Complex materials, often encountered in recent engineering and material sciences applications, show no complete separations between solid and fluid phases. This aspect is reflected in the continuous relaxation time spectra recorded in cyclic load tests. As a consequence the material free energy can not be defined in a unique manner yielding a significative lack of knowledge of the maximum recoverable work that can extracted from the material. The non-uniqueness of the free energy function is removed in the paper for power-laws relaxation/creep function by using a recently proposed mechanical analogue to fractional-order hereditariness.

Authors: Luca Deseri, Mario Di Paola, Massimiliano Zingales., in press on Int. J. Solids Struct. (2014), http://dx.doi.org/10.1016/j.ijsolstr.2014.05.008

Laura Galuppi & Luca Deseri, JoMMS, Vol. 9, No. 1, 2014
dx.doi.org/10.2140/jomms.2014.9.51

http://www.ing.unitn.it/~deseril/

Sintering of precompacted metallic and ceramic micro and nanopowders is a complex problem influenced
by several factors. We quantify the influence of both local capillary stresses acting at the surface
of one pore or particle (usually referred to as Laplace pressure) and the gas pressure in pores during
sintering of precompacted metallic (micro/nano)powdered cylinders. The latter influences only the third
phase of sintering, that is, the phase in which the porosity is closed.
The isostatic pressing loading mode, which also covers the case of free sintering, is considered.
Whereas the Laplace pressure is demonstrated to have a beneficial effect on sintering, the gas pressure
acts against the reduction of the porosity, causing an increase in sintering time. This contribution could
reach the sum of the stress due to loading and the interstitial pressure, thereby preventing the desired
porosity to be reached.
For the sake of illustration, a specific aluminum-zinc-magnesium-copper alloy is examined in this
paper. The purpose is to estimate the effects of sintering time and residual porosity and to determine
thresholds under which the contributions described above are negligible. In order to determine the effects
of Laplace and gas pressure in pores on the stability of the process, a high-order perturbation analysis
has been performed.

Join us to congratulate Professor Kaushik Dayal, from CEE-Carnegie Mellon, for winning the prestigious Leonardo Da Vinci Award from the American Society of Civil Engineers (ASCE) Engineering Mechanics Institute
(EMI) for groundbreaking research on the interactions between materials
and electromagnetism that can be applied to new technologies for energy
storage and generation.

Congratulations Kaushik!

More news can be found at: https://www.cit.cmu.edu/media/feature/2013/08_21_dayal_davinci_award.html

Join us to congratulate Professor Davide
Bigoni, who has just been awarded with the ERC Advanced Grant
Proposal 340561 - Instabilities and nonlocal multiscale modelling of
materials, years 2014-2018, 2.4 M.

Congratulations Davide!

More on Davide's research:

www.ing.unitn.it/~bigoni/

http://ssmg.unitn.it/

http://www.youtube.com/user/SSMGunitnITALY

In this paper the authors introduce a hierarchic fractal model
to describe bone hereditariness. Indeed, experimental data of stress
relaxation or creep functions obtained by compressive/tensile tests have
been proved to be fit by power-law with real exponent 0 ≤β≤
1. The rheological behavior of the material has therefore been
obtained, using the Boltzmann-Volterra superposition principle, in terms
of real order integrals and derivatives (fractional-order calculus). It
is shown that the power-laws describing creep/relaxation of bone tissue
may be obtained introducing a fractal description of bone cross-section
and the Hausdorff dimension of the fractal geometry is then related to
the exponent of the power-law.

By L. Deseri, M. Di Paola , P. Pollaci , M. Zingales

In this work some implications of a recent model for the mechanical behavior of biological membranes [20] are exploited by means of a prototypical one-dimensional problem. We show that the knowledge of the membrane stretching elasticity permits to establish a precise connection among surface tension, bending rigidities and line tension during phase transition phenomena. For a specific choice of the stretching energy density, we evaluate these quantities in a membrane with coexistent fluid phases, showing a satisfactory comparison with the available experimental measurements. Finally, we determine the thickness profile inside the boundary layer where the order-disorder transition is observed.

(Note: Revised pdf file)

Random elastic composites with residual stresses are examined in this paper with the aim of understanding how the prestress may influence the overall mechanical properties of the composite. A fully non-local effective response is found in perfect analogy with the un-prestressed case examined in (Drugan, W.J. and Willis, J.R., A micromechanics-based nonlocal constitutive equation and estimates of representative volume element size for elastic composites, JMPS 44 (4), 497--524, 1996). The second gradient approximation is considered and the impact of the residual stresses on the estimate of the RVE size is studied whenever the local response is used to describe the mechanical properties of the heterogeneous medium. To this aim, total and incremental formulations are worked out in this paper and the influence of both uniform and spatially varying prestresses are studied. Among other results, it is shown how rapid oscillations of relatively "small" residual stresses in most cases may result in the impossibility of describing the overall behavior of the composite with a local constitutive equation. On the other hand, prestresses with relatively high amplitudes and slow spatial oscillations may even reduce the RVE size required for approximating the mechanical properties of un-prestressed heterogeneous media with a local constitutive equation.