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| 3. |
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| 4. |
- Berntsson, Tomas, et al.
(författare)
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Alternatives to lead bath for patenting of high carbon steel wire
- 2004
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Ingår i: Wire Journal International. - 0277-4275. ; 37:5, s. 82-86
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Tidskriftsartikel (refereegranskat)abstract
- The alternatives to lead bath for patenting of high carbon steel wire are discussed. It is found that it is possible to achieve properties of high-speed gas patented music wire without using a soaking furnace. Laboratory experiments with patenting in a fluidized bed, showed that the process could give the required mechanical properties for the valve spring wire. It is also found that small alterations in process parameters in the industrial trials has a large impact on the mechanical properties and microstructures.
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| 5. |
- Berntsson, Tomas, et al.
(författare)
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Blyfri värmebehandling av tråd
- 2002
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Ingår i: Stål 2002. ; , s. 50-51, s. 48-50
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 6. |
- Birznieks, Ingvars, et al.
(författare)
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Mechanisms for force adjustments to unpredictable frictional changes at individual digits during two-fingered manipulation.
- 1998
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Ingår i: Journal of Neurophysiology. - 0022-3077 .- 1522-1598. ; 80:4, s. 1989-2002
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Tidskriftsartikel (refereegranskat)abstract
- Previous studies on adaptation of fingertip forces to local friction at individual digit-object interfaces largely focused on static phases of manipulative tasks in which humans could rely on anticipatory control based on the friction in previous trials. Here we instead analyze mechanisms underlying this adaptation after unpredictable changes in local friction between consecutive trials. With the tips of the right index and middle fingers or the right and left index fingers, subjects restrained a manipulandum whose horizontal contact surfaces were located side by side. At unpredictable moments a tangential force was applied to the contact surfaces in the distal direction at 16 N/s to a plateau at 4 N. The subjects were free to use any combination of normal and tangential forces at the two fingers, but the sum of the tangential forces had to counterbalance the imposed load. The contact surface of the right index finger was fine-grained sandpaper, whereas that of the cooperating finger was changed between sandpaper and the more slippery rayon. The load increase automatically triggered normal force responses at both fingers. When a finger contacted rayon, subjects allowed slips to occur at this finger during the load force increase instead of elevating the normal force. These slips accounted for a partitioning of the load force between the digits that resulted in an adequate adjustment of the normal:tangential force ratios to the local friction at each digit. This mechanism required a fine control of the normal forces. Although the normal force at the more slippery surface had to be comparatively low to allow slippage, the normal forces applied by the nonslipping digit at the same time had to be high enough to prevent loss of the manipulandum. The frictional changes influenced the normal forces applied before the load ramp as well as the size of the triggered normal force responses similarly at both fingers, that is, with rayon at one contact surface the normal forces increased at both fingers. Thus to independently adapt fingertip forces to the local friction the normal forces were controlled at an interdigital level by using sensory information from both engaged digits. Furthermore, subjects used both short- and long-term anticipatory mechanisms in a manner consistent with the notion that the central nervous system (CNS) entertains internal models of relevant object and task properties during manipulation.
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| 7. |
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| 8. |
- Burstedt, Magnus K, et al.
(författare)
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Control of forces applied by individual fingers engaged in restraint of an active object.
- 1997
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Ingår i: Journal of Neurophysiology. - 0022-3077 .- 1522-1598. ; 78:1, s. 117-128
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the coordination of fingertip forces in subjects who used the tips of two fingers to restrain an instrumented manipulandum with horizontally oriented grip surfaces. The grip surfaces were subjected to tangential pulling forces in the distal direction in relation to the fingers. The subjects used either the right index and middle fingers (unimanual grasp) or both index fingers (bimanual grasp) to restrain the manipulandum. To change the frictional condition at the digit-object interfaces, either both grip surfaces were covered with sandpaper or one was covered with sandpaper and the other with rayon. The forces applied normally and tangentially to the grip surfaces were measured separately at each plate along with the position of the plates. Subjects could have performed the present task successfully with many different force distributions between the digits. However, they partitioned the load in a manner that reflected the frictional condition at the local digit-object interfaces. When both digits contacted sandpaper, they typically partitioned the load symmetrically, but when one digit made contact with rayon and the other with sandpaper, the digit contacting the less slippery material (sandpaper) took up a larger part of the load. The normal forces were also influenced by the frictional condition, but they reflected the average friction at the two contact sites rather than the local friction. That is, when friction was low at one of the digit-object interfaces, only the applied normal forces increased at both digits. Thus sensory information related to the local frictional condition at the respective digit-object interfaces controlled the normal force at both digits. The normal:tangential force ratio at each digit appeared to be a controlled variable. It was adjusted independently at each digit to the minimum ratio required to prevent frictional slippage, keeping an adequate safety margin against slippage. This was accomplished by the scaling of the normal forces to the average friction and by partitioning of the load according to frictional differences between the digit-object interfaces. In conclusion, by adjusting the normal:tangential force ratios to the local frictional condition, subjects avoided excessive normal forces at the individual digit-object interfaces, and by partitioning the load according the frictional difference, subjects avoided high normal forces. Thus the local frictional condition at the separate digit-object interfaces is one factor that can strongly influence the distribution of forces across digits engaged in a manipulative act.
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| 9. |
- Burstedt, Magnus K, et al.
(författare)
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Coordination of fingertip forces during human manipulation can emerge from independent neural networks controlling each engaged digit.
- 1997
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Ingår i: Experimental Brain Research. - : Springer Science and Business Media LLC. - 0014-4819 .- 1432-1106. ; 117:1, s. 67-79
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the coordination of fingertip forces in subjects who lifted an object (i) using the index finger and thumb of their right hand, (ii) using their left and right index fingers, and (iii) cooperatively with another subject using the right index finger. The forces applied normal and tangential to the two parallel grip surfaces of the test object and the vertical movement of the object were recorded. The friction between the object and the digits was varied independently at each surface between blocks of trials by changing the materials covering the grip surfaces. The object's weight and surface materials were held constant across consecutive trials. The performance was remarkably similar whether the task was shared by two subjects or carried out unimanually or bimanually by a single subject. The local friction was the main factor determining the normal:tangential force ratio employed at each digit-object interface. Irrespective of grasp configuration, the subjects adapted the force ratios to the local frictional conditions such that they maintained adequate safety margins against slips at each of the engaged digits during the various phases of the lifting task. Importantly, the observed force adjustments were not obligatory mechanical consequences of the task. In all three grasp configurations an incidental slip at one of the digits elicited a normal force increase at both engaged digits such that the normal:tangential force ratio was restored at the non-slipping digit and increased at the slipping digit. The initial development of the fingertip forces prior to object lift-off revealed that the subjects employed digit-specific anticipatory mechanisms using weight and frictional experiences in the previous trial. Because grasp stability was accomplished in a similar manner whether the task was carried out by one subject or cooperatively by two subjects, it was concluded that anticipatory adjustments of the fingertip forces can emerge from the action of anatomically independent neural networks controlling each engaged digit. In contrast, important aspects of the temporal coordination of the digits was organized by a "higher level" sensory-based control that influenced both digits. In lifts by single subjects this control was mast probably based on tactile and visual input and on communication between neural control mechanisms associated with each digit. In the two-subject grasp configuration this synchronization information was based on auditory and visual cues.
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| 10. |
- Edin, Emil
(författare)
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Effect of Stress Relief Annealing: Part Distortion, Mechanical Properties, and Microstructure of Additively Manufactured Austenitic Stainless Steel
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Additive manufacturing (AM) processes may introduce large residual stresses in the as-built part, in particular the laser powder bed fusion process (L-PBF). The residual stress state is an inherent consequence of the heterogeneous heating and subsequent cooling during the process. L-PBF has become renowned for its “free complexity” and rapid prototyping capabilities. However, it is vital to ensure shape stability after the component is removed from the build plate, which can be problematic due to the residual stress inducing nature of this manufacturing process. Residual stresses can be analyzed via many different characterization routes (e.g. X-ray and neutron diffraction, hole drilling, etc.), both quantitatively and qualitatively. From an industrial perspective, most of these techniques are either prohibitively expensive, complex or too slow to be implementable during the early prototyping stages of AM manufacturing.In this work a deformation based method employing a specific geometry, a so called “keyhole”-geometry, has been investigated to qualitatively evaluate the effect of different stress relief annealing routes with respect to macroscopic part deformation, mechanical properties and microstructure. Previous published work has focused on structures with open geometry, commonly referred to as bridge-like structures where the deformation required for analysis occurs during removal from the build plate. The proposed keyhole-geometry can be removed from the build plate without releasing the residual stresses required for subsequent measurement, which enables bulk manufacturing on single build plates, prior to removal and stress relief annealing. Two L-PBF manufactured austenitic stainless steel alloys were studied, 316L and 21-6-9. Tensile specimen blanks were manufactured and the subsequent heat treatments were carried out in pairs of keyhole and tensile blank. Both a contact (micrometer measurement), and a non-contact (optical profilometry) method were employed to measure the residual stress induced deformation in the keyholes. The annealing heat treatment matrix was iteratively expanded with input from the deformation analysis to find the lowest temperature at which approximately zero deformation remained after opening the structure via wire electrical discharge machining. The lowest allowable annealing temperature was sought after to minimize strength loss. After stress relief annealing at 900 ℃ for 1 hour, the 316L keyhole-geometry was considered shape stable. The lateral micrometer measurement yielded a length change of 1 µm, and a radius of 140 m (over the 22 mm top surface) was assigned from curve fitting the top surface height profiles. The complementary microstructural characterization revealed that this temperature corresponded to where the last remains of the cellular sub-grain structures disappears. Tensile testing showed that the specimen subjected to the 900 ℃ heat treatment had a marked reduction in yield stress (YS) compared to that of the as-built: 540 MPa → 402 MPa, whereas ultimate tensile strength (UTS) only reduced slightly: 595 MPa → 570 MPa. The ductility (4D elongation) was found to be ~13 % higher for the specimen heat treated at 900 ℃ than that of the as-built specimen, 76% and 67% respectively. For alloy 21-6-9 the residual stress induced deformation minimum (zero measurable deformation) was found after stress relief heat treatment at 850 ℃ for 1 hour. Slight changes in the microstructure were observable through light optical microscopy when comparing the different heat treatment temperatures. The characteristic sub-grain features associated with alloy 316L were not verified for alloy 21-6-9. Similar to the results for 316L, UTS was slightly lower for the tensile specimen subjected to the heat treatment temperature required for shape stability (850 ℃) compared to the as-built specimen: 810 MPa → 775 MPa. The measured ductility (4D elongation) was found to be approximately equal for the as-built (47%), and heat treated (48%) specimen. As-built material exhibited a YS of 640 MPa while the heat treated specimen had a YS of 540 MPa. For alloy 21-6-9, the lateral micrometer deformation measurements were compared with stress relaxation testing performed at 600 ℃, 700℃ and 800 ℃. Stress relaxation results were in good agreement with the results from the lateral deformation measurements. The study showed that for both steel alloys, the keyhole method could be successfully employed to rapidly find a suitable stress relief heat treatment route when shape stability is vital.
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| 11. |
- Edin, Emil, et al.
(författare)
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Stress relief heat treatment and mechanical properties of laser powder bed fusion built 21-6-9 stainless steel
- 2023
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Ingår i: Materials Science and Engineering A. - : Elsevier. - 0921-5093 .- 1873-4936. ; 868
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Tidskriftsartikel (refereegranskat)abstract
- In this work, the effectiveness of residual stress relief annealing on a laser powder bed fusion (L-PBF) manufactured austenitic stainless steel, alloy 21-6-9 was investigated. Residual stress levels were gauged using geometrical distortion and relaxation testing results. In the investigated temperature interval (600–850 °C), shape stability was reached after subjecting the as-built material to an annealing temperature of 850 °C for 1 h. Microstructural characterization and tensile testing were also performed for each annealing temperature to evaluate the alloy's thermal stability and the resulting tensile properties. In the as-built state, a yield strength (YS) of 640 MPa, ultimate tensile strength (UTS) of 810 MPa and 4D elongation of 47% were measured. Annealing at 850 °C for 1 h had little measurable effect on ductility (48% 4D elongation) while still having a softening effect (UTS = 775 MPa, YS = 540 MPa). From the microstructural characterization, cell-like features were observed sporadically in the annealed condition and appeared stable up until 800 °C after which gradual dissolution began, with the last remnants disappearing after subjecting the material to 900 °C for 1 h.
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| 12. |
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| 13. |
- Edin, Per-Anders, et al.
(författare)
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Time Out of Work and Skill Depreciation
- 2008
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Ingår i: Industrial & labor relations review. - 0019-7939 .- 2162-271X. ; 61:2, s. 163-180
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the role of skill depreciation in the relationship between work interruptions and subsequent wages. Using Swedish data from two waves (1994 and 1998) of the International Adult Literacy Survey, which included results of tests gauging respondents' ability to read and make practical use of printed information, the authors are able to analyze changes in individuals' skills as a function of time out of work. They find statistically strong evidence of a negative relationship between work interruptions and skills. The analysis suggests that depreciation of general skills was economically important. A full year of non-employment, for example, was associated with a 5-percentile move down the skill distribution.
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| 15. |
- Gustavsson, Magnus, 1972-
(författare)
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Empirical Essays on Earnings Inequality
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The thesis consists of four self-contained essays.Essay I decomposes the cross-sectional variance of male annual earnings in Sweden between 1960 and 1990 into permanent and transitory components and compares the results to the U.S. evidence. I find that the transitory variance in Sweden increased until the early 1970s, declined during the remainder of the decade and then rose again during the second half of the 1980s. The permanent variance declined over the whole sample period but its decrease was much more rapid up until the early 1980s than afterwards. Comparing the results for the transitory variance with evidence from the U.S. reveals sharp differences. Most notably, the transitory variance of U.S. earnings rose sharply from the mid 1970s to the mid 1980s. An important explanation for these dissimilarities appears to be labor market institutions. In particular, it is likely that centralized solidarity bargaining in Sweden imposed constraints on earnings instability during the 1970s and early 1980s. Essay II examines changes in the dispersion of permanent and transitory male annual earnings in Sweden between 1991 and 1999. I find that the variance of permanent earnings has increased over this period but that the variance of transitory earnings exhibits no clear trend. The results also show that young workers have the largest dispersion of transitory earnings. Results for wages indicate that increased permanent wage inequality is an important explanation for the increase in permanent earnings inequality.Essay III investigates changes in educational wage differentials in Sweden between 1992 and 2001 and places them in a longer-term perspective. The university wage premium has increased noticeably between 1992 and 2001 while the gymnasium wage premium has been constant. These results, together with previous research for earlier years, suggest that the university wage premium in Sweden has exhibited a clearly positive trend since the early 1980s whilst the gymnasium wage premium has been constant since the mid 1970s. Unlike the 1980s, relative supply changes do not appear to have been responsible for the rise in the university wage premium over the most recent decade.Essay IV (with Per-Anders Edin) investigates the role of skill depreciation in the relationship between work interruptions and subsequent wages. Using a unique longitudinal dataset, the Swedish part of the International Adult Literacy Survey, we are able to analyze changes in literacy skills for individuals as a function of time out of work. In general, we find statistically strong evidence on a negative relationship between work interruptions and skills. Our analysis suggests that depreciation of general (literacy) skills is economically significant. Our estimates imply that a full year of non-employment is associated with skill losses that are equivalent to moving 5 percentiles down the skill distribution.
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| 16. |
- Hultin, Magnus, 1968-, et al.
(författare)
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Inviting the Test Takers to Challenge the Items Might Drive Quality Improvement in National Licensing Tests for International Medical Graduates
- 2020
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Ingår i: EBMA 2020. - : The European Board of Medical Assessors (EBMA).
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Konferensbidrag (refereegranskat)abstract
- Background International medical graduates need to show their proficiencies to obtain a medical license in a new country. In 2016 the Swedish National Board of Health and Welfare redesigned the proficiency test for Doctors of Medicine. The theoretical test consists of around 180 MCQ/SBA. All tests are made public after being used in accordance with the Swedish Public Access to Information and Secrecy Act. Thus, new tests have to be continuously developed. In addition, as a public institution, the test giver is required to reply to all challenges of the items on the test. Summary of Work To involve the stakeholders and to improve the quality of the test, the items and corresponding answer keys were made public immediately after the test was finished. The test takers were invited to challenge any item and correct answer via a web form and support challenge with literature references. The item authors then reviewed and replied to each individual challenge. Based on these challenges and the associated review, definitive answer keys were decided. Three weeks after test admission, the test takers received their results, a copy of their test together with correct answers, and the response to their challenges. Summary of Results So far, 13 different tests have been given to totally 2,328 test takers. 3,047 challenges were submitted and resulted in 87 changes in answer keys or deletions of an item from the test (3.7% of the 2,360 items across all 13 tests). The number of changes/deletions has decreased significantly with the number of developed tests. Discussion & Conclusion We consider the number of test items that have been rejected or adjusted answer keys to be low. Nevertheless, it was necessary to build a system where the challenges from the test takers were built into the test process. In the Swedish educational system appealing a grade is not possible, but if any item in a test is incorrect, the 1992 administrative law requires test givers to promptly adjust test scores. While the implemented process is resource demanding, we believe that it is crucial both for test acceptance among the examinees and to improve the skills of the item authors. Take-home Message Involving the test takers in quality assurance of a national licensing test might improve item quality.
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| 17. |
- Hultin, Magnus, 1968-, et al.
(författare)
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Sänkta krav på utländska läkare vore förödande
- 2018
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Ingår i: Dagens Samhälle. - 1652-6511. ; :4 dec
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- Det är avgörande att det ställs samma höga krav på läkare från länder utanför EU som på svenskutbildade. Bilden av att det ställs olika krav på olika grupper vore förödande, skriver ansvariga för kunskapsprovet för läkare vid Umeå universitet ihop med Socialstyrelsen.
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| 18. |
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| 19. |
- Jarl, Magnus, et al.
(författare)
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Replacement of lead baths for the tempering of spring wire
- 2003
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Ingår i: Scandinavian journal of metallurgy. - : Wiley. - 0371-0459 .- 1600-0692. ; 32:5, s. 241-246
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Tidskriftsartikel (refereegranskat)abstract
- Molten lead is used for tempering of valve-spring wire. Lead has drawbacks due to slow temperature changes. In 1991 the Swedish Parliament passed a Government Bill, in which proposals were made to phase out the use of lead in the long term, primarily through voluntary measures. Tempering of SIS 2090 (SAE 9254, DIN 55SiCr7) wire with different dimensions using induction heating was tested in a pilot process line. An induction coil for six wires and two coils with different lengths designed for single wires were tested. The results showed that an induction coil for six wires gave excessive temperature and property variations between the wires. The shorter of the single wire coils gave fluctuations in temperature and properties using a 3.00-mm wire. No such fluctuations were observed with the longer coil. One of the experiments showed that the process might need time to reach stable conditions. The results so far indicate that it is possible to produce valve-spring wire with induction tempering. The process needs more control and monitoring compared to tempering in molten lead. © Blackwell Munksgaard, 2003.
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| 21. |
- Neikter, Magnus, 1988-, et al.
(författare)
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Tensile properties of 21-6-9 austenitic stainless steel built using laser powder-bed fusion
- 2021
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Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 14:15
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Tidskriftsartikel (refereegranskat)abstract
- Alloy 21-6-9 is an austenitic stainless steel with high strength, thermal stability at high temperatures, and retained toughness at cryogenic temperatures. This type of steel has been used for aerospace applications for decades, using traditional manufacturing processes. However, limited research has been conducted on this alloy manufactured using laser powder-bed fusion (LPBF). Therefore, in this work, a design of experiment (DOE) was performed to obtain optimized process parameters with regard to low porosity. Once the optimized parameters were established, horizontal and vertical blanks were built to investigate the mechanical properties and potential anisotropic behavior. As this alloy is exposed to elevated temperatures in industrial applications, the effect of elevated temperatures (room temperature and 750◦C) on the tensile properties was investigated. In this work, it was shown that alloy 21-6-9 could be built successfully using LPBF, with good properties and a density of 99.7%, having an ultimate tensile strength of 825 MPa, with an elongation of 41%, and without any significant anisotropic behavior. © 2021 by the authors.
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