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.

The state of stress in a structural composite component can influence its integrity, reliability, and safety. In this sense, ultrasonic waves can be used for non-destructive stress measurements based on the acoustoelastic effect that relates wave velocity to the material’s stress state. This work aims to evaluate the acoustoelastic behavior of four types of composite samples made of epoxy resin and carbon fiber. Critically refracted longitudinal (L_cr) ultrasonic waves were employed to obtain the acoustoelastic constants, which relate wave velocity to the stress applied to the samples. PMMA wedges, specially designed for each type of sample, were used to generate the L_cr waves. The results showed that the acoustoelastic constants’ values are higher for samples with more layers of laminate with fiber direction coinciding with the wave propagation direction. The acoustoelastic constants obtained experimentally in this paper can be used in the future for stress evaluations of the composites studied in this work.

Tribological performance of epoxy (EP) composites reinforced with short glass fibers (SGF), graphite, polytetrafluoroethylene (PTFE), and B₄C nanoparticles was investigated under oil lubrication. The effects of different types of SGF, graphite, PTFE, and B₄C nanoparticles on the friction and wear properties of EP were examined using a ball-on-block machine. The worn surfaces were characterized using optical microscopy, SEM-EDX, XPS, and TEM. The anti-wear mechanisms were proposed based on the experimental observations and analysis. The results demonstrate that the addition of SGF significantly reduces wear and friction in the EP matrix. In contrast, the incorporation of B₄C nanoparticles and other solid lubricants does not have a significant effect on friction and wear. The remarkable tribological properties observed in the SGF-reinforced EP composites can be attributed to the superior load-bearing capabilities and wear durability of SGF. These fibers effectively withstand the load and exhibit excellent durability during sliding, resulting in reduced wear and friction.

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.