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Kolupaev V.A.,German Institute for Polymers DKI | Yu M.-H.,Xian Jiaotong University | Altenbach H.,Otto Von Guericke University of Magdeburg
Acta Mechanica | Year: 2013

The theory of plasticity operates with different yield criteria of incompressible behavior for isotropic materials. Mostly known are the criteria of Tresca, Schmidt-Ishlinsky and von Mises. The first two criteria have a hexagonal symmetry, and the criterion of von Mises has a rotational symmetry in the π-plane. All these criteria do not distinguish between tension and compression (no strength differential effect), but numerous problems are treated in the engineering practice using these criteria. Within this paper, the yield criteria with hexagonal symmetry for isotropic incompressible materials are compared. For this purpose, their geometries in the π-plane will be presented in polar coordinates. The radii at the angles of 15â - b and 30â - b will be related to the radius at 0 â - b. Based on these two relations, well-known criteria will be shown in one diagram. The extreme shapes of the yield surfaces are restricted by two criteria: the unified yield criterion (UYC) and the multiplicative ansatz criterion (MAC). The examinations of the UYC and MAC depict a linear combination of these extreme yield surfaces. The resulting criterion with two parameters describes all possible convex forms of hexagonal symmetry. On the other hand, this criterion has one disadvantage: It is not possible to solve explicitly the equation for the equivalent stress. Other known criteria (Sokolovsky, Ishlinsky-Ivlev, Dodd-Naruse, Drucker) are depicted in the proposed diagram and compared with the above mentioned criteria. Further criteria are derived from the consideration of solids with orthogonal symmetry planes in the shear stress space. New criteria are introduced for practical applications. The constraints of convexity are established for them. The proposed consideration of the yield criteria simplifies the selection of a proper criterion. The extreme solutions for the analysis of construction parts can be found using these criteria. © 2013 Springer-Verlag Wien. Source


Kolupaev V.A.,German Institute for Polymers DKI | Yu M.-H.,Xian Jiaotong University | Altenbach H.,Otto Von Guericke University of Magdeburg
Archive of Applied Mechanics | Year: 2013

The Unified Strength Theory (UST) provides the fundamentals for the systematic study of various strength hypotheses and yields criteria for isotropic materials. It shows relationship between known models (Mohr-Coulomb, Pisarenko-Lebedev, Twin-Shear Theory of Yu), and apart from these known models, this model contains also classical models like the normal stress hypothesis, von Mises, Tresca and Schmidt-Ishlinsky. The UST can be adapted for different types of materials. Thus, it is a suitable tool for the analysis of experimental data. For the UST, the inelastic Poisson's ratio and the maximum hydrostatic tension stress will be computed as a function of model parameters which simplifies the comparison with another model. The correlations between uniaxial, biaxial and hydrostatic stress will be illustrated and compared with classical models. For all classical models and for the UST, the uniaxial and biaxial tension failure stress and also the uniaxial and biaxial compression failure stress are equal. In this sense, the UST can be classified as a classical model. The failure behavior of new materials like some polymers and alloys differs from the classical one. The UST can be extended to such failure behavior. For this purpose, the Unified Yield Criterion (UYC) as part of the UST will be modified so that all known criteria of incompressible material behavior can be approximated. With the help of a simple substitution, the UYC can be further developed for compressible material behavior. Different convex lines can be adjust for the form of the meridian. With this substitution, the hydrostatic tension stress will be restricted with one of the parameters. Furthermore, the model can be applied for the description of failure behavior of ceramics, hard foams and sintered materials. For this application, both the hydrostatic tension and compression stress will be restricted too. Some reference values for hydrostatic loading are established. For the visual comparison of different parameter setting of the models, graphical methods can be used. The UST will be represented in the principal stress space. Further considerations will be carried out in the Burzyński-plane and in the π-plane. For engineering applications, the Burzyński-plane is preferred to the meridional cut. For better analysis and a direct comparison of fitted models to the experimental values, the line of the plane stress state will be shown in the Burzyński-plane and in the π-plane. © 2013 Springer-Verlag Berlin Heidelberg. Source


Rajan V.V.,German Institute for Polymers DKI | Rajan V.V.,Dutch Polymer Institute | Waber R.,German Institute for Polymers DKI | Wieser J.,German Institute for Polymers DKI
Journal of Applied Polymer Science | Year: 2012

The polycarbonate/poly(acrylonitrile butadiene styrene) blends, (PC/ABS), are mainly degraded by sunlight known as photodegradation when exposed to outdoor conditions. It is the ultraviolet (UV) radiation that is responsible for the degradation of the blend. To stabilize against the harmful UV radiation and to scavenge the radical species which arise from UV or thermally induced degradation of the PC or the ABS, UV absorbers, and UV stabilizers are used. In this article three different UV absorbers namely, Tinuvin 1577-hydroxyphenyl triazine type, Cyasorb 5411-benzotriazole type, Uvinul 3030-cyanoacrylate type, and two different UV stabilizers, Tinuvin 765-monomeric hindered amine type, Tinuvin 622-oligomeric hindered amine were compounded in different combinations with PC/ABS blend at 240°C using a twin screw extruder. Accelerated aging of the compounded sample was done by Atlas Suntest apparatus. The photodegradation studies were done using UV-vis, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, and Yellowing index measurement. The molecular weight of the compounded sample before aging was determined by gel permeation chromatography (GPC). It was found that samples protected with hydroxyphenyl triazine type UV absorber and oligomeric hindered amine show the best result for decreasing the degradation products, oxidation rate, and yellowing of the PC/ABS blend. © 2011 Wiley Periodicals, Inc. Source


MacKo T.,German Institute for Polymers DKI | Ginzburg A.,German Institute for Polymers DKI | Remerie K.,SABIC | Bruell R.,German Institute for Polymers DKI
Macromolecular Chemistry and Physics | Year: 2012

Fractionation techniques such as temperature rising elution fractionation or crystallization analysis fractionation fail to fractionate the ethylene-propylene (EP) copolymers, which are a component of high-impact polypropylene (hiPP), according to their chemical composition. High-temperature high-performance liquid chromatography separates blends of EP-copolymers and polypropylene. The elution volume of the EP-copolymers depends linearly on the average content of ethylene. The separation according to the chemical composition was hyphenated with size exclusion chromatography. In this way, the relationship between the distribution with regard to chemical composition and molar mass, that is, the full chemical heterogeneity of hiPP, was revealed for the first time. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Kolupaev V.A.,German Institute for Polymers DKI | Bolchoun A.,German Institute for Polymers DKI | Altenbach H.,Martin Luther University of Halle Wittenberg
EPJ Web of Conferences | Year: 2010

For modern applications of hard foams an appropriate description of the limit behavior under different stress states are required. So a newstrength hypothesis based on the stress-angle is proposed. In order to obtain the parameters of the model, relevant tests are discussed. The quality of approximation of the experimental data by a limit surface must be evaluated. Some evaluation criteria are discussed and applied to the measured data from the literature. The results of the fitting are presented in the BURZÝNSKI-plane and in the p-plane. The presented approach reduces the number of errors in fitting of the limit surface. Certain empiric restrictions help to obtain reliable fitting even for insufficient or unsure measurements. © 2010 Owned by the authors, published by EDP Sciences. Source

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