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SUMMARY:Predictive modeling of hydrogen assisted cracking –  a Micromech
 anics  conquest - Dr Emilio Martínez-Pañeda\, CUED
DTSTART:20180223T140000Z
DTEND:20180223T150000Z
UID:TALK99883@talks.cam.ac.uk
CONTACT:Hilde Hambro
DESCRIPTION:The detrimental effect of hydrogen firmly challenges the use o
 f high-performance materials in energy infrastructure - the ductility and 
 toughness of structural alloys are dramatically reduced in corrosive envir
 onments. With current engineering approaches being mainly empirical and hi
 ghly conservative\, there is a strong need to understand the mechanisms of
  such hydrogen-induced degradation and to develop models able to predict t
 he initiation and subsequent propagation of cracks as a function of materi
 al\, environmental and loading variables.\n\nHowever\, hydrogen assisted c
 racking is a very complex mechanical-chemical problem that depends sensiti
 vely on mechanisms that pertain to the micro and atomic scales. The speake
 r and his collaborators have been actively engaged in the development of e
 nriched continuum-like models that aim to incorporate the mechanisms gover
 ning hydrogen-assisted cracking. To this end\, efforts have been devoted t
 o investigating crack tip fields by means of strain gradient plasticity (S
 GP) models\, as classical continuum theories are unable to adequately char
 acterize behaviour at the small scales involved in crack tip deformation. 
 Grounded on the physical notion of geometrically necessary dislocations (G
 NDs)\, SGP formulations have proven to quantitatively capture the hardenin
 g effects associated with large gradients in plastic strain. Finite elemen
 t results reveal that GNDs close to the crack tip promote local strain har
 dening and lead to a much higher stress level as compared with conventiona
 l plasticity.\n\nGradient-enhanced predictions proved to be particularly r
 elevant in hydrogen embrittlement models due to the essential role that th
 e hydrostatic stress has on both interface decohesion and hydrogen diffusi
 on. We show that\, when gradient effects are accounted for\, a small reduc
 tion in the cohesive strength due to hydrogen entails a sharp transition f
 rom microvoid damage to brittle failure. Encouraging agreement with experi
 mental data has been obtained by incorporating the influence of dislocatio
 n hardening in the modelling of hydrogen transport and environmentally ass
 isted cracking. The promising results achieved have attracted the interest
  of industrial partners and technical standards organizations\, ending wit
 h a scientific/engineering handshake a journey that began from fundamental
  micromechanics.\n
LOCATION:Oatley Seminar Room\, Department of Engineering
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