| 1. |
- Fagerström, Martin, 1979, et al.
(författare)
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Verdict Machinery: On the need to automatically make sense of test results
- 2016
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Ingår i: International Symposium on Software Testing and Analysis (ISSTA '16). - New York, NY, USA : ACM. - 9781450343909 ; , s. 225-234
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Konferensbidrag (refereegranskat)abstract
- Along with technological developments and increasing competition there is a major incentive for companies to produce and market high quality products before their competitors. In order to conquer a bigger portion of the market share, companies have to ensure the quality of the product in a shorter time frame. To accomplish this task companies try to automate their test processes as much as possible. It is critical to investigate and understand the problems that occur during different stages of test automation processes. In this paper we report on a case study on automatic analysis of non-functional test results.We discuss challenges in the face of continuous integration and deployment and provide improvement suggestions based on interviews at a large company in Sweden. The key contributions of this work are filling the knowledge gap in research about performance regression test analysis automation and providing warning signs and a road map for the industry.
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| 2. |
- Främby, Johannes, 1983, et al.
(författare)
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ELEMENT-LOCAL STRESS RECOVERY IN LINEAR SHELLS
- 2019
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The introduction of laminated fibre reinforced polymers (FRP) in the automotive industry is strongly dependent on accurate and efficient modelling tools to predict the correct energy absorption in crash simulations. To increase the efficiency of such large-scale simulations, we have implemented an adaptive enrichment methodology for modelling of multiple and arbitrarily located delamination cracks using an equivalent single-layer shell model [1] as a user element in the commercial FE solver LS-DYNA. In summary the methodology starts the simulation with one shell element through the thickness. By identifying critical ply interfaces using a recovery technique of the transverse stresses, the element can then firstly be through-the-thickness refined to improve the stress prediction and secondly cohesive interface elements can be inserted such that delaminations can be modelled. However, in [1] the stress recovery technique was based on a non-local super-convergent patch polynomial fit, which is not suitable for a user LS-DYNA implementation as non-local information is hard to obtain. Instead we aim to utilize the Extended 2D recovery technique by Rolfes and colleagues [2], [3]. A known drawback with this technique is that the recovery of the transverse normal stress, which is made from the in-plane derivatives of the shear force, requires quadratic approximation of the out-of-plane displacements. Again, this is not suitable for our user element implementation in LS-DYNA, which we choose to base on a solid shell formulation with linear approximation due to numerical efficiency. Several authors have presented alternatives to estimate the transverse normal stress in linear shell elements, e.g. by neglecting shear forces [4] or making an assumption on the ratio of the shear force variation [5]. In this contribution we will examine the possibility to utilise the transverse normal stress from the FE-solution, available when using solid shell elements. We will benchmark this approach in a range of geometries with different modelling resolutions. If successful, our methodology will feature an element-wise stress recovery technique capable of estimating all transverse stresses even using a linear element. In the long run the methodology can enable computationally efficient simulations of delamination failure in composite structures and help to develop crash structures made of laminated FRP. References [1] J. Främby, M. Fagerström, and J. Brouzoulis, Int. J. Numer. Methods Eng., vol. 112, no. 8, pp. 882–908, Nov. 2017. [2] R. Rolfes and K. Rohwer, Int. J. Numer. Methods Eng., vol. 40, pp. 51–60, 1997. [3] R. Rolfes, K. Rohwer, and M. Ballerstaedt, Comput. Struct., vol. 68, no. 6, pp. 643–652, Sep. 1998. [4] R. Roos, G. Kress, and P. Ermanni, Compos. Struct., vol. 81, no. 3, pp. 463–470, 2007. [5] R. Tanov and A. Tabiei, Compos. Struct., vol. 76, no. 4, pp. 338–344, 2006.
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| 3. |
- Granlund, Martin, 1992, et al.
(författare)
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Increased impact resistance of cross-country ski poles by improved, simulation assisted composite design
- 2018
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Ingår i: Proceedings.
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Konferensbidrag (refereegranskat)abstract
- High-end carbon fibre reinforced polymer (CFRP) ski poles of today are lighter and stiffer than previous generations, explained by the higher specific stiffness (stiffness to density ratio) for CFRPs in the range of 0.1-0.13 GPa m3/kg compared to approximately 0.03 GPa m3/kg for aluminium. In this study, we have analysed different CFRP pole designs on the market by mechanical testing and microscopy. We conclude that the strive for optimised weight and bending stiffness has generally driven the pole design to be sub-optimal towards stiffness making them unnecessarily sensitive to transverse and impact loads. Based on the experimental findings, we have developed numerical simulation models to predict the bending and stress state in CFRP ski poles under axial as well as transverse (impact) loading conditions. These numerical model has then been used to find a new conceptual pole design with similar weight and stiffness but with seemingly higher impact resistance.
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| 4. |
- Granlund, Martin, 1992, et al.
(författare)
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Supplementary material to the paper: “Increased impact resistance of cross‐country ski poles by improved, simulation assisted composite design”
- 2017
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Supplementary materials to the main paper which could not be included due to the maximum number of pages allowed, but which could still be of interest to many readers. In the paper, results from the mechanical and numerical testing of different pole brands are summarised. Considered poles were: Skigo Race 2.0 (from 2016 and from 2017, denoted SKIGO1 and SKIGO2 respectively), Fischer RCS Carbonlite, Fischer RCS Speedmax and Swix Triac 2.5. The purpose of the mechanical tests was both to characterise material properties needed for the simulations and to better understand how the material architecture, e.g. fibre orientation of the different layers (or plies), influence the material response.Furthermore, numerical finite element models were developed as a tool for simulation driven design process which when fully developed allows for finding an optimal balance between competing requirements on weight, stiffness and strength.
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| 5. |
- Adams, Camiel, 1992, et al.
(författare)
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AN ADAPTIVE ISOGEOMETRIC CONTINUUM SHELL ELEMENT FOR EFFICIENT MODELLING OF DELAMINATION GROWTH
- 2019
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- To accurately predict damage growth in large, thin-walled composite structures, it is required to have models that are both valid and computational efficient. In this respect, isogeometric continuum shell elements provide an interesting option. First of all, the higher order continuity achieved via isogeometric analysis yields an increased in-plane smoothness that enable the use of larger shell elements. In addition, the high in-plane continuity also leads to that in-plane derivatives of in-plane stresses are continuous across element edges, thereby allowing for element-local recovery procedures for the prediction of out-of-plane stresses [2, 3]. Furthermore, as shown by Hosseini et al. [1], it is in an isogeometric continuum shell modelling framework rather straightforward to modify the through-thickness kinematics to incorporate weak and strong discontinuities. By introducing weak discontinuities at ply interfaces, the through-thickness strain discontinuities at these locations are explicitly accounted for. This enables a much better 3D strain and stress prediction, something which is key for a good estimation of the amount of intralaminar damage. By introducing strong discontinuities, the element is also capable to represent initiation and growth of one or several delamination cracks. In the current contribution, we extend the shell formulation from [1] into an adaptive continuum shell that allows for an update of the through-thickness kinematics at any required time instant during the simulation. The adaptivity is facilitated by that the through-thickness kinematical enrichment can be achieved by so-called ”knot insertion”, a step which can be fully automated due to the hierarchical nature of the isogeometric approximation functions. As a result, the current shell provides a good basis for an accurate but also computationally efficient prediction of the progressive failure in laminates, without a-priory knowledge of where damage will occur. Results show that the adaptive modelling framework works well, both to predict the full 3D stress states in multiaxial laminates, but also to capture growth of delaminations. Furthermore, in comparison to a fully resolved model, the adaptive approach gives significant time savings even for simple analyses where significant parts of the domain exhibit delamination growth. This implies that computational efforts (time and memory) can be considerably reduced when using this adaptive concept in large-scale analyses where damage develop only in a confined, but initially unknown area of the structure. [1] S. Hosseini, J.J.C. Remmers, C.V. Verhoosel, and R. de Borst (2015) Int. J. Numer. Meth. Eng., 102, 159–179. [2] M. Fagerström and J.J.C Remmers (2017) Adaptive modelling of delmination growth using isogeometric continuum shell elements. Proc. ICCM21, Xian, China. [3] J.-E. Dufour, P. Antolin, G. Sangalli, F. Auricchio, A. Reali (2018) Composites Part B: Engineering, 138, 12-18.
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| 6. |
- Adams, Camiel, 1992, et al.
(författare)
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Efficient modelling of delamination growth using adaptive isogeometric continuum shell elements
- 2020
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 1432-0924 .- 0178-7675. ; 65:1, s. 99-117
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Tidskriftsartikel (refereegranskat)abstract
- The computational efficiency of CAE tools for analysing failure progression in large layered composites is key. In particular, efficient approximation and solution methods for delamination modelling are crucial to meet today’s requirements on virtual development lead times. For that purpose, we present here an adaptive continuum shell element based on the isogeometric analysis framework, suitable for the modelling of arbitrary delamination growth. To achieve an efficient procedure, we utilise that, in isogeometric analysis, the continuity of the approximation field easily can be adapted via so-called knot insertion. As a result, the current continuum shell provides a basis for an accurate but also computationally efficient prediction of delamination growth in laminated composites. Results show that the adaptive modelling framework works well and that, in comparison to a fully resolved model, the adaptive approach gives significant time savings even for simple analyses where major parts of the domain exhibit delamination growth.
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| 7. |
- Brouzoulis, Jim, 1984, et al.
(författare)
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A shell element formulation for the simulation of propagating delamination and through-thickness cracks
- 2014
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Ingår i: Proceedings of 16th European Conference on Composite Materials - ECCM16. ; , s. (8p)-
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Konferensbidrag (refereegranskat)abstract
- In this contribution, we propose an enhanced shell element formulation for mesh independent FE simulation of through-thickness and multiple delamination crackp ropagation in orthotropic laminates, cf. Figure 1 for an illustration of the possibilities of using this shell element (multiple delaminations). The ambition is to offer a finite element tool to be used for larger component simulations, without having to resort to explicit resolution of each laminae in the laminated structure by three dimensional solid elements or stacked shell elements. The formulation involves three different types of displacement enrichments to make sure that each delaminated subsection which is also cut by a through thickness crack can be individually represented without (unphysical) kinematical couplings to the surrounding structure in the laminate. So far, the proposed modelling framework has been validated against pure deformation modes, in terms of either multiple delaminations or a through-thickness crack.
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| 8. |
- Brouzoulis, Jim, 1984, et al.
(författare)
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An enriched shell element formulation for efficient modeling of multiple delamination propagation in laminates
- 2015
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Ingår i: Composite Structures. - : Elsevier BV. - 0263-8223. ; 126:August 2015, s. 196-206
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Tidskriftsartikel (refereegranskat)abstract
- In the modeling of progressive damage in fiber reinforced polymers, the kinematical representation of delamination is normally treated in one of two ways. Either efficient or accurate modeling of delamination is considered. In the first case, delamination is disregarded or implicitly included in the material modeling. In the second case, delamination is explicitly modeled at a significant numerical cost where all plies are represented by separate elements in the thickness direction, connected by interlaminar cohesive zone elements. In this paper, we therefore aim to take one step closer to more efficient FE analyses by presenting a modeling concept which supports laminate failure analyses requiring only one shell element through the thickness. With this concept, arbitrary delamination propagation is accounted for only in areas where it is needed. In addition, by using this concept, the model preparation time is reduced. We show that the current shell formulation proposed can be utilized to accurately simulate propagating delamination cracks as well as to accurately describe the kinematics of a laminate containing multiple delaminations through the thickness. Thus, we see significant potential for this modeling concept in analyses in which computationally efficiency is of major importance, such as for large scale crash analyses.
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| 9. |
- Brouzoulis, Jim, 1984, et al.
(författare)
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An enriched shell element formulation for modeling of inter- and intralaminar crack propagation in laminates
- 2016
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Ingår i: Composite Structures. - : Elsevier BV. - 0263-8223. ; 136, s. 616-625
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Tidskriftsartikel (refereegranskat)abstract
- In traditional finite element modeling of progressive failure in laminated fiber reinforced polymers, inter- and intralaminar cracks are normally treated in different ways. Interlaminar cracks are normally described explicitly by building up the laminate using stacked elements (solids or shells) connected by cohesive interface elements. Intralaminar cracks, one the other hand, are more often accounted for by using a continuum damage approach, (e.g. a smeared crack approach). In this paper, we propose a modeling concept which instead can accurately represent both intralaminar and interlaminar cracks with an extended kinematical representation, whereby cracks can be explicitly accounted for without excessive use of degrees of freedom. With this concept, we aim to take one step closer to more efficient FE analyses of progressive laminate failure, since only one shell element through the thickness is required, and where arbitrary inter- and intralaminar crack propagation are accounted for only in areas where it is needed. We show that the current shell formulation proposed can be utilized to describe the kinematics of a laminate containing multiple inter- and intralaminar cracks. Thus, we see significant potential for this modeling concept in analyses in which computational efficiency is of major importance.
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| 10. |
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