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Article
Publication date: 15 March 2022

Christos Katsiropoulos, Spyros Pantelakis, Francesca Felline, Giuseppe Buccoliero and Silvio Pappada

The purpose of this paper is to investigate the feasibility to produce a novel aircraft full stiffened panel using entirely a new hybrid thermoplastic composite material allowing…

131

Abstract

Purpose

The purpose of this paper is to investigate the feasibility to produce a novel aircraft full stiffened panel using entirely a new hybrid thermoplastic composite material allowing for appreciably lower processing temperatures as compared to conventional structural thermoplastic composites.

Design/methodology/approach

For stiffening the fuselage skin panel, the out of autoclave welding of four composite stringers was obtained using a modified induction welding (IW) process. The quality of the welds was investigated using micro-tomography and the mechanical strength of the lap joints was assessed by means of single-lap shear strength (SLSS) tests. Moreover, a holistic design index was implemented as a decision support tool for selecting the optimal set of IW process parameters. Based on the index used, the quality as well as the entire life cycle cost and environmental impact are accounted for.

Findings

Low porosity values as well as no deconsolidation were observed at the investigated application, and the average measured SLSS, even found lower, lies within the range of the respective values encountered in other similar high-performance applications. It is exhibited that after the optimization, the IW process offers significant potential to replace the autoclave process in welding applications. Thus, it paves the way for reduced cost and increased sustainability, while still meeting the predefined quality constraints.

Originality/value

Although several studies on the IW application have been conducted, limited results exist by using novel thermoplastic materials for aircraft structural applications.

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Article
Publication date: 1 April 1995

A. Karanikolos, P.K. Pantelakis and E.E. Kriezis

The interaction of ELF‐LF electric fields with the human body is examined with a method based on surface charge‐integral equations. The evaluation of the electric field intensity…

52

Abstract

The interaction of ELF‐LF electric fields with the human body is examined with a method based on surface charge‐integral equations. The evaluation of the electric field intensity on the body surface is performed for a realistic model of the human body. Two examples for different postures of the model are given.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 14 no. 4
Type: Research Article
ISSN: 0332-1649

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Article
Publication date: 25 January 2019

Andreas Loukopoulos, Christos Vasilios Katsiropoulos and Spiros G. Pantelakis

The purpose of this paper is to quantify the environmental footprint and cost and thus compare different manufacturing scenarios associated with the production of aeronautical…

321

Abstract

Purpose

The purpose of this paper is to quantify the environmental footprint and cost and thus compare different manufacturing scenarios associated with the production of aeronautical structural components.

Design/methodology/approach

A representative helicopter canopy, i.e., canopy of the EUROCOPTER EC Twin Star helicopter described in Pantelakis et al. (2009), has been considered for the carbon footprint (life cycle energy and climate change impact analysis) along with the life cycle costing analysis. Four scenarios – combinations of different manufacturing technologies (autoclave and resin transfer molding (RTM)) and end-of-life treatment scenarios (mechanical recycling and pyrolysis) are considered.

Findings

Using the models developed the expected environmental and cost benefits by involving the RTM technique have been quantified. The environmental impact was expressed in terms of energy consumption and of Global Warming Potential-100. From an environmental standpoint, processing the canopy using the RTM technique leads to decreased energy demands as compared to autoclaving because of the shorter curing cycles exhibited from this technique and thus the less time needed. As far as the financial viability of both processing scenarios is concerned, the more steps needed for preparing the mold and the need for auxiliary materials increase the material and the labor cost of autoclaving as compared to RTM.

Originality/value

At the early design stages in aeronautics, a number of disciplines (environmental, financial and mechanical) should be taken into account in order to evaluate alternative scenarios (material, manufacturing, recycling, etc.). In this paper a methodology is developed toward this direction, quantifying the environmental and financial viability of different manufacturing scenarios associated with the production of aeronautical structures.

Details

International Journal of Structural Integrity, vol. 10 no. 3
Type: Research Article
ISSN: 1757-9864

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Article
Publication date: 12 August 2014

Christos Vasilios Katsiropoulos, Evangelos D. Drainas and Spiros G. Pantelakis

– The purpose of this paper is to assess the quality of adhesively bonded joints using an alternative artificial neural networks (ANN) approach.

147

Abstract

Purpose

The purpose of this paper is to assess the quality of adhesively bonded joints using an alternative artificial neural networks (ANN) approach.

Design/methodology/approach

Following the necessary surface pre-treatment and bonding process, the coupons were investigated for possible defects using C-scan ultrasonic inspection. Afterwards, the damage severity factor (DSF) theory was applied in order to quantify the existing damage state. A series of G IC mechanical tests was then conducted so as to assess the fracture toughness behavior of the bonded samples. Finally, the data derived both from the NDT tests (DSF) and the mechanical tests (fracture toughness energy) were combined and used to train the ANN which was developed within the present work.

Findings

Using the developed neural network (NN) the bonding quality, in terms not only of defects but also of fracture toughness behavior, can be accessed through NDT testing, minimizing the need for mechanical tests only in the initial material characterization phase.

Originality/value

The innovation of the paper stands on the feasibility of an alternative approach for assessing the quality of adhesively bonded joints using and ANNs, thus minimizing the necessary testing effort.

Details

International Journal of Structural Integrity, vol. 5 no. 3
Type: Research Article
ISSN: 1757-9864

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Article
Publication date: 24 January 2020

Panagiota Polydoropoulou, Konstantinos Tserpes, Spiros Pantelakis and Christos Katsiropoulos

The purpose of this paper is the development of a multiscale model which simulates the effect of the dispersion, the waviness, the interphase geometry as well as the…

186

Abstract

Purpose

The purpose of this paper is the development of a multiscale model which simulates the effect of the dispersion, the waviness, the interphase geometry as well as the agglomerations of multi-walled carbon nanotubes (MWCNTs) on the Young’s modulus of a polymer filled with 0.4 Vol.% MWCNTs.

Design/methodology/approach

For the determination of the homogenized elastic properties of the hybrid material representative unit cells (RUCs) have been used. The predicted homogenized elastic properties were used for the prediction of the Young’s modulus of the filled material by simulating a finite element (FE) model of a tensile specimen. Moreover, the model has been validated by comparing the predicted values of the numerical analysis with experimental tensile results.

Findings

As the MWCNT agglomerates increase, the results showed a remarkable decrease of the Young’s modulus regarding the polymer filled with aligned MWCNTs while only slight differences on the Young’s modulus have been found in the case of randomly oriented MWCNTs. This might be attributed to the low concentration of the MWCNTs (0.4 Vol.%) into the polymer. For low MWCNTs concentrations, the interphase seems to have negligible effect on the Young’s modulus. Furthermore, as the MWCNTs waviness increases, a remarkable decrease of the Young’s modulus of the polymer filled with aligned MWCNTs is observed. In the case that MWCNTs are randomly dispersed into the polymer, both numerical and experimental results have been found to be consistent regarding the Young’s modulus.

Practical implications

The methodology used can be adopted by any system containing nanofillers.

Originality/value

Although several studies on the effect of the MWCNTs distribution on the Young’s modulus have been conducted, limited results exist by using a more realistic RUC including a periodic geometry of more than 20 MWCNTs with random orientation and a more realistic waviness of MWCNTs with aspect ratio exceeding 150.

Details

Aircraft Engineering and Aerospace Technology, vol. 92 no. 9
Type: Research Article
ISSN: 1748-8842

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Article
Publication date: 3 December 2018

Panagiota Polydoropoulou, Christos Vasilios Katsiropoulos, Andreas Loukopoulos and Spiros Pantelakis

Over the last decades, self-healing materials based on polymers are attracting increasing interest due to their potential for detecting and “autonomically” healing damage. The use…

251

Abstract

Purpose

Over the last decades, self-healing materials based on polymers are attracting increasing interest due to their potential for detecting and “autonomically” healing damage. The use of embedded self-healing microcapsules represents one of the most popular self-healing concepts. Yet, extensive investigations are still needed to convince on the efficiency of the above concept. The paper aims to discuss these issues.

Design/methodology/approach

In the present work, the effect of embedded self-healing microcapsules on the ILSS behavior of carbon fiber reinforced composite materials has been studied. Moreover, the self-healing efficiency has been assessed. The results of the mechanical tests were discussed supported by scanning electron microscope (SEM) as well as by Attenuated Total Reflection–Fourier-transform infrared spectroscopy (ATR–FTIR) analyses.

Findings

The results indicate a general trend of a degraded mechanical behavior of the enhanced materials, as the microcapsules exhibit a non-uniform dispersion and form agglomerations which act as internal defects. A remarkable value of the self-healing efficiency has been found for materials with limited damage, e.g. matrix micro-cracks. However, for significant damage, in terms of large matrix cracks and delaminations as well as fiber breakages, the self-healing efficiency is limited.

Originality/value

The results obtained by SEM analysis as well as by ATR–FTIR spectroscopy constitute a strong indication that the self-healing mechanism has been activated. However, further investigation should be conducted in order to provide definite evidence.

Details

International Journal of Structural Integrity, vol. 9 no. 6
Type: Research Article
ISSN: 1757-9864

Keywords

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Article
Publication date: 1 February 2016

Spiros Pantelakis, Dorothea Setsika, Apostolos Chamos and Anna Zervaki

The purpose of this paper is to quantify the corrosion damage evolution that has occurred on the aircraft aluminum alloy 2024 after the exposure to Exfoliation Corrosion Test…

608

Abstract

Purpose

The purpose of this paper is to quantify the corrosion damage evolution that has occurred on the aircraft aluminum alloy 2024 after the exposure to Exfoliation Corrosion Test (EXCO) solution. Moreover, the effect of the evolving corrosion damage on the materials mechanical properties has been assessed. The relevance of the corrosion damage induced by the exposure to the laboratory EXCO for linking it to the damage developed after the exposure of the material on several outdoor corrosive environments or in service is discussed.

Design/methodology/approach

To induce corrosion damage the EXCO has been used. For the quantification of corrosion damage the metallographic features considered have been pit depth, diameter, pitting density and pit shape. The effect of the evolving corrosion damage on the materials mechanical properties has been assessed by means of tensile tests on pre corroded specimens.

Findings

The results have shown that corrosion damage starts from pitting and evolves to exfoliation, after the development of intergranular corrosion. This evolution is expressed by the increase of the depth of attack, as well as through the significant growth of the diameter of the damaged areas. The results of the tensile tests performed on pre corroded material made an appreciable decrease of the materials tensile properties evident. The decrease of the tensile ductility may become dramatic and increases on severity with increasing corrosion exposure time. SEM fractography revealed a quasi-cleavage zone beneath the depth of corrosion attack.

Originality/value

The results underline the impact of corrosion damage on the mechanical behavior of the aluminum alloy 2024 T3 and demonstrate the need for further investigation of the corrosion effect on the structural integrity of the material. This work provides an experimental database concerning the quantification of corrosion damage evolution and the loss of material properties due to corrosion.

Details

International Journal of Structural Integrity, vol. 7 no. 1
Type: Research Article
ISSN: 1757-9864

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Article
Publication date: 1 March 2013

Costas A. Charitidis, Dimitrios A. Dragatogiannis and Elias P. Koumoulos

Lightweight alloys are of major concern, due to their applicability, in transport and industry applications. The purpose of this paper is to perform a comprehensive analysis of…

1808

Abstract

Purpose

Lightweight alloys are of major concern, due to their applicability, in transport and industry applications. The purpose of this paper is to perform a comprehensive analysis of time dependent properties of aluminum alloy by nanoindentation technique, through investigation of creep behavior. Additionally, possible explanations on the time dependent behavior and the influence of the hold period at maximum load and the loading rate on the elastic modulus and hardness results are also analyzed and discussed.

Design/methodology/approach

In this work, a comprehensive analysis of time dependent properties of aluminum alloy by nanoindentation technique was performed, by varying the loading rate, the maximum applied load and the loading time. The stress exponent values are derived from the displacement‐holding time curves. The present experimental setup includes three different approaches: variation of loading rate, maximum applied load and loading time. The creep deformation mechanisms of the alloy, which are dependent on experiment setup, are discussed and the characteristic “elbow” behavior in the unloading part of the curves is also reported.

Findings

The authors found that the stress exponent values obtained are dependent on the applied peak loads and indentation loading rates. Nanoindentation creep testing of aluminum AA6082‐T6 revealed significant creep displacements, where the strain rate reached a steady state after a certain time and the stress decreased with time as the displacement increased during the creep process. The slopes of strain rate versus stress curves (exponent of power‐law creep) for different maximum loads and various holding times, were investigated.

Originality/value

The stress exponent of the constant‐load indentation creep, in all three types of experiments, was found to reduce at low load region. In case of different holding load and time, the stress exponent increased almost linearly and increased very rapidly as the indent size increased, exhibiting an intense size effect.

Details

International Journal of Structural Integrity, vol. 4 no. 1
Type: Research Article
ISSN: 1757-9864

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Article
Publication date: 13 January 2020

Ş. Hakan Atapek, Spiros Pantelakis, Şeyda Polat, Apostolos Chamos and Gülşah Aktaş Çelik

The purpose of this paper is to investigate the fatigue behavior of precipitation-strengthened Cu‒2.55Ni‒0.55Si alloy, modified by the addition of 0.25 Cr and 0.25 Zr (wt%), using…

238

Abstract

Purpose

The purpose of this paper is to investigate the fatigue behavior of precipitation-strengthened Cu‒2.55Ni‒0.55Si alloy, modified by the addition of 0.25 Cr and 0.25 Zr (wt%), using mechanical and fractographical studies to reveal the effect of microstructural features on the fracture.

Design/methodology/approach

For strengthening, cast and hot forged alloy was subjected to solution annealing at 900°C for 60 min, followed by quenching in water and then aging at 490°C for 180 min. Precipitation-hardened alloy was exposed to fatigue tests at R=−1 and different stress levels. All fracture surfaces were examined within the frame of fractographical analysis.

Findings

Fine Ni-rich silicides responsible for the precipitation strengthening were observed within the matrix and their interactions with the dislocations at lower stress level resulted in localized shearing and fine striations. Although, by the addition of Cr and Zr, the matrix consisted of hard Ni, Zr-rich and Cr-rich silicides, these precipitates adversely affected the fatigue behavior acting as nucleation sites for cracks.

Originality/value

These findings contribute to the present knowledge by revealing the effect of microstructural features on the mechanical behavior of precipitation-hardened Cu‒Ni‒Si alloy modified by Cr and Zr addition.

Details

International Journal of Structural Integrity, vol. 11 no. 6
Type: Research Article
ISSN: 1757-9864

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Article
Publication date: 10 August 2015

Dorothea Setsika, Konstantinos Tserpes and Spiros Pantelakis

– The purpose of this paper is to develop a multi-scale modeling approach for simulating the tensile behavior of corroded aluminum alloy 2024 T3.

232

Abstract

Purpose

The purpose of this paper is to develop a multi-scale modeling approach for simulating the tensile behavior of corroded aluminum alloy 2024 T3.

Design/methodology/approach

The approach combines two FE models: a model of a three-dimensional representative unit cell representing a pit and a model of the tensile specimen. The models lie at the micro- and macro-scales, respectively. The local homogenized mechanical behavior of the corroded material is simulated for different pit configurations. Then, the behavior of the pits is introduced into different areas (elements) of the tensile specimen and final analyses are performed to simulate the mechanical behavior of the corroded material. The approach has been applied to six different exposure periods of the exfoliation corrosion test.

Findings

The numerical results show that the presence of pits and exfoliated areas reduces the yield strength of the material. The comparison of predicted elongation to fracture with the experimental of each exposure period value allows for the indirect assessment of the effect of hydrogen embrittlement.

Originality/value

Since the characteristics of corrosion damage evolution with exposure time are constant for the specific material, the model could be applied for the simulation of the mechanical behavior of any corroded structural part (e.g. a mechanically fastened panel) made from the aluminum 2024 T3 alloy.

Details

International Journal of Structural Integrity, vol. 6 no. 4
Type: Research Article
ISSN: 1757-9864

Keywords

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