Abstract
This work describes the results of a test campaign aimed to measure the propagation of longitudinal, torsional, and flexural stress waves on a drill bit during percussive rock drilling. Although the stress wave propagation during percussive drilling has been extensively modeled and studied in the literature, its experimental characterization is poorly documented and generally limited to the detection of the longitudinal stress waves. The activity was performed under continuous drilling while varying three parameters, the type of concrete, the operator feeding force, and the drilling hammer rotational speed. It was found that axial stress wave frequencies and spectral amplitudes depend on the investigated parameters. Moreover, a relevant coupling between axial and torsional vibrations was evidenced, while negligible contribution was found from the bending modes. A finite element model of the drill bit and percussive element was developed to simulate the impact and the coupling between axial and torsional vibrations. A strong correlation was found between computed and measured axial stress spectra, but additional studies are required to achieve a satisfactory agreement between the measured and the simulated torque vibrations.
Highlights
Sensors 2021, 21, 3677. https://The mining and construction industries exploit percussive drilling to bore and fragment natural rock or concrete
Scale factors of the strain gauges were analytically determined using the known elastic properties and geometry of the drill bit and the gain factor introduced in the measurement chain by the conditioning unit
Complete characterization of the stress wave propagation was performed during percussive drilling on different working conditions, varying the drill rotational speed, the operator feeding force, and the type of worked material
Summary
Sensors 2021, 21, 3677. https://The mining and construction industries exploit percussive drilling to bore and fragment natural rock or concrete. The mining and construction industries exploit percussive drilling to bore and fragment natural rock or concrete. Due to the combined action of drilling and thrust, a high rate of penetration can be achieved. Percussive drilling breaks rock using consecutive blows aimed to create a crack through the worked material while rotation removes the fragmented part. Stress wave propagation occurs through the drill bit. The phenomenon has been well understood and described by analytic modeling in the case of simple and homogeneous geometry [1], i.e., cylindrical bars or rods, but its explanation becomes difficult in most of the practical applications, where real geometries and constraint conditions are present. The mechanics of percussive drilling have been addressed in the literature [2,3,4,5,6]
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