Impact and Ricochet of a High Speed Projectile from a Plate

A computational study of a projectile (either 2024 aluminum or TiAl6V4 titanium alloy) impacting a plate (either titanium alloy or aluminum) is presented in this paper. Projectile velocity (ranging from 250 m/s to 1500 m/s) with varying impact angles are considered. The presence of ricochet (if any) is identified over the ranges of the projectile velocity and impact angle considered. For the cases where ricochet is identified, the ricochet angle and velocity are predicted as functions of the incident angle and the incident velocity. The numerical results are compared with an analytical solution of the ricochet problem. The analytical solutions are from a model developed to predict the ballistic ricochet of a projectile (projectile) penetrator. The dynamics and the deformation of an aluminum (or a titanium alloy) projectile impacting on a finite thickness titanium alloy (or aluminum) plate are simulated. The current work is interesting in that it looks in the field of ballistics of different material combinations than are traditionally studied. The present simulations based on detailed material models for the aluminum and the titanium alloy and the impact physics modelling features in the LS-DYNA code provide interesting details regarding the projectile/plate deformations and post-impact projectile shape and geometry. The present results indicate that for no cases (for specified incoming velocities and impact angles considered) can an aluminum projectile penetrate a titanium alloy plate. The ricochet ‘mode predictions ‘obtained from the present simulations agree well with the ricochet ‘mode predictions’ given in an analytical model.

Generalized Guidance Formulation for Impact Angle Interception with Physical Constraints

This paper proposes an optimal impact angle control guidance law for homing missiles with a narrow field-of-view of the seekers. As groundwork for designing a guidance law, we first present a general guidance structure that can achieve any terminal constraint of the line-of-sight rate based on the optimal control theory. We configure the desired profile of the line-of-sight rate using a saturation function whose exact form is determined to satisfy the required boundary conditions. By combining the line-of-sight rate profile with the optimal guidance structure, we develop a guidance law that achieves an impact angle interception with the field-of-view constraint. Herein, as the entire guidance structure is derived based on exact kinematics without any approximation, the proposed law ensures the accurate impact angle interception for various engagement scenarios. This precise consideration of the engagement kinematics also accurately ensures the energy optimality of preventing the excessive use of control inputs when homing. To evaluate the performance of the proposed method, numerical simulations with various engagement scenarios are conducted, and the results demonstrate that the proposed law allows missiles to accurately intercept their targets with the desired impact angles and without violating the prescribed field-of-view constraint.

FOV constrained guidance law for nonstationary nonmaneuvering target interception with any impact angle

This paper presents the nonstationary nonmaneuvering target interception with all possible desired impact angles in a two-dimensional (2D) aerial engagement scenario, where the target can move in any direction. The paper also considers the field-of-view (FOV) constraint for designing the guidance law so that the target is always visible while following the missile trajectory in the entire engagement time, which makes it feasible for real world applications. The guidance law is based on the pure proportional navigation (PPN) to achieve any impact angle of the entire angular spectrum. The proposed guidance law is then simulated for intercepting a nonstationary nonmaneuvering target using a kinematic model of a missile to demonstrate the efficacy of the presented scheme. A comparison with the related work existing in the literature has also been added to establish the superiority of the present work.

A simple computational method to estimate stance velocity in running

Running dynamical analyses typically approximate a runner's stance velocity as the average stride cycle velocity (the average running speed). That approximation necessarily overestimates stance velocity and biases subsequent results. Stance velocities are crucial in kinetic spring-mass analyses of running, where approximation of a runner's impact angle and calculation of leg stiffness require that input. Here, a new method is presented to approximate a runner's stance velocity via measurement of contact and flight times with the runner's average speed, leg length or height, and mass. This method accurately estimated stance velocities of simulated spring-mass systems across typical running speeds of 3.5-5.5 m/s (r>0.99) and more accurately estimated impact angles of simulations and leg stiffnesses. The method also accurately estimated peak horizontal vertical ground reaction forces across speeds (r=0.82), but the bias magnitude increased with speed. Robustness of the new method was further tested for runners at 2.5, 3.5, and 4.5 m/s, and the new method provided steeper impact angles than those from traditional estimates and correspondingly higher leg stiffnesses, analogous to the observations in the simulation models. Horizontal ground reaction force estimates were weakly correlated in braking and propulsion. They were improved by a corrective algorithm, but the intra- and inter-individual variation persisted. The directionality and magnitude of angle and stiffness estimates in the human runners were similar to simulations, suggesting the new method more accurately modeled runners’ spring-mass characteristics by using an accurate approximation of stance velocity. The new method can improve traditional kinetic analyses of running where stance velocity recordings are not captured with kinematic recordings and extend opportunities for accurate field-based analyses with limited measurement sources.

Research on characteristics of occupant’s chest responses in oblique impact

The oblique impact is the second most common frontal impact, in which both the forward and lateral accelerations are applied to the occupant. It is noticed that the oblique impact is a primary source of serious injuries, in which the chest injuries are mostly fatal through the statistics of traffic accidents. This study aims to investigate the characteristics of the occupant’s chest injury in the frontal oblique impact. First, a model with a sled and a Test Human Occupant Restraint (THOR) dummy is established. Second, an acceleration curve with a peak of 9.0 g is applied to the sled. Then 11 sets of simulations with different impact angles and belt peak loads are conducted to evaluate the occupant’s chest responses. Results indicate that there is a negative correlation between belt peak force and injury outcomes, while there is a weak correlation between chest injury and impact angle. With the increase of the belt force limit, the chest deflection at Lower Left (LL) would increase by 37.9%, and the acceleration at LL would increase by 23.1%. Meanwhile, the Viscous Criterion (VC) at LL would increase by 61.4%. However, the relationship between the impact angle and injury drawn by VC and acceleration is inconsistent. Additionally, in all simulations, the maximum deflections are captured at the LL, while the maximum VCs happens at Upper Right (UR) or LL. It is demonstrated that a seatbelt with a lower peak force is friendly to the occupant’s chest under all the impact angles. This study can provide a reference to the study of chest injury in the oblique impact.

Erosion wear behaviour of A357/fly ash composites

In this article, a new metal–matrix composite was developed with fly ash (an industrial waste from petroleum industries) as reinforcement and aluminium metal (A357) as a matrix by squeeze casting technique. This study was concentrated on the processing of the composites with different weight percentage ranging from 0 to 10 wt.% in a step of 2.5 each and also reported the erosion wear behaviour. Solid particle erosion of A357/fly ash composites was carried out with four velocities (48, 70, 82 and 109 m/s), at impact angles (30°, 45°, 60° and 90°), with silica as an abrasive particle at ambient temperature. The eroded surfaces were analysed by scanning electron microscopy. The results revealed that the impact velocity and impingement angle both affected the erosion wear behaviour of the composites. The erosion rate rises with an increase in impact velocity, irrespective of the change in impingement angle and weight percentage of the fly ash. The erosion mechanism studied for the composites is microploughing and microcutting.

Bouncing behavior of sub-four minute milers

Elite middle distance runners present as a unique population in which to explore biomechanical phenomena in relation to running speed, as their training and racing spans a broad spectrum of paces. However, there have been no comprehensive investigations of running mechanics across speeds within this population. Here, we used the spring-mass model of running to explore global mechanical behavior across speeds in these runners. Ten elite-level 1500 m and mile runners (mean 1500 m best: 3:37.3 ± 3.6 s; mile: 3:54.6 ± 3.9 s) and ten highly trained 1500 m and mile runners (mean 1500 m best: 4:07.6 ± 3.7 s; mile: 4:27.4 ± 4.1 s) ran on a treadmill at 10 speeds where temporal measures were recorded. Spatiotemporal and spring-mass characteristics and their corresponding variation were calculated within and across speeds. All spatiotemporal measures changed with speed in both groups, but the changes were less substantial in the elites. The elite runners ran with greater approximated vertical forces (+ 0.16 BW) and steeper impact angles (+ 3.1°) across speeds. Moreover, the elites ran with greater leg and vertical stiffnesses (+ 2.1 kN/m and + 3.6 kN/m) across speeds. Neither group changed leg stiffness with increasing speeds, but both groups increased vertical stiffness (1.6 kN/m per km/h), and the elite runners more so (further + 0.4 kN/m per km/h). The elite runners also demonstrated lower variability in their spatiotemporal behavior across speeds. Together, these findings suggested that elite middle distance runners may have distinct global mechanical patterns across running speeds, where they behave as stiffer, less variable spring-mass systems compared to highly trained, but sub-elite counterparts.

Numerical modeling of lander interaction with a low-gravity asteroid regolith surface

Context. The JAXA asteroid sample return mission Hayabusa2 reached its target (162173) Ryugu in June 2018 and released the European (CNES-DLR) lander MASCOT in October 2018. MASCOT successfully landed on the surface, and the Hayabusa2 Optical Navigation Camera system has been able to image parts of the MASCOT trajectory. Aims. This work builds on our previous study of interactions between a landing package and a granular material in the context of MASCOT on Ryugu. The purpose is to expand our knowledge on this topic and to help constrain physical properties of surfaces by considering the actual trajectory of MASCOT and observations of Ryugu from Hayabusa2. Methods. We ran a new campaign of numerical simulations using the N-body code pkdgrav with the soft-sphere discrete element method by expanding the parameter space to characterize the actual landing scenario of MASCOT on Ryugu. The surface was modeled as a granular medium, but we also considered a large boulder in the bed at various depths and a rigid wall representing a cliff. MASCOT was faithfully modeled as the actual lander, and we considered different impact angles, speeds, and surface slopes. We were particularly interested in the outgoing-to-incoming speed ratio of MASCOT during the landing process. Results. We found that a boulder in the bed generally increases both the stochasticity of the outcomes and the speed ratio, with larger increases when the boulder sits closer to the surface. We also found that the surface slope does not affect our previous results and that the impact speed does not affect the speed ratio for moderate-friction granular material. Finally, we found that a speed ratio as low as 0.3, as estimated in the actual scenario, can occur with a solid-rock surface, not only with a soft surface, because the geometry of the lander is nonspherical. This means that we must infer the physical properties of the surface from outcomes such as the speed ratio with caution: it depends on the lander geometry.

Autonomous Vehicle Safe Operating Speeds on the Automated Skyway Express in Jacksonville, Florida

Autonomous vehicles (AV) differ significantly from traditional passenger vehicles in both their behavior and physical characteristics. As such, the validity of the guidance provided in the Manual for Assessing Safety Hardware, Second Edition (MASH 2016) is questionable in AV applications. Impact angles, speeds, and vehicle weights specified in MASH 2016 are inextricably linked to the traditional vehicles underlying the estimates. For AV applications, these parameters must be estimated from the ground up, stepping outside the guidance of MASH 2016. In this paper, a conservative method for evaluating existing infrastructure to support AV traffic is proposed. The method integrates traditional structural analyses with unconventional methods of estimating impact conditions. This methodology was developed for the Jacksonville Transportation Authority, who, when faced with unique challenges in maintaining and expanding their Automated Skyway Express, opted to convert the system from monorail to AV traffic. Leading AV developers were surveyed to develop a portfolio of potential candidates for the conversion. Estimated impact conditions were then compared against the capacity of the system’s existing concrete parapets. Ultimately, safe operating speeds for each AV candidate were recommended on the bases of structural capacity and vehicle stability. All but one AV candidate were deemed capable of safely operating at the desired speed of 25 mph without any modifications to the barrier. Although the methodology was developed for a particular case, it is applicable to future implementations of AVs on existing infrastructure, provided the roadway is confined similarly to the Skyway deck.