Key Engineering Materials Vols. 488-489

Abstract: Loading frequency effects on FCGR and fracture surface morphology were investigated on pre-strained low carbon steel in high FCGR range. Loading frequency effects showed the different trend between internal hydrogen and environmental hydrogen. The effects of combined condition hydrogen revealed similar tendency of environmental hydrogen.

Abstract: An approach to predict the overall mechanical properties of materials containing pores of irregular shapes is described. Micromechanical modeling is performed by evaluating cavity compliance contribution tensors of individual pores [1] which are then used as an input for well-developed homogenization models. The cavity compliance contribution tensor can be found either analytically or numerically depending on the pore geometry and the level of anisotropy of the surrounding material. The results of numerical analysis can be used to compare the ability of differently shaped pores to initiate fracture.

Abstract: In modern buildings, glass is increasingly used as a load-carrying material in structural components, such as glass beams. For glass beams especially the edge strength of glass is important. However, the strength of glass is not a material constant but depends on various parameters, which makes glass, amongst other things, a challenging building material. One of the parameters influencing glass strength is the combination of humidity and stress, which may cause stress corrosion. The aim of the current study is to limit the effect of humidity at the glass edge. This is done by the application of a protective coating. In this exploratory study several coating solutions are tested applying the coating at the edge of glass specimens. These specimens are then subjected to in-plane four-point bending tests to determine their failure strength. The effects of the coatings on the edge strength are analyzed using the failure strength data from the bending tests. The results indicate that only one of the tested coatings has an effect on the glass edge strength.

Abstract: This paper describes the numerical analysis method used to estimate welding induced residual stresses in K-shape tubular bridge joints. The knowledge of residual stress distribution is required to design the geometry of K-joints loaded under fatigue stresses. Numerical simulations are focused on the arc welding MAG process, generally used to weld joints in bridge construction. Thermo-mechanical analyses are performed in 3D using two finite element codes:ABAQUS^® and MORFEO^® . ABAQUS has the advantage to offer large analysis capabilities(nonlinear, transient, dynamic, etc.) whereas MORFEO is more dedicated to welding processes and offers the possibility to analyze crack propagation under fatigue loads. Computed residual stresses in the region surrounding the weld are compared with measured residual stresses in order to estimate the ability of the codes to reproduce these stresses. Position, orientation and magnitude of the highest residual stress components are discussed.

Abstract: Polycrystalline materials like metals fail in creep conditions due to development of inter- or intra-granular voids. The model of creep damage is proposed which simulates voids growth on microscale using Cellular Automata (CA) technique at RVE level, coupled with creep deformation on macroscale. It is assumed that experimentally observed creep deformation is a result of interaction between hardening and softening of a material. The softening process is mainly due to voids development and it is built in deformation model by weakening of effective stress by damage parameter calculated by CA part of the model. Parameters of model are based on primary and secondary stages of creep experiments. The results of simulations show that multiscale model predicts quite well times to failure and strains at failure.

Abstract: The work investigates the fatigue behavior of friction stir welded butt joints by means of fracture mechanics techniques. FSW joints of artificially aged AA6060 T6 aluminum alloy were studied. The welding was performed on 8 mm thick butt joined sheets by means of a CNC machine tool. Welding speed in the range between 117 and 683 mm/min and tool rotational speed between 838 and 1262 rpm were considered. Fatigue crack growth tests were performed according to ASTM E647 standard on CT specimens, under constant load amplitude conditions, at 0.1 minimum to maximum load ratio, with the notch placed in the dynamic recrystallization zone of weld nugget, oriented along the welding direction. The comparison of results demonstrates the crack growth rate is always equal or lower than the base material at low values of stress intensity range. At ΔK values above 12 MPa√m, crack growth rate was found to be higher than base material for high feed, low speed and high feed/speed ratio.

Abstract: A new method of repairing damaged structures by injecting the cracks with specially designed polymer mass (flexible two-component grout based on polyurethane resin) has been recently proposed. The technique is mainly dedicated to damaged masonries, especially historical structures where minimum intervention is permitted. The cracks are filled with the special injection, forming the flexible joints bonding the disrupted structural elements. The aim of the present paper is to show the results of the experimental study focused on properties of the polymer mass used for the injections. First, the material has been subjected to static compression tests. Then, the polymer mass has been examined dynamically under harmonic excitations with different frequencies and strain levels. The results of the study indicate that the tested polymer mass shows highly non-linear behaviour with relatively low resistance under small displacements and stiffening effect for higher strain levels. Moreover, it is substantially dependent on the strain rate having higher initial deformation modulus for higher strain rate values. Finally, the observed hysteretic behaviour of the material confirms its potential to dissipate the energy during vibrations preventing from further structural damage in the case of dynamic loading.

Abstract: The efficiency of the energetic network is a very import safety issue in the region experienced by the earthquake. High voltage disconnecting switches are important elements of the energetic infrastructure used to separate electric circuits (i.e. during repairs), which should not be damaged remaining fully operational. The aim of the paper is to show the results of the shaking table experimental investigation focused on damage mechanism of a high voltage disconnecting switch under seismic excitation. The real example of the two-column pantograph-type disconnecting switch was considered in the study. First, the tests were carried out by exciting the unit with the sweep-sine function. Based on the results, the structural dynamic properties of undamaged structure (natural frequencies, damping ratios) could be determined. Then, the so called rumbling seismic tests were conducted in order to determine the seismic strength of disconnecting switch according to the standards PN-EN 60068-3-3. After each experiment, the sweep-sine test was carried out so as to check the decrease in the natural frequencies of the unit. The results of the study show that the lower parts of the columns, which serve as isolators, are the most critical locations of the disconnecting switch considered. The unit was damaged due to failure of one of the rotational mechanisms installed at the bottom of columns.

Abstract: A recently introduced nonlocal peridynamic theory removes the obstacles present in classical continuum mechanics that limit the prediction of crack initiation and growth in materials. Furthermore, damage growth in composites involves complex and progressive failure modes. Current computational tools are incapable of predicting failure in composite materials mainly due to their mathematical structure. However, the peridynamic theory removes these obstacles by taking into account non-local interactions between material points. This study presents an application of the peridynamic theory for predicting damage progression from a central crack in fiber reinforced composite plates subjected to uniaxial tension loading.

Abstract: With 3-story and 6-story RC buildings of ductile frames, previously designed, non-linear static analysis with increased monotonically lateral loads (Push-over) are made in order to determine its collapse and their responses against the inelastic seismic analysis results with the SCT-EW-85 record are compared. It is designed with the Principal Body and with the Appendix A conditions of the Seismic Technical Norms of the Mexico City Code (RDF-04), satisfying the maximum story distortion limits of the service and collapse conditions; the buildings (offices) are in the III_b compressible seismic zone. The non-lineal responses were determined with nominal resistance and over-resistance effects. For the non-linear static analysis with increased monotonically lateral loads, was important to select the type of lateral forces distribution. The comparison were made with base shear force–roof lateral displacement relations.