Experimental Techniques最新文献

Electromagnetic pulse welding (EMPW) is a solid-state joining technique for similar and dissimilar metals. In present work, analysis of the joining between aluminium (AA6061) and stainless steel (SS316) is attempted. A numerical analysis is carried out to establish the relation between electromagnetic and mechanical parameters such as current density, magnetic field, lorentz force, velocity, temperature, and load-bearing capacity. The aluminium alloy tube is joined with the steel rod at varying operating parameters such as voltage (19 and 20 kV), energy (30 and 36.1 kJ), capacitance (150 and 200µF), stand-off distance (1.0, 1.5, 2.0, and 2.5 mm). The joint strength of 114 MPa was obtained at 2.0 mm SOD for 30 kJ of energy and 460 m/sec of impact velocity. Microstructural analysis confirms the formation of wavy and micro-porous interfaces. A severe plastic deformation causes the localized melting of the interface, leading to intermetallic phase formation. A high hardness of ~ 520HV_0.5 was observed at the interface as compared to base metals. A leak-proof test using the hydraulic pressure technique shows no leakage at 100 kg/cm² pressure.

Earthquake is one of the most devastating natural hazards, causing severe consequences worldwide. The direct shear tests provided practical approaches to reveal the shear instability and failure of faults. The undesired friction between the normal loading platen and the specimen edge in the direct shear testing system has a nonnegligible influence on accurately observing the shear rupture process and the slip mechanism of faults or rock discontinuities. Consequently, the instability and failure process of geomaterial discontinuities has been widely evaluated using the double-direct shear tests under static loading. Meanwhile, the dynamic shear rupture and slip process on the fault under in-situ stresses is crucially responsible for investigating the rupture speeds, rupture propagation, and rupture mechanism of the discontinuities. However, the existing double-direct shear methodology and system are not valid for conducting dynamic double-direct shear experiments under high loading rate conditions. Thus, to evaluate the dynamic slip process of discontinuities, a novel dynamic double-direct shear experimental methodology was proposed in this study. The Hopkinson bar is used to exert dynamic shear force on the discontinuities, and the biaxial static loading system is designed to apply normal stress on the discontinuities. The 2D displacement field of the double-fault structure under dynamic loading conditions is quantified to reveal the dynamic slip process of faults. The results indicate that both the dynamic loading rate and the normal stress have considerable effects on the peak shear stress of faults. The displacement of the upper discontinuity is almost identical to that of the bottom discontinuity during the dynamic shear process, demonstrating that this testing system can observe the dynamic shear rupture without the undesired friction. The slip displacements of these two discontinuities are rate-dependent, and the normal stresses effect on the displacement field of these two faults is revealed. Therefore, the proposed dynamic double-direct shear experimental methodology can quantitatively observe the dynamic shear and slip process of faults. This system can be extended to investigate other dynamic responses of faults under complex stress states.

Laser cutting has become a widely used technology in industrial production due to its high precision, fast processing capacity and widespread use in cutting many materials. Laser cutting of polymer materials is a widely preferred processing method. Polymer materials, especially thermoplastics and thermosets, have a wide range of applications and are used in various industries such as construction, automotive, packaging, medicine and electronics. Laser cutting of these materials has many advantages over other conventional cutting methods, as it cuts without contact and provides high precision and control. However, some difficulties are encountered during laser cutting. These difficulties include heat affected zone formation, kerf width at the cutting edge and surface roughness. Therefore, it is important to understand the effect of laser cutting on polymer materials and optimize the cutting parameters to improve the cutting quality. In this study, a comprehensive investigation was conducted to evaluate the effect of different laser cutting parameters (Focal plane, Cutting speed, Laser power) on the cutting quality of polymer materials. 27 different experimental trials were conducted with various combinations and the data obtained were analyzed using machine learning techniques such as artificial neural network (ANN) and adaptive neuro fuzzy inference system (ANFIS). The results of this study provide an important contribution towards determining the optimal cutting parameters for laser cutting of polymer materials and improving the cutting quality.

A physical model consisting of a ball rolling up and down a beam, the latter being subject to forced oscillations from an actuator, was constructed and utilized to track the location of the ball at any instant in time. From this, the response involving the position data collected subsequently enabled for the velocity and acceleration profiles to be determined. A four-bar linkage assembly was engineered and outfitted with an integrated stepper motor to minimize the dynamic unbalance of the motor onto the system and to keep the ball rolling back-and-forth smoothly. The experiment was videotaped to enable data collection of the ball as it rolled through start-and-stop measurements of its position at certain intervals of time. A parametric study on three different spheres consisting of: marble, ABS plastic, and steel, was conducted to gauge differences in the motion data collected based upon the different materials as well as sphere sizes considered. As elaborated upon in the following review of the literature, implications of this study have engineering applications to better understand the dynamics of important mechanisms such as that of pendulum-tuned mass dampers, among others, for seismic energy dissipation.

Condition monitoring is a vital tool for engineers to ensure equipment uptime. Piezoelectric sensors are by far the preferred choice for sensors owing to their high dynamic range and performance. While industrial equipments have a monitoring system based on vibration or lubrication quality, small-scale commercial equipments may not have such sensors and monitoring systems owing to the associated cost and complexity of the system. MEMS based accelerometers are currently popular for a wide range of consumer hardware due to their low cost and satisfactory dynamic range. While a budget MEMS accelerometer cannot be directly compared to standardized piezoelectric accelerometer, they are just a fraction of the cost and have a frequency response range which are suitable for most generic machines. Machines such as water pumps, gearboxes, compressors, exhaust fans and motors in combination with integrated MEMS sensors and IOT hardware will allow for development of smart machines. These machines can stay connected with a modern home or small-scale commercial automation systems which would provide a user with the real time information regarding the machine’s condition. Selecting the appropriate accelerometer while balancing cost and frequency response can have a significant impact on the health prediction capability. This paper reports a study conducted on the MMA7361 Triaxial accelerometer and its feasibility for simple condition monitoring applications implementing machine learning approaches. A benchmarking test was performed on the MEMS accelerometer and compared with a standard Piezoelectric accelerometer. The MEMS accelerometer was also used to diagnose the fault of a compact bevel gearbox.

Due to X-rays’ ability to penetrate materials, flash X-ray radiography can be used for high-speed measurements where direct optical access is not possible. Choice of detector has a pronounced impact on resulting image quality. Four different detector systems were evaluated with a 450kVp flash source to quantitatively compare image quality metrics. The scintillating digital detector had less image noise than the three different storage phosphor computed radiography detectors across all transmission levels, but lacked the spatial resolution of the computed radiography detectors. For the screens tested here, the HPX-DR digital system had the highest signal to noise ratio of 68.24 and contrast to noise ratio of 35.53, but had a the lowest spatial resolution, resolving 2.5 line pairs per millimeter at 1.78(%) contrast. At a value of 37.59, the Flex GP imaging plate had a signal to noise value above its storage phosphor counterparts under a 450kVp flash source. For radiographic setups typically used for dynamic experiments, the Flex XL Blue and Flex HR detectors had signal to noise ratios of 18.44 and 26.56 respectively. The highest resolved spatial frequencies of the Flex GP, Flex XL Blue, and Flex HR with the flash source are 3.85, 5.00, and 3.85 line pairs per millimeter, respectively. The Flex GP detector had the best combination of signal to noise ratio, contrast to noise ratio, and spatial resolution under a flash source.

Folding wings are used in the design of rockets or airplanes to increase space and maneuverability. To ensure proper operation of the folding wing mechanism, some free play is required, causing it to behave non-linearly. This research uses a nonlinear method based on frequency response functions, considering the structure connection's geometry, by creating a nonlinear dynamic model of the assembled structure and through the structural coupling method that includes free play in the connections. Also, a new technique is presented that uses the results of the substructure method to extract energy diagrams, which are useful in determining the frequency range in which linear and nonlinear modes are coupled. These results are significant for understanding the behavior of the structure under aerodynamic loads and optimizing its performance. To verify the results, nonlinear sinusoidal vibration experiments and finite element analysis were performed. The extracted dynamic model in each frequency mode allows for examining the linearity or nonlinearity, stiffness or softness of the modes, and determining the degree of nonlinearity.

The torque transmissibility frequency response functions of four torque converters were measured over a range of operating conditions. In previous works, frequency response function measurements of torque converters contained test setup dynamics which dominated the measurements. Thus, a unique torque converter dynamometer was deployed to measure said frequency response functions and to quantify torsional vibration isolation performance. The frequency response of the hydro-mechanical torque converter was measured under simulated powertrain boundary conditions and separate from other powertrain dynamics. The tested hardware variations covered a range of K-factor, diameter, and lockup clutch damper architectures. The experimental results demonstrated the presence of a damper mode (only present in the turbine damper architectures), which showed that the open torque converter transmits enough torsional vibration to excite downstream damper springs. A lumped parameter model of the torque converter and test setup, containing a widely used hydrodynamic torque converter sub-model, was also validated with the test data. The hydrodynamic torque converter behaved like a low pass filter in the frequency domain, and its performance was characterized with a cutoff frequency. The best correlated model had an average percent error of 10% in the 0–10 Hz frequency range, showing that an accurate prediction of the frequency response could be obtained in the 0–10 Hz range from the hydrodynamic torque converter model. The lumped parameter model consistently overpredicted the natural frequency of the damper mode, and inertial coupling between the working fluid and mechanical torque converter elements or the sensitivity of friction parameters were presented as possible explanations for the natural frequency error.

This study introduces an innovative method for testing the durability of linear actuators using compression springs in a reciprocating motion. The method applies a resistive load to the actuator for a number of cycles, simulating its operational environment. The method is notable for being cost-effective to produce, easy to operate, and characterized by minimal complexity and few moving parts. The load is quantified through a combination of load cell measurements and a precision weighing controller, while the theoretical load is derived from spring specifications and electric current data from the actuator’s software controller. Comparative analysis between the empirical data and FEA results demonstrates the accuracy and versatility of this testing method. This approach allows for customizable resistive load adjustments, ensuring that linear actuators meet stringent standards and specifications prior to deployment. The integration of both empirical measurements and FEA provides a robust framework for assessing actuator durability and performance.