Key Engineering Materials Vols. 385-387

Abstract: Rotating bending fatigue tests were carried out for maraging steels with different grain size in moist air in order to investigate the effects of humidity, grain size and reversion austenite on fatigue strength of the steel. Fatigue strength was decreased by humidity, and the decrease in fatigue strength was large in larger grain sized steel. Both of the initiation and propagation of a crack were promoted by humidity. Many cracks initiated at the specimen surface and intergranular cracks were observed at specimen surface and on fracture surface when humidity was high. The decrease in fatigue strength by humidity was suppressed by formation of reversion austenite.

Abstract: The paper presents a study on the tooth root, rim and web stresses of thin-rimmed spur gear structure with symmetrical web, based upon 3D FEM calculations. In order to identify some gear design directions, the effects of rim and web thickness on gear stress behaviour are investigated, and maximum stresses resulting from actual rim and web contribution are compared.

Abstract: Electrochemical measurement techniques were applied to investigate the polarization and hydrogen permeation behavior of Cu-bearing CrMo steel in a H2S saturated aqueous brine solution. The observation on microstructure and precipitate phases of the steel was conducted by transmission electron microscopy (TEM), and the corrosion product was investigated by using X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). It is disclosed that copper addition could effectively influence the electrochemical behavior of the investigated steel, and the dissolution behavior of iron matrix and carbide precipitates in the H2S solution acts as a key role for the steel resistance to hydrogen sulfide corrosion.

Abstract: Composite materials or generally materials with interfaces are nowadays used in many varied engineering applications. In comparison with classical engineering materials the existence of material interface causes locally different stress distribution, which can strongly influence behaviour of whole structure and can have an important influence on failure mechanisms of such materials. The paper presented is devoted to the investigation of stress singularity exponents of a crack growing in a bimaterial body perpendicularly to the interface and touching the material interface. Discrepancies between value of stress singularity exponent in the centre of bimaterial body and on the free surface were found. The assumptions of linear elastic fracture mechanics (LEFM) and small scale yielding (SSY) are considered. For numerical calculations finite element analysis was used. Results obtained can contribute to a better understanding of failure of materials with interfaces.

Abstract: Magnesium alloy is the lightest metal that is used as a structural material. It has a higher specific tensile strength and specific stiffness than Iron and Aluminum alloy, and the dent is not caused easily from Iron and Aluminum alloy at the impact. Therefore, Magnesium alloy is widely used in many areas, especially as an external shell of a mobile device and automotive parts which replaces iron and plastic, etc., and its demand is expected to grow in the future. In this paper we studied the hypervelocity impact with a ballistic range to clarify the characteristic of Magnesium alloys which had such a characteristic. The effect of impact velocity, temperature and the size of perforation hole were investigated experimentally. The perforation resistance of Magnesium alloys and their impact behavior were characterized.

Abstract: Slurry coatings have been used for the protection of gas turbine materials in power plants during the last years. These coatings can be applied by spaying, brushing or dipping. The main constituent elements are silicon, chromium, potassium, borium, carbon and zirconium. They are characterized by high hardness and very good resistance against corrosion, erosion, abrasive and adhesive wear. To guarantee the reliability of coated steam turbines components used in power plants, the lifetime assessment of the coatings and their failure prediction become very important. Microhardness, scratch, adhesion and pin-on-disk sliding tests are commonly used for rapid evaluation of the mechanical properties of these coatings [F. Loeffler: Thin Solid Films, Vol. 339 (1999), p. 181]. However, the above testing methods do not model the dynamic cyclic fatigue. In this paper we evaluate the fatigue resistance of slurry coatings working under cyclic loading conditions by the impact testing method. The coating failure mode and its extent were assessed by SEM observations and EDX analysis. From the experimental results it was concluded that the Si,Cr,O,B,C coatings deposited on P91 steel substrate showed an improved fatigue strength compared to that of Si,Cr,O deposited on the same substrate.

Abstract: This paper presents a damage model dedicated to unsaturated brittle rocks. It mixes phenomenological and micro-mechanical concepts, and is formulated based on the use of independent state variables (net stress and suction). The expression of the liquid permeability is modified in order to represent the influence of fracturing on interstitial fluid flows.

Abstract: The aim of this experimental investigation is to study the effect of various curing temperatures on crack-front shape and crack growth life of centrally cracked aluminium panels in mode-I condition with single-side glass/epoxy composite patches. The aluminium panels are made of Al 2024-T3 with the thicknesses of 2.29 mm. Unidirectional four layers lay-up perpendicular to the initial crack length were used for the patches of all specimens and the adhesive was Araldite LY564. The cyclic remote stress of 118 MPa with the R-ratio of 0.05 was applied for all models. The experiments were performed for different curing temperatures of room temperature, 50oC, 80oC, 100oC and 120oC. It is shown that the fatigue crack growth life of the repaired panels with curing temperatures of 100oC and 120oC is considerably smaller than those obtained for specimens cured at room temperature and 50oC.

Abstract: Based on experimental investigation under low cyclic reversed loading, the seismic behaviors and seismic damage model for steel reinforced high strength and high performance concrete (SRHSHPC) composite frame columns are studied. Several existing seismic damage models are firstly presented and their characteristics are comparatively analyzed. From the test results of low cyclic reversed loading, the variation history of cumulative dissipated hysteretic energy of the SRHSHPC composite frame columns under different loading cycle levels is figured out, and the influence of axial compression ratio, shear span ratio, stirrup ratio and concrete strength on the cumulative dissipated hysteretic energy is also discussed. The damage index of the SRHSHPC composite frame columns is compared according to the existing seismic damage models, and the seismic damage model adapted for the SRHSHPC composite frame columns is established. According to the variation history of the damage index under different loading cycle levels, the rule of damage development for the SRHSHPC composite frame columns is proposed. The influence of axial compression ratio, shear span ratio, stirrup ratio and concrete strength on the damage development is also discussed. The results indicate that the seismic behaviors of the SRHSHPC composite frame column are outstanding, and the seismic damage model could give a quantitative description for damaging process of the samples, which is reference for establishing more rational damage criteria for the SRHSHPC earthquake-resistant composite structure.

Abstract: The shear behaviors of steel reinforced high strength and high performance concrete (SRHSHPC) composite frame columns are studied through the test on a number of SRHSHPC specimens with grade of concrete strength varied from C80 to C120 subjected to constant axial compression and cyclically varying horizontal load. Four influencing factors, namely, shear span ratio, axial compression ratio, stirrup ratio and concrete strength, are taken into consideration in the test, and strain gauges are respectively placed on steel web, stirrups as well as reinforcement bars to study the shear mechanism of SRHSHPC composite columns. According to test results, the shear failure patterns and shear mechanism of the specimens are discussed. By analyzing the contribution of the steel web, concrete, stirrups and reinforcement bars to the shear capacity, the shear mechanism of the SRHSHPC composite columns is figured out. Therefore, the influence of shear span ratio, axial compression ratio, stirrup ratios and concrete strength on shear behaviors of the SRHSHPC frame columns is clear. Finally, concrete truss model and principle of accumulation are applied to discuss the shear capacity and a calculation model for shear strength of the SRHSHPC composite columns is established. It is indicated that the shear behaviors of the SRHSHPC frame composite columns are excellent, and the calculated results of shear strength have good conformity with test results.