In recent years, light detection and ranging (LiDAR) technology has gained popularity in various applications, including remote sensing of Particulate Matter (PM) absolute concentrations. Raymetrics PMeye is a unique platform consisting... more
In recent years, light detection and ranging (LiDAR) technology has gained popularity in various applications, including remote sensing of Particulate Matter (PM) absolute concentrations. Raymetrics PMeye is a unique platform consisting of a state-of-the-art scanning lidar, innovative algorithms and auxiliary sensors, used for large areas PM concentrations monitoring. Using a novel inversion scheme for transforming raw signals to aerosol concentrations, PMeye is one of its kind for aerosol monitor in urban or/and industrial areas. Measurements performed at a steel factory in Latin America, a highly variable area in terms of emission sources, support the effectiveness of the overall system. Measurements evaluation against a light scattering in situ PM counter, placed at major emission sources on various ranges and directions from the lidar, present high correlation and very low mean relative differences.
Research Interests:
Research Interests:
In the present study the estimation of the blast wave by two types of nite element methods is investigated: Eulerian multi-material modeling and pure Lagrangian. The main goal is to compare and study their ability to predict the clearing... more
In the present study the estimation of the blast wave by two types of nite element methods is investigated: Eulerian multi-material modeling and pure Lagrangian. The main goal is to compare and study their ability to predict the clearing eect during blast. Element shape and improvements on the codes are also considered. For the Lagrangian nite element models the load is applied by using an empirical method, deriving from databases, for the time-spatial distribution of the pressure proles. In the ideal case of the above method the blast load is applied as an equivalent triangular pulse to represent the decay of the incident and reected pressure. The implementation of this method in LS-DYNA is improved and takes a more realistic approach, assuming an exponential decay of the pressure with time. In the case of the Eulerian models the inuence of the shape of elements and its inuence on the incident and reected pressure in three types of simulations, using rectangular, cylindrical and sp...
Research Interests:
The objective of the present study is the assessment of the impact performance and the concluded thermal conductivity of epoxy resin reinforced by layered Graphene Nano-Platelets (GNPs). The two types of used GNPs have different average... more
The objective of the present study is the assessment of the impact performance and the concluded thermal conductivity of epoxy resin reinforced by layered Graphene Nano-Platelets (GNPs). The two types of used GNPs have different average thicknesses, <4 nm for Type 1 and 9–12 nm for Type 2. Graphene-based polymers containing different GNP loading contents (0.5, 1, 5, 10, 15 wt.%) were developed by using the three-roll mill technique. Thermo-mechanical (Tg), impact tests and thermal conductivity measurements were performed to evaluate the effect of GNPs content and type on the final properties of nano-reinforced polymers. According to the results, thinner GNPs were proven to be more promising in all studied properties when compared to thicker GNPs of the same weight content. More specifically, the glass transition temperature of nano-reinforced polymers remained almost unaffected by the GNPs inclusion. Regarding the impact tests, it was found that the impact resistance of the doped...
Research Interests:
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... 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...
Research Interests:
Research Interests:
The paper presents an experimental investigation of the mode II fracture toughness behavior of dissimilar metal-composite adhesive joints using the end-notched flexure (ENF) test. The adhesive joint under study consists of a thin titanium... more
The paper presents an experimental investigation of the mode II fracture toughness behavior of dissimilar metal-composite adhesive joints using the end-notched flexure (ENF) test. The adhesive joint under study consists of a thin titanium sheet joined with a thin CFRP laminate and is envisioned tobe applied in the hybrid laminar flow control system of future aircraft. Four different industrial technologies for the manufacturing of the joint areevaluated; co-bonding with and without adhesive and secondary bonding using either a thermoset or a thermoplastic composite. The vacuum-assisted resin transfer molding (VARTM) technique is employed for the manufacturing of the titanium-CFRP joint. After manufacturing, the joint is stiffened from its both sides with two aluminum backing beams to prevent large deformations during the subsequent ENF tests. Towards the fracture toughness determination from the experimental data, an analytical model recently reported by the authors is applied; that...
Research Interests:
Purpose Utilizing through-the-thickness pin reinforcement in metal-to-composite joints can significantly increase the joint mechanical properties, enabling the introduction to a whole new field of applications in joining technology.... more
Purpose Utilizing through-the-thickness pin reinforcement in metal-to-composite joints can significantly increase the joint mechanical properties, enabling the introduction to a whole new field of applications in joining technology. However, with the rise of advanced pin manufacturing techniques – such as additive layer manufacturing, little research has been performed on the pin shape optimization and its behavior. The paper aims to discuss this issue. Design/methodology/approach In this study, a numerical shape optimization algorithm is used to produce optimized pin shapes for several initial pin dimension parameters, having as objective to achieve a more uniform stress distribution along the surface of the pin, enhancing the pin strength and joint integrity. Findings Results showed that pin shape is a crucial factor in the mechanical response of the pin. In Mode I, the presence of an undercut feature on the pin head can increase the ultimate load of the pin by +250 percent, while...
Research Interests:
The effect of fatigue on the interfacial properties of carbon fibre model composites was investigated, employing the fragmentation test. Continuous and discontinuous single carbon fibre model composites were manufactured and subjected to... more
The effect of fatigue on the interfacial properties of carbon fibre model composites was investigated, employing the fragmentation test. Continuous and discontinuous single carbon fibre model composites were manufactured and subjected to strain controlled fatigue loading. Whilst no effect of cyclic loading on the fibre/matrix interface of continuous fibres was detected, a significant reduction in the interfacial strength of the discontinuous fibre specimens was measured.
Research Interests:
Carbon nanotubes (CNTs) because of their properties are alleged to be the key candidate additives for improving the mechanical properties of polymers and carbon fibre reinforced polymers (CFRPs). Nevertheless in order for the reinforcing... more
Carbon nanotubes (CNTs) because of their properties are alleged to be the key candidate additives for improving the mechanical properties of polymers and carbon fibre reinforced polymers (CFRPs). Nevertheless in order for the reinforcing effect of the nanotubes to be of practical use, the CNTs have to be mixed with the matrix material. In the current work an effort was made to chemically graft Multi-Wall Carbon Nanotubes (MWCNTs) on the actual reinforcing Carbon Fibres (CFs) in order to skip the sometimes complex mixing stage. Two different solutions were used in order to treat/prepare the CNTs; a) an acid solution of H2SO4/HNO3 and, b) a toluene solution. The treated CFs were added to each solution, sonic bathed with deionised water and then dried in an oven. The resulting CFs were examined under SEM and both the solutions used proved to be reasonable successful with further investigation/optimisation to be necessary.
Research Interests:
The free vibration response of [±Θ] ns orthogonal, simply supported (all around) composite laminated plates was studied, assuming linear viscoelastic behaviour of the constitutive lamina material. The problem was solved numerically and... more
The free vibration response of [±Θ] ns orthogonal, simply supported (all around) composite laminated plates was studied, assuming linear viscoelastic behaviour of the constitutive lamina material. The problem was solved numerically and the results were verified in the special case of [0]2 n laminate against the analytical solution, which is also provided. Stability and convergence problems were discussed analytically. Eigenfrequency values and modal damping characteristics were calculated for the first nine mode shapes. Furthermore, keeping constant the plate thickness, the effect of the lamina thickness on the vibration characteristics of the plate was examined.
Research Interests:
Low energy impact in composite laminates is often a crucial and destructive loading condition since it leads to significant internal damage, undetectable by visual inspection. Low velocity impact upon a laminated plate imposes a complex... more
Low energy impact in composite laminates is often a crucial and destructive loading condition since it leads to significant internal damage, undetectable by visual inspection. Low velocity impact upon a laminated plate imposes a complex stress state mainly due to the structural heterogeneity resulting by the ply orientation of the constituent laminae and the contact boundary conditions, which lead to a loading path that varies with the impact energy and the properties of the impactor-impacted plate system. The present work deals with the development of a numerical scheme for the calculation of the dynamic response of any type of laminated composite plates under low-velocity impact. The governing non-linear, second order differential equations are derived using p-Ritz admissible polynomial functions and the elastoplastic version of the Hertzian contact law. The dynamic response of fully clamped, cross ply and angle ply composite plates are investigated.
Research Interests:
Damage developing during fatigue of composite laminates affects both dynamic modulus of elasticity and damping coefficient of the material. It has been shown that the effect of fatigue on the damping coefficient is of particular... more
Damage developing during fatigue of composite laminates affects both dynamic modulus of elasticity and damping coefficient of the material. It has been shown that the effect of fatigue on the damping coefficient is of particular importance. The damping variation could be used to characterise the damage state of the material, produced by fatigue. A model relating damage with damping was developed to correlate damage development to mechanical response. The damping coefficients of the composite of the fatigue test were measured at various stages, using the flexural free vibration of the test coupon hi cantilever configuration. The method was applied both in multidirectional and unidirectional laminates.
Research Interests:
Research Interests:
Research Interests:
... Soc. Am. 92, 5 (1992). 3 SB Sinha, and KA Elsibai, J. Titer. St-r., 19, S (1996). 4 SJ Zinkle, LL Snead, Internal Report, Oak Ridge Notional Laboratory, (1998). 5 Abo-El-Nour N. Abd-Alla, and Amira. AS Al-Dawy, Int. J. Math. Math.... more
... Soc. Am. 92, 5 (1992). 3 SB Sinha, and KA Elsibai, J. Titer. St-r., 19, S (1996). 4 SJ Zinkle, LL Snead, Internal Report, Oak Ridge Notional Laboratory, (1998). 5 Abo-El-Nour N. Abd-Alla, and Amira. AS Al-Dawy, Int. J. Math. Math. Scien. 23, 8 (2000). ...
Research Interests:
We consider the problem of scattering of a longitudinal or a transverse plane elastic wave by a general ellipsoidal cavity in the low-frequency region. Explicit closed-form solutions for the zeroth- and first-order approximations are... more
We consider the problem of scattering of a longitudinal or a transverse plane elastic wave by a general ellipsoidal cavity in the low-frequency region. Explicit closed-form solutions for the zeroth- and first-order approximations are provided in terms of the physical and geometric characteristics of the scatterer, as well as the direction cosines of the incidence and observation points. This was made possible with the introduction of an analytical technique based on the Papkovich representations and their interdependence. The leading low-frequency term for the normalized spherical scattering amplitudes and the scattering cross section are also given explicitly. Degenerate ellipsoids corresponding to the prolate and oblate spheroids, the sphere, the needle, and the disc are considered as special cases.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
ABSTRACT
Research Interests:
ABSTRACT
Research Interests: Engineering, Materials Science, Solid Mechanics, Silicon Carbide, Coating, and 13 morePower Law, Composite Material, High Temperature, Cyclic Stress Ratio, CHEMICAL SCIENCES, Room Temperature, Microstructures, Dynamic Loading, Fatigue Life, Stress (Linguistics), Failure Mechanism, Volume Fraction, and Fatigue Limit
ABSTRACT
Research Interests:
The maximum opening stress and minimum energy density criteria were adopted and modified in order to predict the path of a crack at the interface of two homogeneous, isotropic and elastic solids. The results obtained from the analytical... more
The maximum opening stress and minimum energy density criteria were adopted and modified in order to predict the path of a crack at the interface of two homogeneous, isotropic and elastic solids. The results obtained from the analytical (elastic) solution are compared with these from a FEM analysis (elastic-plastic case) but only for the maximum opening stress criterion. The elastic-plastic analysis revealed that crack advance along the interface is dictated from a combination of critical normal and shear stresses. Experimental data for the Si3N4)Fe/Si3N4 system support this result and indicate the limitation of the elastic solution. For the case of crack advance in one of the two adjacent materials, the comparison between analytical and numerical results has revealed similar values for the crack propagation angle. Comparison of the two criteria with experimental data taken from the Si3N4/Fe/Si3N4 system shows very good agreement between theory and experiment.
Research Interests:
Research Interests:
Research Interests:
A 30KW Wind Turbine, designed and constructed by Greek manufacturers and Research Institutions, is combined with a modular Reverse Osmosis Desalination Plant, in order to: (1) obtain transfer of technology in the design and construction... more
A 30KW Wind Turbine, designed and constructed by Greek manufacturers and Research Institutions, is combined with a modular Reverse Osmosis Desalination Plant, in order to: (1) obtain transfer of technology in the design and construction of all parts of the wind Turbine / Desalination system, with special care to critical components, such as: (1.a) aerodynamic design of rotor (1.b) construction of blades (1.c) selection of membranes (1.d) load management and monitoring system (2) obtain the technical capabilities and infrastructure, which allow in the future for: (2.a) design and commercial exploitation of similar systems (2.b) construction of critical and high-added value components of similar systems (2.c) assembly, procurement and maintenance of similar systems (3) lead to the formation of a consortium of companies and research institutions, housed at the Patras Science Park, which will constitute a pioneering Organisation for the design and construction of integrated systems for ...
Rolling element bearings are of great importance in industrial applications as well as in critical applications in transport. Signal processing techniques can enhance the ability of bearings condition monitoring to identify faults during... more
Rolling element bearings are of great importance in industrial applications as well as in critical applications in transport. Signal processing techniques can enhance the ability of bearings condition monitoring to identify faults during operation. In this work, state of the art signal denoising techniques are applied for condition monitoring of roller bearings. In particular wavelet denoising with NeighBlock threshold technique is applied in vibration waveforms. A standard data base for lifelong operation of roller bearings is used for the tests. The condition monitoring efficiency of a statistical feature is assessed taking into account both raw and denoised bearing vibration signals. A brief assessment shows that such a signal denoising technique can evidently improve the remaining useful life estimation as well as the change point detection of the structural health of the asset.
Research Interests:
Research Interests:
In this work, the aging of two different carbon fiber reinforced cyanate ester polymer matrices (CFRP-A and CFRP-B) was investigated after their exposure to aggressive thermo-oxidative conditions. The materials’ degradation at 230℃ under... more
In this work, the aging of two different carbon fiber reinforced cyanate ester polymer matrices (CFRP-A and CFRP-B) was investigated after their exposure to aggressive thermo-oxidative conditions. The materials’ degradation at 230℃ under 1 atm for 30 days in oxidative atmosphere was evaluated with regard to changes in mass (mass loss), glass transition temperature Tg, interlaminar shear strength, as well as physical characteristics that were examined under scanning electron microscopy. For both the systems, the aging study showed significant mass loss that reached ∼4% in the case of CFRP-B. The mass loss is accompanied with a considerable decrease in interlaminar shear strength and Tg properties. The study of the scanning electron microscopic images clearly shows the surface deterioration due to the oxidation process, accompanied with formation of matrix microcracking and development of matrix-fiber interfacial debonding. The contribution of the chains scission to the materials degr...
Research Interests:
ABSTRACT Based on the resistance curve (R-curve) behaviour of ceramic matrix composites (CMCs) determined under either quasi-static or cyclic loading, the crack-face fibre bridging stress field is determined for the compact tension (CT)... more
ABSTRACT Based on the resistance curve (R-curve) behaviour of ceramic matrix composites (CMCs) determined under either quasi-static or cyclic loading, the crack-face fibre bridging stress field is determined for the compact tension (CT) test specimen geometry. Two different methods have been used for the analysis of the bridging stresses. The first considers a compliance approach. Using the difference in compliance calibration curves with and without bridging and assuming a power-law relation between bridging stress and crack opening displacement, the bridging stress field was calculated. The second approach uses the existence of an invariant stress reversal point in the CT geometry and assuming that the material exhibits linear elastic fracture behaviour, yields a recurrence relation for the bridging stresses resulting in a piece-wise constant stress function. Both models are applied to the experimentally determined fracture behaviour of a 2D carbon/carbon (C/C) composite, and the resulting bridging stress distributions are discussed.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
The acoustic emission (AE) technique is a powerful nondestructive tool for health monitoring of structures and mechanical components, especially due to its sensitivity to capture high frequency signals, which are associated with the early... more
The acoustic emission (AE) technique is a powerful nondestructive tool for health monitoring of structures and mechanical components, especially due to its sensitivity to capture high frequency signals, which are associated with the early stages of damage development and evolution. The aim of the present work is twofold. The first is the evaluation of a new concept of transducer mounting on rotating structures without the use of the expensive solution of the slip ring. The new concept is realized in a single stage in-house built gearbox setup. The second is the evaluation of the potential of the acquired with the new concept AE signals in distinguishing between different types of artificially induced damage on the gears. Run-in tests were carried out to study the effect of gear damage on the AE recordings. The acoustic emission signature of the healthy gears is first acquired. Then artificial defects are seeded and the acquisition is repeated. The AE signals are analyzed, and their ...