New Internal Stress Driven on-Chip Micromachines for Extracting Mechanical Properties of Thin Films

A new concept of micromachines has been developed for measuring the mechanical properties of thin metallic films. The actuator is a beam undergoing large internal stresses built up during the deposition process. Al thin films are deposited partly on the actuator beam and on the substrate. By etching the structure, the actuator contracts and pulls the Al film. Full stress strain curves can be generated by designing a set of micromachines with various actuator lengths. In the present study, the displacements have been measured by scanning electronic microscopy. The stress is derived from simple continuum mechanics relationships. The tensile properties of Al films of various thicknesses have been tested. A marked increase of the strength with decreasing film thickness is observed.Comment: Submitted on behalf of TIMA Editions (http://irevues.inist.fr/tima-editions

Bauschinger effect in thin metallic films by fem simulations

Unpassivated free-standing gold and aluminum thin films (thickness ~ 200-400 nm, mean grain size dm,Au≈ 70-80nm, dm,Al≈ 120-200nm), subjected to tensile tests show Bauschinger effect (BE) during unloading [1, 2]. The focus of this work is to investigate the effect of microstructural heterogeneity such as grain sizes on the BE and the macroscopic deformation behavior in thin metallic films. The finite element code LAGAMINE is used to model the response of films involving sets of grains with different strengths. The numerical results are compared with experimental results from tensile tests on aluminum thin films from the work of Rajagopalan, et al. [2]

Belonging in the Dark: Towards a constructive theology of belonging christianly

This thesis seeks to provide some critical tools and signposts for reflecting constructively and christianly on the concept of belonging. Thus, it is an experiment in magpie theology, seeking to reconfigure creatively a variety of primarily contemporary theological voices, Catholic and otherwise, around the theme of belonging, and a new concept—belonging christianly. More specifically, this thesis endeavours to explore how the Christian story can nurture and affect our ways of understanding and reimagining belonging in a radical and subversive way that does justice to the longing for belonging, whilst also considering contemporary challenges such as the greater awareness of the defectiveness of traditional forms of belonging to which Christianity is not immune. In Part 1, it seeks to identify a grammar of theocentric belonging, that is a grammar of belonging to God, in God, and under God. This will provide the foundations for how our God-talk can inform the way we think about belonging christianly. To do so, it resorts to three key Christian doctrines—The Trinity, creation, and the Incarnation. Part 2 seeks to hold in tension, interrogate, and (re)construct the relationship between the fundamental (and eschatological) reality or mode of theocentric belonging painted in Part 1, and the finite, transitional, performative, fragmented, and often distorted ways in which humans do effectively belong in a finite and fallen world. Here emerge the ideas of postlapsarian belonging, and of belonging christianly as the long journey of discovery from postlapsarian belonging into theocentric belonging. Key doctrines for this second part will include those of original sin and atonement. Part 3 will attempt to reflect further on what belonging christianly might look like through the themes of imitation of and identification with Christ. Here will emerge the ideas of apophatic identification, and that of belonging as fraternal, non-sacrificial, and eucharistic. Key doctrines include the Cross, kenosis, Resurrection, and the Eucharist. The thesis concludes by identifying possible directions of development for the concept of belonging christianly in areas such as ecclesiology, sacramentology, digital theology, eco-theology, queer theology, pneumatology, and practical theology

A New Model for Void Coalescence by Internal Necking

A micromechanical model for predicting the strain increment required to bring a damaged material element from the onset of void coalescence up to final fracture is developed based on simple kinematics arguments. This strain increment controls the unloading slope and the energy dissipated during the final step of material failure. Proper prediction of the final drop of the load carrying capacity is an important ingredient of any ductile fracture model, especially at high stress triaxiality. The model has been motivated and verified by comparison to a large set of finite element void cell calculations.

Permeability evolution and water transfer in the excavation damaged zone of a ventilated gallery

peer reviewedThe fluid transfers occurring around underground galleries are of paramount importance when envisaging the long-term sustainability of underground structures for nuclear waste disposal. These transfers are mainly conditioned by the behaviour of the surrounding material and by its interaction with the gallery air. The hydro-mechanical behaviour of the excavation damaged zone, which develops around galleries due to the drilling process, is thenceforward critical because it is composed of fractures having a significant irreversible impact on flow characteristics and transfer kinetics. Besides, the material interaction with the gallery air may engender water drainage and desaturation. Thus, a gallery air ventilation experiment, preceded by its excavation, is numerically modelled in an unsaturated argillaceous rock to study its influence on hydraulic transfers. The fractures are numerically represented with shear strain localisation bands by means of a microstructure enriched model including a regularisation method. The impact of fracturing on the transport properties is addressed by associating the intrinsic permeability increase with mechanical deformation which is amplified in the strain localisation discontinuities. Such dependence permits us to reproduce a significant permeability increase of several orders of magnitude in the excavation damaged zone, in agreement with available experimental measurements. After the excavation, the hydraulic transfers are studied through the reproduction of a gallery air ventilation experiment that implies drainage and desaturation of the surrounding rock. These transfers depend on liquid water and water vapour exchanges at gallery wall that are introduced through a non-classical boundary condition. The model prediction successfully captures the drainage and desaturation kinetics of undisturbed and damaged rock

Large-scale failure prediction of clay rock from small-scale damage mechanisms of the rock medium using multiscale modelling

Clay rocks are multiphase porous media whose complex structure is characterised by heterogeneity and possible anisotropy on a wide range of scales. The mesoscopic scale plays a particular role in deformation mechanisms under mechanical loading by cracking. The behaviour of rocks at mesoscale is characterised by the material and morphological (shape and size) properties of its components and their interactions. The accurate reproduction and influence of these mesoscale characteristics on the material behaviour and damage at large scale remain a complex issue. This question becomes crucial when investigating the underground stability during excavation works such as tunnels. In this numerical multi-scale study, the mesostructure characteristics are embedded in a Representative Elementary Area (REA) in a 2D configuration. A double-scale numerical framework, with finite element resolution at both scales (FE2) and computational homogenisation, is considered. The influence of the mesostructural characteristics of a heterogeneous rock and the effect of different inter-granular properties on their macroscopic behaviour, are examined. Additionally, a predictive strategy which is based on the connection between the failure modes of the REA and the failure mechanisms of the macroscale structure is also presented. This study investigates the effect of the mesocracking on the shear banding in a rock specimen during laboratory biaxial shear test and the development of the Excavation Damaged Zone (EDZ) around tunnels. The objective of this work is to explain the failure mechanisms observed up to the engineering scale of underground structures through the morphological and material small-scale characteristics of the REA.</p

Large-scale failure prediction of clay rock from small-scale damage mechanisms of the rock medium using multiscale modelling

Clay rocks are multiphase porous media whose complex structure is characterised by heterogeneity and possible anisotropy on a wide range of scales. The mesoscopic scale plays a particular role in deformation mechanisms under mechanical loading by cracking. The behaviour of rocks at mesoscale is characterised by the material and morphological (shape and size) properties of its components and their interactions. The accurate reproduction and influence of these mesoscale characteristics on the material behaviour and damage at large scale remain a complex issue. This question becomes crucial when investigating the underground stability during excavation works such as tunnels. In this numerical multi-scale study, the mesostructure characteristics are embedded in a Representative Elementary Area (REA) in a 2D configuration. A double-scale numerical framework, with finite element resolution at both scales (FE2) and computational homogenisation, is considered. The influence of the mesostructural characteristics of a heterogeneous rock and the effect of different inter-granular properties on their macroscopic behaviour, are examined. Additionally, a predictive strategy which is based on the connection between the failure modes of the REA and the failure mechanisms of the macroscale structure is also presented. This study investigates the effect of the mesocracking on the shear banding in a rock specimen during laboratory biaxial shear test and the development of the Excavation Damaged Zone (EDZ) around tunnels. The objective of this work is to explain the failure mechanisms observed up to the engineering scale of underground structures through the morphological and material small-scale characteristics of the REA.</p

Een onderzoek naar de relatie tussen woordvolgorde en zinsbetekenis in het Nederlands

Janssen, Th.A.J.M. [Promotor