Experimental Techniques最新文献

Grinding is usually adopted as the final step in the workpiece machining to improve the surface quality. The wrapping deformation of sheet parts caused by grinding directly affects the surface accuracy and the performance of the parts. In this paper, the grinding experiments were designed and conducted under different conditions. Combined with theoretical analysis, the finite element model was established to reveal the mechanism of wrapping deformation. A new evaluation method of wrapping deformation in grinding was proposed, and the prediction model of the wrapping deformation and temperature in the grinding zone were established and verified. Finally, the grinding parameters were optimized through genetic algorithm with small error. The optimized grinding parameters were v_s = 28 m/s, a_p = 5 μm, v_w = 3 m/min. This method can provide guidance for the grinding process of sheet parts, which is beneficial for improving efficiency and precision in grinding.

This article presents Namazu, a low-cost tunable shaking table framework for uniaxial vibration experiments in engineering education and research. All components and corresponding assembly are detailed. The design is easy to use and requires minimum maintenance. Open-source software covering signal generation and microcontroller programming is proposed to prescribe the motion of the table. There is no restriction in the programming language used to interface with the table. Communication with the microcontroller is performed via a serial interface, which eliminates the need for additional software. Besides, any displacement signals, including random ones, can be chosen. Due to the open-source nature of the Namazu table, users can also implement custom methods for signal generation and modify the table hardware. Suggestions are given in the paper. Accuracy is analyzed through displacement measurements. In addition, the Shinozuka benchmark is proposed and applied to test the table accuracy in the frequency domain. The results show good consistency of the signals obtained with the setpoints. Thus, Namazu, including the shaking table and a software suite, offers a versatile, accessible, and accurate solution for vibration experiments.

Cast iron is widely used as a grinding tool material in the field of ultra precision manufacturing. To explore the friction and wear properties of cast iron materials under magnetic-mechanical coupling conditions, theoretical research was conducted to reveal the wear mechanism of cast iron materials. A self-developed free abrasive line contact tribometer was used to study the evolution law of different process parameters on the friction and wear properties, surface roughness, and surface morphology of cast iron. The experimental results reveal that, under the magnetic field conditions, the mean value of friction coefficient is less than 0.218, the wear capacity of cast iron rings is less than 42 mg, and the surface roughness value Ra is less than 0.139 μm, additionally, the friction coefficient, wear capacity, and roughness values are all lower than those under no magnetic conditions. For cast iron materials, the surface roughness value Ra ranges from 0.094 to 0.253 μm after the experiment, it is negatively correlated with relative sliding ratio, load, abrasive particle size, and concentration, while is positively correlated with magnetic induction intensity; The friction coefficient is negatively correlated with relative sliding ratio and magnetic induction intensity in the range of 0.051 to 0.268, and positively correlated with abrasive particle size and concentration. With the load increasing, the friction coefficient first decreases and then increases; The wear capacity of cast iron ring is within the range of 8 to 140 mg. It is negatively correlated with magnetic induction intensity, and positively correlated with relative sliding ratio, load, abrasive particle size, and abrasive concentration. This study provides support for the theoretical research of cast iron as a grinding tool material and provides reference for the rational application of cast iron materials in the field of ultra precision manufacturing.

Metal vibration absorber has been widely used to reduce the structural vibration under various complex environmental conditions, the fatigue reliability of which has an important influence on the safety of the structure. In this paper, a novel fatigue failure criterion when the residual preload displacement of metal vibration absorber is equal to the fatigue displacement amplitude is proposed to determine the fatigue life of metal vibration absorber. And a set of fatigue failure life prediction method is developed to obtain the failure life of non-failed metal vibration absorber. The predicted load versus life (P-N) curve of the metal vibration absorber under different load levels shows a good power function relation. Based on the fatigue displacement amplitude-life curves and the residual preload displacement-life curves of the metal vibration absorbers, a fatigue failure assessment diagram is successfully established. Further, the residual fatigue failure life of in-service metal vibration absorber can also be predicted according to the failure assessment diagram. By means of the scanning electron microscopy and the three-dimensional tomography equipment, the microanalyses of metal wire components after fatigue tests are conducted, and the fatigue wear and fracture law of metal wire in the metal vibration absorber is mastered.

Torsional Split Hopkinson Bar (TSHB) is the primary apparatus used to generate non-dispersion shear waves and characterize material behavior under dynamic shear stress. However, challenges associated with specimen gripping, especially at high strain rate conditions have limited its application to low strain rates. In this work, a novel connection using a Male-Female built-in Hexagonal Joint (MFHJ) is proposed as an engineering solution to provide a strong connection between the torsional specimen and the input and output bars of the TSHB apparatus. The male hexagon is formed on the specimen tips and the female hexagon is formed on the input and output ends of the torsional Hopkinson bar. This technique is validated numerically and utilized experimentally to study the dynamic material responses of titanium-G5. This work describes the operating principle, numerical validation, and experimental setup of the TSHB apparatus, MFHJ manufacturing, and testing. The results indicate a stable and consistent loading rate in the specimen in addition to providing equilibrium conditions at a high strain rate.

Carbon fibre reinforced polymers (CFRP) structures, e.g., wind turbine blades, are suspectable to direct lightning strikes due to their semiconductive nature and ability to conduct current. It is critical to identify and evaluate lightning damage as it can cause premature failure of the primary load carrying components. Direct strike lightning damage has been traditionally identified and assessed by ultrasonic (UT) inspection, which is time consuming, usually requires contact, and does not directly provide a measure of damage severity. An appealing alternative to UT is pulsed thermography (PT), which takes minutes to conduct rather than hours and does not require a couplant. The aim of this work is to explore the application of pulse thermography to identify and evaluate the damage state of CFRP panels damaged by simulated lightning strike. A new analysis technique is presented that provides a damage severity metric which allows damage to be categorized, separated, and quantified.

This study examines the influence of direct drive friction welding (DDFW) on Cr-Ni-Mo steel (AISI 316) with a focus on metallurgical, mechanical, and electrochemical properties. Different friction times, ranging from 5.5 s to 12 s, were investigated while keeping other conditions constant. Temperature measurements, Macro-microstructure, microhardness, tensile tests, tensile fracture morphology, and electrochemical tests were performed. The results show that the maximum temperature (Tmax) exhibits a slight increase with an extended friction time. The temperature variation ranges from 826 °C to 879 °C for friction times of 5.5 s and 12 s, respectively, thus, the welded joint is divided into four distinct regions: highly plastically deformed zone (HPDZ), thermo-mechanically affected zone (TMAZ), heat-affected zone (HAZ), and the base metal, with grain sizes of approximately 10 μm, 100 μm, 110 μm, and 25 μm, respectively. The HPDZ is responsible for the microhardness elevation at the interface, while the TMAZ and HAZ are responsible for the microhardness attenuation in the neighboring region and weak in tension. The ultimate tensile strength (UTS) related to AISI 316 decreases from 104.50 to 94.57% for 5.5 s and 12 s, respectively, and the ductility related to AISI 316 decreases from 58.21 to 54.05% for 5.5 s and 12 s, respectively. Tensile fractures occurred at the TMAZ with a ductile fracture mode and cleavage features with irregular forms of microcavities throughout the fingerprints. The results of the electrochemical test clearly indicate that the weld zone (WZ) exhibits superior corrosion resistance compared to the base metal (BM), AISI 316. Further analysis of the results revealed that the TMAZs are more susceptible to pitting than the HAZ. Thus, only a few micro-pits are observed in the HPDZ compared to the pitting state in the TMAZs.

In order to research the laws of roof collapsing and overlaying stratum movement in close distance coal seams mining and prevent roof accidents during such mining. The close distance coal seams mining in a coal mine is used as the study subject in this study, and a similar simulation experiment is conducted. A similar simulation experiment of the close distance coal seams is seen using the digital image correlation. The evolution of roof displacement–strain in the mining process is researched, along with the roof caving features in various coal seam mining processes. The evolution law of roof stress-displacement is revealed in the mining process of close distance coal seams which provides the basis for the roof stability control in close distance coal seams. Lower coal seam mining in close distance coal seams has a larger degree of abutment pressure stress concentration and a higher level of advanced abutment pressure intensity. Greater harm is caused by lower coal seam roof strata mining than by single coal seam mining. The stope support strength design must take upper goaf influence into account. Therefore, to ensure the stope roof stability in close distance coal seams, it is necessary to implement roof pressure monitoring, stope roof’s grouting reinforcement, measures to improve the performance of hydraulic support, and roof effective control in close distance coal seams mining by using the principle of coordinated control.

This contribution presents an evaluation of the effectiveness of the low-cost GNSS technique in structural health monitoring and GNSS-seismology applications. To evaluate the ability of the low-cost GNSS technique, harmonic oscillation, and earthquake tests were carried out employing the ZED-F9P-02B OEM low-cost GNSS receiver and two low-cost antennas (A10 and ANN-MB U-Blox) on a single-axis shake table. Harmonic motion experiments include frequencies ranging from 0.35 to 5.80 Hz and amplitudes between 10 and 25 mm. Moreover, the Loma-Prieta and Kobe earthquakes were simulated using a shake table to evaluate the ability of the low-cost GNSS technique to detect earthquake-induced strong ground motions. GNSS observations collected at a 20 Hz sampling interval were processed using the CSRS-PPP online service, and the ability of the low-cost GNSS technique to detect horizontal directional dynamic behaviors was validated using the relative positioning and Linear Variable Differential Transformer (LVDT) data as a reference both time and frequency domain. The max. RMSE values obtained according to the 15 harmonic oscillation test results are 2.8 mm for Geodetic Antenna Relative results, 3.3 mm for PPP, 3.2 mm for A10 Relative, 3.3 mm for PPP, 3.3 mm for UBX Antenna Relative, and 3.7 mm for PPP Results. According to the earthquake test results, the max. RMSE values obtained are 2.6 mm for Geodetic Antenna Relative results, 3.4 mm for PPP, 2.4 mm for A10 Relative, 3.8 mm for A10 PPP, 2.9 mm for UBX Antenna Relative and 4.2 mm for PPP. All results have shown that the ZED-F9P-02B GNSS receiver efficiently detects natural frequencies and structural behaviors.