Oblique Impact Research Articles

Comparison of Contact Angle Models in Two‐Phase Flow Simulations Using a Conservative Phase Field Equation

ABSTRACTIn phase field methods based on a second‐order Allen‐Cahn (AC) equation, contact angles are prescribed mostly via a geometric formulation. However, it is of great interest to utilize the surface‐energy formulation, which is often employed in the Cahn‐Hilliard (CH) phase field method, in the AC phase field method. This article thus put forward a surface‐energy formulation of contact angles. The model was compared with the geometric one in a number of impact problems, including both normal and oblique impacts. The governing equations were discretized using a finite difference method on a half‐staggered grid. The Navier–Stokes equation was tackled using an explicit projection method. The major findings are as follows. First, the geometric model can maintain a fixed contact angle throughout contact line motion, while the surface‐energy one predicts a changeable contact angle, with a fluctuation of about 5°. In the oblique drop impact, contact angle hysteresis was captured even if a static contact angle was applied in the surface‐energy formulation.

Helmets with lattice liners can mitigate traumatic brain injury from impacts

This study explores the effectiveness of architected lattice structures, specifically made of PA12 material, as potential helmet liners to mitigate traumatic brain injuries (TBI), with a focus on rotational acceleration. Evaluating three lattice unit cell topologies (simple cubic, dode-medium, and rhombic dodecahedron), the research builds upon prior investigations indicating that PA12 lattice liners may outperform conventional EPS liners. Employing a high-fidelity finite element male head model and utilizing direct and oblique impact scenarios, mechanical quantities, such as maximum principal strain (MPS) and shear strain, cumulative strain damage measure and intracranial pressure were measured at the tissue level in different brain regions, Results indicate that lattice liners, especially with dode-medium topology, exhibit promising reductions in brain tissue strains. On average, during oblique impacts, less than 1 % of the brain volume experienced an MPS level of 0.4 when the lattice liners were adopted, whereas that percentage was above 70 % with the expandable polystyrene (EPS) foam liners. Pressure-based assessments suggest that lattice liners may outperform EPS liners in oblique impacts, showcasing the limitations of EPS for effective TBI mitigation. Despite certain model limitations, this study emphasizes the need for advancements in helmet technology, particularly in the development of commercial lattice liners using additive manufacturing, to address the limitations of existing EPS liners in preventing rotational consequences of impacts and reducing TBI.

A piezoelectric driven amphibious microrobot capable of fast and controllable movement

Abstract Due to its excellent adaptability to the environment and flexibility in narrow spaces, amphibious microrobots have become an important research direction recently. This study proposes an amphibious microrobot driven by piezoelectric actuators with a body length of 4.5 cm and a mass of 1.4 g. The microrobot consists of two active front legs, two passive rear legs, two caudal fins, and a support frame. Each front leg and each caudal fin are designed as structures integrated with their respective piezoelectric actuators. The microrobot has a tilted body, and the ground exerts an oblique upward impact force that makes it jump forward when its front legs swing backwards. The opposite swing of the two caudal fins generates propulsion for swimming. The components of the microrobot are manufactured based on the monolithic laminate process. The monolithic front actuator-leg and monolithic actuator-fin both emerge from a multi-layer material laminate. The support frame is designed and fabricated as a monolithic structure to improve assembly accuracy and reduce redundant assembly steps. The manufactured microrobot demonstrates its flexible and fast amphibious movements. Its maximum land walking speed reaches 15.3 cm/s and its turning speed reaches 48.2 degrees per second. The microrobot has a maximum payload capacity of 5 g moving on land. When the front legs and caudal fins work simultaneously, its underwater swimming speed reaches 9.1 cm/s, and the maximum turning speed is 20.5 degrees per second. The microrobot also confirms a maximum payload of 3 g during its underwater movement.

Interaction between multiple convertible child restraint systems and pediatric occupants in oblique impacts

Objectives To assess the interaction of multiple rearward-facing (RF) and forward-facing (FF) CRS restrained pediatric occupants on their kinetics in oblique impacts. Methods A Q3s and a Q1.5 ATD were restrained in 2 CRSs of varying widths—standard (503mm) and slim-fit (425mm)—in the 2 rear outboard seats of a 2023 compact sedan rigidized rear seat bench. A surrogate door structure was mounted at the left outboard location. The Q1.5 was seated in an RF configuration, and the Q3s was seated in RF or FF configurations across tests. The ATDs were restrained as follows: (1) both ATDs in standard CRSs and (2) both ATDs in slim-fit CRSs, switching between the outboard seats for a total of 8 conditions. The condition with the highest head kinetic metrics from these tests was reproduced in a ninth test with the rear seat’s center armrest lowered between CRSs. The entire environment was subjected to an oblique impact at 60° using the FMVSS 213 impact pulse. Results The Q3s’ head contacted the nearby CRS shell when seated farside. When seated nearside, the Q3s’ head contacted the surrogate door structure in 1 of 4 conditions. The Q1.5’s head contacted the nearby CRS in 2 of 4 conditions when seated farside. The Q3s when seated RF had higher HIC15 and head 3ms clip acceleration (H3ms), regardless of farside or nearside position. When seated farside, upper neck tensile force (Fz) for the Q3s in FF configuration (2,317.4 and 2,077.9 N) was higher than that in RF configuration (1,850.8 and 1,802.8 N). When seated nearside, the same in FF configuration (701.3 and 1,029.4 N) was lower than that in RF configuration (997.6 and 1,261.7 N). Repeating the condition with the highest head kinetic metrics (HIC15 = 1246; H3ms = 114.4 g) but lowering the center armrest between the CRSs resulted in lower head kinetic metrics (HIC15 = 916, H3ms = 93.5 g). Conclusions In most cases, the farside seated ATD’s head contacted the nearside CRS shell, resulting in elevated injury metric numbers and higher loading in both CRS types. The nearside ATD did not experience detrimental effects of the interaction with the farside occupant and CRS.

Investigation of droplet splashing behavior during oblique jet impact onto a wall

For the issue of jet impingement on the wall in industrial cooling processes, an experimental setup based on high-speed photography for oblique jet impingement onto the wall was constructed. The experimental focus was on the study of liquid droplet splashing behavior after oblique jet impingement on the wall, discussing the liquid droplet splashing behavior under three jet impingement modes: Rayleigh regime, first wind-induced regime, and secondary wind-induced regime. By employing methods such as trajectory imaging and particle image velocity for liquid droplet parameter image measurement, obtaining the particle size, velocity, and distribution of splashed droplets after oblique jet impact on walls under different working conditions. The impact of jet impingement velocity and angle on droplet splashing parameters was analyzed. The results showed that when the impingement point is before the breakup length, with increasing flow velocity, the surface wave of the liquid column, and the spreading liquid film became more pronounced, but the loss of liquid-phase components due to splashing was relatively small. When the impingement point is after the breakup length, the secondary breakup resulting in a “crown”-shaped liquid film after droplet impingement leads to a significant loss of liquid-phase components through splashing. As the inlet velocity of the jet increases, there is a decreasing trend in droplet size and an increasing trend in droplet velocity. With an increase in jet angle, there is a decreasing trend in droplet size and velocity. Based on the concentration, size, and velocity distribution characteristics of splashing droplets, the area after oblique jet impingement on the wall can be divided into the impingement zone, low-concentration low-velocity zone, high-concentration high-velocity zone, and lateral splashing zone. This has significant implications for understanding the splashing mechanism after oblique jet impingement on the wall and optimizing operating conditions.

A model for oblique impacts on material surfaces

Many practical situations of material damage, wear, and erosion involve collisions between small particles and surfaces at inclined angles. While there are many well-validated models of normal incidence impact situations, elastic-plastic models for oblique incidence impact events are lacking. Here the finite element method is used to predict the normal and tangential coefficient of restitution in oblique impacts for hard, elastic spheres impacting an elastic-perfectly plastic material surface. The proposed model covers various impact angles ranging from 0° to 45°, within a limiting impact velocity below which the effects of heating are negligible. The normal coefficient of restitution follows power-laws with respect to normalized values of the impact velocity. Interestingly, the tangential coefficient of restitution follows a linear relationship with impact velocity. Together, these results provide a semi-empirical set of equations predicting oblique impact rebounds (both velocity and trajectory) for a wide range of conditions and material properties, with which experimental results can be rapidly interpreted. Laser-Induced Particle Impact Test (LIPIT) data are also presented for aluminum particles impacting aluminum substrates, at impact angles of 25° and 40°; the results compare favorably with the model and validate the general use of such models for the analysis of experimental data.

Deflection characteristics and influencing factors of projectile oblique impact on concrete targets

The projectile deflects and even ricochets after an oblique impact on the concrete. However, research on the oblique impact of projectiles on concrete targets mainly focuses on oblique penetration and the critical ricochet angle, and there are few experimental studies on ricochets. Deflection and its influencing factors remain undefined. This study conducted experiments and LS-DYNA numerical simulations on projectiles obliquely impacting C60 concrete targets. The experimental research visually revealed deflection and ricochet phenomena after the oblique impact. The ricochet caused by large-angle impacts can effectively reduce the damaged area of concrete targets. Subsequently, the main governing parameters affecting the deflection angle of the projectile were identified through dimensional analysis, and a sensitivity analysis was performed on these parameters using an orthogonal experimental design. On this basis, the influence of the incident angle, impact velocity, and projectile length-to-diameter ratio on the projectile deflection was further clarified. The results showed that the maximum deflection angle was achieved when a 30 mm caliber projectile obliquely impacted a C60 concrete at an incident angle of ∼45°. In the case of ricochets, the deflection angle increased with an increase in the impact velocity and decreased with an increase in the length-to-diameter ratio. This study aids in predicting and controlling projectile deflection and provides a reference for the innovative design of concrete protective structures.

Numerical investigation on the impact resistance of ceramic-based composite structure with hybrid architecture

As known, ceramics possess desirable strength, hardness and low density, which have been extensively applied in engineering fields. However, the inherent brittleness makes the ceramics present poor toughness and consequently impact resistance as well. In recent decades, some ingenious architectures of biomaterials employed to improve the mechanical properties of brittle bulk materials, such as laminate and brick-mud, have become increasingly popular. Here, in order to further enhance the impact resistance of ceramics, a kind of hybrid ceramic-based composite structure is designed according to the gradient feature in dactyl club of mantis shrimp. The impact resistance performances of bulk, laminate, brick-mud and hybrid structures are investigated by finite element simulation. The results show that the hybrid structure can effectively avoid catastrophic failure, thereby having large scope of deformation area to store energy. Moreover, the damage mass of impactor for the hybrid plate is the largest due to the beginning hard collision between impactor and target plate and long cumulative damaging time of impactor. As a result, with the highest internal energy and eroding kinetic energy of impactor simultaneously, the hybrid structure dissipates the most energy of impactor. Further, under extreme working conditions of oblique and high velocity impact, the hybrid structure still exhibits optical impact resistance performance.

Energy Absorption of a Novel Lattice Structure‐Filled Multicell Thin‐Walled Tubes Under Axial and Oblique Loadings

Multicell design and lattice structure as filling material are two effective methods for enhancing the energy absorption performance of thin‐walled tubes. This study combines these two approaches to present a multicell tube with a novel lattice structure and investigates the energy absorption performances of these hybrid multicell tubes under axial (0°) and oblique (10°, 20°, and 30°) impact loading conditions. As filling structure, β‐Ti3Au lattice geometry with varying lattice strut diameters and the number of lattice unit cells are used, while the single and multicell thin‐walled tubes with different tube thicknesses are employed as main absorbing element. In this context, the effects of numbers of lattice unit cells, lattice strut diameter, cell numbers of the tube, and tube thickness on energy absorption performance of hybrid tubes are examined using validated nonlinear finite element models. This investigation unveils that the synergistic interplay between the multicell tubes and lattice structure during deformation significantly elevates the energy absorption performance of the hybrid structure. Notably, the findings demonstrate that multicell hybrid tubes exhibit a remarkable capacity to absorb up to 30.36% more impact energy compared to the aggregate absorption of individual components in hybrid tubes.

Crustal origin for olivine in the lunar Shioli crater ejecta boulders: Insights from the geological setting of Theophilus crater and Nectaris basin

On the Moon, impact craters and basins expose a wide range of crustal and mantle rocks that provide excellent opportunity for sampling them, understanding their origins and reconstructing spatial and temporal evolution of lunar interior. The previous studies detected olivine-bearing mantle rocks in and around large impact craters and basins. The Japanese SLIM mission landed on the ejecta of a ∼ 280-m-diameter Shioli crater that was emplaced on the ejecta blanket of ∼ 103-km-diameter Theophilus crater, for characterizing potential mantle-derived olivine in the Shioli crater ejecta boulders. To test this hypothesis, we studied the geological setting of Shioli crater, host Theophilus crater and Nectaris multi-ring basin using the orbiter data from Chandrayaan-1 and 2, Lunar Reconnaissance Orbiter, and Kaguya missions and the earth-based Arecibo radar observation. The asymmetrically distributed secondary craters and impact melt ponds around Theophilus crater suggests that a northeast-directed oblique impact produced this crater. Composition of Theophilus crater and surrounding region indicates that the crater excavated a heterogeneous target composed of a thin layer of high-Al olivine basalt (Mare Nectaris) underlain by anorthositic highland rocks possibly intruded by Mg-suite plutons; layers of Cyrillus crater ejecta blanket and Nectaris basin materials (both ejecta and impact melt sheets) were also present beneath the mare basalt flows. Hence, the Theophilus ejecta blanket is a mixture of all these materials. Our dating of Theophilus crater suggests that it is a ∼ 2 Ga Eratosthenian crater. Shioli is a fresh simple crater that was formed at ∼ 1 Ma on the uprange ejecta blanket of Theophilus, where the Arecibo radar data indicated the presence of abundant buried Theophilus ejecta boulders. An ESE-directed hypervelocity oblique impact event produced the elongated Shioli crater and its asymmetrically distributed bright ejecta. Shioli is a primary impact crater indicating the role of impact spallation processes associated with this hyper-velocity impact in producing thousands of ejecta (or spall) boulders around Shioli crater, displaying their asymmetric dispersal pattern and spatial variation of boulder sizes and shapes. The larger and elongated boulders are concentrated near the crater rim, while their size and axial ratio gradually decreases outward from the crater rim. The SLIM mission landed on a thin downrange ejecta of Shioli crater, where fewer large-size boulders are present. Our compositional study suggests that the Shioli ejecta boulders are composed of olivine basalt (Mare Nectaris) mixed with highland anorthositic fragments, including the reworked Cyrillus ejecta and Nectaris basin materials. The Shioli ejecta boulders were produced by complex impact fragmentation of already existing, buried Theophilus ejecta boulders. The regional crustal structure of Nectaris basin and its petrological composition suggest that both Nectaris basin and Theophilus crater did not excavate the lunar mantle. Therefore, the Shioli ejecta boulders are of crustal origin, including the olivine minerals present in them. Our results have important implications for the origin of olivine in the Shioli crater boulders being investigated by the SLIM mission.

Oblique pole-side crash assessment using the six-year-old HBM PIPER

Side impact crashes are one of the most dangerous impact scenarios that a child can suffer. Studies by the National Highway Traffic Safety Administration (NHTSA) have shown that the head and Thorax regions are affected severely. The objective of this work is to perform a numerical evaluation of the oblique pole-side test considering the FMVSS 214-P standard to estimate the Head, Neck, and Thorax injuries for a six-year-old child positioned in the rear seat without any Child Restraint System, two configurations were performed for the oblique pole-side impact: a nearside and a far-side positioning configuration. A six-year-old Human Body Model (HBM) denominated Scalable PIPER Child Model, and the Ford Explorer 2003 were used to perform the test in the LS DYNA® software to assess the biomechanics involved in the crash scenarios. The approach considered a comparative case study with the baseline of the six-year-old child PIPER model to ensure that the positioning adjustment has not affected the mesh quality and interior components for the PIPER child model. The outcomes obtained in case 1 show that the modified PIPER child model has slight outcomes at the shoulder and pelvis zone due to the differences in the body positioning and not by the mesh or the interior interaction between the components. The outcomes obtained in case 2 reflect that the nearside setup obtained the higher measurements for the child occupant. The Ac3ms for Head at nearside test to overcome the Side Criteria established by the Assessment Protocol Child Occupant Protection by Euro NCAP, the kinematics behavior demonstrates the importance of researching children in side crashes to enhance child security, especially in the oblique pole side impact.

The South Pole‐Aitken Basin: Constraints on Impact Excavation, Melt, and Ejecta

AbstractThe formation and evolution of the South Pole‐Aitken (SPA) basin is critical to relating large impact basin formation and modification to lunar geophysical evolution. Most prior models of the SPA impact were conducted in 2D, making it difficult to compare model output to the 3D crustal structure and ejecta distribution. In order to better constrain the parameters of the SPA impactor and the expected post impact distribution of crust and ejecta, we conducted numerical simulations of the SPA impact in 3D. We tested a wide range of impact parameters and constrained model results with recent geophysical data. We found the crustal structure of the SPA basin is best fit by an oblique impact (30–45°) of a 350–400 km diameter projectile impacting at 12–16 km/s. The impact excavated material from as deep as 80–120 km, and ejecta was deposited in a butterfly pattern with a forbidden region uprange of the impact.

Experimental study on the elastic response characteristics of a rotating body under an oblique water impact load

In this study, an integrated experimental model was designed and a data acquisition system was established to capture the structural response of an elastic rotating body throughout the oblique water impact process. This established experimental methodology offers a dependable approach for gathering structural response data during the water impact process. The axial impact loads and effective stress on the rotating body throughout water impact were measured using acceleration sensor and strain gauge rosettes installed in the water impact zone of the structure, while a high-speed camera system captured the evolution of the flow field. Results from the arbitrary Lagrangian-Eulerian (ALE) numerical model were compared with those from repeated experiments, revealing good agreements. The article conducted water impact tests at different impact initial conditions, analyzing the response of the body to the impact load during water entry process across different water impact velocities and angles. Observations during the oblique water impact process revealed that the stress response at the center of the rotating body impact surface is approximately equal to that of the first water impact point, with this effect becoming more pronounced at higher velocities. This study contributes valuable experimental data for numerical investigations into the water impact of elastic structures.

On the Oblique Impact of Rigid Spheres at Metallic Targets

On the Oblique Impact of Rigid Spheres at Metallic Targets

Ejecta splashing and scaling of projectile oblique impact on granular media

Ejecta splashing is accompanied by the formation of impact craters in oblique impact of a sphere onto a granular target. We investigated the morphology and scaling of the ejection, together with the evolution and final size of crater by performing a series of experiments, varying the impact angle θ and impact speed V0. The experiment categorized the crater shapes in the space parameters Fr and θ and revealed that the maximum ejecta height exhibits two regimes related to Froude number, while the crater length, width, and depth are all collapsed to a master line. Then, the evolution characteristics of the corolla dimensions (top diameter, neck size, bottom diameter, and height) are determined. Moreover, a simple ballistic model taking into account the air drag force acting on the ejecta has been proposed to predict the dynamic processes of the corolla in oblique impacts. Furthermore, the opening of the crater formation deduced by the dynamics of the corolla formed and the collapsing process (i.e., the splashed sand avalanching down along the wall of the crater) have been investigated in detail using a simplified Bouchaud–Cates–Ravi–Edwards model. Our theoretical model demonstrated high accuracy in reproducing the evolution of a crater during impacting and in predicting the final crater scaling after avalanching.

Energy absorption characteristics of expansion tube subjected to the coupled loading in near-field explosion

Expansion tube structures (ETSs) are extensively employed as energy-absorbing components in protective structures, yet their dynamic response under near-filed explosion remains inadequately understood, which limits their applications in anti-explosion devices. This paper investigates the response of ETS through explosion experiments, testing both the overpressure history of blast loading and the propagation process of detonation products. Following experimental verification, finite element models are established to obtain the characteristics of explosive loading and the response of ETS. The findings demonstrate that as the velocity of slider increases, the embedding displacement of ETS exceeding its limit induces a local buckling transformation in thin-wall tubes from one end buckling to simultaneous buckling at both ends. In the scaled distance range of 0.4–0.5 m/kg1/3, the energy absorption (EA) of ETS under different explosive masses exhibits distinct trends as the scaled distance increases, despite the decrease in peak pressure of blast loading. This is due to the coupling effect between blast shock waves and detonation products, resulting in diverse alterations in specific impulse with increasing scaled distance for varying explosive masses. In the case of oblique impact of blast loading, the percentage decrease in EA within the near-field range (Z < 0.8 m/kg1/3) is higher than that at mid-to-far range due to the uneven and random ejection of detonation products. The study elucidates the dynamic response of ETS under the coupled loading of blast wave and blast products, and provides valuable insights for optimizing designs of ETS utilized in near-field blast-resistant structures.

Low Speed Impact of an Elastic Ball with Tapes and Clay Court

The study aims to investigate the normal and oblique impact of an elastic sphere (tennis ball) on a granular surface (clay) and two different plastic tape lines. In this research, we model the impact force with a mathematical elastoplastic force model, and a differential approach is used. The model is applied for an impact with granular material (green clay) and plastic surfaces (line tapes). We investigated the normal and oblique impact dynamics of a sphere (tennis ball). The impact duration is divided into two phases: compression with an elastoplastic force and restitution with an elastic force. The laboratory experiments in various configurations are recorded with a high frame-per-second camera and analyzed using image processing methods. The mathematical model for the impact with rebounds is verified with the experimental set-up for the considered surfaces. The viscoelastic and elastic forces agree well with the experimental data. The impact parameters of the granular surface and plastic tapes are compared. The ANOVA test suggests robust statistical significance in the coefficient of restitution between granular surfaces and plastic tapes. Our force model for impact performs well, and the impact responses of the sphere on the granular surface and the plastic line tapes are significantly different.

Copper foil microforming through underwater laser oblique impact

Laser-induced cavitation impact forming is a high-speed forming process that employs a high-energy laser to produce cavitation in a liquid and act on the workpiece. When the laser is irradiated vertically to the workpiece surface through the guide hole, oxidation occurs on the produced workpiece's surface, affecting the surface quality. Laser-induced cavitation oblique impact workpiece formation is proposed in this paper. The surface quality of the workpiece created at various angles is investigated by adjusting the angle between the laser and the guide hole. A finite element model (FEM) was employed to simulate the temperature change and collapse speed of laser-induced cavitation, and a hydrophone was utilized to measure the impact pressure of laser-induced cavitation under various guide holes. The variations in forming depth and surface quality of the workpiece caused by laser-induced cavitation oblique impact were investigated experimentally. The experimental results show that as the angle between the laser and the guide hole increases from 0° to 90°, the width of the oxidized area on the surface of the formed micro-groove decreases from 513 μm to 0 μm, the forming depth of the micro-groove decreases from 80 μm to 20 μm, and the surface roughness of formed parts decreases from 2.93 μm to 0.56 μm. The oxidation of the formed workpiece surface during the oblique laser impact is primarily caused by the laser irradiation, according to the analysis of the surface oxidation mechanism of the formed micro-grooves. When the angle between the laser and the guide hole is 60°, all of the heat emitted by the laser is focused to the guide hole's inner surface. The angle between the laser and the pilot hole was set to 60° in the experiment, and the micro-groove structure was generated by three impacts, with the thickness distribution of the formed groove investigated. The results demonstrate that the largest thinning of the micro-groove cross-section occurs at the mold's entry and the bottom of the micro-groove, with thinning rates of 20 % and 15 %, respectively.

Stability of granular media impacts morphological characteristics under different impact conditions

Abstract 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.

Effect of Oblique and Off-Center Impact on CFRP Laminate Under Low Velocity Impact

Effect of Oblique and Off-Center Impact on CFRP Laminate Under Low Velocity Impact