Beyond a certain loading threshold, glass-fiber-reinforced polymer composites with vinylester matrix can show considerably nonlinear deformation behavior due to damage of the matrix material. To model such nonlinear deformation properties, we follow the approach of a fully anisotropic damage model suggested by Govindjee et al. (Govindjee S, Kay GJ and Simo JC. Anisotropic modelling and numerical simulation of brittle damage in concrete. International Journal for Numerical Methods in Engineering 1995; 38(21): 3611-3633).In addition, the inter-fiber fracture criterion introduced by Puck (Puck A. Festigkeitsanalyse von Faser-Matrix-Laminaten: Modelle für die Praxis. München, Germany: Hanser Fachbuchverlag, 1996) is used for the damage function that defines the damage initiation and the material strength. A particular procedure is chosen to identify the material properties to validate the model: three glass-fiber-reinforced polymer laminates with different layups are tested in tension under different loading orientations, assuming laminate theory to be reasonably well fulfilled. Finally, further experiments are compared with corresponding simulation results to demonstrate the performance of the model.
The Python package mechkit is a toolkit for researchers in the field of continuum mechanics and material modeling. mechkit contains methods and operators for elementary tasks concerning tensor algebra and tensor notation, e.g., linear mapping, base transformations and active as well as passive transformations of tensors.
The overall deformation behavior of rubber-toughened polymers (e.g. PC/ABS blends) exhibits a pronounced plastic dilatancy. As this volume increase results from diverse micromechanisms the appropriate structure of a macroscopic model is not obvious. In this contribution, different material models featuring plastic dilatancy are compared with regard to their ability to capture the deformation behavior of PC/ABS in different loading situations. All models are calibrated to match experimental data under uniaxial tension in terms of true stress-strain curves and the evolution of volume strain. Afterwards they are employed in finite element (FE) simulations of single-edge-notch-tensile (SENT) tests. Patterns of plastic deformation computed from the different material models are compared to experimental findings. Experimental studyUniaxial tensile tests on a commercial PC/ABS blend were carried out at different strain rates. Through the assumption of equal transverse and through-thickness strain, the true stress-strain response and the evolution of the volume strain was determined using digital image correlation (DIC). The stress-strain behavior features a small elastic range up to a distinct yield point at about 5 % strain (Fig. 1). Thereafter, the material exhibits intrinsic softening before progressively rehardening until failure takes place at a logarithmic strain of about 0.7. Moreover, it was found that a ten times higher strain rate leads to increased stress in the plastic range (Fig. 1). Owing to well known [1] yet here not further studied micromechanisms such as void growth and crazing, the overall response of PC/ABS under uniaxial tension exhibits a pronounced plastic dilatancy shown in Fig. 2. In order to analyze the behavior of the PC/ABS material in more complex loading situations SENT tests have been performed. Using DIC plastic deformations were found to localize in an elongated zone ahead of the notch (Fig. 3) which is typical for rubber-toughened polymers [1]. The notch radius in these tests was 1 mm while the specimen thickness was 3 mm. Constitutive modelsThree different isotropic yield functions accounting for a dependence on hydrostatic stress and -in conjunction with an associated flow rule-giving rise to plastic volume strain are analyzed with respect to their capability to describe the behavior of PC/ABS. These are the Drucker-Prager (DP) and the Raghava (R) model featuring a linear and non-linear interrelation between von Mises σ e and hydrostatic stress σ m , respectively, and a simplified Gurson-type (or Green) model (G) where in addition the effect of an evolving porosity f is taken into account [2-4]. The corresponding yield functions readand the plastic part of the rate-of-deformation tensor is given by D p =ε p N with N = (∂Φ/∂σ) / ∂Φ/∂σ . Rate dependence is captured byε p =ε 0 g (Φ) whereε 0 is a reference strain rate and g (Φ) describes the influence of stress. The parameter α, which is different in each model, takes the specific pressure dependency into account and k(ε p ) represent...
Strong efforts are currently undertaken in order to further improve the electrochemical performance of high energy lithium-ion batteries containing thick composite electrode materials. The properties of these electrode materials such as active surface area, film thickness, and film porosity strongly impact the cell life-time and cycling stability. A rather new approach is to generate hierarchical architectures into cathode materials by laser direct ablation as well as by laserassisted formation of self-organized structures. It could be shown that appropriate surface structures can lead to a significant improvement of lithium-ion diffusion kinetics leading to higher specific capacities at high charging and discharging currents. In this paper, the formation of self-organized conical structures in intercalation materials such as LiCoO 2 and LiNi 1/3 Mn 1/3 Co 1/3 O 2 is investigated in detail. For this purpose, the cathode materials are exposed to excimer laser radiation with wavelengths of 248 nm and 193 nm leading to cone structures with outer dimensions in the micrometer range. The process of cone formation is investigated using laser ablation inductively coupled plasma mass spectrometry and laser-induced breakdown spectroscopy (LIBS). Cone formation can be initiated for laser fluences up to 3 J/cm 2 while selective removal of lithium was observed to be one of the key issues for starting the cone formation process. It could be shown that material re-deposition supports the cone-growth process leading to a low loss of active material. Besides the cone formation process, laser-induced chemical surface modification will be analysed by LIBS.
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