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Strömberg, Niclas
Publications (10 of 72) Show all publications
Rashid, A. & Strömberg, N. (2013). Sequential simulation of thermal stresses in disc brakes for repeated braking. Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, 227(8), 919-929
Open this publication in new window or tab >>Sequential simulation of thermal stresses in disc brakes for repeated braking
2013 (English)In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 227, no 8, p. 919-929Article in journal (Refereed) Published
Abstract [en]

In this paper, an efficient sequential approach for simulating thermal stresses in brake discs for repeated braking is presented. First, a frictional heat analysis is performed by using an Eulerian formulation of the disc. Then, by using the temperature history from the first step of the sequence, a plasticity analysis with temperature dependent material data is performed in order to determine the corresponding thermal stresses. Three-dimensional geometries of a disc and a pad to a heavy truck are considered in the numerical simulations. The contact forces are computed at each time step taking the thermal deformations of the disc and pad into account. In such manner, the frictional heat power distribution will also be updated in each time step, which in turn will influence the development of heat bands. The plasticity model is taken to be the von Mises yield criterion with linear kinematic hardening, where both the hardening and the yield limit are temperature dependent. The results show that during hard braking, high compressive stresses are generated on the disc surface in the circumferential direction which cause yielding. But when the disc cools down, these compressive stresses transform to tensile residual stresses. For repeated hard braking when this kind of stress history is repeated, we also show that stress cycles with high amplitudes are developed which might generate low cycle fatigue cracks after a few braking cycles.

Keywords
Eulerian framework, frictional heat, thermal stresses, disc brake, repeated braking
National Category
Applied Mechanics
Identifiers
urn:nbn:se:hj:diva-20986 (URN)10.1177/1350650113481701 (DOI)000321702800014 ()2-s2.0-84884572691 (Scopus ID)
Available from: 2013-04-26 Created: 2013-04-26 Last updated: 2017-12-06Bibliographically approved
Rashid, A. & Strömberg, N. (2013). Thermomechanical Simulation of Wear and Hot Bands in a Disc Brake by Adopting an Eulerian Approach. In: Eurobrake 2013: . Paper presented at Eurobrake, Dresden, Germany, 17-19 June, 2013.
Open this publication in new window or tab >>Thermomechanical Simulation of Wear and Hot Bands in a Disc Brake by Adopting an Eulerian Approach
2013 (English)In: Eurobrake 2013, 2013Conference paper, Published paper (Refereed)
Abstract [en]

In this paper frictional heating of a disc brake is simulated while taking wear into account. By performing thermomechanical finite element analysis, it is studied how the wear history will influence the development of hot bands. The frictional heat analysis is based on an Eulerian formulation of the disc, which requires significantly lower computational time as compared to a standard Lagrangian approach. A real disc-pad system to a heavy truck is considered, where complete three-dimensional geometries of the ventilated disc and pad are used in the simulations. A sequential approach is adopted, where the contact forces are computed at each time step taking the wear and thermal deformations of the mating parts into account. After each brake cycle, the wear profile of the pad is updated and used in subsequent analysis. The results show that when wear is considered, different distributions of the temperature on disc are obtained for each new brake cycle. After a few braking cycles two hot bands appear on the disc surface instead of only one. These results are in agreement with experimental observations.

Keywords
Eulerian framework, frictional heat, hot band, wear history, pad wear, repeated braking
National Category
Applied Mechanics
Identifiers
urn:nbn:se:hj:diva-21220 (URN)
Conference
Eurobrake, Dresden, Germany, 17-19 June, 2013
Available from: 2013-06-24 Created: 2013-05-23 Last updated: 2015-10-23Bibliographically approved
Klarbring, A. & Strömberg, N. (2013). Topology optimization of hyperelastic bodies including non-zero prescribed displacements. Structural and multidisciplinary optimization (Print), 47(1), 37-48
Open this publication in new window or tab >>Topology optimization of hyperelastic bodies including non-zero prescribed displacements
2013 (English)In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 47, no 1, p. 37-48Article in journal (Refereed) Published
Abstract [en]

Stiffness topology optimization is usually based on a state problem of linear elasticity, and there seems to be little discussion on what is the limit for such a small rotation-displacement assumption. We show that even for gross rotations that are in all practical aspects small (<3 deg), topology optimization based on a large deformation theory might generate different design concepts compared to what is obtained when small displacement linear elasticity is used. Furthermore, in large rotations, the choice of stiffness objective (potential energy or compliance), can be crucial for the optimal design concept. The paper considers topology optimization of hyperelastic bodies subjected simultaneously to external forces and prescribed non-zero displacements. In that respect it generalizes a recent contribution of ours to large deformations, but we note that the objectives of potential energy and compliance are no longer equivalent in the non-linear case. We use seven different hyperelastic strain energy functions and find that the numerical performance of the Kirchhoff–St.Venant model is in general significantly worse than the performance of the other six models, which are all modifications of this classical law that are equivalent in the limit of infinitesimal strains, but do not contain the well-known collapse in compression. Numerical results are presented for two different problem settings.

Place, publisher, year, edition, pages
Springer, 2013
Keywords
Hyperelasticity, Potential energy, Compliance, Optimality criteria
National Category
Applied Mechanics
Identifiers
urn:nbn:se:hj:diva-17433 (URN)10.1007/s00158-012-0819-z (DOI)000312878800004 ()2-s2.0-84871979511 (Scopus ID)
Available from: 2012-01-26 Created: 2012-01-26 Last updated: 2018-10-15Bibliographically approved
Klarbring, A. & Strömberg, N. (2012). A Note on the Min-Max Formulation of Stiffness Optimization including Non-Zero Prescribed Displacements. Structural and multidisciplinary optimization (Print), 45(1), 147-149
Open this publication in new window or tab >>A Note on the Min-Max Formulation of Stiffness Optimization including Non-Zero Prescribed Displacements
2012 (English)In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 45, no 1, p. 147-149Article in journal (Refereed) Published
Abstract [en]

The present theoretical note shows how a naturalobjective function in stiffness optimization, including bothprescribed forces and non-zero prescribed displacements,is the equilibrium potential energy. It also shows how theresulting problem has a saddle point character that may beutilized when calculating sensitivities.

Place, publisher, year, edition, pages
Springer, 2012
Keywords
Stiffness optimization, Non-zero prescribed displacements, Saddle point problem, Sensitivity analysis
National Category
Applied Mechanics
Identifiers
urn:nbn:se:hj:diva-17431 (URN)10.1007/s00158-011-0674-3 (DOI)000298195000011 ()2-s2.0-84859606444 (Scopus ID)
Available from: 2012-01-26 Created: 2012-01-26 Last updated: 2018-10-15Bibliographically approved
Rashid, A. & Strömberg, N. (2012). An Efficient Sequential Approach for Simulation of Thermal Stresses in Disc Brakes. In: Nordtrib 2012, 15th Nordic Symposium on Tribology, 2012: . Paper presented at 15th Nordic Symposium on Tribology, NORDTRIB,Trondheim, Norway, 12-15 June, 2012..
Open this publication in new window or tab >>An Efficient Sequential Approach for Simulation of Thermal Stresses in Disc Brakes
2012 (English)In: Nordtrib 2012, 15th Nordic Symposium on Tribology, 2012, 2012Conference paper, Published paper (Other academic)
Abstract [en]

In this paper an efficient approach to simulate thermal stresses due to frictional heating of disc brakes is presented. Inthe approach thermal and stress analysis are performed sequentially. The frictional heat analysis is based on the Eulerianmethod, which requires significantly low computational time as compared to the Lagrangian approach. Completethree-dimensional geometries of a disc and a pad are considered for the numerical simulations. The contact forcesare computed at each time step taking the thermal deformations of the disc into account. The nodal temperaturehistory is recorded at each time step and is used in sequentially coupled stress analysis, where a temperature dependentelasto-plastic material model is used to compute the stresses in a disc brake. The results show that during hard braking,high compressive stresses are generated on the disc surface in circumferential direction which cause plastic yielding. Butwhen the disc cools down, the compressive stresses transform to tensile stresses. Such thermoplastic stress history maycause cracks on disc surface after a few braking cycles. These results are in agreement with experimental observationsavailable in the literature.

Keywords
frictional heating, thermal stresses
National Category
Applied Mechanics
Identifiers
urn:nbn:se:hj:diva-19437 (URN)
Conference
15th Nordic Symposium on Tribology, NORDTRIB,Trondheim, Norway, 12-15 June, 2012.
Available from: 2012-09-17 Created: 2012-09-17 Last updated: 2015-11-02Bibliographically approved
Strömberg, N. (2012). An Eulerian approach for simulating frictional heat bands in rotating discs. Paper presented at Euromech 514: New trends in contact mechanics, 27-31 March, Corsica, France.
Open this publication in new window or tab >>An Eulerian approach for simulating frictional heat bands in rotating discs
2012 (English)Conference paper, Published paper (Other academic)
National Category
Applied Mechanics
Identifiers
urn:nbn:se:hj:diva-19443 (URN)
Conference
Euromech 514: New trends in contact mechanics, 27-31 March, Corsica, France
Available from: 2012-09-17 Created: 2012-09-17 Last updated: 2012-10-15Bibliographically approved
Strömberg, N. (2012). RBDO with Non-Gaussian Variables by using a LHS- and SORM-based SLP approach and Optimal Regression Models. In: : . Paper presented at 3rd International Conference on Engineering Optimization, Rio de Janeiro, Brazil, 1-5 July.
Open this publication in new window or tab >>RBDO with Non-Gaussian Variables by using a LHS- and SORM-based SLP approach and Optimal Regression Models
2012 (English)Conference paper, Published paper (Other academic)
Abstract [en]

A general sequential linear programming (SLP) approach for reliability based design optimization (RBDO) with non-Gaussian random variables is presented. The RBDO problems are formulated by using optimal regression models (ORM) as surrogate models and S-optimal design of experiments (DoE). The S-optimal DoE is obtained by maximizing the average mean of the distances between the nearest neighbors. Finite element simulations are performed for the S-optimal DoE and corresponding ORM are obtained by a genetic algorithm. In such manner not only optimal regression coefficients are generated but also optimal rational base functions. The RBDO problems are solved by introducing intermediate variables defined by the iso-probabilistic transformation at the most probable point. By using these variables in the Taylor expansions, a corresponding deterministic linear programming problem is derived, which is corrected by applying second order reliability methods (SORM) as well as Monte Carlo simulations. For low target values on the reliability crude Monte Carlo simulations are used, but for high targets a Latin hypercube sampling (LHS) approach is utilized. The implementation of the suggested sampling- and SORM-based SLP approach is efficient and robust. This is demonstrated by presenting trade-off curves between the objective function, constraints, variables and the target of reliability.

National Category
Applied Mechanics
Identifiers
urn:nbn:se:hj:diva-19436 (URN)
Conference
3rd International Conference on Engineering Optimization, Rio de Janeiro, Brazil, 1-5 July
Available from: 2012-09-17 Created: 2012-09-17 Last updated: 2018-09-10Bibliographically approved
Tapankov, M. & Strömberg, N. (2012). Sampling- and SORM-based RBDO of a Knuckle Component by using Optimal Regression Models. In: the proceedings of the 14th AIAA/ISSMO Multidisciplinary Analysis and Optimization Conference: . Paper presented at The 14th AIAA/ISSMO Multidisciplinary Analysis and Optimization Conference, Indianapolis, Indiana, 17-19 September. American Institute of Aeronautics and Astronautics
Open this publication in new window or tab >>Sampling- and SORM-based RBDO of a Knuckle Component by using Optimal Regression Models
2012 (English)In: the proceedings of the 14th AIAA/ISSMO Multidisciplinary Analysis and Optimization Conference, American Institute of Aeronautics and Astronautics, 2012Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
American Institute of Aeronautics and Astronautics, 2012
National Category
Applied Mechanics
Identifiers
urn:nbn:se:hj:diva-19435 (URN)10.2514/6.2012-5439 (DOI)978-1-60086-930-3 (ISBN)
Conference
The 14th AIAA/ISSMO Multidisciplinary Analysis and Optimization Conference, Indianapolis, Indiana, 17-19 September
Available from: 2012-09-17 Created: 2012-09-17 Last updated: 2018-09-11Bibliographically approved
Strömberg, N. (2012). Topology Optimization of Bodies in Unilateral Contact by Maximizing the Potential Energy. In: B.H.V. Topping (Ed.), Proceedings the Eleventh International Conferenceon Computational Structures Technology. Paper presented at Eleventh International Conference on Computational Structures Technology, 4-7 September, Dubrovnik, Croatia (pp. Paper 237). Civil-Comp Press
Open this publication in new window or tab >>Topology Optimization of Bodies in Unilateral Contact by Maximizing the Potential Energy
2012 (English)In: Proceedings the Eleventh International Conferenceon Computational Structures Technology / [ed] B.H.V. Topping, Civil-Comp Press , 2012, p. Paper 237-Conference paper, Published paper (Refereed)
Abstract [en]

The modelling of the boundary conditions is crucial in topology optimisation. Small changes in these conditions will typically imply new optimal layouts of material. In many situations the design domain is connected to an assembly of components using contact interfaces. In order to generate proper layouts for this type of design domain one must treat these contact interfaces accurately in the topology optimisation procedure.

The bottle-neck in topology optimisation of non-linear structural problems, such as contact problems, is to solve the state equations and the adjoint equations. By choosing the potential energy as the objective the latter equations are not needed in the sensitivity analysis. In this paper topology optimization of contact problems including non-zero prescribed displacements by maximizing the potential energy is performed. For contact problems with zero initial contact gaps and zero prescribed displacements this is equivalent to minimising the compliance, which is the standard approach in topology optimisation. However, when the compliance is used as objective in topology optimisation of contact problems an extra adjoint equation must be solved. This is not needed in the formulation presented in this paper.

The efficiency of the approach is demonstrated by studying three different problems, two problems in two-dimensions and one in a three-dimensional setting. The method is implemented by using Matlab and Intel Fortran, where the Fortran code is linked to Matlab as mex-files. The implementation can be downloaded as a toolbox (Topo4abq). The three problems have beensolved using this toolbox on a laptop with an Intel Core i7 2.67 GHz processor and a 64 bit version of Windows. It is shown that the CPU-time is reduced as much as 25% compared to an adjoint approach developed in previous works.

Place, publisher, year, edition, pages
Civil-Comp Press, 2012
Series
Civil-Comp Proceedings, ISSN 1759-3433 ; 99
National Category
Applied Mechanics
Identifiers
urn:nbn:se:hj:diva-19438 (URN)10.4203/ccp.99.237 (DOI)
Conference
Eleventh International Conference on Computational Structures Technology, 4-7 September, Dubrovnik, Croatia
Available from: 2012-09-17 Created: 2012-09-17 Last updated: 2012-10-12Bibliographically approved
Strömberg, N. (2012). Topology Optimization of Hyperelastic Bodies by Maximizing the Equilibrium Potential Energy. Paper presented at XXIII ICTAM,19–24 August, Beijing, China.
Open this publication in new window or tab >>Topology Optimization of Hyperelastic Bodies by Maximizing the Equilibrium Potential Energy
2012 (English)Conference paper, Published paper (Other academic)
National Category
Applied Mechanics
Identifiers
urn:nbn:se:hj:diva-19439 (URN)
Conference
XXIII ICTAM,19–24 August, Beijing, China
Available from: 2012-09-17 Created: 2012-09-17 Last updated: 2012-10-15Bibliographically approved
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