Search

Copyright of Journal of Ordnance Equipment Engineering is the property of Chongqing University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Rock shed is an effective protection measure against rockfall. To investigate the influences of falling rock’s shape and impact angle on the impact effect of the cushioned rock shed, a modeling approach for a rock shed with a cushion layer using PFC-FLAC. The granular cushion is modeled as an aggregate of discrete non-cohesion particles, while the concrete plate and the beam are modeled as zones. The falling rock with different sphericities and impact angles is modeled as a rigid assembly. The numerical model is validated by comparing the simulation results with experimental and numerical results from previous literature. This model is applied to analyze the effects of rock shape and impact angle on the dynamic interaction effects between falling rock and cushioned rock shed, including the impact force, transmitted bottom force, penetration depth, and plate deflection. The numerical results show that the variation in the falling rock’s shape has different effects on the falling rock with different impact angles. These findings could support rock shed design by revealing the limitations of the assumptions in the past research, which may result in unsafe rock sheds for some rockfall cases.

Abrasive water jet is a highly efficient cutting technology. Through some sandstone cutting tests, the research on the optimal impact angle and inclined cutting mechanism of rock-like materials is carried out. Based on the macroscopic and microscopic observation of the cut’s inner wall, crystal glass cutting experiments are conducted to investigate the cutting motion process of abrasive water jet under different impact angles, revealing the variation laws of cutting depth, the characteristics of the cut’s inner wall, the trajectory of abrasive particles and the type of crystal destruction under different cutting pressures and impact angles. The test results show that the average cutting depth gradually increases with the increase of cutting pressure, while changing the impact angle can significantly change the jet’s cutting ability, and the best cutting effect is obtained at an impact angle of 75°. With the increase of the cut depth, the curved jet trajectory texture gradually appears in the cut’s inner wall , and in its bottom there are typical erosion pits and trailing phenomenon. The cut’s inner wall is mainly characterized by four types of damage features such as fracture through the crystal, fracture along the crystal, cut grooves or pits, and cement coverage, etc. It is worth noting that the four types of damage features appear at different locations in the cut at different impact angles, and this phenomenon is mainly caused by the deflection of jet, the direction of reflected flow movement, and the change in the reflection of shock wave and expansion wave. The vertical and horizontal jet components (in the same direction as the direction of propulsion), which play a dominant role in the destruction of the target, and the horizontal jet component, which is opposite to the direction of propulsion, play a secondary role in the erosion and polishing of the formed cut, but the degree of action varies under different impact angles. The macroscopic model of the abrasive water jet cutting process is established by combining the trajectory texture of cut’s inner wall and the observation results of the jet cutting process. The research results can provide a technical reference for further improving the efficiency of abrasive water jet cutting.

In planetary surfaces, oblique impact events are commonplace, and their study holds significant importance for understanding planetary impact processes and aiding in the design of landers and impactors. Current research predominantly focuses on simplified models to study the force and motion under vertical impact craters in terms of scale and impact loading. For oblique impacts, investigations have primarily concentrated on the final crater shape. However, the specific influence of impact load motion on particle bed movement and the precise impact angle’s effect on the ultimate crater shape during the impact process remain unclear. In this study, we used a custom-built oblique impact experimental setup to analyze changes in the velocity field of the particle bed and the horizontal movement of the impact load. Using quasi-static region to assess ellipticity, we aimed to reveal the state of particle movement during oblique impacts and explore the impact of impact angles and energies on crater formation. The results indicate that under large impact angles, the obliquely acquired kinetic energy is minimal, leading to a predominant static point source movement of the particle bed. At higher energy levels, the impact load primarily excavates downward, resulting in the formation of circular impact craters. These findings underscore the sensitivity of particle bed motion to impact angles, making it a crucial metric for assessing the impact of oblique angles on final crater morphology.

In order to investigate the effect of the carrier's initial velocity on the jet's damage power, this paper conducted the numerical simulation of a jet penetrating thick‐walled targets at various following velocities (the carrier's initial velocity). For large stand‐off distance (D), the influence on jet formation parameters was revealed under different following velocities (ranging from 0 to 1000 m/s), and the jet's penetration performances were analyzed at various stand‐off distances (ranging from 3D to 10D). Then, taking 3D as an example, the study investigated the influence mechanism of the coupling between following velocity and impact angle (ranging from −60° to 60°) on jet penetration performance. The results show that an increase in the following velocity causes the jet to bend and break at an earlier time. The following velocity has a minimal effect on jet tip velocity. Additionally, the lateral displacement is linearly correlated with stand‐off distance. For normal penetration, the jet penetration depth decreases exponentially as the following velocity increases at the same stand‐off distance. Especially, the penetration depth decreases by over 80% when the following velocity exceeds 600 m/s, and a further increase in the following velocity has a minimal effect on jet penetration depth. A greater jet penetration depth was achieved for the climbing‐oblique penetration (COP) than the diving‐oblique penetration (DOP) due to an increase in dynamic stand‐off distance. Finally, the ratio of oblique to normal penetration depth for a jet with varying following velocities was derived based on the theory of steady‐jet and hole expansion, and its accuracy was verified. [ABSTRACT FROM AUTHOR]

The simultaneous oblique impact of multiple droplets on a liquid film is an intricate phenomenon prevalent in diverse natural and industrial processes. However, previous studies have primarily focused on single droplet impact, while an in-depth understanding of the more complex multi-droplet scenario remains lacking. The current study aims to numerically investigate the simultaneous oblique impact of two droplets on a water film using a three-dimensional Volume of Fluid (VOF) model. The effects of the Weber number and the impact angle on the crown behavior are carefully analyzed. The results demonstrate that increasing the Weber number enhances the central uprising sheet height but has minor influences on the upstream crown radius and central sheet radius. In contrast, the increase in the impact angle leads to a decreased upstream crown radius and an increased central sheet radius, while the central sheet height remains relatively unaffected. In addition, the splashing threshold for the dual droplet impact cases is significantly lower than that of the single droplet impact cases due to the interactions between the adjacent crowns. The present results provide novel insights into the underlying physics and useful supports in developing predictive models for the intricate multi-droplet impact phenomenon. [ABSTRACT FROM AUTHOR]

For flood discharge structures with high water heads, aeration facilities are usually installed in engineering to promote water flow aeration and prevent cavitation damage to the overflow surface. Actual engineering has shown that as the slope of the discharge channel bottom decreases or water level changes lead to a decrease in the Froude number, the cavity morphology after conventional aeration facilities or allotype aerators is poor. This article proposes a curved aeration facility scheme based on the idea of locally increasing the bottom slope to reduce the impact angle, which is formed by the convex parabolic bottom plate and concave parabolic bottom plate. The convex parabolic bottom plate is tangent to a flat bottom plate behind the offset, and the concave parabolic bottom plate is tangent to the downstream. The jet landing point is controlled at the junction of the convex parabolic bottom plate and the concave parabolic bottom plate, and the lower jet trajectory is in line with the parabolic bottom plate. The corresponding parabolic bottom plate calculation formulas were theoretically derived, and the design method of the shape parameters of the aeration facility was provided. Through specific engineering case studies, it was found that: (1) As the ZAC/ZAG value increases, point C becomes closer to point G, the slope of the water tongue landing point C becomes steeper, and the cavity is less likely to return water. (2) When the position of the water tongue landing point is 0.5–0.8 times the height of the water tongue impact point, there is almost no water accumulation in the calculated cavity. At this time, the platform length LAB = 0.5LAF, the convex parabolic section length LBC = (0.45–0.6) LAG, the concave parabolic section length LCD = (0.43–0.11) LAG, the convex parabolic section calculation formula is z (x) = −A1x2 (A1 = 0.0059–0.00564), and the concave parabolic section calculation formula is A2x2 − B2x2 (A2 = 0.003347–0.01927).This solved the problem of aeration and corrosion reduction under small bottom slope, large-unit discharge, and low Froude number engineering conditions. [ABSTRACT FROM AUTHOR]

In order to study the deformation and failure law of bolt-mesh support roadway under roof impact load, taking 250104 transport roadway of Huating Coal Mine as background, FLAC3D was used to analyze the variation characteristics of stress, deformation and plastic zone of surrounding rock of bolt-mesh support roadway under different impact load wave velocities, angles and offset distances. The results show that: under the impact of roof load, the plastic zone of roadway roof and rock mass on both sides will gradually expand to upward and both sides, and its maximum displacement will increase exponentially; with the increase of the wave velocity of the roof impact load, the maximum displacement of the roadway roof and two sides will gradually increases exponentially; with the increase of impact angle of roof impact load, the maximum displacement of the roadway roof and two sides presents an “S-shaped” growth curve, and the impact angle of 90° has the most adverse impact on the stability of the surrounding rock of the roadway with bolt-mesh support; with the increase of the impact offset distance of roof impact load, the maximum displacement of roadway roof and impact side rock will increase first and then decrease. When the impact offset distances is equal to 5.0 m, it will pose the greatest threat to roadway safety.

In bloodstain pattern analysis (BPA), a field of forensic science, there has been active discussion on the estimation of the area of origin of impact spatter. However, there is no established methodology to quantitatively analyze the area of origin of a swing cast-off pattern. To quantitatively analyze the methodology of previous research on estimation of area of origin, a device for generating uniform swing cast-off patterns was produced. Using artificial blood, 10 swing cast-off patterns were generated on porous paper; in each, 10 blood drops were selected for the calculation of the impact angle. Hemospat software was used for individual bloodstain analysis, and an open source code was used for estimation of area of origin. Under the same conditions, an additional 10 swing cast-off patterns were generated, and quantitative analysis was performed using trigonometric functions and an adjustment formula that minimized errors in calculating the impact angle. The adjustment formula was corrected to calculate the impact angle for the bloodstains on the porous surface. As uncertainty decreases, the error increases, and the point at which both uncertainty and error can be minimized is calculated as 75%. The existing formula included the trajectory in the estimated likelihood range in 75% of samples. When the adjustment formula was applied, the accuracy was improved, with the trajectory included in the area with a 90% likelihood. [ABSTRACT FROM AUTHOR]

A novel integrated guidance and control scheme is derived for STT missile with strict constraints as desired impact angle, input saturation and partial system state in three-dimensional space. The backstepping technique and command filter are adopted for achieving input constraints, and the improved compensation signals are constructed to correct tracking errors. The integral barrier Lyapunov function is introduced to prevent the partial system states from exceeding a predefined interval. A modified extended state observer is employed to strengthen the robustness of the system further. Theoretically, the required properties of a closed-form system are proved by Lyapunov theory in detail. Numerical simulations are conducted to exhibit the performance and robustness of the IGC scheme fully. [ABSTRACT FROM AUTHOR]

Erosion is a phenomenon and is the primary cause of failure in numerous slurry transportation equipment such as pump impellers, pipeline fittings, etc. It reduces the working life of the equipment and is thus an essential factor in the design, choice, and operation of any system. Pipeline materials used to convey slurry often experience severe wear from erosive forces. Researchers are interested in minimizing erosion wear using different coatings to increase equipment life. The High-Velocity Oxy-Fuel (HVOF) spray technique was employed to deposit WC-10Co-4cr + 2% TiO2 coating on the SS409. The erosion wear was evaluated using a slurry jet erosion tester of uncoated and coated materials with sand as the erodent. The impact of impingement angle, velocity, time, and other parameters was studied. On the erosion wear of uncoated and coated materials, it was found that the influence of jet velocity was greater than the impact of other parameters. The deteriorated surfaces were analyzed using a scanning electron microscope (SEM). The erosion wear resistance of SS 409 was significantly improved by the WC-10Co-4cr + 2% TiO2 coating. The coating demonstrated a brittle mechanism of erosion wear. Furthermore, image processing software investigated the mechanism of erosion wear.

For the study of ship under large angle and high flow velocity and the collision response of large span cable-stayed bridge, Domestic and foreign relevant specifications for maximum impact force calculation method in ship bridge collision and impact was combined, in the process of inland waterway transport possible collision angle and the way was analyzed, and the outer ring of the Chongqing metro, Yangtze river bridge was taken as the project. The models of 7 000-ton bulk carrier and proportional cable-stayed bridge are established by using the additional mass method, and the maximum impact forces of forward collision, side collision and drift collision are calculated at four navigable water levels. The calculated values of each code are compared with the numerical simulation results, and the calculated results of each code under different conditions are compared. The results show that the domestic and foreign codes are more suitable for the ship impacting the bridge tower, and the maximum impact force is much higher than the calculated value of the code when the impact point is located at the bridge cap. In the case of a frontal collision between a ship and a bridge, the calculated values in AASHTO (American Association of State Highway and Transportation Officials) are in high agreement with the simulated values. In side impact, especially when the impact angle is10° ~ 25°, it is suggested to adopt the Specifications for Collision Design of Highway Bridges. The impact force caused by the ship's floating collision with the bridge tower is about 1 / 4 of the forward collision, which can be calculated by the Code for Design of Railway Bridges and Culverts. The research results of multi-angle ship-bridge collision can provide reference for ship-bridge collision safety risk assessment and bridge anti-collision design under high fluctuating water level in the Three Gorges reservoir area. [ABSTRACT FROM AUTHOR]

A 3D finite element (FE) simulation model was built to investigate the synergistic effects of impact and attack angles on the penetration resistance of relatively thin aramid laminates to flatnoded bullets. Two scenarios of the impact responses of a 4-mm-thick aramid laminate were calculated, i. e., considering the impact angle alone and considering the impact and attack angles together. The penetration resistance of the aramid laminate was reflected by the residual velocity of the bullet, the ballistic limit velocity and the perforation energy threshold of the target plate. Deformation and damage mechanisms of the laminate under different impact conditions were also analyzed. The main findings are: (i) the ballistic limit velocity decreases and then increases with the initial impact angle; (ii) with the increasing impact velocity and the decreasing initial impact angle, the changes of the impact angle and the attack angle both tend to decrease; (iii) for a fixed impact angle, a negative attack angle is not conducive to penetration, but a positive attack angle is conducive to penetration. [ABSTRACT FROM AUTHOR]

Copyright of Control Theory & Applications / Kongzhi Lilun Yu Yinyong is the property of Editorial Department of Control Theory & Applications and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The development of high wear/erosion resistance materials for defense application is found to be a challenging task among the researchers. The current study investigated the reinforcement effect of TiC and Rice husk ash (RHA) on Al6061 hybrid composites made using a two-step ultrasonic-assisted stir casting process. Four distinct Al6061 hybrid composites were created with varying TiC weight percentages (3, 6, 9, and 12 wt.%). RHA weight percentage was kept constant at 3%. The solid particle erosion test was carried out on each composite using a Taguchi L27 (33) orthogonal array. Experiments were conducted by varying the erodent particle impact angle, erodent velocity, and erodent discharge rate. The effect of each parameter on the erosion rate of the TiC/RHA Al6061 composite was discussed. The composite containing 12% TiC and 3% RHA showed improved erosion resistance. It was found that on increasing the TiC addition in the composite resulted in an increase in erosion resistance. SEM images were used to examine the surface failure on the composites caused by erodent impact.

Polyurethane is widely used on the surface of composite materials for rotor blades as sand erosion protection materials. The failure mechanism investigation of polyurethane film under service conditions is useful for developing the optimal polyurethane film for rotor blades. In this article, the sand erosion test parameters were ascertained according to the service environment of the polyurethane film. The sand erosion resistance and failure mechanism of polyurethane film at different impact angles were analyzed by an infrared thermometer, a Fourier transform infrared spectrometer (FTIR), a differential scanning calorimeter (DSC), a field emission scanning electron microscope (FESEM), and a laser confocal microscope (CLSM). The results show that the direct measurement method of volume loss can better characterize the sand erosion resistance of the polyurethane film compared to traditional mass loss methods, which avoids the influence of sand particles embedded in the polyurethane film. The sand erosion resistance of polyurethane film at low-angle impact is much lower than that at high-angle impact. At an impact rate of 220 m/s, the volume loss after sand erosion for 15 min at the impact angle of 30° is 57.8 mm3, while that at the impact angle of 90° is only 2.6 mm3. The volume loss prediction equation was established according to the experimental data. During low-angle erosion, the polyurethane film damage is mainly caused by sand cutting, which leads to wrinkling and accumulation of surface materials, a rapid increase in roughness, and the generation of long cracks. The linking of developing cracks would lead to large-scale shedding of polyurethane film. During high-angle erosion, the polyurethane film damage is mainly caused by impact. The connection of small cracks caused by impact leads to the shedding of small pieces of polyurethane, while the change in the roughness of the film is not as significant as that during low-angle erosion. The disordered arrangement of the soft and hard blocks becomes locally ordered under the action of impact and cutting loads. Then, the disordered state is restored after the erosion test finishes. The erosion of sand particles leads to an increase in the temperature of the erosion zone of the polyurethane film, and the maximum temperature rise is 6 °C, which does not result in a significant change in the molecular structure of the polyurethane film. The erosion failure mechanism is cracking caused by sand cutting and impact. [ABSTRACT FROM AUTHOR]

The simultaneous oblique impact of multiple droplets on a liquid film is an intricate phenomenon prevalent in diverse natural and industrial processes. However, previous studies have primarily focused on single droplet impact, while an in-depth understanding of the more complex multi-droplet scenario remains lacking. The current study aims to numerically investigate the simultaneous oblique impact of two droplets on a water film using a three-dimensional Volume of Fluid (VOF) model. The effects of the Weber number and the impact angle on the crown behavior are carefully analyzed. The results demonstrate that increasing the Weber number enhances the central uprising sheet height but has minor influences on the upstream crown radius and central sheet radius. In contrast, the increase in the impact angle leads to a decreased upstream crown radius and an increased central sheet radius, while the central sheet height remains relatively unaffected. In addition, the splashing threshold for the dual droplet impact cases is significantly lower than that of the single droplet impact cases due to the interactions between the adjacent crowns. The present results provide novel insights into the underlying physics and useful supports in developing predictive models for the intricate multi-droplet impact phenomenon.

For flood discharge structures with high water heads, aeration facilities are usually installed in engineering to promote water flow aeration and prevent cavitation damage to the overflow surface. Actual engineering has shown that as the slope of the discharge channel bottom decreases or water level changes lead to a decrease in the Froude number, the cavity morphology after conventional aeration facilities or allotype aerators is poor. This article proposes a curved aeration facility scheme based on the idea of locally increasing the bottom slope to reduce the impact angle, which is formed by the convex parabolic bottom plate and concave parabolic bottom plate. The convex parabolic bottom plate is tangent to a flat bottom plate behind the offset, and the concave parabolic bottom plate is tangent to the downstream. The jet landing point is controlled at the junction of the convex parabolic bottom plate and the concave parabolic bottom plate, and the lower jet trajectory is in line with the parabolic bottom plate. The corresponding parabolic bottom plate calculation formulas were theoretically derived, and the design method of the shape parameters of the aeration facility was provided. Through specific engineering case studies, it was found that: (1) As the ZAC/ZAG value increases, point C becomes closer to point G, the slope of the water tongue landing point C becomes steeper, and the cavity is less likely to return water. (2) When the position of the water tongue landing point is 0.5–0.8 times the height of the water tongue impact point, there is almost no water accumulation in the calculated cavity. At this time, the platform length LAB = 0.5LAF, the convex parabolic section length LBC = (0.45–0.6) LAG, the concave parabolic section length LCD = (0.43–0.11) LAG, the convex parabolic section calculation formula is z (x) = −A1x2 (A1 = 0.0059–0.00564), and the concave parabolic section calculation formula is A2x2 − B2x2 (A2 = 0.003347–0.01927).This solved the problem of aeration and corrosion reduction under small bottom slope, large-unit discharge, and low Froude number engineering conditions.

In this paper, based on terminal sliding mode control (TSMC), a cooperative impact time and angle constrained guidance (CITACG) law for multi-missile system with switching network topologies is proposed. The obtained CITACG is composed of two parts. One part is designed to make the missiles intercept the target from their predetermined impact angles. And the other part’s goal is to make the multiple missiles intercept the target simultaneously without predefining a common impact time. Sliding mode surface of the first part is designed based on TSMC, meanwhile integral terminal sliding mode control (ITSMC) and graph theory are applied to derive the second part of the CITACG. When the communication network switches between the connected topology and the disconnected one, a Lyapunov candidate function is introduced and the corresponding stability conditions are derived. The proposed guidance law is the summation of the two guidance parts, therefore it is a direct method and do not have to switch the guidance command between the impact angle constrained guidance law and the impact time constrained guidance law. The predetermined common impact time is not required in the proposed CITACG, and the missiles can automatically adjust themselves to intercept the target simultaneously by communicating between their neighbors. Numerical simulations demonstrate the great performance of the proposed guidance law. [ABSTRACT FROM AUTHOR]

Copyright of International Journal of Engineering Research & Development (IJERAD) is the property of International Journal of Engineering Research & Development and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The erosion behavior of a QAl9-4 alloy as a ship propeller material was investigated. The effects of the solution, the impact angles and the sand content were considered. The test results demonstrate that the mass loss of the alloy in 3.5 wt% NaCl solution is 1.35 times that in tap water, due to the corrosive effect of Cl−. The mass loss of the alloy increases as the impact angle increases up to ~ 30° and consequently decreases as the impact angle increases. Also, this feature is typical for the ductile metal behavior. At the impact angle of 0°, this feature is associated with the predominant erosion mechanisms, such as shallow plowing and surface fatigue; at 30°, this feature is micro-cutting, deep plowing and surface fatigue; and at 45°, it becomes indentation accompanied by extruded lips. The mass loss and surface roughness of the alloy increase as the sand content increases under the testing conditions. [ABSTRACT FROM AUTHOR]

In this study, the erosion behaviour of wear-resistant WC/NiCrBSi composite coating deposited by the oxy-acetylene flame welding was investigated. The solid particle erosion wear characteristics of the coatings, tribology, and active erosion micro-mechanisms were investigated carefully under three impact angles of 10°, 45°, and 90°. The observations showed that under the low impact angle, the wear behaviour was ductile, and under the normal impact angle, the dominant wear behaviour was brittle. Under the impact angle of 45°, the simultaneous operation of both ductile and brittle behaviours led to a 62% reduction in erosion resistance. Responsible micro-mechanisms for erosion wear under each impact angle were shown by providing accurate images. [ABSTRACT FROM AUTHOR]

In this paper, the research findings on erosion - corrosion of metal materials at home and abroad in recent years were mainly summarized, including research methods of erosion corrosion and external factors affecting erosion corrosion rate. At present, the research methods of erosion - corrosion were mainly carried out in the form of experimental method, supplemented by numerical simulation. The experimental methods primarily included the classification of experimental devices and the collection and characterization of experimental results. Besides, the influencing factors affecting the erosion corrosion rate were classified and compared. The main influencing factors included flow velocity, sand content, sand size， impact angle, liquid pH value, temperature, oxygen content, etc. In the future, the main developing directions of erosion - corrosion would be the following aspects: optimizing the structure of numerical model to predict the erosion - corrosion rate distribution diagram of materials and determining the weak areas of multiphase flow erosion - corrosion.

This paper proposes predefined-time convergent guidance schemes that can drive the pursuer on a collision course corresponding to the target interception from a pre-specified impact direction, irrespective of initial engagement geometries. The target interception at the desired impact angle is first transformed into a problem of controlling the line-of-sight angle and its rate. Then, guidance commands are derived using sliding mode control (SMC) to ensure the convergence of corresponding errors to zero within a predefined time. A nonlinear disturbance observer is used to estimate the target's maneuver, and the estimation error is treated as an uncertainty while rejecting its effect by virtue of SMC. Guidance commands are also derived for the case where the target maneuver is completely unknown except for its upper bound. It was shown that the gain could be selected based on the maximum bound on target maneuver to enforce sliding mode on the chosen surface, and thus guarantees target interception at a pre-specified impact angle, provided the closing speed of the engagement is positive. Owing to the use of a nonlinear framework while deriving pursuer guidance commands, the proposed guidance strategies remain valid even for engagements with large initial deviations where schemes based on linearized dynamics may fail or have degraded performance. The efficacy of the proposed guidance methods is validated through simulations for the pursuers having constant speed and time-varying speed, for various engagement geometries. The results of proposed strategies are compared with those of existing guidance and shown to be superior. [ABSTRACT FROM AUTHOR]

Copyright of Systems Engineering & Electronics is the property of Journal of Systems Engineering & Electronics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, a red-eared slider turtle is used as the prototype for the bionic design of the foamed silicone rubber sandwich structure. The effect of impact angle on the performance of the foamed silicone rubber sandwich structure against low-velocity impact is studied by the finite element method. The numerical model uses the intrinsic structure model of foamed silicone rubber with porosity and the three-dimensional Hashin fiberboard damage model. The validity of the model was verified after experimental comparison. Based on the finite element simulation of different impact angles and velocities, the relationship between impact velocity and residual velocity, as well as the penetration threshold at various impact angles are obtained, and the change law of impact resistance of foamed silicone rubber sandwich structure with impact angle and velocity, as well as the damage pattern of sandwich structure at different impact angles and velocities are given. The results can provide a basis for the impact resistance design of the bionic foamed silicone rubber sandwich structure. The results show that, at a certain impact speed, the smaller the impact angle, the longer the path of the falling hammer along the plane of the sandwich structure, the lighter the damage to the sandwich structure and the greater the absorbed energy, so that avoiding the impact from the frontal side of the sandwich structure can effectively reduce the damage of the sandwich structure. When the impact angle is greater than 75°, the difference in impact resistance performance is only 2.9% compared with 90°, and the impact angle has less influence on the impact resistance performance at this time. [ABSTRACT FROM AUTHOR]

Powder jet machining is a blast machining process in which micrometer-order particles are projected onto a workpiece at near-supersonic speeds, to remove the workpiece (abrasive jet machining (AJM)) or to deposit the particles (powder jet deposition (PJD)). We report a novel dental treatment method for powder jet machining using hydroxyapatite, which is the main component of teeth, as deposited particles. The surfaces and interdental spaces of human teeth are not only flat, but also have complex groove structures. However, PJD and AJM exhibit impact-angle-dependent machining phases. Therefore, it is necessary to investigate the effect of the particle impact angle on machining, before dental treatment. Furthermore, because machining interacts not only with the particle impact angle but also with the particle impact velocity, a comprehensive investigation of the effects of the machining parameters is required, for delineating the phase-transition conditions. Accordingly, in this study, we conducted machining experiments using hydroxyapatite particles (particle diameter, 2.16 μm) and four different blasting angles of 30°, 45°, 60°, and 90°, to infer the machining amount. Machining efficiency was evaluated based on the amount of machining. The impact angles and velocities of the particles were calculated using computational fluid dynamics (CFD). Three-dimensional process mapping was performed using the machining amount, particle impact angle, and particle impact velocity, obtained from the experiments and CFD calculations. The results showed that PJD crossed to AJM at the impact angle of approximately 60°. Moreover, PJD exhibited high processing efficiency for impact angles above 60° and impact velocities in the 280–310 m/s range. In contrast, AJM exhibited high processing efficiency for impact angles below approximately 35° and impact velocities above 310 m/s. [ABSTRACT FROM AUTHOR]

This paper proposes a closed⁃loop homing guidance law with the constraints of the impact time and angle for the intercepting a constant⁃velocity target. In order to achieve the required terminal constraints，the line⁃of⁃sight （LOS） profile of the missile is modeled as a polynomial with one tuning parameter that is selected via an online optimization routine. Then，a terminal sliding mode guidance law is developed to nullify the tracking error within a fixed time. The key feature of the proposed guidance law is that it does not require the information of time⁃to⁃go estimation and the predictive intercept point. Numerical simulations are conducted to demonstrate the effectiveness and robustness of the proposed guidance law. [ABSTRACT FROM AUTHOR]

Considering the problem that the optimal error dynamics can only converge at the terminal time, an impact angle/time constraint missile guidance law with finite-time convergence is designed in this paper, which is based on the pure proportional navigation (PPN) guidance law and the fast terminal error dynamics (FTED) approach. The missile guidance model and FTED equation are given first, and the dynamic equation of impact angle/time error based on PPN is also derived. Then, the guidance law is designed based on FTED, and the guidance error can converge to 0 in a finite time. Furthermore, considering the field of view constraint, the guidance law is improved by using the saturation function mapping method. Finally, a numerical simulation example is given to verify the effectiveness of the guidance law, which shows that the guidance law proposed in this paper can make the missile quickly adjust to the desired states in advance, and effectively relieve the overload saturation pressure of the actuator. [ABSTRACT FROM AUTHOR]

Polyurethane is widely used on the surface of composite materials for rotor blades as sand erosion protection materials. The failure mechanism investigation of polyurethane film under service conditions is useful for developing the optimal polyurethane film for rotor blades. In this article, the sand erosion test parameters were ascertained according to the service environment of the polyurethane film. The sand erosion resistance and failure mechanism of polyurethane film at different impact angles were analyzed by an infrared thermometer, a Fourier transform infrared spectrometer (FTIR), a differential scanning calorimeter (DSC), a field emission scanning electron microscope (FESEM), and a laser confocal microscope (CLSM). The results show that the direct measurement method of volume loss can better characterize the sand erosion resistance of the polyurethane film compared to traditional mass loss methods, which avoids the influence of sand particles embedded in the polyurethane film. The sand erosion resistance of polyurethane film at low-angle impact is much lower than that at high-angle impact. At an impact rate of 220 m/s, the volume loss after sand erosion for 15 min at the impact angle of 30° is 57.8 mm3, while that at the impact angle of 90° is only 2.6 mm3. The volume loss prediction equation was established according to the experimental data. During low-angle erosion, the polyurethane film damage is mainly caused by sand cutting, which leads to wrinkling and accumulation of surface materials, a rapid increase in roughness, and the generation of long cracks. The linking of developing cracks would lead to large-scale shedding of polyurethane film. During high-angle erosion, the polyurethane film damage is mainly caused by impact. The connection of small cracks caused by impact leads to the shedding of small pieces of polyurethane, while the change in the roughness of the film is not as significant as that during low-angle erosion. The disordered arrangement of the soft and hard blocks becomes locally ordered under the action of impact and cutting loads. Then, the disordered state is restored after the erosion test finishes. The erosion of sand particles leads to an increase in the temperature of the erosion zone of the polyurethane film, and the maximum temperature rise is 6 °C, which does not result in a significant change in the molecular structure of the polyurethane film. The erosion failure mechanism is cracking caused by sand cutting and impact.

In this article, we investigate a cooperative guidance problem against a maneuvering target with impact angle coordination. As is well established, the main challenge is how to design a guidance law for each missile to intercept the target from specified directions with only the local information and information from its connected neighbors. Toward this, we prove that the underlying problem can be treated as a Nash equilibrium (NE) seeking problem, where each missile attempts to minimize its own performance index to achieve interception without unilaterally implicate the team objective, and then we introduce a local observer to facilitate the local implementation of the proposed guidance protocol by ensuring the seeking of NE distributive. Numerical simulations verified the performance of the proposed guidance strategy. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this research is to study the trend of pedestrian lower extremity injuries during vehicle-pedestrian collisions. Methods: In this study, pedestrian’s age, collision angle and pedestrian’s position are considered influencing factors. Nine experiments using a novel lower extremity mechanical model are designed with the orthogonal experiment method. Results: Under the same collision angle, collisions in the left and right positions caused more serious tibia injuries than the middle position. As for the collision angle, the tibial injury at +45° is more significant than the tibial injury at −45°, and the injury of oblique collisions is slightly greater than that at 0°. Moreover, tibial injury is more sensitive to research variables than femoral injury. When the collision angle and position are changed, the difference ratio of tibia stress is by 483.2% higher than that of femur stress. The axial force and bending moment of the quadriceps tendon in the left-position collision reach peak values, which are 3.83 kN and 165.98 Nm, respectively. The peak quadriceps tendon axial force is captured with the collision angle of −45°, and the peak quadriceps tendon bending moment is obtained with a collision angle of +45°. Conclusions: The effects of differences in impact position and angle on lower extremity injury in the elderly were analyzed, and the results of this study can be used as a reference for research on lower extremity protection. [ABSTRACT FROM AUTHOR]

In order to improve the penetration ability of missile and attack the target effectively, the guidance law realizing the control of both impact time and impact angle is studied. Based on a data-driven method, the guidance process is divided into the first stage of impact time control and the second stage of impact angle control. The driving data is generated according to the guidance law of impact angle control, and the mapping network of time to go is established by using artificial neural network technology to obtain the error of impact time in the impact time control stage. Based on the proportional guidance method, the impact time control guidance law is designed with the error of impact time, so that the missile can control the impact time and the impact angle simultaneously. The simulation results show that the proposed guidance law can effectively control the impact time and impact angle under different conditions. Compared with existing literature, the maximum overload is reduced by about 43%, and the total control energy required is reduced by about 46%. [ABSTRACT FROM AUTHOR]

In this study, the effects of impact angle and impactor geometry were investigated on the impact behavior of aluminum honeycombs experimentally and numerically. The high-velocity impact tests were carried out using a gas-gun test machine with flat, spherical and conical-head impactors and impact angles of 0°, 15° and 30° at different incident velocities ranging from 55.8 to 150.5 m/s. The numerical models were developed in LS-Dyna finite element code and well validated against the experimental results. The results showed that the impact behavior of honeycombs is considerably dependent on the impactor head geometry and the impact angle. The honeycomb panel impacted by the conical projectile experienced the highest absorbed energy and ballistic limit velocity. Moreover, it was found out that increasing the impact angle increased the absorbed energy and ballistic limit velocity of honeycombs. Furthermore, different impactor head geometries resulted in different failure mechanisms in the course of impact loading. [ABSTRACT FROM AUTHOR]

Experiments of a single droplet oblique impact on a thin liquid film are carried out. In the experiments, the impact angle is adjusted by varying a horizontal airflow, and three typical initial droplet shapes of the sphere, horizontal spheroid, and vertical spheroid are selected. Effects of impact angle, initial droplet shape, and film thickness on the impact outcomes are mainly studied. Results show that the liquid crown seems to be a beveled round tube in the case of sphere droplet impact. In contrast, it seems to be a ship in the case of vertical spheroid droplet impact, and the liquid crown is less asymmetry for the horizontal spheroid droplet impact. When the Weber number exceeds the critical value, secondary droplets will detach from the rim of the liquid jets. The number and size of the secondary droplets are associated with the impact droplet shapes. For the sphere droplet impact case, the crown radius and the crown height on the front side of the advancing droplet (right side) increase with the impact angle. With an increase in the film thickness, the right crown radius decreases, while the right crown height first increases and then decreases. [ABSTRACT FROM AUTHOR]

The low-velocity impact behavior of carbon-epoxy cross-ply composites was numerically investigated, examining the effect of impact angle. A plastic continuum damage model, introducing the cohesive interface to describe delamination damage, was established and was validated by available experimental data. Impact histories, progressive deformation, stress transfer, and impact damage are respectively discussed. The results show that an increase in impact angle intensifies the action of tangential force, and gradually transfers energy absorption from normal plastic deformation to tangential deformation and friction, which dissipates more energy through relatively longer contact duration and larger impactor displacement. The delamination damage to upper layers is more affected by tangential loads, intensifying with the increase of the impact angle, and the damage area to the top interface is increased by 132.1% from 0° impact to 60° impact. Meanwhile, the delamination damage to lower layers is mainly determined by normal loads, weakening with the increasing impact angle overall, and the damage area of the lowest interface decreases by 36.6% from 0° impact to 60° impact. [ABSTRACT FROM AUTHOR]

Damage induced by coarse particle erosion is the main cause of premature failure of transport structures used in deep-sea mining. In this study, a free fall coarse particle stress-erosion (i.e., the erosion of a highly stresses target material) test method is proposed as an alternative to the traditional impinge jet test. The erosion behavior of stainless steel SS304 under different loads and impact angles was experimentally studied. The related mass loss was quantified, the microscopic wear morphology was observed and the erosion mechanism was revealed. This study indicates that the erosion damage caused by coarse gravels is much severer than that caused by fine sands, while the stress-acceleration effect (generally, the erosion damage will be enhanced when the target material is suffering from high tensile stress) of SS304 is relatively marginal. Finally, the validity of some widely used erosion equation was examined by the test data. [ABSTRACT FROM AUTHOR]

Herein, the influence of the impact angle and Ni content on the wear behavior of Mo 2 NiB 2 –Ni cermets was studied using an erodent-carrying slurry comprising artificial seawater and SiO 2 sands. The results reveal that the material loss may be attributed to the wear damage caused by SiO 2 sands because cermets are expected to exhibit good corrosion resistance in artificial seawater. The relative density of cermets markedly influences their resistance to wear damage, and the material loss experienced by cermets with poor relative density is 2–4 times higher than that of cermets with good relative density; this occurs because a higher relative density can markedly enhance the mechanical properties and reduce the defects in the cermets. Moreover, the results indicate that as the impact angle increases from 0° to 60°, the manifestation of the wear mechanism changes from damaging the Ni binder phase (caused by single cutting wear) to damaging both the Mo 2 NiB 2 ceramic and Ni binder phases due to the combination of cutting wear and impact wear. The wear damage is dominated by the cutting wear and impact wear from SiO 2 sand at the low and high impact angles, respectively. Furthermore, the severe deterioration of the single ceramic skeleton at high impact angles indicates that the synergistic influence of the Mo 2 NiB 2 ceramic and Ni binder phases on enhancing the wear resistance of the cermets intensifies at high impact angles. [ABSTRACT FROM AUTHOR]

In this article, a sliding mode control–based nonlinear guidance scheme for controlling both impact angle and impact time simultaneously is proposed. The problem of impact angle control is first transformed to that of controlling line-of-sight angle and its rate, while the requirement of impact time is achieved by tracking the desired time-to-go. The chosen time-to-go estimate accounts for the curvature required to meet the impact angle requirements toward the target interception. In order to satisfy both of these terminal constraints, the sliding surface is defined as a combination of impact time error and the variable pertaining to the errors in line-of-sight angle and its rate, with appropriate gains assigned to them. The interceptor first performs necessary maneuvers to meet the impact time requirements and then steers its course to achieve the target interception at a desired impact angle. The guidance law is initially derived using nonlinear engagement kinematics against stationary targets and then extended to cater to constant velocity targets using the concept of predicted interception point. Numerical simulations are performed to validate the efficacy of the proposed guidance scheme for various initial engagement geometries. The performance of the proposed guidance scheme is also compared with those of the existing guidance laws and shown to be superior. [ABSTRACT FROM AUTHOR]

The mechanical response of CFRP laminates under low-velocity oblique impact was investigated using finite element simulation and experimental test in this paper. Based on the 3D Hashin failure criterion, bilinear cohesive constitutive model and progressive failure theory, a finite element model of CFRP laminate with hemispherical cylindrical impactor under low-velocity oblique impact was established, by using finite element simulation software ABAQUS. A clamp for multi-angle impact was designed and manufactured. A low-velocity oblique test platform was built based on the clamp. Several groups of experiments with different impact angles and impact energy were carried out. It was found that the damage morphology and energy absorption caused by normal impact and oblique impact is quite different. For normal impact, the main damage mode on the front of the laminate is indentation, while for oblique impact, the main damage mode on the front surface is scratch due to the sliding of the impactor on the laminate. The damage caused by normal impact on the back of the laminate is always more significant than that caused by oblique impact. The simulation results of the contact force and the residual velocity of impactor are compared with the experimental results, and the good agreement verifies the reliability of the simulation model. The mechanical response is studied by simulation, and it is found that the mechanism of normal impact is different from that of oblique impact. The contact force and residual kinetic energy of the impactor decrease with the increase of impact angle, while the contact time and the energy consumed by friction increase are the opposite. The energy absorbed by the laminate is not negatively related to the impact angle. [ABSTRACT FROM AUTHOR]

To explore the influence of impact angle on concrete abrasion deterioration under water-borne sand, a theoretical model for friction-impact deterioration was developed. This model innovatively proposes the inhibition effect of the normal impact action on the tangential friction mass loss and the facilitation effect of the tangential friction action on the normal impact mass loss to rationally explain the effect of impact angle on concrete mass loss. Simultaneously, a water-borne sand accelerated abrasion experiment was conducted to initiate a comprehensive discussion on surface abrasion deterioration indicators, including mass loss, number of holes, aperture, hole area, and hole volume. In addition, the concrete abrasion mass loss rate was evaluated based on the friction-impact deterioration model combined with experimental data. Applying this model facilitates a reliable prediction of concrete's mass loss caused by abrasion. Consequently, this allows for a more accurate assurance of the safety of concrete structures exposed to abrasive conditions throughout their operational life. The results show that the mass loss per unit area, maximum aperture, hole area ratio, and hole volume exhibit a trend of first decreasing, then increasing and finally decreasing with the increase of impact angle. Under 15°, 60°, and 90°, 70 % of the mass loss per unit area of the concrete specimens occurred within the first 6 d of abrasion. When the angles were 30° and 45°, 50 % of the mass loss per unit area of the concrete specimens occurred in the 9–12 d abrasion. It has been revealed that 69° results in the most severe abrasion mass loss. The abrasion deterioration process of concrete can be divided into three primary stages, including surface mortar abrasion, prime aggregate-mortar abrasion, and continuous aggregate-mortar abrasion. Additionally, the friction-impact theoretical model was employed to simulate the abrasion of both single and multiple pier columns, and the simulations provided insights into the non-uniform mass loss rate distribution around the pier columns. • A theoretical model concerning was proposed to quantify the concrete mass loss under abrasion. • The theoretical model characterized the dynamic interplay between tangential friction action and normal impact action. • There exists an impact angle that led to the most severe abrasion mass loss. • A water-borne sand experiment accelerated abrasion experiment on concrete was conducted. • The theoretical model was employed in numerical simulation to investigate the abrasion of pier columns. [ABSTRACT FROM AUTHOR]

Impact direction is one of the critical factors affecting the waterdrop erosion behavior of materials. In this paper, rain erosion damage behavior of a typical carbon fiber reinforced polymer (CFRP) laminate is investigated as a function of the impingement angle (0° as normal impact and 15°, 30°, 45° as oblique impact deviated from the normal) and the relative fiber orientation (parallel PA and perpendicular PE to the fiber direction of the surface layer) under the waterjet velocity of 320 m/s and the impact frequency of 50 Hz via a pulsating waterjet erosion test rig. After continuous impact of multiple waterjets, the typical damage of CFRP laminates is mainly composed of the central erosion crater and the upheaval of the surrounding surface layer. The onset and evolution of damage are mainly driven by the shear action of lateral jetting and stress concentration of hydraulic penetration exerted at the surface irregularities. There is no significant difference in the damage modes between the normal and oblique impacts, except for the asymmetric distributions of matrix cracking in PA-orientation and delamination in PE-orientation caused by the angle inclination. With the impingement angle increasing, the volume loss and erosion depth decrease while the incubation period increases mainly due to the decreases of water hammer pressure and contact area. The PA-orientation can cause lower incubation period and larger erosion mass loss than PE-orientation before the surface ply is penetrated, with the underlying mechanism related to the distinct tensile properties of CFRP laminates along longitudinal and transversal directions and the asymmetric properties of fiber–matrix interface. According to the fitting results of erosion curves, it is possible to describe the incubation period and the erosion rate of CFRP laminates under oblique impact using a two-branch equation, and Springer model can give reasonable prediction for the average incubation period and PA-orientation erosion rate of a certain oblique impact occasion with known 0° impact erosion results. [ABSTRACT FROM AUTHOR]

The role of retained austenite and martensite on impact-wear resistance of 27%Cr cast iron quenched at temperatures of 1223K and 1423K was investigated at various impact angles by impact wear tests using an air blasting machine. Measurement of the hardness and volume fraction of martensite in the matrix of both samples as well as SEM observation were performed. Quenching treatment at 1223K resulted in a higher volume of initial martensite in the matrix, and wear rate reached maximum at 60°. On the contrary, the matrix with a high volume of retained austenite obtained by quenching at 1423K showed a maximum impact-wear rate at 45°. The difference in the wear resistance between the two types of as-quenched samples can be explained by the transformation from metastable austenite to strain induced martensite and self-tempering of the initial martensite occurring under impact wear environment. As the volume of retained austenite increases, hardening due to strain induced martensite was found to overlap with softening due to tempering of the initial martensite, which contributed to the suppression of the wear rate. [ABSTRACT FROM AUTHOR]

In this article, impact time and angle constrained guidance law is proposed using a range‐based line‐of‐sight (LOS) shaping strategy. The relative motion of missile and target is described in a polar coordinate, where the LOS angle can be shaped as a polynomial function of range‐to‐go. The order of the polynomial function is selected according to the number of constraints. Coefficients of the polynomial function are determined by the boundary conditions and solved through a simple integral equation, which facilitates the onboard implementation. Guidance command is designed in a state feedback form to track the shaped trajectory. The proposed guidance law shows some advantages over several similar polynomial shaping based guidance laws. Multiple simulation studies demonstrate the effectiveness of the proposed guidance law. [ABSTRACT FROM AUTHOR]

Conventional guidance law designs can only guarantee steady-state performance. However, transient performance is also the key performance index in practical guidance applications. In this paper, a novel terminal guidance law is presented for missile intercepting maneuvering target with impact angle constraints, which can strictly guarantee the prescribed steady-state and transient performances of interception. By utilizing the prescribed performance control technique, the prescribed performance tracking control problem is transformed into an equivalent unconstrained form such that the tracking error can be limit to the prescribed performance bound. Then, on the basis of transferred the tracking error, a novel nonsingular terminal sliding mode control-based guidance law is proposed with impact angle constraint, and the extended state observer is incorporated to online estimate the external disturbances and unknown target maneuver. The closed-loop system stability and the convergence characteristic are rigorously proved. Finally, extensive contrast simulations are conducted to demonstrate the efficiency and superiority of the proposed guidance law for different engagement scenarios. [ABSTRACT FROM AUTHOR]