To assess the behaviour of porous materials, it is important to consider the influence of material microstructure. In this study, a multiscale experimental analysis is conducted to investigate the ...influence of micromechanical parameters, such as the material properties of metallic phases and porosity, on the macromechanical properties of a porous sintered steel. At the microlevel, indentation is conducted to identify microphases and metallographic analysis has been used on mesoscale to measure porosity. Tension uniaxial tests have been applied to characterize macro properties. The results of the tests suggest that the macromechanical properties of porous sintered metallic materials might be mostly influenced by the porosity, while at the microlevel no significant variation in the mechanical properties of microphases has been detected in samples with different density, i.e., porosity. In addition, porosity is related to the sintering density experimentally and an empirical expression that relates density and porosity is proposed.
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Porosity in sintered materials negatively affects its fatigue properties. In investigating its influence, the application of numerical simulations reduces experimental testing, but they are ...computationally very expensive. In this work, the application of a relatively simple numerical phase-field (PF) model for fatigue fracture is proposed for estimation of the fatigue life of sintered steels by analysis of microcrack evolution. A model for brittle fracture and a new cycle skipping algorithm are used to reduce computational costs. A multiphase sintered steel, consisting of bainite and ferrite, is examined. Detailed finite element models of the microstructure are generated from high-resolution metallography images. Microstructural elastic material parameters are obtained using instrumented indentation, while fracture model parameters are estimated from experimental S-N curves. Numerical results obtained for monotonous and fatigue fracture are compared with data from experimental measurements. The proposed methodology is able to capture some important fracture phenomena in the considered material, such as the initiation of the first damage in the microstructure, the forming of larger cracks at the macroscopic level, and the total life in a high cycle fatigue regime. However, due to the adopted simplifications, the model is not suitable for predicting accurate and realistic crack patterns of microcracks.
•Recently developed generalised phase-field fracture model is employed.•Realistic microstructural geometries of nodular cast iron are analysed.•Model is able to recover brittle/ductile fracture in ...monotonic and fatigue regime.•By changing material properties, a brittle to ductile fracture transition is observed.•Framework is able to solve contact problems coupled with fracture analysis.
The aim of this work is to model complex fracture and fatigue processes in microstructural geometries of nodular cast iron. Herein, recently developed generalised phase-field formulation for modelling fracture in brittle and ductile solids subjected to both monotonic and cyclic loading is employed. Three different sized microstructural specimens are analysed using different modelling options to investigate the transition between brittle and ductile fracture material behaviour. The results demonstrate the ability of the proposed model to reproduce crack nucleation and complex crack propagation patterns. Moreover, the low- and high-cyclic fatigue regime features are presented in terms of fracture patterns and Wöhler-type curve.
Parkinson's disease (PD) is neurodegenerative disease with a multifactorial etiopathogenesis with accumulating evidence identifying microbiota as a potential factor in the earliest, prodromal phases ...of the disease. Previous research has already shown a significant difference between gut microbiota composition in PD patients as opposed to healthy controls, with a growing number of studies correlating gut microbiota changes with the clinical presentation of the disease in later stages, through various motor and non-motor symptoms. Our aim in this systematic review is to compose and assess current knowledge in the field and determine if the findings could influence future clinical practice as well as therapy in PD.
We have conducted a systematic review according to PRISMA guidelines through MEDLINE and Embase databases, with studies being selected for inclusion via a set inclusion and exclusion criteria.
20 studies were included in this systematic review according to the selected inclusion and exclusion criteria. The search yielded 18 case control studies, 1 case study, and 1 prospective case study with no controls. The total number of PD patients encompassed in the studies cited in this review is 1,511.
The link between gut microbiota and neurodegeneration is a complex one and it depends on various factors. The relative abundance of various microbiota taxa in the gut has been consistently shown to have a correlation with motor and non-motor symptom severity. The answer could lie in the products of gut microbiota metabolism which have also been linked to PD. Further research is thus warranted in the field, with a focus on the metabolic function of gut microbiota in relation to motor and non-motor symptoms.
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