Martin Leitner

Martin Leitner
Graz University of Technology | TU Graz · Institute of Structural Durability and Railway Technology

Professor

About

113
Publications
22,200
Reads
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1,121
Citations
Additional affiliations
December 2020 - August 2021
Graz University of Technology
Position
  • Professor (Full)
January 2010 - November 2020
Montanuniversität Leoben
Position
  • Professor (Associate)

Publications

Publications (113)
Article
Full-text available
According to the IIW recommendation, the fatigue strength of welded steel joints is defined as independent of the base material in case of the as-welded condition. However, post-treatment techniques can improve the fatigue performance of welded structures, especially for increased base material strengths. Therefore, this paper investigates the effe...
Article
Full-text available
Wire and arc additively manufactured (WAAM) parts and structures often present internal defects, such as gas pores, and cause irregularities in the manufacturing process. In order to describe and assess the effect of internal defects in fatigue design, this research study investigates the fatigue strength of wire arc additive manufactured structure...
Article
Full-text available
This study presents a basic investigation on angular strain behaviour of substrate using experiment and three different numerical computations based on elastic and elastic–plastic FEM methods. In simulation, a 3D simplified rectangular weld bead geometry was modelled and computed using general purposed numerical software MSC Marc/Mentat. While elas...
Article
Full-text available
An advanced lightweight design in cast aluminium alloys features complexly shaped geometries with strongly varying local casting process conditions. This affects the local microstructure in terms of porosity grade and secondary dendrite arm spacing distribution. Moreover, complex service loads imply changing local load stress vectors within these c...
Article
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This research presents the numerical evaluation of fatigue crack growth of structural steels S355 and S960 based on Paris’ law parameters (C and m) that are experimentally determined with a single edge notched tension (SENT) specimen using optical and crack gauge measurements on an electromotive resonance machine at constant amplitude load. The sus...
Article
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This fundamental research aims to analyse the effect of heat transfer coefficients, plasticity model of evolved material properties and simplified meshing strategy on substrate deformation induced by wire arc additive manufacturing (WAAM) process with dissimilar materials based on experiment and numerical simulation. Throughout the experiment, stai...
Article
This study focuses on prediction of distortion behavior of multi-pass GMAW of structural offshore steel S460G2 + M using thermo-mechanical (TMM) and inherent strain (ISM) methods. In TMM, material properties including plasticity model were obtained from advanced material modeling software based on characterized elemental compositions and double ell...
Article
According to the Recommendations for Fatigue Design of Welded Joints and Components by the International Institute of Welding (IIW), the fatigue strength of welded steel joints is in general independent of the base material strength. Post-treatment methods, such as the High Frequency Mechanical Impact (HFMI) treatment, can significantly increase th...
Article
Full-text available
This research work focusses on the implementation of a viscoplastic creep model in the thermomechanical simulation of the wire arc additive manufacturing (WAAM) process for Ti-6Al-4 V structures. Due to the characteristic layer by layer manufacturing within the WAAM process, viscoplastic material effects occur, which can be covered by implementing...
Article
In components, crack propagation is subjected to crack-closure-mechanisms which affect the build-up of the relevant threshold stress intensity factor range during cyclic loading. As structural parts are exposed to service loads incorporating a variety of load ratios, a significant change of the long-crack threshold value occurs, leading to a severe...
Article
Elastomer components are used in both primary and secondary spring stages in bogies of rail vehicles. The design of spring components of a bogie requires knowledge of the calculation of the elastic properties of these components. An elastomer spring component is typically analyzed in the dimension to be investigated. Calculated force-displacement c...
Article
Railways can transport cargo and persons a great distance. The combination of high axle loads, and the rigid wheels and rails made of steel results in high stresses at the wheel-rail contact. These high stresses cause rolling contact fatigue. To prevent and to forecast the rolling contact fatigue, the knowledge of the stresses and their effect on t...
Article
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This work presents a novel approach for defect based fatigue failure characterization using artificial intelligence (AI). An artificial neural network (ANN) is trained on experimentally determined data that is highly relevant in terms of fatigue. Load stress, hardness and killer defect size are the three main parameters defined as input arguments....
Article
High Frequency Mechanical Impact (HFMI) treatment offers a great opportunity to enhance the lightweight potential of welded structures using high strength steel materials. Focusing on the IIW Recommendations for the HFMI Treatment, a fatigue assessment based on the nominal, structural as well as notch stress approach is considered. Due to its sound...
Article
Nowadays automated welding processes produce high-quality welds with smooth and regular global weld geometry. However, the local geometry of the weld exhibits a certain amount of variance in its topography due to dynamic effects of the welding process itself. The subsequent change in local stress concentrations affects the fatigue behaviour of weld...
Article
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The effect of surface layer properties on the fatigue strength of selectively laser melted 17-4 PH stainless steel flat specimens is presented within this work. X-ray surface residual stress measurements in loading direction show that the residual stresses are negligible if a final heat-treatment is applied, whereas values of only about 3% of the n...
Chapter
This paper presents an investigation on deformation behaviour using elastic inherent strain method (ISM). The deformation of bead-on-plate substrate is induced by GMAW process in which the selected material of filler and substrate is austenitic stainless steel SS316L. A simplified rectangular bead geometry is modelled and the process is simulated u...
Chapter
Full-text available
In this study, the austenitic grain size in bead-on-plate heat-affected zone (HAZ) are predicted as grain size has been widely known as an important factor affecting the deformation mechanism of materials, its microstructures and mechanical properties. At the first stage, a numerical model of bead-on-plate process using Goldak’s double ellipsoid he...
Chapter
This research presents an investigation of material property model effects of thick-walled Wire Arc Additive Manufacturing (WAAM) process on deformation behaviour which involves thermo-mechanical non-linear numerical computation. A 3D thermo-elastic–plastic WAAM model is developed using general purposed FEA software MSC Marc/Mentat. The material mo...
Chapter
Continuing improvement in the field of virtual crack closure technique of metals provides the opportunity for reliable probabilistic fatigue crack growth. The paper presents an analysis of mode I fatigue crack growth in low carbon steel. Experiment was carried out with Single Edge Notched Tension (SENT) specimens to determine its fatigue crack grow...
Article
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This paper extends a previously published fatigue strength estimation methodology for additively manufactured metallic bulk material by additionally accounting for effects of as-built surface layers. Interaction of intrinsic defects and surface texture convergently initiates fatigue failure. Holistic consideration of influencing factors significant...
Article
This work focuses on the technological size effect of the cast aluminium alloy EN-AC 46200. Herewith, specimens inheriting specific local cooling rates and therefore varying local dendrite arm spacings are taken from crankcases with hot isostatic pressing (HIP) post-treatment. In order to evaluate the statistically distributed microstructural prope...
Article
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The objective of this research work is to scientifically contribute to the fatigue strength assessment of selectively laser melted metallic structures and aims to derive a methodology to safely estimate bulk material strength based on experimental data. Investigations focus on determination of the relevant post build and -processing residual stress...
Article
Full-text available
This fundamental research presents an investigation of Wire Arc Additive Manufacturing (WAAM) process on distortion and residual stress using numerical simulation. Further, WAAM geometry was modeled using simplified rectangular bead shape with five layers and three strings. The thermo-mechanical numerical simulation is conducted under consideration...
Article
Full-text available
This fundamental investigation presents the study on the grain growth prediction for bead-on-plate of stainless steel SS316L. At first, the numerical model is developed by using basic equation with ordinary differential equation for calculating the grain growth with the presence of growing precipitates. The modified kinetic constant ( M o * ) is de...
Article
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The International Institute of Welding published IIW-recommendations for the HFMI-treatment, which covers fatigue assessment procedures and quality assurances guidelines. This paper contributes to the validation of the detrimental effect of high R-ratios on HFMI-treated cover plate specimens made of high-strength steel S700. Applying the nominal st...
Article
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A recommendation for the application and fatigue assessment of the HFMI post-treatment was published by the IIW in 2016. Recently, the therein recommended HFMI design curves in case of constant amplitude loading (CAL) were validated involving test data with different base material yield strengths, increased plate thicknesses, and elevated load rati...
Article
Full-text available
Imperfections due to the manufacturing process can significantly affect the local fatigue strength of the bulk material in cast aluminium alloys. Most components possess several sections of varying microstructure, whereat each of them may inherit a different highly-stressed volume (HSV). Even in cases of homogeneous local casting conditions, the st...
Article
Full-text available
In 2016, the International Institute of Welding (IIW) published a recommendation for high-frequency mechanical impact (HFMI) treatment for improving the fatigue strength of welded joints. Since the publication of the HFMI recommendations, numerous of studies have been published with a considerable amount of new fatigue test data focusing on various...
Article
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The local fatigue strength within the aluminium cast surface layer is affected strongly by surface layer porosity and cast surface texture based notches. This article perpetuates the scientific methodology of a previously published fatigue assessment model of sand cast aluminium surface layers in T6 heat treatment condition. A new sampling position...
Article
The issue of transferability of crack propagation parameters from small-scale specimens up to real-scale components is investigated. Crack growth material parameters are determined based on single edge notched bending SE(B) specimen tests and the crack growth model is validated by 1:3 scaled railway axle experiments as well as for 1:1 test axles fo...
Article
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The welding of aluminium high pressure die castings is a well known and broadly investigated challenge in various fields of industry and research. Prior research in this specific field mainly focused on the optimisation of the welding and the casting process and on the cause of the frequently occurring porosity and incomplete fusion phenomena, wher...
Article
The fatigue strength of cast aluminium surface layers is significantly affected by casting imperfections. Experimental work reveals crack initiation due to three failure modes; microporosity, cast surface texture as well as a combination of both. A novel local sub-area evaluation of notch factors for surface texture characterisation utilises areal...
Article
Beside well-known influence factors like residual stresses, component and crack geometry also load sequence effects significantly impact the crack propagation rate. In this paper two major load sequence effects, namely overloads and small loads, and their particular influence on the fatigue crack growth are investigated in detail. Both effects lead...
Article
Full-text available
The division of the total fatigue life into different stages such as crack initiation and propagation is an important issue in regard to an improved fatigue assessment especially for high-strength welded joints. The transition between these stages is fluent, whereas the threshold between the two phases is referred to as technical crack initiation....
Article
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This paper focusses on the effect of hot isostatic pressing (HIP) and a solution annealing post treatment on the fatigue strength of selectively laser melted (SLM) AlSi10Mg structures. The aim of this work is to assess the effect of the unprocessed (as-built) surface and residual stresses, regarding the fatigue behaviour for each condition. The sur...
Article
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Shrinkage porosities and non-metallic inclusions are common manufacturing process based defects that are present within cast materials. Conventional fatigue design recommendations, such as the FKM guideline (“Forschungskuratorium Maschinenbau”), therefore propose general safety factors for the fatigue assessment of cast structures. In fact, these f...
Article
In this work, the strain energy density approach (SED) is utilized to assess the fatigue strength of circumferential V-notched specimens covering axial loading and rotating bending. Subsequent calculations of the linear-elastic SED lead to a statistical proven accordance among about one-hundred experimental tests, thereby introducing extended H-fun...
Article
Areal surface texture characterisation leads to significantly enhanced surface information content. To obtain such an improved data set, several methodological steps are required. A suitable filter and nesting index have to be preselected based on surface topography and targeted structure content of the roughness. To select the nesting index, a fil...
Article
Casting defects as well as sharp notches can serve as initial points for fatigue cracks under cyclic loading. On the contrary, the cyclic material crack resistance counteracts to crack propagation. Hence, an incipient crack can arrest completely, even though a constant cyclic load is applied. Considering a short propagating crack, the local stress...
Conference Paper
Full-text available
This paper presents attempts to assess fatigue crack growth and cycle number applied on high strength steel S960 at constant amplitude loading using analytical and numerical procedures which is further verified with experiment. The geometrical model of specimen and simulation were developed using freeware FEM software (CASCA and Franc2D) and Virtua...
Article
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Manufacturing process based imperfections can reduce the theoretical fatigue strength since they can be considered as pre-existent microcracks. The statistical distribution of fatigue fracture initiating defect sizes also varies with the highly-stressed volume, since the probability of a larger highly-stressed volume to inherit a potentially critic...
Article
The mean stress sensitivity of an imperfective and a near-defect free aluminium cast alloy is analysed in this work. Thereby, metallographical, quasi-static, high cycle fatigue and crack propagation investigations are conducted. The specimens are taken out from an Al–Si–Cu sand cast component with either T6 heat treatment or hot isostatic pressing...
Article
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This paper deals with the fatigue assessment of cast steel defects in terms of macroscopic shrinkage porosity. Within preliminary studies, a generalized Kitagawa diagram GKD was established by numerical analyses of V-notched specimens with varying opening angles. It was experimentally verified by the application of the notch stress intensity factor...
Article
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The majority of fatigue tests of welded specimens is based on shop-made samples generally exhibiting minor misalignment. Due to the challenge of ensuring misalignment-free joints in industrial manufacturing processes, investigations focussing on the effect of misalignment on the fatigue strength are important. Therefore, this paper deals with the i...
Article
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This paper deals with experimental fatigue crack propagation in rotating bending loaded round bar specimens as well as an analytical and numerical analysis of the residual lifetime. Constant amplitude (CA) load tests are performed with the surface crack length being evaluated using an optical measurement system. Fracture surfaces are microscopicall...
Article
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This study shows the effect of hot isostatic pressing (HIP) on the porosity and the microstructure, as well as the corresponding fatigue strength of selectively-laser-melted (SLM) AlSi10Mg structures. To eliminate the influence of the as-built surface, all specimens are machined and exhibit a polished surface. To highlight the effect of the HIP tre...
Article
The weld seam is generally the weak point of welded mechanical parts subject to fatigue loading. For this issue, a post-weld mechanical surface process called high-frequency mechanical impact (HFMI) was developed. This process combines both mechanical effects and a weld geometry improvement by generating compressive residual stresses and making a s...
Article
Full-text available
This work investigates overload-induced retardation effects for semi-elliptically cracked steel round bars. The specimen geometry equals the shaft area of a 1:3 down-scaled railway axle and the material is extracted from railway axle blanks made of EA4T steel. Rotating bending tests under constant amplitude loading as well as overload tests conside...
Article
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This paper presents a numerical simulation chain covering induction hardening (IH), superimposed stroke peening (StrP) as mechanical post-treatment, and a final fatigue assessment considering local material properties. Focusing on a notched round specimen as representative for engineering components, firstly, the electro-magnetic-thermal simulation...
Article
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This research deals with a method and procedure for enhancing the structural life of the commonly used steel structure in oil and gas industries HSLA S460G2+M with a thickness of 10 mm. The type of joint and welding process is T-joint with transverse and longitudinal attachment welded using semi-automated GMAW. Filler wire ER80S-Ni1 and mixed shiel...
Article
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This paper deals with a comprehensive investigation of fatigue life enhancement on semiautomated Gas Metal Arc Welding (GTAW) butt weld joint which is found almost everywhere in Malaysia welding structure steel sectors. The selected material in this study was high strength low alloy steel S460G2+M commonly used extremely in steel structure due to i...
Article
Sand-cast aluminium components enable complex component designs whose surface is partly machined subsequently. Thus, the fatigue strength is affected both by volumetric shrinkage porosity as well as by surface roughness. For as-cast surface characterisation, utilization of area-based roughness parameters is essential. Fatigue tests covering T6 and...
Article
Full-text available
This research focusses on influencing factors on the fatigue strength of selectively laser melted (SLM) aluminum structures. One main effect is detected as the surface condition. Therefore, miscellaneous test series involving the as-built surface as well as machined and polished surface topographies are experimentally investigated. In addition, the...
Article
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Cast parts usually inherit internal defects such as micro shrinkage pores due to the manufacturing process. In order to assess the fatigue behaviour in both finite-life and long-life fatigue regions, this paper scientifically contributes towards a defect-based fatigue design model. Extensive fatigue and fracture mechanical tests were conducted wher...
Article
Full-text available
This paper contributes to the effect of elevated temperature on the fatigue strength of common aluminum cast alloys EN AC-46200 and EN AC-45500. The examination covers both static as well as cyclic fatigue investigations to study the damage mechanism of the as-cast and post-heat-treated alloys. The investigated fracture surfaces suggest a change in...
Article
Aluminium cast components containing intrinsic flaws were investigated in terms of fatigue strength. Therefore, quasi-static, fracture mechanical and fatigue tests were conducted at specimens exhibiting varying microstructural characteristics. Subsequently, the specimens were metallographically and fractographically analysed to evaluate spatial ext...
Article
In general, micropore size acts as one of the most significant influencing factors on the fatigue strength of aluminium castings. Hence, an in-depth knowledge of the occurrence of micropore sizes and their local distributions in different locations in complexly-shaped lightweight components is of great interest to the casting industry. In this work...
Article
Full-text available
This paper focuses on the effect of induction hardening and superimposed stroke peening, as mechanical post-treatment, on the fatigue and fracture behavior of gas engine 50CrMo4 steel crankshafts. Comprehensive analysis in regard to local microstructure, hardness and residual stress profile in depth is performed to examine the local characteristics...