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The industrial current design approach use more and more calculation tools to design technical parts. The more the properties of material are well known, the more the calculation is efficient and reliable. One of the way to recover real properties of a material is to measure them with an ultrasonic technique. This method is based on the fact that ultrasonic wave velocity depends on the material in which it goes through. Ultrasonic technique appears then like a reliable device to study the properties of a material directly on an injected part without destroying it, and can be used in laboratory to characterize plastic or metallic materials.

Engineering plastics, such as polybutylene terephthalate (PBT) with high levels of short glass fibers exhibit unusual flow behavior during injection molding which may affect the final properties of moulded pieces. Through short-shots experiments it is obvious that jetting during cavity filling was systematically associated with highly filled materials, while neat polymers fill cavities through the simple laminar flow. Jetting phenomenon was related with very low, if any, post-extrusion swelling of highly filled materials. In order to study the high shear rheological properties of engineering plastics, in conditions similar to industrial processing, an injection capillary rheometer was developed and fixed on an injection machine. In that case, pressure, shear rate, material plastification and injection are representative of the processing. For comparison, standard laboratory rheometer was performed.

During injection molding of thermoplastics the filling depends on the material's rheological properties, on the characteristics of the mold and also on the process parameters. Thanks to the elaboration of short shots, it is possible to reconstruct the main successive steps of the filling and to know the advancing melt flow. The choice of specific cavities and particular injection gates allow for filling to be studied in many different cases. The disposition of barriers inside the cavities gives opportunity to orient the flow. Experimental studies consider the injection of polyester and polyamide unfilled and reinforced with short glass fibres. Original results in terms of filling are shown on images. We compare experimental fillings with theoretical fillings obtained with a rheological simulation software. Good agreement is proved for unfilled materials.