# Characterisation of Fibre Bundle Deformation Behaviour—Test Rig, Results and Conclusions

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

#### 2.1. Material Specification

#### 2.2. Evaluation Methods

## 3. Experimental Setup

#### 3.1. Equipment for Fibre Bundle Deformation Studies

_{$fe$}and the forming angle $\alpha $; while the diameter varies, the forming angle is constant at 30°.

#### 3.2. Experimental Investigations

_{$fe$}of $1.2$ mm, the achieved deformation ratio is small. Deformation ratio means, in the present paper, the ratio of the initial cross-section of the prepreg material to the final cross-section of the pultrudate. If the ratio is small, this means that the initial material is subjected to a moderate forming force, as a certain oversize of the exit cross-section of the forming element is ensured. The second series of tests was carried out at a forming element temperature of 200 °C, a forming element diameter of $1.2$ mm and staggered pull-off speeds as shown in Table 4. In the following test series, the temperature of the forming element is increased by 10 °C per series up to 220 °C and then the diameter of the forming element is reduced to $0.9$ mm so that the degree of forming increases. Due to the cross-section area of the forming unit ($0.64$ mm

^{2}) and the prepreg ($0.75$ mm

^{2}), the thermoplastic melt must be stripped in the forming element so that a compacted pultrudate can be discharged.

## 4. Results

#### 4.1. Characterization of the Thermoplastic PP Matrix

#### 4.2. Evaluation of the Microscopy Image and CT Reconstruction Data of the Input Material

^{2}. The filament diameter of the GF is assumed to be $15.6$ $\mathsf{\mu}$$\mathrm{m}$ (N = 33) with standard deviation of $1.31$ $\mathsf{\mu}$$\mathrm{m}$ determined by measurements of a detailed micrograph of the cross section (magnification of objective 50×).

#### 4.3. Results of the Forming Behaviour Using the Forming Element with Diameter 1.2 mm

#### 4.4. Results of the Forming Behaviour Using the Forming Element with Diameter 0.9 mm

^{2}, the prepreg became stuck. Due to the smaller cross section area, fibres and matrix are stripped off and, after a critical amount, the required deformation forces exceed the maximum force of the clamping mechanism in the feeder unit. The pregreg remains stuck until the stripped fibres are rearranged. The measured deformation force decreases meanwhile, until the required force is below the clamping mechanism force. Afterwards, the pultrusion process continues since the prepreg became stuck again. It has to be mentioned that the stepper motor also counts the displacement during the stuck state.

#### 4.5. Material Structure Analysis with Computed Tomography

## 5. Discussion

## 6. Conclusions

## Author Contributions

## Funding

## Data Availability Statement

## Conflicts of Interest

## Abbreviations

PREPREG | Preimpregnated continuous fibre-reinforced material |

FRP | Fibre-reinforced plastics |

GF | Glass fibre |

PP | Polypropylene |

3D | Three-dimensional |

TPC | Thermoplastic composite |

CT | Computed tomography |

PPR | Parallel-plate rheometer |

UD | Unidirectional |

FFI | Fibre–fibre interaction |

CF | Carbon fibre |

PBT | Polybutylenterephthalate |

PEEK | Polyetheretherketone |

PA | Polyamide |

PC | Polycarbonate |

PEI | Polyetherimide |

FVC | Fibre volume content |

DSC | Differential scanning calorimetry |

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**Figure 1.**Computed tomography (CT) analysis of initial ${}^{1)}$ and resultant material structure ${}^{2)}$ of the pinning process of [4]. ${}^{1)}$—Different specimen area as resultant material structure; ${}^{2)}$—Pin structure is eliminated for more accurate CT scans.

**Figure 6.**Micrograph of the transversal section of used PP GF 60 prepreg material (magnification of objective 20×).

**Figure 7.**CT reconstruction of used PP GF 60 prepreg material; green—fibres, yellow—thermoplastic matrix, red—void.

**Figure 14.**CT reconstruction data and section cuts of deformed GF-PP 5 mm/s and 200 °C, ${D}_{fe}$ = $1.2$ mm.

**Figure 15.**CT reconstruction data and section cuts of deformed GF-PP 30 mm/s and 200 °C, D

_{$fe$}= $1.2$ mm.

Property | Unit | Abbreviation | Value |
---|---|---|---|

tensile modulus ${0}^{\circ}$ | GPa | ${E}_{0}^{\circ}$ | 28 |

flexural modulus ${0}^{\circ}$ | GPa | ${E}_{f}$ | 21 |

tensile strength ${0}^{\circ}$ | MPa | ${\sigma}_{{0}^{\circ}}$ | 720 |

flexural strength 0° | MPa | ${\sigma}_{f}$ | 436 |

thickness | mm | t | 0.25 |

width | mm | w | 3 |

fibre volume content | % | $\phi $ | 35 |

melting temperature | °C | ${T}_{m}$ | 165 |

processing temperature | °C | ${T}_{p}$ | 180–220 |

Parameter | Unit | Value |
---|---|---|

acceleration voltage | $\mathrm{kV}$ | 60 |

tube current | $\mathsf{\mu}\mathrm{A}$ | 100 |

exposure time | $\mathrm{ms}$ | 2000 |

X-ray projections | 1440 (4 per 1°) | |

source object distance | $\mathrm{m}\mathrm{m}$ | 30 |

source image distance | $\mathrm{m}\mathrm{m}$ | 200 |

voxel size | $\mathsf{\mu}\mathrm{m}$ | 7.5 |

Parameter | Unit | Value |
---|---|---|

acceleration voltage | $\mathrm{kV}$ | 50 |

tube current | $\mathsf{\mu}\mathrm{A}$ | 180 |

exposure time | $\mathrm{ms}$ | 1500 |

X-ray projections | 1440 (4 per 1°) | |

source object distance | $\mathrm{m}\mathrm{m}$ | 30 |

source image distance | $\mathrm{m}\mathrm{m}$ | 200 |

voxel size | $\mathsf{\mu}\mathrm{m}$ | 7.5 |

Series | Velocity mm/s | Temperature °C | Diameter D_{$fe$} $\mathbf{mm}$ |
---|---|---|---|

1 | 5 | 23 | 1.2 |

2 | 5, 10, 15, 20, 25, 30 | 200 | 1.2 |

3 | 5, 10, 15, 20, 25, 30 | 210 | 1.2 |

4 | 5, 10, 15, 20, 25, 30 | 220 | 1.2 |

5 | 5 | 200 | 0.9 |

Temperature °C | Dynamic Viscosity ${\mathit{\eta}}_{0}$ in Pa$\phantom{\rule{0.166667em}{0ex}}\mathit{\xb7}\phantom{\rule{0.166667em}{0ex}}$s |
---|---|

200 | 328 |

210 | 257 |

220 | 225 |

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**MDPI and ACS Style**

Borowski, A.; Gröger, B.; Füßel, R.; Gude, M.
Characterisation of Fibre Bundle Deformation Behaviour—Test Rig, Results and Conclusions. *J. Manuf. Mater. Process.* **2022**, *6*, 146.
https://doi.org/10.3390/jmmp6060146

**AMA Style**

Borowski A, Gröger B, Füßel R, Gude M.
Characterisation of Fibre Bundle Deformation Behaviour—Test Rig, Results and Conclusions. *Journal of Manufacturing and Materials Processing*. 2022; 6(6):146.
https://doi.org/10.3390/jmmp6060146

**Chicago/Turabian Style**

Borowski, Andreas, Benjamin Gröger, René Füßel, and Maik Gude.
2022. "Characterisation of Fibre Bundle Deformation Behaviour—Test Rig, Results and Conclusions" *Journal of Manufacturing and Materials Processing* 6, no. 6: 146.
https://doi.org/10.3390/jmmp6060146