| 1. |
- Hallberg, Håkan, et al.
(författare)
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A constitutive model for the formation of martensite in austenitic steels under large strain plasticity
- 2007
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Ingår i: International Journal of Plasticity. - : Elsevier BV. - 0749-6419. ; 23:7, s. 1213-1239
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Tidskriftsartikel (refereegranskat)abstract
- A constitutive model for diffusionless phase transitions in elastoplastic materials undergoing large deformations is developed. The model takes basic thermodynamic relations as its starting point and the phase transition is treated through an internal variable (the phase fractions) approach. The usual yield potential is used together with a transformation potential to describe the evolution of the new phase. A numerical implementation of the model is presented, along with the derivation of a consistent algorithmic tangent modulus. Simulations based on the presented model are shown to agree well with experimental findings. The proposed model provides a robust tool suitable for large-scale simulations of phase transformations in austenitic steels undergoingz extensive deformations, as is demonstrated in simulations of the necking of a bar under tensile loading and also in simulations of a cup deep-drawing process.
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| 2. |
- Hallberg, Håkan, et al.
(författare)
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Model Describing Material-Dependent Deformation Behavior in High-Velocity Metal Forming Processes
- 2009
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Ingår i: Journal of Engineering Mechanics - ASCE. - 1943-7889 .- 0733-9399. ; 135:4, s. 345-357
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Tidskriftsartikel (refereegranskat)abstract
- A constitutive model for rate-dependent and thermomechanically coupled plasticity at finite strains is presented. The plasticity model is based on a J(2) model and rate-dependent behavior is included by use of a Perzyna-type formulation. Adiabatic heating effects are handled in a consistent way and not, as is a common assumption, through a constant conversion of the internal work rate into rate of heating. The conversion factor is instead derived from thermodynamic considerations. The stored energy is assumed to be a function of a single internal variable which differs from the effective plastic strain. This allows a thermodynamically consistent formulation to be obtained which, as shown, can be calibrated by use of simple procedures. Choosing 100Cr6 steel in two differently heat treated conditions as prototype material, experimental tests are performed, enabling the model to be calibrated. Significant differences in deformation behavior are noted as the differently heat treated specimens are compared. In addition, the local stress-updating procedure is reduced to a single scalar equation, permitting a very efficient numerical implementation of the model. The constitutive formulation proposed was employed in an explicit finite element solver, illustrative simulations of a high-velocity metal forming process being performed to demonstrate the capabilities of the model and certain characteristic traits of the materials that were studied.
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| 3. |
- Hallberg, Håkan, et al.
(författare)
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Modeling of Continuous Dynamic Recrystallization in Aluminum
- 2009
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Ingår i: DCE Technical Memorandum No. 11. - 1901-7278. ; 11, s. 59-62
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Konferensbidrag (refereegranskat)abstract
- A constitutive model is presented, considering grain size refinement through continuous dynamic recrystallization together with an evolving dislocation density. The grain refinement is allowed to influence both the evolution of the dislocation density and the rate dependence of the material. The model is calibrated against experimental data on aluminum and numerical simulations of equal channel angular pressing (ECAP) material processing illustrates the capabilities of the model.
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| 4. |
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| 5. |
- Hallberg, Håkan
(författare)
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Simulation of Material Behavior in Metal Forming Processes
- 2007
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Constitutive models regarding the behavior of metallic materials during forming processes are formulated and implemented. Mechanisms such as phase transformation, large deformations, plastic dissipation in form of heat and viscoplastic behavior in the material is adressed.
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| 6. |
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| 7. |
- Hallberg, Pär, et al.
(författare)
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Digoxin and mortality in atrial fibrillation : a prospective cohort study
- 2007
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Ingår i: European Journal of Clinical Pharmacology. - : Springer Science and Business Media LLC. - 0031-6970 .- 1432-1041. ; 63:10, s. 959-971
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: The Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) study showed that rhythm-control treatment of patients with atrial fibrillation (AF) offered no survival advantage over a rate-control strategy. In a subgroup analysis of that study, it was found that digoxin increased the death rate [relative risk (RR) = 1.42), but it was suggested that this may have been attributable to prescription of digoxin for patients at greater risk of death, such as those with congestive heart failure (CHF). No study has investigated a priori the effect of digoxin on mortality in patients with AF. This study aimed to address this question. METHODS: Using data from the Registry of Information and Knowledge about Swedish Heart Intensive care Admissions (RIKS-HIA), we studied the 1-year mortality among patients admitted to coronary care units with AF, CHF, or AF+CHF with or without digoxin (n = 60,764) during 1995-2003. Adjustment for differences in background characteristics and other medications and treatments was made by propensity scoring. RESULTS: Twenty percent of patients with AF without CHF in this cohort were discharged with digoxin. This group had a higher mortality rate than the corresponding group not given digoxin [adjusted RR 1.42 (95% CI 1.29-1.56)], whereas no such difference was seen among patients with CHF with or without AF, although these patients had a nearly three-times higher mortality. CONCLUSION: The results suggest that long-term therapy with digoxin is an independent risk factor for death in patients with AF without CHF.
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| 8. |
- Hallberg, Pär, 1974-
(författare)
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Pharmacogenomics of Antihypertensive Treatment & Clinical Pharmacological Studies of Digoxin Treatment
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In Part I we found that the CYP2C9 genotype appears to influence the diastolic blood pressure response to the angiotensin II-receptor antagonist irbesartan in patients with hypertension and left ventricular hypertrophy. Those with the *1/*2 genotype (slower metabolism) responded better than those with the *1/*1 genotype (normal metabolism), likely due to a slower elimination of the drug. We further found that a +9/-9 exon 1 polymorphism of the B2 bradykinin receptor gene – shown to affect mRNA expression - appears to influence the regression of left ventricular mass during therapy with irbesartan or the beta-blocker atenolol in the same patients. Subjects with the -9/-9 genotype (higher mRNA expression) had a greater regression than carriers of the +9 allele. In Part II we found that women on digoxin therapeutic drug monitoring have higher serum digoxin concentrations (SDCs) as compared to men (1.54±0.04 [nmol/L±SE] vs 1.20±0.05 [nmol/L±SE], p<0.001), which could be of importance since an SDC >1.4 nmol/L has been associated with increased mortality. We further found that coadministration of P-glycoprotein inhibitors with digoxin was common (47%) among the same patients, and that the SDC increased in a stepwise fashion with the number of P-glycoprotein inhibitors (20-60%). Lastly, we found that patients admitted to Swedish coronary care units with atrial fibrillation without heart failure and who had been given digoxin had a higher 1-year mortality than those not given digoxin (RR 1.44 [95% CI 1.29-1.60], adjustment made for potential confounders). In conclusion, Part I represents a further step in the pharmacogenomic prospect of tailoring antihypertensive therapy. Part II indicates that heightened attention to the digoxin-dose is warranted in women, that there is a need for awareness about P-glycoprotein interactions with digoxin, and that long-term therapy with digoxin is an independent risk factor for death among patients with atrial fibrillation without heart failure.
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| 9. |
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| 10. |
- Kurland, Lisa, 1960-, et al.
(författare)
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The relationship between the plasma concentration of irbesartan and the antihypertensive response is disclosed by an angiotensin II type 1 receptor polymorphism : results from the Swedish Irbesartan Left Ventricular Hypertrophy Investigation vs. Atenolol (SILVHIA) Trial
- 2008
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Ingår i: American Journal of Hypertension. - : Oxford University Press (OUP). - 0895-7061 .- 1941-7225. ; 21:7, s. 836-839
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Tidskriftsartikel (refereegranskat)abstract
- Background The aim of this study was to investigate the effect of the plasma concentration of irbesartan, a specific angiotensin II type 1 receptor (AT1R) antagonist, and the blood pressure response in relation to AT1R gene polymorphisms. Methods Plasma irbesartan was analyzed in 42 patients with mild-to-moderate hypertension and left ventricular hypertrophy from the Swedish Irbesartan Left Ventricular Hypertrophy Investigation vs. Atenolol (SILVHIA) trial, who were treated with irbesartan as monotherapy for 12 weeks. Blood pressure and irbesartan concentration were measured at trough, i.e., 24 ± 3 h after the last dose. Five AT1R gene polymorphisms were analyzed by minisequencing. Results Neither the plasma concentration of irbesartan, nor any of the AT1R polymorphisms were associated with the blood pressure response to irbesartan treatment. However, the interaction term between the plasma concentration of irbesartan and the AT1R C5245T polymorphism was related to the reduction in systolic blood pressure after 12 weeks of treatment (P = 0.025). Furthermore, the plasma concentration of irbesartan was related to the change in systolic blood pressure in individuals homozygous for the AT1R 5245 T allele (r = -0.56, P = 0.030), but not for other genotypes. Conclusions There was an association between plasma concentrations of irbesartan and the blood pressure response for hypertensive patients with AT1R 5245 TT. Because of the small sample size, this study needs to be viewed as hypothesis generating. This is the first study, to our knowledge, indicating that the concentration–response relationship of an antihypertensive drug may be genotype dependent.
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| 11. |
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