The Experts below are selected from a list of 6297 Experts worldwide ranked by ideXlab platform

Meinhard Kuna - One of the best experts on this subject based on the ideXlab platform.

  • usage of the small punch test for the characterisation of reactor vessel steels in the brittle ductile transition region
    2008
    Co-Authors: Thomas Linse, Meinhard Kuna, J Schuhknecht, H W Viehrig
    Abstract:

    Abstract This paper presents a method for the identification of hardening parameters and W eibull -parameters in the brittle and brittle–ductile transition region. A small-punch-test device is developed for hot cells, where a miniaturised disk-like specimen is manufactured and deformed by a spherical punch until failure. Its Load–Displacement-Curve is analysed regarding its information about the material behaviour. Using neural networks, an identification routine is developed, which avoids time-consuming calculations with FEM during an optimisation algorithm. Identified material properties are compared with data from tensile tests. Using the identified hardening parameters, W eibull -parameters are calculated for temperatures at which cleavage fracture occurs.

  • application of the small punch test to irradiated reactor vessel steels in the brittle ductile transition region
    2008
    Co-Authors: Thomas Linse, Meinhard Kuna, J Schuhknecht, H W Viehrig
    Abstract:

    In this paper, a method is applied for the identification of hardening parameters in the brittle-ductile transition region and the determination of Weibull parameters in the brittle region using small-punch tests. A small-punch-test device is developed to measure the Load-Displacement Curve for non-irradiated and irradiated specimens of a reactor vessel steel at different temperatures inside a hot cell. In a global optimization algorithm for the identification of hardening properties, time-consuming finite element method (FEM) calculations are avoided by using neural networks that were trained with the help of a database previously generated by FEM. Identified material properties are compared with data from tensile tests, where available. The influence of irradiation and temperature on the material and fracture behavior is analyzed.

  • determination of deformation and failure properties of ductile materials by means of the small punch test and neural networks
    2003
    Co-Authors: Martin Abendroth, Meinhard Kuna
    Abstract:

    This paper describes an approach to identify plastic deformation and failure properties of ductile materials. The experimental method of the small punch test is used to determine the material response under Loading. The resulting Load Displacement Curve is transferred to a neural network, which was trained using Load Displacement Curves generated by finite element simulations of the small punch test and the corresponding material parameters. The simulated material behavior of the specimen is based on the ductile elastoplastic damage theory of Gurson, Tvergaard and Needleman. During a training process the neural network generates an approximated function for the inverse problem relating the material parameters to the shape of the Load Displacement Curve of the small punch test. This technique was tested for three different materials (ductile steels). The identified parameters are verified by testing and simulating notched tensile specimens.

Jurgen Malzbender - One of the best experts on this subject based on the ideXlab platform.

  • indentation Load Displacement Curve plastic deformation and energy
    2002
    Co-Authors: Jurgen Malzbender
    Abstract:

    Various methods to access indentation data are considered on the basis of the Load P-Displacement h Curve, its derivative, or its integral. This paper discusses and extends the various analytical models to estimate the indentation P-h Curve, the slope, and the dissipated energy to aid the development of a concise methodology to analyze indentation data. Special consideration is given to the effect of pile-up and sink-in. Relationships for sharp and spherical indenters are presented and in addition for sharp indenters with a rounded tip. An overview over analytic expressions for the P-h Curve is given and compared to finite element simulations and experimental data. An expression derived for the representative strain at the onset of yield under sharp and spherical indenters compares well with literature results. The effect of a rounded tip on the yielding under a sharp indenter is discussed. The ratio of Loading to unLoading slope and the ratio of the plastically dissipated energy to the total energy is related to hardness and elastic modulus. In combination these ratios can be used to determine the strain-hardening coefficient.

  • energy dissipation fracture toughness and the indentation Load Displacement Curve of coated materials
    2000
    Co-Authors: Jurgen Malzbender
    Abstract:

    Abstract The energy dissipated during normal indentation of coated materials is analyzed and related to the coating and interfacial fracture toughness. Hybrid organic–inorganic coatings, which were prepared using a sol–gel process, were used as model materials. The Loading and unLoading Curves are integrated and the differences in irreversibly dissipated energy after delamination and chipping are used to calculate the energy release rates. The calculated energy release rates are inversely proportional to the coating thickness and a factor of up two tens larger than previous results. Furthermore, it is shown that the energy dissipated during indentation is a measure of the system's response and that the system's response is altered by the fracture events. Extrapolation to infinite coating thickness leads to values that are in agreement with previously published results. The relationship between irreversibly dissipated energy and the ratio of the hardness to elastic modulus is analyzed in detail and it is shown that this relationship is similar as for monolithic materials, although various fracture events occurred, thus suggesting that the underlying relationship is independent of the history of the coating–substrate system.

  • elastic modulus indentation pressure and fracture toughness of hybrid coatings on glass
    2000
    Co-Authors: Jurgen Malzbender, Den Jmj Jaap Toonder
    Abstract:

    Abstract The indentation Load-Displacement behavior of an organic-inorganic hybrid coating was tested using a Berkovich indenter in an attempt to offer a simple and fast method to analyze the mechanical properties of a coating. The coatings were deposited using a spin-coating technique. The elastic modulus and the indentation pressure as a measure of the hardness were determined on the basis of the Load-Displacement Curve. The effects of the coating thickness and the coating preparation conditions were investigated. Cracks, delamination and chipping were observed and were used to assess the fracture toughness of the coating and the interface. Elastic modulus, indentation pressure and the fracture toughness were dependent on the time elapsed before application of the coating fluid and on the curing temperature.

Faouzi Hadjhassen - One of the best experts on this subject based on the ideXlab platform.

  • a new analytical solution to the mechanical behaviour of fully grouted rockbolts subjected to pull out tests
    2011
    Co-Authors: Laura Blanco Martin, Michel Tijani, Faouzi Hadjhassen
    Abstract:

    Abstract A new analytical approach able to predict the mechanical behaviour of fully grouted rockbolts subjected to pull-out tests is proposed in this paper. Input parameters of such approach are: bolt radius, bolt’s Young modulus, Displacement of the free end of the bolt and the constitutive law of the rockbolt–grout joint interface. The limited circumstances under which it is accurate to determine such constitutive law from pull-out tests are also presented. A solution for the Load–Displacement Curve obtained during pull-out tests has been developed and is detailed in the case of a tri-linear bond-slip model. Comparison with experimental results obtained via in situ pull-out tests has led to the validation of this approach.

Naj Aziz - One of the best experts on this subject based on the ideXlab platform.

  • an analytical model of fully grouted rock bolts subjected to tensile Load
    2013
    Co-Authors: Jan Nemcik, Naj Aziz
    Abstract:

    Abstract An analytical model for fully encapsulated rock bolts subjected to tensile Load in pull-out tests is presented. This model is based on the bond–slip relationship describing the mechanical interaction at the bolt–grout interface. The model takes into account the residual shear stress in addition to the complete decoupling mechanisms. Formulations are also derived for the Load–Displacement Curve, shear stress distribution at the bolt–joint interface and axial Load distribution in the bolt. The model was validated with experimental results from both the laboratory experiments and in situ studies.

Martin Abendroth - One of the best experts on this subject based on the ideXlab platform.

  • determination of deformation and failure properties of ductile materials by means of the small punch test and neural networks
    2003
    Co-Authors: Martin Abendroth, Meinhard Kuna
    Abstract:

    This paper describes an approach to identify plastic deformation and failure properties of ductile materials. The experimental method of the small punch test is used to determine the material response under Loading. The resulting Load Displacement Curve is transferred to a neural network, which was trained using Load Displacement Curves generated by finite element simulations of the small punch test and the corresponding material parameters. The simulated material behavior of the specimen is based on the ductile elastoplastic damage theory of Gurson, Tvergaard and Needleman. During a training process the neural network generates an approximated function for the inverse problem relating the material parameters to the shape of the Load Displacement Curve of the small punch test. This technique was tested for three different materials (ductile steels). The identified parameters are verified by testing and simulating notched tensile specimens.