| 1. |
- Marth, Stefan, et al.
(författare)
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A comparison between Stepwise Modelling and Inverse Modelling methods for characterization of press hardened sheet metals
- 2017
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Ingår i: 6th International Conference Hot Sheet Metal Forming of High-Performance Steel CHS2. - Warrendale, PA : Association for Iron & Steel Technology, AIST. - 9781935117667 ; , s. 281-288
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Konferensbidrag (refereegranskat)abstract
- The demand for weight reduction of cars has increased the number of press hardened sheet metal parts used in the automotive industry. This leads to an increased demand on the precision of simulations of press hardened sheet metals. An accurate prediction of the post-necking behaviour of materials is therefore needed to increase the precision of computer simulations with large deformations, as for example in forming simulations and crash simulations. Especially fracture simulations of press hardened steel parts with tailored properties have a huge demand on precise material models.Inverse modelling is a common engineering tool to characterize the elasto-plastic behaviour of materials. Taking experimental data, such as force and displacement data, the material model parameters are optimised until the simulated output reaches a target function. Then inverse modelling is highly time demanding and needs nonlinear hardening material models. Lately a new fast method for post necking characterisation of sheet metals, called the Stepwise Modelling Method (SMM), was presented. This method uses full field measurements to obtain the strain field on the surface of sheet metal tensile specimens. Furthermore, the stepwise modelling method models an experimental hardening curve in a stepwise process. This hardening curve is a piecewise linear curve and not restricted to any specific material model.In this paper SMM is used to characterize the hardening behaviour for thermally treated boron steel. These results are compared with the results of inverse modelling. Three different material models are used. The comparison shows a minor deviation in the resulting hardening relations between stepwise modelling and inverse modelling. Since the efficiency is an important factor in product development calculation times are taken into account. Comparing calculation time using SMM is considerably more efficient than using inverse modelling. Furthermore another advantage of SMM is shown in the fact that the piecewise linear hardening curves can be fitted to almost any material model without computational costs.
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| 2. |
- Alam, M. Minhaj, et al.
(författare)
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The influence of surface geometry and topography on the fatigue cracking behaviour of laser hybrid welded eccentric fillet joints
- 2010
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 265:6, s. 1936-1945
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Tidskriftsartikel (refereegranskat)abstract
- Laser hybrid welding of an eccentric fillet joint causes a complex geometry for fatigue load by four point bending. The weld surface geometry and topography were measured and studied in order to understand the crack initiation mechanisms. The crack initiation location and the crack propagation path were studied and compared to Finite Element stress analysis, taking into account the surface macro- and micro-geometry. It can be explained why the root and the upper weld toe are uncritical for cracking. The cracks that initiate from the weld bead show higher fatigue strength than the samples failing at the lower weld toe, as can be explained by a critical radius for the toe below which surface ripples instead determine the main stress raiser location for cracking. The location of maximum surface stress is related to a combination of throat depth, toe radius and sharp surface ripples along which the cracks preferably propagate.
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| 3. |
- Alam, Md. Minhaj, et al.
(författare)
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Fatigue behaviour study of laser hybrid welded eccentric fillet joints : Part II: State-of-the-art of fracture mechanics and fatigue analysis of welded joints
- 2009
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Ingår i: 12th NOLAMP proceeding 2009. - Kgs. Lyngby : ATV-SEMAPP.
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Konferensbidrag (refereegranskat)abstract
- Simplified fatigue and fracture mechanics based assessment methods are widely used by the industry to determine the structural integrity significance of postulated cracks, manufacturing flaws, service-induced cracking or suspected degradation of engineering components under normal and abnormal service loads. In many cases, welded joints are the regions most likely to contain original fabrication defects or cracks initiating and growing during service operation. The welded joints are a major component that is often blamed for causing a structure failure or for being the point at which fatigue or fracture problems initiate and propagate. Various mathematical models/techniques for various classes of welded joints are developed by analytically or by simulation software's that can be used in fatigue and fracture assessments. This literature survey compiled useful information on fracture and fatigue analysis of various welded joints. The present review is divided into two major sections- fracture mechanics and fatigue analysis with widely used models. A survey table is also introduced to get the outlook of research trend on fatigue and fracture over last 3 decades. Although tremendous research effort has been implemented on fatigue and fracture analysis of conventional welding, research on relatively new welding technology (laser welding, hybrid laser welding) is still limited and unsatisfactory. In order to give guarantee or make welding standard for new welding technology, further research is required in the field of fatigue and fracture mechanics including FEM and multi-scale modeling.
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| 4. |
- Alam, Md. Minhaj, et al.
(författare)
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Fatigue behaviour study of laser hybrid welded eccentric fillet joints : Part I
- 2009
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Ingår i: 12th NOLAMP proceeding 2009. - Kgs. Lyngby : ATV-SEMAPP.
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Konferensbidrag (refereegranskat)abstract
- Welded joints are a major component that is often responsible for causing a structure failure or for being the point at which fatigue cracking initiates and propagates. Despite tremendous research efforts, the understanding of fatigue behaviour is still limited, particularly for new techniques like laser hybrid welding. Beside a comprehensive state-of-the-art study, the paper presents a fatigue study of laser hybrid welded eccentric fillet joint of stainless steel of 10 mm thickness, with 5 mm displacement. Motivation is to study the influence of the surface geometry shape on fatigue performance under a four point bending test. 13 samples were produced, measuring the toe radii and testing under constant amplitude loading with stress ratio R=0. Different techniques have been used to measure local weld geometry, like plastic replica, a 3D optical profiler and a 3D-digitizer. The influence of the local weld geometry, like the toe radii, on the stress concentration was studied by FE-analysis. Occasionally lack of fusion was observed, which was taken into account in the FE-analysis. Based on the nominal stress approach, SN-curves were designed for laser hybrid welded eccentric fillet joints. Macro hardness tests were carried out and the crack surfaces were observed in order to detect crack initiation and propagation. Correlations between the toe radii, the corresponding stress maxima and crack initiation locations were studied between the different samples and even along the welds.
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| 10. |
- Lindgren, Lars-Erik, et al.
(författare)
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Thermo-mechanical FE-analysis of residual stresses and stress redistribution in butt welding of a copper canister for spent nuclear fuel
- 2002
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Ingår i: Nuclear Engineering and Design. - 0029-5493 .- 1872-759X. ; 212:1-3, s. 401-408
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Tidskriftsartikel (refereegranskat)abstract
- The transient and residual temperature, stress and strain field present during electron beam welding of a plane copper end to a canister for spent nuclear fuel is calculated by the use of FEM. The subsequent stress redistribution is calculated up to 10,000 years. The canister consists of two concentric cylinders, an inner steel cylinder containing the spent nuclear fuel and an outer copper cylinder. It was found that the maximum plastic strain (plastic+creep) accumulated in the (possibly brittle) heat affected zone is ≈7%, which seems to be well below the reported ductility for the copper used.
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