Pavel Hutar

• Group Leader at Czech Academy of Sciences, Institute of Physics of Materials

Statistical distribution of residual fatigue life (RFL) of railway axles under given loading was computed using the Monte Carlo method by considering random variation of the selected input parameters. Experimental data for the EA4T railway axle steel, the loading spectrum, the press fit loading and the residual stress induced by surface hardening w...

This paper aims to investigate the impact of braking with brake blocks on the fatigue lifetime of the train wheel web. Braking generates heat, causing uneven thermal stress and residual stresses as it cools. This can lead to the initiation of fatigue cracks in the wheel web. Therefore, the main issue is the numerical modelling of the railway wheel...

The work investigates nonvalidity of the common presumption that the nondamaging cycles do not influence residual fatigue life. Paradoxically, application of the full loading spectrum (more cycles) resulted in approximately 2.3 times longer life of the fatigue crack growth specimens than application of the spectrum with 33% of the smallest amplitud...

Among polymer materials, high-density polyethylene (HDPE) is one of the most demanded polymers for packaging as well as in sectors with higher material requirements, such as the plastic pipe industry. The extensive use of HDPE means it is often present in municipal waste. Therefore, there is a high potential for reprocessing and exploring new appli...

Due to the very long operational lifetimes (up to 100 years) of polyethylene pipes, there is a strong demand for accelerated testing of pipe materials to experimentally prove the ability of a certain material to achieve such lifetime. Among the accelerated tests of performance, the cracked round bar (CRB) test is the most convenient. The CRB test t...

The presented study is focused on experimental results of high-cycle fatigue life of a cast polycrystalline nickel-based superalloy IN 738LC at temperatures of 800, 900, and 950°C. The absence of hot isostatic pressing (HIP) led to the occurrence of casting defects in the microstructure. The fatigue tests were performed in symmetrical loading in la...

The study is focused on the characterization of three microalloyed 38MnSiV6 steel variants in terms of microstructure, mechanical properties, and crack initiation. Conventional steel was used as reference material, while the two other variants with reduced sulfur content and Bi or Se addition were prepared. To determine the influence of the non-met...

Joining dissimilar metals is a frequent task for engineers in the power industry. The resulting dissimilar joints are then critical parts of the constructions and have to be able to withstand various loads during the operation of power devices. Due to the metals dissimilarity, the interface between ferritic side and the austenitic side of the joint...

Very often a manufacturing process is followed by some surface treatment. Such a process induces residual stress into the manufactured component. Compressive residual stress is desirable for enhancing the fatigue properties of the component. The residual stress is often measured only at the surface, if at all. However, residual stress is equilibrat...

The manufacturing process of railway axles usually includes axle surface treatment to induce compressive residual stress on the axle surface to increase impact resistance and fatigue lifetime. A proper determination of residual stress enables to obtain correct input data for other procedures, e.g., optimization of specialized treatment or lifetime...

Crack closure is a phenomenon which slows down fatigue crack propagation and leads to higher residual life of components and to a change in the crack front curvature. Because of the significant impact on the fatigue crack growth rate, the scientific and engineering community has been trying to describe this phenomenon very precisely. One of the mos...

The experimental determination of the resistance to fatigue crack propagation in steel, particularly in the so-called near-threshold regime, is a crucial issue for safety-relevant components which are designed to operate for a large number of loading cycles before undergoing periodic inspections. This work summarizes the most relevant results of ex...

Low-cycle fatigue behaviour and fatigue crack kinetics of the 316L austenitic stainless steel were studied under cyclic axial, torsional and in-phase combined loading using hollow cylindrical (tubular) specimens with a small hole for crack initiation. The concept of plastic J-integral was used, which was shown in previous studies to unify the crack...

Bulge testing is an experimental technique applied to the characterization of thin films, with which the mechanical properties are obtained employing numerical and analytical approaches. For rectangular and circular thin films, classical methods have been well adopted to calculate the stresses and strains at the central point without the dependency...

Complicated geometry in combination with surface treatment strongly deteriorates fatigue resistance of metallic dental implants. Mechanical properties of pure Ti grade 2, usually used for dental implant production, were shown to be significantly improved due to intensive grain refinement via Conform SPD. The increase of the tensile strength propert...

The problem of crack propagation from internal defects in thermoplastic cylindrical bearing elements is addressed in this paper. The crack propagation in these elements takes place under mixed-mode conditions—i.e., all three possible loading modes (tensile opening mode I and shear opening modes II and III) of the crack are combined together. Moreov...

Underload cycles with small load amplitudes below the fatigue crack growth threshold are dominantly considered as insignificant cycles without any influence on fatigue lifespan of engineering structural components. However, this paper shows that in some cases these underload cycles can retard the consequent crack propagation quite significantly. Th...

The effects of environment (in air and 3.5 wt. % NaCl solution) and artificially-induced surface scratches are investigated on the fatigue properties of railway EA4T (also called 25CrMo4) alloy steel. This steel is found to be markedly sensitive to the chloride-containing environment, with cracking at stresses two thirds of the in-air fatigue limit...

In this work two approaches to the description of short fatigue crack growth rate under large-scale yielding condition were comprehensively tested: (i) plastic component of the J-integral and (ii) Polák model of crack propagation. The ability to predict residual fatigue life of bodies with short initial cracks was studied for stainless steels Sanic...

In this work, we have applied an improved method to determine the yield stress and residual stress in a freestanding thin aluminum film by analysing experimental data obtained by the bulge test. The Al thin film was deposited by a magnetron sputtering technique. The film was cyclically loaded with increasing maximum gas pressure. The method to dete...

The applicability of the cracked round bar (CRB) test according ISO 18489 for the characterization of slow crack growth (SCG) in unplasticized polyvinylchloride (PVC-U) was analyzed by testing three PVC-U pipe compounds with different molecular mass, represented by different intrinsic viscosity numbers (K-values). The tests were conducted at lower...

Mixed mode I/III fatigue fracture behaviour of bulk polymers is scarcely investigated. Thus, the aim of this work is to focus on the comparison of pure mode I and mixed mode I/III fatigue loading of polyethylene. During mixed mode I/III testing, both increases and decreases of lifetime were observed, depending on the levels of applied mode I and mo...

Residual fatigue lifetime assessment of a cracked structure is a common task for engineering and scientific community. Fatigue crack may appear on the surface or in the initial defect, e.g. pores in weldments. Such a structure needs to be examined, whether is it safe to be operated. Various assessment methods of different difficulties exist. In thi...

Since numerous service failures are reportedly occurring due to the cracks exposed to mixed-mode loading conditions, this topic started to attract more attention recently. Therefore, a special device was designed to study mixed mode loading conditions of polymer materials. CRB (cracked round bar) specimen was not loaded conventionally in tension or...

While additive manufacturing of polymers, especially material extrusion-based methods such as fused filament fabrication, has become increasingly popular for design studies, rapid prototyping and the production of non-critical spare parts, its application in structurally loaded components is still scarce. One of the reasons for this might be scepti...

Cast polycrystalline superalloys are widely used for critical components in aerospace and automotive industries, such as turbine blades or turbocharges. Therefore, their fatigue endurance belongs to one of the most essential mechanical characteristics. Full-scale testing of such components involves great technical difficulties and requires signific...

Assessment of residual fatigue life of railway axles commonly does not include effect of residual stress. This paper presents advanced methodology for estimation of residual fatigue life of railway axles considering not only external loading but also internal residual stresses. The studied axles made of the EA4T steel were treated by induction hard...

Commercially pure Ti is a typical material for dental implants. Besides oral environmental effects, implants are seriously mechanically loaded during the lifetime. Mechanical resistance of coarse and ultra-fine grained Ti grade 4 was investigated. Significant grain size refinement resulting in the 65% increase of the proof stress is reported. The f...

One of the most loaded components of the train, with very long operation time, is a railway axle. During its operation, the conventional fatigue limit of 10⁷ cycles is reached easily and information about fatigue behavior for a higher number of cycles is missing. Therefore, the fatigue behavior of railway axle EA4T heat-treated steel with a bainiti...

Decomposition of the resistance to fatigue crack growth into the intrinsic and extrinsic component is very important for understanding of fatigue failure mechanisms, relation to microstructure and modelling of residual fatigue life. Crack closure for four grades of steel were estimated by the difference between Kmax values and the effective ΔKeff v...

Propagation and behavior of fatigue cracks are governed by strain fields in the vicinity of the crack tip. The numerical description of strains in the crack tip presents some challenges in the modelling by the multiscale involved in the fracture analysis. In this study, it is proposed a 2D finite element analysis conducted for fatigue crack propaga...

This paper presents a finite element analysis of a pre-cracked freestanding gold thin film subjected to bulge test. These tests were conducted in order to determine the elasto-plastic properties and fracture toughness of the gold films. For the experimental tests, a pre-crack was introduced in the center of the film by focused ion beam (FIB) millin...

While mixed-mode loading conditions became hot topic recently, it is still quite unexplored area, even in case of metals. In case of polymers, this is even more complex problem, thanks to their higher sensitivity on higher temperatures connected with friction. Since polymer materials are very popular, this topic is of high interest. One of the best...

Outstanding durability of plastic pressure and non-pressure pipes can cause difficulties, when a reasonable lifetime estimation is needed. It is impossible to prove the lifetime by testing, but there is a method of calculation that can provide a certain idea about the expected lifetime. The lifetime estimation is based on the assumption that the fa...

The hybrid laser-tungsten inert gas welding technology was applied to butt weld 3-mm-thick S460MC and S700MC high-strength low-alloy steel sheets. The intent of low-current arc addition was to preheat the material to reduce extremely fast cooling rate accompanying laser welding. High-cycle fatigue tests were performed to evaluate the effect of weld...

Lifetime of plastic pipes can be estimated by integration of a power law describing the crack kinetics. However, this procedure requires an FEM (finite element method) calculation of the possible crack propagation in the pipe to obtain stress intensity factor dependency on the crack length. It is very important for the simulation to consider every...

The crack growth behaviour of thermoplastic polymers is a relevant topic in current research. While a dominant portion of studies in fracture mechanics investigates Mode I loading situations, very little is done to better understand Mixed Mode crack growth, which can be equally important to accurate live time predictions of polymer parts. In this r...

The paper analyses fatigue crack closure in the near-threshold regime of the EA4T railway axle steel. The dependence of fatigue crack growth threshold on air humidity was experimentally obtained. Varying air humidity led to changes of fatigue threshold values K max,th in the range from 4 to 7 MPa m 0.5 , which was explained by the effect of oxide-i...

B1914 is a nickel-based superalloy with an increased amount of B (boron) and C (carbon) to reach an adequate amount of borides and carbides in the cast structure ensuring improved creep properties. However, the influence of the structure on the material high-cycle fatigue properties is not sufficiently described. The present study brings the experi...

Plastic pipe producers are forced by various initiatives to increase the content of recycled material in their products. The performance of the recycled material is worse than the performance of the virgin material. That is why plastic pipes made entirely of recycled material are now allowed for non-pressure applications only. It would be theoretic...

Residual stresses play an important role in propagation of potential fatigue cracks and they influence residual fatigue lifetime of railway axles. Essential step for assessment of residual fatigue lifetimes of railway axles is determination of magnitudes and distribution of residual stress in axle. This paper deals with determination of tangential...

Resistance to fatigue crack propagation is divided into the intrinsic (effective) component and the extrinsic component, represented by crack closure, which is very significant in the near-threshold regime. Crack growth rate measurements were done on the compact tension specimens made of the ferritic-pearlitic steel for automotive at the stress rat...

Fatigue growth of the crack may be retarded as a consequence of the fatigue crack closure occurrence. Complete understanding of the closure process and ability of its accurate assessment is in best interest of scientific and engineering community. In this paper, three-dimensional numerical model of M(T) specimen with straight crack front was create...

Lifetime of MAR-M 247 Ni-based superalloy was experimentally studied under high-frequency cyclic loading (120 Hz) with constant tensile mean stress σm = 300 MPa at temperature 900 °C in air. The stress amplitude σa was changed in order to investigate the superalloy lifetime in a wide range of conditions, from pure creep to pure fatigue. The superpo...

This paper describes and applies a methodology to determine the elastic properties of freestanding thin membranes by means of a bulge test and a numerical approach. The numerical procedure is based on the combination of two standard methods i.e. finite element analysis and classical analytical solutions to calculate elastic properties of thin films...

Polyethylene pressure pipes are designed for service lives of at least 50 years. While so far lifetimes have been assessed by pipe pressure tests, due to improved slow crack growth (SCG) resistance and increased testing times such tests are not suitable anymore for modern pipe grades. The paper presents an alternative methodology for lifetime predi...

SHORT SUMMARY This paper investigates possible use of recycled material as a part of a multilayer polyethylene pressure pipe system. Crack propagation in different configurations is simulated. Lifetimes of pipes containing recycled material are calculated. Results are compared with lifetimes of pipes made of virgin materials. ABSTRACT Significant e...

The presented work shows a load-deflection bulge test method to characterize mechanical parameters of thin films by means of a numerical modelling approach. A methodology based on the combination of finite element analysis and classical analytical equations is presented and discussed. Finite element modeling was conducted for monolayer (Si3N4) and...

Mixed mode loaded fatigue specimens are not used very frequently. The main reason is that there are still very few qualitative results, which would help with better understanding of how the mode II and mode III are affecting the overall crack propagation. On the other hand, there is considerable number of parts loaded in mixed mode. Studying fatigu...

As polymer parts are made by injection molding, most defects are usually caused by the shrinkage of material during solidification. These defects are then source of cracks in these parts. Present contribution is dealing with central cracked compression loaded polymer cylinder. In order to describe crack behavior under operational load, parametrical...

The purpose of this paper is to investigate the effect of the vertex singularity on the fatigue crack front behaviour. Single edge notch bend specimens of steel EA4T and aluminium alloy 7075 of various thicknesses are subjected to the cyclic loading and the angles of the fatigue crack front curvature was measured. The experimental procedure is simu...

The Cracked Round Bar (abbreviated as CRB in the following) test is used as standardized accelerated testing method for simple ranking of polyethylene pipes based on measuring number of cycles to failure of the cyclically loaded CRB specimen. It can also be used for the slow crack growth rate evaluation of the tested material. This paper deals with...

This article deals with lifetime calculations of electrofusion socket joint. Lifetime (in the sense of remaining time of propagating crack without the crack initiation period) of electrofusion socket is calculated using a combination of linear elastic fracture mechanics and finite element modelling. The lifetimes are calculated for a basic situatio...

This study shows a methodology to estimate mechanical parameters of thin films by means of a bulge test and a numerical approach. The methodology is based on the combination of finite element analysis with a classical analytical method. Finite element modelling was conducted for monolayer (Si3N4) membranes of 2x2mm with the aim to approximate both...

The operation of railway axles should fulfill at least two main demands: safety and low operation costs. A significant part of operation costs is given by the length of regular inspection intervals which should reveal potential fatigue cracks in railway axle. The detection of cracks is of a probabilistic nature, therefore their detection is not ens...

Description of stress singularity in the vicinity of a free surface is presented. Its presence causes the retardation of the fatigue crack growth in that region and fatigue crack is being curved. Numerical model is used to study dependence of the stress singularity exponent on Poisson’s ratio. Estimated values are compared to those already publishe...

To apply the load separation method on different materials - amorphous and semicrystalline . To compare results of the load separation method with the standard test method (ASTM D 6068-96 Standard Test Method for Determining J-R Curves of Plastic Materials; ISO/CD 28660 Plastics — Test Method for Determining J and R Curves).

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...

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 c...

The aim of this paper is to estimate the critical applied stress value for a crack initiated from a sharp V-notch tip. The classical approach of linear elastic fracture mechanics (LELM) was generalized because the stress singularity exponent differs from 0.5 in the studied case. The value of the stress singularity exponent depends on the V-notch op...

The overall stable crack initiation and propagation behaviour of fracture mechanics specimens cut from plastic pipes that were composed of different polyolefin materials were investigated using concepts of elastic–plastic fracture mechanics including the crack propagation kinetics. The effect of specimen shape, orientation, welding and lading rate...

Pipe failure in long-term applications is characterised by creep crack initiation and creep crack growth. Both can be determined by fracture mechanics-based tests of the pipe materials. Nowadays, several accelerated tests are available: PENT (Pennsylvania Edge Notch Tensile Test), FNCT (Full Notch Creep Tensile Test), CRB (Cracked Round Bar Test) o...

The main aim of the paper is to study the influence of both material inhomogeneity and weld bead geometry on crack propagation in welded polyolefin pipes. Lifetime of three pipes welded by different welding procedures is numerically estimated. Experimentally observed shapes of weld bead and change of material properties inside the welded region (th...

This paper addresses the important issue of the description of short fatigue crack behaviour. It is typical for these cracks that they propagate under large scale yielding conditions at the crack tip, which means that the non-linear fracture mechanics has to be applied. This paper presents results of experiments designed to measure the short crack...

Pipe failure in long-term applications is characterized by creep crack initiation and creep crack growth. Both can be determined by fracture mechanics based tests of the pipe materials. Nowadays, several accelerated tests are available: PENT (Pennsylvania Edge Notch Tensile test), FNCT (Full Notch Creep Tensile test), CRB (Cracked Round Bar test) o...

The paper is focused on fatigue crack propagation in the threshold area of the EA4T railway axle steel. Railway axles represent one of the most critical components for safety of trains. The main aim of this paper is to describe fatigue crack closure mechanisms in EA4T, which significantly influence the threshold value – a crucial parameter for dete...

The effect of high-frequency cycling (120 Hz) superimposed on high tensile mean stress on a lifetime of cast Ni-base superalloys IN 713LC at 800 °C and MAR-M 247 at 900 °C was investigated. It has been found that both the alloys exhibit qualitatively similar behavior in creep/fatigue loading conditions. Superposition of small stress amplitudes on t...

Railway axles are subjected to cyclic loading, which could lead to fatigue failure. Therefore, it is desired to know residual fatigue lifetime of railway axles to ensure safe operation of trains. Because of detection of relatively small fatigue cracks is not guaranteed an estimation of residual fatigue lifetime is based on damage tolerance approach...

Measurement of the short fatigue crack propagation can come across a lot of difficulties from the experimental point of view and interpretation of the results is also sometimes controversial. For simplicity, usual description of the short cracks is based on linear elastic fracture mechanics (using the concept of stress intensity factor). In this ca...

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...

The contribution deals with the issue of residual stresses in particulate ceramic composites used in microelectronics. Residual stresses are developed in the composite due to cooling during manufacturing process. Different coefficients of thermal expansions of particles and matrix cause important residual stresses in the composite influencing their...

© 2017 Trans Tech Publications, Switzerland. The study deals with the interaction of creep and high cycle fatigue of cast polycrystalline nickel-based superalloy IN 713LC at high temperatures. Previous works indicated that creep lifetime of superalloy structures was un-affected or even slightly increased in the cases with superimposed vibrations. T...

Railway axles are subjected to cyclic amplitude loading which can lead to fatigue failure. For safe operation of railway axles a damage tolerance approach taking into account a possible defect in railway axle is often required. Because of different operation regimes of trains (fast/slow ride, ride on straight track, on curved track, over switches e...

The overall stable crack initiation and propagation behaviour of specimens cut from plastic pipes that were composed of different polyolefin materials were investigated using concepts of elastic–plastic fracture mechanics including the crack propagation kinetics. The effect of specimen shape, orientation, welding, lading rate, composition/microstru...

Accelerated tests of the polyethylene pipes are necessary for the pipe lifetime calculations. Accepted methodology for prediction of slow crack grow rate in these materials is fatigue testing of CRB (cracked round bar) specimens. This paper deals with the FEM modelling of the crack propagation during the CRB test under the influence of residual str...

Railway axles are subjected to cyclic loading which can lead to fatigue failure. For safe operation of railway axles a damage tolerance approach taking into account a possible defect on railway axle surface is often required. The contribution deals with an estimation of residual fatigue lifetime of railway axle with initial inclined surface crack....

Purpose Polymeric particulate composites with thermoplastics, especially polypropylene (PP) matrix with mineral fillers, are of great practical importance due to their simple possibility of modifying mechanical properties and reducing the price/volume ratio of the resulting material. Both filler properties and interface properties have a great effe...

The contribution deals with the issue of mechanical response of the particulate ceramic composites used in microelectronic. Mechanical properties and behaviour of composites are highly influenced by residual stresses which are developed in material during cooling in manufacturing process due to the different coefficients of thermal expansions of in...

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 significantl...

Due to the high slow crack growth resistance of modern polyethylene pipe grades a reliable lifetime assessment of pipes with focus on stage II failure has become challenging. The current paper presents a scientific approach for a fracture mechanics lifetime prediction based on Cyclic Cracked Round Bar (CRB) Tests. Based on this standardized tests (...

This paper deals with residual stress in polyethylene (PE) pipes as an important factor that influences their lifetime. Residual hoop stress distribution in a PE pipe was determined using a methodology previously carried out by the authors on polypropylene pipes. Axial residual stress magnitude was determined by comparison of experimental data and...

Nickel base superalloys exhibit fatigue fracture behavior with features of brittle-like cleavage cracking under high cycle fatigue loading at temperatures up to approximately 800 °C. This specific fracture behavior was already documented in several studies, but a possible mechanism of fatigue crack propagation under this mode has not been made comp...

Over the last years many researchers have put a lot of effort into designing layered structures combining different materials in order to improve low fracture toughness and mechanical reliability of ceramics. It has been proven that an effective way is to create layered ceramics with strongly bonded interfaces. Significant internal residual stresse...

High cycle fatigue tests of the MAR-M 247 superalloy under constant load were conducted with the aim to determine S–N curves at temperatures 650, 800, 900 and 950 °C. It has been found that the slope of the S–N curves reflects changes of the cyclic deformation mechanism with temperature. At temperatures 650 and partly at 800 °C, fatigue crack propa...

The paper deals with an estimation of residual fatigue lifetime of railway axles under real loading spectrum. The residual fatigue lifetime is given by magnitude of fatigue crack propagation rate. This rate depends predominantly on load, geometry and material of the axle. Standard steel EA4T for manufacturing of railway axles is considered in this...