) of 0.5 wt%, using granule‐shape. On the other hand, a reaction time of 180 min, a weight ratio (catalyst to PET) of 0.25 wt%, and glycol/PET molar ratio of 5 were obtained as the suitable conditions of BHET production. Then, endcapped PET oligomers, as a compatibilizer for preparing PET nanocomposites, were produced via reaction between maleic anhydride/phthalic anhydride (MA/PhA) composition. The combination of reaction time of 106 min and PhA/MA molar ratio of 0.85 produced the best results based on d‐spacing and peak shift of nanocomposite samples. Moreover, the reaction of MA and BHET from glycolyzation of PET was successfully performed at 160°C and 190°C for 8 h. The optimum conditions were compared with a synthesized PET. POLYM. ENG. SCI., 54:417–429, 2014. © 2013 Society of Plastics Engineers     

Modeling for Shell-Side Heat Transfer Coefficient and Pressure Drop of Helical Baffle Heat Exchangers

This study has suitably modified the existing heat transfer and pressure drop correction factors of the modified Bell–Delaware method used for heat exchangers with segmental baffles, taking into consideration the helical baffle geometry. These correction factors are presented in parametric formulas based on the Taborek presented procedure for segmental baffles. These formulas are functions of the geometrical and physical parameters of discontinuous helical baffles. In addition, the parametric formulas are presented graphically based on the Stehlik method. The correction design method proposed by Stehlik for the helical baffle is presented in detail and a theoretical model for shell-side heat transfer and pressure drop is developed. In general, the results show that the present model matches more closely with the graphically proposed correction factors of Stehlik. In order to calculate the shell-side heat transfer coefficient and pressure drop using the present method, a computational code has been developed by the authors. In addition, in order to examine the validity, the results of the code for a case study are compared with the results obtained from EXPRESS software and experimental formulas presented by Zhang. The results of comparison show that the proposed method is accurate and can be used by designers confidently.