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Sequential simulation of thermal stresses in disc brakes for repeated braking
Tekniska Högskolan, Högskolan i Jönköping, JTH. Forskningsmiljö Produktutveckling - Simulering och optimering.
Tekniska Högskolan, Högskolan i Jönköping, JTH. Forskningsmiljö Produktutveckling - Simulering och optimering.
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, 919-929 p.Article 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.

Place, publisher, year, edition, pages
Sage Publications, 2013. Vol. 227, no 8, 919-929 p.
National Category
Applied Mechanics
Identifiers
URN: urn:nbn:se:liu:diva-94283DOI: 10.1177/1350650113481701OAI: oai:DiVA.org:liu-94283DiVA: diva2:631333
Available from: 2013-04-26 Created: 2013-06-20 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Simulation of Thermal Stresses in a Brake Disc
Open this publication in new window or tab >>Simulation of Thermal Stresses in a Brake Disc
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis thermal stresses in a brake disc during a braking operation are simulated. The simulations are performed by using a sequential approach where the temperature history generated during a frictional heat analysis is used as an input for the stress analysis. The frictional heat analysis is based on the Eulerian method, which requires signicantly lower computational time as compared to the Lagrangian approach. The stress analysis is performed using a temperature dependent material model both with isotropic and kinematic hardening behaviors. The results predict the presence of residual tensile stresses in circumferential direction for both hardening behaviors. These residual stresses may cause initiation of radial cracks on the disc surface after a few braking cycles. For repeated braking an approximately stable stress-strain loop is obtained already after the rst cycle for the linear kinematic hardening model. So, if the fatigue life data for the disc material is known, its fatigue life can be assessed. These results are in agreement with experimental observations available in the literature.

The simulation results predict one hot band in the middle of the disc for a pad with no wear history. It is also shown that convex bending of the pad is the major cause of the contact pressure concentration in middle of the pad which results in the appearance of a hot band on the disc surface. The results also show that due to wear of the pad, dierent distributions of temperature on the disc surface are obtained for each new brake cycle and after a few braking cycles, two hot bands appear on the disc surface.

This sequential approach has proved tremendously cheap in terms of computational time so it gives the freedom to perform multi-objective  optimization studies. Preliminary results of such a study are also presented where the mass of the back plate, the brake energy and the maximum temperature generated on the disc surface during hard braking are optimized. The results indicate that a brake pad with lowest possible stiness will result in an optimized solution with regards to all three objectives. Another interesting result is the trend of decrease in maximum temperature with an increase in back plate thickness.

Finally an overview of disc brakes and related phenomena is presented as a literature review.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. 23 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1603
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-94345 (URN)LIU-TEK-LIC-2013:37 (Local ID)978-91-7519-575-9 (ISBN)LIU-TEK-LIC-2013:37 (Archive number)LIU-TEK-LIC-2013:37 (OAI)
Presentation
2013-08-29, Sal A33, A-huset, Campus Valla, Linköpings universitet, Linköping, 13:15 (English)
Opponent
Supervisors
Available from: 2013-06-24 Created: 2013-06-24 Last updated: 2013-06-25Bibliographically approved
2. Finite Element Modeling of Contact Problems
Open this publication in new window or tab >>Finite Element Modeling of Contact Problems
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Contact is the principal way load is transferred to a body. The study of stresses and deformations arising due to contact interaction of solid bodies is thus of paramount importance in many engineering applications. In this work, problems involving contact interactions are investigated using finite element modeling.

In the first part, a new augmented Lagrangian multiplier method is implemented for the finite element solution of contact problems. In this method, a stabilizing term is added to avoid the instability associated with overconstraining the non-penetration condition. Numerical examples are presented to show the influence of stabilization term. Furthermore, dependence of error on different parameters is investigated.

In the second part, a disc brake is investigated by modeling the disc in an Eulerian framework which requires significantly lower computational time than the more common Lagrangian framework. Thermal stresses in the brake disc are simulated for a single braking operation as well as for repeated braking. The results predict the presence of residual tensile stresses in the circumferential direction which may cause initiation of radial cracks on the disc surface after a few braking cycles. It is also shown that convex bending of the pad is the major cause of the contact pressure concentration in middle of the pad which results in the appearance of a hot band on the disc surface. A multi-objective optimization study is also performed, where the mass of the back plate, the brake energy and the maximum temperature generated on the disc surface during hard braking are optimized. The results indicate that a brake pad with lowest possible stiffness will result in an optimized solution with regards to all three objectives. Finally, an overview of disc brakes and related phenomena is presented in a literature review.

In the third part, a lower limb donned in a prosthetic socket is investigated. The contact problem is solved between the socket and the limb while taking friction into consideration to determine the contact pressure and resultant internal stress-strain in the soft tissues. Internal mechanical conditions and interface stresses for three different socket designs are compared. Skin, fat, fascia, muscles, large blood vessels and bones are represented separately, which is novel in this work.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2016. 34 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1736
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:liu:diva-124572 (URN)10.3384/diss.diva-124572 (DOI)978-91-7685-847-9 (ISBN)
Public defence
2016-03-04, E1405, Tekniska Högskolan, Jönköping University, Jönköping, 10:00 (English)
Opponent
Supervisors
Available from: 2016-02-04 Created: 2016-02-04 Last updated: 2017-05-15Bibliographically approved

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