Key Engineering Materials Vols. 385-387

Abstract: The stress intensity factor (SIF) for tubular specimens were calculated based on virtual crack closure technique （VCCT）. The effects of geomet rical factors (inner radius, wall thickness and relative crack length) and external loads on the SIF were analyzed, respectively, by use of the single-variable approach. Finally, an approximate formula for SIF of compact-tensile tubular specimens was obtained as all factors mentioned were considered, which was presented as a reference for the tubular engineering design.

Abstract: This study proceeded to find the optimum mixing rate of a high strength concrete with 80MPa of compressive strength using meta-kaolin, waste tire chips, polypropylene, and steel fiber together for improvement of fire resistance performance. To estimate of optimum mixing rate, the orthogonal array method was used to plan the factors (slump flow, air content, compressive and flexural strength, steel bar temperature and concrete spalling volume) of high strength concretes and experiment was executed. Then the functional relationship of each factor was valuated by general linear model of ANOVA and functional relation between the factors and the data was estimated using response surface analysis. The optimum mixing rate was computed as 80% replacement of silica fume volume by meta-kaolin, 3% replacement of fine aggregates volume by waste tire chips and 0.2% additive rate of polypropylene fiber without steel fiber to the total mixed volume with this modeling of the functional relationship.

Abstract: The effects of equal channel angular pressing (ECAP) and subsequent heat treatment on the low cycle fatigue properties of 6005 Al alloy were investigated. The ECAPed specimens showed cyclic softening, whereas the peak aged specimens showed cyclic hardening at all strain amplitudes. After ECAP, artificial aging was performed at 175°C to observe the change of the low cycle fatigue properties due to precipitation. The fatigue life and behavior of the unECAPed and ECAPed 6005 Al alloys were discussed in terms of the microstructural changes and aging conditions.

Abstract: The low cycle fatigue(LCF) test was performed to characterize the influences of the equal channel angular pressing(ECAP) and subsequent annealing of Al 5052 alloy. In the present research, one group of Al 5052 alloy specimens was directly subjected to ECAP, while another was subjected to ECAP and subsequent annealing. It was found that the tensile strength of the Al 5052 alloy increased, while its elongation decreased, with increasing number of ECAP passes. The LCF test was conducted at constant total strain amplitudes of 0.5%, 0.7%, 0.9% and 1.1%. Only cyclic hardening was observed as the number of fatigue cycles increased at all strain amplitudes in the specimen without ECAP. However, the ECAPed specimens showed a slight amount of cyclic hardening in the beginning and then saturation until fracture.

Abstract: This paper presents a primary study for a method of measurement using PZT sensors which is widely used for SHM. PZT sensor has many advantages when using smart material. It is easy to be shaped to various forms and can be embedded on the materials more conveniently. The development for a practical and quantitative technique for assessment of the structural health condition by PZT sensor associated with wave propagation is investigated. Two aluminum specimens bonded with PZT sensors tested for estimating characteristics of the wave propagate on specimens change by various damage condition cf. line crack, bolt loosening. To estimate condition of the specimens numerically, we suggest impedance and guided wave method in this paper.

Abstract: We consider a pre-stressed material containing an oblique crack of a length 2a situated in x1x3 plane. We supposed that the material is unbounded and the crack faces are acted by constant normal incremental stresses p. The initial applied stress ◦ is in direction of the crack. Our first aim is to determine the elastic state produced in the body using Guz’s representation theorem. Our second aim is to determine the critical values of the incremental stresses and the direction of crack propagation. To do this, we use Sih’s generalised fracture criterion for an orthotropic elastic composite. In the last part we find the critical values of the initial applied stress ◦ for which the phenomenon of resonance can appear in a pre-stressed Glass-Epoxy composite.

Abstract: In this paper some results of 3D-finite element analyses of a modified CTS-specimen with an inclined crack plane are presented. It will be shown, that through the inclination of the crack plane, even under pure tension loading of the specimen, a superposition of all fracture modes I, II and III can be generated along the straight crack front of the inclined crack plane. Furthermore, mixed-mode I, II and III loading conditions can also be generated if this modified CTS-specimen is subject to an in-plane tension/shear loading. The computational fracture analysis is based on the calculation of separated energy release rates GI, GII and GIII along the crack front by the numerically highly effective modified virtual crack closure integral(MVCCI)-method and for the finite element(FE)-modelling the commercially available FE-code ANSYS is utilized.

Abstract: Impact properties of a solder ball joint with a Sn-0.75mass%Cu lead-free solder were investigated under aging conditions at 393 K. Moreover, obtained impact properties were compared with those of the joints with Sn-3.5mass%Ag and Sn-3.5mass%Ag-0.5mass%Cu solders. Ball impact force of a Sn-0.75Cu joint was stable at 4.5~5 N, which is similar to that of a Sn-3.5Ag-0.5Cu joint without aging, upon aging at 393 K for 1000 h. In the Sn-0.75Cu joint without aging, main fracture mode was complex fracture of the solder and an intermetallic compound (IMC) formed in a joint interface. Main fracture mode changed from the complex mode to solder fracture upon aging, and thus the impact toughness improved.

Abstract: This paper deals with the dynamic failure elongation of mild steel, SGACD and advanced high strength steel sheets such as TRIP600, DP600 and TWIP steels. The failure elongation has been obtained from the high speed tensile testing machine with various strain rates ranged from 0.003/s to 200/s. The experimental result demonstrates that the tensile elongation does not simply decrease as the strain rate increases, but it decreases from the quasi-static state to the strain rate of 0.1 or 1/s and increases again up to the strain rate of 100/s. Furthermore, some high strength steels have the tendency that the tensile elongation increases as the strain rate increases. Moreover, the localized strain rate hardening in the necking region induces the increase of elongation.

Abstract: It is currently interesting to use thermal or electrical conductive asphalt mixtures for snow-melting and maintenance of asphalt pavements in winter or strain-sensing application. Graphite is the principal conductive filler for asphalt mixtures. The addition of Graphite not only makes asphalts conductive but also has effects on other properties. Considering the visco-elastic property of asphalt, the effects of graphite on rheological properties of asphalt binders were investigated by Viscosity Test(VT) and Dynamic Shear Rheometer(DSR). The results of Viscosity Test indicate that viscosity of asphalt binder increases with an increasing amount of graphite. And the effect is more prominent at higher amount and lower temperature. It means that graphite makes asphalt binders stiffer. The results from DSR tests present that the values of complex modulus increase while phase angles decrease under a proper amount of graphite. It infers that proper amount of graphite can make asphalt a more elastic like material. And the results of rutting parameter point out that graphite can improve the rutting resistance of asphalts.