The tool:workpiece interaction when machining welded hardfacing using PCBN tools

The work presented in this thesis is concerned with turning chromium carbide based hardfacings using PCBN tools. The chip formation and tool wear process was studied by quick-stop and machining tests. Cutting temperature was investigated by means of a remote thermocouple and the chip-tool interface temperature was simulated by an ANSYS Finite Element Analysis model. Cutting performance of PBN tools from different suppliers was compared in field cutting tests. Hardness, microstructure and the adhesion between the workpiece and cutting tool material were assessed.ln the turning process, saw-tooth chips were formed, with a short chip:tool contact length. Quick-stop tests revealed that the machining process involved fracture of large carbides ahead of the cutting edge in the primary zone. Temperature measurements showed that the cutting temperature for the hard facing material was lower than that with titanium alloy but much higher than that with machining mild steel. The cutting temperature predicted at the tool chip interface was in the range of 600-700°C when cutting hard facing.The tool wear process was found to involve three main progressive stages - from small scale edge chipping to large scale flaking and fracture. Four types of wear were identified: flank wear, microchipping, flaking of the rake face and delamination of the flank face. Abrasion appears to be the principal flank wear mechanism and it showed a minimum value for different speeds but increased with feedrate. The main mechanism for microchipping involved failure through the CBN particle boundaries. Flaking of the rake face occurred in the later stages and transgranular fracture was the main mechanism.In field tests, PCBN material from various sources achieved different cutting performance, which reflected the structural differences in the PBN materials. A dense structure with strong particle binding is essential for satisfactory performance of PCBN in this application

New criteria on global asymptotic synchronization of Duffing-type oscillator system

In this paper, we are concerned with global asymptotic synchronization of Duffing-type oscillator system. Without using matrix measure theory, graph theory and LMI method, which are recently widely applied to investigating global exponential/asymptotic synchronization for dynamical systems and complex networks, four novel sufficient conditions on global asymptotic synchronization for above system are acquired on the basis of constant variation method, integral factor method and integral inequality skills.&nbsp

NUMERICAL INVESTIGATION OF HEEL-SHOE INTERACTION IN RUNNING

Human heel sensitivity to mechanical loading, which is associated with the strain/stress state around the sensory receptors, is an important body function for sport, exercise and other daily activities (Lake & lafortune, 1998; Patritti, 2002). The sensory receptors within the heel transmit the mechanical signals (e.g. strains) into neural signals and enable human body to sense and adapt to changes of external loadings. To improve the understanding of the mechanics of this process, a realistic numerical model was developed in this work to establish quantitative relationships between the external loads and the state of stresses/strains at sensory receptor locations in running

Detection of 5 kinds of common foodborne pathogens by GeXP multiplex polymerase chain reaction

Objective To establish a new and rapid GeXP (GenomeLabTM eXpress Profiling) based multiplex polymerase chain reaction (PCR) assay for the detection of five common foodborne pathogens. Methods Nucleotide sequences of specific gene (invA, rfbE, PfrA, IpaH, tlh) of the five pathogens (Salmonella, Escherichia coli O157:H7, Listeria monocytogenes, Shigella, Vibrio parahaemolyticus) were obtained and compared. The primers were then designed and the multiplex PCR assay was evaluated. Optimized assay was further validated with the detection of the unknown strains and artificially contaminated samples. Results The GeXP multiplex PCR with five sets of specific primers can be used to detect five foodborne pathogens simultaneously within 5 hours. The specificity was examined by specimens confirmed previously. The detection limit was 103 CFU/mL. Conclusion The results suggested this GeXP multiplex PCR assay was a fast, high throughput test for foodborne bacterial pathogens

Welding of High Entropy Alloys A Review

High-entropy alloy (HEA) offers great flexibility in materials design with 3–5 principal elements and a range of unique advantages such as good microstructure stability, mechanical strength over a broad range of temperatures and corrosion resistance, etc. Welding of high entropy alloy, as a key joining method, is an important emerging area with significant potential impact to future application-oriented research and technological developments in HEAs. The selection of feasible welding processes with optimized parameters is essential to enhance the applications of HEAs. However, the structure of the welded joints varies with material systems, welding methods and parameters. A systemic understanding of the structures and properties of the weldment is directly relevant to the application of HEAs as well as managing the effect of welding on situations such as corrosion that are known to be a service life limiting factor of welded structures in conditions such as marine environments. In this paper, key recent work on welding of HEAs is reviewed in detail focusing on the research of main HEA systems when applying different welding techniques. The experimental details including sample preparation, sample size (thickness) and welding conditions reflecting energy input are summarized and key issues are highlighted. The microstructures and properties of different welding zones, in particular the fusion zone (FZ) and the heat affected zones (HAZ), formed with different welding methods are compared and presented in details and the structure-property relationships are discussed. The work shows that the weldability of HEAs varies with the HEA composition groups and the welding method employed. Arc and laser welding of AlCoCrFeNi HEAs results in lower hardness in the FZ and HAZ and reduced overall strength. Friction stir welding results in higher hardness in the FZ and achieves comparable/higher strength of the welded joints in tensile tests. The welded HEAs are capable of maintaining a reasonable proportion of the ductility. The key structure changes including element distribution, the volume fraction of face centered cubic (FCC) and body centered cubic (BCC) phase as well as reported changes in the lattice constants are summarized and analyzed. Detailed mechanisms governing the mechanical properties including the grain size-property/hardness relationship in the form of Hall–Petch (H–P) effect for both bulk and welded structure of HEAs are compared. Finally, future challenges and main areas to research are highlighted

Intrinsic defects, Mo-related defects, and complexes in transition-metal carbide VC: A first-principles study

Intrinsic defects and Mo‐related defects in vanadium carbide VC, as well as the defect complexes between vacancies and Mo defects were investigated by means of first‐principles calculations within the framework of density functional theory. In addition, Mo diffusion in VC was also studied using LST/QST method. The formation energies of defects have clearly shown that except C vacancy (VC) all other point defects are not energetic favorable compared to perfect VC. VC can exist in the lattice forming nonstoichiometric carbide VCx (x < 1), and also can stabilize the Mo‐related defects (SMo‐V, SMo‐C, and TMo). Free Mo atoms have the strong tendency to enter the already formed VV and occupy the lattice position of V atoms. Meanwhile, Mo atom in C lattice (SMo‐C) and interstitial Mo (IMo) atom can also enter the VV position stabilizing the lattice structure. SMo‐C + VV will transform into SMo‐V + VC and IMo + VV will transform into SMo‐V during optimization, and large binding energy makes Mo atom tend to exist in the interstitial position. From the perspective of energy, Mo atom tends to diffuse through the interstitial position

Study on crustal deformation of the Ms6. 6 Damxung earthquake in 2008 by InSAR measurements

Abstract:Three Envisat images from ESA were used to derive the pre – and co-seismic deformation interfereograms caused by the Damxung Ms6. 6 earthquake of Oct. 6, 2008, by using InSAR. The result shows no significant crustal motion more than 4 months before the earthquake, but a maximum co-seismic displacement of about 0.3m in an epicentral area of 20km × 20km. The deformation field was symmetrically distributed about a NS axis, where the west side subsided and the east side uplifted. We used a linear elastic dislocation model in half space and a nonlinear constraint optimized algorithm to estimate the slip distribution along the fault. The results indicates that the epicenter is located at 90.374°E, 29.745°N with a moment magnitude of Mw6. 35. The earthquake is dominated by normal faulting with a maximum slip of 3m on a 12km × 11km fault plane striking S189°W, dipping 60° to NW at a depth of 9.5km, and is located at a sub-fault of the southeastern Piedmont of the Nyainqentanglha mountains. The relatively shallow depth of earthquake is related to relatively high heat flow in the area