Advanced Materials Research Vols. 314-316

Abstract: Dislocation distribution functions of the edges of mode III propagation crack subjected to Moving unit step load from a point was studied by the methods of the theory of complex variable functions.By the methods, the problems researched can be facilely transformed into Riemann-Hilbert problems and Keldysh-Sedov mixed boundary value problems. Analytical solutions of stresses, displacements, dynamic stress intensity factor and dislocation distribution function were obtained by the methods of the theory of self-similar functions.In terms of the relationship between dislocation distribution functions and displacements, analytical solutions of dislocation distribution functions were attained.

Abstract: Based on the theory of structural mechanics, it has established that a simplified mechanical model of suspension platform of ZLP800 suspended access equipment (SAE) in this paper. Under the two common combinations we could calculate and comparatively analyse deflection of variable stiffness structure of suspension platform. On this basis, 15m span suspension platform module combination was obtained by the enumeration method. Moreover, by deflection calculations of the platform structure in different combinations，we could obtain the best module combination so as to provide a theoretical basis for the design of large span suspension platform.

Abstract: In this study, we present the characterisation of damage in polymer concrete using coda waves interferometry (CWI). The latter takes into account the multi-scattered acoustic waves, whose travelling distances are considerably longer than the one corresponding to the direct wave (emitter-receiver direct distance). Experimentally, we prove that CWI is not always appropriate to detect damage. Therefore, we propose an original approach through which the interaction CWI with damage is optimised. This is done using nonlinear resonance (NR) method, where bending modes are excited, at the time when acoustic waves are multi-scattered. Experiments show an important increase in the sensitivity to damage with interesting perspectives in terms of damage location and characterisation.

Abstract: A new concavo-convex electrode has been designed and employed and it was reported that electrical discharge machining (EDM) of particulate reinforced metal matrix composites with this kind of new electrode can accelerate the debris discharge during machining so that it has a higher material removal rate (MRR) compared to the case where a normal electrode was employed. Since there are many factors that can affect the MRR in the EDM process with the concavo-convex electrode, in order to determine which is the most important factor and to optimize the machining parameters, the relative importance of the various cutting parameters on material removal rate was established using an orthogonal experimental analysis in this study. The results of the analysis suggest that to achieve a high MRR for particulate reinforced aluminum 6061 with 10-vol% Al2O3 (10ALO) or 20vol% Al2O3 (20ALO) using a concavo-convex electrode, the duty cycle is the most influential factor among current, pulse duration and duty cycle.

Abstract: In order to improve the simulation accuracy for arc welded structures, the refined numerical simulation approach using the solid model with material mechanical properties has been presented. The arc welded joints are frequently utilized in the manufacture of neighborhood electric vehicle. Firstly, the mechanical properties of the base metal and three types of welded joints were determined by the uniaxial tensile experiments, and experimental results revealed that the mechanical property significantly reduced after welding. Then the numerical simulation approach using solid model and approach using weld constraint were conducted on the butt welded joints of 6061 aluminum alloy in LS-DYNA software, the simulation results were compared with experimental results. Moreover, the refined simulation approach using solid model was validated by different types of arc welded joints and their corresponding experiments. It is concluded that the proposal simulation approach using solid model shows higher accuracy than the approach using weld constraint on predicting deformation of butt welded and fillet welded joints.

Abstract: On the basis of metal cutting and rigid-plastic finite element theories, taking cutting force in turning process as the research object, a FEA model for turning process using a MDT cutter on a centre lathe CA6140 is constructed to simulate its metal cutting process. Using Deform 3D, cutting forces are calculated according to different cutting parameters. The influences of the cutting parameters on the cutting forces are investigated. In order to validate the FEA model, cutting experiments are conducted. Comparison between simulated cutting forces and experimental forces shows similar trends and reasonable agreement.

Abstract: Edge distance is the main factor inducing edge chipping. An edge chipping experiment is designed to study the relationships between edge distance and the edge chipping from the aspect of fracture process, the load-displacement curves and AE signals are documented. The results show that the fracture processes of edge chipping at different edge distances are similar and could be divided into four stages, AE signals could reflect the fracture process features of edge chipping. As edge distance increases, the displacements of indenter and critical loads would increase correspondingly, while the peak values of count and duration would decrease. The critical edge distance for Al2O3 is about 0.75mm; the displacements of indenter would keep invariable, while the peak values of count and duration would get to the minimum.

Abstract: In this paper, four types P turning insert groove with 3D chip-breaker are investigated for the influence of cutting force, cutting temperature and chip deformation. The experimental result shows that cutting force and total cutting heat corresponding different insert type are not the same between each other. These experiments also show that the arrangement sequence of chips deformation is consistent with that of cutting temperature for four kind of turning insert. The greater chip deformation indicates more work done, thus the more cutting heat taken away.

Abstract: The influence of physical aging on mechanical properties of glassy polymers was investigated in this paper. After annealing above T_g to release the previous thermal and stress history, the polymethyl methacrylate (PMMA) samples were quenched to 27°C, aged for various times (t_a), and were then stretched at the same temperature by two ways: (1) step stresses with four different magnitudes varying from 15MPa to 30MPa; (2) constant rate stretch up to fracture. The physical aging effect was monitored by measuring the initial instantaneous elastic modulus (E) and the fracture strength (σ_f) from the stress-strain curves as a function of t_a up to 1368h. It is shown that both E and σ_f of the material increase with aging time and approach to their asymptotic values, which satisfy the KWW rule, while the isochronous creep compliance decreases with log t_a in a linear manner within the aging time range considered in this paper.

Abstract: Abstract. 7A52 aluminum alloy plate was welded using twin-wire metal inert gas arc welding (TANDEM welding). Corrosion behavior of the welded joint was investigated by immersion in 3.5% NaCl solution. Scanning electron microscopy (SEM) and electrochemical inspections, specifically, polarization curves and electrochemical impedance spectroscopy (EIS), were conducted to understand corrosion behavior of the TANDEM welding joint of 7A52 aluminum alloy. It was found that the heat affected zone (HAZ) exhibited higher corrosion susceptibility than the weld beam (WB), fusion zone (FZ) and base metal (BM). The electrochemical results showed that the WB with higher corrosion potential and larger impedance had highest corrosion resistance. Variations in the composition and grain size might have led to the differences in corrosion resistance because the welding process influenced microstructures of the TANDEM welding joint of 7A52 aluminum.