Advanced Materials Research Vols. 875-877

Abstract: The 30CrMnSiNi2A steel has been commonly used in the national defense industry and engineering areas. The fracture properties of the material are studied by dynamic tensile tests on a traditional Hopkinson system and three-point bend tests on a modified Hopkinson loading system. The dynamic tensile experiments results show that 30CrMnSiNi2A steel is sensitive of the strain rate. The dynamic fracture toughness of the material increases with the rise of loading rate, but its value is less than the static fracture toughness value. Move over, the fracture mechanism is investigated through macroscopic and microstructural analysis, which reveals that the fracture mechanism of 30CrMnSiNi2A belongs to quasi-cleavage fracture.

Abstract: The hemp fibres present specific fibre morphology and a complex non homogeneous cross section which changes in function of the location along the fibre length. Thus the mechanical properties of hemp fibres request a specific characterization method. In this study, firstly, a digital treatment method was developed allowing to consider different geometrical modelling methods: homogeneous or non-homogenous cross section, average global cross section, and cross section measured at the rupture location, including a 3D CAD model reconstruction of the fibre.

Abstract: This research is part of an extensive developing line at the Laboratory of Structures at Faculty of Civil Engineering in State University of Campinas, UNICAMP, about the behavior of columns in fire situation. In this paper, experimental results on the behavior of steel columns, slender, unfilled or filled with usual strength concrete in fire situation, are presented and compared with standard codes. It was observed that concrete filling of columns made of tubular steel profiles may provide significant improvement in structures fire safety.

Abstract: The contribution deals with measurement of the coefficient of friction in the sliding joint. Rotanional sliding pair, which was tested, is described in this paper. Their tribological characteristics were measured by test equipment Tribotestor`89. The value of the coefficient of friction for the bushings from brass, aluminium and polyamide for chosen load (the sliding speed, loading, duration) are analysed in the paper. The largest decrease in the size of the coefficient of friction was recorded for bushings from aluminium, its value have decreased by 87.5% during the run up. Decrease of the coefficient of friction was recorded about 82% for bushings from brass and about 72% for bushings from polyamide. Run up lasted 10 minutes in all tests.

Abstract: The critical components of industrial plants, in this the high-pressure steam pipelines undergo continued destroy process. For this reason, an efficient diagnostic procedure during the whole operating period is required. Particularly, the most important are creep measurements performed periodically. The numerical simulations of steam pipeline creep phenomenon refer to the influence wall thickness nonuniformity on obtaining creep strain. The calculation was carried out with finite element model using computer software ANSYS Multiphysics. The obtained results present acceptable accordance with the long time measurements executed on the real object.

Abstract: Fatigue life is one of the most important physical characteristic that is investigated by materials engineers and scientists. The high dynamic loading experienced by machine parts necessitates understanding fatigue properties in critical components. Despite this requirement, elastomer fatigue criteria are imperfectly understood and even less is known about fatigue resistance in the emerging range of smart elastomers. In this paper, initial research into the equi-biaxial fatigue behaviour of magnetorheological elastomers (MREs) is described. Physical testing was carried out using a bubble inflation testing system. Silicone rubber based test samples were fatigued at different stress amplitudes ranging between 0.75MPa and 1.4MPa using engineering stress as the control mode. S-N (Wöhler) curves showing the plots of stress amplitude (σ_a) versus cycles to failure (N) are presented. Stress-strain behaviour throughout fatigue process is also described. For a fatigue test at a stress amplitude of 0.75MPa and no pre-stressing, it was found that stress softening occurred for the entire duration of the test, but was particularly pronounced in the first 100 cycles of testing.

Abstract: In this paper, band gaps for two-dimensional phononic crystals consisting of hollow square water columns immersed in a mercury host are investigated by plane-wave-expansion (PWE) method, in which cross sections of the scattering objects are hollow-square and hollow water columns are arranged in simple lattices (square, and triangular lattices). In order to regulate band gaps, we alter inner side lengths of hollow-square column, and change the filling ratio at the same time. From the results, It can be found that the band gap width and the number of the bad gaps can be changed by lattice shapes and corresponding filling fraction. This could be very useful in the design of phononic crystals band gaps and frequency filtering.

Abstract: The Natural Strain suggested in this paper satisfies the additive law of strain on an identical line element in a body. Therefore, it can be defined from anywhere on the basis of the deformed intermediate state. So, this is an effective strain notation to describe the phenomenon that depends on the deformation history such as the plastic deformation. In this paper, the shape of the yield surface generated after applying the pre-deformation of large simple shear is estimated on the basis of the Natural Strain theory. Using the test pieces made of pure copper, which is already subjected to the pre-deformation of large simple shear, the proportional loading tests for combined loading of tension and torsion are carried out beyond the elastic region. The yield stress for each direction in the stress space is determined by investigating the tangent modulus of deviatoric stress- deviatoric strain curve, and the shape of yield surface is elucidated by comparing with the shape by conventional proof stress.

Abstract: This paper aims at studying the effect of interfacial damage on the mechanical behavior of starch - hemp composite. The procedure encompasses an experimental investigation towards the determination of microstructural features and mechanical testing of the material. A finite element model is developed to account for a particular damage kinetics that triggers failure properties. Our results show that the experimental evidence of interfacial damage driven failure is achieved. Finite element model is able to capture this feature using an abrupt damage criterion. But in order to identify the observed behavior, the experimental response is matched with the numerical one. This process tunes the mechanical parameters to fit the experimental response. The optimization process conducted in this way leads to a precise determination of the mechanical parameters that quantifies the observed ultimate properties.

Abstract: Measurements of wax-in-feedstock parameters are vital tools for successful simulation of the wax crystallization phenomena in the solvent dewaxing process. In this paper, comparisons are implemented between different methods to investigate the wax characteristics of SN500 feedstock before and after dewaxing. The measurements involved were the wax content, wax appearance temperature, wax disappearence temperature, solid mass yield of the wax removal. The measurement methods adopted in the analysis are the modified Universal Oil Production method 46-64, Differential Scanning Calorimetry thermal analyzer, Cross Polar Microscopy technique, and Gas Chromatography analysis. Results have demonstrated that the modified Universal Oil Production method is slightly under estimating the wax content in the feedstock compared to the DSC results. This under estimation becomes larger for the wax content in the base stock.