prof. RNDr. Jaroslav Pokluda, CSc.
E-mail:   pokluda@fme.vutbr.cz  WWW:   http://physics.fme.vutbr.cz/people/pokluda Dept.:   Institute of Physical Engineering Dept. of Micromechanics of Materials and Engineering Acoustics Position:   Professor Room:   A1/1435

Supervised courses:

• Micromechanics of Deformation and Fracture of Advanced Materials (DS207A)
• Micromechanics of deformation and fracture of advanced materials (DS207)
• Physical Base of Materials Fracture (9FZM)

Publications:

• POKLUDA, J.; PIPPAN, R.; VOJTEK, T.; HOHENWARTER, A.:
  Near-threshold behaviour of shear-mode fatigue cracks in metallic materials, Wiliey
  journal article in Web of Science
• VOJTEK, T.; PIPPAN, R.; HOHENWARTER, A.; HOLÁŇ, L.; POKLUDA, J.:
  Near-threshold propagation of mode II and mode III fatigue cracks in ferrite and austenite, Elsevier
  journal article in Web of Science
• ČERNÝ, M.; ŠESTÁK, P.; POKLUDA, J.; ŠOB, M.:
  Shear instabilities in perfect bcc crystals during simulated tensile tests
  journal article in Web of Science
• POKLUDA, J.:
  Dislocation-based model of plasticity and roughness-induced crack closure
  journal article in Web of Science
• ČERNÝ, M.; POKLUDA, J.:
  Ideal tensile strength of cubic crystals under superimposed transverse biaxial stresses from first principles
  journal article in Web of Science
• POKLUDA, J.; SLÁMEČKA, K.; ŠANDERA, P.:
  Mechanism of Factory-Roof Formation,
  Engineering Fracture Mechanics, Vol.77, (2010), No.1, pp.1763-1771, ISSN 0013-7944
  journal article - other
• POKLUDA, J.; ŠANDERA, P.:
  Micromechanisms of Fracture and Fatigue: In a Multiscale Context,
  ISBN 978-1-84996-265-0, (2010), Springer
  book

List of publications at Portal BUT

Abstracts of most important papers:

• POKLUDA, J.; PIPPAN, R.; VOJTEK, T.; HOHENWARTER, A.:
  Near-threshold behaviour of shear-mode fatigue cracks in metallic materials, Wiliey
  journal article in Web of Science
  This review paper presents a brief state-of-the art of the research on long fatigue shearmode cracks and describes some recent results on effective crack growth thresholds and mode I branching conditions achieved by the authors for ARMCO iron, titanium with two different microstructures, nickel and stainless steel. A special technique for preparation of fatigue precracks enabled us to substantially suppress the crack closure (friction) effects at the beginning of the experiment, and the measured threshold values could be considered to be very close to the effective ones. In all investigated materials, the effective thresholds under the remote mode II loading were found to be about 1.7 times lower than those under the remote mode III loading. Effective thresholds under mode II loading of investigated materials were found to follow a simple formula assembled by the shear modulus G, the magnitude of Burgers vector b and a goniometrical function of the mean deflection angle that depends on the number of available crystallographic slip systems. These quantities determine the intrinsic material resistance to mode II crack propagation at the threshold. A simple criterion for mode I branching in terms of effective threshold values well reflects a transition from the shear-mode to the opening-mode controlled crack propagation at the threshold. The associated transition deflection angle of 40 degrees is a material independent constant.
• POKLUDA, J.:
  Dislocation-based model of plasticity and roughness-induced crack closure
  journal article in Web of Science
  The paper presents a discrete dislocation model of contact shielding effects in the case of small-scale yielding under plane-strain conditions. The model is physically transparent and, unlike continuum-based models for plane stress, it enables us to directly assess the magnitude of both plasticity and roughness-induced components of crack closure. Moreover, it reflects an influence of microstructure on the roughness-induced term. The closure components can be simply extracted from experimentally measured values of the remote DK using standard data on mechanical properties and microstructure. Thus, the effective threshold DKeff,th can be obtained as nearly independent of microstructure coarseness and applied cyclic ratio as shown for several important engineering materials
• ČERNÝ, M.; POKLUDA, J.:
  Ideal tensile strength of cubic crystals under superimposed transverse biaxial stresses from first principles
  journal article in Web of Science
  Elastic response and strength of perfect crystals is calculated for triaxial loading conditions from first principles. The triaxial stress state is constituted by uniaxial tensile stress and superimposed transverse biaxial stresses. The maximum uniaxial tensile stress is evaluated as a function of the transverse stresses. Results for eight crystals of cubic metals and two orientations <110> and <111> of the primary loading axis are presented and compared with data for <100> direction of loading. Obtained results show that, within a studied range of biaxial stresses, the maximum tensile stress monotonically increases with increasing biaxial tensile stress for most of the studied metals. Within a certain range, the dependence can be mostly approximated by a linear function.
• POKLUDA, J.; ŠANDERA, P.:
  Micromechanisms of Fracture and Fatigue: In a Multiscale Context,
  ISBN 978-1-84996-265-0, (2010), Springer
  book
  First chapter deals with calculaton of theoretical strenght of crystala and their applications to nanocomposite properties and nanoindentation testing. Second chapter describes micro-degradation processes of brittle and ductile fracture of materials. Third chapter is devoted to dislocation mechanisms of iniiiation and propagation of fatigue cracks under loading modes I, II, III and the mixed mode. This chapter presents applications to a determinations of inherent threshold values, evaluation of materiáls fracture with surface coating and for failure analysis.
• POKLUDA, J., ČERNÝ, M., ŠANDERA, P., ŠOB, M.:
  Calculations of Theoretical Strength: State of the Art and History.,
  Journal of Computer-Aided Materials Design, Vol.11, (2004), No.1, pp.1-28, ISSN 0928-1045
  journal article - other
  Current state and historical evolution of theoretical strength calculations is presented as a brief overview completed by a database of selected theoretical and experimental results. Principles of a sophisticated analysis of mechanical stability of crystals are elucidated by means of a schematic example. Stability conditions and Jacobian matrixes are presented for selected crystalline symmetries and deformation paths. The importance of this analysis for understanding micromechanics of fracture is shown on the background of the influence of crystal defects. Differences between theoretical and experimental TS values are discussed and some challenging tasks are outlined for the near future.