Luca Esposito - Academia.edu (original) (raw)

Papers by Luca Esposito

Convegno Igf Xxi Cassino 2011, Jun 9, 2011

Although primary stage is often neglected in creep design, in several alloys for high temperature... more Although primary stage is often neglected in creep design, in several alloys for high temperature applications, most of the allowable design strain can occurs before reaching the minimum creep rate. The kinetic of the primary creep stage is important since it determines the microstuctural conditions for the subsequent creep regime. Under rapid stress change creep transient occurs and, according to the developed dislocation substructure, a stress dependence of the creep rate is observed. In order to account for these features in the material response, an appropriate modelling is required. Assuming that the current creep rate in the transient regime can be expressed as a function of the steady state creep rate, a model based on the evolution of the internal stress is derived. The proposed model does not rely on any particular formulation for the steady state creep and therefore is of general applicability. In the present paper, a mechanism based secondary creep stage model, with an explicit dependence of the creep exponent n on stress, as proposed by the authors, has been used . An application to polycrystalline copper is presented.

Journal of Engineering Materials and Technology Transactions of the Asme, Apr 1, 2010

The increasing demand of reliable creep design for very long lives (exceeding 100.000 h), as thos... more The increasing demand of reliable creep design for very long lives (exceeding 100.000 h), as those for high stress-low temperatures and high temperature-low stress regimes, requires a model formulation capable to account for the nonlinearity in the stress dependence of the ...

/¿ L.Esposito et. al, Frattura ed Integrità Strutturale, 5 (2008) 22 - 26; DOI: 10.322MGF-ESIS.05... more /¿ L.Esposito et. al, Frattura ed Integrità Strutturale, 5 (2008) 22 - 26; DOI: 10.322MGF-ESIS.05.02 ^ A model for steady state stage III creep regime at low-high stress/temperature range Luca Esposito, Nicola Bonora DiMSAT - Dept. of Mechanics, Structures and Environment, ...

Differential and Integral Equations

The comprehension of blunt eye trauma pathogenic mechanism is largely incomplete. Proposed theori... more The comprehension of blunt eye trauma pathogenic mechanism is largely incomplete. Proposed theories include globe deformation, vitreous traction and differential elasticity of the ocular structures. In order to test the hypothesis of shockwave-induced retinal damage and calculate the positive (compression) and negative (traction) pressures dynamically generated, a finite element analysis of an experimental BB pellet impact in vitreous filled eye has been performed.

Nel lavoro vengono riportati i risultati di uno studio condotto per riprogettare ed ottimizzare l... more Nel lavoro vengono riportati i risultati di uno studio condotto per riprogettare ed ottimizzare la forma di un componente motociclistico. Il componente, denominato cursore, è ottenuto tramite stampaggio ad iniezione ed è parte di un sottoassieme, utilizzato come sistema di aggancio al telaio di un bauletto portaoggetti motociclistico, ed assolve alle operazioni di aggancio e sgancio. Attraverso un sistema laser è stata acquisita la forma del cursore, sono stati effettuati i controlli dimensionali rispetto al modello di progetto, verificando la bontà del processo di produzione e lo stato d’usura dello stampo. Successivamente, sono state condotte delle simulazioni FEM per caratterizzare e validare le diverse soluzioni utilizzate nel tempo.

1DiMSAT, University of Cassino, Via G. Di Biasio, 43 03043, Cassino, ITALY 2Los Alamos National... more 1DiMSAT, University of Cassino, Via G. Di Biasio, 43 03043, Cassino, ITALY 2Los Alamos National Laboratory, Los Alamos NM 87545 ... Abstract. The calculated energy dissipation associated with the pull-back signal amplitude in plate impact experiment is usually larger than that ...

Discrepancies between the calculated and observed velocity vs time plot, relatively to the spall ... more Discrepancies between the calculated and observed velocity vs time plot, relatively to the spall signal portion in terms of both signal amplitude and frequency, in numerical simulations of flyer plate impact test are usually shown. These are often ascribed either to material model or the numerical scheme used. Bonora et al. (2003 )[Bonora N., Ruggiero A. and Milella P.P., 2003,

Volume 6A: Materials and Fabrication, 2014

Volume 6A: Materials and Fabrication, 2013

ABSTRACT Materials creep resistance is usually determined under uniaxial constant load condition ... more ABSTRACT Materials creep resistance is usually determined under uniaxial constant load condition while the state of stress in real components is multiaxial in general. How to correlate multiaxial creep behavior to uniaxial creep data is still an open issue. Most of the theories available in the literature are phenomenological in nature and limited to few classes of metals and stress triaxiality ranges. From the computational point of view, stress field relaxation depends on the creep model formulation. Therefore, it is necessary to use a refined creep model capable to reproduce the effective state of stress in the material. In the present work, a mechanism based creep model proposed by Bonora and Esposito [1] was used to predict creep life of P91 high chromium steel under multiaxial state of stress. This creep model is capable to reproduce all creep stages and was validated for different classes of metals and alloys. The performance of different reference stress definitions (i.e. the principal facet stress, skeletal stress and a new formulation) was investigated. Results were compared with available creep life data obtained on round notched samples at different temperatures.

Volume 6: Materials and Fabrication, Parts A and B, 2008

Although it is often said that diffusional flow creep is out of the practical engineering applica... more Although it is often said that diffusional flow creep is out of the practical engineering applications, the need for a unified model capable to account for the resulting action of both diffusional and dislocation type creep is justified by the increasing demands of reliable ...

Volume 3: Design and Analysis, 2008

ABSTRACT In the last decades damage mechanics has received a lot of attention and has proved to b... more ABSTRACT In the last decades damage mechanics has received a lot of attention and has proved to be a powerful approach to describe the occurrence of failure in materials. In order to became an effective tool of practical application in the industrial design world, clear, reliable, and — when possible — simple procedures and practices, aimed to perform damage measures and to identified damage model parameters, are needed. In the literature, only a limited number of papers addresses the issue of the damage measurements. Among the possible different techniques, the measure of the progressive loss of stiffness as a function of the increasing inelastic strain level, is the most commonly used and referred. Even though this technique is conceptually simple, it can be affected by a number of error that can invalidated the measures. In this paper a clear and effective procedure based on the use of finite element simulation and experiments is presented. The proposed procedure allows one to correctly account for the geometry changes occurring in the sample even in the post necking regime where stresses and strain are no longer uniform along the section and the gauge length. The proposed methodology has been used to measure damage in 99.99% pure copper.

Journal of Physics: Conference Series, 2014

ABSTRACT The detachment or tearing of the retina in the human eye as a result of a collision is a... more ABSTRACT The detachment or tearing of the retina in the human eye as a result of a collision is a phenomenon that occurs very often. Reliable numerical simulations of eye impact can be very useful tools to understand the physical mechanisms responsible for traumatic eye injuries accompanying blunt impact. The complexity and variability of the physical and mechanical properties of the biological materials, the lack of agreement on their related experimental data as well as the unsuitability of specific numerical codes and models are only some of the difficulties when dealing with this matter. All these challenging issues must be solved to obtain accurate numerical analyses involving dynamic behavior of biological soft tissues. To this purpose, a numerical and experimental investigation of the dynamic response of the eye during an impact event was performed. Numerical simulations were performed with IMPETUS-AFEA, a new general non-linear finite element (FE) software which offers non uniform rational B-splines (NURBS) FE technology for the simulation of large deformation and fracture in materials. IMPETUS code was selected in order to solve hourglass and locking problems typical of nearly incompressible materials like eye tissues. Computational results were compared with the experimental results on fresh enucleated porcine eyes impacted with airsoft pellets.

ABSTRACT Human eye subjected to non penetrating impact (blunt-impact) may experience severe damag... more ABSTRACT Human eye subjected to non penetrating impact (blunt-impact) may experience severe damage. The most common type is partial tearing of the retina at specific eye locations. In ophthalmology, based on impact experiment performed by Delori et al. (1967), it is commonly accepted that the mechanism responsible for retinal damage is the vitreous pull-traction action and the equatorial expansion of the sclera. Based on the evidence of a vitrectomized patient who reported retinal damage after blunt impact, an investigation on the possible role of shockwave dynamics in the retinal damage has been performed by means of hydrocode numerical simulation. A FEM model of the eye has been developed and the experiment of Delori et al. has been reproduced. Soft tissues constitutive response has been determined by means of reverse engineering approach. It has been demonstrated that release waves at the retina-choroid interface are generated in the early time of the blunt impact and can cause retina tearing when the eye bulb is still undeformed. This result has been also confirmed for the case of blast-load exposure