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Petkov, V., Bianchi, O., Pacheco Vaghetti, J. C. & Fernberg, P. (2025). Assessing the Thermo‐Oxidative Degradation of 6FDA‐Based Thermosetting Polyimides Using a Combination of Isothermal and Non‐Isothermal TGA. Journal of Applied Polymer Science, 142(30), Article ID e57221.
Open this publication in new window or tab >>Assessing the Thermo‐Oxidative Degradation of 6FDA‐Based Thermosetting Polyimides Using a Combination of Isothermal and Non‐Isothermal TGA
2025 (English)In: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 142, no 30, article id e57221Article in journal (Refereed) Published
Abstract [en]

This study investigates and compares the thermal stability of two 6FDA-based thermosetting polyimide formulations with varied amounts of internal crosslinkers. The baseline formulation is a commercially available polyimide with good resin transfer molding processability and a high glass transition temperature, Tg, in the range of 340°C–466°C. The altered formulation has a reduced amount of internal crosslinkers. In the current study, the materials are studied through multiple thermogravimetric analysis (TGA) scans to investigate how the polyimide formulation affects the thermo-oxidative properties in the cured state. The measurements and the subsequent analyses reveal that the two polyimides have similar thermal oxidation behavior after curing, despite the changes. A combined model-based approach, utilizing both isothermal and non-isothermal TGA data, is used for the analysis and to create conversion-time–temperature diagrams for both materials. The combined method is compared to pure isoconversional and non-isothermal model-based methods and shows improvement in the ability to model the degradation of the materials.

Place, publisher, year, edition, pages
John Wiley & Sons, 2025
Keywords
degradation, polyimides, theory and modeling, thermogravimetric analysis (TGA), thermosets
National Category
Polymer Technologies
Research subject
Soil Mechanics; Polymeric Composite Materials
Identifiers
urn:nbn:se:ltu:diva-112623 (URN)10.1002/app.57221 (DOI)001475573600001 ()2-s2.0-1050038159382-s2.0-105003815938 (Scopus ID)
Note

Validerad;2025;Nivå 2;2025-07-03 (u5);

Full text license: CC BY-NC-ND 4.0;

Available from: 2025-05-09 Created: 2025-05-09 Last updated: 2025-07-03Bibliographically approved
Pakkam Gabriel, V. R., Fernberg, P. & Varna, J. (2025). Transverse cracking in non-crimp fabric cross-ply laminate under tension–tension cyclic loading at room and elevated temperature. Composites. Part A, Applied science and manufacturing, 192, Article ID 108796.
Open this publication in new window or tab >>Transverse cracking in non-crimp fabric cross-ply laminate under tension–tension cyclic loading at room and elevated temperature
2025 (English)In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 192, article id 108796Article in journal (Refereed) Published
Abstract [en]

The effect of test temperature, maximum stress, and stress-ratio on transverse cracking development in cross-ply laminates subjected to tension–tension cyclic loading was analysed. A two-parameter Weibull distribution model was used to predict transverse cracking, wherein the Weibull scale parameter was assumed to be test temperature and number of cycles dependent. By introducing an equivalent stress in the model, it was possible to account for the effect of the stress ratio in cyclic loading over a range of different loading conditions. To verify the model, tests on temperature resistant cross-ply composites were performed at room temperature and at 150 °C with different stress levels and local 90-layer stress ratios. For both test temperatures, increase in stress level increased the transverse cracking tendency. At 150 °C, despite the lower maximum thermo-mechanical ply-stress level compared to room temperature, transverse cracking tendency was found to be higher.

Place, publisher, year, edition, pages
Elsevier, 2025
Keywords
Polymer-matrix composites, Transverse cracking, Fatigue, Statistical methods
National Category
Composite Science and Engineering
Research subject
Polymeric Composite Materials
Identifiers
urn:nbn:se:ltu:diva-111726 (URN)10.1016/j.compositesa.2025.108796 (DOI)001431027300001 ()2-s2.0-85217927472 (Scopus ID)
Note

Validerad;2025;Nivå 2;2025-02-26 (u4);

Funder: Swedish Aeronautical Research Program NFFP 7 (2019–02777); NFFP 8 (2023–01199); GKN Aerospace, Sweden;

Fulltext license: CC BY

Available from: 2025-02-26 Created: 2025-02-26 Last updated: 2025-06-24Bibliographically approved
Pakkam Gabriel, V. R., Petkov, V. I., Fernberg, P. & Varna, J. (2024). Effect of heat treatment and test temperature on transverse cracking in tensile loading. Composites. Part A, Applied science and manufacturing, 181, Article ID 108149.
Open this publication in new window or tab >>Effect of heat treatment and test temperature on transverse cracking in tensile loading
2024 (English)In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 181, article id 108149Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier, 2024
Keywords
Polymer matrix composite, Transverse cracking, Statistical methods, CT analysis
National Category
Composite Science and Engineering
Research subject
Polymeric Composite Materials
Identifiers
urn:nbn:se:ltu:diva-104370 (URN)10.1016/j.compositesa.2024.108149 (DOI)001217570700001 ()2-s2.0-85188665648 (Scopus ID)
Note

Validerad;2024;Nivå 2;2024-04-12 (signyg);

Funder: Swedish Aeronautical Research Program NFFP 7 [project number 2019-02777]; Swedish Aeronautical Research Program NFFP 8 [project 2023-01199]; GKN Aerospace Sweden AB;

Full text license: CC BY

Available from: 2024-02-23 Created: 2024-02-23 Last updated: 2024-11-20Bibliographically approved
Pakkam Gabriel, V. R., Sahbi Loukil, M., Fernberg, P. & Varna, J. (2024). Equivalent stress concept to account for the effect of local cyclic stress ratio on transverse cracking in tension–tension fatigue. International Journal of Fatigue, 187, Article ID 108482.
Open this publication in new window or tab >>Equivalent stress concept to account for the effect of local cyclic stress ratio on transverse cracking in tension–tension fatigue
2024 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 187, article id 108482Article in journal (Refereed) Published
Abstract [en]

Presented test results on transverse cracking in cross-ply laminates upon tension–tension cyclic loading show that the increase of crack density depends not only on the maximum transverse stress in the cycle but also on the local cyclic stress ratio RTloc in the analyzed layer. To include the effect of the RTloc in the model with statistical failure stress distribution for crack initiation (based on Weibull distribution) adapted for fatigue, an equivalent stress is introduced in a similar manner as the equivalent strain energy release rate has been used for delamination crack propagation. The equivalent stress in the layer is defined as a power function of the maximum stress and the stress ratio in the layer. It was found, testing laminates with two different fiber contents that higher the local stress ratio in 90-layer, higher the transverse cracking resistance. Transverse crack density simulation using the developed equivalent stress model has been validated against test results. 

Place, publisher, year, edition, pages
Elsevier, 2024
Keywords
Fatigue, Polymer-matrix composites, Statistical methods, Transverse cracking
National Category
Applied Mechanics Composite Science and Engineering
Research subject
Polymeric Composite Materials
Identifiers
urn:nbn:se:ltu:diva-108399 (URN)10.1016/j.ijfatigue.2024.108482 (DOI)001269306200001 ()2-s2.0-85197612883 (Scopus ID)
Note

Validerad;2024;Nivå 2;2024-07-31 (signyg);

Funder: Swedish Aeronautical Research Program NFFP 7 (2019-02777); Swedish Aeronautical Research Program NFFP 8 (2023-01199); GKN Aerospace, Sweden;

Full text license: CC BY

Available from: 2024-07-31 Created: 2024-07-31 Last updated: 2024-07-31Bibliographically approved
Bianchi, O., Cruz, J. A., Paim, L., Lavoratti, A., Al-Maqdasi, Z., Amico, S. C., . . . Joffe, R. (2024). Rheology, curing and time-dependent behavior of epoxy/carbon nanoparticles systems. Journal of Applied Polymer Science, 141(3), Article ID e54821.
Open this publication in new window or tab >>Rheology, curing and time-dependent behavior of epoxy/carbon nanoparticles systems
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2024 (English)In: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 141, no 3, article id e54821Article in journal (Refereed) Published
Place, publisher, year, edition, pages
John Wiley & Sons, 2024
National Category
Composite Science and Engineering
Research subject
Polymeric Composite Materials
Identifiers
urn:nbn:se:ltu:diva-101958 (URN)10.1002/app.54821 (DOI)001089771700001 ()2-s2.0-85174582769 (Scopus ID)
Note

Validerad;2024;Nivå 2;2024-04-04 (signyg);

Funder: Conselho Nacional de Desenvolvimento Científico e Tecnológico (305814/2021-4); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (FinanceCode 001); STINT/CAPES (88881.304743/2018-01)

Available from: 2023-10-31 Created: 2023-10-31 Last updated: 2024-11-20Bibliographically approved
Petkov, V. I., Pakkam Gabriel, V. R. & Fernberg, P. (2024). Semantic segmentation of progressive micro-cracking in polymer composites using Attention U-Net architecture. Tomography of Materials and Structures, 5, Article ID 100028.
Open this publication in new window or tab >>Semantic segmentation of progressive micro-cracking in polymer composites using Attention U-Net architecture
2024 (English)In: Tomography of Materials and Structures, ISSN 2949-673X, Vol. 5, article id 100028Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier BV, 2024
Keywords
Polymer composites, Micro-cracking, X-ray computed tomography, Image analysis, Deep learning, Attention U-Net
National Category
Composite Science and Engineering
Research subject
Polymeric Composite Materials
Identifiers
urn:nbn:se:ltu:diva-104991 (URN)10.1016/j.tmater.2024.100028 (DOI)
Projects
INTDEMO MOTOR
Funder
Vinnova, 2020-00188
Note

Godkänd;2024;Nivå 0;2024-04-08 (marisr);

Funder: KN Aerospace,Trollhättan, Sweden;

Full text license: CC BY

Available from: 2024-04-05 Created: 2024-04-05 Last updated: 2024-12-06Bibliographically approved
Forsberg, F., Fernberg, P., Al-Maqdasi, Z., Petkov, V., Lycksam, H. & Joffe, R. (2023). Efficient Use of Micro-Tomography for In-Depth Characterization of Composites. In: Brian G. Falzon; Conor McCarthy (Ed.), ICCM 2023 - Proceedings of the 2023 23rd International Conference on Composite Materials: . Paper presented at 23rd International Conference on Composite Materials (ICCM 2023), Belfast, United Kingdom, July 30-August 4, 2023. Queen's University Belfast, Northern Ireland
Open this publication in new window or tab >>Efficient Use of Micro-Tomography for In-Depth Characterization of Composites
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2023 (English)In: 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, Poster (with or without abstract) (Refereed)
Place, publisher, year, edition, pages
Queen's University Belfast, Northern Ireland, 2023
Series
ICCM International Conferences on Composite Materials
National Category
Applied Mechanics
Research subject
Experimental Mechanics; Polymeric Composite Materials; Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-105053 (URN)2-s2.0-85187561369 (Scopus ID)
Conference
23rd International Conference on Composite Materials (ICCM 2023), Belfast, United Kingdom, July 30-August 4, 2023
Available from: 2024-04-11 Created: 2024-04-11 Last updated: 2024-04-11Bibliographically approved
Fernberg, P., Bru, T. & Joffe, R. (2023). Scrapped Composite Ice-Hockey Stick Shafts For Resuse in Crash Energy Absorbers. In: Brian G. Falzon; Conor McCarthy (Ed.), ICCM 2023 - Proceedings of the 2023 23rd International Conference on Composite Materials: . Paper presented at 23rd International Conference on Composite Materials (ICCM 2023), Belfast, United Kingdom, July 30-August 4, 2023. Queen's University Belfast, Northern Ireland
Open this publication in new window or tab >>Scrapped Composite Ice-Hockey Stick Shafts For Resuse in Crash Energy Absorbers
2023 (English)In: 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, Poster (with or without abstract) (Refereed)
Place, publisher, year, edition, pages
Queen's University Belfast, Northern Ireland, 2023
Series
ICCM International Conferences on Composite Materials
National Category
Mechanical Engineering
Research subject
Polymeric Composite Materials
Identifiers
urn:nbn:se:ltu:diva-105055 (URN)2-s2.0-85187575571 (Scopus ID)
Conference
23rd International Conference on Composite Materials (ICCM 2023), Belfast, United Kingdom, July 30-August 4, 2023
Projects
RE:Source
Funder
Swedish Research Council FormasSwedish Energy AgencyVinnovaLuleå University of Technology
Available from: 2024-04-11 Created: 2024-04-11 Last updated: 2024-04-11Bibliographically approved
Petkov, V. I., Pelcastre, L., Solano, C. & Fernberg, P. (2023). The Influence of Ethynyl In-Chain Crosslinkers on the Properties of 6FDA-Based Polyimides. Materials, 16(1), Article ID 169.
Open this publication in new window or tab >>The Influence of Ethynyl In-Chain Crosslinkers on the Properties of 6FDA-Based Polyimides
2023 (English)In: Materials, E-ISSN 1996-1944, Vol. 16, no 1, article id 169Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
MDPI, 2023
Keywords
Polyimide, Fracture toughness, Thermal oxidative aging, DSC, Nano-indentation
National Category
Textile, Rubber and Polymeric Materials
Research subject
Machine Elements; Polymeric Composite Materials
Identifiers
urn:nbn:se:ltu:diva-93612 (URN)10.3390/ma16010169 (DOI)000909327000001 ()36614507 (PubMedID)2-s2.0-85145654445 (Scopus ID)
Note

Validerad;2023;Nivå 2;2023-01-16 (hanlid);

This article has previously appeared as a manuscript in a thesis.

Available from: 2022-10-14 Created: 2022-10-14 Last updated: 2025-03-13Bibliographically approved
Petkov, V., Fernberg, P. & Solano, C. (2022). Assessment of the Properties of two High-Temperature Thermosetting Polyimides. In: Vassilopoulos, Anastasios P.; Michaud, Véronique (Ed.), ECCM 2022 - Proceedings of the 20th European Conference on Composite Materials: Composites Meet Sustainability. Paper presented at 20th European Conference on Composite Materials (ECCM20), Lausanne, Switzerland, June 26-30, 2022 (pp. 8-15). EPFL Lausanne, Composite Construction Laboratory, 6
Open this publication in new window or tab >>Assessment of the Properties of two High-Temperature Thermosetting Polyimides
2022 (English)In: 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, Published 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.

Place, publisher, year, edition, pages
EPFL Lausanne, Composite Construction Laboratory, 2022
Keywords
Ductile fracture, Glass transition, Polyimides, Resin transfer molding, Resins, Thermosets, Ageing behavior, Chemical compositions, Composite manufacturing, Cross-linking density, DSC, Highest temperature, Processable, Property, Resin-transfer molding, Thermosetting polyimides, Fracture toughness
National Category
Composite Science and Engineering
Research subject
Polymeric Composite Materials
Identifiers
urn:nbn:se:ltu:diva-96908 (URN)2-s2.0-85149412073 (Scopus ID)
Conference
20th European Conference on Composite Materials (ECCM20), Lausanne, Switzerland, June 26-30, 2022
Note

ISBN för värdpublikation: 978-2-9701614-0-0

Available from: 2023-05-15 Created: 2023-05-15 Last updated: 2023-05-15Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-5948-7525

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