Wouter Grouve

PhD Researcher

Contact information:

University of Twente

Faculty of Engineering Technology

Chair of Production Technology

P.O. Box 217

7500 AE Enschede

The Netherlands

P +31 (0)53 489 4346

w.j.b.grouve[a]utwente.nl

Publication List

0075

Project:

Optimisation of the Laser-Assisted Tape Placement Process

Start / End:

June 2007 to June 2011

This project is part of the ECO-Design ITD within the European Clean Sky project.

Partners:

The tape placement equipment is kindly provided by AFPT Advanced Fiber Placement Technology, while Ten Cate Advanced Composites supplies the fibre reinforced tape material.

Motivation:

The high degree of automation and ’out-of-autoclave’ potential make tape placement technologies attractive for aerospace applications. The process under consideration involves welding of fibre reinforced thermoplastic tapes under the application of heat and pressure onto a laminate or previously deposited tape. The final product properties can be tailored by incrementally adding tapes in the desired orientation. The application of a laser increases the efficiency of the welding process. The laser applies heat locally and instantaneously, which allows fast process control necessary for products with a complicated geometry. Currently, the processing window for new materials is determined by trial and error procedures involving extensive material inspection. The laser-assisted tape placement (LATP) process lacks reliable predictive process simulation tools. The interrelation between material properties, processing parameters and weld strength requires further investigation to help the LA tape placement technology evolve into a true ’out-of-autoclave’ technology.

Focus:

The final properties of an ‘in situ’ consolidated product are determined by the interrelation between material properties and processing parameters. The research concerning the LATP process focuses on the following:

·	Weld strength – The weld strength of the tapes is absolutely critical. Research focuses on the influence of processing parameters and material properties on final weld strength. A predictive process model will be developed to optimize the process and/ or materials.

·	Consolidation quality – The tapes needs to be consolidated properly (in terms of void content and fibre/resin distribution) to ensure proper product performance. The relation between processing parameters, material properties and consolidation quality is investigated.

·	Tape deformation – During the placement process the fibre reinforced tape deforms, which might have a detrimental effect on the mechanical performance of the final product. The influence of the tape material properties and welding processing parameters is subject of current research.

…

LATP process:

Figure 1 schematically shows the laser-assisted tape placement process. A unidirectional ﬁbre reinforced thermoplastic tape is welded on predeﬁned paths in this continuous process. A laser heats the incoming tape and substrate, while simultaneously the tape is guided between the compaction roller and the substrate. The tape and substrate are welded together under the applied heat and pressure.

The welding process itself, schematically shown in Figure 2, comprises two different, but simultaneously occurring phenomena: I. Intimate contact develops between the two surfaces and II. Intermolecular diffusion, a process which is also known as healing, takes place between the surfaces in intimate contact [1].

The time required to achieve intimate contact depends on the roughness of the surfaces brought into contact and the applied pressure and temperature at the interface[2]. The application of pressure ﬂattens the surface asperities in contact, thereby increasing the total contact area. The matrix deformability increases at elevated temperatures, because of the temperature dependence of the viscosity. An increase of the welding temperature or pressure therefore results in a decrease of the time required to achieve intimate contact [3].

Interdiffusion of polymer chains will occur at the interfaces where intimate contact is achieved. In this diffusion process, also known as healing, polymer chains migrate across the interface. The healing process is generally described using the reptation theory of chain mobility [4]. The matrix material is considered as an entanglement of polymer chains, in which the movement of the individual chains is restricted. The mobility of the polymer chains and thereby the diffusion rate increases with increasing temperature, improving the weld strength.

$P:\My Documents\PhD work\articles\mandrel peel\figures\tapeplacement_smallc.png$

$P:\My Documents\PhD work\articles\mandrel peel\figures\healing.png$

Fig 1. Schematic representation of the LATP process

Fig 2. Welding process: (a) tape and substrate are brought into contact, (b) intimate contact develops and (c) healing occurs

Peel testing

The influence of the processing parameters on weld strength is investigated experimentally. A straightforward experimental procedure was desired and for this purpose a mandrel peel test set-up [5] was developed. The set-up is schematically shown in figure 3. The test method involves peeling the tape from a substrate while applying an alignment force F_drag. The alignment force ensures conformity of the peel arm to the mandrel.

The set-up is used to study the influence of placement velocity, welding temperature and roller pressure on the weld strength. The physical phenomena involved in the process and their relative importance is investigated. The obtained weld strength data will furthermore be used for the validation of the developed processing models.

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$P:\My Documents\PhD work\experimental\peel set-up\pics\photo\DSC00645.JPG$

Fig 3. Schematic representation of the

mandrel peel test set-up

Fig 4. IAF peel set-up v1.0

Current work

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Current work focusses on the development of a processing model to predict the weld strength of the tapes as a function material properties (e.g. resin content and thermal properties) and processing parameters (e.g. laser power, incident angle and velocity). The process model consists of three parts. An optical model is used to determine how the laser light reflects (figure 5) on the tape and substrate and how much energy is ultimately absorbed by the material. The calculated energy absorbed by the tape and laminate will serve as an input for a thermal model which

will then predict the temperature history under the compaction roller. A healing model is subsequently used to predit the weld strength as a function of this temperature history. The developed process model will be validated by experimentally obtained weld strength data.

$C:\Documents and Settings\GrouveWJB\Desktop\raytrac.png$

Fig 5. Ray tracing to determine the incident flux:

the colour of the dots show intensity of absorbed light

References

W.I. Lee and G.S. Springer. A model of the manufacturing process of thermoplastic matrix composites. Journal of Composite Materials, 21(11):1017–1055, 1987.

L. J. Bastien and J.W. Gillespie. A non-isothermal healing model for strength and toughness of fusion bonded joints of amorphous thermoplastics. Polym.Eng.Sci., 31(24):1720–1730, 1991.

C.A. Butler, McCullough R.L., Pitchumani R., and J.W. Gillespie Jr. An analysis of mechanisms governing fusion bonding of thermoplastic composites. Journal of Thermoplastic Composite Materials, 11:338–363, 1998.

R. P. Wool and K. M. O’Connor. A theory of crack healing in polymers. Journal of Applied Physics, 52(10):5953–5963, 1981.

L. F. Kawashita, D. R. Moore, and J. G. Williams. Comparison of peel tests for metal-polymer laminates for aerospace applications. Journal of Adhesion, 81(6):561–586, 2005.

Posters:

2009

W.J.B. Gouve, R. Akkerman, Optimising the production process of glass/PPS laminates, Engineering Mechanics Symposium, Lunteren, The Netherlands, 2009.

2008

W.J.B. Gouve, R. Akkerman, A meso-scale BC to include micro-scale effects in textile impregnation processes, Engineering Mechanics Symposium, Lunteren, The Netherlands, 2008.

2007

W.J.B. Gouve, R. Akkerman, Optimising the consolidation of thermoplastic composite laminates, Engineering Mechanics Symposium, Lunteren, The Netherlands, 2007.