Petr Kabele

Analysis of Stability of Mode II Crack Growth

As the previous part of authors ́ research deals with numerical modelling of functionally graded members in general, the following part is focused on analysis of the interface between individual layers. For correct description of interface behavior in numerical simulations, interface model parameters must be determined by appropriate physical tests. Testing methods for the tensile properties are known while the shear tests may face some difficulties. Shear test configurations for measuring interface behavior after the peak which is related to the stable crack growth along the interface are analyzed. The subject of presented paper is to evaluate tests in terms of stable mode II crack growth along the interface. Stable crack growth is assessed by stress intensity factor and finite element method.

Durability under Chemical Loads

This chapter summarizes mostly experimental findings on the effects of various types of aggressive environment on the mechanical performance of SHCC materials. In many of the reported works, a multiscale approach to durability of SHCC is adopted; consequently influence on individual constituents (matrix, fibre and interface) and behaviour on different scales of resolution are investigated.

Nanoindentation of Cement Pastes and Its Numerical Modeling

This paper focuses on experimental investigations and numerical modeling of micromechanical behavior of cement paste. Cement paste is taken as a fundamental representative of building materials with heterogeneous microstructure. The main studies are devotes to experimental nanoindention and its implications to evaluation of material properties. The paper concerns the appropriateness of conventional methods used for evaluation of micromechanical properties and investigates possibilities of the use of enhanced methods for better description of the nanoindentation process. Limitation of traditional elastic solution is shown on the unique experimental program. Better descriptions of indentation based on analytical viscoelastic solution and finite element model with general visco-elasto-plastic constitutive relation are proposed. These models are used for simulation of indentation and for estimation of material parameters at micrometer scale.

COMPARISON OF FAILURE CRITERIA FOR WOOD IN TENSILE-SHEAR STRESS STATE

An orthotropic failure criterion enhancing the Lourencos criterion by a shear strength multiplier and a maximum shear strength upper bound has been recently proposed and validated for timber under tensile and shear loading by the authors. The paper discusses its applicability for predicting strength in comparison with Tsai-Hill criterion, Hankinsons and Hyperbolic formula applying the two above mentioned enhancements of the Lourencos criterion. Experimental data available in the literature for off-axis tensile and shear test of Sitka spruce (Picea sitchensis Carr.), Katsura (Cercidiphyllurn japonicurn Sieb. and Zucc.), Douglas fir (Pseudotsuga menziesii), Douglas fir laminated veneer and Cupiuba (Goupia glabra) are used for the purpose of this study.

Influence of the Bell-Jar Magma Chamber Geometry on a Caldera Formation

The formation of a caldera poses a serious risk for the society and the environment. There are several established processes (mostly dealing with the conditions inside the reservoir), which must take place in order to reach a collapse leading to the caldera. The role of magma chamber geometry is investigated in this paper, exploiting the numerical modeling. The results indicates that the knowledge of the magmatic system dimensions can provide a helpful factor for an assessment of the caldera formation scenario.

Mechanical Properties of Fiber Reinforced Lime-Based Mortars Evaluated from Four-Point Bending Test

In the study, the bending behavior of high-performance fiber reinforced lime-based mortars is experimentally investigated using four-point bending test. From the experimental data, the influence of the mortar’s composition on its stiffness, cracking strength and ultimate strength are investigated. It is also studied, whether the response has strain-softening or strain-hardening character and whether the material exhibits multiple cracking. Such behavior is very important for the durability of the material, because it allows carrying load during imposed deformations (due to thermal effects, movements of foundations, seismicity, etc.). The number of formed cracks is examined using digital image correlation method. The mortar composition is considered with two types of binder (pure lime, lime-metakaolin), with two types of polyvinyl alcohol fibers in four volume fractions (0.5÷2.0%). As the reference, we consider two sets of specimens made of plain mortar without fiber reinforcement.

Constitutive Model for Timber Fracture under Tensile and Shear Loads

A 2D homogeneous orthotropic constitutive model of tensile and shear fracture in timber based on fixed smeared crack approach has been developed and implemented in ATENA® finite element software. The model captures (1) elastic and inelastic behavior in small deformations range, (2) material orthotropy, both in linear and non-linear range, (3) cracking across or along fibers, and (4) behavior under unloading/reloading. In this contribution we present model validation through numerical simulations of compact tension shear (CTS) tests of Radiata Pine timber.

Numerical Analysis of Masonry Enhanced by Fiber Reinforced Lime-Based Render

Out of plane load bearing capacity of a masonry structure enhanced by surface render made of high performance lime-based mortar is investigated by numerical simulations using the finite element method (FEM). The response of the wall is simulated firstly without render (as a reference) then with surface render consisting of conventional lime mortar with increased tensile strength (by addition of the metakaolin) without fibers and finally with the proposed lime-metakaolin mortar reinforced with PVA fibers. The thickness of the surface render is considered in two configurations (20 mm and 40 mm). Material parameters of masonry units (bricks), joints (mortar between bricks) and conventional plain render are chosen with regard to investigations of historic structures (reported in the literature), material characteristics of fiber reinforced render are evaluated based on experiments or numerical simulations of these experiments. Using these parameters and characteristics, the numerical simulations of masonry wall subjected to out of plane bending are performed. The results allow us to identify influence of the thickness and the material of render on load-bearing and deformation capacity, failure mode and amount and width of cracks. The results show that the conventional plain mortar improves load-bearing capacity and deformation capacity proportionately to the thickness of render, but the response remains brittle. Fiber reinforced mortar significantly increases the deformation capacity and load-bearing capacity and the amount of absorbed energy is significantly improved.