Search Results (68)

Short fiber-reinforced polymer (SFRP) has been extensively applied in structural engineering due to its exceptional specific strength and superior mechanical properties. Its mechanical behavior under medium strain rate conditions has become a key focus of ongoing research. A comprehensive understanding of the response characteristics and underlying mechanisms under such conditions is of critical importance for both theoretical development and practical engineering applications. This study proposes an innovative three-dimensional (3D) multiscale constitutive model that comprehensively integrates mesoscopic fiber–matrix interface effects and pore characteristics. To systematically investigate the dynamic response and damage evolution of SFRP under medium strain rate conditions, 3D-printed SFRP porous structures with volume fractions of 25%, 35%, and 45% are designed and subjected to drop hammer impact experiments combined with multiscale numerical simulations. The experimental and simulation results demonstrate that, for specimens with a 25% volume fraction, the strain rate strengthening effect is the primary contributor to the increase in peak stress. In contrast, for specimens with a 45% volume fraction, the interaction between damage evolution and strain rate strengthening leads to a more complex stress–strain response. The specific energy absorption (SEA) of 25% volume fraction specimens increases markedly with increasing strain rate. However, for specimens with 35% and 45% volume fractions, the competition between these two mechanisms results in non-monotonic variations in energy absorption efficiency (EAE). The dominant failure mode under impact loading is shear-dominated compression, with damage evolution becoming increasingly complex as the fiber volume fraction increases. Furthermore, the damage characteristics transition from fiber pullout and matrix folding at lower volume fractions to the coexistence of brittle and ductile behaviors at higher volume fractions. The numerical simulations exhibit strong agreement with the experimental data. Multi-directional cross-sectional analysis further indicates that the initiation and propagation of shear bands are the principal drivers of structural instability. This study offers a robust theoretical foundation for the impact-resistant design and dynamic performance optimization of 3D-printed short fiber-reinforced polymer (SFRP) porous structures. Full article

Continuous SiC fiber-reinforced SiC matrix composites (SiC/SiC), as structural heat protection integrated materials, are often used in parts for large-area heat protection and sharp leading edges, and there are a variety of low-velocity impact events in their service. In this paper, a drop hammer impact test was conducted using narrow strip samples to simulate the low-velocity impact damage process of sharp-edged components. During the test, different impact energies and impact times were set to focus on investigating the low-velocity impact damage characteristics of 2.5D SiC/SiC composites. To further analyze the damage mechanism, computed tomography (CT) was used to observe the crack propagation paths and distribution states of the composites before and after impact, while scanning electron microscopy (SEM) was employed to characterize the differences in the micro-morphology of their fracture surfaces. The results show that the in-plane impact behavior of a 2.5D needled SiC/SiC composite strip samples differs from the conventional three-stage pattern. In addition to the three stages observed in the energy–time curve—namely in the quasi-linear elastic region, the severe load drop region, and the rebound stage after peak impact energy—a plateau stage appears when the impact energy is 1 J. During the impact process, interlayer load transfer is achieved through the connection of needled fibers, which continuously provide significant structural support, with obvious fiber pull-out and debonding phenomena. When the samples are subjected to two impacts, damage accumulation occurs inside the material. Under conditions with the same total energy, multiple impacts cause more severe damage to the material compared to a single impact. Full article

To clarify the potential failure modes of reinforced concrete (RC) beams under impact and understand their impact resistance safety, a comprehensive study was conducted by focusing on the failure mode discrimination and failure probability of RC beams under impact loads. This research utilized drop hammer impact tests, ABAQUS2022 software, and theoretical methods. The study examined three typical failure modes of RC beams under impact loads: flexural failure, flexural-shear failure, and shear failure. A discrimination criterion based on the flexural-shear capacity–effect curve was developed. Utilizing this criterion, along with the basic principles of structural reliability theory, the failure probability of RC beams under impact loads was calculated and analyzed using the Monte Carlo method. The results indicate that the criterion based on the flexural-shear capacity–effect curve can be used for discriminating failure modes of RC beams under impact loads. The impact velocity and stirrup ratio were identified as crucial factors that influenced the failure modes of RC beams under impact. Specifically, an increase in the stirrup spacing reduced the reliability of the RC beams under impact, while an increase in the stirrup ratio could significantly enhance their impact resistance. Furthermore, with a constant impact energy, an increase in beam span correlated with the improved reliability of RC beams under impact, where larger spans yielded a better impact resistance. Full article

The objective of this work was the synthesis and characterization of novel, insensitive high explosives. 1-hydroxy-5-methyltetrazole served as both a scaffold and anion for preparing various nitrogen-rich energetic salts. The compounds were characterized using ¹H and ¹³C NMR spectroscopy, high-resolution mass spectrometry, elemental analysis, low-temperature single-crystal X-ray diffraction, and IR spectroscopy. Thermal stability was investigated via differential thermal analysis (DTA). Sensitivities towards mechanical stimuli were measured using a BAM drop hammer for impact sensitivity and a BAM friction apparatus for friction sensitivity, employing one of six testing procedures. Energetic performance parameters were calculated using the EXPLO5 code, incorporating room-temperature X-ray densities and solid-state heats of formation obtained via CBS-4M calculations using the Gaussian 16 program. Full article

This paper presents the results of quasi-static tests carried out using a texturometer and of impact tests combined with stress relaxation on a stand equipped with a heavy pendulum of the hammer type. The tests were carried out using fresh roots and those stored at 20 °C for 120 h. The impact velocities V_d were 0.001, 0.002, 0.01, 0.02, 0.75, and 1.25 m·s⁻¹. Compiling the relaxation times T₁ for V_d indicated their large drops for both fresh and stored roots. The largest average values T₁ were obtained in the range from 0.197 s to 0.111 s at the small velocities of deformation 0.001–0.02 m·s⁻¹ and the smallest ones in the range from 0.0252 to 0.0228 s at the V_d equal to 0.75 and 1.25 m·s⁻¹. A decrease in T₂ values was observed in the average range of 8.02–4.27 s at V_d = 0.001–0.02 m·s⁻¹ for fresh beets. For the velocities 0.75 m·s⁻¹ and 1.25 m·s⁻¹ and stored roots, the range of average values was smaller and ranged from 6.13 s to 4.54 s. The reaction forces of the F_p sample reached the highest average levels from 168.2 N to 190.8 N for fresh roots and 46.5 to 56.2 N for 5-day-old roots. However, the lowest F_p was recorded at speeds (0.001–0.02 ms⁻¹) 57.5–62.3 N for the fresh roots and 46.5–56.2 N for the 5-day-old roots. For the velocities greater than 0.75 m·s⁻¹ and 1.25 m·s⁻¹, the values of reaction forces increased at the average values 168.2–190.8 N for the fresh roots and 158.2–175.4 N for 5-day-old ones. Full article

As a by-product of phosphate fertilizer production, phosphogypsum (PG) poses pressing environmental challenges that demand urgent resolution. To address the research gap in dynamic impact behavior of PG-modified concrete (PGC), this study developed truss-reinforced PGC slabs (PG volumetric fractions: 0% and 2%) and evaluated their impact resistance through drop-weight tests from a 3.75 m height. A systematic parametric investigation was conducted to quantify the effects of slab thickness (100–120 mm), steel plate reinforcement at the tension zone, PG content, and impact cycles. Experimental results revealed that increasing slab thickness to 120 mm reduced mid-span displacement by 13%, while incorporating steel plate reinforcement provided an additional 5.3% reduction. Notably, PG addition effectively suppressed crack propagation, transitioning failure modes from radial fracture patterns to localized mid-span damage. Finite element modeling ABAQUS (2022) validated experimental observations, demonstrating strong agreement. While optimized PG dosage (2%) exhibited limited influence on impact resistance, it enhanced PG utilization efficiency by 18%. Combined with increased slab thickness (displacement reduction: 13%), this study establishes a design framework balancing environmental sustainability and structural reliability for impact-resistant PGC applications. Within the framework of truss-reinforced concrete slabs with constant PG dosage, this study established a numerical model for geometric parameter modulation of impactors. Through systematic adjustment of the drop hammer’s contact width (a) and vertical geometric height (h), a dimensionless control parameter—aspect ratio c = h/a (0.2 ≤ c ≤ 1.8)—was proposed. Nonlinear dynamic analysis revealed that the peak impact load demonstrates an inverse proportional functional decay relationship with increasing c, yielding an empirical predictive model. These parametrized regularities provide theoretical foundations for contact interface optimization in impact-resistant structural design. Full article

With the continuous development of the new energy vehicle industry, in order to further improve the safety and range of electric vehicles, vehicle lightweighting has been a key focus of major car companies. However, research on lightweighting and the impact protection effect of battery pack protective plates is lacking. The bottom protective plate of the battery pack in this study has a sandwich-type multi-layer structure, which is mainly composed of upper and lower glass-fiber-reinforced resin protective layers, steel plate impact resistant layers, and honeycomb buffer layers. In order to study the relationship between the impact damage response and material characteristics of the multi-material battery pack protective plate, a matrix experimental design was adopted in this study to obtain the energy absorption ratio of different material properties when the protective plate is subjected to impact damage. This work innovatively used a low-cost equivalent model method. During the drop hammer impact test, a 6061-T6 aluminum plate in direct contact with the lower part of the bottom guard plate test piece was used to simulate the deformation of the water-cooled plate in practical applications. High-strength aluminum honeycomb was arranged below the aluminum plate to simulate the deformation of the battery cell. This method provides a scientific quantitative standard for evaluating the impact resistance performance of the protective plate. The most preferred specimen in this work had a surface depression deformation of only 8.44 mm after being subjected to a 400 J high-energy impact, while the simulated water-cooled plate had a depression deformation of 4.07 mm. Among them, the high-strength steel plate played the main role in absorbing energy during the impact process, absorbing energy. It can account for about 34.3%, providing reference for further characterizing the impact resistance performance of the protective plate under different working conditions. At the same time, an equivalence analysis of the damage mode between the quasi-static indentation test and the dynamic drop hammer impact test was also conducted. Under the same conditions, the protective effect of the protective plate on impact damage was better than that of static pressure marks. From the perspective of energy absorption, the ratio coefficient of the two was about 1.2~1.3. Full article

This paper investigates the dynamic performance of web frame structures under the impact of a conical hammer head. Compared with existing research on flat plates and stiffened panels, web frame structures exhibit significant differences in load-bearing mechanisms and design principles. To address these limitations, a series of drop-weight impact tests under different impact conditions are conducted, and the effects of drop heights on the dynamic responses of the web frame structure are systematically analyzed. By measuring the impact force responses and damage shapes, nonlinear dynamic characteristics and damage modes of the web frame structures under conical hammer head impacts can be revealed. The results indicate that higher drop heights lead to more severe damage areas, and damage area is more concentrated in the contact area of the indenter. Meanwhile, the peak impact force increases from 429.06 MN to 606.62 MN as the drop height increases from 1 m to 2.5 m, indicating a 41.38% rise. Additionally, the maximum energy absorbed by the structure reaches 62.89 KJ, and the energy loss ratio ranges from 18.58% to 30.73%. The findings offer critical theoretical insights and technical support for the optimization of impact resistant designs in web frame structures. Full article

As coal resources deplete and deep mining in high-stress environments becomes more challenging, ensuring safety and sustainability in coal production is a growing concern. This study investigates the dynamic of external load on the oxidation kinetics of coal in goaf, focusing on the resulting physical and chemical changes. Thermogravimetric (TG), differential thermogravimetric (DTG), and differential scanning calorimetry (DSC) tests were conducted on long-flame coal samples under varying hammer-drop heights. Impact-loaded coal shows a shorter reaction time, higher peak intensity, and lower apparent activation energy than untreated coal. These effects intensify with increasing drop height, resulting in a 13–40% reduction in apparent activation energy. A six-step reaction pathway for pyrolysis and oxidation was developed, and kinetics parameters were determined using genetic algorithms (GA). GA-based inverse modeling produced a comprehensive reaction model for coal oxidation under dynamic load. This work presents a detailed kinetic model for coal oxidation under impact, contributing to better understanding the challenges of safety and sustainability in deep coal mining. Full article

Conventional concrete does not often meet engineering needs in high-impact scenarios, such as airport runways and bridges, due to its brittleness, low tensile strength and insufficient resistance to dynamic loading. Although existing rubberized concrete exhibits an enhanced toughness, granular rubber exhibits significantly poorer mechanical properties, limiting its wide application. For this reason, in this study, we propose incorporating rubber in the form of fiber and systematically investigate the effects of the rubber fiber type (NBR, silicone rubber, EPDM), admixture amount (5%, 10%, 15%) and length (6, 12, 18 mm) on the mechanical properties and impact resistance of concrete. Through cubic compression, split tensile and drop hammer impact tests, combined with SEM microanalysis and Weibull distribution modeling, the trends in properties and the mechanisms of action were revealed. The key findings included the following: (1) The equal-volume replacement of fine aggregates with fibrous rubber significantly reduced the static strength, with NBR exhibiting the lowest compressive strength loss (13.12%) compared to silicone rubber (30.86%) and EPDM (21.52%). The splitting tensile strength decreased by 10.11%, 23.67% and 13.56%, respectively. (2) The rubber dosage was negatively correlated with static strength, while an increased fiber length partially mitigated strength degradations. (3) Fibrous rubber markedly enhanced impact resistance: the final crack impact cycles of NBR, silicone rubber and EPDM were increased by 255%, 147.5% and 212.5%, respectively, compared to plain concrete. The optimal mix (15% dosage, 12mm NBR) improved the impact life by 330%. (4) Weibull distribution analysis confirmed that the impact resistance data conformed to a two-parameter model (R² ≥ 0.808), with a high consistency between the predicted and experimental results. The results of this research can be applied to transportation infrastructures (e.g., heavy-duty pavements, bridges) that require a high impact resistance, with environmental benefits. However, the study did not analyze the long-term durability (e.g., effects of freeze–thaw and chemical corrosion) or perform an economic analysis of rubber fiber processing costs; this needs to be further explored in the future to promote practical engineering applications. Full article

The investigation of wave propagation in the geological environment is warranted, and will ultimately help to provide a better understanding of the response of subsoil to excitation. Frequently utilized physical modeling represents a simplification of the global natural system for the needs of the investigation of static and dynamic phenomena with regard to the time domain. The determination of appropriate model materials is probably the most important task for physical model creation. Considering that subsoil represents a crucial medium for wave propagation, an evaluation of suitable model materials was carried out. A plate load test with a circular plate is a non-destructive method for determining the static bearing capacities of soils and aggregates, which are usually expressed by the deformation modulus E_def,2 (MPa) and the static modulus of elasticity E (MPa). A lightweight deflectometer test was used to characterize the impact modulus of deformation E_vd (MPa), which is determined based on the pressure under the load plate due to the impact load. A representative propagation of the load–settlement curve for the PLT and the acceleration–time curve for the hammer drop test were investigated. The calculated E values were found to be in the interval between 2.6 and 5.7 kPa, and depending on the load cycle, the values of E ranged from 2.6 to 3.1 kPa. The modulus E from the hammer drop test was significantly larger than the interval between 10.6 and 40.4 kPa. The values of the dynamic multiplier, as a ratio of the hammer drop value to the PLT value, of the modulus E ranged from 4.1 to 13.0. The output of the plate load testing was utilized for the calibration of the finite element method (FEM) numerical model. Both the physical and numerical models showed practically ideal linear behavior of the mass. However, the testing of gelatin-like materials is a complex process because of their viscoelastic nonlinear behavior. Full article

The prestress loss of prefabricated continuous beam bridges directly affects their stress state and operating conditions. Excessive prestress loss can lead to increased mid span deflection of the main beam, cracking of the web and bottom plates, reduced bearing capacity, and even affect the safety of the structure. This study focuses on urban highway overpasses and measures the deflection of the bridge deck using the drop hammer impact method. The impact test of prefabricated segmental beam bridges was simulated using a finite element model, and the influence of prestress loss at different positions on the deflection basin of the bridge deck during operation was studied. The research results indicate that the factor causing the greatest damage to bridge stiffness is the loss of prestress in the bottom plate. When the prestress loss reaches 30%, the maximum response value increases by 33.6%. In contrast, the prestress loss of the roof has a smaller impact on deflection, with a maximum response value increase of 18.7%. This study provides important reference for evaluating prestress loss through impact testing methods in the future. Full article

In industrial production, 7075 aluminum alloy (A7075) is prized for its strength and light weight. However, heat treatment can reduce its hardness and wear resistance. Therefore, proper surface treatments are often necessary to optimize its mechanical properties. In this work, a hammering tool attached to a robotic arm was employed to impact the surface of A7075 using different impact energies, and the surface hardness, morphology, roughness, and frictional characteristics of samples subjected to machine hammer peening (MHP) treatment were analyzed to explore the strengthening mechanism of MHP. The results indicate that the hardness increased to a maximum value of 235 HV with rising impact energy, whereas the depth of influence (2 mm) was almost unaffected by the impact energy. Microstructural analysis revealed significant grain refinement, especially at 2.7 J. The surface roughness increased significantly to about 7.2 μm, then dropped to around 3.7 μm when the impact energy increased to 2.7 J. Finally, the roughness decreased to ~6.8 μm. In addition, the samples that were strengthened by MHP demonstrated low friction coefficients (about 0.27) and wear volume (minimum value of 7.67/10⁻⁴ mm³), implying that MHP can effectively improve the wear resistance of A7075. Observation by SEM revealed that the corresponding wear mechanism is mainly attributable to mild oxidative wear and three-body wear. Full article

This paper investigates the low-velocity impact response and damage behavior of glass fiber reinforced polymer (GFRP) hollow ribbed emergency pipes of our design under different impact heights. Drop hammer impact tests with impact velocities of 8.41 m/s, 8.97 m/s, and 9.50 m/s were conducted using an impact platform. A progressive damage model for low-velocity impact was developed using Abaqus/Explicit finite element software. The model used the three-dimensional Hashin damage initiation criteria and a damage evolution model based on the equivalent strain method to simulate the initiation and evolution of intralaminar damage in the pipe ring. A cohesive zone model (CZM) based on a bilinear traction-separation law was used to simulate delamination. The results show that the pipe rings experienced fiber or matrix fractures and delamination damage during the impact process. Additionally, the pipe ring specimens underwent bending vibrations under the impact load, leading to fluctuating contact forces at all three impact heights. Analysis of the simulation results reveals that the primary damage modes in the GFRP hollow ribbed emergency pipe are fiber tension damage, matrix tension damage, and fiber compression damage, with delamination occurring mainly in the impact area and the interface area on both sides of the rib. Full article

In this study, the high-temperature deformation behaviour of the UNS S32750 Super Duplex Stainless Steel (SDSS) alloy was investigated by means of deformability and microstructure evolution in the (1050–1200) °C temperature (T) range. The deformability of the UNS S32750 SDSS alloy was investigated by the up-setting method using a gravity-drop hammer, with the following deformation energy/impact energy ($E^{\ast }$): 545.2 J, 1021.5 J, 1480.6 J, and 1905.3 J. Data referring to deformation resistance (${\sigma }_c^{\prime }$) and mechanical work ($A^{\ast }$) as a function of deformation temperature (T) and deformation energy/impact energy ($E^{\ast }$) were obtained and analysed. It was shown that increasing the deformation temperature leads to an increase in the obtained deformation degree (degree of reduction in height). By analysing the rate of increase in the deformation degree as a function of the applied impact energy, it was shown that the rate of increase in the deformation degree rises with the increase in the applied impact energy. Also, it was observed that the evolution of the deformation resistance (${\mathsf{\sigma }}_{\mathrm{c}}^{\prime }$) as a function of temperature (T) shows a decreasing tendency while increasing the deformation temperature for all impact energies and that the evolution of the mechanical work (${\mathrm{A}}^{\ast }$) as a function of temperature (T) shows a decreasing tendency while increasing the deformation temperature for all impact energies. The microstructure evolution of the UNS S32750 SDSS alloy was investigated by X-ray diffraction (XRD) and Scanning Electron Microscopy-Electron Backscatter Diffraction (SEM-EBSD) techniques. It was observed that, in all cases, the microstructure shows intensely deformed grains, strongly elongated in the rolling direction in both ferrite (δ) and austenite (γ) intensely deformed grains. The intensity of grain deformation is increasing with the increase in the applied deformation degree. Also, it was observed that increasing the deformation temperature leads to a strong increase in the weight fraction of the dynamically recrystallised (DRX) ferrite (δ) grains. Full article