Mechanical and Materials Engineering

Metal additive manufacturing is a method of producing metallic parts layer-by-layer. Some drawbacks, including anisotropy in mechanical properties, detrimental residual stresses, and the presence of columnar grain structures can affect the quality and performance of additively manufactured metallic parts. Therefore, different industrial sectors have employed intuitive ancillary processes to improve the quality of additively manufactured parts. Of particular interest is in-situ ancillary processes that are more applicable than other procedures due to their utmost importance to reduce manufacturing cycle time. In this review article, after introducing various metal additive manufacturing technologies, some of the common alloys utilized in those processes were discussed. With an eye toward improving the quality of additively manufactured components, the focus of the review was then shifted toward the effects of building direction, processing parameters, and Alloying composition Modification on microstructure and mechanical properties. The efficacy of ancillary processes such as metalworking, in-situ heat treatment, and in-situ thermo hydrogen process in reducing defects and improving physical and mechanical properties was then presented.

Using advanced high-strength steels in automobiles has created a new challenge to achieve acceptable welds. The present study evaluates the weldability of the new generation of advanced high-strength steels in the FeCrNiSi alloy group. Hence, utilizing the design of experiment (DOE), it was obtained how the parameters namely the welding current, welding time, and electrode force affect the final properties. Additionally, the acceptable range of parameters for achieving an acceptable weld nugget in terms of size and strength was obtained. Accordingly, the nugget size effects on mechanical properties, namely energy absorption capability, failure mode in tensile-shear test, and microhardness were evaluated. The parameters were statistically significant and showed a high degree of reliability (95%) in terms of nugget size. The range of acceptable parameters for 1 mm thick steel and type A electrode was 9e21 cycles for welding time, whereas for welding current were 4e7 KA, 5 to 6.5 KA, and 5.7 to 6.5 KA at 2, 3, and 4 KN electrode force, respectively. Due to the grain growth in the heat-affected zone (HAZ), the HAZ softening was observed in the microhardness profile. All samples demonstrated desired fracture mode due to the HAZ softening, the ductile austenitic microstructure, the absence of brittle phases, and easy nugget rotation in the tensile-shear test. By increasing the nugget diameter from 3 to 5.1 mm, the peak load and the energy absorption of the spot welds exceeded from 5.4 KN to 6.5 KN and from 10 to 31 J, respectively.

Abstract—Nowadays, Quadrotor helicopters are
becoming very popular platform for unmanned aerial
vehicle (UAV) research, due to their capability of
hovering, vertical takeoff and landing (VTOL) and
simplicity of their design and maintenance. To date, the
control of most Quadrotor aerial robots have been
based on their dynamical models, but in this research
it`s been tried to control the vehicle without any model.
In this paper, a fuzzy controller will be designed to
regulate the attitude of one degree of freedom (DOF)
arm, and then in our future efforts we will try to control
a large Quadrotor with the help of four controllers,
based on aforementioned method. At the end of this
paper, the experimental result of controlling one degree
of freedom arm will be presented and the advantages of
this type of controller will be discussed.

Considerable research has been conducted on the control of pneumatic systems. However,nonlinearities continue to limit their performance. To compensate, advanced nonlinear and adaptive
control strategies can be used. But the more successful advanced strategies typically need a mathematical model of the system to be controlled. The advantage of neural networks is that they do not require a model. This paper reports on a study whose objective is to explore the potential of a novel adaptive on-line neural network compensator (ANNC) for the position control of a pneumatic gantry robot. It was found that by combining ANNC with a traditional PID controller, tracking performance could be improved on the order of 45% to 70%. This level of performance was achieved after careful tuning of both the ANNC and PID components. The paper sets out to document the ANNC algorithm, the adopted tuning procedure, and presents experimental results that illustrate the adaptive nature of NN and confirms the performance achievable with ANNC. A major contribution is demonstration that tuning of ANNC requires no more effort than the tuning of PID.

Applied and residual lattice strains were determined by neutron diffraction during a tensile test of a weakly textured austenitic stainless steel and were compared to the predictions of a self-consistent polycrystal deformation model. Parallel to the tensile axis the model predictions are generally within the resolution of the diffraction measurements, but perpendicular to the tensile axis discrepancies are noted. Discrepancies between model and measurements were greater for the residual lattice strains than during loading. It is postulated that this is because the model does not predict reverse plasticity during unload.

The results of both a line-broadening study on a ceria sample and a size-strain round robin on diffraction line-broadening methods, which was sponsored by the Commission on Powder Diffraction of the International Union of Crystallography, are presented. The sample was prepared by heating hydrated ceria at 923 K for 45 h. Another ceria sample was prepared to correct for the effects of instrumental broadening by annealing commercially obtained ceria at 1573 K for 3 h and slowly cooling it in the furnace. The diffraction measurements were carried out with two laboratory and two synchrotron X-ray sources, two constant-wavelength neutron and a time-of-flight (TOF) neutron source. Diffraction measurements were analyzed by three methods: the model assuming a lognormal size distribution of spherical crystallites, Warren-Averbach analysis and Rietveld refinement. The last two methods detected a relatively small strain in the sample, as opposed to the first method. Assuming a strain-free sample, the results from all three methods agree well. The average real crystallite size, on the assumption of a spherical crystallite shape, is 191 (5) Å . The scatter of results given by different instruments is relatively small, although significantly larger than the estimated standard uncertainties. The Rietveld refinement results for this ceria sample indicate that the diffraction peaks can be successfully approximated with a pseudo-Voigt function. In a common approximation used in Rietveld refinement programs, this implies that the size-broadened profile cannot be approximated by a Lorentzian but by a full Voigt or pseudo-Voigt function. In the second part of this paper, the results of the round robin on the size-strain line-broadening analysis methods are presented, which was conducted through the participation of 18 groups from 12 countries. Participants have reported results obtained by analyzing data that were collected on the two ceria samples at seven instruments. The analysis of results received in terms of coherently diffracting, both volume-weighted and area-weighted apparent domain size are reported. Although there is a reasonable agreement, the reported results on the volume-weighted domain size show significantly higher scatter than those on the area-weighted domain size. This is most likely due to a significant number of results reporting a high value of strain. Most of those results were obtained by Rietveld refinement in which the Gaussian size parameter was not refined, thus erroneously assigning size-related broadening to other effects. A comparison of results with the average of the three-way comparative analysis from the first part shows a good agreement. electronic reprint research papers 912 D. Balzar et al. Size-strain line-broadening analysis

The macroscopic load-bearing capability of a composite is directly related to the strain partitioning due to load transfer between the component phases. Using neutron diffraction, the elastic mean phase strains were measured during in-situ loading of a Cu-15 vol pct Mo particulate metal-matrix composite (MMC) at 25 °C, 300 °C, and 350 °C. The degree of load sharing at each temperature was compared to finite-element (FE) results. The load transfer from the matrix to reinforcement is both qualitatively and quantitatively different at low and high temperatures. When the matrix creeps, load transfer is less effective than when the matrix deforms by slip; also, load transfer at elevated temperatures decreases with increasing applied stress.

Synchrotron energy-dispersive X-ray diffraction experiments on station 16.3 at the SRS for residual strain mapping are reported. A white beam with an energy-discriminating detector allows measurements to be made through 3 mm Al, Ti, Fe and Cu alloys with acquisition times of $ 30 s per 0.3 mm 3 sampling volume. The collected pro®les were analysed using single-peak ®tting and wholepattern Pawley re®nement, and produced strain accuracy better than 10 À4 . This con®guration is therefore highly ef®cient for fast strain mapping in thin components using a second-generation synchrotron source.