Radu Negru - Academia.edu (original) (raw)

ISI Journals by Radu Negru

The notch effect in Polyurethane materials of different densities is investigated. Tensile specim... more The notch effect in Polyurethane materials of different densities is investigated. Tensile specimens with lateral V and U symmetric notches and with holes of different diameters were tested. The material parameters inherent stress and critical distance are determined using a linear elastic finite element analysis in conjunction with experimental results of average maximum load. The paper proposed an original correlation between critical distance and the cell diameter of the cellular structure, respectively between inherent stress and the ultimate tensile strength of Polyurethane materials. Then for single edge notch specimens a relationship between critical distance and applied mixed mode is found and successfully applied to assess the brittle mixed mode of Polyurethane materials.

Papers by Radu Negru

Materials

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

Journal of Adhesion Science and Technology, 2014

ABSTRACT Sealant materials are typically employed in dentistry in order to prevent the developmen... more ABSTRACT Sealant materials are typically employed in dentistry in order to prevent the development of cavities on the teeth. They prevent bacterial adhesion to enamel, thus arresting the development of demineralization and of caries. In this study, the critical zone of the interface between different sealant materials and the results of the dental work for the teeth processed were investigated ex vivo using swept source (SS) optical coherence tomography (OCT). Optical inspection and X-ray investigation revealed no defects, while SS-OCT proved capable to asses exactly the position, the nature, and the dimensions of each type of these defects. Specifically, different failures were targeted into the structure of pit and fissure sealants, including bubbles, internal cracks, structural defects of sealant material, and structural defects of enamel, with uncovered sealant material and enamel/sealant interface (marginal integrity and marginal adaptation of dental sealant). The investigation of the possible types of defects that may appear into this dental interface was thus accomplished – for the dental practitioner.

Key Engineering Materials, 2013

Using the asymmetric semi-circular bend specimen (ASCB) a set of mixed-mode fracture tests were c... more Using the asymmetric semi-circular bend specimen (ASCB) a set of mixed-mode fracture tests were carried out in the full range from pure mode I to pure mode II. The tests were conducted on two polyurethane materials characterized by different properties. The fracture parameters were obtained from experiments and are compared with the predictions based on the generalized MTS criterion (GMTS). The agreement between the experimental results and those predicted based on the GMTS criterion is discussed finally.

Fatigue & Fracture of Engineering Materials & Structures, 2014

ABSTRACT The paper is focused on failure assessment of the shaft of a pumped storage unit. The sh... more ABSTRACT The paper is focused on failure assessment of the shaft of a pumped storage unit. The shaft failure occurred during normal operation of the hydropower unit after 35 years of service. Three different methods are applied in order to assess its lifetime. Firstly, a finite element analysis was performed in order to obtain the static stress distribution and to apply a strain-based crack initiation for the shaft under torsion load. The number of cycles for crack propagation was obtained using the Paris law for mode III. More precisely, the lifetime assessment of the shaft is obtained based on a low-cycle fatigue analysis for estimating the number of cycles for crack initiation and then followed by that for fatigue crack propagation. Secondly, an analytical estimation based on failure assessment diagram is carried out for circumferential crack in order to determine the safe/unsafe region, where the shaft can operate with a crack. The failure assessment diagram for mode III loading was plotted in order to obtain the critical circumferential crack using the stress intensity factor solution and three analytical solutions for plastic zone. Thirdly, the theory of critical distance is employed for estimating the shaft life under torsional loading. A good agreement is obtained between the estimated results and experimental data for the shaft life and the crack length.

Computational Materials Science, 2012

ABSTRACT In this paper the hydraulic stresses induced in a Francis turbine runner blade by steady... more ABSTRACT In this paper the hydraulic stresses induced in a Francis turbine runner blade by steady fluid flow were investigated. Based on the one-way coupled simulation, the approach consists of a fluid flow analysis which provides the distribution of the fluid pressure on the blade, followed by the structural finite element analysis. The three dimensional turbulent flow in both distributor and runner of Francis turbines were computed. The computational domains correspond to interblade channels for the Francis turbine distributor and runner, respectively. In order to couple the steady absolute distributor flow field with the runner steady relative flow, a mixing interface technique is used on the conical distributor–runner interface. The hydrodynamic field is computed in seven operating points at constant head from part load to full load conditions. The pressure coefficient distribution on the blade is plotted in order to evaluate the blade loading and region with cavitational risk. Further, the stress distributions were obtained by a structural finite element analysis performed for the steady loading in order to determine the areas with highest stress values.

imsar.bu.edu.ro

Abstract: Digital image correlation and three-dimensional finite element investigations are done ... more Abstract: Digital image correlation and three-dimensional finite element investigations are done for analyzing strain concentration for a semicircular notch and two V-notches with different radii. Along the notch bisector normalized true opening strains are represented as a ...

Mathematics, 2021

In this article, the yielding and plastic flow of a rapid-prototyped ABS compound was investigate... more In this article, the yielding and plastic flow of a rapid-prototyped ABS compound was investigated for various plane stress states. The experimental procedures consisted of multiaxial tests performed on an Arcan device on specimens manufactured through photopolymerization. Numerical analyses were employed in order to determine the yield points for each stress state configuration. The results were used for the calibration of the Hosford yield criterion and flow potential. Numerical analyses performed on identical specimen models and test configurations yielded results that are in accordance with the experimental data.

The analysis results of flow induced stress field in a Francis turbine runner blade is presented.... more The analysis results of flow induced stress field in a Francis turbine runner blade is presented. The geometrical model was reduced to one blade, due to the periodical symmetry of the runner. The pressure field obtained from computational fluid dynamics (CFD) was applied as a mechanical load on the blade surface in the structural finite element analysis (FEA). The stress distributions obtained for different operating regimes are presented and sensitive areas to fatigue crack initiation are identified.

ACTA Universitatis Cibiniensis, 2017

The use of magnesium alloys in the automotive industry increased in the last decade because of th... more The use of magnesium alloys in the automotive industry increased in the last decade because of their low weight and relative good mechanical properties. However, the variable loading conditions require a good fatigue behavior. This paper summaries the fatigue properties of magnesium alloys and presents new fatigue curve results for die cast AM50 magnesium alloy.

Theoretical and Applied Fracture Mechanics, 2017

The Averaged Strain Energy Density (ASED) criteria is applied herein to reinterpret the fracture ... more The Averaged Strain Energy Density (ASED) criteria is applied herein to reinterpret the fracture data of PUR foams. Four type of specimens were used in fracture tests. The ASED parameters were determined based on micromechanical models. The volume control for cracked components is represented by a circle with the centre at the crack tip for all type of fracture modes. It was also demonstrated that the SED parameters obtained from pure mode I could be applied successfully for mixed modes and mode II. This approach represents an useful engineering tool for the assessment of brittle fracture of components made of cellular materials.

Frattura ed Integrità Strutturale, 2014

This paper investigates the fracture properties and notch effect of PUR materials with four diffe... more This paper investigates the fracture properties and notch effect of PUR materials with four different densities. The asymmetric semi-circular bend specimen was adapted to perform mixed mode fracture toughness tests. This semi-circular specimen with radius R, which contains an edge crack of length a oriented normal to the specimen edge, loaded with a three point bending fixture, was proved to give wide range of mixed modes from pure mode I to pure mode II, only by changing the position of one support. Different types of notched specimens were considered for notch effect investigations and the Theory of Critical Distances was applied. It could be seen that the critical distances are influenced by the cellular structure of investigated materials.

A corner joint was investigated using finite element method. Since the geometry along the width o... more A corner joint was investigated using finite element method. Since the geometry along the width of the corner joint is uniform and load does not change in that direction, the problem was assumed to be plane strain. In addition, it was assumed that the adherents (aluminum) and adhesive (epoxy resin) had linear properties. The joint was analysed under one loading condition, a bending moment applied at the upper end of the right-angled plate. The stress distributions in the joint area are given by the stress contours and XY plots. Since the geometry of the joint affects the analysis, in addition were investigated the influences on the stress distributions of the bonding length and adhesive thickness. From the results it was found that the stress distributions are similar for different bond lengths, but the maximum stresses are increased with decreasing adhesive thickness. These results can be useful in adhesive-bonded corner joints design.

Design, Fabrication and Economy of Metal Structures, 2013

ABSTRACT This paper presents the numerical determination of stress intensity factor for a 3D crac... more ABSTRACT This paper presents the numerical determination of stress intensity factor for a 3D cracked T – joint using FRANC 3D software. The analysis preformed were linked between the finite element analysis using Abaqus software to obtain the stress state used in Franc 3D for stress intensity factor determination in crack resence in structure. For many applications like hydraulic Francis turbine rotors, the joints between blades and crow, and blades and rings are T-joints types with connections radius. In this paper an example of simplified T-joint with cracks presence is presented. For this cracked T joint structure a numerical analysis in bending and tension loadings was performed to obtain the stress intensity factors. The material used in analysis is a stainless steel named AISI 304. A stress state analysis was performed to obtain the maximum stress zone in T joint from where the crack can occurs. From this zone were initiate a quarter elliptical corner crack and propagated in the structure. For this crack propagated were obtained the stress intensity factors KI in loading mode I along the crack fronts. The stress intensity factor offer information for a future analysis, when in structure occur defects of cracks type related the operating condition

Advanced Engineering Forum, 2013

The key ingredient for any turbine runners design procedure and failure analysis is the material ... more The key ingredient for any turbine runners design procedure and failure analysis is the material and its mechanical and fatigue properties. Starting from this observation, a series of static and dynamic tests were performed on the T10CuNiCr180 stainless steel after more than three decades of service. The fatigue tests were carried out under constant amplitude at a stress ratio of 0.1 and a frequency of 20 Hz. In the high cycle fatigue range, the S-N median curve was plotted and the fatigue limit for 3106 cycles to failure was determined at 93.35 [MPa] expressed in stress amplitude. The casting and welding defects that were observed on fracture surfaces explained this lower fatigue limit. The fatigue crack growth tests were performed on compact tension specimens and a three-parameter model was used to plot the crack length versus number of cycles curves. In addition, the material constants from Paris law were determined. Finally, the experimental results are compared against publishe...

International Journal of Fracture, 2013

Using the asymmetric semi-circular bend specimen (ASCB) with vertical crack, a series of mixed mo... more Using the asymmetric semi-circular bend specimen (ASCB) with vertical crack, a series of mixed mode I/II fracture tests were performed on two different rigid polyurethanes materials. The experimental results obtained for brittle fracture are compared with the theoretical predictions based on MTS and SED criteria. The results demonstrate that the SED criterion gives better results for mode II loading conditions, while for mode I and predominantly mode I both criteria are accurate.

Polymers

This work investigates the critical plastic strain variation with stress triaxiality and the Lode... more This work investigates the critical plastic strain variation with stress triaxiality and the Lode angle parameter for an Acrylonitrile butadiene styrene (ABS)-based proprietary blend compound (commercial name VeroWhitePlus™ RGD835) manufactured through photopolymerization. Various triaxial states of stress and Lode angles were obtained with the help of notched flat specimens used in tensile loadings, notched round specimens used in compression (upsetting) tests and butterfly specimens used in Arcan tests. The tests were replicated using finite element analyses in order to evaluate the aforementioned parameters.

IOP Conference Series: Materials Science and Engineering, 2018

This paper investigates the compressive and flexural behavior of a closed-cell fly ashbased geopo... more This paper investigates the compressive and flexural behavior of a closed-cell fly ashbased geopolymer foam with a density of 240 kg/m 3. The influence of loading speed (0.1, 10, 100, 250 and 500 mm/min) and anisotropy (in-plane and out-of-plane directions) on the compressive mechanical properties at room temperature were investigated. Under compressive loads, the stress-strain curves shows a cellular material typical behavior with three different regions: linear-elastic, plateau and densification region. On the other hand, the three-point bending tests were carried out on both un-notched and notched specimens (for fracture toughness determination). In compression, the foam progressively collapsed with a complete destruction of the successive rows of cells, while in the case of bending it exhibited a brittle behavior without plastic deformation, the fracture occurring by the propagation of a single crack.

Theoretical and Applied Fracture Mechanics, 2015

The notch effect in Polyurethane materials of different densities is investigated. Tensile specim... more The notch effect in Polyurethane materials of different densities is investigated. Tensile specimens with lateral V and U symmetric notches and with holes of different diameters were tested. The material parameters inherent stress and critical distance are determined using a linear elastic finite element analysis in conjunction with experimental results of average maximum load. The paper proposed an original correlation between critical distance and the cell diameter of the cellular structure, respectively between inherent stress and the ultimate tensile strength of Polyurethane materials. Then for single edge notch specimens a relationship between critical distance and applied mixed mode is found and successfully applied to assess the brittle mixed mode of Polyurethane materials.

The notch effect in Polyurethane materials of different densities is investigated. Tensile specim... more The notch effect in Polyurethane materials of different densities is investigated. Tensile specimens with lateral V and U symmetric notches and with holes of different diameters were tested. The material parameters inherent stress and critical distance are determined using a linear elastic finite element analysis in conjunction with experimental results of average maximum load. The paper proposed an original correlation between critical distance and the cell diameter of the cellular structure, respectively between inherent stress and the ultimate tensile strength of Polyurethane materials. Then for single edge notch specimens a relationship between critical distance and applied mixed mode is found and successfully applied to assess the brittle mixed mode of Polyurethane materials.

Materials

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

Journal of Adhesion Science and Technology, 2014

ABSTRACT Sealant materials are typically employed in dentistry in order to prevent the developmen... more ABSTRACT Sealant materials are typically employed in dentistry in order to prevent the development of cavities on the teeth. They prevent bacterial adhesion to enamel, thus arresting the development of demineralization and of caries. In this study, the critical zone of the interface between different sealant materials and the results of the dental work for the teeth processed were investigated ex vivo using swept source (SS) optical coherence tomography (OCT). Optical inspection and X-ray investigation revealed no defects, while SS-OCT proved capable to asses exactly the position, the nature, and the dimensions of each type of these defects. Specifically, different failures were targeted into the structure of pit and fissure sealants, including bubbles, internal cracks, structural defects of sealant material, and structural defects of enamel, with uncovered sealant material and enamel/sealant interface (marginal integrity and marginal adaptation of dental sealant). The investigation of the possible types of defects that may appear into this dental interface was thus accomplished – for the dental practitioner.

Key Engineering Materials, 2013

Using the asymmetric semi-circular bend specimen (ASCB) a set of mixed-mode fracture tests were c... more Using the asymmetric semi-circular bend specimen (ASCB) a set of mixed-mode fracture tests were carried out in the full range from pure mode I to pure mode II. The tests were conducted on two polyurethane materials characterized by different properties. The fracture parameters were obtained from experiments and are compared with the predictions based on the generalized MTS criterion (GMTS). The agreement between the experimental results and those predicted based on the GMTS criterion is discussed finally.

Fatigue & Fracture of Engineering Materials & Structures, 2014

ABSTRACT The paper is focused on failure assessment of the shaft of a pumped storage unit. The sh... more ABSTRACT The paper is focused on failure assessment of the shaft of a pumped storage unit. The shaft failure occurred during normal operation of the hydropower unit after 35 years of service. Three different methods are applied in order to assess its lifetime. Firstly, a finite element analysis was performed in order to obtain the static stress distribution and to apply a strain-based crack initiation for the shaft under torsion load. The number of cycles for crack propagation was obtained using the Paris law for mode III. More precisely, the lifetime assessment of the shaft is obtained based on a low-cycle fatigue analysis for estimating the number of cycles for crack initiation and then followed by that for fatigue crack propagation. Secondly, an analytical estimation based on failure assessment diagram is carried out for circumferential crack in order to determine the safe/unsafe region, where the shaft can operate with a crack. The failure assessment diagram for mode III loading was plotted in order to obtain the critical circumferential crack using the stress intensity factor solution and three analytical solutions for plastic zone. Thirdly, the theory of critical distance is employed for estimating the shaft life under torsional loading. A good agreement is obtained between the estimated results and experimental data for the shaft life and the crack length.

Computational Materials Science, 2012

ABSTRACT In this paper the hydraulic stresses induced in a Francis turbine runner blade by steady... more ABSTRACT In this paper the hydraulic stresses induced in a Francis turbine runner blade by steady fluid flow were investigated. Based on the one-way coupled simulation, the approach consists of a fluid flow analysis which provides the distribution of the fluid pressure on the blade, followed by the structural finite element analysis. The three dimensional turbulent flow in both distributor and runner of Francis turbines were computed. The computational domains correspond to interblade channels for the Francis turbine distributor and runner, respectively. In order to couple the steady absolute distributor flow field with the runner steady relative flow, a mixing interface technique is used on the conical distributor–runner interface. The hydrodynamic field is computed in seven operating points at constant head from part load to full load conditions. The pressure coefficient distribution on the blade is plotted in order to evaluate the blade loading and region with cavitational risk. Further, the stress distributions were obtained by a structural finite element analysis performed for the steady loading in order to determine the areas with highest stress values.

imsar.bu.edu.ro

Abstract: Digital image correlation and three-dimensional finite element investigations are done ... more Abstract: Digital image correlation and three-dimensional finite element investigations are done for analyzing strain concentration for a semicircular notch and two V-notches with different radii. Along the notch bisector normalized true opening strains are represented as a ...

Mathematics, 2021

In this article, the yielding and plastic flow of a rapid-prototyped ABS compound was investigate... more In this article, the yielding and plastic flow of a rapid-prototyped ABS compound was investigated for various plane stress states. The experimental procedures consisted of multiaxial tests performed on an Arcan device on specimens manufactured through photopolymerization. Numerical analyses were employed in order to determine the yield points for each stress state configuration. The results were used for the calibration of the Hosford yield criterion and flow potential. Numerical analyses performed on identical specimen models and test configurations yielded results that are in accordance with the experimental data.

The analysis results of flow induced stress field in a Francis turbine runner blade is presented.... more The analysis results of flow induced stress field in a Francis turbine runner blade is presented. The geometrical model was reduced to one blade, due to the periodical symmetry of the runner. The pressure field obtained from computational fluid dynamics (CFD) was applied as a mechanical load on the blade surface in the structural finite element analysis (FEA). The stress distributions obtained for different operating regimes are presented and sensitive areas to fatigue crack initiation are identified.

ACTA Universitatis Cibiniensis, 2017

The use of magnesium alloys in the automotive industry increased in the last decade because of th... more The use of magnesium alloys in the automotive industry increased in the last decade because of their low weight and relative good mechanical properties. However, the variable loading conditions require a good fatigue behavior. This paper summaries the fatigue properties of magnesium alloys and presents new fatigue curve results for die cast AM50 magnesium alloy.

Theoretical and Applied Fracture Mechanics, 2017

The Averaged Strain Energy Density (ASED) criteria is applied herein to reinterpret the fracture ... more The Averaged Strain Energy Density (ASED) criteria is applied herein to reinterpret the fracture data of PUR foams. Four type of specimens were used in fracture tests. The ASED parameters were determined based on micromechanical models. The volume control for cracked components is represented by a circle with the centre at the crack tip for all type of fracture modes. It was also demonstrated that the SED parameters obtained from pure mode I could be applied successfully for mixed modes and mode II. This approach represents an useful engineering tool for the assessment of brittle fracture of components made of cellular materials.

Frattura ed Integrità Strutturale, 2014

This paper investigates the fracture properties and notch effect of PUR materials with four diffe... more This paper investigates the fracture properties and notch effect of PUR materials with four different densities. The asymmetric semi-circular bend specimen was adapted to perform mixed mode fracture toughness tests. This semi-circular specimen with radius R, which contains an edge crack of length a oriented normal to the specimen edge, loaded with a three point bending fixture, was proved to give wide range of mixed modes from pure mode I to pure mode II, only by changing the position of one support. Different types of notched specimens were considered for notch effect investigations and the Theory of Critical Distances was applied. It could be seen that the critical distances are influenced by the cellular structure of investigated materials.

A corner joint was investigated using finite element method. Since the geometry along the width o... more A corner joint was investigated using finite element method. Since the geometry along the width of the corner joint is uniform and load does not change in that direction, the problem was assumed to be plane strain. In addition, it was assumed that the adherents (aluminum) and adhesive (epoxy resin) had linear properties. The joint was analysed under one loading condition, a bending moment applied at the upper end of the right-angled plate. The stress distributions in the joint area are given by the stress contours and XY plots. Since the geometry of the joint affects the analysis, in addition were investigated the influences on the stress distributions of the bonding length and adhesive thickness. From the results it was found that the stress distributions are similar for different bond lengths, but the maximum stresses are increased with decreasing adhesive thickness. These results can be useful in adhesive-bonded corner joints design.

Design, Fabrication and Economy of Metal Structures, 2013

ABSTRACT This paper presents the numerical determination of stress intensity factor for a 3D crac... more ABSTRACT This paper presents the numerical determination of stress intensity factor for a 3D cracked T – joint using FRANC 3D software. The analysis preformed were linked between the finite element analysis using Abaqus software to obtain the stress state used in Franc 3D for stress intensity factor determination in crack resence in structure. For many applications like hydraulic Francis turbine rotors, the joints between blades and crow, and blades and rings are T-joints types with connections radius. In this paper an example of simplified T-joint with cracks presence is presented. For this cracked T joint structure a numerical analysis in bending and tension loadings was performed to obtain the stress intensity factors. The material used in analysis is a stainless steel named AISI 304. A stress state analysis was performed to obtain the maximum stress zone in T joint from where the crack can occurs. From this zone were initiate a quarter elliptical corner crack and propagated in the structure. For this crack propagated were obtained the stress intensity factors KI in loading mode I along the crack fronts. The stress intensity factor offer information for a future analysis, when in structure occur defects of cracks type related the operating condition

Advanced Engineering Forum, 2013

The key ingredient for any turbine runners design procedure and failure analysis is the material ... more The key ingredient for any turbine runners design procedure and failure analysis is the material and its mechanical and fatigue properties. Starting from this observation, a series of static and dynamic tests were performed on the T10CuNiCr180 stainless steel after more than three decades of service. The fatigue tests were carried out under constant amplitude at a stress ratio of 0.1 and a frequency of 20 Hz. In the high cycle fatigue range, the S-N median curve was plotted and the fatigue limit for 3106 cycles to failure was determined at 93.35 [MPa] expressed in stress amplitude. The casting and welding defects that were observed on fracture surfaces explained this lower fatigue limit. The fatigue crack growth tests were performed on compact tension specimens and a three-parameter model was used to plot the crack length versus number of cycles curves. In addition, the material constants from Paris law were determined. Finally, the experimental results are compared against publishe...

International Journal of Fracture, 2013

Using the asymmetric semi-circular bend specimen (ASCB) with vertical crack, a series of mixed mo... more Using the asymmetric semi-circular bend specimen (ASCB) with vertical crack, a series of mixed mode I/II fracture tests were performed on two different rigid polyurethanes materials. The experimental results obtained for brittle fracture are compared with the theoretical predictions based on MTS and SED criteria. The results demonstrate that the SED criterion gives better results for mode II loading conditions, while for mode I and predominantly mode I both criteria are accurate.

Polymers

This work investigates the critical plastic strain variation with stress triaxiality and the Lode... more This work investigates the critical plastic strain variation with stress triaxiality and the Lode angle parameter for an Acrylonitrile butadiene styrene (ABS)-based proprietary blend compound (commercial name VeroWhitePlus™ RGD835) manufactured through photopolymerization. Various triaxial states of stress and Lode angles were obtained with the help of notched flat specimens used in tensile loadings, notched round specimens used in compression (upsetting) tests and butterfly specimens used in Arcan tests. The tests were replicated using finite element analyses in order to evaluate the aforementioned parameters.

IOP Conference Series: Materials Science and Engineering, 2018

This paper investigates the compressive and flexural behavior of a closed-cell fly ashbased geopo... more This paper investigates the compressive and flexural behavior of a closed-cell fly ashbased geopolymer foam with a density of 240 kg/m 3. The influence of loading speed (0.1, 10, 100, 250 and 500 mm/min) and anisotropy (in-plane and out-of-plane directions) on the compressive mechanical properties at room temperature were investigated. Under compressive loads, the stress-strain curves shows a cellular material typical behavior with three different regions: linear-elastic, plateau and densification region. On the other hand, the three-point bending tests were carried out on both un-notched and notched specimens (for fracture toughness determination). In compression, the foam progressively collapsed with a complete destruction of the successive rows of cells, while in the case of bending it exhibited a brittle behavior without plastic deformation, the fracture occurring by the propagation of a single crack.

Theoretical and Applied Fracture Mechanics, 2015

The notch effect in Polyurethane materials of different densities is investigated. Tensile specim... more The notch effect in Polyurethane materials of different densities is investigated. Tensile specimens with lateral V and U symmetric notches and with holes of different diameters were tested. The material parameters inherent stress and critical distance are determined using a linear elastic finite element analysis in conjunction with experimental results of average maximum load. The paper proposed an original correlation between critical distance and the cell diameter of the cellular structure, respectively between inherent stress and the ultimate tensile strength of Polyurethane materials. Then for single edge notch specimens a relationship between critical distance and applied mixed mode is found and successfully applied to assess the brittle mixed mode of Polyurethane materials.

Procedia Structural Integrity, 2016

During their operation, modern aircraft engine components are subjected to increasingly demanding... more During their operation, modern aircraft engine components are subjected to increasingly demanding operating conditions, especially the high pressure turbine (HPT) blades. Such conditions cause these parts to undergo different types of time-dependent degradation, one of which is creep. A model using the finite element method (FEM) was developed, in order to be able to predict the creep behaviour of HPT blades. Flight data records (FDR) for a specific aircraft, provided by a commercial aviation company, were used to obtain thermal and mechanical data for three different flight cycles. In order to create the 3D model needed for the FEM analysis, a HPT blade scrap was scanned, and its chemical composition and material properties were obtained. The data that was gathered was fed into the FEM model and different simulations were run, first with a simplified 3D rectangular block shape, in order to better establish the model, and then with the real 3D mesh obtained from the blade scrap. The overall expected behaviour in terms of displacement was observed, in particular at the trailing edge of the blade. Therefore such a model can be useful in the goal of predicting turbine blade life, given a set of FDR data.