AI中文摘要
岩石天体(如行星或小行星)的表土通常在不同于地球的重力条件下沉降。颗粒材料的行为在不同重力下难以缩放。为了预测这些高度复杂的系统,其中颗粒间的粘性力可与重力相当,我们需要模拟和实验。我们在变化的低重力下对三种不同颗粒样品进行了沉降实验,并检查了它们的堆积密度。我们使用高精度线性平台在ZARM落塔提供的零$g$环境内人为诱导低重力,并观察样品的沉降。三种样品为:粒径$1 ext{-}200\,μ$m的细玄武岩、$2 ext{-}5\,$mm的粗玄武岩和$750 ext{-}1000\,μ$m的玻璃珠。人为重力为$150,\,250,\,500,\,750$和$1000\,$mm/s$^2$,因此范围从小行星重力到接近月球重力。我们观察到颗粒样品在较低重力下体积更大,因此堆积密度更低;我们还发现细玄武岩对重力变化最敏感,在$250\,$mm/s$^2$时体积增加$+19.6\,\%$,其次是粗玄武岩,在$150\,$mm/s$^2$时增加$+12.2\,\%$,而玻璃珠的堆积密度对重力变化最不敏感,在$250\,$mm/s$^2$时增加$+4.25\,\%$。通过这些实验,我们表明体积变化不仅取决于粒径,还取决于粗糙度和均匀性,我们提供了真实实验数据以验证理论工作,并强调了低重力环境中粘性力的作用。
英文摘要
The regolith of rocky bodies, such as planets or asteroids, generally settles under gravity conditions different from those of Earth. The behavior of granular material is not easily scalable for different gravities. To predict these highly complex systems where cohesive inter particle forces can be comparable to gravitational forces, we need simulations and experiments. We did experiments on settling of three different granular samples in varying reduced gravities and examined their packing densities. We used a high precision linear stage to artificially induce reduced gravities inside the zero $g$ environment provided by the ZARM drop tower and observe the settling of our samples. The three samples were fine basalt with particle diameters of $1\text{-}200\,μ$m, coarse basalt with $2\text{-}5\,$mm and glass beads with $750\text{-}1000\,μ$m. The artificial gravities were $150,\,250,\,500,\,750$ and $1000\,$mm/s$^2$ and therefore ranged from large asteroid gravity to almost moon gravity. We saw the granular samples have higher volumes in lower gravities and therefore lower packing densities, we also saw the fine basalt be the most sensitive to changes in gravity, up to $+19.6\,\%$ in volume for $250\,$mm/s$^2$, followed by the coarse basalt particles, up to $+12.2\,\%$ for $150\,$mm/s$^2$ and the glass beads packing density being the least sensitive to changes in gravity, up to $+4.25\,\%$ for $250\,$mm/s$^2$. With these experiments we show change in volume is not solely dependent of particle size but also roughness and uniformity, we provide real life experimental data to validate theoretical works and highlight the role of cohesive forces in low gravity environments.