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  • 1.
    Bianchi, Otávio
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Materials Engineering (DEMAT), Federal University of Rio Grande do Sul (UFRGS), Porto Alegre, Brazil.
    Cruz, Joziel A.
    Department of Materials Engineering (DEMAT), Federal University of Rio Grande do Sul (UFRGS), Porto Alegre, Brazil.
    Paim, Lucas
    Department of Materials Engineering (DEMAT), Federal University of Rio Grande do Sul (UFRGS), Porto Alegre, Brazil.
    Lavoratti, Alessandra
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Materials Engineering (DEMAT), Federal University of Rio Grande do Sul (UFRGS), Porto Alegre, Brazil.
    Al-Maqdasi, Zainab
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Amico, Sandro C.
    Department of Materials Engineering (DEMAT), Federal University of Rio Grande do Sul (UFRGS), Porto Alegre, Brazil.
    Fernberg, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Rheology, curing and time-dependent behavior of epoxy/carbon nanoparticles systems2024In: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 141, no 3, article id e54821Article in journal (Refereed)
  • 2.
    Fernberg, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Swerea SICOMP AB, Box 271, Piteå, SE-941 26, Sweden.
    Fibre reinforced polyimide composites and structures manufactured with resin transfer moulding: Overview of procedures and properties2016In: ECCM 2016: Proceeding of the 17th European Conference on Composite Materials, European Conference on Composite Materials , 2016Conference paper (Refereed)
    Abstract [en]

    In this paper, the major outcomes from a recently completed research program with ambition to develop polyimide carbon fibre composites with temperature ability above 360°C are reported. Data from characterisation of the processing properties such as viscosity and cure behaviour are presented alongside with data on the mechanical properties at room temperature of quasi-isotropic composites based on the developed resin and 8-harness satin weave carbon fibre fabrics. The paper also contains a demonstration of the use the material system in a demonstrator component.

  • 3.
    Fernberg, Patrik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Bru, Thomas
    Dept of Polymers, Fibres and Composites, RISE Research Institutes of Sweden, Sweden.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Scrapped Composite Ice-Hockey Stick Shafts For Resuse in Crash Energy Absorbers2023In: ICCM 2023 - Proceedings of the 2023 23rd International Conference on Composite Materials / [ed] Brian G. Falzon; Conor McCarthy, Queen's University Belfast, Northern Ireland , 2023Conference paper (Refereed)
  • 4.
    Fernberg, Patrik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Swerea SICOMP AB.
    Gong, Guan
    Swerea SICOMP AB.
    Mannberg, Peter
    Swerea SICOMP AB.
    Processing and properties of new polyimide composites with high temperature ability2014In: 16th European Conference on Composite Materials, ECCM 2014: Seville, Spain, 22 - 26 June 2014, European Conference on Composite Materials, ECCM , 2014Conference paper (Refereed)
    Abstract [en]

    The communication present results from work on development and evaluation of new polymeric carbon fiber composites with extreme temperature performance: Tg up to 360°C is targeted. The anticipated use of such composites is found in aeroengine-applications. In the work we are exploring a new and tailored phenyl ethynyl terminated imide (PETI) formulation, specially developed for the program. The formulation utilizes crosslinkers of the Nexamide" type (from Nexam Chemical AB, Sweden). The resins are initially evaluated from a processing and property perspective. Both DSC-measurements and rheology characterization are utilized in the development. Suitable RTM-processing schemes are investigated from a viscosity point of view. The schemes are used in the composite sample manufacturing. Besides a processing perspective the study also present the first results on physical behavior of the polymers and their composites.

  • 5.
    Fernberg, Patrik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Gong, Guan
    Swerea SICOMP AB, Piteå.
    Mannberg, Peter
    Swerea SICOMP AB, Piteå.
    Tsampas, Spyros
    Swerea SICOMP AB, Mölndal.
    Development of novel high Tg polyimide-based composites: Part I: RTM processing properties2018In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 52, no 2, p. 253-260Article in journal (Refereed)
    Abstract [en]

    In this study, an assessment of the composite processing-related properties of a newly developed 6-FDA-based phenylethynyl-terminated polyimide (available under the tradename NEXIMID®MHT-R) is presented. Processing schemes, used for preparing high quality carbon fibre-reinforced composites by the use of conventional resin transfer moulding are developed and presented. The influences of manufacturing parameters on glass transition temperature of the composites are presented. The results confirm that composites with exceptionally high Tg, in the range between 350 and 460℃ can be achieved. A manufacturing scheme that yields in composites with Tg of 370℃ is presented and proposed as a good candidate to serve as baseline for further studies.

  • 6.
    Fernberg, S. Patrik
    et al.
    Luleå University of Technology. Swerea SICOMP AB, Piteå, Sweden.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Swerea SICOMP AB, Piteå, Sweden.
    Tsampas, Spyros
    Swerea SICOMP AB, Mölndal, Sweden.
    Mannberg, Peter
    Swerea SICOMP AB, Piteå, Sweden.
    Influence of post-cure on carbon fibre polyimide composites with glass transition temperatures above 400ºC2015Conference paper (Refereed)
    Abstract [en]

    The current communication present results from work on polymeric composites with extreme temperature performance. We are studying carbon fibre composites based on a new phenyl ethynyl terminated polyimide formulation NEXIMID® MHT-R (Nexam Chemicals AB, Sweden) based on hexafluoroisopropylidene bisphthalic dianhydride (6-FDA), 4-(Phenylethynyl)Phthalic Anhydride (4-PEPA) and ethynyl bis-phthalic anhydride (EBPA). This study in particular investigates how post-cure conditions such as time, temperature and atmosphere influence Tg of the composites. In addition to this we also trace and analyse the consequences of post-cure on weight loss and occurrence of micro-cracks. We are considering three different post-curing temperatures: 400°C, 420°C and 440°C in the study. Two different atmospheres, air and inert by nitrogen, were also investigated. In summary the results reveal that remarkably high Tg, up to around 460°C, is achieved with only very limited weight loss. It was also observed that some, but limited amounts of, micro-cracks are developed within the laminates due to the inevitable high thermal stresses generated upon cooling from cure temperature.

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  • 7.
    Forsberg, Fredrik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Fernberg, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Al-Maqdasi, Zainab
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Petkov, Valeri
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lycksam, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Efficient Use of Micro-Tomography for In-Depth Characterization of Composites2023In: ICCM 2023 - Proceedings of the 2023 23rd International Conference on Composite Materials / [ed] Brian G. Falzon; Conor McCarthy, Queen's University Belfast, Northern Ireland , 2023Conference paper (Refereed)
  • 8.
    Gonçalves Nunes, Stephanie
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Riga Technical University, Institute of Mechanics and Mechanical Engineering, Latvia; Federal University of Rio Grande do Sul, Materials Engineering Department, Brazil.
    Saseendran, Sibin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Research Institutes of Sweden, Department of Polymer Materials and Composites, Sweden.
    Fernberg, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Esposito, Antonella
    Normandie Univ, UNIROUEN, INSA Rouen, CNRS, Groupe de Physique des Matériaux, France.
    Campos Amico, Sandro
    Federal University of Rio Grande do Sul, Materials Engineering Department, Brazil.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Riga Technical University, Institute of Mechanics and Mechanical Engineering, Latvia.
    Shift factor dependence on physical aging and temperature for viscoelastic response of polymers2022In: ECCM 2022 - Proceedings of the 20th European Conference on Composite Materials: Composites Meet Sustainability / [ed] Vassilopoulos, Anastasios; Michaud, Véronique, Lausanne: EPFL Lausanne, Composite Construction Laboratory , 2022, Vol. 1, p. 431-438Conference paper (Other academic)
    Abstract [en]

    As polymeric resins are used as matrix in reinforced composites, understanding of their viscoelastic-viscoplastic response is critical for long-term performance design. However, during service life, thermosets are not in a thermodynamic equilibrium state, resulting in physical aging, which affects failure and viscoelastic (VE) properties, becoming a concern for industries. In this paper, an alternative methodology for testing and parameter determination for aging polymer, at different temperatures (TA) and times (tA), is proposed. The experimental data analysis was performed using a Schapery's type thermo-aging-rheologically simple VE model with constant coefficients in Prony series and the effect of temperature and aging included by two shift factors (aT, aA). Results showed that the shift factor can be presented as the product of shifts aT and aA. Furthermore, for short tA the change rate of the aA with tA does not depend on TA, whereas for long tA at high TA the rate increases.

  • 9.
    Mellin, Pelle
    et al.
    KTH XPRES – Initiative for Excellence in Production Research.
    Jönsson, Christina
    KTH XPRES – Initiative for Excellence in Production Research.
    Åkermo, Malin
    KTH XPRES – Initiative for Excellence in Production Research.
    Fernberg, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Nordenberg, Eva
    Siemens Industrial Turbomachinery AB.
    Brodin, Håkan
    Siemens Industrial Turbomachinery AB.
    Strondl, Annika
    KTH XPRES – Initiative for Excellence in Production Research.
    Nano-sized by-products from metal 3D printing, composite manufacturing and fabric production2016In: Journal of Cleaner Production, ISSN 0959-6526, E-ISSN 1879-1786, Vol. 139, p. 1224-1233Article in journal (Refereed)
    Abstract [en]

    Recently, the health and environmental perspective of nano-materials has gained attention. Most previous work focused on Engineered Nanoparticles (ENP). This paper examines some recently introduced production routes in terms of generated nano-sized by-products. A discussion on the hazards of emitting such particles and fibers is included.

    Fine by-products were found in recycled metal powder after 3D printing by Selective Laser Melting (SLM). The process somehow generated small round metal particles (∼1–2 μm) that are possibly carcinogenic and respirable, but not small enough to enter by skin-absorption. With preventive measures like closed handling and masks, any health related effects can be prevented.

    The composite manufacturing in particular generated ceramic and carbonaceous particles that are very small and respirable but do not appear to be intrinsically toxic. The smallest features in agglomerates were about 30 nm. Small particles and fibers that were not attached in agglomerates were found in a wide range of sizes, from 1 μm and upwards. Preventive measures like closed handling and masks are strongly recommended.

    In contrast, the more traditional production route of fabric production is investigated. Here, brushing residue and recycled wool from fabric production contained few nano-sized by-products.

  • 10.
    Monti, M.
    et al.
    Proplast Consortium, Strada Comunale Savonesa 9, Rivalta Scrivia (AL).
    Tsampas, S.A.
    Swerea SICOMP AB, Mölndal.
    Fernberg, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Blomqvist, P.
    SP Technical Research Institute of Sweden, Borås.
    Cuttica, F.
    Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, sede di Alessandria.
    Fina, A.
    Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, sede di Alessandria.
    Camino, G.
    Proplast Consortium, Strada Comunale Savonesa 9, Rivalta Scrivia (AL).
    Fire reaction of nanoclay-doped PA6 composites reinforced with continuous glass fibers and produced by commingling technique2015In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 121, p. 1-10Article in journal (Refereed)
    Abstract [en]

    In this paper, we report the development of a glass fiber commingled composite (GFCC) based on a nanoclay-doped polyamide 6 (PA6) and the evaluation of its fire reaction. The preparation of the composite comprised several steps. Firstly, the nanoclay was dispersed in the PA6 matrix. Then, the produced compound was spun in filaments and commingled with continuous glass fibers. Finally, the laminate preform was consolidated. Reference samples based on the neat PA6 were produced as well. As a results, although it is well known that, in the presence of a relevant amount of continuous fibers, the behavior of the material is mainly driven by the fibers themselves (e.g. mechanical, thermal, conductive, and so on), the effect of the clay was interesting, especially in flammability test (UL94 vertical burning test), where the total burning time passes from 227 s to 146 s.

  • 11.
    Nunes, S. G.
    et al.
    Materials Engineering Department, Federal University of Rio Grande do Sul (UFRGS), Porto Alegre, Brazil.
    Saseendran, S.
    Department of Polymer Materials and Composites, RISE Research Institutes of Sweden, Piteå, Sweden.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Amico, S. C.
    Materials Engineering Department, Federal University of Rio Grande do Sul (UFRGS), Porto Alegre, Brazil.
    Fernberg, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Laboratory of Experimental Mechanics of Materials, Riga Technical University, Riga, Latvia.
    On Temperature-Related Shift Factors and Master Curves in Viscoelastic Constitutive Models for Thermoset Polymers2020In: Mechanics of composite materials, ISSN 0191-5665, E-ISSN 1573-8922, Vol. 56, no 5, p. 573-590Article in journal (Refereed)
    Abstract [en]

    Reliable accelerated testing routines involving tests at enhanced temperatures are of paramount importance in developing viscoelastic models for polymers. The theoretical basis, the time-temperature superposition (TTS) principle, is used to construct master curves and temperature-dependent shift factor, which is the necessary information to simulate the material response in arbitrary temperature and strain regimes. The Dynamic Mechanical and Thermal Analysis (DMTA) TTS mode, being one of the most promising approaches in terms of time efficiency and maturity of the software, is compared in this paper with macrotests at enhanced temperatures in their ability to give reliable master curves. It is shown, comparing simulations with test data for a chosen epoxy polymer, that none of the three DMTA TTS mode-based attempts used (at different temperature steps during frequency scanning) was successful in predicting the epoxy behavior in tests. On the contrary, using one-hour macrotests at enhanced temperatures gives a viscoelastic model with a very good predicting accuracy. Simulations were performed using an incremental formulation of the previously published VisCoR model for linear viscoelastic materials.

  • 12.
    Nunes, Stephanie Goncalves
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Institute of Mechanics and Mechanical Engineering, Riga Technical University, Riga, Latvia; Materials Engineering Department, Federal University of Rio Grande do Sul, Porto Alegre, Brazil.
    Al-Maqdasi, Zainab
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Fernberg, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Amico, Sandro Campos
    Materials Engineering Department, Federal University of Rio Grande do Sul, Porto Alegre, Brazil.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Institute of Mechanics and Mechanical Engineering, Riga Technical University, Riga, Latvia.
    Does the viscoelastic behavior of fully cured epoxy depend on the thermal history during curing?2022In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 56, no 22, p. 3439-3453Article in journal (Refereed)
    Abstract [en]

    Residual strains and shape distortions in a polymer-based composite structure may depend on the cure schedule used for manufacture. Aiming to understand the cure history effects, the influence of the curing “path” (time tc and temperature Tc path during curing) on viscoelastic (VE) response of a fully cured (FC) (alpha = 0.992) epoxy was investigated. Five different “families” of the same epoxy were manufactured in constraint-free conditions using different sets of curing parameters. Then, tensile tests were performed at different temperatures (T = 30 to 110 °C), and the time-temperature superposition principle (TTSP) and Schapery’s type of linear viscoelastic (VE) model, accounting for physical aging of specimens tested at high temperature, were used. The results show that the VE properties of the studied epoxy are independent of the curing history provided that at the end all specimens are fully cured. Also, the physical aging rate at high temperatures of all “families” is the same and it can be described by a simple aging-temperature independent equation reported in Nunes et al1 It is expected that curing history of unconstrained and fully cured epoxy has an insignificant effect on final viscoelastic behavior, a knowledge which could assist in developing more time and cost-efficient cure cycles.

  • 13.
    Nunes, Stephanie
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Materials Engineering Department, Federal University of Rio Grande do Sul, Porto Alegre, Brazil; Institute of Mechanics and Mechanical Engineering, Riga Technical University, Riga, Latvia.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Fernberg, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Saseendran, Sibin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Polymer Materials and Composites, Research Institutes of Sweden, Piteå, Sweden.
    Esposito, A.
    Normandie Univ, UNIROUEN, INSA Rouen, CNRS, Groupe de Physique des Matériaux, 76000 Rouen, France.
    Amico, S.C.
    Materials Engineering Department, Federal University of Rio Grande do Sul, Porto Alegre, Brazil.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Physical aging effect on viscoelastic behavior of polymers2022In: Composites Part C: Open Access, ISSN 2666-6820, Vol. 7, article id 100223Article in journal (Refereed)
    Abstract [en]

    The effect of physical aging on the viscoelastic (VE) behavior of epoxy resin is investigated experimentally performing strain-controlled tests at various temperatures on specimens aged at different temperatures (TA) for different times (tA). The aging effect is analyzed using as a framework Schapery's type of thermo-aging-rheologically simple (T-A-R simple) VE model that contains aging-state and test-temperature dependent shift factor. Experiments show that in first approximation, the shift factor can be presented as the product of aging related shift factor aA and temperature related factor aT. It is found that for short aging times the change rate of the aging shift factor with tA does not depend on TA, whereas for long tA at high TA the rate increases. Shift factors alone are not able to explain differences in relaxation curves for almost “fully” aged specimens aged at different high TA, It is shown that a T-A-R complex VE model with two additional aging-dependent functions can describe the observed discrepancies.

  • 14.
    Pakkam Gabriel, Vivek Richards
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Fernberg, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Fatigue Damage Model of High Temperature Polymer Composites in Aero-Engines2022In: ICAS Proceedings 33rd Congress of the International Council of the Aeronautical Sciences, Stockholm, Sweden, The International Council of the Aeronautical Sciences , 2022, Vol. 5, p. 3805-3812Conference paper (Refereed)
    Abstract [en]

    High Temperature Polymer Cross-ply (HTPC) laminate specimens are subjected to tension-tension fatigue loading at 3 different maximum stress levels at room temperature. Transverse cracking in 90° layer in the crossply laminate upon fatigue tests is analyzed. Based on probabilistic approach, using Weibull distribution, a prediction model for the increase in number of transverse cracks upon fatigue loading at different stress levelsis developed. The predicted crack density (number of cracks per unit length) development shows good agreement with the test results for fatigue at the higher stress levels considered. A slight overprediction is observed at lowest stress level.

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  • 15.
    Pakkam Gabriel, Vivek Richards
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Fernberg, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Prediction of transverse cracks in damaged layers of compositelaminates2022In: Svenska Mekanikdagar 2022 / [ed] Pär Jonsén; Lars-Göran Westerberg; Simon Larsson; Erik Olsson, Luleå tekniska universitet, 2022Conference paper (Refereed)
  • 16.
    Pakkam Gabriel, Vivek Richards
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Fernberg, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Tsampas, Spyros
    Huntsman Advanced Materials Gmbh, 4052 Basel, Switzerland.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Laboratory of Experimental Mechanics of Materials, Riga Technical University, Riga, Latvia.
    Transverse Cracking Characterization and Prediction in Heat Treated Polymer Composites under Quasi-Static Tensile Loading at Elevated Temperature2022In: ECCM 2022 - Proceedings of the 20th European Conference on Composite Materials: Composites Meet Sustainability / [ed] Anastasios P. Vassilopoulos; Véronique Michaud, EPFL Lausanne, Composite Construction Laboratory , 2022, Vol. 6, p. 23-30Conference paper (Other academic)
    Abstract [en]

    Transverse cracking in high temperature polymer cross-ply composite laminate was experimentally studied. In the tests, pristine as well as heat treated cross-ply laminate specimens were subjected to quasi-static tensile loading at room temperature and 150°C. Microscopy studies revealed that manufacturing induced transverse cracks were present in 90° layer of pristine cross-ply laminates. An increase in number of transverse cracks were observed after the heat treatment. Transverse crack density (number of cracks/unit length) growth upon applied thermo-mechanical transverse stress in 90° layer was analyzed using 3-parameter Weibull failure stress distribution. The Weibull location parameter, in efforts to address the influence of temperature and heat treatment of crack density growth, is modified based on empirical data. The predicted results were in good agreement with the test results.

  • 17.
    Pakkam Gabriel, Vivek Richards
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Fernberg, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Transverse cracking in cross-ply laminate under tension-tension fatigue loading at room and elevated temperatureManuscript (preprint) (Other academic)
  • 18.
    Pakkam Gabriel, Vivek Richards
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Loukil, Mohamed Sahbi
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Fernberg, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Equivalent stress concept to account for the effect of local cyclic stress ratio on transverse cracking in tension-tension fatigueManuscript (preprint) (Other academic)
  • 19.
    Pakkam Gabriel, Vivek Richards
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Loukil, Mohamed Sahbi
    Department of Management and Engineering, Linköping University, Sweden.
    Fernberg, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Laboratory of Experimental Mechanics, Riga Technical University, Latvia.
    Methodology for transverse cracking simulation in 90 plies of composite laminate under fatigue loading2022In: ECCM 2022 - Proceedings of the 20th European Conference on Composite Materials: Composites Meet Sustainability / [ed] Vassilopoulos, Anastasios P.; Michaud, Véronique, EPFL Lausanne, Composite Construction Laboratory , 2022, Vol. 6, p. 16-22Conference paper (Other academic)
    Abstract [en]

    Methodology for crack density evolution simulation in tension-tension fatigue and parameter determination in a model that relies on failure stress distribution (Weibull) in the 90 ply is presented. Cyclic loading is performed at one stress level to obtain detailed crack density dependence on the number of cycles. In addition, one data point (crack density at specified number of cycles) is necessary at a different stress level. Non-interactive crack density region is used to determine Weibull parameters. Then, crack density in a whole crack density range and for arbitrary stress level is predicted using the obtained Weibull parameters, the Monte Carlo method for failure stress distribution and a novel model for stress distribution between cracks. The predictions are in good agreement with test results.

  • 20.
    Pakkam Gabriel, Vivek Richards
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Petkov, Valeri Ivanov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Fernberg, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Laboratory of Experimental Mechanics of Materials, Riga Technical University, LV-1048 Riga, Latvia.
    Effect of heat treatment and test temperature on transverse cracking in tensile loading2024In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 181, article id 108149Article in journal (Refereed)
    Abstract [en]

    Accumulation of transverse cracks in carbon fiber heat resistant polymer (with bismaleimide formulation) cross-ply laminates during tensile loading at elevated temperatures and after long heat treatment is analysed. Data shows that both the iso-thermal heat treatment and testing at elevated temperatures reduce the transverse cracking resistance. A two-parameter Weibull failure stress distribution model with scale parameter degrading with heat treatment and elevated temperature is used for crack initiation analysis. The degradation is described by polynomial expansion including interaction terms. Data shows that the scale parameter dependence on the heat treatment time and the test temperature is rather linear. The same expansion parameters have been successfully used for laminates with the same constituents but with a different layup and fiber content.

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  • 21.
    Petkov, Valeri
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Fernberg, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Solano, Carlos
    Nexam Chemical AB.
    Assessment of the Properties of two High-Temperature Thermosetting Polyimides2022In: ECCM 2022 - Proceedings of the 20th European Conference on Composite Materials: Composites Meet Sustainability / [ed] Vassilopoulos, Anastasios P.; Michaud, Véronique, EPFL Lausanne, Composite Construction Laboratory , 2022, Vol. 6, p. 8-15Conference paper (Other academic)
    Abstract [en]

    A novel thermosetting polyimide, NEXIMID R300, is introduced and compared with the commercial MHT-R in terms of fracture toughness, thermal properties and ageing behaviour. The new R300 formulation has an altered chemical composition compared to the MHT-R, resulting in a reduced cross-linking density, and was presented as a less susceptible to cracking and a more processable alternative during composite manufacturing with resin transfer moulding. The study uses fracture toughness with single edge notched beam setup, DSC, dilatometry, weight loss measurements and optical microscopy for investigation of the neat resin properties of both material. A slight increase in fracture toughness and a decrease in glass transition temperature for the R300 formulation is observed.

  • 22.
    Petkov, Valeri Ivanov
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Fernberg, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Damage development during thermal ageing in carbon fibrereinforced polyimide composites2022In: Svenska Mekanikdagar 2022 / [ed] Pär Jonsén; Lars-Göran Westerberg; Simon Larsson; Erik Olsson, Luleå tekniska universitet, 2022Conference paper (Refereed)
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  • 23.
    Petkov, Valeri Ivanov
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Fernberg, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Thermal oxidative aging of satin weave and thin-ply polyimide composites2022In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 43, no 5, p. 2615-2627Article in journal (Refereed)
    Abstract [en]

    The weight loss and damage development of satin weave and thin-ply carbon fiber-reinforced polyimide composites are studied during high temperature (288 and 320°C) aging in air. Two distinct regions are identified in the weight loss measurements—a rapid initial desorption and a subsequent slower weight loss, which is attributed to matrix degradation. The initial desorption stage is modeled by combining material constitutive properties from literature, micro-mechanics and a one-dimensional Fickian diffusion model. Two different damage patterns are observed by using optical microscopy and X-ray computed tomography on specimens before and after aging. Crack clusters form a network in satin weave composites, while edge delaminations are observed in thin-ply laminates, which are known for their enhanced resistance to matrix cracking.

  • 24.
    Petkov, Valeri Ivanov
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pakkam Gabriel, Vivek Richards
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Fernberg, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Semantic segmentation of progressive micro-cracking in polymer composites using Attention U-Net architecture2024In: Tomography of Materials and Structures, ISSN 2949-673X, Vol. 5, article id 100028Article in journal (Refereed)
    Abstract [en]

    The present study delivers a methodology for investigating the gradual damage development in a carbon fibre-reinforced cross-ply polymer composite during a sequence of thermo-mechanical loadings with the help of X-ray computed tomography. The procedure allows an in-depth analysis of the occurrence and nature of the multiple cracks that form within layers oriented perpendicular, or transverse, to the loading direction. This is achieved by using Attention U-Net architecture for semantic segmentation of the transverse cracks. The model shows promising results, through an ability to identify all the transverse cracks and reflect the damage progression. The described method provides a robust routine for analysing challenging polymer composite tomographic datasets.

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    fulltext
  • 25.
    Petkov, Valeri Ivanov
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pelcastre, Leonardo
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Solano, Carlos
    Nexam Chemical AB, 234 35 Lomma, Sweden.
    Fernberg, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    The Influence of Ethynyl In-Chain Crosslinkers on the Properties of 6FDA-Based Polyimides2022In: Materials, E-ISSN 1996-1944, Vol. 16, no 1, article id 169Article in journal (Refereed)
    Abstract [en]

    Two 4,4′-(hexafluoroisopropylidene)diphthalic anhydride-based thermosetting polyimide formulations with varied amounts of crosslinking sites were compared to understand the influence of crosslinking density on fracture toughness, glass transition temperature and thermal oxidative stability. The thermal and mechanical properties of both materials were investigated through a series of single-edge notched beams, differential scanning calorimetry, dilatometry, weight loss, light optical microscopy and nanoindentation experiments. It was found out that the reduced crosslinking resulted in slightly increased fracture toughness but decreased the Tg of the material. No significant difference could be observed in the thermal oxidative stability with the experimental techniques considered.

  • 26.
    Tsampas, Spyros
    et al.
    Swerea SICOMP AB, Mölndal.
    Fernberg, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Development of novel high Tg polyimide-based composites: Part II: Mechanical characterisation2018In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 52, no 2, p. 261-274Article in journal (Refereed)
    Abstract [en]

    In this study, the mechanical performance assessment of a newly developed carbon fibre-reinforced polyimide composite system T650/NEXIMID® MHT-R is presented. This system was subjected to a series of mechanical tests at ambient and elevated temperature (320℃) to determine basic material properties. Moreover, an additional test was conducted, using a T650/NEXIMID® MHT-R laminate in which the fibre sizing was thermally removed prior to laminate manufacturing, to investigate the effect of fibre treatment on mechanical performance. The experimental results indicated that the T650/NEXIMID® MHT-R composites along with exceptionally high Tg (360–420℃) exhibited competitive mechanical properties to other commercially available polyimide and epoxy-based systems. At elevated temperature, the fibre-dominated properties were not affected whilst the properties defined by matrix and fibre/matrix interface were degraded by approximately 20–30%. Finally, the fibre sizing removal did not affect the tensile and compressive strength, however, the shear strength obtained from short-beam shear test was deteriorated by approximately 15%. to serve as baseline for further studies.

  • 27.
    Tsampas, Spyros
    et al.
    Swerea SICOMP AB.
    Fernberg, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    The effect of high temperature on the mechanical performance of novel high Tg polymide-based carbon fibre-reinforced laminates2016In: ECCM 2016: Proceeding of the 17th European Conference on Composite Materials, European Conference on Composite Materials , 2016Conference paper (Refereed)
    Abstract [en]

    In this study, the outcomes from the mechanical testing of the carbon fibre-reinforced polyimide composite system T650/NEXIMID® MHT-R at ambient and elevated temperatures are presented. These results are compared to assess the effect of mechanical loading at 320°C on the performance of the system in tension, compression and Short-Beam Shear. The experimental campaign indicated that the mechanical loading at 320°C had a trivial effect on the tensile properties (fibre-dominated) whilst a more pronounced effect was noted on the compression and Short-Beam Shear (matrix and fibre/matrix interface-dominated properties).

  • 28.
    Varna, Janis
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Zrida, Hana
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Fernberg, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Microdamage analysis in thermally aged CF/polyimide laminates2016In: IOP Conference Series: Materials Science and Engineering, ISSN 1757-8981, E-ISSN 1757-899X, Vol. 139, article id 012050Article in journal (Refereed)
    Abstract [en]

    Microdamage in layers of CF Thornel® T650 8-harness satin woven composite with thermosetting polyimide NEXIMID® MHT-R resin was analysed. After cooling to room temperature multiple intra-bundle cracking due to tensile transverse thermal stresses was observed in the studied [(+45/-45)/(90/0)]2s composite. The composite was subjected to thermal cycling quantifying the increase of crack density in layers. Comparison of two ramps with the same lowest temperature shows that the highest temperature in the cycle has a significant detrimental effect. Exposure for 40 days to 288°C caused many new cracks after cooling down to room temperature. Both aged and not aged specimens were tested in uniaxial quasi-static tension. Cracking was analysed using fracture mechanics and probabilistic approaches. Cracking in off-axis layers was predicted based on Weibull analysis of the 90- layer. The thermal treatment degraded the cracking resistance of the surface layer and of the next layer.

  • 29.
    Zrida, Hana
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Fernberg, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ayadi, Zoubir
    Institut Jean Lamour, Ecole Européenne d’Ingénieurs en Génie des Matériaux, Université de Lorraine.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Microcracking in thermally cycled and aged Carbon fibre/polyimide laminates2017In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 94, no 1, p. 121-130Article in journal (Refereed)
    Abstract [en]

    Carbon fibre T650 8-harness satin weave fabric composites with thermosetting polyimide resin designed for high service temperatures are solidified at 340 °C. High thermal stresses develop after cooling down to room temperature, which lead to multiple cracking in bundles of the studied quasi-isotropic composite. The composites are subjected to two thermal cycling ramps and the increase of crack density in each bundle is quantified. Comparison of two ramps with the same lowest temperature shows that the highest temperature in the cycle has a significant effect on thermal fatigue resistance. During thermal aging tests at 288 °C the mechanical properties are degrading with time and the crack density after certain aging time is measured. Aging and fatigue effects are separately analysed showing that part of the cracking in thermal cycling tests is related to material aging during the high temperature part of the cycle. Numerical edge stress analysis and fracture mechanics are used to explain observations. The 3-D finite element edge stress analysis reveals that there is large edge effect that induces a large difference in the damage state between the different layers on the edge. The linear elastic fracture mechanics explains the higher initiated and propagated crack density in the surface layers comparing to the inner layers.

  • 30.
    Zrida, Hana
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Fernberg, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Swerea SICOMP AB, Piteå.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Effect of extreme temperatures on micro-damage development in CF/polyimide laminates2015In: 20th International Conference on Composite Materials: Copenhagen, 19-24th July 2015, ICCM , 2015, article id 2204-2Conference paper (Refereed)
    Abstract [en]

    CF Thornel® T650 8-harness satin weave fabric composite with thermosetting polyimide NEXIMID® MHT-R resin designed for high service temperatures is produced at around 390°C and therefore high thermal stresses develop after cooling down to room temperature. Thermal transverse stresses in bundles/layers are tensile and lead to multiple intra-bundle /intra-laminar cracking. When the composite plate is subjected to large and repeated temperature variations, new cracks can appear due to thermally induced fatigue stress. Experimental results show that the highest temperature inthe cycle, where thermal stresses are low, has a significant detrimental effect on thermal fatigue resistance. Another observed phenomenon is thermal aging: at high temperature the mechanical properties are degrading with time. Aging and fatigue effects were separately analyzed for quasi-isotropic laminates with lay-up [(+45/-45)/(90/0)]2s.

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