Morphometric Study of Craters on Saturn’s Moon Rhea

Morphometric studies of impact craters on icy moons can be used to understand modification of crater topography. Several processes (e.g., viscous relaxation, ejecta deposition, repeated and overlapping impacts) act to shallow crater depth and relax the crater wall slope to similar or varying extents. Resolving these processes can help constrain the interior structure and surface properties of icy moons. Here, using morphometric measurements of craters on Rhea, we aim to constrain the processes that led to the observed crater population. We measured crater diameter, depth, and wall slope, as well as overall crater morphology (e.g., simple versus complex craters). Our results indicate that there exists a linear correlation between impact crater depth-to-diameter ratio and crater wall slope. This may suggest that the dominant modification process on Rhea is one that affects both properties simultaneously, which supports past heating events as the primary post-impact modification process. Additionally, the simple-to-complex crater transition for Rhea was found to be 12 ± 2 km, which is consistent with reported transition diameters for comparably sized icy bodies, indicating similar surface properties. A transition to shallower crater depths for large complex craters was not documented, indicating the absence of a rheological transition at depth in Rhea’s icy lithosphere, which may support the interpretation that Rhea is not fully differentiated.

Time-Domain Analysis of Tamper Displacement during Dynamic Compaction Based on Automatic Control

Crater depth is a vital issue in dynamic compaction (DC) because it is a controlling parameter in DC and a characterization index of soil properties. A continuous mathematical model capturing the time-domain process of tamper displacement is presented in this paper. The model is simple and the parameters involved are easy to obtain. It was found that the accumulated crater depth increases but its increment in the crater depth decreases with multiple impacts. Three groups of large-scale DC tests with 10,000 kN∙m were conducted to evaluate the performance of the proposed model. The results showed that the proposed model captures the typical trends in the tamper displacement of single and multiple impacts. In addition, a concept of the crater depth ratio is proposed based on the proposed model, and the concept is used to evaluate the efficiency of DC and to predict the optimum tamping number of DCs.

Effect of arc extinction on formation of interlayer faulty fusions during consumable electrode arc welding of pipelines

Virtual study is performed using deterministic mathematical model of the welding process to assess the effect of arc interruptions on the formation of the weld pool and seam. It is found that interruptions in arc burning lead to the appearance of craters, the depth of which can reach the thickness of the filling layer. It is shown that the effect of the duration of the interruptions in arc burning on the crater depth depends weakly on the welding speed, but noticeably depends on the spatial position of the weld pool. It is necessary to take into account the criteria for the formation of defects from disturbances in the thermal circuit of the arc when analyzing of the welding monitoring data.

Laser-induced ablation of tantalum in a wide range of pulse durations

We present data and analysis of the laser-induced ablation of pure tantalum (Ta, $$Z=73$$ Z = 73 ). We have identified different physical regimes using a wide range of laser pulse durations. A comparison of the influence of strongly varying laser pulse parameters on high-Z materials is presented. The crater depth caused by three different laser systems of pulse duration $${\varDelta }\tau _1=5\,\mathrm {ns}$$ Δ τ 1 = 5 ns and wavelength $$\lambda _1=1064\,\mathrm {nm}$$ λ 1 = 1064 nm , $${\varDelta }\tau _2=35\,\mathrm {ps}$$ Δ τ 2 = 35 ps , $$\lambda _2=355\,\mathrm {nm}$$ λ 2 = 355 nm and $${\varDelta }\tau _3=8.5\,\mathrm {fs}$$ Δ τ 3 = 8.5 fs , $$\lambda _3=790\,\mathrm {nm}$$ λ 3 = 790 nm are analyzed via confocal microscopy as a function of laser fluence and intensity. The minimum laser fluence needed for ablation, called threshold fluence, decreases with shorter pulse duration from $$1.10\,\mathrm {J/cm}^2$$ 1.10 J / cm 2 for the nanosecond laser to $$0.17\,\mathrm {J/cm}^2$$ 0.17 J / cm 2 for the femtosecond laser.