Non-tubular bonded joint under torsion: Theory and numerical validation

Pugno, Nicola,Surace, Giuseppe Techno-Press 2000 Structural Engineering and Mechanics, An Int'l Jou Vol.10 No.2

The paper analyzes the problem of torsion in an adhesive non-tubular bonded single-lap joint. The joint considered consists of two thin rectangular section beams bonded together along a side surface. Assuming the materials involved to be governed by linear elastic laws, equilibrium and compatibility equations were used to arrive at an integro-differential relation whose solution makes it possible to determine torsional moment section by section in the bonded joint between the two beams. This is then used to determine the predominant stress and strain field at the beam-adhesive interface (stress field along the direction perpendicular to the interface plane, equivalent to the applied torsional moment and the corresponding strain field) and the joint's elastic strain (absolute and relative rotations of the bonded beam cross sections). All the relations presented were obtained in closed form. Results obtained theoretically are compared with those given by a three dimensional finite element numerical model. Theoretical and numerical analysis agree satisfactorily.

Evaluation of torsional natural frequencies for non-tubular bonded joints

Pugno, Nicola,Ruotolo, Romualdo Techno-Press 2002 Structural Engineering and Mechanics, An Int'l Jou Vol.13 No.1

During the last several years, research activity on non-tubular bonded joints has concentrated on the effects of normal stress, bending moments and shear. Nevertheless, in certain situations, the structure may be subjected to twisting moments, so that the evaluation of its dynamic behaviour to torsional vibrations becomes of great importance even though evaluations of such loading conditions is entirely lacking in the literature. The aim of this article is to show that torsional natural frequencies of the non-tubular joint can be evaluated by determining the roots of a determinantal equation, derived by taking advantage of some analytical results obtained in a previous paper dealing with the analysis of the state of stress in the adhesive. Numerical results related to clamped-free and clamped-clamped joints complete the article.

Generalized fracture toughness for specimens with re-entrant corners: Experiments vs. theoretical predictions

Carpinteri, Alberto,Cornetti, Pietro,Pugno, Nicola,Sapora, Alberto,Taylor, David Techno-Press 2009 Structural Engineering and Mechanics, An Int'l Jou Vol.32 No.5

In this paper the results of a series of experimental tests upon three-point bending specimens made of polystyrene and containing re-entrant corners are firstly described. Tests involved different notch angles, different notch depths and finally different sizes of the samples. All the specimens broke at the defect, as expected because of the material brittleness and, hence, the generalized stress intensity factor was expected to be the governing failure parameter. Recorded failure loads are then compared with the predictions provided by a fracture criterion recently introduced in the framework of Finite Fracture Mechanics: fracture is assumed to propagate by finite steps, whose length is determined by the contemporaneous fulfilment of energy balance and stress requirements. This fracture criterion allows us to achieve the expression of the generalized fracture toughness as a function of the tensile strength, the fracture toughness and the notch opening angle. Comparison between theoretical predictions and experimental data turns out to be more than satisfactory.

Entrepreneurship and the Hidden Economy: an Extended Matching Model

Gaetano Lisi,Maurizio Pugno 한국국제경제학회 2010 International Economic Journal Vol.24 No.4

This paper develops a labour market matching model in order to address the problem of the persistence of the hidden sector and of its regional concentration, as in Italy and in the enlarged Europe. The main novel features of the model are that entrepreneurial ability affects job productivity, and that regular firms receive negative externalities from the hidden sector, which may capture the pressure typically exerted by corruption and organised crime, and positive externalities from the other regular firms. At least one interior equilibrium emerges, thus providing an explanation for the so-called 'shadow puzzle', with the possibility that tougher monitoring may reduce both the hidden sector and unemployment. If externalities are non-linear, two equilibria may emerge, thus accounting for regional dualism. The 'better' equilibrium is in fact characterised by a smaller hidden sector, higher levels of overall productivity, output, entrepreneurial ability used, extra-profits, relative wages, and more favourable externalities.

Atomistic modelling of the hypervelocity dynamics of shock-compressed graphite and impacted graphene armours

Signetti, Stefano,Kang, Keonwook,Pugno, Nicola M.,Ryu, Seunghwa Elsevier 2019 Computational materials science Vol.170 No.-

<P><B>Abstract</B></P> <P>We present a molecular dynamics (MD) simulation study on the hypervelocity dynamics of shock compressed graphite -up to hundreds of gigapascals- and impacted multilayer graphene armours by employing the AIREBO-M potential. The Morse-type non-singular intermolecular interaction allows the usage of relatively large integration timesteps for simulating materials’ response at such high strain-rate. The MD simulation results are in good agreement with the shock Hugoniot curves and with graphite-to-diamond transition obtained from both density functional theory (DFT) and experiments available in literature. We then show that thermodynamic properties of graphite from MD calculations can be used as input for a reliable equation of state to be employed in continuum simulations. Finally, we find that the size-scaling of the hypervelocity impact properties of graphene armours matches well with the DFT results and theoretical predictions of earlier studies. Our results open a concrete possibility towards accurate and fast multiscale simulation from atomistic to continuum level of shock propagation, shock-induced phase transformation, and dynamic fracture in large or hierarchical carbon systems, such as graphene-based foams and nanocomposites.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Generalized fracture toughness for specimens with re-entrant corners: Experiments vs. theoretical predictions

Alberto Carpinteri,Pietro Cornetti,Nicola Pugno,David Taylor,Alberto Sapora 국제구조공학회 2009 Structural Engineering and Mechanics, An Int'l Jou Vol.32 No.5

In this paper the results of a series of experimental tests upon three-point bending specimens made of polystyrene and containing re-entrant corners are firstly described. Tests involved different notch angles, different notch depths and finally different sizes of the samples. All the specimens broke at the defect, as expected because of the material brittleness and, hence, the generalized stress intensity factor was expected to be the governing failure parameter. Recorded failure loads are then compared with the predictions provided by a fracture criterion recently introduced in the framework of Finite Fracture Mechanics: fracture is assumed to propagate by finite steps, whose length is determined by the contemporaneous fulfilment of energy balance and stress requirements. This fracture criterion allows us to achieve the expression of the generalized fracture toughness as a function of the tensile strength, the fracture toughness and the notch opening angle. Comparison between theoretical predictions and experimental data turns out to be more than satisfactory.

금속 나노선-고분자 복합재 기반 변형 센서의 시뮬레이션 해석

이상륜(Sang Ryun Lee),Morteza Amjadi,Nicola Pugno,박인규(In Kyu Park),유승화(Seung Hwa Ryu) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.4

An analytical benchmark and a <i>Mathematica</i> program for MD codes: Testing LAMMPS on the 2nd generation Brenner potential

Favata, Antonino,Micheletti, Andrea,Ryu, Seunghwa,Pugno, Nicola M. Elsevier 2016 Computer physics communications Vol.207 No.-

<P><B>Abstract</B></P> <P>An analytical benchmark and a simple consistent <I>Mathematica</I> program are proposed for graphene and carbon nanotubes, that may serve to test any molecular dynamics code implemented with REBO potentials. By exploiting the benchmark, we checked results produced by LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator) when adopting the second generation Brenner potential, we made evident that this code in its current implementation produces results which are offset from those of the benchmark by a significant amount, and provide evidence of the reason.</P> <P><B>Program summary</B></P> <P> <I>Program title:</I> MDBenchmarks</P> <P> <I>Catalogue identifier:</I> AFAS_v1_0</P> <P> <I>Program summary URL:</I> http://cpc.cs.qub.ac.uk/summaries/AFAS_v1_0.html </P> <P> <I>Program obtainable from:</I> CPC Program Library, Queen’s University, Belfast, N. Ireland</P> <P> <I>Licensing provisions:</I> GNU GPL v3</P> <P> <I>No. of lines in distributed program, including test data, etc.:</I> 22854</P> <P> <I>No. of bytes in distributed program, including test data, etc.:</I> 369171</P> <P> <I>Distribution format:</I> tar.gz</P> <P> <I>Programming language:</I> Mathematica 9.</P> <P> <I>Computer:</I> Any PC.</P> <P> <I>Operating system:</I> Any which supports Mathematica; tested under OS Yosemite.</P> <P> <I>RAM:</I> < 5 gigabytes</P> <P> <I>Classification:</I> 7.7, 16.1, 16.13.</P> <P> <I>Nature of problem:</I> Testing commercial or open-source molecular dynamics codes implementing off-the-shelf REBO potentials on an analytical benchmark.</P> <P> <I>Solution method:</I> Analytical equilibrium conditions for achiral carbon nanotubes are implemented and solved, delivering benchmark values for the corresponding natural radius and cohesive energy; material properties (Young’s modulus and Poisson coefficient) are also computed.</P> <P> <I>Running time:</I> Instantaneous, or a few seconds, depending on computer hardware</P>

MICROMECHANICS MODEL FOR RUBBER BLENDS FILLED BY A NANO-REINFORCED DEVULCANIZED RECYCLED RUBBER: APPLICATION IN THE AUTOMOTIVE INDUSTRY

Jalali Seyed Kamal,Busfield James,Pugno Nicola 한국자동차공학회 2023 International journal of automotive technology Vol.24 No.4

The present report proposes a micromechanics model for predicting the dynamic modulus of rubber blends consisting of a base rubber and devulcanized recycled rubbers reinforced by nanofillers. A four-step hierarchical homogenization is established to relate the properties of components from the nano-sized reinforcements to the macro-scaled final blend. The developed model accounts for the effect of agglomeration and geometry of nano-fillers, the quality of the devulcanization process, and the properties of the interphase surrounding the nanofillers on the dynamic modulus of the rubber blend. A comprehensive dimensionless parametric study is performed whose output in terms of graphical maps can be used as a design guideline for practical cases in industries like automotive. A case study for recycled end-of-life tires (ELTs) reinforced by nano clays is presented and it is found that the nano reinforcement of devulcanized rubbers has a remarkable potential to compensate for the weakness compared to its virgin counterpart.

Tribological characteristics of few-layer graphene over Ni grain and interface boundaries

Tripathi, Manoj,Awaja, Firas,Paolicelli, Guido,Bartali, Ruben,Iacob, Erica,Valeri, Sergio,Ryu, Seunghwa,Signetti, Stefano,Speranza, Giorgio,Pugno, Nicola Maria The Royal Society of Chemistry 2016 Nanoscale Vol.8 No.12

<P>The tribological properties of metal-supported few-layered graphene depend strongly on the grain topology of the metal substrate. Inhomogeneous distribution of graphene layers at such regions led to variable landscapes with distinguishable roughness. This discrepancy in morphology significantly affects the frictional and wetting characteristics of the FLG system. We discretely measured friction characteristics of FLG covering grains and interfacial grain boundaries of polycrystalline Ni metal substrate<I>via</I>an atomic force microscopy (AFM) probe. The friction coefficient of FLG covered at interfacial grain boundaries is found to be lower than that on grains in vacuum (at 10<SUP>−5</SUP>Torr pressure) and similar results were obtained in air condition. Sliding history with AFM cantilever, static and dynamic pull-in and pull-off adhesion forces were addressed in the course of friction measurements to explain the role of the out-of-plane deformation of graphene layer(s). Finite element simulations showed good agreement with experiments and led to a rationalization of the observations. Thus, with interfacial grain boundaries the FLG tribology can be effectively tuned.</P>