Search results for "cracking"
showing 10 items of 102 documents
A Grain-Scale Model of Inter-Granular Stress Corrosion Cracking in Polycrystals
2017
In this contribution, we propose a cohesive grain-boundary model for hydrogen-assisted inter-granular stress corrosion cracking at the grain-scale in 3D polycrystalline aggregates. The inter-granular strength is degraded by the presence of hydrogen and this is accounted for by employing traction-separation laws directly depending on hydrogen concentration, whose diffusion is represented at this stage through simplified phenomenological relationships. The main feature of the model is that all the relevant mechanical fields are represented in terms of grain-boundary variables only, which couples particularly well with the employment of traction-separation laws.
A Microstructural Model for Micro-Cracking in Piezoceramics
2018
Piezoelectric ceramics are employed in several applications for their capability to couple mechanical and electrical fields, which can be advantageously exploited for the implementation of smart functionalities. The electromechanical coupling, which can be employed for fast accurate micro-positioning devices, makes such materials suitable for application in micro electro-mechanical systems (MEMS). However, due to their brittleness, piezoceramics can develop damage leading to initiation of micro-cracks, affecting the performance of the material in general and the micro-devices in particular. For such reasons, the development of accurate and robust numerical tools is an important asset for th…
A microstructural model for homogenisation and cracking of piezoelectric polycrystals
2019
Abstract An original three-dimensional generalised micro-electro-mechanical model for computational homogenisation and analysis of degradation and micro-cracking of piezoelectric polycrystalline materials is proposed in this study. The model is developed starting from a generalised electro-mechanical boundary integral representation of the micro-structural problem for the individual bulk grains and a generalised cohesive formulation is employed for studying intergranular micro-damage initiation and evolution into intergranular micro-cracks. To capture the electro-mechanical coupling at the evolving damaging intergranular interfaces, standard mechanical cohesive laws are enriched with suitab…
Early-stage detection of surface stress corrosion cracking at the subgranular level
2014
The strain field at the interface between an alloy and its oxide layer has been mapped using nanopatterned gauges resistant to the environment of the primary nuclear medium. It was found that oxidation has decreased the alloy ductility, thereby enabling some grain boundary opening to be detectable from 1.8 % strain. It is shown that statistics of extreme rare events of hotspots quantify the occurrence of the local opening of intergranular cracks, and thereby the ageing process.
Damage in composites : from physical mechanisms to modelling
2006
International audience; The most critical types of damage in composite materials are transverse cracking, delamination and fiber breaking. The simulation of the behaviour and the rupture of these materials shows that it is important to consider failure mechanism in the design of structures. Each mechanism induces local deteriorations which can be accelerated when they are coupled with other mechanisms. Global criteria are unable to predict neither these processes nor their interactions. This paper is an attempt to propose realistic criteria which are the witness of local degradations and can be used for the design of composite structures.
Grain-boundary modelling of hydrogen assisted intergranular stress corrosion cracking
2018
Abstract A novel hybrid strategy for modelling intergranular hydrogen embrittlement in polycrystalline microstructures is proposed. The technique is based on a grain-boundary integral representation of the polycrystalline micro-mechanics, numerically solved by the boundary element method, coupled with an explicit finite element model of the intergranular hydrogen diffusion. The intergranular interaction between contiguous grains in the aggregate is modelled through extrinsic cohesive-frictional traction-separation laws, whose parameters depend on the concentration of intergranular hydrogen, which diffuses over the interface according to the Fick’s second law, inducing the weakening of the i…
Progressive cracking mastercurves of the transverse ply in a laminate
2009
In this study, progressive cracking of a transverse layer in a cross-ply composite laminate subjected to tensile loading is considered. Using the results of a probabilistic cracking model, approximate relations for crack density as a function of stress are derived for initiation-controlled and propagation-controlled cracking. It is shown that the crack density evolution in the transverse ply can be represented by a mastercurve in suitably normalized coordinates. The mastercurve approach is applied to progressive cracking in glass/epoxy laminates. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers
Coating fragmentation by branching cracks at large biaxial strain
2007
The fragmentation behaviour of a thin brittle coating attached to a ductile substrate subjected to equibiaxial quasi-static in-plane tension is studied. The experimentally observed cracking patterns are related to repetitively branching coating cracks. The fragmentation process is modelled by the rate equation approach. It is established that fragmentation by branching cracks leads to a qualitatively different fragment distribution compared to binary fragmentation. The fragmentation model is applied to identify crack branching and coating/substrate stress transfer parameters.
Investigation on Application of Basalt Materials as Reinforcement for Flexural Elements of Concrete Bridges
2015
Basalt polymers are rather new materials for civil engineering; therefore, identification of peculiarities and limitations of application of such polymers in concrete structures (particularly bridges) is of vital importance. This paper experimentally investigates deformation behaviour and cracking of flexural elements, which are predominant parameters governing serviceability of the bridges. Unlike a common practice, the present study is not limited by the analysis of concrete beams reinforced with the polymer bars; it also considers effectiveness of basalt fibre reinforced polymer sheets for repairing the beams. The analysis has revealed that a combination of the high strength and elastici…
Engineering failure analysis of corroded R.C. beams in flexure and shear
2018
Abstract In the present paper, a simple model to reproduce the load-deflection response of corroded beams failing in flexure and shear is presented and discussed. Effects of diffused and pitting corrosion on steel bars, compressive concrete strength degradation and concrete bond strength degradation due to rust formation are included in the model. Engineering approach based on limit state theory was here adopted to predict the peak and the residual flexural and shear strength of corroded beams with corresponding deflections and ductility estimation. Calculation of deflection at cracking taking into account of rust formation and deflection at yielding and the ultimate state taking into accou…