phd project

Welding Technologies

Start / End:

June 2013 to June 2017

Contact

TPRC
Palatijn 15
7521 PN Enschede
P.O. Box 770
7500 AT Enschede
The Netherlands
Phone: +31 888773815
E-mail: francisco.sacchetti[a]tprc.nl

University of Twente
Faculty of Engineering Technology
Chair of Production Technology
P.O. Box 217
7500 AE Enschede
The Netherlands
E-mail: f.sacchetti[a]utwente.nl

Funding

This project is funded by the Thermoplastic Composite Research Centre (TPRC). The support of the Region Twente and the Gelderland & Overijssel team for the TPRC, by means of the GO Programme EFRO 2007-2013, is gratefully acknowledged.

Introduction

The development of fusion bonding procedure for thermoplastic composites based on different heating strategies has been and currently is the focus of several research groups and companies. The development of new processes has however not been accompanied so far by the definition of specific testing methods to robustly asses the mechanical performance of the thermoplastic composite joints. The strength of fusion bonded joints is usually characterized through single lap shear testing. Single lap shear samples are simple to manufacture and the testing is fast and straightforward. However, complex stress distributions, characterized by peel and shear concentrations towards the edges of the overlap, are generated at the bond line during the test. Moreover, these stresses are sensitive to factors like the thickness and stiffness of the adherents, thickness and stiffness of the bond line, overlap length, etc. As a result, the apparent shear strength as provided by single lap shear test is generally not valid for comparison of different fusion bonding techniques [1], comparison with a benchmark or comparison among the results of different research groups.

Objective

To put forward robust testing procedures for the assessment of the mechanical properties of fusion bonded joints in thermoplastic composites and to generate relevant data on the static and dynamic performance of fusion bonded and benchmark joints.

Approach

Induction welding (figure 1), ultrasonic welding (figure 2), and (autoclave) co-consolidation will be investigated within this research project. A fracture mechanics approach will be followed for the deep analysis of the performance and damage tolerance of these type of joints under well-defined and controlled stress condition. Test procedures will be define considering the specific nature of thermoplastic composite fusion bonded joints. Likewise, adequate fusion bonding procedures to consistently and practically produce the required test samples will be developed. The failure mechanisms and their relationship with processing conditions and material properties will be investigated. Data will be generated for different joining techniques under consideration and for different thermoplastic composite materials.The research approach will be mainly experimental supported by the development of numerical or analytical models for the understanding of stress scenarios and underlying phenomena.



Figure 1: Scheme of Induction Welding setupFigure 2: Scheme of Ultrasonic Welding setup.

Expected outcome and deliverables

Likewise, the results are very well suited for training of designers and engineers in thermoplastic composites. The deliverable of this project are:

  • Extended test methodology for thermoplastic composite fusion bonding joints.
  • Process and material recommendation for the optimization of the joints performance.
  • Improve understanding of the mechanical performance of fusion bonded joints and data collection on mechanical properties of selected joints.

References

  • [1] Villagas I.F., Moser L. Yousefpour A. Mitshang P., Bersee .E.N. Process and performance evaluation of ultrasonic, induction an resistance welding. Journal of Thermoplastic Composites. Available online Sept 2012.
  • [2] Dube M., Hubert P., Yousefpour A., Denault J. Fatigue failure characterisation of resistance welded thermoplastic composites skin/stringer joints. International Journal of Fatigue 31 (2009)
  • [3] Stavrov D., Bersee H.E.N. Resistance welding of thermoplastic composites- An overview. Composites Part A: Applied science and Manufacturing 36(1), 2005