| 41. |
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| 42. |
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| 43. |
- Wahlström, Jens
(författare)
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A study of airborne wear particles from automotive disc brakes
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- During braking, both the disc and 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 anassociation 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 discbrakes. This thesis deals with experimental and computational methods focusing on airborne wearparticles from disc brakes. The eight appended papers discuss the possibility to both measure andnumerically determine the concentration and size distribution of airborne wear particles thatoriginate from the pad-to-disc contact. The objective is to increase the scientific knowledge ofairborne wear particles generated from disc brakes. Papers A, B and C describe tests of disc brake materials conducted in a modified pin-on-discmachine. The results show that the test set-up can be used to measure and rank disc brakematerials with respect to the concentration of airborne particles generated. Ultrafine (nanosized),fine and coarse airborne wear particles that contain metals such as iron, copper and tin werefound. Papers D and E describe a novel disc brake assembly test stand and tests of disc brake materialsconducted in it. The results show that the test set-up can be used to measure the concentrationand size distribution of airborne wear particles generated from disc brake materials. The resultsalso indicate an ability to rank different pad/disc combinations with respect to the concentrationof airborne wear particles. Furthermore, the results suggest that this test stand can be used tostudy rust layer removal from the disc and that airborne particles are generated even at low brakepressures, such as used to remove dirt from the disc. Paper F compares measurements made in passenger car field tests with measurements made in adisc brake assembly test stand and in a pin-on-disc machine. A promising correlation between thethree different test methods is found. Paper G presents and discusses a simulation methodology that numerically determines theconcentration and size distribution of airborne wear particles generated from the pad-to-disccontact in disc brakes by using general-purpose finite element software. Paper H discusses a cellular automaton model that describes the microscopic contact situationbetween the pad and disc in disc brakes. This model is used to numerically determine the amountof wear that leaves the contact. The results correlate qualitatively with experimental observationsfound in the literature.
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| 44. |
- Wahlström, Jens, et al.
(författare)
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Airborne wear particles from passenger car disc brakes : a comparison of measurements from field tests, a disc brake assembly test stand, and a pin-on-disc machine
- 2010
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Ingår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology. - England : Professional Engineering Publishing. - 1350-6501 .- 2041-305X. ; 224:J2, s. 179-188
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Tidskriftsartikel (refereegranskat)abstract
- Most modern passenger cars have disc brakes on the front wheels. Unlike drum brakes, disc brakes are not sealed off from the ambient air. During braking, both the rotor and the pads wear, and this wear process generates particles that may become airborne. In field tests it is difficult to distinguish these particles from others in the environment. It is thus preferable to conduct tests using laboratory test stands where the cleanness of the surrounding air can he controlled. However, the validity of results from these test stands Should be verified by comparison with field tests. This article presents a comparison of the number and Volume distributions of airborne wear particles as measured online in field tests, in a disc brake assembly test stand, and in a pin-on-disc machine. In all cases, grey cast iron rotors and low metallic pads were tested. A promising correlation between the three different test methods is shown. The number- and volume-weighted mean particle diameter for all test methods is about 0.4 and 2-3 mu m, respectively.
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| 45. |
- Wahlström, Jens, et al.
(författare)
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Risk factors for hospitalization due to lumbar disc disease
- 2012
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Ingår i: Spine. - 0362-2436 .- 1528-1159. ; 37:15, s. 1334-1339
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Tidskriftsartikel (refereegranskat)abstract
- Study Design. Prospective cohort studyObjective. To study biomechanical factors in relation to symptomatic lumbar disc diseaseSummary of Background Data. The importance of biomechanical factors in lumbar disc disease have been questioned the past decade and knowledge from large prospective studies is lacking.Methods. The study basis is a cohort of 263 529 Swedish construction workers who participated in a national occupational health surveillance programme from 1971 until 1992. The workers' job title, smoking habits, body weight, height and age were registered at the examinations. The occurrence of hospitalization due to lumbar disc disease from January 1 1987 until December 31 2003 was collected from a linkage with the Swedish Hospital Discharge Register.Results. There was an increased risk for hospitalization due to lumbar disc disease for several occupational groups compared to white-collar workers and foremen. Occupational groups with high biomechanical loads had the highest risks, e.g the relative risk for concrete workers was 1.55 (95% CI 1.29-1.87). A taller stature was consistently associated with an increased risk. The relative risk for a man of 190-199 cm height was 1.55 (95% CI 1.30-1.86) compared to a man being 170-179 cm. Body weight and smoking were also risk factors, but weaker than height. Workers in the age span of 30-39 had the highest relative risk (RR = 1.87; 95% CI 1.58-2.23) compared to those 20-29, while men 60-65 years old had a lower risk (RR = 0.86; 95%CI 0.68-1.09).Conclusions. This study indicates that factors increasing the load on the lumbar spine are associated with hospitalization for lumbar disc disease. Occupational biomechanical factors seem to be important, and a taller stature was consistently associated with an increased risk.
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| 46. |
- Wahlström, Jens, et al.
(författare)
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Size, Shape, and Elemental Composition of Airborne Wear Particles from Disc Brake Materials
- 2010
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Ingår i: Tribology letters. - : Springer Science and Business Media LLC. - 1023-8883 .- 1573-2711. ; 38:1, s. 15-24
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Tidskriftsartikel (refereegranskat)abstract
- During braking, both the rotor and pads experience wear, generating particles that may become airborne. In field tests, it is difficult to distinguish these particles from others in the surrounding environment, so it is preferable to use laboratory test stands to study the amount of airborne wear particles generated. The purpose of this work is to investigate the possibility of separate, capture, and analyze airborne wear particles generated by a disc brake in a disc brake assembly test stand. This test stand used allows the cleanliness of the air surrounding the test specimens to be controlled and thus the airborne portion of the wear particles to be studied separately. One pair each of low-metallic (LM) and non-asbestos organic (NAO) brake pads was tested against grey cast iron rotors. Before testing, the elemental contents of the brake materials were analyzed using glow discharge optical emission spectroscopy (GDOES). The concentration and size of airborne wear particles were measured online during testing. In addition, airborne wear particles were collected on filters during the tests and afterward analyzed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The analyzed wear particles contained elements such as iron, titanium, zinc, barium, manganese, and copper. Both the low-metallic and non-asbestos organic type of brake pads tested display a bimodal size distribution with peaks at 280 and 350 nm. Most of the airborne particles generated have a diameter smaller than 2.5 mu m.
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| 47. |
- Wahlström, Jens, et al.
(författare)
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The effect of flooring on musculoskeletal symptoms in the lower extremities and low back among female nursing assistants
- 2012
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Ingår i: Ergonomics. - London : Taylor & Francis. - 0014-0139 .- 1366-5847. ; 55:2, s. 248-255
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Tidskriftsartikel (refereegranskat)abstract
- This study examines the effect of changing the floor from a 2-mm homogenous vinyl floor to a 4-mm heterogeneous vinyl floor (1.5-mm wear layer and 2.5-mm foam layer) on musculoskeletal symptoms in the lower extremities and low back among nursing assistants in a geriatric care centre. A pre-post design with a reference group consisting of nursing assistants from a similar geriatric care centre was used. Follow-up measurements were carried out 12 and 24 months after the intervention by means of questionnaires. At the 1-year follow-up, the pain intensity score in the feet of the intervention group had decreased compared with the baseline value and remained statistically significant at the 2-year follow-up. The decrease in pain intensity score of the feet in the intervention group was statistically significantly different from the reference group, both after 1 and 2 years. Statement of Relevance: The results show the importance of flooring in the workplace with regard to reducing musculoskeletal symptoms. Appropriate flooring is especially important in the female-dominated health care sector, where workers must stand or walk for long periods.
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| 48. |
- Wahlström, Jens
(författare)
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Towards a cellular automaton to simulate friction, wear, and particle emission of disc brakes
- 2014
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Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 313:1-2, s. 75-82
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Tidskriftsartikel (refereegranskat)abstract
- Particle emissions originating from the sliding disc brake contact in disc brakes are a main contributor to PM10 in Europe. The macroscopic friction and wear behaviour can be explained, at the mesoscopic scale level, by the growth and destruction of contact plateaus. This paper further develops a cellular automaton that describes the mesoscopic contact situation by implementing friction, wear, and particle emission models based on data found in the literature. Three simulations at different load levels were conducted to investigate how contact pressure and temperature affect friction, wear, and particle emissions. The simulated behaviour correlates qualitatively with experimental observations found in the literature, but further work is necessary to obtain a quantitative correlation.
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| 49. |
- Wahlström, Jens, et al.
(författare)
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Upper arm postures and movements in female hairdressers across four full working days
- 2010
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Ingår i: Annals of Occupational Hygiene. - : Oxford University Press. - 0003-4878 .- 1475-3162. ; 54:5, s. 584-594
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: To describe upper arm postures and movements among female hairdressers, including the variability between hairdressers, between days within hairdresser, and between tasks, as a basis for understanding the characteristics of exposures in the job, considering possible sources of variation and recovery, and discussing appropriate exposure assessment strategies.Methods: Data on upper arm postures were collected using inclinometers during four working days the same week from 28 female hairdressers working in 13 salons. Twenty of the hairdressers noted customer on and off times in a diary, to allow separate analyses of customer tasks (CT) and auxiliary non-customer tasks (AT), including breaks. For a number of posture and movement variables, mean values and variance components between subjects (BS) and within subjects between days (BD) were estimated using restricted maximum likelihood algorithms in one-way random effect models.Results: For the 20 hairdressers with diaries, CT accounted for 279 min (58%) (SDBS = 39 min and SDBD = 85 min) of the working day and AT and breaks for 207 min (42%) (SDBS = 46 min and SDBD = 88 min). The hairdressers worked with the right arm elevated >60° for 6.8% of the whole job (SDBS = 2.8% and SDBD = 2.0%). On average, the hairdressers worked with the right arm elevated >60° for 9.0% of the time during CT, compared to 3.7% during AT, resulting in a contrast between tasks of 0.35.Conclusions: Hairdressers may be at risk for developing musculoskeletal disorders in the neck and shoulders due to a considerable occurrence of highly elevated arms, especially during CT. On the other hand, we do not find reasons to classify hairdressing as a job with too little variation. Posture variability between days within hairdressers was in the same order of magnitude as that between hairdressers, suggesting that ‘typical’ workdays do not exist. The exposure contrast between CT and AT for variables describing elevated arm postures indicates that for these variables a simple task-based approach for estimating job exposure could be successful.
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