Particle Sizing by Quantitative Acoustic Emission

Optical Detection of Impact Contact Times with a Beam Deflection Probe

“…Of these, PZ sensors are the most sensitive [30], making them particularly useful to detect low momentum-transfer impacts. Ball-rod [18], [27] and ball-plate [7], [8], [9], [10], [19], [31], [32], [33] experiments involving the detection of ballimpact-induced elastic waves were realized. Long-enough rods allow the elimination of the disturbance caused by the wave reflections.…”

“…All the methods described above were used for ball diameters larger than about 10 mm, which are capable of producing impacts with contact times in the 100 µs range. For impacts involving balls with diameters as small as 35 µm [8], PZ detection of elastic waves seems to be the only alternative due to unmatched sensitivity of this detection technique. McLaskey and Glaser experimented with glass, ruby and hardened steel balls 0.4 mm to 2.5 mm in diameter.…”

“…Accurate measurements of the contact time are not only important in the basic studies of contact mechanisms in order to assess the validity of the proposed theory [2], [3], they are also important in a wide range of different applications related to, for example, contact mechanics, tribology, shot peening, wear, erosion, rock falls, military ballistics, measurements of hardness at high strain rates and granular matter research. Due to its linear dependence on the radius, the contact time of spherical particles impacting thick plates is, for instance, a good criterion for their size [4], [5], [6], [7], [8] whereas particle sizing is an important requirement in many areas of industrial processing and manufacture [8]. If the velocity of the particle is known with some uncertainty, the size of the particle can be determined via its impact with another solid more accurately by measuring the contact time than the maximum force [5], [6], [8], because the contact time has a more gentle dependence on the approach velocity as opposed to the maximum force.…”

“…Due to its linear dependence on the radius, the contact time of spherical particles impacting thick plates is, for instance, a good criterion for their size [4], [5], [6], [7], [8] whereas particle sizing is an important requirement in many areas of industrial processing and manufacture [8]. If the velocity of the particle is known with some uncertainty, the size of the particle can be determined via its impact with another solid more accurately by measuring the contact time than the maximum force [5], [6], [8], because the contact time has a more gentle dependence on the approach velocity as opposed to the maximum force. A sphere drop on a stationary plate or a block is also often used as a standard acoustic source of ultrasonic waves.…”

“…Until now, measurements of short contact times of µs order of magnitude could only be accomplished by PZ detection of elastic waves generated during the impact [7], [8], [9], [10]. The accuracy of such measurements was primarily undermined by the need to remove the distortion effects of the sensor through a numerical deconvolution.…”