| 1. |
- De Vin, Leo, 1957-
(författare)
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Credibility of Simulation Results – a Philosophical Perspective on Virtual Manufacturing
- 2012
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Ingår i: Proceedings of the 13th Mechatronics Forum International Conference. - Linz : TRAUNER Verlag. - 9783990330463 ; , s. 784-791
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Konferensbidrag (refereegranskat)abstract
- This paper describes the factors that play a role in credibility of simulation results. It focuses on virtual manufacturing and in particular resource simulation as an example. However, a simulation model can be used in a number of different ways. Verification and validation of models is amongst other factors important for credibility. In this area, much work has been carried out in defense research. There are also some striking similarities between virtual manufacturing and information fusion, in particular in the field of human competence development related to credibility of simulations.
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| 2. |
- Tofique, Muhammad Waqas, 1986-, et al.
(författare)
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Development of the distributed dislocation dipole technique for the analysis of closure of complex fractures involving kinks and branches
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents the development of the distributed dislocation dipole technique (DDDT) for the analysis of crack surface closure of crack cases involving kinks and branches. Crack cases in which closure occurs are analyzed by reformulating the Bueckner's principle taking the contact stresses at the contacting portions of the crack surfaces into account. Stress intensity factors corresponding to opening and sliding mode of deformation at the crack tips are computed. Three test cases involving kinked and/or branched cracks with at least one of the crack segments undergoing crack surface closure when subjected to remote tensile loading are analyzed. The results obtained from the DDDT are compared to those obtained from the Finite Element Method (FEM) analysis of the same crack cases. This comparison shows that the computation of stress intensity factors for the crack cases involving crack surface closure are less acurate compared to fully open crack cases. However, the stress intensity factors are still computed to an accuracy of within 2 percent if the Jacobi polynomial expansions of at least the sixth order are used to represent the crack surface opening and sliding displacements. Higher order Jacobi polynomials lead to increased accuracy.
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| 3. |
- Esmaeili, Ali, 1983, et al.
(författare)
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Modelling of temperature and strain rate dependent behaviour of pearlitic steel in block braked railway wheels
- 2021
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Ingår i: Railway Engineering Science. - : Springer. - 2662-4745 .- 2662-4753. ; 29:4, s. 362-378
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Tidskriftsartikel (refereegranskat)abstract
- Block braked railway wheels are subjected to thermal and rolling contact loading. The thermal loading results in high temperatures and thermal stresses which cause slow time dependent processes such as creep, relaxation and static recovery of the wheel material. At the same time, the rolling contact loading implies a very fast mechanical load application. This paper is focused on material modeling of pearlitic steel for a wide range of loading rates at elevated temperatures. The starting point is a viscoplasticity model including nonlinear isotropic and kinematic hardening. The Delobelle overstress function is employed to capture strain rate dependent response of the material. The model also includes static recovery of the hardening to capture slower viscous (diffusion dominated) behaviour of the material. Experiments for the pearlitic wheel steel ER7 in terms of cyclic strain-controlled uniaxial tests with hold-time, uniaxial ratchetting tests including rapid cycles and biaxial cyclic tests with tension/compression and torsion are used to calibrate the material model. These experiments were performed under isothermal conditions at different temperatures. In the ratchetting tests, higher loading rates are obtained and these have been used to calibrate the high strain rate response of the viscoplasticity model. The paper is concluded with a numerical example of a block braked wheel where the importance of accounting for the viscoplasticity in modelling is highlighted.
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| 4. |
- Johansson, Daniel, et al.
(författare)
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Design and development of an augmented environment with high user mobility for training purposes
- 2008
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Ingår i: Mechatronics 2008. - Limerick, Ireland : University of Limerick. - 9781905952052 - 1905952058
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Konferensbidrag (refereegranskat)abstract
- The paper describes the design and development of a novel cost effective simulator for training of situation awareness, strategy and co-operation. By mixing real and virtual realities in combination with wireless and body-mounted hardware, the result is an augmented environment that allows for high physical mobility against a relatively low cost.
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| 5. |
- Walander, Tomas, et al.
(författare)
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Prediction of mixed-mode cohesive fatigue strength of adhesively bonded structure using Mode I data
- 2016
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Ingår i: International Journal of Adhesion and Adhesives. - : Elsevier. - 0143-7496 .- 1879-0127. ; 66, s. 15-25
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Tidskriftsartikel (refereegranskat)abstract
- A cohesive zone model is presented for analyzing the fatigue life of an adhesive joint in the range of 104–106 load cycles. The parameters of the model are derived from Mode I double cantilever beam experiments. Fatigue experiments with adhesively joined components from the automotive industry are performed, and the results from the experiments are compared to the results of simulations. The error in the predicted fatigue strength is of the same order as the statistical deviation of the fatigue experiments, indicating that the simulation method produces acceptable predictions of the fatigue strength for applications in e.g. early product development.
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| 6. |
- Stigh, Ulf, 1956-
(författare)
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Applications of equilibrium of configurational forces for the measurement of cohesive laws
- 2016
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Ingår i: Proceedings ECCM17. - : European Conference on Composite Materials, ECCM. - 9783000533877 - 3000533877
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Konferensbidrag (refereegranskat)abstract
- A methodology to develop experimental methods to measure cohesive laws is introduced. This methodology is based on the property of all configurational forces equilibrium acting on a specimen to be in equilibrium. Two applications are given. The first shows a method to measure the cohesive law for shear representing the mechanical behaviour of an adhesive layer. The second application is a method to measure the cohesive law for the formation of a kink-band in a unidirectional composite. It is concluded that the methodology is critically dependent on the ability to associate a pseudopotential to the inelastic properties of the deforming material where the fracture process takes place. The importance to clearly identify the material that is modelled with the cohesive zone is also stressed.
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| 7. |
- Stigh, Ulf, et al.
(författare)
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Cohesive zone modelling and the fracture process of structural tape
- 2016
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Ingår i: Proceedia Structural Integrity. - : Elsevier. - 2452-3216. ; 2, s. 235-244
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Tidskriftsartikel (refereegranskat)abstract
- Structural tapes provide comparable toughness as structural adhesives at orders of magnitude lower stresses. This is potentially useful to minimize the effects of differences in thermal expansion in the joining of mixed materials. The strength properties are modelled using the cohesive zone model. Thus, a cohesive zone represents the tape, i.e. stresses in the tape are transmitted to the substrates through tractions determined by the separations of the surfaces of substrates. This simplification allows for structural analysis of large complex structures. The relation between the traction and the separation is measured experimentally using methods based on the path independence of the J-integral. Repeated experiments are performed at quasi-static loading. A mixed mode cohesive law is adapted to the experimental data. The law is implemented as a UMAT in Abaqus. Simulations show minor thermal distortions due to thermal loading and substantial structural strength in mechanical loading of a mixed material structure.
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| 8. |
- Svensson, Daniel, et al.
(författare)
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Measurement of cohesive law for kink-band formation in unidirectional composite
- 2016
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Ingår i: Engineering Fracture Mechanics. - : Elsevier. - 0013-7944 .- 1873-7315. ; 151, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- Kink-band formation is an important mechanism limiting the compressive strength of high strength composites. A cohesive zone model is used to model the material in a unidirectional carbon fibre composite that forms the kink-band. Equilibrium of configurational forces is used to design and evaluate the experiments. Microscopic studies show that a kink-band is formed with the height of about 200 μm. The corresponding cohesive law has a peak stress of about 1.5 GPa, a compression at failure of about 50 μm and a fracture energy of about 25 kJ/m2.
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| 9. |
- Svensson, Daniel, et al.
(författare)
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On the ability of coupled mixed mode cohesive laws to conform to LEFM for cracks in homogeneous orthotropic solids
- 2016
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Ingår i: Engineering Fracture Mechanics. - : Elsevier. - 0013-7944 .- 1873-7315. ; 163, s. 426-448
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Tidskriftsartikel (refereegranskat)abstract
- The ability of coupled cohesive laws to conform to the predictions of linear elastic fracturemechanics (LEFM) in the case of small-scale-yielding (SSY) is explored. The study is concerned with cracks in homogeneous orthotropic solids and the results apply also for the case of isotropy. Both potential based and non-potential based cohesive laws are considered. It is shown that the initial stiffnesses of the cohesive law must be matched to the elastic moduli of the orthotropic solid in order to achieve a constant ratio of the cohesive stress components ahead of the crack tip. A simple condition for this is provided. For non potential based laws an additional apparently sufficient condition on the non-linear part of the cohesive law is identified: The traction vector must not change direction if the directionof the separation vector is constant. Fulfillment of this condition provides a uniform local mode mix in the cohesive zone with a value equal to the global mode mix. It is demonstrated that potential based cohesive laws display a varying local mode mix at the crack tip for cases with a mode dependent work of separation. This is identified as acomplicating feature in terms of calibrating the parameters of a cohesive law to experimental data.
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| 10. |
- Saglietti, Clio, et al.
(författare)
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Topology optimization of heat sinks in a square differentially heated cavity
- 2018
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Ingår i: International Journal of Heat and Fluid Flow. - : Elsevier B.V.. - 0142-727X .- 1879-2278. ; 74, s. 36-52
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Tidskriftsartikel (refereegranskat)abstract
- Innovative designs of heat sinks are generated in the present paper through numerical optimization, by applying a material distribution topology optimization approach. The potential of the method is demonstrated in a two-dimensional differentially heated cavity, in which the heat transfer is increased by means of introducing a solid structure that acts as a heat sink. We simulate the heat transfer in the whole system by performing direct numerical simulations of the conjugated problem, i.e. temperature diffusion and convection in the entire domain and momentum conservation in the fluid surrounding the solid. The flow is driven by the buoyancy force, under the Boussinesq approximation, and we describe the presence of solid material as the action of a Brinkman friction force in the Navier–Stokes equations. To obtain a design with a given length scale, we apply regularization techniques by filtering the material distribution. Two different types of filters are applied and compared for obtaining the most realistic solution. Given the large scale of the problem, the optimization is solved with a gradient based method that relies on adjoint sensitivity analysis. The results show the applicability of the method by presenting innovative geometries that are increasing the heat flux. Moreover, the effect of various factors is studied: We investigate the impact of boundary conditions, initial designs, and Rayleigh number. Complex tree-like structures are favored when a horizontal temperature gradient is imposed on the boundary and when we limit the amount of solid volume in the cavity. The choice of the initial design affects the final topology of the generated solid structures, but not their performance for the studied cases. Additionally, when the Rayleigh number increases, the topology of the heat exchanger is able to substantially enhance the convection contribution to the heat transfer.
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