# Stiffness Degradation under Cyclic Loading Using Three-Point Bending of Hybridised Carbon/Glass Fibres with a Polyamide 6,6 Nanofibre Interlayer

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Methodology and Materials

#### 2.1. Resin and Fibre Characteristics

^{2}square spacer with a depth of 2 mm and compressed under 18 MPa using a Labtech heated press, as per Table 1.

#### 2.2. Fatigue Testing Cycles

#### 2.3. Optical and SEM Analysis of Composite Laminates

#### 2.4. Assessment of the Kink Band Angle Is Taken Using the Angle Measurement Function of ImageJ to Assess the Kink Band

## 3. Results

#### 3.1. Stiffness Degradation as a Function of Maximum Flexural Strength

#### 3.2. Fatigue Failure Mechanisms of Glass Fibre under Cyclic Loading

#### 3.3. Fatigue Failure Mechanisms of Hybrid Glass and Carbon Fibre under Cyclic Loading

#### 3.4. Comparison of Cycles and Flexural Modulus Retention

#### 3.5. Rubber Toughening Comparison

## 4. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

## References

- Chai, B.X.; Eisenbart, B.; Nikzad, M.; Fox, B.; Blythe, A.; Blanchard, P.; Dahl, J. Simulation-based optimisation for injection configuration design of liquid composite moulding processes: A review. Composites. Part A Appl. Sci. Manuf.
**2021**, 149, 106540. [Google Scholar] [CrossRef] - Elias, P.K.; Aikaterini-Flora, T.; Raquel-Miriam, S.; Marta, M.; Cláudio Monterio Dos, S.; Vanessa, I.; Robert, B.; Guan, G.; Agustin, C.; Ignaas, V.; et al. Research and development in carbon fibers and advanced high-performance composites supply chain in europe: A roadmap for challenges and the industrial uptake. J. Compos. Sci.
**2019**, 3, 86. [Google Scholar] [CrossRef] - Heckadka, S.S.; Nayak, S.Y.; Narang, K.; Vardhan Pant, K. Chopped Strand/Plain Weave E-Glass as Reinforcement in Vacuum Bagged Epoxy Composites. J. Mater.
**2015**, 2015, 957043. [Google Scholar] [CrossRef] - Rashid, B.; Sadeq, A.; Ebraheem, M.; Mohammed, A.R. Mechanical properties of hybrid woven roving and chopped strand mat glass fabric reinforced polyester composites. Mater. Res. Express
**2019**, 6, 105208. [Google Scholar] [CrossRef] - Dong, C.; Davies, I.J. Effect of stacking sequence on the flexural properties of carbon and glass fibre-reinforced hybrid composites. Adv. Compos. Hybrid Mater.
**2018**, 1, 530–540. [Google Scholar] [CrossRef] - Naito, K. Flexural Properties of Carbon/Glass Hybrid Thermoplastic Epoxy Composite Rods Under Static and Fatigue Loadings. Appl. Compos. Mater.
**2021**, 28, 753–766. [Google Scholar] [CrossRef] - Adam, H. Carbon fibre in automotive applications. Mater. Des.
**1997**, 18, 349–355. [Google Scholar] [CrossRef] - Kalantari, M.; Dong, C.; Davies, I.J. Numerical investigation of the hybridisation mechanism in fibre reinforced hybrid composites subjected to flexural load. Compos. Part B Eng.
**2016**, 102, 100–111. [Google Scholar] [CrossRef] - Wang, Q.; Wu, W.; Gong, Z.; Li, W. Flexural Progressive Failure of Carbon/Glass Interlayer and Intralayer Hybrid Composites. Materials
**2018**, 11, 619. [Google Scholar] [CrossRef] - Ribeiro, F.; Sena-Cruz, J.; Vassilopoulos, A.P. Tension-tension fatigue behavior of hybrid glass/carbon and carbon/carbon composites. Int. J. Fatigue
**2021**, 146, 106143. [Google Scholar] [CrossRef] - Naito, K. Static and fatigue tensile properties of carbon/glass hybrid fiber-reinforced epoxy composites. Sci. Rep.
**2022**, 12, 6298. [Google Scholar] [CrossRef] [PubMed] - Swolfs, Y.; Gorbatikh, L.; Verpoest, I. Fibre hybridisation in polymer composites: A review. Compos. Part A Appl. Sci. Manuf.
**2014**, 67, 181–200. [Google Scholar] [CrossRef] - Qingtao, W.; Weili, W.; Wei, L. Compression Properties of Interlayer and Intralayer Carbon/Glass Hybrid Composites. Polymers
**2018**, 10, 343. [Google Scholar] [CrossRef] - Wu, W.W.; Wei, Q.L. Comparison of tensile and compressive properties of carbon/glass interlayer and intralayer hybrid composites. Materials
**2018**, 11, 1105. [Google Scholar] [CrossRef] - Ikbal, H.; Wang, Q.; Azzam, A.; Li, W. GF/CF hybrid laminates made through intra-tow hybridization for automobile applications.(Report). Fibers Polym.
**2016**, 17, 1505. [Google Scholar] [CrossRef] - Dong, C. Uncertainties in flexural strength of carbon/glass fibre reinforced hybrid epoxy composites. Compos. Part B Eng.
**2016**, 98, 176–181. [Google Scholar] [CrossRef] - Swolfs, Y.; Verpoest, I.; Gorbatikh, L. Maximising the hybrid effect in unidirectional hybrid composites. Mater. Des.
**2016**, 93, 39–45. [Google Scholar] [CrossRef] - Kar, N.K.; Barjasteh, E.; Hu, Y.; Nutt, S.R. Bending fatigue of hybrid composite rods. Compos. Part A Appl. Sci. Manuf.
**2011**, 42, 328–336. [Google Scholar] [CrossRef] - Ray, D.; Comer, A.J.; Rosca, I.; Obande, W.; Clancy, G.; Stanley, W. Core-shell rubber nanoparticle toughened carbon fibre/epoxy composites. In Proceedings of the 16th European Conference on Composite Materials, ECCM 2014, Seville, Spain, 22–26 June 2014. [Google Scholar]
- Puglia, D.; Kenny, J.M. Cure Kinetics of Epoxy/Rubber Polymer Blends. In Handbook of Epoxy Blends; Parameswaranpillai, J., Hameed, N., Pionteck, J., Woo, E.M., Eds.; Springer: New York, NY, USA, 2017. [Google Scholar]
- Kim, D.S.; Kim, S.C. Rubber modified epoxy resin. I: Cure kinetics and chemorheology. Polym. Eng. Sci.
**1994**, 34, 625–631. [Google Scholar] [CrossRef] - Sinclair, J.W. Effects of Cure Temperature on Epoxy Resin Properties. J. Adhes.
**1992**, 38, 219–234. [Google Scholar] [CrossRef] - Bard, S.; Demleitner, M.; Weber, R.; Zeiler, R.; Altstädt, V. Effect of Curing Agent on the Compressive Behavior at Elevated Test Temperature of Carbon Fiber-Reinforced Epoxy Composites. Polymers
**2019**, 11, 943. [Google Scholar] [CrossRef] [PubMed] - Felice, R.; Antonio, N.; Fausto, T.; Pierpaolo, C. Marine Application of Fiber Reinforced Composites: A Review. J. Mar. Sci. Eng.
**2020**, 8, 26. [Google Scholar] [CrossRef] - Leon, M.; Kim, B.; Helga Nørgaard, P.; Justine, B.; Malcolm, M.; Bent, F.S. Materials for wind turbine blades: An overview. Materials
**2017**, 10, 1285. [Google Scholar] [CrossRef] - Wu, Z.; Wang, X.; Iwashita, K.; Sasaki, T.; Hamaguchi, Y. Tensile fatigue behaviour of FRP and hybrid FRP sheets. Compos. Part B Eng.
**2010**, 41, 396–402. [Google Scholar] [CrossRef] - Liu, B.; Xu, A.; Bao, L. Preparation of carbon fiber-reinforced thermoplastics with high fiber volume fraction and high heat-resistant properties. J. Thermoplast. Compos. Mater.
**2015**, 30, 724–737. [Google Scholar] [CrossRef] - Carolan, D.; Ivankovic, A.; Kinloch, A.J.; Sprenger, S.; Taylor, A.C. Toughened carbon fibre-reinforced polymer composites with nanoparticle-modified epoxy matrices. J. Mater. Sci.
**2017**, 52, 1767–1788. [Google Scholar] [CrossRef] - Thomas, R.; Yumei, D.; Yuelong, H.; Le, Y.; Moldenaers, P.; Weimin, Y.; Czigany, T.; Thomas, S. Miscibility, morphology, thermal, and mechanical properties of a DGEBA based epoxy resin toughened with a liquid rubber. Polymer
**2008**, 49, 278–294. [Google Scholar] [CrossRef] - Mohammadi, R.; Ahmadi Najafabadi, M.; Saghafi, H.; Saeedifar, M.; Zarouchas, D. A quantitative assessment of the damage mechanisms of CFRP laminates interleaved by PA66 electrospun nanofibers using acoustic emission. Compos. Struct.
**2021**, 258, 113395. [Google Scholar] [CrossRef] - Quan, D.; Yue, D.; Ma, Y.; Zhao, G.; Alderliesten, R. On the mix-mode fracture of carbon fibre/epoxy composites interleaved with various thermoplastic veils. Compos. Commun.
**2022**, 33, 101230. [Google Scholar] [CrossRef] - Shekar, C.; Singaravel, B.; Deva Prasad, S.; Venkateshwarlu, N.; Srikanth, B. Mode-I fracture toughness of glass/carbon fiber reinforced epoxy matrix polymer composite. Mater. Today: Proc.
**2021**, 41, 833–837. [Google Scholar] [CrossRef] - Hojo, M.; Matsuda, S.; Tanaka, M.; Ochiai, S.; Murakami, A. Mode I delamination fatigue properties of interlayer-toughened CF/epoxy laminates. Compos. Sci. Technol.
**2006**, 66, 665–675. [Google Scholar] [CrossRef] - Zhou, H.; Du, X.; Liu, H.-Y.; Zhou, H.; Zhang, Y.; Mai, Y.-W. Delamination toughening of carbon fiber/epoxy laminates by hierarchical carbon nanotube-short carbon fiber interleaves. Compos. Sci. Technol.
**2017**, 140, 46–53. [Google Scholar] [CrossRef] - Song, Y.; Zheng, N.; Dong, X.; Gao, J. Flexible carboxylated CNT/PA66 nanofibrous mat interleaved carbon fiber/epoxy laminates with improved interlaminar fracture toughness and flexural properties. Ind. Eng. Chem. Res.
**2020**, 59, 1151–1158. [Google Scholar] [CrossRef] - Zheng, N.; Huang, Y.; Liu, H.-Y.; Gao, J.; Mai, Y.-W. Improvement of interlaminar fracture toughness in carbon fiber/epoxy composites with carbon nanotubes/polysulfone interleaves. Compos. Sci. Technol.
**2017**, 140, 8–15. [Google Scholar] [CrossRef] - Pozegic, T.R.; King, S.G.; Fotouhi, M.; Stolojan, V.; Silva, S.R.P.; Hamerton, I. Delivering interlaminar reinforcement in composites through electrospun nanofibres. Adv. Manuf. Polym. Compos. Sci.
**2019**, 5, 155–171. [Google Scholar] [CrossRef] - Cristina, M.; Miren, B.; Nieves, M.; Ana, P.-M.; Jon, M.; Jorge, G.; Jose Manuel, L.; Estíbaliz, A.; Jose Luis, V. Effect of Different Types of Electrospun Polyamide 6 Nanofibres on the Mechanical Properties of Carbon Fibre/Epoxy Composites. Polymers
**2018**, 10, 1190. [Google Scholar] [CrossRef] - Ahmadloo, E.; Gharehaghaji, A.A.; Latifi, M.; Saghafi, H.; Mohammadi, N. Effect of PA66 nanofiber yarn on tensile fracture toughness of reinforced epoxy nanocomposite. Proc. Inst. Mech. Eng. Part C J. Mech. Eng. Sci.
**2018**, 233, 2033–2043. [Google Scholar] [CrossRef] - Del Saz-Orozco, B.; Ray, D.; Stanley Walter, F. Effect of thermoplastic veils on interlaminar fracture toughness of a glass fiber/vinyl ester composite. Polym. Compos.
**2015**, 38, 2501–2508. [Google Scholar] [CrossRef] - Jiang, S.; Chen, Y.; Duan, G.; Mei, C.; Greiner, A.; Agarwal, S. Electrospun nanofiber reinforced composites: A review. Polym. Chem.
**2018**, 9, 2685–2720. [Google Scholar] [CrossRef] - Arinstein, A.A. Electrospun Polymer Nanofibers. A Physicist’s Point of View. Singapore: Jenny Stanford Publishing; Pan Stanford Publishing: Singapore, 2018. [Google Scholar]
- Alam, P.; Mamalis, D.; Robert, C.; Floreani, C.; Ó Brádaigh, C.M. The fatigue of carbon fibre reinforced plastics—A review. Composites. Part B Eng.
**2019**, 166, 555–579. [Google Scholar] [CrossRef] [Green Version] - Wang, C.; Zhang, J. Experimental and analytical study on residual stiffness/strength of CFRP tendons under cyclic loading. Materials
**2020**, 13, 5653. [Google Scholar] [CrossRef] [PubMed] - DorMohammdi, S.; Godines, C.; Abdi, F.; Huang, D.; Repupilli, M.; Minnetyan, L. Damage-tolerant composite design principles for aircraft components under fatigue service loading using multi-scale progressive failure analysis. J. Compos. Mater.
**2017**, 51, 2181–2202. [Google Scholar] [CrossRef] - Yang, Y.; Liu, X.; Wang, Y.-Q.; Gao, H.; Li, R.; Bao, Y. A progressive damage model for predicting damage evolution of laminated composites subjected to three-point bending. Compos. Sci. Technol.
**2017**, 151, 85–93. [Google Scholar] [CrossRef] - ASTM D7264/D7264M-07; Standard Test Method for Flexural Properties of Polymer Matrix Composite Materials. ASTM International: West Conshohocken, PA, USA, 2015.
- Sieberer, S.; Nonn, S.; Schagerl, M. Fatigue behaviour of discontinuous carbon-fibre reinforced specimens and structural parts. Int. J. Fatigue
**2020**, 131, 105289. [Google Scholar] [CrossRef] - Wang, Y.; Emerson, M.J.; Conradsen, K.; Dahl, A.B.; Dahl, V.A.; Maire, E.; Withers, P.J. Evolution of fibre deflection leading to kink-band formation in unidirectional glass fibre/epoxy composite under axial compression. Compos. Sci. Technol.
**2021**, 213, 108929. [Google Scholar] [CrossRef] - Javaid, U.; Ling, C.; Cardiff, P. Mechanical performance of carbon-glass hybrid composite joints in quasi-static tension and tension-tension fatigue. Eng. Fail. Anal.
**2020**, 116, 104730. [Google Scholar] [CrossRef]

**Figure 1.**Fracture behaviour under cyclic loading of CFRP and CFRP-Veil, where the red lines represent crack propagation within the composite laminate. Phase I, inter fibre failure (IFF); Phase II delamination (DEL); Phase III fibre failure (FF).

**Figure 3.**Optical microscopy of CFRP with veil to determine fibre alignment, void content in CFRF and GFRP.

**Figure 4.**Kink band formation in CFRP, where α is the rotation angle of fibre and β is the kink band angle.

**Figure 5.**CFRP stiffness degradation 1,000,000 cycles at 50% maximum flexural loading for 100,000 and 1 million cycles of 330 MPa cycle.

**Figure 6.**Total of 50% maximum flexural loading CF tested at (

**A**) 100,000 and 1 million cycles, and (

**B**) CFT tested at 100,000 and 1 million cycles.

**Figure 7.**Cyclic loading of CFRP and CFRP veil toughened with PA 6,6 for 100,000 cycles at 50, 70, and 90% maximum flexural strength. Designated CF and CFT for the control CFRP and veil toughened control CFRP, respectively. Samples individual loading for CF is 330 MPa, 500 MPa, and 544 MPA and CFT loaded at 390 MPa, 550 MPa, and 705 MPa.

**Figure 9.**Glass fibre at 50% flexural strength cyclic loading. Samples designated GF and GFT, cycled for 100,000 cycles at 400 N loading for 100,000 and 1 million cycles.

**Figure 10.**Optical analysis of GFRP after at 50% maximum flexural loading for (

**A**) GF for 100,000 cycles and after 1 million cycles (

**B**) GFT for 100,000 cycles and after 1 million cycles.

**Figure 11.**Optical imaging of glass fibre at 70% maximum loading: (

**A**) GF after 4000 and 100,000 cyles and (

**B**) veil toughened GFT after 4000 cycles and 100,000 cycles.

**Figure 12.**Flexural moduli change after 4000 and 100,000 cycles for GF and GFT loaded at 70% maximum flexural loading.

**Figure 13.**Glass fibre samples tested under cyclic loading at 50, 70, and 90% of their maximum loading. For GF the maximum flexural strength for each percentage was 260, 360, and 600 MPa, respectively.

**Figure 15.**Hybrid fibre at 50% flexural strength cyclic loading. HF and HFT under cyclic 3 point bending for 100,000 and 1,000,000 cycles.

**Figure 16.**Optical images of hybrid carbon and glass fibre after three-point bending at 50% maximum flexural strength for: (

**A**) HF after 100,000 and 1,000,000 cycles; (

**B**) HFT 100,000 and 1,000,000 cycles.

**Figure 17.**Modulus drop for hybrid HF and HFT composites after 4000 and 100,000 cycles at 70% maximum flexural strength.

**Figure 18.**Hybrid fibre reinforced plastic cycled at 70% maximum flexural loading under SEM imaging to image glass fibres for HF after (

**A**) 4000 cycles and HFT after (

**B**) 4000.

**Figure 19.**Cyclic loading of HFRP under 50, 70, and 90% loading in three-point bending for (

**A**) HF and (

**B**) HFT.

**Figure 20.**Cyclic loading of hybrid and veil toughened hybrid with PA 6,6 for 100,000 cycles at 50, 70, and 90% maximum flexural strength. Samples individual loading for HF is 240, 365, and 450 MPA and HFT loaded at 245, 380, and 450 MPa.

**Figure 22.**Number of cycles, compared with the modulus of CFRP, GFRP, and HFRP and their veil toughened counterparts.

**Figure 23.**Rubber toughened CFRP after 100,000, with 1,000,000 cycles at 470 N flexural modulus loss graph.

**Figure 24.**Stress and cycles of CFRP-R at 700 N and comparison to veil and control CFRP microscopy of failure area.

**Figure 25.**Microscopy of the (

**A**) CFRP-R and (

**B**) CF samples to determine cross-stitching compression.

Curing Cycle | Temperature | Preheat (Seconds) | Degassing (Seconds) | Full Pressed (Seconds) | Cooling (Seconds) |
---|---|---|---|---|---|

1 | 100 °C | 30 | 30 | 540 | 0 |

2 | 130 °C | 60 | 0 | 540 | 300 |

**Table 2.**CFRP and GFRP composite flexural strength, including hybrid CFRP/GFRP of 1:3 FVF ratio or 1:1 ply ratio, denoted as HF, where C denotes carbon fibre ply G denotes glass fibre and T denotes PA 6,6 veil interlayer.

Sample Name | Flexural Strength (MPa) | Flexural Modulus (GPa) |
---|---|---|

CF (CCCCCC) | 950.55 | 64.09 |

CFT (CTCTCTCTCTC) | 995.85 | 69.85 |

GF (GGG) | 856.27 | 43.89 |

GFT (GTGTG) | 797.18 | 41.57 |

HF (CCGG) | 495.83 | 42.40 |

HFT (CCTGG) | 547.09 | 53.99 |

**Table 3.**Flexural loading for cyclic testing in N. With carbon fibre ply’s labelled with C and glass fibre ply’s labelled G the inclusion of veil toughening is labelled with a T.

Sample Name | 90% Maximum Loading (N) | 70% Maximum Loading (N) | 50% Maximum Loading (N) |
---|---|---|---|

CF (CCCCCC) | 600 | 500 | 330 |

CFT (CTCTCTCTCTC) | 700 | 550 | 390 |

GF (GGG) | 600 | 360 | 200 |

GFT (GTGTG) | 600 | 360 | 200 |

HF (CCGG) | 450 | 380 | 240 |

HFT (CCTGG) | 450 | 380 | 240 |

Load Case Scenario | 4000 Cycles | 100,000 Cycles | 100,000,000 Cycles |
---|---|---|---|

50% maximum flexural strength | 5 Hz | 5 Hz | 5 Hz |

70% maximum flexural strength | 5 Hz | 5 Hz | |

90% maximum flexural strength | 5 Hz | 5 Hz |

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. |

© 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Blythe, A.; Fox, B.; Nikzad, M.; Eisenbart, B.; Chai, B.X.
Stiffness Degradation under Cyclic Loading Using Three-Point Bending of Hybridised Carbon/Glass Fibres with a Polyamide 6,6 Nanofibre Interlayer. *J. Compos. Sci.* **2022**, *6*, 270.
https://doi.org/10.3390/jcs6090270

**AMA Style**

Blythe A, Fox B, Nikzad M, Eisenbart B, Chai BX.
Stiffness Degradation under Cyclic Loading Using Three-Point Bending of Hybridised Carbon/Glass Fibres with a Polyamide 6,6 Nanofibre Interlayer. *Journal of Composites Science*. 2022; 6(9):270.
https://doi.org/10.3390/jcs6090270

**Chicago/Turabian Style**

Blythe, Ashley, Bronwyn Fox, Mostafa Nikzad, Boris Eisenbart, and Boon Xian Chai.
2022. "Stiffness Degradation under Cyclic Loading Using Three-Point Bending of Hybridised Carbon/Glass Fibres with a Polyamide 6,6 Nanofibre Interlayer" *Journal of Composites Science* 6, no. 9: 270.
https://doi.org/10.3390/jcs6090270