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In this work a Ritz model for progressive non-linear damage analysis of variable angle tow composite plates is presented. The damage is treated in the framework of continuum damage mechanics and its evolution is based on a linear softening law with which four damage indices are computed for degrading the mechanical properties of the material. A set of analyses have been carried out to investigate how damage evolves in VAT composite plates under progressive loading.

A mixed finite element formulation for the Eringen’s nonlocal analysis of smart, magneto-electro-elastic, multilayered plates is presented. Finite elements for different refined higher order plate layerwise theories are systematically developed. They ensure interface continuity and allow associating different values of the nonlocal parameter to the laminate layers. Standard 9-node and 16-node isoparametric, quadrilateral finite elements have been implemented and tested, showing the characteristics and limitations of the proposed approach.

Composite materials are nowadays widely used in the aerospace sector both for primary and secondary structures for their high mechanical properties and the ability to model them according to project needs. Therefore, accurately predicting material behaviour when subjected to operating loads is extremely important in making the design process more efficient. For this purpose, computational approaches based on continuum damage mechanics have been largely used to study the progressive loss of material integrity due to the propagation and coalescence of microscopic defects. In this contribution, a recently developed hybrid computational technique, which combines the Virtual Element Method (VEM) with the well-known Boundary Element Method (BEM), is employed to study unidirectional fibrereinforced composite material’s transverse behaviour in the presence of inclusions with complex geometries. BEM is used to model the stiffer inclusion phase, which is considered a linear elastic material and maintains its pristine state. VEM is adopted to study the softer matrix phase, using VEM’s peculiar feature, which can simulate general nonlinear phenomena with a straightforward implementation like that of the standard FEM one. An application of the hybrid formulation mentioned above is presented to simulate damage onset and propagation in the matrix phase of the transverse section of a composite unite cell. Numerical results are discussed and compared with known results available in the relevant literature.

A microscale formulation for low-cycle fatigue degradation in heterogeneous materials is presented. The interface traction-separation law is modelled by a cohesive zone model for low-cycle fatigue analysis, which is developed in a consistent thermodynamic framework of elastic-plastic-damage mechanics with internal variables. A specific fatigue activation condition allows to model the material degradation related to the elastic-plastic cyclic loading conditions, with tractions levels lower than the static failure condition. A moving endurance surface, in the classic framework of kinematic hardening, enables a pure elastic behaviour without any fatigue degradation for low levels of cyclic traction. The developed model is then applied to micro-structured materials whose micromechanics is analysed using a boundary integral formulation. Preliminary results demonstrate the potential of the developed cohesive model. The future application of the proposed technique is discussed in the framework of multiscale modelling of engineering components and design of micro-electro-mechanical devices (MEMS).

A grain-scale formulation for high-cycle fatigue inter-granular degradation in polycrystalline aggregates is presented. The aggregate is represented through Voronoi tessellations and the mechanics of individual bulk grains is modelled using a boundary integral formulation. The inter-granular interfaces degrade under the action of cyclic tractions and they are represented using cohesive laws embodying a local irreversible damage parameter that evolves according to high- cycle continuum damage laws. The consistence between cyclic and static damage, which plays an important role in the redistribution of inter-granular tractions upon cyclic degradation, is assessed at each fatigue solution jump, so to capture the onset of macro-failure. Few polycrystalline aggregates are tested using the developed technique, which may find application in multiscale modelling of engineering components as well as in the design of micro-electro-mechanical devices (MEMS).

A computational preliminary study on the fracture behaviour of two kinds of finite-size bio-inspired lattice configurations is presented. The study draws inspiration from recent investigations aimed at increasing the fracture energy of some materials through small modifications of their microstructure. Nature provides several examples of strategies used to delay or arrest damage initiation and crack propagation. Striking examples are provided by the micro- architecture of several kinds of wood. In this study, the effects on crack propagations induced by architectural alterations inspired by the microstructure of wood are computationally investigated. In an age in which tight control of the micro-architecture can be achieved, e.g. through high-resolution 3D printing, it is of interest to investigate whether, starting from a baseline cellular architecture, it is possible to achieve superior material performance by simple but smart topological modifications.

A two-scale three-dimensional approach for degradation and failure in polycrystalline materials is presented. The method involves the component level and the grain scale. The damageinduced softening at the macroscale is modelled employing an initial stress boundary element approach. The microscopic degradation is explicitly modelled associating Representative Volume Elements (RVEs) to relevant points of the macro continuum and employing a cohesive-frictional 3D grain-boundary formulation to simulate intergranular degradation and failure in the Voronoi morphology. Macro-strains are downscaled as RVEs' periodic boundary conditions, while overall macro-stresses are obtained upscaling the micro-stress field via volume averages. The comparison between effective macro-stresses for the damaged and undamaged RVEs allows to define a macroscopic measure of local material degradation. Some attention is devoted to avoiding pathological damage localization at the macro-scale. The multiscale processing algorithm is described and some preliminary results are illustrated.

An effective computational framework for homogenization and microcracking analysis of polycrystalline RVEs is presented. The method is based on a recently developed grain-boundary formulation for polycrystalline materials and several enhancements over the original technique are introduced to reduce the computational effort needed to model three-dimensional polycrystalline aggregates, which is highly desirable, especially in a multiscale perspective. First, a regularization scheme is used to remove pathological entities, usually responsible for unduly large mesh refinements, from Voronoi polycrystalline morphologies. Second, an improved meshing strategy is used, with an aim towards meshing robustness, a requirement often challenged by the inherent high statistical variability of Voronoi tessellations. Additionally, for homogenization purposes, the use of periodic non-prismatic polycrystalline RVEs is proposed as an alternative to the classical prismatic RVEs, generally employed in the literature. The proposed overall scheme promotes a remarkable reduction in the number of DoFs of the problem in hand, and thus outstanding savings in terms of computational time and memory storage. Furthermore, the smoother meshing strategy, combined with a Newton-Raphson method, enhances the convergence of the microcracking algorithm.

Nutritional abnormalities and physical inactivity are risk factors of increased morbidity and mortality in patients with ESRD. Identify and define malnutrition, in particular protein-energy depletion (PEW), is an important task in the management of renal patients. The aim of this multicenter observational study was to implement the assessment of nutritional status and functional capacity in patients on peritoneal dialysis, including tests and validated methods which are relatively easy to apply in daily clinical practice. The study includes all the 133 prevalent patients (80 m, 53 f, age 65 14 years), in peritoneal dialysis treatment (vintage 26 19 months) in 9 centers in Tuscany. We performed anthropometry, bioimpedance (BIA), clinical biochemistry, evaluation of habitual physical activity (RAPA tests) and performance (Sit-To-Stand test), appetite-evaluation questionnaire, and indices including the Malnutrition Inflammation Score (MIS), Geriatric Nutrition Risk Index (GNRI), Charlson comorbidity index, Barthel and Karnowsky index. The latter showed a condition of dependence in 7.2% and 19.7% of cases, respectively. Poor appetite was recorded in 48.2%. The majority of patients fell within the overweight / obesity range (51%) with waist circumference values associated with increased cardiovascular risk in 51% of males and 60% of females. At the BIA analysis, a BCMI8 kg/m2 was detected in 39% of patients; an estimated protein intake1.0 g / kg/d was found in 59% of cases; 34% of patients had serum albumin3.5 g / dl; control of acidosis was good (bicarbonate 25.4 3.8 mM) but hyperphosphatemia was present in 64.6% of patients. A condition of sedentary or light physical activity was reported by 65.1% of patients, vigorous activity only by 11.9%. The 86.5% of patients able to perform the Sit-to-stand test reported a lower than the reference values for age and sex. A diagnosis of PEW was possible in 8% of our series, while a MIS score11, indicative of PEW, took place in 12.7% of cases. The values of the MIS correlated directly with age and the degree of comorbidity and inversely with the sit-to-stand test, RAPA tests and appetite level. The data in this study show that single tests indicative of malnutrition disorders are frequent to be found in our series of peritoneal dialysis patients. However, a diagnosis of PEW is quite infrequent. A large percentage of patients are overweight with increased abdominal adiposity, and reduced cell mass and protein intake below recommended levels; the level of habitual physical activity is low, and the level of physical capability is scarce. Therefore it is conceivable a nutritional counseling intervention to increase the intake of proteins, limiting the phosphorus and (when indicated) energy intake and to stimulating spontaneous physical activity or arranging assisted programs for functional rehabilitation. Close monitoring of the nutritional status and implementation of programs of adapted physical activity should have a prominent role in the clinical management of patients on peritoneal dialysis.