Finite element modeling of heat transfer in single and multilayered deposits of Ni-WC produced by the laser-based powder deposition process

The localized high-energy input and high-cooling rate inherent in the laser-based powder deposition (LBPD) process yield deposits with superior mechanical and metallurgical properties. However, these characteristics induce thermal stresses within the deposited material that subsequently lead to cracks. This tendency is predominant in the LBPD of metal–ceramic composite materials such as nickel (Ni) and tungsten carbide (WC). In this study, the thermal behavior of single and multilayered compositionally graded Ni-WC composite material during LBPD is studied using an experimentally verified three-dimensional finite element model. The model incorporates both directional- and temperature-dependent material properties. The effect of the mass fraction of the reinforcement, laser power, scanning speed, powder flow rate, and preheating temperature on temperature, temperature gradient, cooling rate, and molten pool evolution are investigated. The distribution and dissolution of WC in Ni-WC deposits are analyzed in the light of the scanning electron microscope, energy-dispersive spectroscopy, and microhardness distribution. The dissolution of WC in the molten Ni varies based on the mass fractions of the Ni and WC and the prevailing thermal conditions such as molten pool temperature and cooling rate. Experimental and numerical results confirm that the desired composition gradient can be achieved in a multilayered Ni-WC composite material deposit by adjusting the laser power. The developed heat transfer analysis may be used to select the suitable process variables needed to achieve the desired properties in the LBPD of single and multilayered Ni-WC composite material.     

Comparison of non-traditional technologies for material cutting from the point of view of surface roughness

The contribution deals with comparing non-traditional cutting technologies from the point of view of generated surface roughness. The comparison is carried out for technologies of abrasive waterjet cutting, oxygen cutting, laser and plasma cutting. As an experimental material, EN S355J0 structural steel and titanium CP-Ti Grade 2 was used. Surface topography measurement was done using a Mitutoyo Surftest SJ-401 instrument, and an optical profilometer MicroProf FRT was used for comparison and verification of acquired surface data. The aim of the contribution is to clarify, on the basis of experimental measurements, the behaviour of a topographic function after various ways of cutting; the knowledge of the function is necessary for solving both theoretical and practical technological tasks. The topographic function, which is a basis for the prediction of quality and control of the cutting processes, was derived in an original way. The use of individual technologies depends on technical and economical possibilities and on environmental influences. The results of measurement of cut surface roughness are in good accordance with the results of theoretical analysis.     

Development of a real-time laser-based machine vision system to monitor and control welding processes

In this study, a laser-based machine vision system is developed and implemented to monitor and control welding processes. The system consists of three main modules: a laser-based vision sensor module, an image processing module, and a multi-axis motion control module. The laser-based vision sensor is designed and fabricated based on the principle of laser triangulation. By developing and implementing a new image processing algorithm on the platform of LabVIEW, the image processing module is capable of processing the images captured by the vision sensor, identifying the different types of weld joints, and detecting the feature points. Based on the detected feature points, the position information and geometrical features of the weld joint such as its depth, width, plates mismatch, and cross-sectional area can be obtained and monitored in real time. Meanwhile, by feeding these data into the multi-axis motion control module, a non-contact seam tracking is achieved by adaptively adjusting the position of the welding torch with respect to the depth and width variations of the weld joint. A 3D profile of the weld joint is also obtained in real time for the purposes of in-process weld joint monitoring and post-weld quality inspection. The results indicate that the developed laser-based machine vision system can be well suited for the measurement of weld joint geometrical features, seam tracking, and 3D profiling.     

On-line monitoring of depth of cut in AWJ cutting

Monitoring of the abrasive waterjet (AWJ) cutting process has become increasingly important. The present paper proposes a model for on-line depth of cut monitoring based on the acoustic emission (AE) response to the variation in AWJ depth of cut, instead of the expensive and impractical vertical cutting force monitoring. The main objective is to use the AE technique in order to predict the actual depth of cut in AWJ cutting under normal cutting conditions. It was found that the root mean square of the acoustic emission energy (AErms) increases linearly with an increase in the depth of cut and could be used for its on-line monitoring. The results show that the AE is the most suitable technique for AWJ monitoring, as the AE signal has high sensitivity to the variation in the depth of cut.     

Inhibiting Islet Amyloid Polypeptide Fibril Formation by the Red Wine Compound Resveratrol

Grapes for amyloids : The red wine compound resveratrol can effectively inhibit the formation of IAPP amyloid that is found in type II diabetes. Our in vitro inhibition results do not depend on the antioxidant activity of resveratrol. Further, the markedly enhanced cell survival in the presence of resveratrol also indicates that the small oligomeric structures that are observed during β‐sheet formation are not toxic and could be off‐pathway assembly products.

     

Hardness prediction in multi-pass direct diode laser heat treatment by on-line surface temperature monitoring

This study was attempted to develop a process model, using the temperature values measured by the coupled infrared temperature measurement system (pyrometer and camera) correlated with the measured values of case depth hardness of the tool steel AISI S7 (hypo-eutectoid steel) for the specified multi-pass laser heat treatment conditions (1000–2500 J). A number of heat treatment experiments by changing the laser power (1400–1800 W), scanning speed (15–25 mm/s), size of overlap (1–6 mm), and the length of scan (10–30 mm) on the tool steel AISI S7 were carried out by using a 2-kW direct diode laser. The results indicated that the loss of case depth hardness uniformity was highly influenced by the tempering temperature and the change of cooling rate. The combination of higher laser power, lower scanning speed, smaller size of overlap, and the longer length of scan were influenced the formation of mixture of phases (martensite, bainite, ferrite, and pearlite) which in turn affected the case depth hardness uniformity. The process model can be used as a handy tool for the process engineers to configure the processing conditions in order to obtain the desired case depth hardness for the hypo-eutectoid steels.     

Infrared sensing of full penetration state in gas tungsten arc welding

The objective of this study is to present an applicable top-side infrared sensing technique for the prospective closed-loop control of weld penetration in gas tungsten arc welding (GTAW). A model is developed to calculate the full penetration state, which is specified by the back-side bead width, from the sensed infrared images. To ensure the model validity in the prospective closed-loop control, the experiments, which generate the data for the model identification, are conducted under the experimental conditions that will be encountered during practical closed-loop control of the welding process. The heat transfer condition and electrode tip angle may vary during welding or from case to case. Also, the control variables which are used to adjust the weld process in order to reach the required weld penetration will also change. In many cases, the current can be employed as an on-line adjustable control variable because of the implementation ease, when the welding speed and arc length are maintained at the preset values. Thus, different currents, workpiece sizes, and electrode tip angles are arranged in the experiments to emulate the possible current adjustments, case to case heat transfer variations, and electrode wear. The infrared characteristics of the effects of these parameters are extracted to regress the full penetration state. Finally, the back-side weld width (the full penetration state) is calculated using the resultant model from the sensed infrared data.     

Flux Dynamics in Tl2Ba2CaCu2O8 Thin Films

Investigations on flux dynamics of ring-shaped T1₂Ba₂CaCu₂O₈ superconducting thin films have been carried out by measuring the temperature dependent magnetization M(T) during field-cooling (FC) and zero-field-cooling (ZFC) processes. For a given magnetic field, from the magnetization behavior two distinct temperatures, T_kink and T_irr, can be defined. Below T_kink, a clear hysteretic behavior of M(T) is observed leading to a large irreversible signal M = M_FC – M_ZFC. Above T_kink, this irreversible signal, though being very small, is still non-zero until it eventually vanishes at a higher temperature T_irr. Above T_irr, both curves M_FC(T) and M_ZFC(T) merge together and become temperature independent. We attribute the first region ( T< T_kink) to a 3D vortex-glass phase, the second region (T_kink < T < T_irr) to a vortex line liquid state and the third region (T_irr < T < T_c) to a pancake liquid state.     

An approach to instruction set compiled simulator development based on a target processor C compiler back-end design

Many instruction set simulation approaches place the retargetability and/or cycle-accuracy as the key features for easier architectural exploration and performance estimation early in the hardware development phase. This paper describes an approach in which importance of speed and controllability is placed above the cycle-accuracy and retargetability, thus providing a better platform for software development. The main idea behind this work is to associate the compiled simulator effort with the development of the C language compiler for the target embedded processor, using the knowledge related to compilers and reusing some common software elements. Through the prototype design of a compiled simulator for the Cirrus Logic Coyote DSP architecture, many implementation aspects are presented showing that this approach has great potential.     

Energy Dissipation Control in Hydro-Abrasive Machining Using Quantitative Acoustic Emission

The efficiency and product quality of hydro-abrasive machining (HAM) could be considerably improved if the energy dissipation phenomenon of the jet-like tool during the material removal is clearly understood. An on-line technique for quantifying the amount of energy dissipated in the workpiece during HAM using acoustic emission (AE) measurements is presented in this paper. The measured AE-signals are linked to a physical energy dissipation model. Stochastic modelling of the AE-signals provides more information on the physics of the energy dissipation process.