TWI Industrial Member Report Summary 753/2002
J T Wescott, K L Anderson, A H Windle (University of Cambridge) R J Wise and S D Rostami (TWI)
The welding of thermoplastics is of growing interest to many industries. In the welding process, two amorphous polymer surfaces are brought in contact at temperatures above the glass transition temperature of the polymer to form a weld. The mechanical properties of the weld depend on several factors including temperature, time, pressure, roughness of the surfaces, processing histories and distribution of polymer chains within the component.
The ability to predict the optimum welding conditions to maximise, for example, the weld strength while minimising processing time is always desirable. Performing an extensive set of welding experiments on the chosen material is one way to decide upon the optimum conditions. An alternative method is the use of a suitable computer model that simulates the process responsible for the build-up of weld strength. The first step in this process is to simulate one aspect of the welding process, ie the inter-diffusion of polymer chains.
The aim of this project was to develop such a model based on a Monté Carlo statistical simulation of polymer chains at the 'meso' scale, ie without details of polymer chemistry, and to validate the model using the results of mechanical tests.
This report summarises the results of a three-year project to develop and validate such a computer model.
- Develop a suitably detailed computer model capable of simulating conditions for polymer chain movements crossing the interface under defined welding conditions.
- Validate the model by experimental measurement of interfacial toughness of welded polymer.