Lifetime Assessment of Particulate Ceramic Composite with Residual Stresses

2017 ◽  
Vol 754 ◽  
pp. 107-110
Author(s):  
Luboš Náhlík ◽  
Zdeněk Majer ◽  
Kateřina Štegnerová ◽  
Pavel Hutař
Keyword(s):  
Residual Stresses ◽  
Crack Propagation ◽  
Mechanical Loading ◽  
Ceramic Composite ◽  
Subcritical Crack Growth ◽  
Particulate Composites ◽  
Time To Failure ◽  
Complex Load ◽  
Composite Surface

A micro-crack propagation in particulate ceramic based composite was studied using finite element method (FEM). Subcritical crack growth (SCG) was numerically simulated under complex load conditions (mechanical loading and loading by internal residual stresses). The effect of residual stresses on the crack propagation was studied. Two-dimensional computational model of particulate ceramic composite with material properties corresponding to low temperature co-fired ceramics (LTCC) was developed. The results indicate that the presence of residual stresses significantly reduces values of stress intensity factor in the vicinity of composite surface and the direction of residual stresses around the particles contributes to the micro-crack deflection from the particles. The time to failure of the composite under mechanical loading was determined. Results obtained contribute to a better understanding of the role of residual stresses during micro-crack propagation in ceramic particulate composites.

3D Model of Crack Propagation in Particulate Ceramic Composite Containing Residual Stresses

2017 ◽  
Vol 754 ◽  
pp. 103-106
Author(s):  
Kateřina Štegnerová ◽  
Zdeněk Majer ◽  
Pavel Hutař ◽  
Luboš Náhlík
Keyword(s):  
Residual Stresses ◽  
Crack Propagation ◽  
Ceramic Composite ◽  
Volume Fraction ◽  
Numerical Models ◽  
Ceramic Composites ◽  
Fe Method ◽  
Critical Crack ◽  
Alumina Particles

A crack propagation and fracture behaviour of particulate ceramic composite were investigated. Influence of 3D shape of particles on the crack propagation was studied together with influence of the presence of residual stresses, which are developed inside the composite during manufacturing process. Finite element (FE) method was used for numerical simulation of propagating crack in the composite. Basic numerical models of low-temperature co-fired ceramics (LTCC) with alumina particles homogenously dispersed in the glass matrix were developed. Volume fraction of alumina phase was 20vol.%, which is typical amount for LTCC. The results show that existence of residual stresses retards the crack propagating under conditions of sub-critical crack growth (SCG). Presented results contribute to a better understanding of the role of residual stresses in particulate ceramic composites.

Study of Influence of Residual Stresses on Crack Propagation in Particulate Ceramic Composites

2016 ◽  
Vol 258 ◽  
pp. 178-181 ◽  
Author(s):  
Zdeněk Majer ◽  
Luboš Náhlík ◽  
Kateřina Štegnerová ◽  
Pavel Hutař ◽  
Raúl Bermejo
Keyword(s):  
Residual Stresses ◽  
Crack Propagation ◽  
Element Model ◽  
Ceramic Composites ◽  
Particulate Composites ◽  
Micro Cracks ◽  
Dimensional Finite Element ◽  
Density Factor ◽  
Energy Density Factor

The aim of the present work is to analyze the influence of residual stresses in the particulate ceramic composite on the crack propagation. The crack propagation direction was estimated using Sih’s criterion based on the strain energy density factor. A two-dimensional finite element model was developed for determination of crack path. The residual stresses resulting from the mismatch of coefficients of thermal expansion during the fabrication process of the composite were implemented to the computational model. The effect of the particles shape on the crack propagation was investigated. Conclusions of this paper can contribute to a better understanding of the propagation of micro-cracks in particulate composites in the field of residual stresses.

The Role of Residual Stresses in Particulate Composite with Glass Matrix

2015 ◽  
Vol 665 ◽  
pp. 173-176 ◽  
Author(s):  
Zdeněk Majer ◽  
Luboš Náhlík ◽  
Pavel Hutař
Keyword(s):  
Finite Element ◽  
Residual Stresses ◽  
Crack Propagation ◽  
Glass Matrix ◽  
Particulate Composite ◽  
Element Model ◽  
Propagation Path ◽  
Particulate Composites ◽  
Stress Criterion ◽  
Finite Element Software

The particulate composites with glass matrix are widely used in many engineering applications. The mismatch of coefficients of thermal expansion during the fabrication process usually causes the presence of the residual stresses around particles. The influence and the understanding of the effects of residual stresses on the material response is required. The main aim of the present paper was to create a two-dimensional finite element model to analyze the influence of residual stresses on micro-crack behavior of glass and ceramics-based particulate composites. The maximum tangential stress criterion (MTS) was used to predict the direction of the micro-crack propagation. The modelled material was a kind of Low Temperature Co-fired Ceramics (LTCC) containing alumina particles embedded in a glass matrix. The influence of the micro-crack length and magnitude of loading on the micro-crack propagation path were investigated. The finite element software ANSYS was used. Conclusions of this paper can contribute to a better understanding of the propagation of micro-cracks in particulate composites in the field of residual stresses.

Description of Strengthening Mechanism in Layered Ceramic Composites

2015 ◽  
Vol 665 ◽  
pp. 93-96 ◽  
Author(s):  
Kateřina Štegnerová ◽  
Luboš Náhlík ◽  
Pavel Hutař
Keyword(s):  
Residual Stresses ◽  
Crack Propagation ◽  
Ceramic Composite ◽  
Strengthening Mechanism ◽  
Ceramic Composites ◽  
Zirconia Ceramic ◽  
Linear Elastic ◽  
Density Factor ◽  
Elastic Fracture ◽  
Layered Ceramic

The aim of this paper is to describe specific crack behaviour in the layered alumina-zirconia ceramic composite with strong interfaces and its strengthening mechanism. Different coefficients of thermal expansion of individual constituents of ceramic composite cause high residual stresses inside the layers during the sintering process. Compressive residual stresses can significantly influence the crack propagation through the laminate hereby improve the resistance of the material to the crack propagation. Estimation of crack behaviour in laminate was performed assuming the validity of linear elastic fracture mechanics using the criterion based on the strain energy density factor derived by Sih. This paper describes the strengthening mechanism in layered ceramic composites and prediction of their failure which contributes to better understanding of the fracture behaviour of the layered ceramic composites.

Residual Lifetime Determination of Low Temperature Co-Fired Ceramics

2016 ◽  
Vol 713 ◽  
pp. 266-269
Author(s):  
Zdeněk Majer ◽  
Kateřina Štegnerová ◽  
Pavel Hutař ◽  
Martin Pletz ◽  
Raul Bermejo ◽  
...  
Keyword(s):  
Low Temperature ◽  
Residual Stresses ◽  
Crack Propagation ◽  
Crack Growth ◽  
Subcritical Crack Growth ◽  
Particulate Composite ◽  
Ceramic Materials ◽  
Ceramic Composites ◽  
Residual Lifetime ◽  
Density Factor

The effect of subcritical crack growth is nowadays intensively studied mainly in relation to the strength of ceramic materials. The main aim of the contribution is to describe behavior of micro-crack propagating in the Low Temperature Co-fired Ceramics (LTCC) under subcritical crack growth (SCCG) conditions. The micro-crack behavior is significantly influenced by residual stresses developed in the LTCC due to different coefficients of thermal expansion of individual components. Two-dimensional numerical model was developed to simulate micro-crack propagation through the composite. The micro-crack propagation direction was determined using Sih’s criterion based on the strain energy density factor and the micro-crack path was obtained. The residual lifetime of the specific ceramic particulate composite (LTCC) was estimated on the basis of experimental data. The paper contributes to a better understanding of micro-crack propagation in particulate ceramic composites in the field of residual stresses.

scholarly journals Reconstruction of river valley evolution before and after the emplacement of the giant Seymareh rock avalanche (Zagros Mts., Iran)

2019 ◽  
Vol 7 (4) ◽  
pp. 929-947 ◽  
Author(s):  
Michele Delchiaro ◽  
Marta Della Seta ◽  
Salvatore Martino ◽  
Maryam Dehbozorgi ◽  
Reza Nozaem
Keyword(s):  
Slope Failure ◽  
Rock Avalanche ◽  
Evolutionary Model ◽  
River Valley ◽  
Time To Failure ◽  
Stress Release ◽  
Seismic Triggering ◽  
Rock Creep ◽  
Before And After

Abstract. The Seymareh landslide, detached ∼10 ka from the northeastern flank of the Kabir-kuh fold (Zagros Mts., Iran), is recognized worldwide as the largest rock slope failure (44 Gm3) ever recorded on the exposed Earth surface. Detailed studies have been performed that have described the landslide mechanism and different scenarios have been proposed for explaining the induced landscape changes. The purpose of this study is to provide still missing time constraints on the evolution of the Seymareh River valley, before and after the emplacement of the Seymareh landslide, to highlight the role of geomorphic processes both as predisposing factors and as response to the landslide debris emplacement. We used optically stimulated luminescence (OSL) to date lacustrine and fluvial terrace sediments, whose plano-altimetric distribution has been correlated to the detectable knickpoints along the Seymareh River longitudinal profile, allowing the reconstruction of the evolutionary model of the fluvial valley. We infer that the knickpoint migration along the main river and the erosion wave propagation upstream through the whole drainage network caused the stress release and the ultimate failure of the rock mass involved in the landslide. We estimated that the stress release activated a mass rock creep (MRC) process with gravity-driven deformation processes occurring over an elapsed time-to-failure value on the order of 102 kyr. We estimated also that the Seymareh damming lake persisted for ∼3500 years before starting to empty ∼6.6 ka due to lake overflow. A sedimentation rate of 10 mm yr−1 was estimated for the lacustrine deposits, which increased up to 17 mm yr−1 during the early stage of lake emptying due to the increased sediment yield from the lake tributaries. We calculated an erosion rate of 1.8 cm yr−1 since the initiation of dam breaching by the Seymareh River, which propagated through the drainage system up to the landslide source area. The evolutionary model of the Seymareh River valley can provide the necessary constraints for future stress–strain numerical modeling of the landslide slope to reproduce the MRC and demonstrate the possible role of seismic triggering in prematurely terminating the creep-controlled time-to-failure pathway for such an extremely large case study.

An Equivalent Circuit Approach to Evaluating Conductivity of Polymer-Filler Composites

2002 ◽  
Vol 734 ◽  
Author(s):  
Vladislav Skorokhod
Keyword(s):  
Equivalent Circuit ◽  
Equivalent Circuit Model ◽  
Conductive Filler ◽  
Size Ratio ◽  
Particulate Composites ◽  
Mathematical Representation ◽  
Matrix Size ◽  
Linear System Of Equations ◽  
Polymer Filler

ABSTRACTAn equivalent circuit model of electrical conduction in polymer-filler particulate composites was developed in this study. The equivalent circuit was constructed for an individual composite particle with a sub-monolayer of conductive filler, where the filler particles play the role of circuit nodes, and inter-particle contacts are represented by resistors between the nodes. The mathematical representation of the equivalent circuit in the form of a linear system of equations for nodal potentials was solved numerically with Matlab software to calculate conductance of the composite as a function of the amount of conductive filler, filled fraction of the monolayer, filler-to-matrix size ratio and the degree of structuredness (non-randomness) of the filler material. Additionally, percolation concentrations and statistical distributions of composite conductance were calculated as functions of the filler-to-matrix size ratio.

Influence of the Interface and Residual Stresses on the Apparent Fracture Toughness of Layered Ceramic Composites Based on Alumina-Zirconia

2014 ◽  
Vol 606 ◽  
pp. 209-212
Author(s):  
Luboš Náhlík ◽  
Bohuslav Máša ◽  
Pavel Hutař
Keyword(s):  
Residual Stresses ◽  
Crack Propagation ◽  
Ceramic Composites ◽  
Layered Composites ◽  
Material Interfaces ◽  
Linear Elastic ◽  
Apparent Fracture Toughness ◽  
Elastic Fracture ◽  
Layered Ceramic ◽  
Good Agreement

This paper deals with the fracture behaviour of layered ceramic composite with residual stresses. The main goal is to investigate the effect of residual stresses and material interfaces on crack propagation by more complex 3D finite element models. The crack behaviour was described by analytical procedures based on linear elastic fracture mechanics (LEFM) and generalized LEFM. The influence of laminate composition with residual stresses on critical values for crack propagation through the laminate interfaces was also determined. Good agreement has been found to exist between numerical results and experimental data. The results obtained can be used for a design of new layered composites with improved resistance against crack propagation.

Sign in / Sign up

Export Citation Format

Share Document