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Short fiber reinforced thermoplastics are used extensively due to their high mechanical properties and low processing costs. Long fiber reinforced thermoplastics (LFT) show an even more interesting property profile and are used more and more often for structural parts. However, processing is not that simple and their anisotropic properties resulting from the fiber microstructure pose a challenge in terms of engineering design process. To reliably predict the structural mechanical properties of LFT, it is necessary to investigate a method that allows comprehensive consideration of the existing fiber microstructure within the engineering design process. For this purpose, a micromechanical approach developed at IKT has been extended to include the necessary process variables and the associated models. [ABSTRACT FROM AUTHOR]

Particularly in the automotive industry, continuous fiber-reinforced thermoplastics are currently enjoying steadily rising demand. Thermoplastic matrix systems promise shorter cycle times and enhanced joining and recycling characteristics when compared to fiber reinforced thermosets. In order to process continuous fiber reinforced thermoplastics, semi-finished parts are produced first. These are heated and post-processed in a back injection molding process. Design elements such as load transfer elements and ribs are injected onto the flat semi-finished part. To heat the parts, the effect of Joule heating can be utilized. The electrically conductive carbon fibers are heated by an applied voltage. The temperature is distributed through heat conduction into the part’s matrix. The use of Joule heating enables high heating rates with low energy consumption. The industrial application of Joule heating of continuous fiberreinforced thermoplastics requires the specification and investigation of further relationships between the influencing variables. The quality of the heating is significantly influenced by the contacting of the part. Within the scope of this study, heating experiments are compared using a thermographic image system. It is found that higher contact areas yield better heating quality and that rounded corners for the contact pieces additionally improve the temperature distribution. [ABSTRACT FROM AUTHOR]

The description of the specific volume under practical conditions during the processing of plastics still poses a challenge. For the processing of thermoplastic materials, the cooling process is particularly of high relevance. Since integral values for the specific volume are determined with conventional measurements, the local temperatures and cooling rates must already be taken into account during the evaluation of the measurements. The non-isothermal effects are difficult to determine with current analytical devices and yet lack a mathematical model that describes them sufficiently. In this work, the authors present an approach, which considers local temperatures and cooling rates. This is a basic requirement for the optimization of cooling rate dependent material models. The approach is implemented by means of numerical methods using the example of an amorphous thermoplastic material. The results, which are based on a cooling rate independent model, are promising and set the base for further work with cooling rate dependent constitutive models. [ABSTRACT FROM AUTHOR]

Thermoforming generally describes the shaping of a thermoplastic semifinished part above its softening temperature to a three dimensional part. The sub-step of heating the sheet can be seen as the very crucial process step. In most thermoforming machines, the sheet is heated by means of infrared radiation inside a radiation furnace. Depending on the thickness and the absorption characteristics of the sheet material as well as the working temperature of the radiators, different temperature profiles along the sheet thickness will occur. The knowledge of this temperature distribution is important to control the heating step since the sheet temperature directly influences process stability and part quality like sagging, burnings, orientations and wall thickness distribution of the part or accurate reproduction of surface details. In this paper a new approach by combining three different infrared sensors for determining the temperature distribution along the sheet thickness at any time of the heating phase will be presented. At first, the different amounts of radiation will be calculated in order to separate reflected and transmitted radiation from the actual measuring signals. At second the sheet will be divided into a certain number of layers and the amount of emitted radiation of each layer will be calculated and compared to measured signals in order to finally determine the real temperature distribution along sheet thickness. Calculated and measured results will be shown using polypropylene as sheet material. [ABSTRACT FROM AUTHOR]

The shrinkage and warpage behavior of injection molded parts is very complex. By using a new measuring method it was shown for the first time that the warpage can be classified as warping and distortion. In general, warpage can only be reduced substantially by a sufficiently high volumetric compensation in the holding pressure phase. The shrinkage and warpage behavior of injection molded parts is very complex. By using a new measuring method it was shown for the first time that the warpage can be classified as warping and distortion. In general, warpage can only be reduced substantially by a sufficiently high volumetric compensation in the holding pressure phase. [ABSTRACT FROM AUTHOR]