G. Sotiriadis | University of Patras (original) (raw)

Papers by G. Sotiriadis

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Resources, Conservation and Recycling

These data were produced acquired by the AML Group at UPAT for the needs of CompInnova's (H20... more These data were produced acquired by the AML Group at UPAT for the needs of CompInnova's (H2020 FETOPEN, Grant Agreement No. 665238) during WP5 "Laser-assisted repair and related modules development" The files are in easy read formats as office files, pdf and jpeg. Also raw files are included. The data were used in the deliverables D5.1, D5.2, D5.3 and D5.4.

The paper presents the results obtained in the first two years of the H2020 CompInnova project wh... more The paper presents the results obtained in the first two years of the H2020 CompInnova project which deals with the development of an innovative approach for inspection and repair of damage in aeronautical composites. The development of a newly designed robotic platform for autonomous inspection using combined infrared thermography (IRT) and phased array (PA) non-destructive investigation for damage detection and characterization, while integrated with laser repair capabilities. PA and IRT are combined in order to detect near-surface and sub-surface damages. Development of a novel thermographic technique termed Pulsed Phase-informed Lock-In Thermography, enables for the first time the rapid and quantitative assessment of damage in the materials. Furthermore, the results are fused using machine learning and image processing techniques for detection and sizing in real time. This will provide the information needed for an automatic laser repair procedure capable of removing precisely p...

World Journal of Mechanics, 2021

In an effort to expand the insulating behavior of adhesives, incorporated nano-sized fillers, suc... more In an effort to expand the insulating behavior of adhesives, incorporated nano-sized fillers, such as multi-walled carbon nanotubes (MWCNTs) and graphene nanoplatelets (GNPs), are usually selected. Including both MWCNTs and GNPs into polymers is assumed to have complementary influence (synergy), providing a new research area. Nevertheless, limited studies have been carried out towards this hybrid direction, as it is challenging to achieve a uniform distribution of both fillers into the polymer matrix. In this work, the addition of MWCNTs and GNPs into the epoxy adhesives has been studied to increase their thermal and electrical conductivity without diminishing their mechanical properties. Three types of nano-reinforced adhesives were developed by using: 1) 2%wt. MWCNTs, 2) 8%wt. GNPs and 3) 1%wt. MWCNTs and 8%wt. GNPs. The production of nano-reinforced adhesives was achieved by using a three-roll milling technique, while during the experimental characterization single lap shear tests, thermal and electrical conductivity measurements were performed. According to the results, the introduction of nano-particles caused significant increases in electrical and thermal conductivity. MWCNTs in content of 2%wt. showed the highest improvement in the electrical conductivity (9 orders of magnitude), while GNPs in content of 8%wt. recorded the highest increase (207%) in the thermal conductivity of nano-reinforced adhesives. Finally, it was observed that the hybrid system successfully contributed to the development of a multi-functional epoxy adhesive with improved thermal and electrical properties without significantly compromising its mechanical properties.

In composites aerospace structures, there is a constant demand for multi-functional material solu... more In composites aerospace structures, there is a constant demand for multi-functional material solutions that provide enhanced electrical and thermal performance combined with increased mechanical performance, mainly concerning inter-laminar fracture characteristics. Such approaches are driven by the systemic design requirements of mass and cost reduction. The introduction on nanotechnology in the field of composites has opened new horizons towards this direction offering unique capabilities for the on demand tuning of the material properties. Nevertheless a key challenge yet exists to answer on the integration routes of nano-materials in already established and commonly used pre-impregnated fibrous reinforcements (prepreg). This paper will review various technologies developed towards this direction under the framework of ELECTRICAL project.

Polymers, 2020

Graphene nanoplatelets (GNPs) are of particular interest to the field of nano-reinforced composit... more Graphene nanoplatelets (GNPs) are of particular interest to the field of nano-reinforced composites since they possess superior mechanical, fracture, thermal, and barrier properties. Due to their geometrical characteristics, high aspect ratio (AR)/specific surface area (SSA) and their planar structure, GNPs are considered as high-potential nanosized fillers for improving performance of composites. The present study investigates the effect of SSA of GNPs on fracture properties of carbon fiber reinforced polymers (CFRPs). For this reason, two nano-doped CFRPs were produced by using two types of GNPs (C300 and C500) with different SSAs, 300 and 500 m2/g, respectively. Both types of GNPs, at the same content of 0.5 wt%, were added into the epoxy matrix of composites by applying a three-roll milling technique. The nanomodified matrix was used for the manufacturing of prepregs, while the final composite laminates were fabricated through the vacuum-bag method. Mode I and II interlaminar fr...

Polymer Composites, 2018

In this study, an optimization of a laser‐based ablation process of aeronautical carbon‐fiber rei... more In this study, an optimization of a laser‐based ablation process of aeronautical carbon‐fiber reinforced polymers is aimed via statistical tools such as the design of experiments, the analysis of variance and response surface methodologies. Three basic process parameters and their interactions is under examination that is, the laser beam scanning speed, the pulse repetition frequency and the hatching distance between two scan lines. A green short‐pulsed laser with a central wavelength at 532 nm is for the first time utilized for the ablation task with the purpose of bulk material removal prior to a structural repair. The Box–Behnken Design and a three‐level factorial design are implemented to define the minimum number of experimental trials and build an appropriate test matrix. The results identify the statistically significant parameters that affect five selected responses namely the material removal rate, the shear strength of a stepped‐lap joint and the heat affected zones measur...

Smart Intelligent Aircraft Structures (SARISTU), 2015

Improved robustness is seen as a key technology enabler for reducing the required thicknesses of ... more Improved robustness is seen as a key technology enabler for reducing the required thicknesses of composite structural parts; this reduction would, in turn, lead to direct savings in the structural mass. The aim of this study was to produce one reference and two nano-treated lower panel demonstrators for investigating the effect of nano-reinforcement on the damage tolerance behaviour of skin, stringers, bondline and on the electrical conductivity of CFRP. The selected technology, resulting from development and experiments undertaken within the SARISTU project, is carbon nanotube (CNT)-integrated prepreg material M21/34%/UD194/T800S, which is treated by University of Patras. The studies on damage tolerance improvement performed within the scope of Application Scenario 09 were used as input during determination of the manufacturing parameters for the selected co-bonding process. The demonstrators are curved panels whose overall dimensions are 2868 mm length and 1120 mm width, and that are stiffened with four omega stringers and four mechanically fastened frame pieces. This chapter reviews the design and fabrication of manufacturing tooling, the design and production of the various individual components, integration of the DiAMon Plus™ online cure monitoring system by INASCO and the assembly at TAI of the stiffened skin with the composite mousehole frames designed and manufactured by SABCA.

World-wide interest on the use of ceramic coatings as key load-bearing components for gas turbine... more World-wide interest on the use of ceramic coatings as key load-bearing components for gas turbine, aerospace and other advanced engineering applications, has led to the need for inspection techniques capable of detecting unusually small structural anomalies in these components. Modern ceramic materials offer many attractive physical and mechanical properties for a wide and

These data were produced acquired by the AML Group at UPAT for the needs of CompInnova's (H20... more These data were produced acquired by the AML Group at UPAT for the needs of CompInnova's (H2020 FETOPEN, Grant Agreement No. 665238) for the laser module trials during WP7 "Integration and validation of the prototype system and performance trials" The files are in easy read formats as office files, pdf and jpeg. Also raw files are included. The data were used in the deliverable D7.3

Materials, Oct 5, 2021

Due to their high specific strength and stiffness, Fiber Reinforced Polymers are of increasingly ... more Due to their high specific strength and stiffness, Fiber Reinforced Polymers are of increasingly demand as structural materials not only in the weight-sensitive aerospace and aeronautic industries, but also in automotive, marine, armor and sporting goods industries. However, the poor out-of-plane performance of composites has acted as a barrier for extending their use in further applications. Epoxy resin is the most commonly used polymer matrix for advanced composite materials. A considerable amount of research has been conducted regarding the toughening of epoxy resins to enhance the interlaminar fracture toughness and generally the damage tolerance of CFRPs. In the past decade, the incorporation of nanoparticles [1, 2] into the epoxy matrices offers new possibilities toward this direction.

International Journal of Impact Engineering, 2022

Abstract The constant requirement of aerospace industry to enhance the structural efficiency has ... more Abstract The constant requirement of aerospace industry to enhance the structural efficiency has driven to the usage of high-performance composite materials, either monolithic or sandwich. However, aerospace composite structures are prone to damage due to high-velocity impact events such as bird strike, hail impact, etc. These impact events can result in extensive damage including structure perforation, which will eventually degrade its post-impact residual strength. Therefore, the early detection of damage in composite structure is imperative to avoid catastrophic failure. This paper develops the computational models which predict the dynamic behavior of a helicopter composite sandwich structure undergoing a bird strike. The models are aimed to be used as virtual tools for a future digital-twin-assisted fault detection technique. Firstly, a high-fidelity (HF) FE/SPH model was developed in LS-DYNA, and it was validated against the soft body impact experiments. Afterwards, a computationally efficient low-fidelity (LF) model was developed and correlated with the high-fidelity model. It was concluded that the high-fidelity model can sufficiently accurately predict the strain history experimentally recorded by the FBG sensors, and that size of the predicted delamination area at the front face of the sandwich structure agrees very well with the experimentally observed delamination area. It was also shown that the LF model can rapidly predict the global dynamic response of sandwich panel under the impact loading, through the good agreement between the numerical strain histories with the FBG measurements. Consequently, the LF model can be used as a quick numerical guide for the identification of the loading condition, whereas the HF model can be used as virtual damage detector and estimator of damage extension before the scheduled inspection.

Journal of Composite Materials, 2020

The numerical prediction of impact-induced damage to composite materials and the subsequent resid... more The numerical prediction of impact-induced damage to composite materials and the subsequent residual strength under compression loading continue to be a challenging task. The current study proposes a calibration routine for optimizing the set of material model parameters prior to the virtual simulation of impact tests, which also simplifies the process of parameter determination. The calibration algorithm is based on the comparison of the numerical force-strain or force-displacement curves with the corresponding experimental ones to get the optimal input data, and it includes basic quasi-static material characterization tests. For the sake of simplicity, the calibration process was divided into two parts. The first part includes the in-plane loading tests (tension 0° & 90°, compression 0° & 90°, shear and open-hole tension) for calibration of orthotropic damage material model; whereas the second one consists of the mode I and mode II interlaminar fracture tests as well as the short ...

Energies, 2019

Ceramic-coated materials used in different engineering sectors are the focus of world-wide intere... more Ceramic-coated materials used in different engineering sectors are the focus of world-wide interest and have generated a need for inspection techniques that detect very small structural anomalies. Non-destructive testing is increasingly being used to evaluate coating thickness and to test for coating flaws. The main pros of non-destructive testing is that the tested object remains intact and available for continued use afterward. This paper reports on an integrated, non-destructive testing approach that combines infrared thermography and acousto-ultrasonics to evaluate advanced aerospace sandwich structure materials with the aim of exploring any potential for detecting defects of more than one type. Combined, these two techniques successfully detected fabrication defects, including inclusions and material loss.

CEAS Space Journal, 2016

The past decade extensive efforts have been invested in understanding the nano-scale and revealin... more The past decade extensive efforts have been invested in understanding the nano-scale and revealing the capabilities offered by nanotechnology products to structural materials. Integration of nano-particles into fiber composites concludes to multi-scale reinforced composites and has opened a new wide range of multi-functional materials in industry. In this direction, a variety of carbon based nano-fillers has been proposed and employed, individually or in combination in hybrid forms, to approach the desired performance. Nevertheless, a major issue faced lately more seriously due to the interest of industry is on how to incorporate these nano-species into the final composite structure through existing manufacturing processes and infrastructure. This interest originates from several industrial applications needs that request the development of new multi-functional materials which combine enhanced mechanical, electrical and thermal properties. In this work, an attempt is performed to review the most representative processes and related performances reported in literature and the experience obtained on nano-enabling technologies of fiber composite materials. This review focuses on the two main composite manufacturing technologies used by the aerospace industry; Prepreg/Autoclave and Resin Transfer technologies. It addresses several approaches for nano-enabling of composites for these two routes and reports latest achieved results focusing on performance of nano-enabled fiber reinforced composites extracted from literature. Finally, this review work identifies the gap between available nano-technology integration routes and the established industrial composite manufacturing techniques and the challenges to increase the Technology Readiness Level to reach the demands for aerospace industry applications.

Plastics, Rubber and Composites, 2009

Damage tolerance" is used to describe the attribute of a structure associated with the retention ... more Damage tolerance" is used to describe the attribute of a structure associated with the retention of the required residual strength throughout its service life, while irreversible damage mechanisms are active within the structure itself. "Design for damage tolerance" is based on the identification and quantification of the various damage mechanisms that result in the alteration-mainly deterioration-of the material properties. These may result to different material response to thermomechanical loads. In the present paper, transparent glass-fibre reinforced epoxy laminates were used to study the damage evolution sequence under tensile loading. In parallel, Acoustic Emission (AE) was employed as a non-destructive technique for the in-situ monitoring of the active damage mechanisms until the final failure of the material. Pattern recognition algorithms were utilised to classify and associate the acquired AE signals to the material's damage mechanisms. Experimental findings were compared to theoretical model predictions.

2019 15th International Conference on Distributed Computing in Sensor Systems (DCOSS)

The development of the emerging Smart Cities concept aims to enhance city infrastructures and ser... more The development of the emerging Smart Cities concept aims to enhance city infrastructures and services via the capabilities offered by information and communication technologies (ICT). One of the Smart City main pillars is Smart Mobility. Improvements to the existing physical transportation infrastructure are necessary, to accommodate safety and efficiency. This paper provides a technical overview regarding energy harvesting and packaging issues of the European Horizon 2020 funded project on Safe and green Sensor Technologies for self-explaining and forgiving Road Interactive aPplications (SAFE STRIP). In particular, it focuses on the integration of a number of on-road entities, named as On Road Units (ORU), into an intelligent road tapes/markers in order to improve road surface condition monitoring, traffic and safety. Even though ORU consists of multiple modules (ambient condition sensors, traffic sensors, communication, etc.), here we choose to discuss critical aspects regarding energy provisioning and harvesting, and packaging of this particular system. Particularly, besides primary and secondary batteries, we incorporate solar and piezoelectric harvesters as well as wireless charging receivers and antennas, while all of them co-exist under a hierarchical schema. Finally, we provide a design and implementation study, while results from a number of simulations are also outlined.

$Research paper thumbnail of Effects of graphene geometrical characteristics to the interlaminar fracture toughness of CFRP laminates$

Engineering Fracture Mechanics