Advanced Materials Research Vols. 753-755

Abstract: In recent years friction stir welding process has received a great deal of attention from the transport industry. During the process, heat generation and material stirring induce significant microstructural alteration in the base material, affecting the properties of the welded assembly. In this paper the influence of process parameters, namely rotating speed and welding speed, on mechanical properties of AA2024-T3 friction stir butt welds is experimentally investigated. An increase of the yield stress has been found decreasing the heat input, while an opposite variation was measured for the elongation.

Abstract: The microstructure and cracking characteristics of MIG welded magnesium alloy (AZ91D) joint, and the effect of welding speed on cracking susceptibility have been investigated. The result indicates the welded joint consists of primary α-Mg and divorced phases (eutectic α-Mg + eutectic β-Mg₁₇Al₁₂), the latter mainly distributing along the α-Mg grain boundaries. The weld of the magnesium alloy displays a high cracking susceptibility. The cracks are mainly formed in the arc crater at the end of the weld. These cracks propagate along the α-Mg grain boundary, and they belong to the solidification cracking. These solidification cracks are resulted by the joint function of the low melting point liquid film in the weld and the tensile stress suffered by the weld metal during the solidification process. The low melting point liquid film is the internal cause to form the solidification cracks, while the tensile stress is a necessary condition. Limiting the amount of the low melting point eutectic and decreasing the tensile stress of the welding joint are two effective methods to improve the solidification cracking susceptibility of the magnesium alloy weld.

Abstract: The clinch joining is a new technique to join light alloy materials. This paper studies the process of clinching in joining Copper alloy sheets based on the method of numerical simulation combined with experiment. The studies are performed by employing software ansys/ls-dyna considering with the contact conditions and material models in the model. Efficient analytic results of forming of clinching in Copper alloy sheets are provided. The experiments of clinched joints in Copper alloy sheets are carried out to validate the simulation. It is shown that the simulation of process of clinching joints in Copper alloy sheet has a good agreement with the experimental result. That suggests the developed finite element model, considering the contact conditions of materials and the material models can be used to predict the joint forming of Copper alloy by clinching ideally.

Abstract: To study downward flame spread across XPS surface, a series of laboratory-scale experiments were conducted. Typical flame spread characteristics were obtained. The flame spread process comprises four stages. There are twice accelerations during flame spread. The influence of maximum flame height on flame spread rate is not significant. The predicted flame spread rate utilizing mass loss rate is lower than the measured value. Three stages: increasing stage, stable stage and decreasing stage are observed in both change of maximum flame height and flame area. The changing trend of mass loss rate is similar to that of maximum flame height. For stage 1 and stage 3, exponential change of mass loss rate with time is found. The mass loss rate is constant for stage 2. The heat flux to the preheating zone is higher than that to surrounding environment. Experimental results agree well with theoretical analysis.

Abstract: In order to analyze the mechanism of backfill and surrounding rock of open stope during subsequent backfill mining, take M1 ore body mining in a mine as engineering background, and simulate the mechanism of surrounding rock and backfill by using FLAC3D numerical software. Results show that the backfill can effectively alleviate or transfer the stress concentration state of the room floor and pillar, apparently restrain the displacement of the cavity plate and pillar, and improve the plasticity distribution range in a limited degree.

Abstract: Combining the current research method of rock mass parameters, to the RuMei hydropower station in Tibet as the background, using the finite element calculation software, and using the two section for numerical analysis, considering all kinds of conditions under the condition of the simulated stress strain and displacement, the distribution of plastic failure, comprehensive analysis and evaluation of its stability.

Abstract: Steel pile-concrete abutment connection in integral abutment bridges is vulnerable to cyclic bridge movement as well as seismic loads. Although this connection may determine the bridge strength and performance against the above loads, previous researches have merely focused on this connection. This study has investigated crack patterns using finite element analyses. The bridge movements were classified into three cases: (1) translation only; (2) rotation only; and (3) simultaneous translation and rotation. The identified cracks were diagonally occurred from the steel pile. PennDOT DM-4 reinforcement detail was hardly effective in controlling crack growing. This study also investigated spiral type reinforcement for the connection, and this type of reinforcement detail significantly improved the crack control capacity in integral abutment bridges.

Abstract: The aim of this study was to obtain special cathodic protection (CP) behavior in coastal bridge structures. This bridge structure was located to the area where repetition between fresh water and sea water taken place due to ebb and flood tide. In this study, zinc-mesh anode was used as a sacrificial anode. Thus, it was a good opportunity to verify the effectiveness of sacrificial anode CP (SACP) in this special location. Measurement was conducted for three years. Test Factors were corrosion potential, CP potential, 4 hour depolarization potential, and CP current. Moreover, resistivity and corrosion rate were measured by the multi-functional corrosion monitoring sensor (DMS-100, Conclinic Co. Ltd) that could measure potential, galvanic current, corrosion rate, concrete resistivity, and temperature. After three years from installation of CP, it could confirm that although some pier showed low depolarization potential less than 100mV, most piers showed good protection both electrochemical and physical aspects.

Abstract: In this paper, we study the integration of principal component analysis and wavelet neural net work to establish the principle component wavelet neural network model, and apply the model to predict the strength of cement, and using the average prediction error of the strength of cement by the model to compare with the results through the BP neural network model and the principal component neural network model, the average prediction error in this paper is the smallest. Therefore, the method in this paper has guiding significance to control the quality of the cement production.

Abstract: Light components in the asphalt can volatilize under the circumstances of high temperature or long-term service process, leading to the deteriorating of the asphalt pavement. This paper tried to discuss the influences of volatile organic compounds (VOC) emission from the asphalt on physical properties in the high temperature (at 180) by grey system theory. Both Heat and Vacuum environment were monitored as the emission conditions and the emission temperature was 180°C, physical properties of asphalt, released and unreleased were analyzed. Basic tests, including mass change, chemical compositions, penetration and soften point, were used to compare the influences of VOC emission on the asphalts performances. Meanwhile, grey system theory was used to investigate the sequent performances influenced by VOC emission. Results show that physical properties and four generic components of the asphalts are affected obviously in these two emission conditions, and the oxygen may promote VOC emission from the asphalt. In additional, the greatest factor associating with VOC emission is light components in the asphalt.