The ricochet of spherical projectiles off sand

Plough development with time has been studied for the ricochet of 1 in. dia. spherical projectiles off sand for various entry speeds 0(10²) m/sec but with a fixed initial impact angle of 15°. Results show that retardations, of the order of 10⁵ m/sec², are associated with the penetration phase and that instantaneous longitudinal retardations are proportional to velocity squared; in the ascending phase retardations are very much smaller and the speed almost constant.The critical angle of ricochet is also shown to depend slightly on speed. For a 0·5 in. ball the critical angle reduces from 20° at 100 m/sec to 18° at 375 m/sec.     

The ricochet of dumb-bell shaped projectiles

Retardations and rotations were measured for five double-ended or dumb-bell shaped (d.s.) projectiles having spheres separated by a light weight rod at specific distances. The projectiles were fired into sand at approximately 100 m/sec and at an impact angle of 10°. Experimental data indicate that for identical sizes of sphere, initial speed, impact angle and projectile mass, the forces of ricochet are independent of the interspherical distance and seem to depend only on the geometry of the leading face.Tests were also carried out with two spherical and five d.s. projectiles at various entry speeds with 5°, 10° and 15° impact angles and it was found that the crater volume in sand is proportional to the initial momentum of the projectile.     

High velocity oblique impact and ricochet mainly of long rod projectiles: An overview

A review of the literature on high velocity oblique impact and the ricochet of projectiles of various shapes is given, with emphasis on long rod projectiles. Aspects of cratering and penetration in oblique impact are highlighted and the mechanics of ricochet off solid, fluid and granular media are also discussed.     

The effect of spherical projectile speed in ricochet off water and sand

Experimental results are reported for the ricochet of steel and duralumin spheres ( and 1 in. dia.), from shallow depths of water and dry sand. The critical angle for ricochet off water is shown to increase with speed to approach the theoretical limit of . For ricochet off sand the critical angle decreases with speed but a cut-off angle exists, , for which no ricochet occurs at any speed.     

The ricochet of spheres and cylinders from the surface of water

A theory of ricochet is proposed which permits the effect of projectile spin to be accounted for. This effect is not explained by previous theories. The critical angles for ricochet for a sphere and for a spinning cylinder are calculated, and the theory of the spinning cylinder is applied to the Barnes Wallis “bouncing bomb” developed during World War II.     

入射角对跳弹现象影响的数值模拟

利用ANSYS/LS-DYNA3D有限元分析软件,选择适当的弹丸和土壤材料参数建立了弹丸侵彻靶板的有限元实体模型,在同一初始入射速度条件下,对弹丸不同入射角斜侵彻半无限厚土壤靶进行了数值模拟.结果表明当入射角不大于75°时不能出现跳弹现象,当入射角由小变大时,弹丸从侵入靶板演变为出现跳弹现象,随着入射角的增大,越容易产...     

Plasticine modelled high velocity oblique impact and ricochet of long rods

A review of the literature on high velocity oblique impact and the ricochet of projectiles of various shapes is given, with emphasis on long rod projectiles. Aspects of cratering and penetration in oblique impact are highlighted and the mechanics of ricochet off solid, fluid and granular media are also discussed.     

Acoustic-emission location of flaws during multiple-run welding of contours with complex shapes

A modified tabular method for locating acoustic-emission signals, which is intended for determining the coordinates of flaws when inspecting a multiple-run welding process with a lower error rate, and the result of using this method for determining the coordinates of flaws when welding a circular contour using a piezoelectric antenna, which consists of four acoustic-emission transducers, are considered. It is shown experimentally that the application of the modified tabular method allowed an increase in the accuracy of determining the coordinates of introduced flaws when using the acoustic-emission testing method.     

Parameterization of prismatic shapes and reconstruction of free-form shapes in reverse engineering

This article proposes an adaptive loss function (AL) control chart for statistical process control (SPC). This chart is able to monitor process shifts in the mean and variance simultaneously. It is appealing for its effectiveness in detecting process shifts and simplicity in operation under a computerized SPC environment. By using a fixed sample size and a fixed sampling interval, the AL chart can be operated as easily as the conventional ${\bar X}$ and S charts from the stand of the operators. Nevertheless, via the computer-aided adaption of some charting parameters, the AL chart is not only significantly more effective than the ${\bar X}$ and S charts, but it also outperforms the cumulative sum (CUSUM) charts for most of the combinations of mean and increasing variance shifts.     

Thermal stress developed during the laser cutting process: consideration of different materials

The laser cutting of metallic substrates results in the development of thermal stresses around the cut edges. Depending on the cutting speed, laser power intensity, and material properties, stress levels reaching and exceeding the yielding limit of the substrate material can result. In the present study, the laser cutting situation is simulated and temperature as well as thermal stress fields are computed for steel, Inconel 625, and Ti-6Al-4V alloy. The cutting speed of the laser is considered to be constant and a constant temperature heat source with a focused spot diameter is assumed along the kerf surface at the cut edge, resembling the laser heat source. The equations for energy and thermal stresses are solved numerically using the finite element method (FEM). It is found that the temperature decays sharply in the vicinity of the cut edges and that the equivalent stress attains high values in this region. Inconel 625 results in the highest thermal stress levels in the vicinity of the cut edges and is then followed by steel and titanium alloy.     

Elastic modulus and thermal stress in coating during heat cycling with different substrate shapes

The elastic modulus of a deposit (E_d) can be obtained by monitoring the temperature (∆T) and curvature (∆k) of a one-side coated long plate, namely, a one-dimensional (1D) deformation model. The aim of this research is to design an experimental setup that proves whether a 1D deformation model can be scaled for complex geometries. The setup includes a laser displacement sensor mounted on a robotic arm capable of scanning a specimen surface and measuring its deformation. The reproducibility of the results is verified by comparing the present results with Stony Brook University Laboratory’s results. The ∆k-∆T slope error is less than 8%, and the E_d estimation error is close to 2%. These values reveal the repeatability of the experiments. Several samples fabricated with aluminum as the substrate and 100MXC nanowire (Fe and Cr alloy) as the deposit are analyzed and compared with those in finite element (FE) simulations. The linear elastic behavior of 1D (flat long plate) and 2D (squared plate) specimens during heating/cooling cycles is demonstrated by the high linearity of all ∆k-∆T curves (over 97%). The E_d values are approximately equal for 1D and 2D analyses, with a median of 96 GPa and standard deviation of 2 GPa. The correspondence between the experimental and simulated results for the 1D and 2D specimens reveals that deformation and thermal stress in coated specimens can be predicted regardless of specimen geometry through FE modeling and by using the experimental value of E_d. An example of a turbine-blade-shaped substrate is presented to validate the approach.     

大型异形件冲模凹模设计

阐述了镶拼式组合凹模的冲模结构特点 ,着重介绍了组合凹模的设计要求 ,通过实例 ,分析了冲模分块位置及分模面设计。     

承墙基础梁与其他基础梁在设计中的区别

通过内力分析论述承墙基础梁与其他基础梁的区别。     

考虑定位力及波纹力的电磁悬架作动器波动力抑制方法

针对轮边驱动电动汽车设计了一种直驱式的电磁悬架作动器。针对作动器存在的电磁力波动大的问题,提出了从空载定位力及负载波纹力两方面进行抑制的方法。建立作动器的磁场理论计算模型,通过对绕组磁链及感应电动势进行解析,验证了有限元模型的正确性。空载情况下基于有限元模型参数化分析了端部齿长度对定位力的影响,改进了定子长度。以感应电动势总谐波畸变率THD值作为评价指标,考虑了负载情况下的波纹力,通过改进槽口的宽度,以减小THD值及电磁力的波动。结果表明：当定子长度为182 mm时,定位力最小为24.0N,减小了75.6N;当槽口宽度为4.5 mm时,感应电动势THD值最小为4.5%,波纹力减小了3.2N。改进后作动器电磁力波动值仅为20.8N,降幅为80.1%,有效解决了波动力大的问题。     

双管齐射武器弹丸速度和着靶坐标测试方法研究

为了解决靶场测试中对于双管齐射武器飞行矢量和着靶坐标的测量问题,提高测试精度,介绍了一种基于多幕面装置的非接触测试方法.文中详细介绍了装置的构成,分析了测试方法的原理,并利用MatLab软件进行了仿真测试,根据其技术特点和仿真结果,对工程应用存在的实际问题进行了讨论.装置系统可以完成对双管齐射武器的测试,能够区分弹丸穿...     

Grinding Forces in the Presence of Ultrasound

Formulas are derived for calculation of the grinding force in the presence of ultrasound whose amplitude changes the microcutting kinematics of the abrasive grains. The formulas are verified experimentally.     

滚柱轴承离合器的运动及受力分析

对滚柱轴承离合器进行了运动及受力的分析,推导了滚柱轴承离合器轴向位移量ΔＬ与工作扭矩Ｍ之间的关系,并讨论了载荷与应力分布和预紧弹簧的预紧力,为我国开发设计同类产品提供了理论依据。     

丝锥槽形的计算机辅助设计与改进

主要介绍丝锥槽形的改进和加工不同金属材料时丝锥槽形的设计.尤其被加工材料是特种金属时,根据丝锥所适合的前角、刃瓣、心径以及所允许容屑槽大小,运用计算机辅助设计改进丝锥槽形,使得丝锥前角、槽底圆弧以及齿背角光滑连接,切屑成流线形卷屑.生产实践表明,该方法有效地规范了丝锥槽形的设计与制造,提高了产品质量.