Phase-field modelling of fracture in single crystal plasticity

We propose a phase-field model for ductile fracture in a single crystal within the kinematically linear regime, by combining the theory of single crystal plasticity as formulated in Gurtin et al. (2010) and the phase-field formulation for ductile fracture proposed by Ambati et al. (2015) . The model introduces coupling between plasticity and fracture through the dependency of the so-called degradation function from a scalar global measure of the accumulated plastic strain on all slip systems. A viscous regularization is introduced both in the treatment of plasticity and in the phase-field evolution equation. Testing of the model on two examples for face centred cubic single crystals indicates that fracture is predicted to initiate and develop in the regions of the maximum accumulated plastic strain, which is in agreement with phenomenological observations. A rotation of the crystallographic unit cell is shown to affect the test results in terms of failure pattern and corresponding global and local response

Data-driven fracture mechanics

We present a new data-driven paradigm for variational brittle fracture mechanics. The fracture-related material modeling assumptions are removed and the governing equations stemming from variational principles are combined with a set of discrete data points, leading to a model-free data-driven method of solution. The solution at a given load step is identified as the point within the data set that best satisfies either the Kuhn–Tucker conditions stemming from the variational fracture problem or global minimization of a suitable energy functional, leading to data-driven counterparts of both the local and the global minimization approaches of variational fracture mechanics. Both formulations are tested on different test configurations with and without noise and for Griffith and R-curve type fracture behavior

Disfunctions in the anthocyanin accumulation of Vitis vinifera L. varieties studied by a targeted resequencing approach

BACKGROUND: The pathway of anthocyanin biosynthesis, and its alterations leading to berry colour modification, are well known in grape skin. This variability could affect both quantity and quality of pigment accumulation. OBJECTIVE: The present work is focused on 15 grapevine cultivars selected to represent a high variability in the phenotypical colour traits in order to highlight new polymorphisms related to the flavonoid pathway. METHODS: Twenty-one genes involved in the biosynthetic pathway of anthocyanins were studied via targeted resequencing and were correlated with phenotypic data ( anthocyanin profiles and spectroscopy indices). RESULTS: Single nucleotide polymorphism (SNP) and InDel (insertion/deletion) polymorphisms were detected. Out of 1751 polymorphic loci, 68% were SNPs and 32% were InDels (568). Cluster analysis and SPLS-DA were used to investigate the genetic relationships among the cultivars, confirming the large range of phenotypical variability. Statistically significant correlations were detected between accumulation of 3\u2019 anthocyanins and genetic polymorphisms in two structural genes and one transcription factor putatively involved in the anthocyanin biosynthetic pathway. CONCLUSIONS: The understanding of the polymorphisms related to the anthocyanin accumulation could support future selection of new pink table grape varieties with increased appeal on the consumers

A consistency assessment of coupled cohesive zone models for mixed-mode debonding problems

Due to their simplicity, cohesive zone models (CZMs) are very attractive to describe mixed-mode failure and debonding processes of materials and interfaces. Although a large number of coupled CZMs have been proposed, and despite the extensive related literature, little attention has been devoted to ensuring the consistency of these models for mixed-mode conditions, primarily in a thermodynamical sense. A lack of consistency may affect the local or global response of a mechanical system. This contribution deals with the consistency check for some widely used exponential and bilinear mixed-mode CZMs. The coupling effect on stresses and energy dissipation is first investigated and the path-dependance of the mixed-mode debonding work of separation is analitically evaluated. Analytical predictions are also compared with results from numerical implementations, where the interface is described with zero-thickness contact elements. A node-to-segment strategy is here adopted, which incorporates decohesion and contact within a unified framework. A new thermodynamically consistent mixed-mode CZ model based on a reformulation of the Xu-Needleman model as modified by van den Bosch et al. is finally proposed and derived by applying the Coleman and Noll procedure in accordance with the second law of thermodynamics. The model holds monolithically for loading and unloading processes, as well as for decohesion and contact, and its performance is demonstrated through suitable examples

Energy harvesting from electrospun piezoelectric nanowires for structural health monitoring of a cable-stayed bridge

Wireless monitoring could greatly impact the fields of structural health assessment and infrastructure asset management, but some technological challenges pose unsolved issues toward its reliable use in continuous large-scale applications. Among the others, it is worth highlighting that power supply by means of batteries is usually implemented within wireless sensor networks, even though it causes practical concerns that heavily prevent the development of efficient monitoring systems for large structures and infrastructures. Conversely, scavenging ambient energy can alleviate or eventually eliminate the problem of electrical supply by batteries, a strategy that has emerged in recent years as a promising technological solution for bridges. Within this framework, the present work proposes to harvest ambient-induced vibrations of bridge structures using a new class of piezoelectric textiles. The considered case study is an existing cable-stayed bridge located in Italy along the high-speed road that connects Rome and Naples, for which a recent monitoring campaign has allowed to record the dynamic responses of deck and cables. In order to enhance the electric energy that can be converted from wind- and traffic-induced bridge vibrations, the energy harvester exploits a piezoelectric nanogenerator built using arrays of piezoelectric electrospun nanofibers. Particularly, several fiber arrangements are studied at the nano/micro-scale leading to different macro constitutive laws and different electric energy output. A computational study is performed to demonstrate that such nanogenerator is able to provide higher energy levels from recorded dynamic loading time histories than a standard piezoelectric energy harvester. The feasibility of this piezoelectric nanogenerator for bridge monitoring applications is finally discussed

Numerical homogenization of piezoelectric textiles with electrospun fibers for energy harvesting

Piezoelectric effects are exploited in an increasing number of micro- and nano-electro-mechanical systems. In particular, energy harvesting devices convert ambient energy (i.e. mechanical pressure) into electrical energy and their study is nowadays a very important and challenging field of research. In this paper, the attention is focused on piezoelectric textiles. Due to the importance of computational modeling to understand the influence that micro-scale geometry and constitutive variables have on the macroscopic behavior, a homogenization strategy is developed. The macroscopic structure behaviour is obtained defining a reference volume element (RVE) at the micro-scale. The geometry of the RVE is based on the microstructural properties of the material under consideration and consists in piezoelectric polymeric nano-fibers subjected to electromechanical contact constraints. This paper outlines theory and numerical implementation issues for the homogenization procedure. Moreover, within this approach the average response resulting from the analysis of different fiber configurations at the microscale is determined providing a multiphysics constitutive model for the macro-scale

A comparative evaluation of coupled mixed-mode cohesive zone laws for interfacial debonding

WCCM XI, 11th World Congress on Computational Mechanics, Barcelona, Spain, 20-25 July 2014