Key Engineering Materials Vols. 462-463

Abstract: This paper investigates failure behavior tests of T300/AG80 composite laminated specimens under tensile and compressive preload using a load holding device and laser irradiation from an Nd: YAG laser. By changing the magnitudes of the preload and the power densities of the laser, the effects of preload and laser power density on the time-to-failure of the specimens were observed. The response process of specimens was synchronized taken in using high-speed camera in experiment. The experimental results showed that tensile mechanical properties of T300/AG80 composite laminated specimens were obviously superior to ones in compression test. The relational expressions between the time-to-failure of specimens and pre-loads as well as with laser power densities were acquired through fitting experiment data. The time-to-failure reduced with the pre-load increasing, the relationship is approximating linear when the laser power density kept invariable. When the pre-load kept unchanged, the time-to-failure reduced as the laser power density increased. The relationship is approximating exponential. A basis for life prediction of structure mechanically loaded in either tension or compression during the irradiation by laser is provided by fitting expression.

Abstract: This paper demonstrates sensitive analyses of probabilistic fracture mechanics (PFM) for reactor pressure vessel (RPV) during pressurized thermal shock (PTS) loading, and comparison of our calculation with the results of the international round robin (RR) analyses in Asian countries (Korea, Taiwan and Japan). The international Round Robin activity was performed in PFM sub-committees in the Atomic Energy Research Committee of Japan Welding Engineering Society (JWES) in conjunction with Korea and Taiwan research groups. The purposes of this program are to establish reliable procedures to evaluate fracture probability of reactor pressure vessels during pressurized thermal shock and to maintain the continuous cooperation among Asian institutes in the probabilistic approach to nuclear safety. Some parameters to RPV failure probabilities are chosen to evaluate their significance quantatively. The differences caused by selection of analyzing programs and some input parameters will be discussed.

Abstract: All over the world at present, injuries and fatalities from road accidents are a significant problem, especially occurred to pedestrians from passenger cars. Most of the fatal accidents between car and pedestrians prove deadly because of the head to hood impact. This paper aims to develop a bumper to avoid from passenger car’s fatal head impact for pedestrian protection, and most importantly, the impact of different objects with passenger car bumper needs to be recognized. Firstly, a pendulum system is constructed to perform the fundamental research which is concentrated on the response pattern of impact-object simulation tests, and we confirmed the application possibility for the method of discriminable pattern recognition whether impact-object is human-like or not by means of neural networks using smart PZT materials. Finally, the impact characteristics analyses can provide enough pattern recognition indices which can be developed and then used to recognize the impact information by two different neural networks.

Abstract: In this study, the stiffness and the flexibility of welded metal bellows of mechanical seal is studied numerically by changing the number of bellows membrane and the loading condition. The relationship between the number of membrane and the displacement, the stress and the flexibility are analyzed. For further improved the axial displacement, overall stiffness and the flexibility of the welded metal bellows membrane, the finite element analysis are conducted. The numerical results show that the maximum stress keeps constant value with increasing the number of bellows membrane under the same loading condition. The relationship between number of bellows membrane and stiffness as will as the flexibility are obtained. It is shown, stiffness is decreased and flexibility is increased with increasing of the number of the bellows membrane.

Abstract: The authors have been developing a crack propagation analysis system that can deal with arbitrary shaped cracks in three-dimensional solids. The system is consisting of mesh generation software, a large-scale finite element analysis program and a fracture mechanics module. To evaluate the stress intensity factors, a Virtual Crack Closure-Integral Method (VCCM) for the second-order tetrahedral finite element is adopted and is included in the fracture mechanics module. The rate and direction of crack propagation are predicted using appropriate formulae based on the stress intensity factors.

Abstract: Creep deformation process of austenitic stainless steel foil with thickness 0.25 mm was investigated. The foil specimen was creep tested at 750oC, 54 MPa to establish baseline behavior for its extended use as primary surface recuperator in advanced microturbine. The creep curve of the foil shows that the primary creep stage is brief and creep life is dominated by tertiary creep deformation. The curve is well represented by the modified theta-projection concept model with hardening and softening terms. Morphology of fractured foil surface reveals intergranular fracture with shallow network of faceted voids. The formation of w-type creep cavities is significant, as revealed by microstructure of ruptured specimen. Composition analysis indicates the formation of carbides, namely, Cr23C6, NbC and Fe3Nb3C.

Abstract: Specimens of 2024-T351 aluminium alloy under different three shot peening intensities were studied. The modifications of the surface layers of the shot peened specimens were investigated through microhardness, surface microstructure and residual stress relaxation after the first and second load cycles under two cyclic loads. No significant changes in microstructure after the three shot peeing intensities were observed with respect to untreated specimens. Rapid residual stress relaxation was observed in specimens after the first cycle. Relaxation of residual stresses occurred within first loading cycles were increased with increasing loading stress amplitude and due to quasi-static relaxation effects.

Abstract: The aim of this review is to gain the informations on applications and approaches that are presently available for non-destructive techniques (NDT) in composite materials. This review also will enhanced the knowledge in the NDT fields with available studies theories and research works done currently. Thus, it has been concluded the research that have been done in the past for military purpose but nowadays (NDT) technique is widely used in other various applications including composite materials, fire safety, land determine, food safety and quality and also famously practice in medical used.

Abstract: This study presents an investigation of the effects of Ethylene Vinyl Acetate (EVA) on Polypropylene (PP)/Clay type of composite. The PP/EVA/clay composite samples are prepared via melt blending technique. The chemical characterization is carried out using fourier transform infrared (FT-IR) spectroscopy. The mechanical properties are characterized in terms of tensile, flexural and impact tests. The presence of high EVA content in PP nanoclay decreases the flexural and tensile strength. The addition of EVA reveals significant increment in impact strength. Thermal properties of composites are studied using thermogravimetric analysis (TGA). The decomposition temperature increases with an addition of EVA content up to 15 phr, but decreases of the crystallinity and melting temperature.

Abstract: The objective of this paper is to understand the abrasive wear mechanism for producing a nano scale groove on a bulk material through nano machining. A nano indenter equipped with a nano scratching attachment was used for nano machining operation and in situ observation of the machined surfaces. Two different tools (Berkovich and Conical) with the same tip radius (100nm) but different edge geometries were used to machine both Copper and Nickel coatings. It was found that the percentage of elastic recovery was lower for Cu than Ni during this nano machining operations. Hence, the deformation mechanism in nano machining operation was identified as elasto-plastic in nature as opposed to the well established completely plastic mode of conventional machining operations. The pile up volume due to plastic deformation was utilized to distinguish between the ploughing and cutting modes of abrasive wear mechanisms. The results reveal that the ploughing mechanism was dominant for Cu and the cutting mechanism was dominant for Ni machining. Moreover, both mechanisms ploughing and cutting were the dominant modes of abrasive wear using the Berkovich tip compared to the Conical tip for producing a nano scale groove through nano machining.