| 1. |
- Cedergren, Joakim
(författare)
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Modelling of compaction of metal powder and damage accum ulation due to fatigue in powder materials
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis addresses powder manufactured (P/M) components, with special attention to the compaction process and to the sensitivity to damage accumulation due to fatigue within powder compacted specimens. Three dimensional simulations of the compaction process have been performed, using an explicit dynamic dilatant finite strain finite element code supplemented with the effects from contact friction within the die, modelled by Coulomb friction. The final porosity distribution as well as friction force characteristics obtained from simulations of compaction of specimens with circular and quadratic cross section were found to correlate with experimental findings. Two different porous material models where implemented using a viscoplastic formulation, the Shima Oyane and the combined Fleck – Kuhn – McMeeking (FKM) and Gurson material models. Parameters in the constitutive models calibrated from experiments were found to be adjustable so as to capture the overall final porosity distributions. The possibility to determine the final porosity distribution within complex geometries at different compaction speeds was demonstrated for gear wheels using the combined FKM and Gurson model. The damage accumulation due to fatigue loading has been modelled in two dimensions using the Gurson material model, supplemented to account for isotropic as well as kinematic hardening, rate effects and adiabatic heat accumulation. Gear root damage at the center plane and at the surface of a gear wheel have been studied, with initial porosity distributions transferred from three dimensional simulations. The damage accumulation process was found to be highly localized, which points to the importance of correctly determining the porosity at critical regions of a component, thus diminishing the importance of an accurate overall porosity distribution description. A life estimate model, relating the number of cycles to failure to the applied fatigue load and initial porosity was also presented.
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| 2. |
- Cedergren, Joakim, et al.
(författare)
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Numerical investigation of powder compaction of gear wheels
- 2003
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Ingår i: International Journal of Solids and Structures. - 0020-7683. ; 40:19, s. 4989-5000
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Tidskriftsartikel (refereegranskat)abstract
- A method to judge the porosity distribution within complex powder compacted 3D structures using a dynamic 3D dilatant finite strain finite element program is presented. The method is demonstrated for a gear wheel, using a combined FKM Gurson model with parameters calibrated from experiments to model a ferrous powder. Compaction is pursued until a final average porosity of 3% in the gear. The method is shown successful in judging the influence on local as well as average properties from change in geometrical parameters and compaction speed. (C) 2003 Elsevier Ltd. All rights reserved.
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| 3. |
- Cedergren, Joakim, et al.
(författare)
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Numerical investigation of Powder Metallurgy manufactured gear wheels subjected to fatigue loading
- 2005
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Ingår i: Powder Technology. - : Elsevier BV. - 0032-5910. ; 160:3, s. 161-169
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Tidskriftsartikel (refereegranskat)abstract
- A 2D numerical study of the damage accumulation at the root of a Powder Metallurgy (PM) manufactured gear wheel subjected to frequent overloads, i.e. low cycle fatigue loading, has been performed. The initial porosity distribution of the gear was obtained from a 3D simulation of double action compaction of the gear. The porosity distributions over the centre plane and at the surface were transferred into 2D, and the damage accumulation was followed using the Gurson material model. The initial damage within the gear is here interpreted as the porosity distribution resulting from the manufacturing compaction process. It was found that an accurate description of initial damage distribution only has a small narrow influence on the resulting damage. The damage accumulation is a highly local phenomenon, and that the damage development is highly dependent on the local initial damage at the gear root. Based on this, a simple life estimate model, relating the number of cycles to accumulate a pre-described amount of damage to applied load and initial damage, is also presented.
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| 4. |
- Cedergren, Joakim, et al.
(författare)
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Numerical modelling of P/M steel bars subjected to fatigue loading using an extended Gurson model
- 2004
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Ingår i: European Journal of Mechanics. A, Solids. - : Elsevier BV. - 1873-7285 .- 0997-7538. ; 23:6, s. 899-908
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Tidskriftsartikel (refereegranskat)abstract
- The possibility of modelling experiments conducted on P/M steel bars subjected to strain controlled fatigue loading is investigated. The constitutive relation is an extended Gurson model, using a viscoplastic formulation with plasticity driven damage accumulation supplemented by kinematic as we'll as isotropic hardening. The total damage is modelled as the sum of void growth and void nucleation. Plasticity driven heat accumulation under adiabatic conditions is furthermore included in the model. The damage accumulation was monitored after choosing a kinematically hardening material model. Also rate effects were investigated. It was shown that by assuming the reference viscoplastic strain rate to be constant, increases in damage accumulation and temperature per load cycle with decreasing loading frequency is obtained. This unrealistic behaviour was shown to be eliminated by choosing the reference viscoplastic strain rate a function of the first invariant of the rate of deformation tensor.
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| 5. |
- Cedergren, Joakim, et al.
(författare)
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Three-dimensional analysis of compaction of metal powder
- 2002
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Ingår i: Mechanics of Materials. - 0167-6636. ; 34:1, s. 43-59
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Tidskriftsartikel (refereegranskat)abstract
- Three-dimensional compaction simulations of geometries with circular and quadratic cross-sections are reported using dilatant viscoplastic material models representing a ductile steel powder. The simulations are compared with experiments using in situ measurements of the wall-tractions within the die. Two different porous viscoplastic material models have been used: the combined Fleck-Kuhn-MeMeeking (FKM) and Gurson model and the Shima-Oyane model. The contact between the die and the powder was modelled with Coulomb-type friction. Effects such as the applied traction-density response and average relations for the upper, lower and the normal tractions against the die wall are compared. Comparisons between the numerical results and experimental results show that both material models can well be used to capture the overall density distributions for the geometries studied and that many of the coarse three-dimensional features of the powder-pressing process are well described by the simulations. (C) 2002 Elsevier Science Ltd. All rights reserved.
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| 6. |
- Cedergren, Stefan, et al.
(författare)
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A road map for future research on industrial product-service systems (IPS2) : a systematic review
- 2012
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Ingår i: The Philosopher's Stone for Sustainability. - Berlin, Heidelberg : Encyclopedia of Global Archaeology/Springer Verlag. - 9783642328466 - 9783642328473 ; , s. 185-190
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Konferensbidrag (refereegranskat)abstract
- There is an ongoing trend to expand traditional offerings of selling goods towards providing value through services to customers. In academia the term Industrial Product-Service Systems (IPS2) describes this phenomenon. Although many articles have been published on IPS2 a systematic review is lacking. This paper presents a systematic review of the IPS2 domain. Five themes characterizing IPS2 are revealed: delivery, processes, value creation networks, knowledge management, and business models. IPS2 is concluded to be both a young and distributed field of research, with a scope that needs to expand in terms of the themes covered and number of empirical studies
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| 7. |
- Cedergren, Stefan, et al.
(författare)
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Analysis of the industrial product-service systems (IPS2) literature : A systematic review
- 2012
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Ingår i: IEEE 6th International Conference on Management of Innovation and Technology, ICMIT 2012. - Piscataway, NJ : IEEE Communications Society. - 9781467301084 ; , s. 733-740
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Konferensbidrag (refereegranskat)abstract
- Successful industrial goods-delivering companies are always looking for ways to develop and grow their business. A strong present trend is to expand the traditionally tangible offering by integrating intangible offerings i.e. services. In academia the term industrial product-service systems (IPS2) are being used to describe this paradigm shift. However, a systematic review of the IPS2 literature is lacking. In this paper publications regarding IPS2 are systematically reviewed. The result of our review has been categorized under five themes that we found characterizes IPS2: delivery, processes, value creation networks, knowledge management, and business models. Based on our findings a discussion is made and future research directions are identified
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| 8. |
- Cedergren, Stefan, 1982, et al.
(författare)
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Influence of deformed surface layer when machining wrought alloy 718 in an annealed and in a pre-strained condition
- 2014
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Ingår i: 8th International Symposium on Superalloy 718 and Derivatives 2014; Pittsburgh; United States; 28 September 2014 through 1 October 2014. - Hoboken, NJ, USA : John Wiley & Sons, Inc.. - 9781634396424 ; , s. 263-271
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Konferensbidrag (refereegranskat)abstract
- Superalloys are difficult to cut, mainly due to their preserved strength at elevated temperatures and their exceptional work hardening, where the latter results in a deformed layer on the machined surface. The thickness and degree of deformation of this layer depends on several parameters, such as cutting speed, uncut chip thickness, tool material and edge geometry. This layer enters the cutting zone of subsequent revolutions in turning or in milling. Under certain circumstances, as when the uncut chip thickness is small, all deformation at subsequent machining takes place within the deformed layer. The same phenomenon may occur at the outer edge of the cutting zone where the unrestricted material flow leads to burr formation. The deformed layer at the outer edge is suggested as the cause for notch wear often found when machining Superalloys. In this paper the effect of deformed layer on machining is examined through controlled experiments on the material in to different states of strain; in the annealed state without any remaining strain and with a substantial amount introduced by tensile straining. The results showed that cutting forces were reduced when pre-straining the material. Tool wear was similar in both materials, with large scatter due to built-up edge formation.
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| 9. |
- Cedergren, Stefan, et al.
(författare)
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Making the Important Measurable
- 2011
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Ingår i: International Association for Management of Technology IAMOT 2011 Proceedings. - Miami Beach, USA.
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Konferensbidrag (refereegranskat)abstract
- Performance measurements related to product development typically focuses on what is easy to quantify and not necessarily what is important to measure. This research uses a case study approach to test a new model for designing performance indicators (DPI) based on what is important for a specific organization developing new products. The foundation for an effective performance measurement system is that the performance measurements are derived from relevant performance criteria and objectives. The proposed DPI method is therefore based on three consecutive steps. The first step is to decide what performance objectives are needed to be fulfilled in order to realize the pursued strategy. This step is followed by the identification of performance criteria / success factors that will contribute to the realization of the performance objectives. Performance criteria are typically related to what needs to be achieved in order to fulfill the objectives while success factors focus more on how they are to be fulfilled. Based on the most important performance criteria /success factors the supporting performance indicators can be derived from the literature or by using the performance measure record sheet. The performance allocation tracker is developed as a result of applying the DPI method in a real case and it is an indicator of the performance of the studied development project. The properties of the indicators resulting from using the DPI method include similar characteristics as leading indicators of performance. It is concluded that by focusing on performance criteria and success factors in the development of performance indicators, leading indicators of performance is derived.
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| 10. |
- Cedergren, Stefan, et al.
(författare)
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What is Performance in Complex Product Development?
- 2008
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Ingår i: Proceedings of the R&D Management Conference. 2008.
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Konferensbidrag (refereegranskat)abstract
- The process of developing new products is one of the key business processes in a company, especially technology intensive ones. In order to continuously improve this capability of developing new products it is important to be able to measure the performance in the product development process. The dilemma though is that there are no good performance measurements available within complex product development. One reason, as argued in presented research may be the lack of a holistic perception of performance within the development process. Data from a five case explorative study including 49 semi-structured open interviews regarding performance within complex product development is presented and analyzed. The results clearly indicate a need for further development of the perception of performance by managers and decision makers within the process of developing complex products. To meet this need, a Product Development Organizational Performance Model (PDOPM) is proposed, consisting of three generic levels of activities: Product strategy, Project management, and Product activities. These generic activities are modelled in accordance with the IDEF0 making it possible to conceptually reason about uncertainty, effectiveness, and efficiency at each activity level. Further, the term product development efficacy is introduced to describe the capability of identifying or creating a market opportunity and being able to develop and deliver a product fulfilling exactly what was identified as the market opportunity. High performance in product development is achieved when there is efficacy throughout the complete product development portfolio.
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