Influence of Bifilm Defects Generated during Mould Filling on the Tensile Properties of Al–Si–Mg Cast Alloys

Entrapped double oxide film defects are known to be the most detrimental defects during the casting of aluminium alloys. In addition, hydrogen dissolved in the aluminium melt was suggested to pass into the defects to expand them and cause hydrogen porosity. In this work, the effect of two important casting parameters (the filtration and hydrogen content) on the properties of Al–7 Si–0.3 Mg alloy castings was studied using a full factorial design of experiments approach. Casting properties such as the Weibull modulus and position parameter of the elongation and the tensile strength were considered as response parameters. The results suggested that adopting 10 PPI filters in the gating system resulted in a considerable boost of the Weibull moduli of the tensile strength and elongation due to the enhanced mould filling conditions that minimised the possibility of oxide film entrainment. In addition, the results showed that reducing the hydrogen content in the castings samples from 0.257 to 0.132 cm3/100 g Al was associated with a noticeable decrease in the size of bifilm defects with a corresponding improvement in the mechanical properties. Such significant effect of the process parameters studied on the casting properties suggests that the more careful and quiescent mould filling practice and the lower the hydrogen level of the casting, the higher the quality and reliability of the castings produced.

Sequential Probabilistic Ratio Test for the Scale Parameter of the P -Norm Distribution

We consider a series of independent observations from a P -norm distribution with the position parameter μ and the scale parameter σ . We test the simple hypothesis H 0 : σ = σ 1 versus H 1 : σ = σ 2 . Firstly, we give the stop rule and decision rule of sequential probabilistic ratio test (SPRT). Secondly, we prove the existence of h σ which needs to satisfy the specific situation in SPRT method, and the approximate formula of the mean sample function is derived. Finally, a simulation example is given. The simulation shows that the ratio of sample size required by SPRT and the classic Neyman–Pearson N − P test is about 50.92 % at most, 38.30 % at least.

Dynamic test of laminated veneer lumber elastic modulus and its probability distribution

The vibrational frequency method was used to measure the elastic modulus of laminated veneer lumber (LVL), and the feasibility of using Weibull distribution to analyze the elastic modulus data of LVL was considered. Samples were randomly selected as test pieces at the factory. The sponge support structure was used to realize the free beam state, and the modal test results verified the accuracy of realizing the free beam. Under transient excitation, the elastic modulus of the specimen was obtained by testing the first-order bending frequency. The Weibull distribution fitting test, Weibull distribution K-S test, and normal distribution K-S test were used for the test data. The probability of LVL elastic modulus was calculated under a given value. The results showed that the LVL elastic modulus did not obey the two-parameter Weibull distribution (Eu=0). The LVL elastic modulus fit to the three-parameter Weibull distribution (Eu) was greater than half of the minimum test value and the normal distribution. When 9 GPa and 8 GPa were used as the setting values of Eu, the calculated probability value was relatively stable. At this time, Eu was 81% and 92% of the minimum elastic modulus 9.815 GPa. Therefore, it was recommended to use 80% to 90% of the minimum value of the measured data as the setting value of the position parameter Eu. The three-parameter Weibull distribution and the normal distribution calculated LVL elastic modulus have the same probability under the given value.

Modeling of Thermal Contact Resistance of Ball Screws Considering the Load Distribution of Balls

A new analytical method for the modeling of the thermal contact resistance of ball screws considering the load distribution of balls is proposed in this research. The load on balls is analyzed by the force analysis of ball screws, and then, the thermal contact resistance is obtained by the minimum excess principle and Majumdar–Bhushan (MB) fractal theory. The proposed method is validated by experimental results. The comparison with experimental and former results indicates that it is an effective method to evaluate the thermal contact resistance of ball screws. On that basis, effects of axial load, axial pretension, and geometry error of balls are discussed. It is concluded that the thermal contact resistance of ball screws increases along with axial load increase. The load on balls all decreases with axial pretension increase, and the thermal contact resistance of ball screws decreases with the axial pretension increase as well. When the axial load is applied on the nut in an axial-pretension ball screw, the load distribution in Nut A or B becomes less homogenized when the nut moves from nut position parameter ξ = 0 to 1. When the nut moves to ξ = 0.25, the thermal contact resistance will reach a minimum value, and it gets a maximum value at the nut position ξ = 1. The interval range of load and thermal contact resistance are obtained via uncertain analysis. It is concluded that the geometry error has much greater effects on the balls far away from the spacer.

Optimization of Thin Walls with Sharp Corners in SS316L and IN718 Alloys Manufactured with Laser Metal Deposition

In this work, the manufacture of thin walls with sharp corners has been optimized by adjusting the limits of a 3-axis cartesian kinematics through data recorded and analyzed off-line, such as axis speed, acceleration and the positioning of the X and Y axes. The study was carried out with two powder materials (SS316L and IN718) using the directed energy deposition process with laser. Thin walls were obtained with 1 mm thickness and only one bead per layer and straight/sharp corners at 90°. After adjusting the in-position parameter G502 for positioning precision on the FAGOR 8070 CNC system, it has been possible to obtain walls with minimal accumulation of material in the corner, and with practically constant layer thickness and height, with a radii of internal curvature between 0.11 and 0.24 mm for two different precision configuration. The best results have been obtained by identifying the correct balance between the decrease in programmed speed and the precision in the positioning to reach the point defined as wall corner, with speed reductions of 29% for a programmed speed of 20 mm/s and 61% for a speed of 40 mm/s. The walls show minimal defects such as residual porosities, and the microstructure is adequate.

Comfort Evaluation and Position Optimization of the Clutch Pedal in Agricultural Machinery Based on a Multi-Level Evaluation System

HighlightsComfort evaluation and position parameter optimization of the clutch pedal were conducted.A comprehensive evaluation system was established for sitting comfort and operating comfort.A single-factor test and a response surface optimization test were carried out.Pedal inclination and its left-right distance synergistically influenced operating comfort.Abstract. The clutch pedal is the most frequently used control device in agricultural machinery and is an important component that affects operating comfort and safety. This study focused on the comfort evaluation and position parameter optimization of the clutch pedal based on a multi-degree-of-freedom test platform of an agricultural machinery cab. First, the H point (hip point) was determined based on a human body model of the operator’s sitting posture as a reference. Two position parameters were then determined: the pedal inclination angle, and the left-right distance of the pedal relative to the operator’s centerline. On this basis, a comprehensive evaluation system for sitting comfort and operating comfort was established. Single-factor tests were used to determine the comfort range and optimal levels of the two position parameters. A response surface optimization was then performed to determine the optimal parameter combination, and a first-order regression model of the response surface was established and corrected using the variance analysis method. The analysis results showed that the pedal inclination angle and its interaction with the left-right distance had a significant effect on comfort (a = 0.05). Based on the evaluation results, the mechanism underlying the influence of the position parameters on pedal comfort was analyzed. Finally, optimization and verification of the pedal position parameters were performed. The results showed that the expected comprehensive score for pedal comfort was 0.831, with an average relative error of 3.64% from the measured value, indicating that the optimization of the position parameters was reliable. The findings of this study may provide a reference for the optimal design of clutch pedals in agricultural machinery. Keywords: Agricultural machinery, Clutch pedal, Comfort evaluation, Parameter optimization, Response surface method.

Optimization of Thin Walls With Sharp Corners in SS316L and IN718 Alloys Manufactured with Laser Metal Deposition

In this work, the manufacture of thin walls with sharp corners has been optimized by adjusting the limits of a 3-axis cartesian kinematics through data recorded and analyzed off-line, such as axis speed, acceleration and the positioning of the X and Y axes. The study was carried out with two powder materials (SS316L and IN718) using the directed energy deposition process with laser. 1 mm thick walls were obtained with only one bead per layer and straight/sharp corners at 90º. After adjusting the in-position parameter G502 for positioning precision on the FAGOR 8070 CNC system, it has been possible to obtain walls with minimal accumulation of material in the corner, and with practically constant layer thickness and height, with a radii of internal curvature between 0.11 and 0.24 mm for two different precision configuration. The best results have been obtained by identifying the correct balance between the decrease in programmed speed and the precision in the positioning to reach the point defined as wall corner, with speed reductions of 29% for a programmed speed of 20 mm/s and 61% for a speed of 40 mm/s. The walls show minimal defects such as residual porosities, and the microstructure is adequate.

Love-Type Wave in PMN-PT Single Crystal Layered Structures with Periodic Undulations

Love-type wave propagation has been studied in a layered structure consisting of a thin layer of PMN-PT single crystal deposited on an elastic half-space. The weakly periodic undulations of the upper surface of the layered system and the common interface between the PMN-PT layer and the elastic substrate are considered. The PMN-PT single crystal is poled along the [011]_c direction so that the macroscopic symmetry is orthonormal mm2. The dispersion relations for electrically open and shorted circuits are obtained. The effects of various parameters including corrugation, undulatory, position and electrical boundary conditions on dispersion properties of Love-type waves are discussed. The results show that corrugations of the surface and the interface play a dominant role in the propagation of a Love-type wave, especially, the interfacial corrugation can produce an anomalous dispersion in the case of an electrically shorted condition. The surface corrugation enhances the phase velocity of a Love-type wave while the interface corrugation reduces the phase velocity in the range of relatively smaller wavenumber, and these variations gradually tend to vanish with increase in wavenumber. The undulatory parameter and the position parameter present a secondary impact on the dispersion behaviors of a Love-type wave compared with the corrugation parameters, both of them slightly enhance the phase velocity. The obtained results can offer some fundamentals for improving the efficiency and sensitivity of the interface response in the design and application of piezoelectric SAW devices.

Mhd Mixed Convection in Copper-Water Nanofluid Filled Lid-Driven Square Cavity Containing Multiple Adiabatic Obstacles with Discrete Heating

The objective of the present work is to investigate the influence of nanoparticles of copper within the base fluid (water) on magneto-hydrodynamic mixed-convection flow in a square cavity with internal generation. A control finite volume method and SIMPLER algorithm are used in the numerical calculations. The geometry is a lid-driven square cavity with four interior square adiabatic obstacles. A uniform heat source is located in a part of the left wall and a part of the right wall of the enclosure is maintained at cooler temperature while the remaining parts of the two walls are thermally insulated. Both the upper and bottom walls of the cavity are considered to be adiabatic. A comparison with previously published works shows a very good agreement. It is observed that the Richardson number, Ri, significantly alters the behavior of streamlines when increased from 0.1 to 100.0. Also, the heat source position parameter, D, significantly changes the pattern of isotherms and its strength shifted when D moves from 0.3 to 0.7.