Constitutive characterisation of rubber blends by means of genetic algorithms

In this contribution a new procedure for parameter identification for the material characterisation of rubber blends is proposed which is based on genetic algorithms. Such a model has to consider the effect of wall slippage on the viscous properties as well as the identification of a new material parameter regarding die swell. As basis serves an experimental investigation of the viscous properties of rubber blends by means of a capillary-viscometer. Because of the consideration of wall slippage, the temperature and the die swell the resulting material characterisation is represented by a coupled system of nonlinear equations. Describing their solution requires a numerical integration algorithm. For this purpose a genetic algorithm has been adopted. The verification of the developed parameter identification was done by means of comparison with the classical material characterisation based on correction methods. Figure 1. Position of the high speed camera. 2.1 Adaptation with high speed camera PCI 1000 Because the highest exit speed of a die through a capillary is up to 1000 mm/s, the shooting of the exit of capillaries cannot be investigated with common cameras. With the used high speed camera 1000 photographs per second can be taken. By using a reference wire with a known diameter the swell diameter can be determined by comparing the corresponding photographs. Figure 1 shows the situation of the camera in front of the exit of the capillary. 2.2 Microscopical investigations An effective method to determine the diameter of a strand without consideration of time effects is the measurement with a microscope. Because no time dependent properties are considered this method is only for validation and not for characterisation. 2.3 Swell value measuring unit The fastest method to determine the diameter of a strand is the usage of the so-called swell value measuring unit. It measures the diameter by means of a laser beam with a wave-length of approximately 700 nm. In this contribution the dimensionless swell value represents a strand cross-sectional area ratio. It is defined as follows: