1:45 PM - 3:15 PM
[PPS03-P13] A new method for measuring elastic properties of extraterrestrial materials: Evaluation of elastic wave velocity of irregularly shaped samples
The solar system is thought to have experienced some evolution processes until today, such as the accumulation of gas and dust, and collisions between planetesimals. Among various celestial bodies in the solar system, small bodies (e.g., asteroids) have less metamorphism and contain more primitive information. Along with the chemical and mineralogical properties, the elastic property is one of the important parameters characterizing solid celestial bodies. Elastic property is particularly important in modeling asteroid formation [1] as well as resurfacing effects caused by seismic shaking [2]. In this study, we are developing a new method for measuring elastic wave velocities of extraterrestrial materials.
As representative approaches to measure the elastic wave velocity of rock samples, there are pulse transmission, pulse reflection, and resonance methods. Among them, the pulse transmission method has been used to measure elastic wave velocities of the lunar samples [3], meteorites [4], and rock samples from the asteroid Ryugu [5]. One problem with the pulse transmission method is that, when handling fragile samples (e.g., CI chondrites or Ryugu samples), there is a risk of artificially inducing cracks and/or destruction of samples over the series of sample preparation. To address these issues, this study aims to estimate elastic wave velocities by (i) measuring extraterrestrial material samples embedded in high-strength epoxy resin and (ii) modeling the measured waveforms with numerical simulations.
The development of the method consists of three phases: Select a resin and measure its elastic wave velocity. Apply our method to a simple system (i.e., embedding a flattened sample, whose elastic wave velocities are known, in a resin), and assess the validity of the obtained values. Measure an irregularly shaped sample embedded in resin and estimate its elastic wave velocity.
In this report, we describe the obtained elastic wave velocity of the selected resins (EPOXY RESIN CY 232) in the first phase. We cured four epoxy resins at 40 °C for 15 hours, and then flat-plated them with a grinder to thicknesses of 3, 5, 7, and 10 mm to first verify whether P- and S-waves can propagate through each epoxy sample without significant attenuation.
We have confirmed that P-waves can be clearly received for any thickness cases under a 20 N weight. Whereas, we did not detect transmitted S-waves when the epoxy thickness exceeds 3 mm, which might be attributed to a strong attenuation while traveling the medium. This result suggests that when measuring elastic wave velocities with the selected epoxy resin, the thickness of the target material (i.e., rock samples embedded in the epoxy resin) should be less than 3 mm. We also estimated P- and S-wave velocities for a 3 mm-thick resin sample, and obtained the values of 2.618 ± 0.001 km/s and 1.239 ± 0.002 km/s, respectively. Moreover, to evaluate the reproducibility of the measurements, we measured the elastic wave velocities of several resin samples. Consequently, we found that the elastic wave velocities varied by about ± 0.02 km/s. This value would be an important indicator for evaluating the accuracy of this method in the next phases.
The presentation will outline the new method of measuring elastic wave velocities and report the current status.
[1] Nakamura et al. (2022), Science, DOI: 10.1126/science.abn8671
[2] Honda et al. (2021), Icarus, 336, 114530.
[3] Kanamori et al. (1970), Science, 167, Issue 3918, pp. 726-728
[4] Ostrowski and Bryson, (2019), Planetary and Space Science, 165, pp. 148-178
[5] Ino et al. (2022), The Japanese Society for Planetary Sciences fall meeting 2022, OA-13. (In Japanese)
As representative approaches to measure the elastic wave velocity of rock samples, there are pulse transmission, pulse reflection, and resonance methods. Among them, the pulse transmission method has been used to measure elastic wave velocities of the lunar samples [3], meteorites [4], and rock samples from the asteroid Ryugu [5]. One problem with the pulse transmission method is that, when handling fragile samples (e.g., CI chondrites or Ryugu samples), there is a risk of artificially inducing cracks and/or destruction of samples over the series of sample preparation. To address these issues, this study aims to estimate elastic wave velocities by (i) measuring extraterrestrial material samples embedded in high-strength epoxy resin and (ii) modeling the measured waveforms with numerical simulations.
The development of the method consists of three phases: Select a resin and measure its elastic wave velocity. Apply our method to a simple system (i.e., embedding a flattened sample, whose elastic wave velocities are known, in a resin), and assess the validity of the obtained values. Measure an irregularly shaped sample embedded in resin and estimate its elastic wave velocity.
In this report, we describe the obtained elastic wave velocity of the selected resins (EPOXY RESIN CY 232) in the first phase. We cured four epoxy resins at 40 °C for 15 hours, and then flat-plated them with a grinder to thicknesses of 3, 5, 7, and 10 mm to first verify whether P- and S-waves can propagate through each epoxy sample without significant attenuation.
We have confirmed that P-waves can be clearly received for any thickness cases under a 20 N weight. Whereas, we did not detect transmitted S-waves when the epoxy thickness exceeds 3 mm, which might be attributed to a strong attenuation while traveling the medium. This result suggests that when measuring elastic wave velocities with the selected epoxy resin, the thickness of the target material (i.e., rock samples embedded in the epoxy resin) should be less than 3 mm. We also estimated P- and S-wave velocities for a 3 mm-thick resin sample, and obtained the values of 2.618 ± 0.001 km/s and 1.239 ± 0.002 km/s, respectively. Moreover, to evaluate the reproducibility of the measurements, we measured the elastic wave velocities of several resin samples. Consequently, we found that the elastic wave velocities varied by about ± 0.02 km/s. This value would be an important indicator for evaluating the accuracy of this method in the next phases.
The presentation will outline the new method of measuring elastic wave velocities and report the current status.
[1] Nakamura et al. (2022), Science, DOI: 10.1126/science.abn8671
[2] Honda et al. (2021), Icarus, 336, 114530.
[3] Kanamori et al. (1970), Science, 167, Issue 3918, pp. 726-728
[4] Ostrowski and Bryson, (2019), Planetary and Space Science, 165, pp. 148-178
[5] Ino et al. (2022), The Japanese Society for Planetary Sciences fall meeting 2022, OA-13. (In Japanese)