Fatigue crack shape prediction based on vertex singularity

Due to the existence of vertex singularity at the point where the crack intersects the free surface, stress distribution around the crack tip and the type of the singularity is changed. In the interior of the specimen the classical singular behaviour of the crack is dominant and can be described using analytic equations. Contrary to this, at the free surface or in the boundary layer close to free surface the vertex singularity is significant. The influence of vertex singularity on crack behaviour and a crack shape for a three-dimensional structure is described in this paper. The results presented make it possible to estimate fatigue crack growth rate and crack shape using the concept of the generalized stress intensity factor. The estimated fatigue crack shape can help to provide a more reliable estimation of the fatigue life of the structures considered

Analysis of crack growth in 3D printed plastic wrench

This research has been supported by Polymer Competence Center Leoben GmbH (PCCL, Austria) and the Ministry of Education, Youth and Sports of the Czech Republic under the project m- IPMinfra (CZ.02.1.01/0.0/0.0/16_013/0001823) and the equipment and the base of research infrastructure IPMinfra were used during the research activities.Fused filament fabrication (FFF) is a type of extrusion-based additive manufacturing technique also known as fused deposition modeling (FDM) or 3D-printing. It is possible to use the process of additive manufacturing for manufacturing of prototypes and also the final products. It is widely believed that parts produced by this method have the disadvantage of slightly worse mechanical properties because of consisting of many weld-lines in layers. However, newer studies confirm that this negative effect can be significantly reduced by appropriate choice of welding conditions of the printing process [3]. Mechanical properties like ultimate tensile strength, modulus, etc. of printed parts can then be similar to properties of injection molded or compressed parts

Fracture mechanics description of the defect in rolling cylinder

project m- IPMinfra (CZ.02.1.01/0.0/0.0/16_013/0001823

Numerical Analysis of Sub-critical Crack Growth in Particulate Ceramic Composites

AbstractThe strength of glass or ceramic containing materials can be affected by the environment (“stress corrosion”). Under applied stress, crack-like defects may grow (sub-critically) for stress intensity factors, KI, below the fracture toughness of the material, KIc. The aim of the present work was to develop a two-dimensional finite element model to analyze the subcritical crack growth behavior of ceramic-based particulate composites. The maximum tangential stress criterion (MTS) was used to predict the direction of the crack propagation, in the framework of linear elastic fracture mechanics. The modeled material was a Low Temperature Co-fired Ceramic (LTCC), containing alumina particles embedded in a glass matrix. The experimentally determined SCCG material behavior (i.e. v-KI data) was implemented in the numerical model. The effect of the elastic modulus of the particles on the subcritical crack propagation was investigated. The conclusions of this paper can contribute to a better understanding of the subcritical propagation of cracks in particulate composites

Analytical model of asymmetrical Mixed-Mode Bending test of adhesively bonded GFRP joint

This paper presents new analytical model of asymmetric mixed-mode bending (MMB) specimen of adhesively bonded pultruded GFRP joints. An easily applicable relationship for the calculation of the strain energy release rate of the asymmetric MMB specimens is proposed based on the beam theory. The model is capable to analyze stacking sequence as well as various crack propagation paths. In the paper the effect of the various fiber bridging length and different crack propagation paths is analyzed analytically and supported by experimental results. The methodology and results presented in this paper could be utilized for the design of both joint geometry and lay-up of the laminates constituting the joint or for the prediction of the fracture behavior of such structures

Role of air humidity in residual fatigue lifetime of railway axle

This research was funded by grant No. CK03000060 “Advanced design methodology of railway axles for safe and efficient operation” of The Technology Agency of the Czech Republic

Comparison of Different Load Spectra on Residual Fatigue Lifetime of Railway Axle

AbstractThe railway axles are subjected to variable amplitude loading. The variability is caused by many different regimes of train operation. The dominant load is caused by the weight of the vehicle, which generates rotary bending during train movement. Nevertheless, there are additional forces, which are generated when train goes through curved track, over crossovers, switches, rail joints etc. Present non-destructive defectoscopy can reliably detect only relatively long cracks (approximately 2mm long or longer). Hence there is a risk that the existing crack is not detected. Therefore, for conservative estimation of the residual fatigue lifetime the railway axle with a crack should be considered. The behaviour of the crack depends on load spectrum of railway axle. Hence for accurate determination of residual fatigue lifetime of the railway axle is necessary to know representative load spectrum. This paper compares several measured load spectra of railway axles, which are available in the literature. The effect of different load spectra is shown on two widely used materials for railway axles: EA1N and EA4T steels. Obtained results could be used for safer operation of railway axles

Estimation of stepwise crack propagation in ceramic laminates with strong interfaces

During the last years many researchers put so much effort to design layered structures combining different materials in order to improve low fracture toughness and mechanical reliability of the ceramics. It has been proven, that an effective way is to create layered ceramics with strongly bonded interfaces. After the cooling process from the sintering temperature, due to the different coefficients of thermal expansion of individual constituents of the composite, significant internal residual stresses are developed within the layers. These stresses can change the crack behaviour. This results to the higher value of so-called apparent fracture toughness, i.e. higher resistance of the ceramic laminate to the crack propagation. The contribution deals with a description of the specific crack behaviour in the layered alumina-zirconia ceramic laminate. The main aim is to clarify crack behaviour in the compressive layer and provide computational tools for estimation of crack behaviour in the field of strong residual stresses. The crack propagation was investigated on the basis of linear elastic fracture mechanics. Fracture parameters were computed numerically and by author’s routines. Finite element models were developed in order to obtain a stress distribution in the laminate containing a crack and to simulate crack propagation. The sharp change of the crack propagation direction was estimated using Sih’s criterion based on the strain energy density factor. Estimated crack behaviour is qualitatively in a good agreement with experimental observations. Presented approach contributes to the better understanding of the toughening mechanism of ceramic laminates and can be advantageously used for design of new layered ceramic composites and for better prediction of their failure