Experimental Techniques最新文献

As one of the lightest metal structural materials, there are a broad application of magnesium alloys. In this paper, a second-stage box-shaped product of AZ31 magnesium alloy are formed by deep drawing with sand die. The effects of three different kinds of driving modes on the forming results will be compared. In order to expand the types of sheets, AZ31 magnesium alloy sheet with or without hole in the center are also taken as the research object. The influences of the key parameters such as: temperature, sheet thickness, sand filling height and hole diameter on the drawing performance will be all investigated by the experiments and simulations. The shape, mechanical properties, and surface quality of the box-shaped products will be discussed. Around the above factors, some forming strategies for a good drawing performance are received. The study will show the optimal strategy for the sand die forming of intricate box-shaped products welded from magnesium alloy, contingent upon various actuation modalities.

A novel closed-loop control principle was proposed for precisely controlling the attitude of full-scale aircraft during static test under large deformation. The test system was developed by integrating a displacement acquisition system, an industrial computer platform, a coordinated control system and hydraulic actuators. The displacement acquisition system was employed to facilitate the real-time sensing of the aircraft attitude changes. This was subsequently analyzed by computers to calculate attitude errors, based on which the compensation values were calculated for attitude correction. The correction was converted into voltage signals through an in-house program pre-integrated into the industrial computer platform. Finally, the MTS coordinated control system generates new control parameters based on the voltage signals, enabling a real-time adjustment on the movement of hydraulic actuators, which modifies the aircraft attitude. A device was developed for simulating the deformation characteristics of aircrafts under large deformation. A six-degree-of-freedom restraint system has been installed on the device according to the principle. Experiments were conducted to verify the capability of the approach for precisely controlling the aircraft attitude under various deformation states. Results showed that the aircraft attitudes were all restored to a value close to the theoretical attitude via displacement compensation scheme proposed, with the translational error less than ± 2 mm and the rotational error less than ± 0.02°. Whilst these errors were successfully reduced by applying the compensation algorithm during loading, they cannot be completely eliminated due to the influence of measurement and control errors.

The present study is focused on the reflection and transmission of a longitudinal elastic stress pulse at a discontinuity between two cylindrical bars subjected to impact loading at one end. Experiments were conducted to investigate the propagation of the longitudinal elastic stress pulse in the two cylindrical bars with discontinuities in the cross section and/or material properties using a split Hopkinson pressure bar setup, without a specimen. The reflection and transmission coefficients for stress and energy were investigated across a wide range of cross section and impedance ratios and compared with theoretical predictions from one-dimensional elastic wave theory. The accuracy of the measured reflected and transmitted stress pulses was verified by a two-dimensional axisymmetric dynamic finite element analysis. The applicability and limitations of one-dimensional elastic wave theory were discussed in terms of wave dispersion.

With the rapid development of micro/nano-electromechanical systems (MEMS/NEMS), the issue of thermoelastic coupling and buckling in micro/nano-structures has become a key area of research. The classical continuum mechanics theories struggle to effectively detail the mechanical characteristics of micro/nano-structures under non-uniform temperature distributions, the current research primarily concentrates on the micro-scale effects of single strain fields, with limited analysis on the combined impacts of thermal and mechanical nonlocal effects. This paper explores the thermomechanical buckling of micro/nano-beams under nonuniform temperature distributions using nonlocal strain gradient theory with thermal considerations. The study finds that nonlocal effects in micro-scale phenomena lead to a decrease in critical load, while higher-order strain gradients tend to increase the critical load. Additionally, thermal effects also contribute to an increase in critical load. It is known that buckling can affect the load-bearing capacity and stability of a structure, thereby ensuring the safety and reliability of structures in engineering. The present study focuses on enriching micro-scale theories for stability analysis of micro/nano-scale structures, consequently offering valuable insights for enhancing structural stability and optimizing the performance of micro/nano devices.

Recently, there has been significant interest in mechanical joint identification through dual substructure decoupling. In this method, each component of a complex mechanical system is handled as an independent substructure. The joint is then identified by subtracting the measured dynamics of the connected subsystems from those of the assembled system. A major challenge with this approach is the need to measure both translational and rotational Frequency Response Functions (FRFs) at the interface between subsystems (interface DoFs). This is often impractical due to the limited space available to place instrumentation. To address this challenge, several techniques available in the literature can be used to derive FRFs at the interface between components using the available measurements. This paper presents a comparative study of three joint identification methods that use two state-of-the-art techniques for obtaining the interface FRFs required for the decoupling process, based on available measurements: Virtual Point Transformation (VPT) and System Equivalent Model Mixing (SEMM). In particular, the advantages and disadvantages of the three methods that combine decoupling with VPT, SEMM, or both, are discussed. Special attention is given to the error propagation associated with each technique. The study is conducted using experimental data from a laboratory benchmark. The results show that the direct VPT approach and the one combining SEMM with VPT give similar results, suggesting that the SEMM is able to accurately reconstruct the FRFs at the boundary DoFs.

Mechanical vibrations, which adversely affect the surface quality of machined components, pose critical challenges in machining processes. This study uses a predictive diagnostic performance system (PDPS) and ChatterPro software to investigate the relationship between vibration signals and surface quality. Experiments were conducted on a milling machine at various spindle speeds, with ten machining tests repeated five times under identical parameters, using consistent material and tooling for side milling. Vibration signals were processed through PDPS and analyzed via principal component analysis (PCA). The principal component distribution map and the correlation between chatter frequency and surface roughness were examined. The surface roughness measurements in the five groups with lower chatter vibrations (groups 1, 2, 3, 7, and 8) ranged from 0.36 to 0.68 µm, while those in the five groups with higher chatter vibrations (groups 4, 5, 6, 9, and 10) ranged from 0.98 to 2.26 µm. This demonstrates a proportional relationship between surface roughness and chatter frequency. Results indicated that increased chatter frequencies were associated with rougher surface finishes. This analysis demonstrates how specific vibration signals can detect chatter and assess cutting conditions in real-time. In future applications, software-based detection of vibration signals could allow for real-time monitoring of machining processes, enabling machine networking, mobile alerts, and reduced operator supervision.

Ultrasonic thermography, also known as sonic infrared imaging, is a promising technique that excites ultrasonic elastic waves and is commonly used in the automotive and aerospace sectors to detect and evaluate flaws in solid specimens. This method employs ultrasound-generated thermal waves to enable defect-specific imaging. The present paper reviews new findings and significant advancements in ultrasonic thermography. The paper is structured as follows: an introduction to ultrasonic thermography is first provided, followed by a discussion on improvements made to enhance the reliability of vibrothermography. Next, an analytical study of different excitation methods and structural parameters is presented, along with an examination of the effects of various excitation parameters on the system's performance. Subsequently, a vibration monitoring method is introduced. Finally, the key causes of heat generation in this technique, along with analytical approaches, critical factors, and limitations in vibrothermography, are discussed.

Engineering components such as bearings, pistons, and sliding contact are subjected to wear losses, and understanding and quantifying wear rates are essential for designing and maintaining various engineering components. The present work employs a dimensional analysis to derive a relationship for finding the specific wear rate. A comprehensive investigation of wear was carried out using the linear reciprocating wear method through the lens of dimensional analysis. The dimensional analysis is a promising method for developing a relationship between the dependent and independent variables. A Taguchi L27 full factorial (3³) orthogonal array experimental design was considered in executing the experiment for the data collection. The developed mathematical relation was further validated with the experimental result, and the best-obtained result supports the experimental result with a 2.34% error.

The rolling resistance of pneumatic tires is one of the important factors that affects the mechanical properties and fuel consumption of vehicles. This paper presents work the authors carried out in theoretical modeling and experimental research of tire rolling resistance. The aims of this research and paper are to reveal the active mechanism of tire rolling resistance, to develop a method of calculating the rolling resistance coefficients, and to research a new test method for measuring rolling resistance parameters. Firstly, the energy dissipation mechanism of tire tread rubber and the action mechanism of tire rolling resistance are analyzed. A hysteretic force model for tire tread rubber is developed based on the brush model framework. A tire rolling deformation detection system is subsequently designed by means of strain sensor technology. Furthermore, a novel calculation method for the rolling resistance coefficient and rolling resistance, integrating the rubber dissipative mechanism with the hysteretic force model, is presented. The findings indicate that an increase in the vertical load of the rolling tire leads to a reduction in rolling radius and an elongation of the rolling contact patch. Additionally, as both the vertical load and rolling speed increase, the tire's rolling deflection becomes more pronounced. A comparative analysis reveals that the discrepancy in rolling resistance between experimental and simulated results remains within 10%, thereby confirming the feasibility of the proposed tire rolling resistance model.

Fatigue damage represents a significant risk to the structural integrity of engineering components. However, current experiments on fatigue crack propagation struggle to fundamentally elucidate the mechanisms governing crack initiation and propagation. Based on the Digital Image Correlation (DIC) method, this article investigates techniques that effectively measure the displacement field at the fatigue crack tip. Methodologically, the traditional DIC displacement mode has been refined to introduce incomplete second-order displacement shape functions, findings indicate that a suitable incomplete second-order displacement function closely approximates the second-order shape function in terms of measurement accuracy, yielding an additional 12% improvement in measurement efficiency. Regarding instrumentation, the integration of an electrically tunable lens (ETL) into DIC is employed to establish a zoom Two-Dimensional Digital image correlation (2D-DIC) measurement system. This configuration effectively addresses the focusing challenge inherent in traditional small Field-of-View (FOV) 2D-DIC systems, facilitating efficient experimental measurements. Moreover, a speckle translation-based method is introduced for calibrating the distortion coefficients of zoom 2D-DIC, thereby alleviating the considerable calibration workload associated with ETL. Ultimately, the deformation field at the small-scale fatigue crack tip is measured to validate the practical utility of the developed measurement system and the effectiveness of the enhanced displacement shape functions.