Applied Mechanics and Materials Vol. 784

Abstract: Controlled chip breakage is important for machining process. In order to investigate the chip breakage behaviour in turning process, damage mechanics approach is applied in FE simulation of chip breakage. In this work, an advanced damage mechanics model is implemented for description of the plastic flow and damage behaviour of chip material in simulation. This material model takes the temperature, strain rate as well as state of stress into consideration, which are essential for application in machining processes.

Abstract: This study focuses on the flexural behavior of timber beams externally reinforced using Carbon Fibre Reinforced Plastics (CFRP). A non-linear finite element analysis is proposed in order to complete the experimental analysis of the flexural behavior of the beams. An elasto-plastic behavior is assumed for reinforced Timber and interface elements are used to model the interaction between CFRP and timber.The predicted and measured load–midspan deflection response results in addition to the failure modes are compared. It was observed that the predicted FE results are in good agreement with the experimental measured test data.

Abstract: Hot stamped boron steel panels with tailored properties are popular as car safety components for maximised energy absorption. In this study, dynamic and quasi-static tensile tests (strain rate: 0.001/s – 500/s) combined with microstructural observation were carried out to study the mechanical properties of press hardened boron steel with various microstructures (martensite volume fraction: 0 – 100%) at room temperature. Based on the test results, a physically-based unified viscoplastic-damage constitutive model has been developed and determined, which takes the volume fraction of martensite into account. Thus the crashworthiness and failure mode of boron steel parts having graded microstructure distributions can be described through a single set of equations.

Abstract: For electrical impedance tomography (EIT) to be useful in monitoring transverse cracks in composites, it is imperative to establish the relation between conductivity and cracking density. Micro to meso scale homogenization has been developed for classical carbon fiber reinforced polymer (CFRP) laminate which provides such a relationship. However, we have shown in previous studies that the detectability of transverse cracks in such CFRP, which are characterized by very anisotropic electrical properties, is poor. Then, it is better to lower the electrical anisotropy, which can be achieved by various technologies including doping the polymeric resin by conductive nanoparticles. However, the validity of mesoscale homogenization for laminates with such low anisotropy has not been tested before. Here, we show that the mesoscale damage indicator is intrinsic for composites with varying anisotropy.

Abstract: In this work, a three-parameter Weibull methodology for fracture prediction of brittle and ductile materials is presented. The approach proposed requires previous definition of the failure criterion to be applied. The parameter estimation is achieved for proportionally and non-proportionally increasing stresses. The case of two concurrent failure types is also handled. The resulting primary failure distribution can be expressed as a function of an effective size (length, area or volume) for its subsequent application in practical design of specimens or components using FEM.

Abstract: Within the nuclear power plant operational life management, components lifetime extension requires information on structural material degradation. Innovative testing methods of Small punch testing and Automated ball indentation test are based on the determination of material properties from sub-sized specimens. Present paper is focused on the employment of these techniques in the NPP irradiated materials testing and evaluation at the accredited hot cell testing laboratory of ÚJV Řež, a. s., Mechanical testing department. Comparison with the testing results from the conventional methods is depicted.

Abstract: This paper presents a novel strain-based continuum damage mechanics (CDM) model for predicting forming limit curve (FLC) of AA5754 under warm forming conditions. The model is formulated and calibrated based on two different sets of experimental data; isothermal uniaxial tensile data at temperature range of 20-300°C and strain rate range of 0.001-10 s^-1 and isothermal FLC data at temperatures range of 20-300°C and forming speeds of 20-300 mm s^-1. A good agreement has been achieved between the experimental and numerical results.

Abstract: Dynamic fragmentation of ceramic samples with different porosity were carried out using modified Hopkinson bar setup, which allow us to keep samples safe (in order to define fragment size distribution) and to measure fractoluminescence impulses occurred on the fracture surfaces (in order to establish the distribution of intervals between impulses). The analysis of experimental data reveals that the fragment size distribution and distribution of interval between fractoluminescence impulses obeys a power law, which exponent depends on ceramics porosity.

Abstract: Scaling regularities that reveal the power law statistics of fragmentation and self-similarity of damage-failure transitions are linked to specific type of critical phenomena in ensembles of typical mesoscopic defects – structural-scaling transition. Taking into account nonlinearity of damage-failure transition the scaling effects were explained as the consequence of subjection of damage kinetics to the intermediate asymptotical (self-similar) solution. This solution has the nature of multiscale blow-up dissipative structures, represents the set of collective modes of defects responsible for the damage localization stage. Original in-situ experiments supported the assumption concerning the role of multiscale blow-up collective modes of defects in qualitative different scenario of dynamic crack propagation, failure of shocked materials, fragmentation statistics.

Abstract: Aim of this study is to describe the ductile damage of metastable austenitic steels which show TRansformation Induced Plasticity (TRIP). Therefore, a criterion for the austenite to martensite transformation, the caused additional hardening and evolution equations for the TRIP-strain are incorporated into the damage model of Rousselier. As a first approach, the model is calibrated against unit cell simulations of the porous material for different stress triaxialities.