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  • Wahlström, Jens, 1979- (författare)
  • Towards a simulation methodology for prediction of airborne wear particles from disc brakes
  • 2009
  • Licentiatavhandling (övrigt vetenskapligt)abstract
    • During braking, both the rotor and the pads in disc brakes are worn. Since disc brakes are not sealed, some of the wear particles generated can become airborne. Several studies have found an association between adverse health effects and the concentration of particles in the atmosphere, so it is of interest to improve our knowledge of the airborne wear particles generated by disc brakes. However, in field tests it is difficult to distinguish these particles from others in the surrounding environment, so it may be preferable to use laboratory test stands and/or simulation models to study the amount of airborne wear particles generated. This thesis deals with a simulation methodology for prediction of airborne wear particles from disc brakes and three experimental methods for testing disc brake materials with focus on airborne wear particles. The four appended papers discuss the possibility to both measure and predict the number and size distribution of airborne wear particles that originate from the pad to rotor contact. The objective is to develop a simulation methodology that predicts the number and size distribution of airborne wear particles from disc brakes. Paper A describes how a modified pin-on-disc machine was used to study airborne wear particles originating from different disc brake materials. The results indicate that the test setup can be used to measure and rank the number concentration and size distribution of the airborne wear particles generated. Paper B describes a disc brake assembly test stand for measurements of airborne wear particles from disc brakes. The results indicate that the test setup can be used to measure the number concentration and size distribution of airborne wear particles generated from disc brake materials. The results also indicate a promising ability to rank different pad/rotor material combinations with respect to the number concentration of airborne wear particles. Paper C compares measurements made in passenger car field tests with measurements made in a disc brake assembly test stand and in a pin-on-disc machine. A promising correlation between the three different test methods is found. Paper D presents a simulation methodology for predicting the number and size distribution of airborne wear particles using finite element analysis (FEA). The simulated number distribution is compared with experimental measurements at component level. The result indicates that the proposed methodology may be used to predict the number concentration and size distribution of airborne particles generated in the pad-to-rotor contact.
  • Alemani, M., et al. (författare)
  • Scaling effects of measuring disc brake airborne particulate matter emissions – A comparison of a pin-on-disc tribometer and an inertia dynamometer bench under dragging conditions
  • Ingår i: Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology. - : Professional Engineering Publishing. - 1350-6501 .- 2041-305X. ; 232:12, s. 1538-1547
  • Tidskriftsartikel (refereegranskat)abstract
    • An important contributor to non-exhaust emissions in urban areas is airborne particulate matter originating from brake systems. A well-established way to test such systems in industry is to use inertia dynamometer benches; although they are quite expensive to run. Pin-on-disc tribometers, on the other hand, are relatively cheap to run, but simplify the real system. The literature indicates promising correlations between these two test stands with regard to measured airborne number distribution. Recent studies also show a strong dependency between the airborne number concentration and the disc temperature. However, a direct comparison that also takes into account temperature effects is missing. The aim of this paper is, therefore, to investigate how the transition temperature is affected by the different test scales, under dragging conditions, and the effects on total concentration and size distribution. New and used low-steel pins/pads were tested against cast iron discs/rotors on both the aforementioned test stands, appositely designed for particulate emission studies. A constant normal load and constant rotational velocity were imposed in both test stands. Results show that a transition temperature can always be identified. However, it is influenced by the test scale and the frictional pair status. Nevertheless, emissions are assessed similarly when an equivalent frictional pair status is analysed (e.g. run-in). Further investigations for fully run-in samples on the pin-on-disc should be performed in order to finally assess the possibility of using the tribometers for the initial assessment of different friction materials.
  • Jackson, Jennie A., et al. (författare)
  • Is what you see what you get? : Standard inclinometry of set upper arm elevation angles
  • 2015
  • Ingår i: Applied Ergonomics. - 0003-6870 .- 1872-9126. ; 47, s. 242-252
  • Tidskriftsartikel (refereegranskat)abstract
    • Previous research suggests inclinometers (INC) underestimate upper arm elevation. This study was designed to quantify possible bias in occupationally relevant postures, and test whether INC performance could be improved using calibration. Participants were meticulously positioned in set arm flexion and abduction angles between 0 degrees and 150 degrees. Different subject-specific and group-level regression models comprising linear and quadratic components describing the relationship between set and INC-registered elevation were developed using subsets of data, and validated using additional data. INC measured arm elevation showed a downward bias, particularly above 600. INC data adjusted using the regression models were superior to unadjusted data; a subject-specific, two-point calibration based on measurements at 0 and 900 gave results closest to the 'true' set angles. Thus, inclinometer measured arm elevation data required calibration to arrive at 'true' elevation angles. Calibration to a common measurement scale should be considered when comparing arm elevation data collected using different methods.
  • Kutelia, E. R., et al. (författare)
  • The tribological efficiency and the mechanism of action of nano-porous composition base brake lining materials
  • Ingår i: 1st International Congress on Advances in Applied Physics and Materials Science, APMAS2011,Antalya, Turkey,2011-05-12 - 2011-05-15. ; 1400, s. 546-554
  • Konferensbidrag (refereegranskat)abstract
    • Based on the comparative analysis of the experimental values determined for the tribological parameters for the three novel nano-porous composition base and two conventional brake lining materials while friction with the grey cast iron disc, it was shown the considerable high tribological efficiency of the novel nano-porous composition base lining materials in comparison with the conventional (from EU and USA market) brake lining materials. The explanation is given to the action mechanism of nano-porous composition base brake lining material and its tribological efficiency basing on the "triple phase" tribo-pair model.
  • Lindegård Andersson, Agneta, 1955, et al. (författare)
  • The impact of working technique on physical loads - an exposure profile among newspaper editors.
  • 2003
  • Ingår i: Ergonomics. - : Taylor & Francis. - 0014-0139 .- 1366-5847. ; 46:6, s. 598-615
  • Tidskriftsartikel (refereegranskat)abstract
    • The aim of this study was to investigate the possible associations between working technique, sex, symptoms and level of physical load in VDU-work. A study group of 32 employees in the editing department of a daily newspaper answered a questionnaire, about physical working conditions and symptoms from the neck and the upper extremities. Muscular load, wrist positions and computer mouse forces were measured. Working technique was assessed from an observation protocol for computer work. In addition ratings of perceived exertion and overall comfort were collected. The results showed that subjects classified as having a good working technique worked with less muscular load in the forearm (extensor carpi ulnaris p=0.03) and in the trapezius muscle on the mouse operating side (p=0.02) compared to subjects classified as having a poor working technique. Moreover there were no differences in gap frequency (number of episodes when muscle activity is below 2.5% of a reference contraction) or muscular rest (total duration of gaps) between the two working technique groups. Women in this study used more force (mean force p=0.006, peak force p=0.02) expressed as % MVC than the men when operating the computer mouse. No major differences were shown in muscular load, wrist postures, perceived exertion or perceived comfort between men and women or between cases and symptom free subjects. In conclusion a good working technique was associated with reduced muscular load in the forearm muscles and in the trapezius muscle on the mouse operating side. Moreover women used more force (mean force and peak force) than men when operating the click button (left button) of the computer mouse.
  • Lyu, Yezhe, 1987-, et al. (författare)
  • A Friction, Wear and Emission Tribometer Study of Non-Asbestos Organic Pins Sliding Against AlSiC MMC Discs
  • 2018
  • Ingår i: ; 40:2, s. 274-282
  • Tidskriftsartikel (refereegranskat)abstract
    • The friction, wear and particle emission from an AlSiC MMC brake disc/non-asbestos organic brake pad system is studied using a pin-on-disc tribometer. The results show that this unconventional AlSiC MMC brake disc system presents friction performance as good as a conventional cast iron brake disc system. During braking, brake pad materials are transferred to the brake disc surface to form a protective third body tribo-layer, resulting in a negative specific wear rate of the brake disc. A higher contact load is likely to make it easier to generate the tribo-layer. The tribo-layer also seems to depend on the disc surface grinding features and the contact temperature during braking. By reusing an AlSiC MMC disc where the tribo-layer is already formed, the airborne emission in terms of mass is about 50% lower and in terms of number about the same as the conventional brake contact pair under a similar braking condition. Further full-scale studies are suggested to determine the validity of the findings.
  • Riva, Gabriele, et al. (författare)
  • Simulation of contact area and pressure dependence of initial surface roughness for cermet-coated discs used in disc brakes
  • Ingår i: Tribology in Industry. - : Masinski Fakultet - Kragujevac. - 0354-8996 .- 2217-7965. ; 41:1, s. 1-13
  • Tidskriftsartikel (refereegranskat)abstract
    • Friction, wear, and emission performance strongly depend on the contact pressure and area at the interface of the pad and disc. The contact situation at the pad-to-disc interface can be explained by the formation and destruction of mesoscopic sized contact plateaus on the pad surface. Experimental studies report that the initial surface roughness of cermet-coated discs strongly affects friction, wear and emission performance. This is explained by the formation of secondary plateaus on the disc surface. The aim of this work is to extend an existing cellular automaton approach to include the formation of secondary plateaus on the disc surface in order to explain experimental results reported in the literature. First, to investigate the validity of the novel simulation approach, a cermet-coated cast iron disc is tested against a low-met pad material with a pin-on-disc tribometer. The same conditions are used as input in a simulation. Then, the initial disc roughness influence on contact pressure and area of the same cermet-coated disc is compared with results reported in the literature. The topographies of the measured and simulated disc surfaces are qualitatively in line. An initial rougher disc surface results in a considerably lower contact area than does a smother surface.
  • Wahlström Edling, Cecilia, 1959- (författare)
  • Besvär i rörelseorganen hos musiklärare och deras syn på musikelevers hälsa : visioner och verklighet på kollisionskurs
  • 2017
  • Licentiatavhandling (övrigt vetenskapligt)abstract
    • The overall aim of the licentiate thesis was to reach a better understanding of music teachers' health, with focus on musculoskeletal disorders, and music teachers' view on young music students' health, from a gender perspective.A cross-sectional study was directed to music teachers employed at a municipality music- and culture school, in order to investigate the relationship between physical workload and work-related disorders among music teachers. Out of 61 music teachers 47 agreed to participate. The study group was divided into two groups depending on if they had an asymmetric or symmetric upper extremity and back playing posture. Musculoskeletal disorders were frequent among the music teachers. Women music teachers reported significantly more musculoskeletal disorders than their male collegues and music teachers with asymmetric work posture had significantly higher amount of musculoskeletal disorders than those who had a symmetric playing posture.A qualitative interview study with semi-structured interviews with 18 music teachers were conducted to explore music teachers' experiences of health and gender among young music students. An interview guide was used, with topic areas concerning experiences and perceptions of positive health aspects and health problems among young music students, taking part in music education. The interviews were analysed with qualitative content analysis according to Graneheim and Lundman. The analysis resulted in an overarching theme "Visions and reality in contradiction" and three categories: "Music making to feel good", "Pressure on girls, acceptance for boys" and "Blame on the individual".Music teachers at music- and culture schools seem to be at high risk of developing musculoskeletal disorders, especially music teachers playing an instrument that requires an asymmetric playing position. Young musicians' teachers need a better knowledge in the field of prevention of music students' health problems and physiotherapists and ergonomists may assist and collaborate in this. A gender perspective in music medicine research may contribute to a better understanding of musicians' health.
  • Wahlström, J., et al. (författare)
  • A cellular automaton approach to numerically simulate the contact situation in disc brakes
  • Ingår i: Tribology Letters. - : Springer. - 1023-8883 .- 1573-2711. ; 42:3, s. 253-262
  • Tidskriftsartikel (refereegranskat)abstract
    • Since brake wear is an important contributor to the concentration of airborne particles in urban atmospheres, it is important to increase our understanding of the origin of these particles. The contact situation between the pad and disc is complicated. Metal fibres in the pad (or other hard materials) form stable contact plateaus, which carry the main part of the load. A flow of wear particles in the boundary layer between the pad and disc partially stack up against these plateaus (and increase their area), and some will escape from the contact and become airborne. The purpose of this article is to investigate the possibility to numerically simulate the contact situation in the boundary layer between the pad and disc and the amount of wear that leaves the contact using a cellular automaton approach. To do so, the contact pressure, pad temperature and wear are determined in that order. Based on these results, the creation, growth and destruction of contact plateaus are simulated using a cellular automaton model. Finally, the amount of wear that leaves the contact is determined. The simulated behaviour of the contact situation correlates qualitatively with experimental observations found in the literature.
  • Wahlström, J., et al. (författare)
  • A pin-on-disc investigation of novel nanoporous composite-based and conventional brake pad materials focussing on airborne wear particles
  • Ingår i: Tribology International. - : Elsevier. - 0301-679X .- 1879-2464. ; 44:12, s. 1838-1843
  • Tidskriftsartikel (refereegranskat)abstract
    • Wear particles originating from disc brakes contribute to particulate concentration in the urban atmosphere. In this work novel nanoporous composite-based and conventional brake materials were tested against cast-iron discs in a modified pin-on-disc machine. During testing airborne wear particles were measured online and collected on filters, which were analysed using SEM and EDX. The morphology of airborne wear particles containing elements such as iron, oxygen, and copper is presented. These results show that two of the nanoporous materials generated 37 times less airborne wear particles than the conventional materials. Both the conventional and nanoporous materials displayed a bimodal number distribution.
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