LINUL EMANOIL | Politehnica University of Timisoara (original) (raw)

Papers by LINUL EMANOIL

Fatigue & Fracture of Engineering Materials & Structures, 2016

This work investigates the fatigue response of a class of ductile closed-cell aluminium alloy foa... more This work investigates the fatigue response of a class of ductile closed-cell aluminium alloy foams, known by their commercial name Alulight M8. In order to determine the yield stress of the used foams, preliminary experimental tests were performed, at room temperature, in monotonic compression on cylindrical specimens of 25 mm diameter and 25 mm height, with a loading speed of 10 mm/min. Fatigue tests were performed in uniaxial compression on cylindrical specimens (25 mm × 25 mm) with a stress ratio of R = 0.1, at a frequency of 10 Hz. The peak stress was varied from 110 to 135% of the yield stress in compression. Tested specimens were cut from the same cylindrical bar, and the density of the investigated material was 500 kg/m3 ± 10%, or a total of 18 specimens being investigated. With the gathered experimental data, S–N curve was generated, and the effect of cellular structure (e.g. structure irregularity–the number and the size of cells) being investigated and discussed.

Theoretical and Applied Fracture Mechanics, 2019

Abstract Rigid polyurethane (PUR) foams can be subjected to complex loading conditions when they ... more Abstract Rigid polyurethane (PUR) foams can be subjected to complex loading conditions when they are utilized as a structural material in engineering components. Under the influence of tensile or shear loads, the crack growth is one of the major failure modes for such cellular materials. Understanding the critical load carrying capacity and also the direction or path of crack growth in PUR foams is of practical interest for designers of foam made structures. The focus of this paper is to study the fracture initiation angle (θ0) and the trajectory of fracture path for rigid PUR foam materials subjected to in-plane mixed mode I/II and out-of-plane mixed mode I/III fracture deformations. A number of mixed mode I/II fracture experiments using asymmetric-semi-circular bend (ASCB) and compact tension-shear (CTS) specimens and also mixed mode I/III fracture tests using the edge notch disc bend (ENDB) specimen were conducted on closed-cell foam with different densities. The corresponding values of critical fracture resistance (KIc, KIIc, or KIIIc), fracture initiation direction and fracture growth trajectory was obtained for the tested specimens made of PUR foam. The results showed the significant influence of specimen type and mode mixity on both fracture resistance value and fracture initiation direction. While the crack growth trajectory of mixed mode I/II (i.e. tensile/in-plane shear) was along the plane of initial crack but the mixed mode I/III (i.e. tensile/out-of-plane tear) trajectory of ENDB specimens was twisted from the crack front. For all tested specimen the trajectory of fracture for symmetric loading condition was self-similar and along the direction of initial crack plane. However, by adding the contribution of in and out of plane sliding to the crack growth mechanism of tested specimens, the fracture trajectory was kinked from the crack front and extended along a curvilinear path relative to the crack plane. The most deviation in the fracture trajectories were observed under pure modes II and III loading conditions. Despite the fracture toughness value that was significantly dependent on the foam density the direction of fracture initiation angle and the path of fracture growth was not affect noticeably by the density of foam. The mixed mode fracture initiation angles were also in good agreement with the prediction of maximum tangential stress theory.

IOP Conference Series: Materials Science and Engineering, 2018

Key Words: Prediction of Fracture Toughness for Open CellPolyurethane Foams By Finite-elementMicr... more Key Words: Prediction of Fracture Toughness for Open CellPolyurethane Foams By Finite-elementMicromechanical Analysis Emanoil Linul and Liviu Marsavina * Strength of Materials Department, Polytechnic University of Timisoara, Timisoara-300222, RomaniaReceived 9 April 2011; accepted 17 August 2011 T he fracture toughness was determined for cellular polymers by micromechanicalmodelling using finite element analysis. In this study, mode I and mode II of fracture toughness were evaluated with a 2D-solid model using fracture analysiscode FRANC2D/L. Simulation was performed for open cell polyurethane foams of different densities. Two cases were considered: constant cell length, l, and variable cellwall thickness; the former for constant cell wall thickness, t, and the latter for variablecell length. For estimation of fracture toughness the applied loads were progressivelyincreased to the point reaching the fracture strength of the solid material (130 MPa) inan un-cracked strut in front of ...

A cellular structure is made up by an interconnected network of beams or plates which forms the e... more A cellular structure is made up by an interconnected network of beams or plates which forms the edges and faces of cells. This paper proposes three different micromechanical models to determine the fracture toughness values of cellular materials such as rigid polyurethane foams using the finite element micromechanical analysis and Abaqus software. This study was carried out for mode I fracture and fracture toughness was predicted based on linear elastic fracture mechanics. Models of two-dimensional cellular solids with square, hexagonal and circular cells were generated for five different relative densities (0.077, 0.105, 0.133, 0.182 and 0.333). A study of the influence of geometrical parameters on fracture toughness was also conducted. Based on the finite-element simulations, three linear correlations are proposed which could be useful for estimation of fracture toughness values if relative densities are in the considered range of 0.077 (90 kg/m3 density) and 0.333 (390 kg/m3 density). Finally, the authors validate their proposed micromechanical models presenting a comparison of analytical, numerical and experimental results of fracture toughness of cellular materials. It was found that at low relative densities (between 0.077 and 0.333), the proposed micromechanical models predict the fracture toughness values similar to experimental and numerical ones, but they must be used according with the real cellular structure.

IOP Conference Series: Materials Science and Engineering, Oct 26, 2018

This paper presents the effect of loading rate, (ELR), and direction of formation, (DF), of rigid... more This paper presents the effect of loading rate, (ELR), and direction of formation, (DF), of rigid polyurethane foams, (PUR 40 and PUR 140), on fracture toughness. Nominal densities of used foams in the experimental program were 140 kg/m 3 , (for ELS) and 40 kg/m 3 , (for DF), which is closed-cell rigid foams widely used for sandwich cores. Determination of fracture toughness for Mode I fracture of studied materials has made by three-point bending tests, (3PB), on specimens with notches, at room temperature (20 ± 2 ºC). All the specimens were cut from one and the same plate. The specimens were subjected to 3PB at a loading speed of 2 mm/min, except samples for determining the ELR where 2, 20, 200 and 400 mm/min loading speeds were used, and were taken into account the fact that the load must act exactly on the notch direction. All the specimens present brittle failure without plastic deformation.

Fatigue & Fracture of Engineering Materials & Structures, 2016

This work investigates the fatigue response of a class of ductile closed-cell aluminium alloy foa... more This work investigates the fatigue response of a class of ductile closed-cell aluminium alloy foams, known by their commercial name Alulight M8. In order to determine the yield stress of the used foams, preliminary experimental tests were performed, at room temperature, in monotonic compression on cylindrical specimens of 25 mm diameter and 25 mm height, with a loading speed of 10 mm/min. Fatigue tests were performed in uniaxial compression on cylindrical specimens (25 mm × 25 mm) with a stress ratio of R = 0.1, at a frequency of 10 Hz. The peak stress was varied from 110 to 135% of the yield stress in compression. Tested specimens were cut from the same cylindrical bar, and the density of the investigated material was 500 kg/m3 ± 10%, or a total of 18 specimens being investigated. With the gathered experimental data, S–N curve was generated, and the effect of cellular structure (e.g. structure irregularity–the number and the size of cells) being investigated and discussed.

Theoretical and Applied Fracture Mechanics, 2019

Abstract Rigid polyurethane (PUR) foams can be subjected to complex loading conditions when they ... more Abstract Rigid polyurethane (PUR) foams can be subjected to complex loading conditions when they are utilized as a structural material in engineering components. Under the influence of tensile or shear loads, the crack growth is one of the major failure modes for such cellular materials. Understanding the critical load carrying capacity and also the direction or path of crack growth in PUR foams is of practical interest for designers of foam made structures. The focus of this paper is to study the fracture initiation angle (θ0) and the trajectory of fracture path for rigid PUR foam materials subjected to in-plane mixed mode I/II and out-of-plane mixed mode I/III fracture deformations. A number of mixed mode I/II fracture experiments using asymmetric-semi-circular bend (ASCB) and compact tension-shear (CTS) specimens and also mixed mode I/III fracture tests using the edge notch disc bend (ENDB) specimen were conducted on closed-cell foam with different densities. The corresponding values of critical fracture resistance (KIc, KIIc, or KIIIc), fracture initiation direction and fracture growth trajectory was obtained for the tested specimens made of PUR foam. The results showed the significant influence of specimen type and mode mixity on both fracture resistance value and fracture initiation direction. While the crack growth trajectory of mixed mode I/II (i.e. tensile/in-plane shear) was along the plane of initial crack but the mixed mode I/III (i.e. tensile/out-of-plane tear) trajectory of ENDB specimens was twisted from the crack front. For all tested specimen the trajectory of fracture for symmetric loading condition was self-similar and along the direction of initial crack plane. However, by adding the contribution of in and out of plane sliding to the crack growth mechanism of tested specimens, the fracture trajectory was kinked from the crack front and extended along a curvilinear path relative to the crack plane. The most deviation in the fracture trajectories were observed under pure modes II and III loading conditions. Despite the fracture toughness value that was significantly dependent on the foam density the direction of fracture initiation angle and the path of fracture growth was not affect noticeably by the density of foam. The mixed mode fracture initiation angles were also in good agreement with the prediction of maximum tangential stress theory.

IOP Conference Series: Materials Science and Engineering, 2018

Key Words: Prediction of Fracture Toughness for Open CellPolyurethane Foams By Finite-elementMicr... more Key Words: Prediction of Fracture Toughness for Open CellPolyurethane Foams By Finite-elementMicromechanical Analysis Emanoil Linul and Liviu Marsavina * Strength of Materials Department, Polytechnic University of Timisoara, Timisoara-300222, RomaniaReceived 9 April 2011; accepted 17 August 2011 T he fracture toughness was determined for cellular polymers by micromechanicalmodelling using finite element analysis. In this study, mode I and mode II of fracture toughness were evaluated with a 2D-solid model using fracture analysiscode FRANC2D/L. Simulation was performed for open cell polyurethane foams of different densities. Two cases were considered: constant cell length, l, and variable cellwall thickness; the former for constant cell wall thickness, t, and the latter for variablecell length. For estimation of fracture toughness the applied loads were progressivelyincreased to the point reaching the fracture strength of the solid material (130 MPa) inan un-cracked strut in front of ...

A cellular structure is made up by an interconnected network of beams or plates which forms the e... more A cellular structure is made up by an interconnected network of beams or plates which forms the edges and faces of cells. This paper proposes three different micromechanical models to determine the fracture toughness values of cellular materials such as rigid polyurethane foams using the finite element micromechanical analysis and Abaqus software. This study was carried out for mode I fracture and fracture toughness was predicted based on linear elastic fracture mechanics. Models of two-dimensional cellular solids with square, hexagonal and circular cells were generated for five different relative densities (0.077, 0.105, 0.133, 0.182 and 0.333). A study of the influence of geometrical parameters on fracture toughness was also conducted. Based on the finite-element simulations, three linear correlations are proposed which could be useful for estimation of fracture toughness values if relative densities are in the considered range of 0.077 (90 kg/m3 density) and 0.333 (390 kg/m3 density). Finally, the authors validate their proposed micromechanical models presenting a comparison of analytical, numerical and experimental results of fracture toughness of cellular materials. It was found that at low relative densities (between 0.077 and 0.333), the proposed micromechanical models predict the fracture toughness values similar to experimental and numerical ones, but they must be used according with the real cellular structure.

IOP Conference Series: Materials Science and Engineering, Oct 26, 2018

This paper presents the effect of loading rate, (ELR), and direction of formation, (DF), of rigid... more This paper presents the effect of loading rate, (ELR), and direction of formation, (DF), of rigid polyurethane foams, (PUR 40 and PUR 140), on fracture toughness. Nominal densities of used foams in the experimental program were 140 kg/m 3 , (for ELS) and 40 kg/m 3 , (for DF), which is closed-cell rigid foams widely used for sandwich cores. Determination of fracture toughness for Mode I fracture of studied materials has made by three-point bending tests, (3PB), on specimens with notches, at room temperature (20 ± 2 ºC). All the specimens were cut from one and the same plate. The specimens were subjected to 3PB at a loading speed of 2 mm/min, except samples for determining the ELR where 2, 20, 200 and 400 mm/min loading speeds were used, and were taken into account the fact that the load must act exactly on the notch direction. All the specimens present brittle failure without plastic deformation.