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…
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.
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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.
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.
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Michael G. Papanikolaou, Michael G. Farmakopoulos and Chris A. Papadopoulos
Wear in journal bearings occurs when the operating conditions (high load, high temperature, low angular velocity or low viscosity), downgrade the ability of the bearing to carry…
Abstract
Purpose
Wear in journal bearings occurs when the operating conditions (high load, high temperature, low angular velocity or low viscosity), downgrade the ability of the bearing to carry load. The wear depth increases because the rotor comes in contact with the bearing surface. Wear in journal bearings affects their characteristics because of its influence on the thickness of the fluid film. This influence can be detected in the dynamic behavior of the rotor and especially in the dynamic stiffness and damping coefficients. The paper aims to discuss these issues.
Design/methodology/approach
In this paper, the effect of wear on the rotor dynamic stiffness and damping coefficients (K and C) of a short journal bearing is investigated. K and C in this work are estimated by using two methods a semi-analytical method and finite element (FE) analysis implemented in the ANSYS software.
Findings
The main goal of this research is to make the identification of wear in journal bearings feasible by observing the alternation of their dynamic coefficients. Both of the methods implemented are proven to be useful, while FE analysis can provide more accurate results.
Originality/value
This paper is original and has not been published elsewhere.
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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…
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.
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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.
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.
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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…
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.
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Michael Papadopoulos and Spiros Pantelakis
The Lack of Penetration (LoP) defect is one of the flaws that can be generated during the friction stir welding (FSW) process. Depending on the size, the depth and the severity of…
Abstract
Purpose
The Lack of Penetration (LoP) defect is one of the flaws that can be generated during the friction stir welding (FSW) process. Depending on the size, the depth and the severity of the LoP defect, it is possible that it is hardly detectable by optical inspection or other NDT methods. Whether detectable or not, this defect may lead to a significant degradation of the fatigue properties of the welded material, as the improperly welded zone can act as a fracture initiation site. The paper aims to discuss these issues.
Design/methodology/approach
In this experimental investigation, an attempt is made to assess and compare the fatigue behavior of FSW aluminum joints with and without the LoP defect.
Findings
It was found that the LoP defect affects the fatigue behavior of the welded material at high stress levels whereas the effect diminishes with decreasing stress levels.
Originality/value
Depending on the design stress levels, the LoP defect may dominate fracture and thus, the welding parameters should be carefully selected so as to avoid such defect.
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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…
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.