Miroslav Španiel

Calibration of Selected Ductile Fracture Criteria Using Two Types of Specimens

This paper presents the calibration of three universal ductile fracture criteria with the stress triaxiality and the normalized third invariant of deviatoric stress dependence. Xue-Wierzbicki, Bai-Wierzbicki and Extended Mohr-Coulomb criteria are calibrated using butterfly specimen and newly designed notched tube specimen for an austenitic stainless steel. Different stress states necessary for successful calibration are generated by suitable combination of tension/compression-shear or tension/compression-torsion loading of both specimens, respectively. Suitability of the specimens for ductile fracture criteria calibration is evaluated comparing the range of reached stress states, the homogeneity of stress in process zone and appropriateness for the computational simulation of tests. Possible combination of above mentioned results with tensile testing of standard and notched cylindrical specimens is discussed, too.

Microstructural residual stress in particle-filled dental composite

The main goal of this study is to develop a micromechanical model of a particle-filled dental composite focused on the residual stress (RS) field developed during the curing process in its microstructure. A finite element model of a representative volume element of filler and resin was developed, and volumetric shrinkage was simulated during the curing process. Four material models (von Mises plasticity model, Drucker–Prager plasticity model, von Mises plasticity model with stress relaxation and Drucker–Prager plasticity with stress relaxation) of the polymer resin were built to assess the influence of the material model on the resulting internal stress. The relationship between the curing process and the magnitude of the stress components will be described, and an analysis of the post-curing state of the material in particular microstructure locations will be conducted in this study. Obtained RS is comparable to the stresses developed in the material under the external load. The substantial dependence on the choice of material model for resin is to be observed, and the suitability of particular models is discussed.

Strain-amplitude dependent cyclic hardening of 08Ch18N10T austenitic stainless steel

In this paper, cyclic plasticity response of 08Ch10N10T austenitic steel under large strain amplitude loading is presented. Non-Masing behaviour and strain-amplitude dependent cyclic hardening is observed and analysed. Impact on testing and modelling associated with this phenomenon are described.

Ballistic Impact Experiments and Numerical Modelling of Parts of Sandwich Armor

This paper presents some experimental results of a bullet impact on composite armor together with numerical modeling approaches. The development of light composite sandwiches for ballistic protection is the target of a project in terms of which the research is being conducted. Traditionally, a vehicle ballistic protection is mainly achieved through metal-based armor which is extremely heavy, hence the increasing popularity of composite sandwiches. Numerical simulations allow for a reduction of the number of experiments needed to obtain appropriate design of ballistic protection, but they require verified modeling approaches and proper material data. Therefore, different modelling approaches for both parts of the composite sandwich have been tested and possibilities to adjust these models to experimental data were investigated.

Computational Assessment of Remaining Load Carrying Capacity of Pipes With Areal Surface Defects

This paper reports on two criteria for burst pressure prediction of pipe with the areal surface defect. The criteria deal with not circumferential defects in internally pressured pipes without significant global bending loads. On the basis of the experimental analysis relatively simple methodologies of prediction were designed. They are based on finite element (FE) analysis and representing transition between analytical approaches and full failure simulations employing material failure models. Concept of presented methodologies is based on similarity of stress, strain and material state when plastic collapse starts in the defect domain. The similarity is expressed in terms of simple one-parametric criteria: (i) geometry and topology of the domain at which the plastic state of material is reached, (ii) amount of specific energy dissipated by plastic deformation in the regions, where the ratio of energy dissipated by plastic deformation compared to elastic stress energy is too high. Calibration of these methodologies is based on burst tests of DN800 pipes made of X60 steel with artificial defects. The ranges of defects dimensions are: longitudinal from 120 mm to 340 mm; circumferential from 60 mm to 180 mm; remaining thickness from 2.7 mm to 6.1 mm.© 2009 ASME