RESPONSE OF SANDWICHES UNDERGOING STATIC AND BLAST PULSE LOADING WITH TAILORING OPTIMIZATION AND STITCHING

A numerical study is presented where tailoring optimization and stitching are applied to improve the structural performances of sandwich plates undergoing static and blast pulse pressure loading. The purpose is to recover the critical interlaminar stresses at the interface with the core and contemporaneously keep maximal the flexural stiffness. Optimized distributions of the stiffness properties for the faces are obtained solving an extremal problem whose target is the minimization of the energy due to transverse shear and bending stresses under spatial variation of the stiffness properties, along with the maximization of the energy due to in-plane stresses. The contribution of stitching is computed through 3-D finite element analysis and it is incorporated as modified elastic moduli into the refined, hierarchic zig-zag model employed as structural model to carry out the analysis accurately accounting for the layerwise effects of the out-of-plane transverse shear and transverse normal stresses and deformations. Approximate solutions giving the ply fibre orientation at any point (compatible with the current manufacturing technologies) are considered in the numerical applications. The numerical results show that stitched sandwiches incorporating optimized low-cost glass-fibre plies can achieve the same bending stiffness as sandwiches with uniform stiffness carbon fibre faces, with a consistent reduction of critical out-of-plane stresses. The amplitude of vibrations under blast pulse loading can be consistently reduced with a proper choice of the curvilinear paths of fibres incorporated in the faces

Extension of the strain energy updating technique to a multilayered shell model with adaptive displacements and fixed DOF

The strain energy updating technique (SEUPT) is extended to a new zigzag shell model with a hierarchical piecewise representation of displacements, which can adapt to a variation of solutions across the thickness. This model has the capability of being refined across the thickness without increasing the number of functional DOF (the traditional midplane displacements and shear rotations). The purpose of the SEUPT is to improve the accuracy of standard finite elements based on equivalent single-layer models with transverse shear deformations up to the level of the zigzag model. The strain and kinetic energies and the work of external forces are updated through a postprocessing iterative procedure by starting from a local interpolation of the results of the finite-element analysis. Because no derivatives of in-plane stresses are involved, updating is fast. The current version of the SEUPT obtains accurate predictions of interlaminar stresses from constitutive equations; thus, it does not require integration of local differential equilibriums, which is unwise for finite elements and can be inaccurate in certain cases. Because of its adaptive capability, the SEUPT efficiently treats thick laminated plates and shells with distinctly different properties of layers, strong anisotropy, and significant transverse normal stresses and strains. Accuracy is assessed by considering the stresses under static loading and the response to blast pulse loading of undamaged and damaged sandwich shells with laminated faces. The results show that the SEUPT preserves the accuracy of the zigzag shell model and efficiently improves the accuracy of standard finite element

Lignocellulose degradation: a proteomic and metagenomic study

Wood decay processes have recently attracted so much attention, as lignocellulose biomass (LCB) represents the most abundant renewable resource on the Earth and can provide fermentable sugar monomers convertible into value-added products. In order to improve the efficiency and ecological sustainability of the process, new insights about lignocellulosic biomass microbial degradation could be of fundamental importance. Organic matter rich environmental samples may host a large variety of microbes, most of them specialized in the degradation of LCB and thus important as potential sources of biochemical catalysts for value added products production, as well as for the global carbon cycle. The aim of this thesis is to study the LCB degradation by two different approaches, exploiting proteomic and metagenomic tools. Proteomic analyses were conducted on the secretomes of a bacterium, Cellulomonas fimi, grown in presence of carboxymethyl-cellulose or different pretreated LCBs as unique carbon sources. Zymography and enzyme activity assays confirmed the lignocellulose degrading capabilities of C. fimi, showing endoglucanase and xylanase activities. The comparison among secretomes (in terms of enzymatic activities and protein composition) obtained after growth on different substrates highlighted: i) the major proteins and CAZymes (Carbohydrate Active enZymes) secreted and involved in LCB degradation and ii) the substrate influence on the secretome protein composition and enzymatic activity. Metagenomic analyses were indeed conducted on two groups of representative samples (two decaying woods and two control soils) in order to characterize the microbial communities inhabiting them. The microorganisms (bacteria and fungi) found to be more represented in decaying wood samples than in soils could be considered the most probably responsible for wood degradation

HPV vaccination in Italy: perspectives after 1-year experience

Focus No Summar

Does workplace training participation vary by type of secondary level qualification? England and Germany in comparison

Existing evidence shows that the higher the level of education the higher the likelihood to participate in workplace training. However, we know little about training participation of individuals educated to the secondary level, and whether this may vary by the type of qualification attained, i.e. vocational or general. Vocational qualification holders are known to find employment sooner after school than those with a general qualification but we do not know whether they are also more likely to participate in workplace training. Using data from the 2012 Programme of International Assessment of Adult Competencies (PIAAC) and logistic regressions, we investigate whether vocational qualification holders are more likely to participate in workplace training than general ones in Germany and England. Germany is a coordinated labour market economy with a large emphasis on the provision of vocational qualifications which facilitate school-to-work transitions whereas England is an example of liberal labour markets where the focus is on general qualifications. Results show that in Germany general qualification holders are more likely to participate in training compared to vocational ones; however, differences reduce when controlling for endogeneity. In contrast, in England there is no difference between types of qualification

Indentation of Sandwiches Using a Refined Zig-Zag Model and a Mesoscale Damage Model

An accurate and cost effective zig-zag plate model with variable kinematics and fixed degrees of freedom recently developed by the authors, which a priori fulfills the stress and displacement continuity requirements, is applied to study indentation of sandwiches with honeycomb/foam core. The variable elastic properties of the core during crushing are evaluated apart and once at a time through a 3D finite element analysis. Shell elements with elastic-plastic isotropic properties are adopted to discretize honeycomb cores and faces, instead solid elements with nonlinear material behavior are used for foam cores. To keep low the computational burden, the structural response is computed in closed form by the zig-zag model using these elastic properties. The damage analysis is carried out through a mesoscale model that determines the degraded properties of failed regions in a physically consistent way. A good agreement with experiments taken from the literature being shown, the present simulation procedure with a low computational effort is proven to be an efficient alternative to the ones currently employed

Ruined for Life

As a first-generation college student from a low income family, Gonzalez Icardi never thought he would have the chance to travel outside his home country. This reflection expresses his deep gratitude for the opportunity to study at LMU, and his eagerness to take advantages of the services that the university provides. Gonzalez Icardi found his Ignacio Companions trip to be eye opening, expanding his awareness of how other cultures live; though heartbreaking at times, Gonzalez Icardi remains grateful for the experience

Multilayered shell model with variable representation of displacements across the thickness

A multilayered zig-zag shellmodel is developed; it has a hierarchic representation of displacementsacross the thickness that a priori fulfils the interfacial stress contact conditions on interlaminar shear and normal stresses. Like for classical models, the functional d.o.f. are the mid-plane displacements and the shear rotations. Characteristic feature, the representation can vary from point to point across the thickness, in order to adapt to the variation of solutions. The coefficients of the higher-order terms are determined as functions of the d.o.f. by enforcing equilibrium conditions at discrete points across the thickness. The Lame's coefficients are expanded up to the second order. As shown by the numerical tests, it accurately predicts the stress fields of thick laminated and sandwich shells with abruptly changing material properties with a lower overall processing time than for the fixed representation, since post-processing is unnecessar