H. Afifi

National Institute of Standards

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A Combined Approximation Based MATLAB Code for Dynamic Re-Analysis of Aerospace Structures

H. Afifi Efstratios Nikolaidis Emily K. Afifi Sathya Gangadharan

Achieving a high strength-to-weight ratio is one of the most important goals in the design of aerospace structures. Designers are continuously striving to find the optimum solutions that will make aerospace vehicles simultaneously strong and light. During the design process, the structure experiences several changes to reach this goal. Any change to the geometry and/or material property directly influences the global stiffness of the structure. Modification of the applied loading or stiffness impacts the solution of displacements. Each design change requires the implicit analysis equation to be resolved. In large scale models with thousands of degrees of freedom, the cost and time of repeated reanalysis, even for a small change, is significant. A combined approximation approach (CA) was previously developed to provide an efficient and accurate reanalysis of large structures, even with great changes in the design. High quality results have also been obtained through utilizing the CA method for dynamic reanalysis. This approach involves the combination of local and global approximation methods including series expansion, reduced basis vector, matrix factorization, and Gram-Schmidt orthonormalization. In this study, a combined approximation based MATLAB code for dynamic reanalysis has been developed. Changes in both baseline design properties and excitation frequency range have been introduced. The response of the modified system is calculated as a function of these changes, directly via inversion of the dynamic stiffness matrix and approximately via combined approximation method. A reanalysis example of a simplified aircraft wing spar model using this code is presented. Both methods are compared for solution accuracy.

10.1115/imece2009-12922

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Structure and Ultrasonic Properties of Vanadium Tellurite Glasses ContainingCopper Oxide

Archives of Acoustics (2009)

N.S. Abd El-Aal H. Afifi

The elastic properties of vanadium tellurite glasses, 65TeO2-(35-x)V2O5-xCuO, with different compositions of Copper (x=7.5 to 17.5mol% in steps of 2.5mol%) have been studied at room temperature (300K). The ultrasonic velocity measurements have been made, using a transducer having resonating frequency of 4MHz (both longitudinal and shear). The density, molar volume, and ultrasonic velocities show interesting features, which are used to explore the structural changes in the network. Elastic moduli, Poisson ratio, crosslink density, Microhardnes, and Debye temperature of the glasses have been determined using the experimental data. The composition dependence of the elastic properties explores useful information about the physical properties of the vanadium tellurite glasses doped with Copper. Quantitative analysis has been carried out in order to obtain more information about the structure of the glass under the study, based on bond compression model and the Makishima [ampersand] Mackenzie model. The observed results through ultrasonic non-destructive evaluation, investigate the structural changes and mechanical properties of the glass.

Debye model

Poisson's ratio

Source

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Citations (17)

Structural Investigation of Semi Crystalline LDPE Nano-polymer

Journal of Engineering and Applied Sciences (2016)

M.S. Gaafar H. Afifi Kh. Zenidy

Low density polyethylene (LDPE) nano-polymers were subjected to a high power ultrasonic irradiation as a polymerization initiator, for different times (0, 5, 10 and 15 minutes). Characterization was performed on the non-irradiated and irradiated LDPE samples by measuring the low power ultrasonic wave velocities (Longitudinal and Shear) along with density measurements. X-ray diffraction (XRD) patterns revealed that the percentage crystallinity and crystalline size had changed significantly with exposure to ultrasonic irradiation. The XRD patterns showed, the usual peaks relative to the planes (110) and (200). The XRD parameters indicated the formation of LDPE nano-polymer and the increase in the degree of crystallinity, lattice constants (a & b) and crystallite size for nano-LDPE samples with exposure time from 0 to 10 min, while with exposure time up to 15 min they decreased. However, the results obtained by the X-ray diffraction have been confirmed by the ultrasonic wave velocities together with densities of the samples.

Low-density polyethylene

10.5455/jeas.2016110104

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Citations (1)

Relaxation phenomena in tellurite glasses

Journal of Applied Physics (2010)

R. El‐Mallawany M. Sidky H. Afifi

The new semiconducting noncrystalline solid “tellurite glasses” of the form 0.7 TeO2–(0.3−x)V2O5–xAnOm have been prepared in bulk form with different compositions where AnOm is CeO2 or ZnO and x=0.03,0.05,0.07,0.10 mol %. Longitudinal ultrasonic attenuation in these glasses has been measured at frequencies of 2, 4, 6, and 8 MHz and in the temperature range of 100–300 K. The results showed the presence of a very well defined peak which shifts to higher temperature with increasing frequency, suggesting a kind of relaxation process. The acoustic activation energy, as well as the relaxation frequency, has been calculated and correlated with the relaxation strength for each composition. Correlations between the present low temperature of ultrasonic attenuation and the previous room temperature elastic moduli have been achieved for both glass series.

Atmospheric temperature range

Ultrasonic attenuation

10.1063/1.3311551

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Citations (14)

Interpretation of mechanical properties and structure of TeO2–Li2O–B2O3 glasses

Physica B Condensed Matter (2007)

Yasser B. Saddeek H. Afifi N.S. Abd El-Aal

Lithium borate

Debye model

10.1016/j.physb.2007.04.011

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Citations (79)

AN EFFICIENT DYNAMIC RE-ANALYSIS OF AEROSPACE STRUCTURES USING COMBINED APPROXIMATION TECHIQUE THROUGH MATLAB SIMULATION

H. Afifi Efstratios Nikolaidis Emily K. Afifi Sathya Gangadharan

Achieving a high strength-to-weight ratio is one of the most important goals in aerospace structures. During the design process, the structure experiences several changes to reach this goal. Any change to the geometry and/or material directly influences the global stiffness of the structure. Modification of the applied loading or stiffness impacts the solution of displacements. Each design change requires the implicit analysis equation to be resolved. In large scale models with thousands of degrees of freedom, the cost and time of repeated reanalysis, even for a small change, is significant. Kirsch developed the combined approximation approach (CA) to provide an efficient and accurate reanalysis of large structures, even with great changes in the design. In this study, the CA method has been extended to approximate the steady state response of structures and a MATLAB code has been developed to approximate the new response of a wing box model subjected to a harmonic wind gust load. The response of the modified design is approximated, as a

10.2514/6.2010-2640

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Citations (1)

Elastic constants of semiconducting tellurite glasses

Materials Chemistry and Physics (1994)

R. El‐Mallawany M.A. Sidkey A. H. Khafagy H. Afifi

Debye model

Poisson's ratio

Elasticity

10.1016/0254-0584(94)90167-8

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Citations (63)

Ultrasonic studies on polystyrene/styrene butadiene rubber polymer blends filled with glass fiber and talc

Ultrasonics (2006)

A. A. Higazy H. Afifi A. H. Khafagy M.A. El-Shahawy A. M. Mansour

Talc

Polystyrene

10.1016/j.ultras.2006.05.142

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Citations (40)

Improvement of the compatibility of natural rubber/ethylene–propylene diene monomer rubber blends via natural rubber epoxidation

Journal of Applied Polymer Science (2002)

A. Mounir El Sayed H. Afifi

Abstract The longitudinal ultrasonic velocity, longitudinal ultrasonic absorption (attenuation coefficient), glass‐transition temperature, and Mooney viscosity for epoxidized natural rubber/ethylene–propylene diene monomer blends were measured. The variation of the longitudinal ultrasonic velocity with the blend ratios was linear, indicating a compatible system in comparison with the same system without epoxidation (natural rubber/ethylene–propylene diene monomer), which was incompatible. Also, the behavior was confirmed by heat of mixing calculations as well as Mooney viscosity measurements. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2816–2819, 2002

Ethylene propylene rubber

Diene

EPDM rubber

Mooney viscosity

10.1002/app.11263

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Citations (14)

The influence of talk filling on the ultrasonic properties of EPDM rubber toughened PS

H. Afifi M. A. El-Shahawya

10.3728/icultrasonics.2007.vienna.1037_afifi

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Citations (0)