Peak Deflection Research Articles

Determination of high‐strength polymer composite reinforcement effect on the armor‐grade aluminum plates' explosion resistance—A computational perspective

AbstractThe selection of highly efficient materials is a crucial task for designing protective structures or armor against extreme explosive loadings. Due to the high strength‐to‐weight ratio of various grades of aluminum alloys and composites, they are mostly preferred for making protective structures. Investigation of their explosion resistance characteristics through experiments is very costly, dangerous, and time‐consuming. Hence, the present work deals with a cost‐effective numerical analysis on explosion resistance performance evaluation of various armor‐grade aluminum alloy plates of the same areal densities under 1–3 kilograms of trinitrotoluene explosions at a 100 mm stand‐off distance. The superior‐performance aluminum alloy plate is further reinforced with a high‐strength carbon/epoxy polymer composite to enhance its performance. The masses of the plates are maintained constant throughout the study. The Johnson‐Cook rate‐dependent material model and a progressive damage model including Hashin with Puck‐Schumann failure criteria were used to determine the realistic failures in the aluminum alloys and polymer composites, respectively. The outcomes of the study showed that the AA7075‐T6 plate has the highest deformation resistance under extreme explosion loadings. Carbon fiber‐reinforced aluminum laminate (CRALL) showed improved deformation resistance and energy absorption than those of the same mass of monolithic plate.Highlights Explosion resistance of various aluminum alloys of equal masses is compared. AA7075‐T6 provides better protection against blast compared with other alloys. To design CRALL, a carbon/epoxy composite used to reinforce the AA7075‐T6. CRALL provides 16.3% smaller peak deflection than the same mass of AA7075‐T6. CRALL improved energy absorption by 29.3% compared with same mass of AA7075‐T6.

Grain-size composition effect on flexural response and pore structure of cementitious tail-rock fills with fiber reinforcement

This paper explores the grain-size composition effect on flexural and micro-structural features of fiber reinforced cementitious tail-rock fill (FRCTRF). The FRCTRF mixes considered contained a stationary solid concentration of 70 wt% and a cement/tail rate of 1:6, and were cured for an age of 7-day for strength tests and microstructure. Three-point bending test shows that FRCTRF’s bending property is upgraded by totaling gravel rock. Adding fiber to FRCTRF’s bottom can enhance its peak deflection. With rising gravel particle size/dosage, FRCTRF’s peak deflection displays a trend of falling first and then growing. Accumulating polypropylene fiber could advance FRCTRF’s post-peak strength features as well. FRCTRF sample containing gravel has a large stress drop, and adding gravel rock could essentially boost FRCTRF’s post-peak brittle-ability. In conclusion, this study provides a strong scientific and theoretical underpinning for optimizing artificial false roofs employed recently in modern underground metalliferous mining operations.

Autonomous nervous system responses to environmental-level exposure to 5G's first deployed band (3.5GHz) in healthy human volunteers.

Following the global progressive deployment of 5G networks, considerable attention has focused on assessing their potential impact on human health. This study aims to investigate autonomous nervous system changes by exploring skin temperature and electrodermal activity (EDA) among 44 healthy young individuals of both sexes during and after exposure to 3.5GHz antenna-emitted signals, with an electrical field intensity ranging from 1 to 2V/m. The study employed a randomized, cross-over design with triple-blinding, encompassing both 'real' and 'sham' exposure sessions, separated by a maximum interval of 1week. Each session comprised baseline, exposure and postexposure phases, resulting in the acquisition of seven runs. Each run initiated with a 150s segment of EDA recordings stimulated by 10 repeated beeps. Subsequently, the collected data underwent continuous decomposition analysis, generating specific indicators assessed alongside standard metrics such as trough-to-peak measurements, global skin conductance and maximum positive peak deflection. Additionally, non-invasive, real-time skin temperature measurements were conducted to evaluate specific anatomical points (hand, head and neck). The study suggests that exposure to 3.5GHz signals may potentially affect head and neck temperature, indicating a slight increase in this parameter. Furthermore, there was a minimal modulation of certain electrodermal metrics after the exposure, suggesting a potentially faster physiological response to auditory stimulation. However, while the results are significant, they remain within the normal physiological range and could be a consequence of an uncontrolled variable. Given the preliminary nature of this pilot study, further research is needed to confirm the effects of 5G exposure.

On the role of temperature in the response of air-backed composites to hydrodynamic loading: An experimental study

Understanding the role of temperature in the dynamic response of composite plates is critical for naval systems operating in extreme environments like the Arctic. Despite the advantages of composite materials in improving corrosion resistance and enabling the customization of material properties to their environment, their behavior at cold temperature, especially under dynamic loading, remains elusive. This research gap hinders the effective use of composite materials in extreme environments. Here, we study the dynamic response of air-backed fiberglass epoxy plates under hydrodynamic loading at room temperature and 4∘C. By employing digital image correlation and particle image velocimetry, we investigated the interplay between fluid–structure interactions and cold temperatures. Our findings reveal the critical role of temperature in shaping the dynamic response of air-backed composites through changes in the stiffness and damping properties. At cold temperature, the plate experiences a larger (smaller) deformation in the initial (latter) phase of the dynamic response. Furthermore, we observed a pronounced coupling between the structural response and the flow physics, with peaks of the hydrodynamic loading synchronized with the peak deflections. Our results underscore the importance of considering temperature in the design of naval systems for extreme environments, providing key insights into fluid–structure interactions at cold temperature.

Multiple impact tests on precast reinforced concrete beams with pressed sleeve connections

Buildings may experience impact loads or even multiple impacts during their service life. Precast concrete (PC) structures have been widely used in engineering, with PC beams serving as the primary load-bearing components in these structures. In this study, six PC beams and two cast-in-place reinforced concrete (RC) beams were designed and manufactured, and drop hammer impact tests were conducted. Additionally, static load tests were conducted on two corresponding PC and RC beams. The experimental study provided benchmark data examining the influence of varying drop hammer mass, impact velocity, and level of pre-damage on the dynamic response of the PC beams, including their failure mode, mid-span deflection, impact force, deflection recovery ratio, and deformation energy consumption. The experimental results confirmed the reliability of using pressure sleeve connection as the assembly and connection form of PC beams. Under equivalent energy conditions, an increase in impact mass simultaneously leads to a decrease in peak and residual deflection of PC beams. This reduction is accompanied by an increase in their average impact force. Under the same impact mass and velocity conditions, the peak deflection of beams exhibiting different degrees of damage exceeded that of undamaged beams, although their residual deflection was relatively lower. In addition, the deflection recovery rate of damaged beams is slightly higher than that of undamaged beams.

Behind Armor Blunt Trauma: Liver Injuries Using a Live Animal Model.

While the 44-mm clay penetration criterion was developed in the 1970s for soft body armor applications, and the researchers acknowledged the need to conduct additional tests, the same behind the armor blunt trauma displacement limit is used for both soft and hard body armor evaluations and design considerations. Because the human thoraco-abdominal contents are heterogeneous, have different skeletal coverage, and have different functional requirements, the same level of penetration limit does not imply the same level of protection. It is important to determine the regional responses of different thoraco-abdominal organs to better describe human tolerance and improve the current behind armor blunt trauma standard. The purpose of this study was to report on the methods, procedures, and data collected from swine. Live swine tests were conducted after obtaining approvals from the local institution and the Army Care and Use Review Office of the U.S. Department of Defense. Trachea tubes and an intravenous line were introduced before administering anesthesia. Pressure transducers were inserted into the lungs and aorta. An indenter simulating the backface deformation profiles produced by body armor from military-relevant ballistics to human cadavers was used to deliver impact loading to the liver region. A triaxial accelerometer was included in the indenter design. The animals were monitored for 6 hours, necropsies were performed, and injuries were identified. Biomechanical data of the energy, velocity, deflection, viscous criterion, force, and impulse variables were obtained for each test. Peak accelerations, velocities, deflections, forces, impulse, and energies ranged from 897 to 5,808 g, 21 to 59 m/s, 1.96 to 8.87 cm, 2.3 to 13.1 kN, 1.1 to 7.1 Ns, and 58 to 387 J, respectively. The peak viscous criterion ranged from 0.8 to 5.8 m/s. All animals survived the 6-hour survival period. Three animals responded with liver lacerations while the remaining 4 did not have any injuries. The experimental design based on parallel tests with whole body human cadavers and cadaver swine was found to be successful in delivering controlled impacts to the liver region of live swine and reproducing liver injuries. Previously used biomechanical measures as potential candidates for injury criteria development were obtained. Using this proven model, tests with additional samples are needed to develop injury risk curves for liver impacts and obtain regional (liver) injury criteria.

Assessment of dynamic response of armor grade steel plates and FMLs under air-blast loads

This numerical study represents an effort to characterize the dynamic behavior of distinct armor-grade steel plates and fiber metal laminates (FMLs) of the same masses under blast loads. The blast resistance of finite element models of square steel plates and FMLs is evaluated by applying conventional weapon effects program air-blast loading ranging from 1 to 3 kg of trinitrotoluene (TNT) at a fixed stand-off distance (SoD) of 0.1 m. A user-defined subroutine is used to implement a failure criterion to determine realistic failures in the composite. A variation of kinetic energy, radial deflection, and energy absorptions of the steel plates and FMLs are determined to discover their blast mitigation performance. The deformation modes and equivalent plastic strain of both the steel plate and FMLs are also compared. The obtained results show that the armor-grade AISI 4340 steel has up to 50.5% smaller peak deflection than the other armor-grade steels. The use of FML with multi-thin layers of composite laminate and steel sheets instead of equivalent AISI 4340 steel plate significantly reduces the peak deflection up to 23.9% under similar blast loading conditions. The findings of steel plates and FMLs also represent their applicability for making complex protective structures.

Force magnitude and distribution during impacts to the hip are affected differentially by body size and body composition

Hip fractures are a severe health concern among older adults. While anthropometric factors have been shown to influence hip fracture risk, the low fidelity of common body composition metrics (e.g. body mass index) reduces our ability to infer underlying mechanisms. While simulation approaches can be used to explore how body composition influences impact dynamics, there is value in experimental data with human volunteers to support the advancement of computational modeling efforts. Accordingly, the goal of this study was to use a novel combination of subject-specific clinical imaging and laboratory-based impact paradigms to assess potential relationships between high-fidelity body composition and impact dynamics metrics (including load magnitude and distribution and pelvis deflection) during sideways falls on the hip in human volunteers.Nineteen females (<35 years) participated. Body composition was assessed via DXA and ultrasound. Participants underwent low-energy (but clinically relevant) sideways falls on the hip during which impact kinetics (total peak force, contract area, peak pressure) and pelvis deformation were measured. Pearson correlations assessed potential relationships between body composition and impact characteristics.Peak force was more strongly correlated with total mass (r = 0.712) and lean mass indices (r = 0.510–0.713) than fat mass indices (r = 0.401–0.592). Peak deflection was positively correlated with indices of adiposity (all r > 0.7), but not of lean mass. Contact area and peak pressure were positively and negatively associated, respectively, with indices of adiposity (all r > 0.49). Trochanteric soft tissue thickness predicted 59 % of the variance in both variables, and was the single strongest correlate with peak pressure. In five-of-eight comparisons, hip-local (vs. whole body) anthropometrics were more highly associated with impact dynamics.In summary, fall-related impact dynamics were strongly associated with body composition, providing support for subject-specific lateral pelvis load prediction models that incorporate soft tissue characteristics. Integrating soft and skeletal tissue properties may have important implications for improving the biomechanical effectiveness of engineering-based protective products.

Behaviour of rectangular concrete-filled steel tube beams under monotonic and cyclic loadings

Concrete filled steel tube (CFST) has been extensively explored for columns but limitedly explored for beams. This current study investigates the behaviour of rectangular CFST beams under monotonic and cyclic loadings. Experiments were conducted for 12 CFST beams with depth-to-thickness (D/t) ratios of 66.7–111.1, followed by theoretical analyses. The experimental results indicated that tensile yielding and compressive local buckling of steel tubes governed the plastic behaviour of the tested CFST beams. The buckling significantly degraded the strength of CFST beams. When the D/t ratio decreased from 111.1 to 66.7, the stiffness, yield load, and ultimate load increased by 33.2%, 49.4%, and 40.0%, respectively, but the ultimate deflection was reduced by ∼19.5%. The effect of cyclic loading induced a degradation of stiffness of 0.85–2.85%/cycle, depending on the increment of the peak cycle deflection. The buckling negatively affected the ultimate state, significantly reducing the ductility. Investigations into solutions to delay the buckling of steel tubes should be encouraged. Three approaches based on concepts of composite sections, fully plastic sections of steel tubes, and the proposed decoupling were applied to compute the ultimate strengths of the tested beams. The calculation results indicated that the model of fully plastic sections of steel tubes exhibited the best agreement with the test results. The fully plastic and proposed decoupling models provided reasonable results, while the composite model slightly overestimated the ultimate load of CFST beams. The results provide some technical information for structural engineers in designing rectangular CFST beams.

Electrocardiogram predictors of leadless pacemaker implantation in the right ventricular free wall

Abstract Background Leadless pacemakers (LLP) carry the potential risk of cardiac injury, especially when implanted in the free wall of the right ventricle. Purpose To investigate the ECG criteria for distinguishing free wall implantation of LLP, further clarification is needed. Methods We conducted a retrospective study involving 17 patients who underwent LLP implantation, followed by chest computed tomography to confirm the implantation site. Patients were categorized into three groups based on the location of implantation (septum [Sep], apex [Apex], and free wall [FW]), and we compared the morphology of the 12-lead ECG during LLP pacing. Results Among the implantation sites, nine were in the Sep (52.9%), five in the Apex (29.4%), and three in the FW (15.8%). In terms of pacing QRS morphology, the FW group exhibited significantly longer QRS duration (Sep: 145.6±15.2 vs. Apex: 161.6±3.6 vs. FW: 175.3±16.6, P&amp;lt;0.01), a notched QRS complex in lead III (Sep: 0.0% vs. Apex: 0.0% vs. FW: 100.0%, P&amp;lt;0.01), and a shorter peak deflection index (PDI) in lead V1 (Sep: 0.59±0.07 vs. Apex: 0.55±0.06 vs. FW: 0.40±0.02, P&amp;lt;0.01) than the other two groups. Receiver operating curve analysis to predict FW implantation revealed that a PDI of 0.42 in lead V1 (Area under the curve [AUC]=1.00, specificity=100.0%, sensitivity=100.0%, P&amp;lt;0.01) and a QRS duration of 173 msec (AUC=0.89, specificity=100%, sensitivity=66.7%, P&amp;lt;0.01) were the optimal cutoff values. Conclusion The LLP FW implantation group had a longer QRS duration, a notched QRS complex in lead III, and a shorter PDI in lead V1 compared to the other pacing sites.

Volume Stability and Frost Resistance of High-Ductility Magnesium Phosphate Cementitious Concrete.

To address the issue of pavement cracking due to brittle concrete in road and bridge engineering, this study explores the use of high-ductility magnesium phosphate cementitious concrete (HD-MPCC) for rapid repairs. The deformation and frost properties of HD-MPCC are analyzed to assess its suitability for this application. Deformation properties were tested for HD-MPCC specimens cured in both air and water. Subsequent tests focused on the frost performance and mechanical properties after freeze-thaw cycles. A mercury penetration technique was utilized to examine the pore structure. The findings reveal that the expansion deformation of HD-MPCC increases with curing age in both air and water conditions, and the quantitative relationship between the expansion deformation and curing age of HD-MPCC was analyzed. Additionally, the freeze-thaw cycles led to a decrease in mass loss, the relative dynamic elastic modulus, the ultimate tensile strength, the ultimate tensile strain, the flexural strength, and the peak deflection. The volume fraction of harmless and less harmful pores gradually decreased as the freeze-thaw cycle increased, while the volume fraction of more harmful pores increased, resulting in a decrease in the strength, ultimate tensile strain, and peak deflection.

Experimental Study on the Performance of Glass/Basalt Fiber Reinforced Concrete Unidirectional Plate under Impact Load

Fiber-reinforced composite materials have emerged as essential solutions for addressing the durability challenges of traditional reinforced concrete, owing to their lightweight nature, high strength, ease of construction, superior tensile capacity, robust corrosion resistance, and excellent electromagnetic insulation properties. This paper delves into the influence of loading rate and fiber bar type on the mechanical characteristics of concrete one-way plates through impact experiments on such plates fitted with glass/basalt fiber bars at varying drop weight heights. The test results reveal a direct correlation between increasing loading rates and escalating damage in fiber-reinforced concrete one-way plates, reflected in the progressive rise in peak deflection and residual displacement at the mid-span of the specimens. Notably, when subjected to higher impact loads, glass fiber-reinforced concrete specimens exhibit amplified deformation and intricate crack formations, consequently diminishing the overall deformation resistance of the plate. Furthermore, glass/basalt fiber-reinforced composites demonstrate notable vibration damping qualities, characterized by substantial residual displacement, minimal rebound, and rapid decay following vibration stimulation. Overall, glass fiber-reinforced one-way plates display marginally superior impact resistance compared to their basalt fiber-reinforced counterparts.

Enhancing Structural Performance: Fiber Reinforcement in Sintered Flyash Lightweight Concrete for Impact Resistance and Toughness

Objectives: The goal of this project is to better understand the interaction between fibers and concrete in order to produce Light Weight Aggregate Concrete (LWAC) with improved structural performance that is made from recycled materials, such as sintered flyash aggregate, and LWAC structures that are more resistant to impact loads and other dynamic forces. Methods: The sintered flyash aggregates are added as coarse aggregate to the concrete and basalt fiber (0.25% of mix) is used as a secondary reinforcement to improve the energy absorption, impact resistance and toughness behaviour. M30 grade of concrete was arrived after laboratory trials after which the mechanical properties were evaluated. The effect of drop impact load on slabs of size 300mm x 300mm x 50mm reinforced with two layers of bundled wire mesh was studied. The flexural properties of concrete reinforced with fiber prism of size 500mm x 100mm x 100mm were evaluated. Findings: With the addition of fiber, flexural toughness index and post-cracking toughness were increased notably on the initial deflections and cracks. The conventional fiber reinforced concrete exhibited a superior peak load capacity compared to normal weight concrete, with a measured increase of 7.5%. Conversely, normal-weight concrete demonstrated a significantly higher deflection under load, exceeding that of fiber reinforced concrete by 47%. LWAC displayed a distinct increase in both peak load (18.7%) and deflection (39.13%) when compared to Normal Weight Aggregate Concrete (NWAC). The incorporation of basalt fiber enhanced the energy absorption by 150% in NWAC and 80% in LWAC. Novelty: The incorporation of fiber into lightweight concrete reduces the brittle nature of failure. The post-cracking toughness behaviour was enhanced because of the effect of crack-arresting by fibers. After the first break, it was discovered to retain residual strength, and removing the fibers from the matrix required more force. Keywords: Sintered flyash aggregate, Light weight concrete, Basalt fiber, Toughness, Impact load, Energy absorption

Efficient design of composite honeycomb sandwich panels under blast loading

Hybrid composite honeycomb sandwich structures (HCHSS) were employed due to high specific strength and stiffness and higher impact resistance property required for the aerospace and defence fields. The numerical modelling of the efficient HCHSS was developed for the core, front and back face plate using the C3D8R elements to determine the realistic failure behaviour for the honeycomb sandwich structure. The ConWep blast simulation loading was applied for the HCHSS. Advanced composite materials were used for the blast analysis of the HCHSS (carbon/epoxy, graphite/epoxy, woven basalt fibres/polypropylene and woven Kevlar fibres/polypropylene). The damage initiation and damage propagation based progressive damage modelling was developed and implemented in the VUMAT code for composite materials to determine the actual failure behaviour of the HCHSS. The face sheets used in this model were of a stainless-steel alloy AL-6XN. The sandwich structure was subjected to blast loads of 1, 2 and 3 kg of TNT and their performance was compared w.r.t both front and back-face deflection. The effectiveness of sandwich panels was further examined by altering the thickness of the core. Fibre-metal laminates (FML) were used in place of the steel face sheets in the panel in order to minimise its mass, and a thorough analysis of the panel’s mass in relation to its peak deflection was carried out. Upon analysing the results, it was noted that the panel with the basalt fibre reinforced polymer (BFRP) core gave the best results compared to other composite materials. For a blast load of 3 kg TNT, the peak back face deflection (PBFD) of HCHSS with a BFRP core decreased by 10.64%, 7.61% and 4.75%, respectively, compared to panels with CFRP, GFRP, and KFRP cores. The peak deflection of the panel decreased as the BFRP core thickness increased. The energy absorption capacity of the panel also increased with increasing thickness. Additionally, it was found that panels with BFRP cores and KFRP-steel laminate face sheets provided the optimum balance of strong blast resistant performance and light weight. Compared to the metallic (steel) sandwich panel, the mass of the sandwich panel with KFRP-steel laminate face sheets and BFRP core was reduced by 33%, but at the same time, its PBFD increased by almost 50%.

Mechanical Analysis of Semi-Rigid Base Asphalt Pavement under the Influence of Groundwater with the Spectral Element Method

Over prolonged exposure to groundwater conditions, semi-rigid base asphalt pavements can undergo significant changes in their internal moisture field, resulting in substantial variations in the pavement’s stiffness and, consequently, affecting the overall load-bearing capacity and stability of the road structure. This paper employs FWD non-destructive testing equipment to assess its mechanical performance and conduct data analysis and conducts a mechanical response study of asphalt road surfaces, considering the influence of roadbed moisture levels. Using the dynamic analytical theory, the fundamental equations and stiffness matrices for a linear elastic half-space model were established, leading to the development of a computational model for the mechanical response of semi-rigid base asphalt pavements under FWD dynamic loading, with an examination of the surface deflection in relation to changes in groundwater levels. Numerical examples and engineering applications were employed to validate the proposed model. The research findings indicate: With the passage of time, surface deflection values initially increase and then decrease, exhibiting a sinusoidal variation pattern similar to that of the applied load. As the distance from the loading center increases, the moment of peak deflection continually lags behind. The average absolute relative error between the results obtained using the method proposed in this study and the traditional ABAQUS finite element method was only 0.70%. The correlation coefficient between the theoretically computed deflection curve and the measured deflection curve using the spectral element method was greater than 0.9, with an average absolute relative error of 4.92% between the theoretical peak deflection and the measured peak deflection. As the groundwater level rises, surface deflection noticeably increases, with an approximately 40% increase in deflection values at the loading center. These research findings can be utilized to analyze the dynamic deflection of semi-rigid base asphalt pavements under various groundwater conditions, providing significant practical value for assessing road structural performance and serviceability.

Polypropylene Fiber’s Effect on the Features of Combined Cement-Based Tailing Backfill: Micro- and Macroscopic Aspects

In undercut-and-fill mining, backfills show weak tensile strength and poor ductility properties since they act as artificial pillars to support stope roofs. Hence, the enhancement of the stability of mining structures and backfills is a crucial requisite for underground mining backfill operations. This study addresses the reinforcing effect of polypropylene (PP) on the strength features of combined cement-based tailing backfill (CCTB) with varied cement/tail ratios (c/t: 1:8 to 1:4) at both macroscopic and microscopic levels. Fill specimens containing a fixed solid content of 70 wt% were reinforced with fiber (0.6 wt%) and with no fiber (classified as a reference sample). They were then cast in mold sizes of 160 × 40 × 40 mm3, and cured for 7 days. Following curing, some experiments covering three-point bending assisted by DIC and SEM were performed to inspect the microstructure and strength features of CCTB. The results illustrate that the flexural strength of fiber-oriented CCTB increases along with the c/t fraction, but it is not greater than that of specimens with a high c/t fraction without fiber. Adding PP fiber, the peak deflection of CCTB specimens was improved, and the increment of peak deflection increased linearly with rising c/t fraction, enhancing CCTB’s bending characteristics. CCTB damage starts from the bottom to the middle, and the main cause of the damage is the stress distribution at the lowest section. The addition of fiber to CCTBs increases the ability to dissipate energy, which helps to hinder crack extension and prevent brittle damage from occurring. The microstructure shows that AFt and CSH were key hydrate materials in CCTB. As a result, this study develops the security of mining with backfill and helps to determine its design properties for safe production inputs and sustainable filling operations.

Dynamic Response Analysis of Reinforced Column Subjected To Shock Wave Loading

This study focuses on the dynamical response of reinforced concrete members subjected to shock-wave loading, which can cause catastrophic damage to structures. The effects of high strain rate loading and lateral confinement on the member’s behavior are considered in the analysis. The Moment-Curvature (M-ϕ) relations are assessed using stress block equilibrium at yield and ultimate state, and an analytical model is developed that integrates the high strain rate material behavior to predict the peak deflection of the structural member. The study evaluates the dynamic response of the member using a simplified model based on single degree of freedom (SDOF) idealization, and the response of the member in elastic and elastic-plastic phases is modelled using the bilinear resistance function. The governing equation of motion is explained using the Newmark-Beta algorithm, and the shock spectrum predicting the maximum deflection is developed by varying the load duration and magnitude. Additionally, a Finite Element (FE) model is developed to provide a more detailed understanding of the member’s behavior under shock loading. The results obtained from the FE model are compared with the analytical deflection for extreme combinations of load duration and magnitude. The study provides valuable insights into the behavior of reinforced concrete members under extreme loads, which can help structural designers in predicting and design structures that can withstand such loading conditions. The results can also be used in the development of building codes and standards to improve the safety and resilience of structures subjected to shock-wave loading.

Влияние полипропиленового волокна на цементный закладочный композит на основе хвостов обогащения

Introduction. The advantages of technology with backfill in minerals extraction predetermined their widespread use despite the high cost of production. One of the ways to reduce the backfilling cost is the use of tailings. However, earlier studies did not consider the inhomogeneity of shapes, sizes and internal mutual arrangement of particles, as well as the inhomogeneity of phases and density, which is characterized by the presence of pores. Materials and methods. Comparative analysis of samples with different recipes was used to investigate the bending strength of polypropylene fiber-reinforced backfill. A high-frequency automatic laboratory setup with strength transducers (load cells) was used to measure the bending characteristics. Optical moving digital image correlation (3D-DIC) method was used to track and automatically store the obtained results. Microstructure of the prepared and cured backfill was studied to correlate the obtained values. Results. 1. Maximum bending strength was demonstrated by unreinforced samples with 1:4 cement/tailings combination compared to the rest of samples regardless of the presence or absence of reinforcing fiber in the composition; 2. Directly proportional dependence between the increase in bending strength of samples and increase in the cement/ tailings ratio in backfill was established; 3. Increase in bending strength of the samples is maximum at low cement/tailings ratio in backfill composite; 4. There is a linear increase in peak strength and deflection values as the cement/tailings ratio in reinforced backfill increases. Discussion. Compaction of the internal structure is observed when reinforcing the composite with polypropylene fiber. It is noticeable that the compaction occurs due to fiber bonding, which allows improving the bending characteristics of samples. Such compaction is observed in all the investigated reinforced composites with ratios of 1:4, 1:6, 1:8. In some cases a decrease in fiber diameter is observed, which can be explained by the factor of occurrence of yanking or torsional forces at the moment of fracture. All the changes in reinforcing fibers confirm the fact that they are prone to deformations. Conclusion. The following conclusions can be drawn from the research conducted: 1. Unreinforced samples with a cement/tailings combination of 1:4 have the maximum bending strength in comparison with other samples, regardless of the presence or absence of reinforcing fiber in the composition; 2. Reinforcement of backfill with polypropylene fiber changes the fracture behavior of samples and passes from brittle to ductile at maximum strain rate; 3. Reinforcing fibers in the cement backfill have an overlapping effect, which significantly slows the development of cracks and increases the ductility of the material. Resume. The results of the research can be useful in the creation of high-strength and resistant to increased bending stresses artificial mass where tailings are used as an aggregate. In the future there is a need to study the cement backfill with different types of reinforcing fibers.

Response and damage mechanism of carbon/aramid intra-ply hybrid weft-knitted reinforced composites under low-velocity impact

Carbon and aramid fiber hybridization is an effective method to improve the impact toughness of composites, thus this paper attempts to develop carbon/aramid hybrid weft-knitted reinforced composites to improve the impact resistance of carbon fiber composites. Three hybrid and two non-hybrid weft-knitted reinforced composites employing carbon and aramid bundles were prepared. Low-velocity impact tests at different impact energies were performed, and the impacted samples were analyzed for visual and internal damages utilizing a three-dimensional optical microscope, ultrasonic C-scan, and micro-CT to explore the damage mechanisms. The results demonstrate that the knitted stitches and loop configuration affect the peak load, deflection, and damage crack initiation and expansion of the composites. The alternating configurations of carbon and aramid fiber in the in-plane and thickness directions incorporate the advantages of the high strength of carbon fibers and the toughness of aramid, exhibiting good impact mechanical properties and damage tolerance. The tight loop laminated structure had excellent impact resistance, with prominent peak loads and tiny damage volumes, but it encountered internal delamination and loop breakages.

Lateral impact behaviour of CCFT columns with spherical-cap gap imperfection: Numerical modelling and design method

To clarify the influence of gap imperfection on the impact behaviour of the concrete-filled steel tube (CFT) column, this paper performs numerical modelling on the mechanical responses of the circular CFT columns holding spherical-cap gaps (CCFT-SG) under lateral impact load. The effects of gap ratio, axial compression ratio, impact position, diameter/thickness ratio, boundary condition and material strength on the energy dissipation (Ea), the maximum (Fm) and equivalent impact forces (Feq), the peak (δm) and residual lateral deflections (δr) are analyzed after establishing and validating the finite element (FE) model. The typical failure pattern, time-history curve and contact response between the tube and concrete of the laterally impacted CCFT-SG column are revealed as well. The result declares that the overall failure morphology of the CCFT-SG column imposed with lateral impact showing as overall bending, is similar to that of the common CFT column, but distinct local depression is obtained because of the existence of spherical-cap gaps. With the gap ratio increasing, the Feq, Fm and Ea decrease gradually, while the δm and δr rise slowly. The calculation formulae for predicting the dynamic impact force and resistance of the CCFT-SG column are presented and validated against the existing test and numerical results.