Increasing Impact Speed Research Articles

Investigating the erosive wear characteristics of AISI 420 martensitic stainless steel after surface hardening by boriding

Erosive wear degrades industrial components, causing surface deterioration and material loss. Understanding and mitigating this wear enhances component longevity and efficiency. Little research has been conducted to investigate the influence of particle angle, speed, and concentration on boronized surfaces. Therefore, in this study, the erosive wear behaviors of raw and boronized AISI 420 martensitic stainless steels were investigated. The samples were subjected to erosive wear testing using SiO2 abrasive particles with impact velocities of 2, 4, and 6 m/s, impact angles of 30°, 60°, and 90°, and concentration values of 5%, 10%, and 15% by weight in an abrasive sand slurry environment. Experimental runs were designed using the Taguchi L9 method. The wear test results were analyzed in terms of mass loss, surface roughness, and temperature change of the boronized and raw AISI 420 samples before and after the test. The results showed that the impact speed and concentration were statistically significant parameters compared with the impact angle, which had a negligible effect. Furthermore, with increasing impact speed and concentration, all measured responses increased in both sample groups. The surface roughness values and mass loss increased by lower margins for the boronized samples (58.40% and 188.49%, respectively) compared to those of the raw samples (61.40% and 254.38%, respectively). This study demonstrates the potential of boriding as a surface treatment technique for enhancing the erosive wear performance of martensitic stainless steels, which require improved durability and longevity of materials subjected to erosive environments.

Dynamic Analysis of Rockfall Impact on Bridges: Implications for Train Safety

The threat of rockfall impacting bridges in mountainous areas poses a great risk to the safety of passing trains. This study delves into the dynamics of rockfall impact and its implications on the interaction between train vehicles and bridges. Leveraging LS-DYNA, this study first captured the force–time history of rockfall impact on bridge structures. Subsequently, there was a comparison with the impact forces generated at various speeds with those predicted by established formulas, validating the accuracy of simulations. Employing BANSYS software, the dynamic responses of both bridge structures and the vehicle–bridge coupling system to falling rocks were analyzed. The investigation encompassed parameters such as impact speed, position, and train location. The findings reveal that escalating impact speeds correlate with increased average and maximum impact forces from falling rocks. Notably, the average impact force does not linearly correspond with rock speed and often exceeds values calculated by conventional formulas. Impact position minimally affects maximum impact force, yet alterations in position prolong impact duration, consequently reducing average impact force. Rockfall-induced impacts precipitate notable spikes in train lateral acceleration, lateral wheelset force, wheel unloading rate, and derailment coefficient, albeit with a comparatively lesser impact on vertical acceleration. Increasing impact speed and altering position intensifies the vehicle’s response, particularly when the train is in close proximity to the impact site.

Dynamic mechanical response and constitutive model of (Ti37.31Zr22.75Be26.39Al4.55Cu9)94Co6 high-entropy bulk metallic glass

In this work, the mechanical response and fracture characteristics of (Ti37.31Zr22.75Be26.39Al4.55Cu9)94Co6 high-entropy bulk metallic glass (HE-BMG) were investigated in detail over a wide range of strain rates (10−4–105 s−1). The HE-BMG exhibited a negative strain rate sensitivity under uniaxial compression, with the strength showing more significant rate dependence under dynamic conditions. The shear band behavior translated from the dominance of multiple shear bands propagations under quasi-static compression to the rapid propagation of a single shear band to form cracks under dynamic compression. Under dynamic loading, the shearing velocity increased along an arc-shaped displacement path, and the local stress state on the shear fracture surface shifted from compressive-shear to tensile-shear, accompanied by changes in fracture morphologies. The spall strength of HE-BMG decreased as flyer impact speed increased, while the long-term dependence of spall strength on strain rate may be positive. With the increase of impact speed, the main microstructural features of the spalling surface translated from flat regions accompanied by dimples to cup-cone structures. Furthermore, the complete parameters of the Johnson–Holmquist II (JH-2) model for HE-BMG were obtained based on experimental data. Numerical simulations of planar impact, penetration, and hypervelocity impact are in good agreement with experimental results, demonstrating the validity of the JH-2 model parameters. The current work has important guiding value for the application of HE-BMG in space debris protection.

Static and dynamic fracture toughness of graphite materials with varying grain sizes

Graphite materials play critical roles as moderators, reflectors, and core structural components in high-temperature gas-cooled nuclear reactors. During the reactor operation, graphite materials may experience a variety of loads, including thermal, radiation, fatigue, and dynamic loads, potentially leading to crack initiation and propagation. Therefore, it is imperative to investigate their fracture properties. Despite this, there remains a paucity of comprehensive studies on the fracture toughness of graphite materials with varying grain sizes, particularly concerning dynamic fracture toughness. This study addresses this gap by employing a digital-image-correlation-based virtual extensometer to analyze crack propagation in graphite materials of different grain sizes, enabling precise measurement of crack propagation length and fracture toughness. Findings reveal that static fracture toughness increases with larger grain sizes, while under dynamic loading, smaller grain sizes exhibit greater fracture toughness. Additionally, dynamic fracture toughness shows a near-linear increase with impact speed. Scanning electron microscopy analysis of fracture surface morphology highlights the impact of grain size and impact speed on fracture toughness. Nuclear graphite specimens with larger grain sizes have more irregular grain and pore distributions, enhancing crack deflection and propagation resistance, thereby increasing fracture toughness. The observed loading rate dependence of dynamic fracture toughness is attributed to a gradual transition from intergranular to transgranular fracture modes with increasing impact speed.

Investigating the Impact Behavior of Carbon Fiber/Polymethacrylimide (PMI) Foam Sandwich Composites for Personal Protective Equipment.

To improve the shock resistance of personal protective equipment and reduce casualties due to shock wave accidents, this study prepared four types of carbon fiber/polymethacrylimide (PMI) foam sandwich panels with different face/back layer thicknesses and core layer densities and subjected them to quasi-static compression, low-speed impact, high-speed impact, and non-destructive tests. The mechanical properties and energy absorption capacities of the impact-resistant panels, featuring ceramic/ultra-high molecular-weight polyethylene (UHMWPE) and carbon fiber/PMI foam structures, were evaluated and compared, and the feasibility of using the latter as a raw material for personal impact-resistant equipment was also evaluated. For the PMI sandwich panel with a constant total thickness, increasing the core layer density and face/back layer thickness enhanced the energy absorption capacity, and increased the peak stress of the face layer. Under a constant strain, the energy absorption value of all specimens increased with increasing impact speed. When a 10 kg hammer impacted the specimen surface at a speed of 1.5 m/s, the foam sandwich panels retained better integrity than the ceramic/UHMWPE panel. The results showed that the carbon fiber/PMI foam sandwich panels were suitable for applications that require the flexible movement of the wearer under shock waves, and provide an experimental basis for designing impact-resistant equipment with low weight, high strength, and high energy absorption capacities.

Parametric analysis of craniocerebral injury mechanism in pedestrian traffic accidents based on finite element methods

PurposeThe toughest challenge in pedestrian traffic accident identification lies in ascertaining injury manners. This study aimed to systematically simulate and parameterize 3 types of craniocerebral injury including impact injury, fall injury, and run-over injury, to compare the injury response outcomes of different injury manners. MethodsBased on the total human model for safety (THUMS) and its enhanced human model THUMS-hollow structures, a total of 84 simulations with 3 injury manners, different loading directions, and loading velocities were conducted. Von Mises stress, intracranial pressure, maximum principal strain, cumulative strain damage measure, shear stress, and cranial strain were employed to analyze the injury response of all areas of the brain. To examine the association between injury conditions and injury consequences, correlation analysis, principal component analysis, linear regression, and stepwise linear regression were utilized. ResultsThere is a significant correlation observed between each criterion of skull and brain injury (p < 0.01 in all Pearson correlation analysis results). A 2-phase increase of cranio-cerebral stress and strain as impact speed increases. In high-speed impact (> 40 km/h), the Von Mises stress on the skull was with a high possibility exceed the threshold for skull fracture (100 MPa). When falling and making temporal and occipital contact with the ground, the opposite side of the impacted area experiences higher frequency stress concentration than contact at other conditions. Run-over injuries tend to have a more comprehensive craniocerebral injury, with greater overall deformation due to more adequate kinetic energy conduction. The mean value of maximum principal strain of brain and Von Mises stress of cranium at run-over condition are 1.39 and 403.8 MPa, while they were 1.31, 94.11 MPa and 0.64, 120.5 MPa for the impact and fall conditions, respectively. The impact velocity also plays a significant role in craniocerebral injury in impact and fall loading conditions (the p of all F-test < 0.05). A regression equation of the craniocerebral injury manners in pedestrian accidents was established. ConclusionThe study distinguished the craniocerebral injuries caused in different manners, elucidated the biomechanical mechanisms of craniocerebral injury, and provided a biomechanical foundation for the identification of craniocerebral injury in legal contexts.

Моделювання коливальних процесів віброударних систем

In order to improve the efficiency of methods and means of mathematical modeling of vibro-impact systems, a generalized function of the periodic mode of movement of the executive body has been developed. It is presented in the form of the dependence of the shock impulse on the ratio of the angular velocities of the linear conservative system and its own. When obtaining this function, the Heaviside integral jump function and the periodic Green's function were used. The function of the dependence of the oscillation frequency on the impact impulse is determined from the impact conditions for the function of the system's response to a periodic sequence of impulses. The design model of a vibroimpact system is considered, both with one impact element and a motion limiter, and with a double-sided impact pair with alternate impact interactions with the limiters. In the intervals between impacts, there is a linear force interaction. When developing the mathematical model, a stereomechanical impact model was used, which is characterized by the velocity recovery coefficient after the impact. The analysis of the dependence function of the oscillation frequency on the shock impulse made it possible to obtain skeletal diagrams of resonant and quasi-resonant oscillations of vibro-impact systems with one and many degrees of freedom. Based on the obtained phase diagrams of the state of vibro-impact systems, it was determined: in a system with a gap, an increase in the impact speed increases the oscillation frequency, and the vibro-impact nonlinearity is «hard»; in a system with tension, with an increase in the value of the shock impulse, the oscillation frequency decreases (nonlinearity is «soft»). In the absence of a gap, the system is isochronous. Depending on the initial energy reserve and the location of the limiters in an asymmetric oscillatory system, with one degree of freedom, there can be vibro-impact modes with both one (closer located) and both limiters. In a linear conservative system with several degrees of freedom, a single-impact T-periodic regime is realized. If the dissipation during motion and impact is very small, then a regime close to resonant can exist in the system. In this case, periodic oscillations are supported by a weak external periodic force. The developed mathematical model makes it possible to fully describe the process of changing the relative coordinate of the movement of the working body, both in transient and in the established modes of movement of the system.

Dynamic Compressive Mechanical Properties of UR50 Ultra-Early-Strength Cement-Based Concrete Material under High Strain Rate on SHPB Test

UR50 ultra-early-strength cement-based self-compacting high-strength material is a special cement-based material. Compared with traditional high-strength concrete, its ultra-high strength, ultra-high toughness, ultra-impact resistance, and ultra-high durability have received great attention in the field of protection engineering, but the dynamic mechanical properties of impact compression at high strain rates are not well known, and the dynamic compressive properties of materials are the basis for related numerical simulation studies. In order to study its dynamic compressive mechanical properties, three sets of specimens with a size of Φ100 × 50 mm were designed and produced, and a large-diameter split Hopkinson pressure bar (SHPB) with a diameter of 100 mm was used to carry out impact tests at different speeds. The specimens were mainly brittle failures. With the increase in impact speed, the failure mode of the specimens gradually transits from larger fragments to small fragments and a large amount of powder. The experimental results show that the ultra-early-strength cement-based material has a greater impact compression brittleness, and overall rupture occurs at low strain rates. Its dynamic compressive strength increases with the increase of strain rates and has an obvious strain rate strengthening effect. According to the test results, the relationship curve between the dynamic enhancement factor and the strain rate is fitted. As the impact speed increases, the peak stress rises, the energy absorption density increases, and its growth rate accelerates. Afterward, based on the stress–strain curve, the damage variables under different strain rates were fitted, and the results show that the increase of strain rate has a hindering effect on the increase of damage variables and the increase rate.

Dynamics of an impacting emulsion droplet.

Emulsions are widely used in agriculture where oil-based pesticides are sprayed as an emulsion. However, emulsion droplets can bounce off hydrophobic plant surfaces, leading to major health and environmental issues as pesticides pollute water sources and soils. Here, we report an unexpected transition from bouncing to sticking to bouncing as the droplet impact speed increases. We show that the physics are governed by an in situ, self-generated lubrication of the surface leading to a suction force from the nascent oil layer around the droplet. We demonstrate that this phenomenon can be controlled by a careful balance of three time scales: the contact time of the droplet, the impregnation time scale of the oil, and the oil ridge formation time scale. We lastly build a design map to precisely control the bouncing of droplets and the oil coverage of the target surface. These insights have broad applicability in agriculture, cooling sprays, combustion, and additive manufacturing.

Measurement of fragments generated by hypervelocity impacts of micron-sized iron particles at grazing incidents

• Fragments of hypervelocity dust impacts are measured using a Delay Line Detector. • Majority of fragments created at grazing incidences are composed of dust projectile. • Fragmentation of projectiles increase with impact speed for grazing incidences. • The fragment speeds are distributed around 80% of the projectile impact speed. In this study, we present results from hypervelocity impacts of iron particles onto smooth surfaces under shallow incidence. For the first time, the submicron fragments of the projectiles were measured using a delay-line detector combined with a multichannel plate. Micron-sized spherical iron particles with speeds between 4–40 km/s are fired by a dust accelerator facility and impact on an optical mirror target at grazing angles of 2 ° , 4 ° , and 6 ° from the horizontal. Individual fragments generated in each impact event have been measured and analyzed including their speeds, masses, and trajectories. The total mass and momentum of fragments are comparable to their parent projectile. It is observed that most fragments have speeds exceeding 80 % of pre-impact velocities. Fragments generated at incident angle of 2 ° leave the target surface with even lower elevation angles of around 1 ° . The majority of impact fragments generated under incident angles of 4 ° and 6 ° form a spatial distribution centered an axis of 5 ° elevation, which increases with increasing impact speed. Furthermore, azimuthal scattering occurs with a distribution concentrated within ± 10 ° .

Analysis of safety impact of paved shoulder width on Czech secondary roads

Traffic safety is influenced, among other factors, by characteristics of the roads, which include the width of the shoulder. Shoulder width was noted to have a large effect on crash frequency, as well as on traffic speed. In this paper, we focused on paved shoulders. Previous studies confirmed that increasing the width of the paved shoulder is associated with a decrease in crash frequency. However, wider shoulders may encourage higher driving speed, which is related to an increase of impact speed and crash severity – this issue was hypothesized, but not statistically investigated. Thus, conclusions based on crashes and speeds contradict each other, and there is no simple answer to the question of the safety impact of wide shoulders. To address this gap, we analyzed a sample of two most typical categories of Czech secondary roads, which differ only in the paved shoulder width (S9.5 roads with 0.75m-wide shoulder, and S11.5 roads with 1.75m-wide shoulder) and thus present a suitable example for studying the safety impact of paved shoulder width. We used generalized linear models of crash frequency, and multinomial logistic models of crash severity (separately for single-vehicle and multi-vehicle crashes), as well as a statistical test of differences in speed for the two road categories. The results showed that: Firstly, there were fewer crashes on S11.5 roads compared to S9.5 roads; this was true for both single-vehicle and multi-vehicle crashes. Secondly, single-vehicle crashes on S11.5 roads were more severe compared to S9.5 roads; the change of severity in multi-vehicle crashes was not statistically significant. Thirdly, driving speeds on S11.5 roads were approx. by 7 km/h higher compared to S9.5 roads. These findings support the hypothesis of an association between wider shoulders, higher speeds, and increased crash severity, especially in the case of single-vehicle crashes. As a practical solution, various speed management measures, including widening to a 2+1 road, may be recommended.

Mechanical reinforcement mechanism of a hierarchical Kagome honeycomb

A hierarchical Kagome honeycomb with triangular sub-structures (KHT) is proposed in this study. KHT is constructed by introducing hierarchical configurations to conventional Kagome honeycomb. The theoretical model is established to analyze the compressive behaviors in terms of plateau stress and specific energy absorption (SEA) based on two-scale analysis method. Compared to the conventional Kagome honeycomb (KH), subjected to y-direction loading, the improvement of mean crushing force (MCF) and SEA of KHT is up to 104% and 83%, respectively. The remarkable enhancement on crashworthiness induced by the hierarchical configuration is demonstrated by the theoretical spectrum. The predicted plateau stress and SEA show high agreement with the simulated results. The mechanical reinforcement can be further realized by tailoring the topology and the number of sub-structures and the structure relative density. Subjected to the increasing impact speed, the reinforcement generated by the hierarchical design is gradually eclipsed by the inertial effect. The reinforcement mechanism is explicitly revealed from the aspects of macroscopic wall interactions and microscopic sub-structures collapse patterns. This study provides insight and opportunities into the role of structural hierarchy in designing hierarchical honeycombs equipped with extraordinary energy absorption properties.

Dynamic fracture mechanics and energy distribution rate response characteristics of coal containing bedding structure.

To investigate the influence of bedding structure and different loading rates on the dynamic fracture characteristics and energy dissipation of Datong coal, a split Hopkinson bar was used to obtain the fracture characteristics of coal samples with different bedding angles. The process of crack initiation and propagation in Datong coal was recorded by the high-speed camera. The formula for the model I fracture toughness of the transversely isotropic material is obtained on the basis of the finite element method (FEM) together with the J-integral. By comparing the incident energy, absorbed energy, fracture energy and residual kinetic energy of Datong coal samples under various impact speeds, the energy dissipation characteristics during the dynamic fracture process of coal considering the bedding structure is acquired. The experimental results indicate that the fracture pattern of notched semi-circular bending (NSCB) Datong coal is tensile failure. After splitting into two parts, the coal sample rotates approximately uniformly around the contact point between the sample and the incident rod. The dynamic fracture toughness is 3.52~8.64 times of the quasi-static fracture toughness for Datong coal. Dynamic fracture toughness increases with increasing impact velocity, and the effect of bedding angle on fracture toughness then decreases. In addition, the residual kinetic energy of coal samples with the same bedding angle increases with the increase of impact speed. The energy utilization rate decreases continuously, and the overall dispersion of statistical data decreases gradually. In rock fragmentation engineering, the optimum loading condition is low-speed loading regardless of energy utilization efficiency or fracture toughness. These conclusions may have significant implications for the optimization of hydraulic fracturing process in coal mass and the further understanding of crack propagation mechanisms in coalbed methane extraction (CME). The anisotropic effect of coal should be fully considered in both these cases.

The effect of slenderness ratio on water entry

In the paper, the air cavity created by vertical water entry of cylinders with different slenderness ratio (defined as “s=L/D”) is investigated experimentally, theoretically, and computationally. The study is focused on the range of Froude numbers,Fr=V/(gr) 0.5, (12&lt;Fr&lt;30). Particular attention is given to the effect of slenderness ratios on the surface seal time, the evolution process of the cavities. To understand the water entry physical processes, we conduct several experiments of water entry of different length cylinders. A theory model considering the added mass (induced by the water motion), buoyancy force, gravity, and water-resisting force is developed to predict the relationship between the falling distance and evolution time. Studies show that for the same size bullet the surface seal time of the cavity decreases with the increase of impact speed. Under the identical impact speed, the cavity seal time decreases with the increase of the slenderness ratio. For the consistent impact speed, with the value of “s” increase, the falling distance increase (the same moment). The falling distance captured by the developed theoretical model match with the experimental and numerical data.

Analysis on the Difference of Impact Response between Single Coal‐Rock Particle and the Box Structure‐Based Tail Beam

In the process of coal caving, the basis of identifying coal and rock by the vibration signal is the difference of the tail beam response when coal‐rock impacts the tail beam, and the tail beam in the hydraulic support is a complex box structure with multiplate transverse and longitudinal welding, and the response difference of the box structure‐based tail beam under the impact of coal‐rock is not clear. Therefore, this paper studies the response difference of box structure‐based tail beam when coal‐rock particle impacts on the box structure‐based tail beam. Firstly, through the construction and analysis of the impact theoretical model of the coal‐rock particle and metal plate, it is found that the complex box structure of the tail beam makes it extremely difficult to establish the impact theoretical model of the coal‐rock and box structure‐based tail beam, so it is impossible to directly study the response of the box structure‐based tail beam when the coal‐rock impacts on the box structure‐based tail beam by the theoretical method. Therefore, the impact simulation model of coal‐rock particle and box structure‐based tail beam is further established. Through the changes of kinetic energy and internal energy of the box structure‐based tail beam system, the contact response of collision contact zone, and noncollision contact zone of the box structure‐based tail beam, the response difference of box structure‐based tail beam when coal‐rock particle impacts on the box structure‐based tail beam is analyzed. Then, by changing the impact speed and contact mode of the coal‐rock particle, the effects of impact speed and the contact mode on the response difference of the box structure‐based tail beam are studied separately. The conclusion shows that the response difference of the box structure‐based tail beam under the impact of the coal particle and rock particle is obvious, and the difference increases as the impact speed increases, and the difference increases as the contact range increases.

Shock responses of nanoporous gold subjected to dynamic loadings: Energy absorption

Using the finite element analysis, we investigate the shock response, deformation behavior and energy–absorbing characteristics of stochastic bicontinuous nanoporous gold computationally, considering the effects of impact speed and relative density of materials. Three deformation modes during shocking, quasi–static compression, transition state and dynamic compression, are observed with the increasing impact speeds and the corresponding internal deformation mechanisms are demonstrated. The shock response under low–speed loading is similar to the R–LHP–L materials model, and it is more inclined to the R–S–H model as the impact speed rises. The peak stress, plateau stress, densification strain, energy, specific energy absorption (per unit volume) are assessed quantitatively. The peak stress shows a monotonous increase with impact speed, due to the enhanced inertial effect. The plateau stress and energy–absorbing efficiency are insensitive to low impact velocity, but significantly enhanced under high–speed loading. Remarkably, the results show that the energy absorption efficiency of nanoporous gold is better than conventional foam materials and nanofluidic energy absorption and dissipation system. The research not only further clarifies the shock responses and associated mechanisms of NPG, but also promotes its industrial application as an energy–absorbing material.

Numerical Investigation of Effect of Operating Parameters on the Phase Transformation During Vibration-Assisted Nano-Impact Machining of Silicon by Loose Abrasives

Abstract Vibration-assisted nano-impact machining by loose abrasives (VANILA) is a newly developed process based on the atomic force microscope (AFM) platform, where the nanoabrasive (diamond particles) slurry is injected between the workpiece and the vibrating AFM probe. This study aims to use the commercial finite element method (FEM) software package abaqus to simulate the phase transformation experienced by the silicon workpiece and to study the effects of VANILA process parameters, such as impact speed, impact angle, and coefficient of friction between the nanoabrasive and silicon workpiece, on the volume of phase transformation of silicon. Among these three parameters, impact speed is found to have the most dominating effect on the phase transformation process, followed by impact angle and friction coefficient. It is found that the volumes for Si-VII, Si-VIII, and Si-X phases increase with the increase of impact speed from 100 m/s to 200 m/s. The phase volumes of Si-VII and Si-VIII are found to decrease slightly with the increase of friction coefficient from 0.05 to 0.5. The phase volumes for Si-VII, Si-VIII, and Si-X are found to increase with the increase of impact angles from 20 deg to 90 deg. Finally, the multiple linear regression modeling using a design of experiments is carried out to study the relationship among the three parameters and the volume of different phases of silicon.

Laser-induced control of a cavity bubble behind a sinking sphere in water entry: Dependency on the surface temperature and impact velocity

We investigate the effect of continuous-wave laser irradiation on the cavity evolution behind a sphere in water entry. By tuning the irradiation time, the surface temperature (Ts) of the sphere before the impact varies in 105–355 °C. We change the radius and impact velocity of the sphere, by which both the shallow and deep seals are considered. Compared to the reference case (the sphere was roughened to have a cavity initially), we find that the cavity expands or shrinks depending on Ts. Overall, for all cases, the cavity bubble expands to the maximum size and shrinks steeply with increasing Ts. At higher Ts, the cavity is destroyed significantly, even smaller than the reference case. However, the detailed interaction between the cavity and laser-induced cavitation bubbles is quite different. In a shallow-seal case, nucleate boiling occurs on the sphere surface and vapor bubbles merge into the cavity, resulting in the expansion of the cavity. At a highly subcooled condition, on the other hand, the vapor bubble collapses into microbubbles as soon as it contacts water, resulting in the cavity reduction. As the impact speed increases (for a deep-seal condition), the flux of entrained air becomes dominant and the stage of cavity expansion is quite narrow. As Ts increases, the heated cavity collapses into microbubbles and almost 90% is destroyed. Finally, we investigate the effects of modified cavity on hydrodynamic forces on the sphere. While the temporal variation of hydrodynamic forces is complex, the drag reduction over 40% is achieved.

Peridynamic modeling of dynamic damage of polymer bonded explosive

Dynamic damage response of 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) based polymer bonded explosive (PBX) is investigated by using recently developed three dimensional Peridynamic (PD) method, allowing natural evolution of defects such as cracks or voids. An in-house PD codes are developed and verified by comparing with published results on Kalthoff-Winkler (KW) and crack branching benchmark tests. Numerical modeling of PBX is constructed via random micro-modulus approach, capable of capturing inherent microstructural heterogeneity of PBX materials. The simulation results indicate that damage process depends on both impact speed and interfacial property. Damage mode index (DMI), defined as the ratio of HMX-HMX damage to the summation of Binder-Binder and HMX-Binder damage, is proposed to quantify competitive damage mechanisms between trans- and inter-granular damage. The analyses of DMI exhibit that the inter-granular damage is dominant for the low adhesive strength of interface. However, the trend of trans-granular damage increases with increasing impact speed. The trans-granular damage mode becomes dominant for the high adhesive strength of interface. But the trend of inter-granular model increases with increasing impact speed. The current research highlight the competitive mechanisms of two typical damage modes as a function of material property and external loading conditions in a quantitative manner, providing additional insight into the damage mechanisms of PBX under impact loading.

Numerical investigation of impact breakage mechanisms of two spherical particles

Recently developed peridynamic (PD) simulations, allowing spontaneous crack nucleation and propagation, have been conducted to investigate the dynamic breakage behavior of impact spherical particles as a function of impact speeds. With the increase of impact speed, the Hertzian cracks, primary meridian cracks, secondary meridian cracks, circumferential cracks, and crack bifurcations are observed. The crack propagation speeds can reach 62% Rayleigh wave speed at impact speed of 20 m/s. Then with the further increase of impact speed, crack bifurcation is observed due to dynamic path instability, leading to the catastrophic failure of impact spheres. The evolution of damage ratio, defined as the ratio of broken bonds to total initial bonds in PD model, agrees with previous results using discrete element method (DEM), validating the current model. Furthermore, the comparison between computed and theoretic contact force is performed along with experimental measurements. The research provides additional insights into breakage mechanisms of particles.