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Assessing fibre orientation quality in reclaimed carbon
fibre materials from flow, thermal andmechanical
properties
J. Kratz, Arthur Lévy
To cite this version:
J. Kratz, Arthur Lévy. Assessing fibre orientation quality in reclaimed carbon fibre materials from flow, thermal andmechanical properties. 11th International Conference on Manufacturing of Advanced Composites, Jul 2018, Nottingham, United Kingdom. �hal-02385016�
Assessing fibre orientation quality in reclaimed carbon fibre
materials from flow, thermal and mechanical properties.
James Kratz, University of Bristol, Bristol, United Kingdom.
Arthur Levy, Laboratoire de Thermique et Energie de Nantes (LTEN), Nantes, France.
I - Introduction
Background
To date, advanced composites are mostly made by encapsulating long, stiff, slender carbon fibres in a thermosetting matrix because of excellent properties and ease of processing the polymer from a liquid into a glassy solid. However, their long-term sustainability has recently been questioned because of high scrap volume, and no viable recyclable methods.
An increasing effort is being put towards developing more sustainable composite materials and associated forming processes. For example, fibres and polymers are combined at the last possible stage of the manufacturing process to avoid expiry dates. In addition, any waste fibre is reclaimed and reprocessed into non-critical composite parts. Recycled materials have found limited application to date because the fibre orientation is random, negating the performance benefit of the carbon fibre materials.
Material
Blab la on the process of reclaiming.
Figure 1: reclaimed carbon fibre bed [
Objectives
This work aims at characterizing the quality of the fibre orientation in the commercially available reclaimed carbon fibre bed. Firstly, better orientation in the fibre bed enable to taylor blanks with respect to the expected loading. Secondly, a better orientation of the fibre usually result in a better fibre packing and thus a better fibre content, desirable for proper mechanical properties.
Kratz et al. Resource friendly carbon fiber composites
Advanced Manufacturing: Polymer & Composites Science 2017 VOL. 3 NO. 4
122
to 85% and stiffness reductions up to 45%.12–14 The reduction
in properties at the laminate level arises from the loss of align-ment of reprocessed short fibers,4,15 larger pieces of reclaimed
product acting as a failure initiation site,7 and low fiber volume
fractions.2,4 Random fiber mats experience less fiber nesting
during consolidation due to less alignment within the fiber bed.16 Techniques to align short fibers to a much higher degree
than conventional methods have been proposed,17 and until
the recycled product is improved, it will be limited to non-crit-ical applications.8
A current barrier to adopting reclaimed fiber composites is the lack of an established market for the recycled product.4
Reclaimed materials suffer from poor fiber alignment and unac-ceptably low fiber volume contents required for structural com-ponents. The aim of this study was to investigate the potential to incorporate a commercially available reclaimed carbon fiber material into structural composites. The mechanical properties and re-manufacturing of virgin and reclaimed carbon fiber prod-ucts were investigated. A resource efficient composite laminate where the waste feedstock is incorporated back into the parent waste generating virgin fiber laminate is proposed to continue structural light-weighting with high-value carbon fiber.
Experimental methods
Raw materials
Commercially available virgin and reclaimed carbon fiber materials were investigated in this study. Type 62 RECATEX non-woven complex with an areal density of 200 g/m2
from SGL Automotive Carbon Fibers (ACF) was used as the reclaimed product. This mat is created from dry fiber produc-tion waste that is shredded, carded, and then sewn to improve product handling using similar process to non-crimp fabric materials.18 A picture of the reclaimed fiber mat is shown in
Fig. 1. A preferred fiber direction parallel to the sewing yarn is visible, but fibers are oriented in multiple directions at various lengths and sewing yarns from the original NCF is also present. Reported anisotropy in the reclaimed fiber material is 2.4 times higher modulus and 2.3 times higher strength parallel to the sewing direction.18 A virgin fiber counterpart, also from SGL
ACF, SIGRATEX C U320-0/ST was supplied as a unidirectional non-crimp fabric (NCF) with an areal density of 320 g/m2, and
is shown alongside the reclaimed fiber mat in Fig. 1. The NCF material included a powder binder.
Test matrix
An experimental campaign was performed to measure the compaction response of the dry reinforcements and the mechanical properties of the resulting composites. The test matrix is presented in Table 1. Plies of reclaimed carbon fiber were designated by an R before the material direction – where 0° is the roll direction. Hybrid laminates of reclaimed mat and virgin continuous material were also investigated.
The total fiber volume fraction of the composite laminates was measured by acid digestion or pyrolysis, and the density of the fiber is required for these calculations. The density of the virgin carbon fiber was taken as 1.8 g/cm3 from the material
datasheet.19 The reclaimed fiber mat is reportedly composed
of 75% carbon fiber, 11% glass fiber, 11% polyester fiber, and 3% binder.18 The exact type of glass and polyester fiber
were unknown therefore density values were assumed to be 2.5 g/cm3 and 1.3 g/cm3, respectively.20 The binder was
unknown, however assuming a low molecular weight poly-mer with a 1.2 g/cm3 density yields a representative density
of 1.7 g/cm3 for the reclaimed carbon fiber mat. The resulting
fiber volume fraction is then calculated as follows:
Figure 1 Reclaimed carbon fiber mat (left) and unidirectional carbon fiber non-crimp fabric (right)
Table 1 Lay-up sequences and laminates investigated in this study
aResin transfer molding.
bVolume fraction by acid digestion.
Lay-up Stacking sequence Compaction pressure during manufacture (MPa) Fiber volume fraction (%) Reclaimed [R0]4 2.2a 29.0 0.8a 23.0 0.1 13.5b Hybrid [0, R03, 0] 3.2a 45.0 0.9a 36.2 0.1 23.5 Unidirectional [0]8 0.1 54.6b Quasi-Isotropic [−45, 0, +45, 90]S 0.1 – Thick Reclaimed [R0]8 0.1 – Thick Unidirectional [0]16 0.1 –
II – Methods
A quantification of the orientation of the fibres in this random map can make use of the classical orientation tensor mathematical tool [3]. In this framework, the second order orientation tensor a is sufficient to determine any second order tensorial material properties as long as two scalars (obtained from a unidirectional analysis) are known.
In this work, tensorial properties of the material are quantified (permeability, heat conductivity, linear elasticity) and can thus infer the orientation tensor.
The orientation tensor itself gives a quantification of the quality of the fibre orientation. The degree of orientation D can indeed be quantified as:
𝐷 = max (|𝜆*|) ∑𝜆⁄ * where 𝜆* are the eigenvalues of the tensor a.
Effect on heat transfer
The anisotropic conductivity tensor of the dry reclaimed fibre bed is characterized using the PIMS bench [4]. It consists of an inverse method applied on the temperature measured using a planar instrumented heating pad that generates tridimensional heat fluxes in the sample (fig. 1).
Figure 2: PIMS bench. The instrument pad applies a heat source and measure the temperature to two composite samples. An inverse method enables to obtain the anistropic conductivity tensor.
Effect on resin flow
The anisotropic permeability tensor is obtained by instrumenting an RTM mould with a 2D pressure sensor device [5]. The pressure map versus time is acquired during infusion. The flow front position and permeability tensorial property can thus be assessed.
Effect on final elastic properties
The elastic properties of virgin unidirectional and reclaimed carbon fibre composites were investigated in previous work [1,2,5].
III - Results and Discussion
IV - Conclusion
Quality of a reclaimed fibre bed strongly relies on the quality of the fibre orientation. This orientation quality can be quantified using a norm of the orientation tensor.
In this work, the orientation tensor of a reclaimed fibre bed was assessed using various characterization techniques (heat transfer, permeability, elasticity).
[1] B. Fox, “An investigation into increasing the structural suitablity of reclaimed carbon fibre mat materials”, University of Bristol, 2016
[2] Y. S. Low, “Mechanical Properties of Hybrid and Fully Reclaimed Carbon Fibre Laminates,” University of Bristol, 2015.
[3] Advani, S., & Tucker III, C. L. (1987). The use of tensors to describe and predict fiber orientation in short fiber composites. Journal of Rheology, 31(8), 751–784.
[4] Thomas, M., Boyard, N., Lefèvre, N., Jarny, Y., & Delaunay, D. An experimental device for the simultaneous estimation of the thermal conductivity 3-D tensor and the specific heat of orthotropic composite materials. Int. J. of Heat and Mass Transfer, 53(23–24). 2010
[5] Kratz, Zschenderlein, Levy, “In-process flow front detection in reclaimed carbon fibre materials using surface mapping sensors”, FPCM 14 Conference, Lulea, Sweden, 2018
[6] Kratz, J., Low, Y. S., & Fox, B. Resource-friendly carbon fiber composites: combining production waste with virgin feedstock. Advanced Manufacturing: Polymer & Composites Science, 3(4), 2017