Robert Eberlein; Lucian Pasieka
Abstract
Thermoplastic polyurethanes (TPU) are often subject to highly dynamic loading conditions in engineering applications. Due to their robust mechanical properties, TPU materials form an excellent fit for dynamically loaded system components in many cases. However, for dynamically loaded TPU the long-term ...
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Thermoplastic polyurethanes (TPU) are often subject to highly dynamic loading conditions in engineering applications. Due to their robust mechanical properties, TPU materials form an excellent fit for dynamically loaded system components in many cases. However, for dynamically loaded TPU the long-term material behavior is of special interest, since TPU shows distinct creep, as generally observed in polymers. This article illustrates a rather simple but efficient and consistent method for predicting the long-term material behavior of a selected TPU grade under uniaxial dynamic loading conditions. The research arises from practical challenges of design engineers. These are often confronted with lifetime quantification issues of critical components, e.g. in a mechanical damping element under cyclic loading conditions, for which a permissible deformation may not be exceeded. In those cases the transient stress-strain behavior of the material is of special interest. As will be shown an important prerequisite for the derivation of a reliable material model is the acquisition of relevant creep data for the respective TPU material. In a second step, the creep data is extrapolated in time by employing a suitable method resulting in a time-dependent stress relaxation modulus function. Parallel Maxwell models expressed by Prony parameters yield the rheological properties of this function. Due to their derivation, these Prony parameters represent quasi-static material response. Nevertheless, by employing a novel dynamic-static loading analogy the Prony parameters form the basis for TPU lifetime prediction under uniaxial dynamic loading conditions. By comparing numerical FE results for a damper with experimental results from an endurance test, the proposed modeling concept demonstrates its validity.
Robert Eberlein; Lucian Pasieka; Dimosthenis Rizos
Abstract
Thermoplastic polyurethanes (TPU) have become preferred materials for demanding high strain rate applications in many industries throughout past years. Due to their comparatively high abrasion resistance and toughness, TPU materials form an excellent fit for critical components sustaining high pressures ...
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Thermoplastic polyurethanes (TPU) have become preferred materials for demanding high strain rate applications in many industries throughout past years. Due to their comparatively high abrasion resistance and toughness, TPU materials form an excellent fit for critical components sustaining high pressures in combination with harsh ambient conditions. This presentation illustrates a comparatively new field of critical applications for TPU components. While the operational pressures remain rather moderate at maximum 50 bar, challenges arise from high-frequency, cyclic loading conditions. In order to design robust dynamic TPU components, two main tasks must be accomplished: (i) visco-elastic-plastic material modeling and parameter identification, and (ii) material validation under realistic dynamic loading conditions on system level by means of advanced finite element (FE) simulations. This article puts (i) emphasis on the material calibration process and (ii) specifically demonstrates material validation on system level for selected TPU materials. In this context strain rate dependency of various TPU grades is discussed, which illustrates deficiencies of classical material modeling techniques available in commercial finite element software versus advanced nonlinear models. Eventually, recommendations are provided for an efficient but also accurate material calibration process of solid TPU materials that can significantly enhance product innovation processes. Copyright © VBRI Press.