We conducted four sets of impact experiments using sedimentary rock targets and three different kinds of projectiles at a variety of impact angles in order to examine how the density of a projectile affects the dimensions of a crater as the angle of impact decreases, the threshold angle for the formation of elliptical craters, and the threshold angle for the formation of pits. The crater profiles, crater volume, equivalent diameter, length, width, depth, and ellipticity of each set were carefully measured to be used in comparison with small craters that formed on the weak rocky surfaces of planetary bodies. The results indicate that the crater volume, equivalent diameter, width, and depth decrease with the impact angle, while the length of the crater within a set does not decrease monotonically with impact angle. This trend in crater length is consistent with the results of previous studies. Although craters formed at higher impact angles have a central pit, the pit becomes unclear and eventually disappears as the impact angle decreases. A larger threshold angle is required for the formation of pits at slower impact velocity than at higher impact velocity. Our results suggest that the presence of a central pit is indicative of impacts at higher angles and/or higher velocity. The ratio of the volume of craters resulting from oblique impacts to that of craters formed by normal impacts was proportional to the power of the sine of the impact angle. The power index was found to range between 1.46 and 2.20, with an average of 1.57. Comparison of the averaged power index to the power index of the π-group crater scaling rules, it is experimentally suggested that the hypothesis indicating that the vertical velocity component controls crater formation is plausible on a brittle target. The threshold angles for the formation of elliptical craters for three different kind of projectiles were almost consistent with those obtained in previous studies. Our results strongly suggested that the threshold angle for the formation of elliptical craters for high-density impactor, such as iron meteorites, are higher than for rocky impactors. We then obtained a relationship between the threshold angle for the formation of pits and the cratering efficiency. It is revealed that the threshold angle for the formation of pits is greater than the threshold angle for the formation of elliptical craters, when the cratering efficiency is in the range 7–30. A well-developed pit-spall structure in the crater may be used to indicate both, the impact angle and the vertical component of the impact velocity.

中文翻译：

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低、高密度弹丸斜向撞击沉积岩的实验研究

我们使用沉积岩目标和三种不同类型的弹丸在不同的撞击角度进行了四组撞击实验，以研究当撞击角度减小时，弹丸的密度如何影响弹坑的尺寸，阈值角度为椭圆形陨石坑的形成，以及凹坑形成的阈值角度。每组陨石坑的轮廓、陨石坑体积、当量直径、长度、宽度、深度和椭圆率都经过仔细测量，用于与行星体软弱岩石表面上形成的小陨石坑进行比较。结果表明，陨石坑体积、当量直径、宽度和深度随着撞击角度的增加而减小，而一组内陨石坑的长度并不随撞击角度单调减小。陨石坑长度的这一趋势与之前的研究结果一致。虽然在较高的撞击角度下形成的陨石坑有一个中心凹坑，但随着撞击角度的减小，该凹坑变得不清晰并最终消失。在较慢的冲击速度下比在较高的冲击速度下形成凹坑需要更大的阈值角度。我们的结果表明，中心凹坑的存在表明存在更高角度和/或更高速度的撞击。倾斜撞击形成的弹坑体积与正向撞击形成的弹坑体积之比与撞击角度的正弦幂成正比。功效指数介于 1.46 至 2.20 之间，平均值为 1.57。将平均功率指数与 π 群陨石坑缩放规则的功率指数进行比较，实验表明垂直速度分量控制陨石坑形成的假设在脆性目标上是合理的。三种不同类型弹丸形成椭圆形弹坑的阈值角度与之前的研究几乎一致。我们的结果强烈表明，高密度撞击体（例如铁陨石）形成椭圆形陨石坑的阈值角度高于岩石撞击体。然后我们获得了凹坑形成的阈值角度与缩孔效率之间的关系。结果表明，当凹坑效率在7-30范围内时，凹坑形成的阈值角度大于椭圆形凹坑形成的阈值角度。陨石坑中发育良好的凹坑剥落结构可用于指示撞击角度和撞击速度的垂直分量。