Numerical and experimental assessment of the static behavior of 3D printed reticular Al structures produced by Selective Laser Melting: progressive damage and failure

Abstract In recent decades, the interest of the manufacturing industry towards additive manufacturing techniques has increased considerably. Speed and ease of implementation are just some of the factors that helped making this type of production one of the most developed in the world, considering also the possibility of creating complex geometries. The present research uses of a series of Al A357 specimens produced by SLM method. The experimental measurements on a first geometry have been used to calibrate the ductile damage model implemented in the FE code. The material model is based on both classical incremental model of plastic response with isotropic hardening and phenomenological concept of damage in continuum mechanic. The result of the calibration process was verified through the comparison of FE simulation of reticular specimens with the measured experimental response. Comparison between experimental data and numerical results will be discussed

Occupancy of the territory by Lymantria dispar (L.) (Lepidoptera Erebidae) egg masses as a predictive index of damage

In Sardinia (Italy) the population abundance of the defoliator gypsy moth Lymantria dispar (L.) (Lepidoptera Erebidae) has been regularly sampled for over thirty years by counts of egg masses. This monitoring activity allows annual identification of the areas with the highest abundance of infestation in order to define the areas to be subjected to phytosanitary treatments and thus to confine the damage caused by gypsy moth defoliation. However, the identification of areas to be treated have been defined exclusively according to the experience gained over the years by the operators. To overcome the limitation of this empirical approach we have developed an objective method supporting decision making based on the relationship between the percentage of infested sites and the intensity of defoliation. For this purpose the radius of annual gypsy moth expansion was estimated in a cork oak district: the estimated value was ca. 6 km per year. This value was used to calculate the percentage of sites occupied by at least 1 egg mass within that radius. A generalized linear model was used to evaluate the statistical significance of the relationship between percentage of occupied sites and presence of damage. According to what we know from literature a monitoring site was considered damaged when defoliation level of foliage was greater than 50%. We then used the historical series of data to calculate the probability that a defoliation event would occur according to the estimated model. The logit model confirmed the validity of the predictor with respect to the presence of damage, with a general accuracy greater than 90%. The results suggest a revision of the sampling protocol used thus far, which requires a particularly costly and prolonged sampling effort. The method described herein should allow easier identification of forest areas exposed to damage and timelier planning of control interventions

Evolution of magneto-orbital order upon B-site electron doping in Na1-xCaxMn7O12 quadruple perovskite manganites

We present the discovery and refinement by neutron powder diffraction of a new magnetic phase in the Na1-xCaxMn7O12 quadruple perovskite phase diagram, which is the incommensurate analogue of the well-known pseudo-CE phase of the simple perovskite manganites. We demonstrate that incommensurate magnetic order arises in quadruple perovskites due to the exchange interactions between A and B sites. Furthermore, by constructing a simple mean field Heisenberg exchange model that generically describes both simple and quadruple perovskite systems, we show that this new magnetic phase unifies a picture of the interplay between charge, magnetic and orbital ordering across a wide range of compounds.Comment: Accepted for publication in Physical Review Letter

The effects of fecundity, mortality and distribution of the initial condition in phenological models

Pest phenological models describe the cumulative flux of the individuals into each stage of the life cycle of a stage-structured population. Phenological models are widely used tools in pest control decision making. Despite the fact that these models do not provide information on population abundance, they share some advantages with respect to the more sophisticated and complex demographic models. The main advantage is that they do not require data collection to define the initial conditions of model simulation, reducing the effort for field sampling and the high uncertainty affecting sample estimates. Phenological models are often built considering the developmental rate function only. To the aim of adding more realism to phenological models, in this paper we explore the consequences of improving these models taking into consideration three additional elements: the age distribution of individuals which exit from the overwintering phase, the age- and temperature-dependent profile of the fecundity rate function and the consideration of a temperature-dependent mortality rate function. Numerical simulations are performed to investigate the effect of these elements with respect to phenological models considering development rate functions only. To further test the implications of different models formulation, we compare results obtained from different phenological models to the case study of the codling moth (Cydia pomonella) a primary pest of the apple orchard. The results obtained from model comparison are discussed in view of their potential application in pest control decision support

A numerical investigation on significant parameters influencing the flatwise compressive behaviour of a NomexTM Honeycomb

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evaluation of the effects of the numerical modelling choices on the simulation of a tensile test on cfrp composite

Abstract The goal of the present work is to define a method to build a FE model which is able to reproduce an experimental tensile test on CFRP specimen with different stacking sequences (UD and balanced). The defined method assesses the material numerical parameters by means of a simulation that replicates, as a virtual test, the experimental tensile one, and in the future, it will be possible to exploit the data obtained to create a reliable model for the simulation of low velocity impacts. Analyses have been performed using the non-linear solver ABAQUS Explicit. The current work further studies how to model damage and the effect of modifications of the numerical parameters on the results. Indeed, the numerical simulation of composite materials is very sensitive to the numerical choices made. Moreover, from the literature and experiments, the mechanical properties of composites are very variable and hence the evaluation of the model response to such modifications is of particular interest

Optical study of the vibrational and dielectric properties of BiMnO3

BiMnO3 (BMO), ferromagnetic (FM) below Tc = 100 K, was believed to be also ferroelectric (FE) due to a non-centro-symmetric C2 structure, until diffraction data indicated that its space group is the centro-symmetric C2/c. Here we present infrared phonon spectra of BMO, taken on a mosaic of single crystals, which are consistent with C2/c at any T > 10 K, as well as room-temperature Raman data which strongly support this conclusion. We also find that the infrared intensity of several phonons increases steadily for decreasing T, causing the relative permittivity of BMO to vary from 18.5 at 300 K to 45 at 10 K. At variance with FE materials of displacive type, no appreciable softening has been found in the infrared phonons. Both their frequencies and intensities, moreover, appear insensitive to the FM transition at Tc