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Publikasjoner (10 av 113) Visa alla publikasjoner
Mussa, A., Krakhmalev, P. & Bergström, J. (2019). Failure analyses and wear mechanisms of rock drill rods: a case study. Engineering Failure Analysis, 102, 69-78
Åpne denne publikasjonen i ny fane eller vindu >>Failure analyses and wear mechanisms of rock drill rods: a case study
2019 (engelsk)Inngår i: Engineering Failure Analysis, ISSN 1350-6307, E-ISSN 1873-1961, Vol. 102, s. 69-78Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Rock drill rod failure is a big concern for the mining industry. The tough conditions required to break down rock material into small pieces subject rock drill components to high mechanical stresses and corrosion that lead to the failure of the drill rods. This paper describes a detailed examination of rock drill rods failed during field operations. The drill rods were manufactured from a high strength, hardened and tempered steel 22NiCrMo12-5F, carburized for better surface performance. The examination was carried out by means of light optical microscopy and scanning electron microscope. Microhardness profiles were performed for the studied rods. The focus of the present case study was to characterize the failure mechanisms and surface damages of the failed drill rods. The examined drill rods failed due to the initiation and propagation of fatigue microcracks at the outer surface of the thread. Surface cracks propagated to a certain crack length until the fracture toughness of the drill rod was exceeded and the final failure occurred. Multiple short cracks were observed on the fracture surface of the failed rods. The observed cracks propagated perpendicularly to the impacting direction towards the inner surface of the rods. Two different crack initiation mechanisms were observed in the present study, crack initiation from pits and crack initiation from severe plastic surface deformation. Sliding and abrasive wear damage, severe plastic deformation and pitting corrosion were observed on the threaded portion of the rods. Sliding wear was the most common wear damage mechanism observed in the thread joint. Pitting corrosion and severe plastic deformation, made the worn surface susceptible to crack initiation.

sted, utgiver, år, opplag, sider
PERGAMON-ELSEVIER SCIENCE LTD, 2019
HSV kategori
Identifikatorer
urn:nbn:se:kau:diva-72222 (URN)10.1016/j.engfailanal.2019.04.028 (DOI)000467804800007 ()
Tilgjengelig fra: 2019-05-31 Laget: 2019-05-31 Sist oppdatert: 2019-06-10bibliografisk kontrollert
Sadek, M., Bergström, J., Hallbäck, N. & Burman, C. (2018). 20 kHz 3-point bending fatigue of automotive steels. In: MATEC Web of Conferences: . Paper presented at 12th International Fatigue Congress, FATIGUE 2018, 27 May 2018 through 1 June 2018 (pp. 1-7). EDP Sciences, 165, Article ID 22020.
Åpne denne publikasjonen i ny fane eller vindu >>20 kHz 3-point bending fatigue of automotive steels
2018 (engelsk)Inngår i: MATEC Web of Conferences, EDP Sciences, 2018, Vol. 165, s. 1-7, artikkel-id 22020Konferansepaper, Publicerat paper (Fagfellevurdert)
Abstract [en]

The 20 kHz load frequency enables fatigue tests for very high cycle fatigue life, 109-1013 cycles, within conveniently short time. In automotive applications, many components are subjected to flexural loading and hence bending fatigue is an important test mode. Ultrasound fatigue test instruments have been used successfully in several assessments of fatigue strength and more commonly in uniaxial loading. Here, a 3-point bending fatigue test rig operating in resonance at 20 kHz load frequency has been designed to test plane specimens at R=0.1 loading. The test rig design and stress calculations are presented. Testing for fatigue strength was conducted using the staircase method with 15 specimens of each steel grade, specimens reaching 108 cycles were considered run-outs giving fatigue strength at 108 cycles. Additional 15 specimens of each grade were tested for S-N curves with the upper limit above 109 cycles. Two different common automotive steels, 38MnSiV5, a micro-alloyed ferritic-pearlitic steel, and 16MnCr5, a carburizing martensitic steel, were tested. The fatigue strengths achieved from the staircase testing are 340 and 419 MPa stress amplitudes for the 38MnSiV5 and 16MnCr5 steels, respectively. The S-N curves of the steels appear to be quite flat in the tested life range 107 - 109.

sted, utgiver, år, opplag, sider
EDP Sciences, 2018
Emneord
Automotive steels, Carburized steel, Ferritic-pearlitic steel, Three-point bending, VHCF, Binary alloys, Chromium alloys, Fatigue of materials, Fatigue testing, Ferrite, Ferritic steel, Pearlite, Silicon alloys, Stairs, Steel metallography, Steel testing, Pearlitic steels, Three point bending, Manganese alloys
HSV kategori
Forskningsprogram
Materialvetenskap
Identifikatorer
urn:nbn:se:kau:diva-68076 (URN)10.1051/matecconf/201816522020 (DOI)000478990600218 ()2-s2.0-85048089977 (Scopus ID)
Konferanse
12th International Fatigue Congress, FATIGUE 2018, 27 May 2018 through 1 June 2018
Tilgjengelig fra: 2018-06-26 Laget: 2018-06-26 Sist oppdatert: 2019-08-29bibliografisk kontrollert
AlMotasem, A. T., Posselt, M. & Bergström, J. (2018). Nanoindentation and nanoscratching of a ferrite/austenite iron bi-crystal: An atomistic study. Tribology International, 127, 231-239
Åpne denne publikasjonen i ny fane eller vindu >>Nanoindentation and nanoscratching of a ferrite/austenite iron bi-crystal: An atomistic study
2018 (engelsk)Inngår i: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 127, s. 231-239Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Molecular dynamics simulations are applied to investigate the wear/friction behavior of a ferrite/austenite iron bi-crystal, as a model system for duplex stainless steels. The plasticity of the ferrite phase is dominated by dislocations while both dislocations and stacking faults are the primary cause of plastic deformation of the austenite phase. Interestingly, the responses of tribological parameters vary depending on the scratch direction. For instance, the scratch hardness is increased by about 46% whereas the friction coefficient is reduced by about 22% when scratch starts from austenite to ferrite. At the interface, a local softening/hardening occurs because of dislocation-interface interaction. The present results demonstrate that martensitic phase transformation is responsible for experimentally observed high amount of ferrite of the pile-up.

sted, utgiver, år, opplag, sider
Elsevier, 2018
HSV kategori
Forskningsprogram
Materialteknik
Identifikatorer
urn:nbn:se:kau:diva-69118 (URN)10.1016/j.triboint.2018.06.017 (DOI)000442334100022 ()
Tilgjengelig fra: 2018-09-07 Laget: 2018-09-07 Sist oppdatert: 2018-09-13bibliografisk kontrollert
AlMotasem, A. T., Bergström, J., Gåård, A., Krakhmalev, P. & Holleboom, T. J. (2017). Atomistic insights on the wear/friction behavior of nanocrystalline ferrite during nanoscratching as revealed by molecular dynamics. Tribology letters, 65(3), 101
Åpne denne publikasjonen i ny fane eller vindu >>Atomistic insights on the wear/friction behavior of nanocrystalline ferrite during nanoscratching as revealed by molecular dynamics
Vise andre…
2017 (engelsk)Inngår i: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 65, nr 3, s. 101-Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Using embedded atom method potential, extensive large-scale molecular dynamics (MD) simulations of nanoindentation/nanoscratching of nanocrystalline (nc) iron have been carried out to explore grain size dependence of wear response. MD results show no clear dependence of the frictional and normal forces on the grain size, and the single-crystal (sc) iron has higher frictional and normal force compared to nc-samples. For all samples, the dislocation- mediated mechanism is the primary cause of plastic deformation in both nanoindentation/nanoscratch. However, secondary cooperative mechanisms are varied significantly according to grain size. Pileup formation was observed in the front of and sideways of the tool, and they exhibit strong dependence on grain orientation rather than grain size. Tip size has significant impact on nanoscratch characteristics; both frictional and normal forces monotonically increase as tip radii increase, while the friction coefficient value drops by about 38%. Additionally, the increase in scratch depth leads to an increase in frictional and normal forces as well as friction coefficient. To elucidate the relevance of indentation/scratch results with mechanical properties, uniaxial tensile test was performed for nc-samples, and the result indicates the existence of both the regular and inverse Hall-Petch relations at critical grain size of 110.9 angstrom. The present results suggest that indentation/scratch hardness has no apparent correlation with the mechanical properties of the substrate, whereas the plastic deformation has.

sted, utgiver, år, opplag, sider
New York: Springer, 2017
HSV kategori
Identifikatorer
urn:nbn:se:kau:diva-63698 (URN)10.1007/s11249-017-0876-y (DOI)000405488400027 ()
Tilgjengelig fra: 2017-09-14 Laget: 2017-09-14 Sist oppdatert: 2019-07-12bibliografisk kontrollert
Tofique, W., Bergström, J., Svensson, K., Johansson, S. & Peng, R. L. (2017). ECCl/EBSD and TEM analysis of plastic fatigue damage accumulation responsible for fatigue crack initiation and propagation in VHCF of duplex stainless steels. International Journal of Fatigue, 100, 251-262
Åpne denne publikasjonen i ny fane eller vindu >>ECCl/EBSD and TEM analysis of plastic fatigue damage accumulation responsible for fatigue crack initiation and propagation in VHCF of duplex stainless steels
Vise andre…
2017 (engelsk)Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 100, s. 251-262Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Fatigue test data of duplex stainless steel grades, LDX 2101 and 2304 SRG, in the Very High Cycle Fatigue (VHCF) regime is presented. Fatigue testing was conducted using ultrasonic fatigue test equipment operating at 20 kHz under fully reversed tension-compression load condition. Scanning Electron Microscope (SEM) analysis of the fracture surfaces and external surfaces of failed specimens was conducted. Electron Channelling Contrast Imaging (ECCI) and Electron Back Scattered Diffraction (EBSD) studies of the axially cut surface of the failed specimens was done to analyse the accumulation of plastic fatigue damage and fatigue crack growth in the grains adjacent to the external surface and crack initiation site. Transmission Electron Microscope (TEM) analysis of thin foils cut from failed specimens of LDX 2101 was carried out to examine the effect of fatigue loading on dislocation structure. SEM studies of the Crystallographic Growth Region (CGR) showed features like grain boundaries and fatigue striations on the fracture surfaces. SEM analysis of the external surfaces of fatigue loaded specimens showed inhomogeneous accumulation of plastic fatigue damage. ECCl/EBSD analysis showed Persistent Slip Bands (PSBs) in ferrite grains in LDX 2101 grade but no PSBs were observed in any grains of 2304 SRG specimens. The barrier effect of grain and phase boundaries on short fatigue crack propagation was observed. TEM analysis of thin foils cut from the failed specimens of LDX 2101 showed stacking faults in austenite grains and they were seen to stop at the grain and phase boundaries. (C) 2017 Elsevier Ltd. All rights reserved.

sted, utgiver, år, opplag, sider
Elsevier, 2017
Emneord
Duplex stainless steel, High frequency testing, Crack initiation, Damage accumulation, Fatigue crack growth, Short cracks
HSV kategori
Identifikatorer
urn:nbn:se:kau:diva-65533 (URN)10.1016/j.ijfatigue.2017.03.035 (DOI)000402217000024 ()
Tilgjengelig fra: 2018-01-05 Laget: 2018-01-05 Sist oppdatert: 2018-06-27bibliografisk kontrollert
AlMotasem, A. T., Bergström, J., Gåård, A., Krakhmalev, P. & Holleboom, T. (2017). Tool microstructure impact on the wear behavior of ferrite iron during nanoscratching: An atomic level simulation. Wear, 370-371, 39-45
Åpne denne publikasjonen i ny fane eller vindu >>Tool microstructure impact on the wear behavior of ferrite iron during nanoscratching: An atomic level simulation
Vise andre…
2017 (engelsk)Inngår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 370-371, s. 39-45Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

In the present work, molecular dynamics simulations were used to investigate the impact of the tool microstructure on the wear behavior of ferrite workpiece during nanoscratching. The tool microstructure was modified by varying the carbide (cementite) contents. The simulation results show that dislocations are the primary mechanism for plastic deformation of the workpiece material. It is found that total dislocation length varies significantly depending on the carbide content in the tool. Furthermore, other tribological phenomena were also observed to depend on the carbide contents. For example, the average value of frictional forces decreased while the normal force increases with increasing carbide contents, and hence the friction coefficient was decreased. Additionally, the shape and size of lateral and frontal pileups are lowered. The structural analysis of the pileup region reveals the loss of long range order and start of amorphisation. The temperature distribution of the pileup regions showed an increase of the pileup temperature when carbide is added into tool. The wear volume is considerably reduced when the carbide content increases. The average scratch hardness was found to decrease and the result was analyzed with the theoretical Taylor hardening model.

sted, utgiver, år, opplag, sider
Elsevier, 2017
Emneord
Molecular dynamics, Carbide, Wear volume, Dislocation, Pileup
HSV kategori
Identifikatorer
urn:nbn:se:kau:diva-55215 (URN)10.1016/j.wear.2016.11.008 (DOI)000392776300005 ()
Tilgjengelig fra: 2017-06-20 Laget: 2017-06-20 Sist oppdatert: 2019-06-17bibliografisk kontrollert
Tofique, M. W., Bergström, J. & Svensson, K. (2017). Very High Cycle Fatigue of cold rolled stainless steels, crack initiation and formation of Fine Granular Area. International Journal of Fatigue, 100(1), 238-250
Åpne denne publikasjonen i ny fane eller vindu >>Very High Cycle Fatigue of cold rolled stainless steels, crack initiation and formation of Fine Granular Area
2017 (engelsk)Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 100, nr 1, s. 238-250Artikkel i tidsskrift (Annet vitenskapelig) Published
Abstract [en]

Fatigue tests of cold rolled strip materials, a duplex stainless steel and a martensitic stainless steel, were performed using an ultrasonic fatigue test equipment operating at 20 kHz under a completely reversed tension compression load ratio R =-1. Fatigue test data (SN data) was generated in the VHCF regime and fracture surfaces of the failed specimens were investigated using a Scanning Electron Microscope (SEM). In the duple stainless steel grade, fatigue failures were found to be initiated at surface defects on the side surfaces or corners, created due to cold rolling, of the strip specimens. Features of a Fine Granular Area (FGA) were observed around the crack initiating surface defects on the fracture surfaces. In the martensitic stainless steel grade, fatigue crack initiation occurred due to aluminium-silicon oxide inclusions or surface defects created due to cold rolling of the material. In situ Focussed Ion Beam (FIB) technique was used to extract cross-sections from the FGA around the crack initiating defect on the fracture surface. Transmission Electron Microscope (TEM) investigations of the extracted cross-sections revealed FGAs in immediate vicinity of the crack initiating surface defects. The observed fine grained layers seemed to be composed of nano-sized grains and, thus, could be distinguished from the bulk material. The FGA around the surface crack initiating defects seems to have formed due to localized plastic deformation by stress concentration at the defects.

sted, utgiver, år, opplag, sider
oxford: Elsevier, 2017
Emneord
Duplex stainless steel, Martensitic stainless steel, Fatigue, High frequency testing, Crack initiation, Fine granular area
HSV kategori
Forskningsprogram
Materialteknik; Maskinteknik
Identifikatorer
urn:nbn:se:kau:diva-47126 (URN)10.1016/j.ijfatigue.2017.03.037 (DOI)000402217000023 ()
Forskningsfinansiär
Knowledge Foundation
Tilgjengelig fra: 2016-11-07 Laget: 2016-11-07 Sist oppdatert: 2018-06-27bibliografisk kontrollert
Almotasem, A., Bergström, J., Gåård, A., Krakhmalev, P. & Holleboom, T. J. (2016). A molecular dynamic study on the influence of carbide particles in ferrite on material transfer during nanoscratching of ferritic iron. In: Simancik, Frantisek (Ed.), Proceedings of the 10th International Tool Conference: TOOL, 10th International TOOL Conference : 04th to 07th October 2016, Bratislava, Slovakia. Paper presented at 10th TOOL Conference 2016 - TOOL 2016, Bratislava, Slovakia.
Åpne denne publikasjonen i ny fane eller vindu >>A molecular dynamic study on the influence of carbide particles in ferrite on material transfer during nanoscratching of ferritic iron
Vise andre…
2016 (engelsk)Inngår i: Proceedings of the 10th International Tool Conference: TOOL, 10th International TOOL Conference : 04th to 07th October 2016, Bratislava, Slovakia / [ed] Simancik, Frantisek, 2016Konferansepaper, Publicerat paper (Fagfellevurdert)
HSV kategori
Forskningsprogram
Materialteknik
Identifikatorer
urn:nbn:se:kau:diva-63702 (URN)9783200047860 (ISBN)
Konferanse
10th TOOL Conference 2016 - TOOL 2016, Bratislava, Slovakia
Tilgjengelig fra: 2017-09-14 Laget: 2017-09-14 Sist oppdatert: 2019-07-12bibliografisk kontrollert
AlMotasem, A. T., Bergström, J., Gåård, A., Krakhmalev, P. & Holleboom, T. (2016). Adhesion between ferrite iron-€“iron/cementite countersurfaces: A molecular dynamics study. Tribology International, 103, 113-120
Åpne denne publikasjonen i ny fane eller vindu >>Adhesion between ferrite iron-€“iron/cementite countersurfaces: A molecular dynamics study
Vise andre…
2016 (engelsk)Inngår i: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 103, s. 113-120Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The adhesive properties of Fe(110)/Fe(110) and Fe3C(001)/Fe(110) countersurfaces have been investigated by using classical molecular dynamics simulations. The simulation results show that Fe3C/Fe exhibits a relatively lower adhesion compared to the Fe/Fe. Additionally, the temperature dependence of the adhesive properties between 300–700 K has been examined. The results demonstrate that, with increasing the temperature, the values of the adhesion force and the work of adhesion continuously decrease in the case of Fe3C/Fe; they initially slightly increase up to 500 K then decrease in the case of Fe/Fe. Furthermore, the effect of lattice coherency between Fe/Fe has been examined and found to slightly reduce the adhesion. These results explain how carbides improve galling resistance of tool steel observed during dry sliding. 

sted, utgiver, år, opplag, sider
Elsevier, 2016
Emneord
Adhesion; Carbides; Iron; Temperature distribution; Tool steel, Adhesive properties; Cementite; Classical molecular dynamics; Commensurability; Galling resistance; Lattice coherency; Temperature dependence; Work of adhesion, Molecular dynamics
HSV kategori
Forskningsprogram
Materialteknik
Identifikatorer
urn:nbn:se:kau:diva-45815 (URN)10.1016/j.triboint.2016.06.027 (DOI)000384777100012 ()2-s2.0-84978120893 (Scopus ID)
Tilgjengelig fra: 2016-09-09 Laget: 2016-09-09 Sist oppdatert: 2019-07-12bibliografisk kontrollert
Sadek, M., Bergström, J., Hallback, N. & Burman, C. (2016). Computation of and testing crack growth at 20 kHz load frequency. In: F. Iacoviello, L. Susmel, D. Firrao, G. Ferro, (Ed.), 21ST EUROPEAN CONFERENCE ON FRACTURE, (ECF21): . Paper presented at 21st European Conference on Fracture (ECF), JUN 20-24, 2016, Catania, ITALY (pp. 1164-1172). Elsevier
Åpne denne publikasjonen i ny fane eller vindu >>Computation of and testing crack growth at 20 kHz load frequency
2016 (engelsk)Inngår i: 21ST EUROPEAN CONFERENCE ON FRACTURE, (ECF21) / [ed] F. Iacoviello, L. Susmel, D. Firrao, G. Ferro,, Elsevier, 2016, s. 1164-1172Konferansepaper, Publicerat paper (Fagfellevurdert)
Abstract [en]

Fatigue properties are evaluated in a large span of fatigue lives ranging from a few load cycles to more than 1013 load cycles. If the interest is focused on fatigue lives above 10(7) load cycles, we speak of the very high cycle fatigue (VHCF) range. For evaluation of properties in the VHCF range one often needs to use higher load frequencies to be able to perform testing within a reasonable time. Therefore, the influence of load frequency on fatigue strength and fatigue crack growth is an important issue, both from testing and design perspectives. Within an EU-RFCS research project on the frequency influence on high strength steel fatigue properties the present study has been conducted on fatigue crack growth testing to determine threshold values and crack growth material parameters. The testing was analyzed by FE-computation to determine geometry factors for AK-determination. The testing was performed in a 20 kHz ultrasound resonance instrument. In such a system the whole load train needs to be designed to run at a resonance frequency of 20 kHz, and it implies that the specimen needs to be designed and computations performed by dynamic computational methods. As the crack grows the dynamic response of the specimen will change, and hence calculation to obtain the geometry factor is made with a progressing crack length. A uniaxial tensile load at 20 kHz frequency is applied to a single edged notched side-grooved flat specimen. The specimen dimensions are calculated in order to have a resonance frequency of 20 kHz, which is the frequency used for the experiments. Dynamic FEM computation, with a 3D-model and a quarter symmetry was used with one of the symmetry planes parallel to and in the crack growth line. To avoid crack surface interpenetration during the simulations a rigid thin sheet was introduced and used as a counter-face to the crack surface. The solution obtained was then combined with the breathing crack model proposed by Chati et. al. (1997) in order to solve for the irregularities observed when crack surface interpenetration occurs. Finally, the whole load train was considered. Thus, also the computed frequencies were very close to frequencies observed in experiments. The computation of stress intensities was made for varying crack lengths in a series of simulations. The geometry factor relation was determined and used in 20 kHz crack growth testing to control the actual stress intensity at the advancing crack tip. Comparison of computations and experimental results were made.

sted, utgiver, år, opplag, sider
Elsevier, 2016
Serie
Procedia Structural Integrity, ISSN 2452-3216 ; 2
Emneord
Crack growth, High frequency, Dynamic analysis, steel, threshold testing
HSV kategori
Forskningsprogram
Materialvetenskap
Identifikatorer
urn:nbn:se:kau:diva-62609 (URN)10.1016/j.prostr.2016.06.149 (DOI)000387976801029 ()
Konferanse
21st European Conference on Fracture (ECF), JUN 20-24, 2016, Catania, ITALY
Tilgjengelig fra: 2017-08-10 Laget: 2017-08-10 Sist oppdatert: 2019-06-17bibliografisk kontrollert
Organisasjoner
Identifikatorer
ORCID-id: ORCID iD iconorcid.org/0000-0001-6029-2613