Load Drop Research Articles

Influence of available impact energy of the testing machine on drop weight tear test characteristics of high toughness pipeline steels

Abstract. Problem. Currently, the problem he methodological issues related to drop load testing (DLT) of rolled plates and pipes made of highviscosity steel for high-pressure gas mains are considered. The imperfection of the current standards in terms of selecting the values of the stored energy of the copra, ensuring the correct testing of metal of the entire size range, is note. Goal Evaluation of the influence of stored copra energy on the results of WIP in terms of the amount of viscous component and absorbed fracture energy of full-thickness specimens of high-viscosity pipe steels widely used in the construction of high-pressure gas pipelines. Methodology. We examined sheets and base metal of pipes of strength classes X65, X70 and X80 of various thicknesses manufactured using thermomechanical rolling technology. The falling load tests were performed on Zwick copters of different capacities. Results The limits of application of the recommendations of APIRP5L3 and EN10274 standards for the choice of the value of the stored energy of the copra during the falling load test of high-viscosity pipe steels have been clarified. The recommendations are applicable only for steels with a thickness of less than 25 mm. Recommendations for selecting the optimal values of the stored energy of the copra at the HDM of high-viscosity pipe steels with a thickness of 25 mm and more are given Originality. The influence of stored copra energy on the results of WIP of high-viscosity pipe steels is estimated. Practical value. Recommendations were issued on the choice of the value of the stored energy of the ERW copra during testing, which will increase the measurement accuracy and reliability of the assessment of the resistance to destruction of gas pipelines

Brittle failure analysis and modeling of high-burnup PWR fuel cladding alloys

Abstract The aim of this research is the development of methods for predicting mechanical behavior and identification of limiting conditions to prevent brittle failure of high-burnup (HBU) pressure water reactor (PWR) fuel cladding alloys. A finite element (FE) model of the ring compression test (RCT) was created to analyze the failure behavior of zirconium-based alloys with radial hydrides during the RCT. An elastic-plastic material model describes the zirconium alloy. The stress-strain curve needed for the elastic-plastic material model was derived by inverse finite element analyses. Cohesive zone modeling is used to reproduce sudden load drops during RCT loading. Based on the failure mechanism in non-irradiated ZIRLO® claddings, a micro-mechanical model was developed that distinguishes between brittle failure along hydrides and ductile failure of the zirconium matrix. Two different cohesive laws representing these types of failure are present in the same cohesive interface. The key differences between these constitutive laws are the cohesive strength, the stress at which damage initiates, and the cohesive energy, which is the damage energy dissipated by the cohesive zone. Statistically generated matrix-hydride distributions were mapped onto the cohesive elements and simulations with focus on the first load drop were performed. Computational results are in good agreement with the RCT results conducted on high-burnup M5® samples. It could be shown that crack initiation and propagation strongly depend on the specific configuration of hydrides and matrix material in the fracture area.

Anisotropy and Temperature Dependence of Annealing During Mechanical Bending in Ni-Mn-Ga-Based Melt-Spun Ribbons

AbstractMechanical response during bending experiments of Ni-Mn-Ga-Co-Cu melt-spun ribbons with the L21 austenite structure was studied. This material exhibited anisotropy in mechanical properties depending on the side to which the applied bending force was directed. When force was applied to the “free side,” a substantial load drop was observed in the initial stage of bending. On the other hand, no load drop anomalies were observed when force was applied to the “wheel side.” Additionally, mechanical training effects were assessed by applying up to 10 bending cycles. It was demonstrated that with an increase in the number of bending cycles, there was no significant decrease in bending force, and the load–displacement curve remained unaltered. The temperature dependence of annealing of the ribbons' mechanical properties was also examined. The Ni-Mn-Ga-Co-Cu melt-spun ribbons were annealed at 373 K, 573 K, 773 K, 973 K, and 1173 K for 30 min, followed by subsequent bending tests. Annealing influenced bending response through two major phenomena detected. The first was associated with crystal structure ordering and recovery; while, the second was attributed to grain growth. Changes in mechanical properties influenced by different annealing temperatures were correlated with alterations in the microstructure of the studied ribbons.

Comparative retrospective study of injuries during military parachuting training and airborne operations from 2013 to 2020

IntroductionFrench paratroopers have been deployed during airborne operations for nearly a century. Parachute operations have increased since the start of Operations Serval and Barkhane in the Sahelo-Saharan strip. These military...

Wire Electrochemical Machining of Multiscale Superhydrophobic Arrays with Specific Unit Shapes on Stainless Steel.

The multiscale superhydrophobic array with a specific unit shape has a broader prospect for application in engineering materials, such as stainless steel (SS). However, the fabrication of the multiscale superhydrophobic array with a specific unit shape remains limited by several aspects, mainly including the complexity and controllability of multiscale integration of microstructures and arrays, the difficulties in obtaining specific unit shapes, and the low safety. Therefore, there is an urgent need for a relatively controllable, simple, and safe method to achieve a multiscale superhydrophobic array with a specific unit shape. Here, a safe and controllable method of integrating the array and microstructure into a multiscale superhydrophobic array is proposed by only wire electrochemical machining (WECM) in a harmless neutral electrolyte with controllable construction of different unit shapes. Here, first, the simulation and experiment of unit shapes by WECM is conducted to reduce the complexity of selecting parameters for different unit shapes; then, an integration of the microstructure and array is conducted; finally, hydrophobicity performances of multiscale superhydrophobic arrays are tested, including the drop loading test and drop impact test. The results show that multiscale superhydrophobic arrays by WECM exhibit excellent anti-intrusion performance and reduce solid-liquid contact time significantly, indicating only WECM can construct multiscale superhydrophobic arrays on SS with good controllability and safety.

Fracture behavior of SiCf/SiC cladding with prefabricated cracks on the inner/outer wall

This study investigated the fracture behavior of SiCf/SiC cladding with axial cracks in the CMC layer/monolithic SiC layer on the inner and outer wall via an expanding plug test. The specimen with a prefabricated crack on the outer wall fractured in no specific direction. After the first load drop, fracture sources can be detected not only near the notch but also in other directions within the CMC layer. The simulation shows a homogeneous stress distribution resulting in a similar hoop strength to the specimen without prefabricated cracks. In contrast, the specimen with a prefabricated crack on the inner wall fractured along the notch. After the first load drop, fracture sources can be detected only near the notch. The simulation demonstrates stress concentration, resulting in a lower hoop strength. Therefore, considering the nuclear application of SiCf/SiC cladding, we are supposed to pay more attention to the defects in CMC layer in the fabrication process of SiCf/SiC cladding.

Modeling of the damage and fracture behaviors of a SiC triplex tube during the burst test with elastomeric insert

The Silicon Carbide (SiC) triplex cladding tube has been regarded as one of the leading structures for the next-generation light water reactors, because of its larger safety margins under beyond-design basis transient conditions. In this study, a numerical simulation method is developed to reproduce the damage and fracture behaviors of a nuclear-grade SiC triplex cladding tube during the burst test. Especially, a three-dimensional continuum damage mechanics based (CDM-based) constitutive model is developed and validated for the SiCf/SiC composites, with the predictions agreeing well with the experimental data under different loading conditions. By introducing cohesive surfaces in the monolithic layers of a SiC triplex tube, cracking of the monolithic layers and the subsequent local damage behaviors within the SiCf/SiC composite layer are captured. The local tensile strength of ∼402 MPa is identified for the monolithic layers, corresponding to the first load drop during the burst test. The simulation results indicate that cracking of the monolithic layers leads to sharp increases in the locally enhanced hoop stresses and damage factors for the SiCf/SiC composite layer, with slight influences on the field variables far away from the main crack; after the fast increase the evolution velocity of local damage factors slows down, reflecting the toughening effects of SiCf/SiC composite. An assessment strategy for the gas leak tightness and structural integrity of the SiC triplex cladding during the accident sceneries is proposed to predict failure of the SiCf/SiC composites with the critical damage factor, and it is necessary to simulate the damage and fracture behaviors in the multi-layer models with the cracking process of monolithic layers involved.

Predicting soil hydraulic conductivity using random forest, SVM, and LSSVM models

AbstractUnderstanding the hydraulic properties of soil is essential to solve many management problems in agriculture and the environment. Water quality affects soil hydraulic conductivity. Soil hydraulic properties play an important role in nature's water cycle and are used as basic information in designing irrigation and drainage systems, hydrological issues, and soil quality assessment. In the current study, soil sampling is performed from different areas and its hydraulic conductivity was measured using the drop load method and then predicted using support vector machine (SVM) and least‐squares support vector machine (LSSVM) models. The model inputs were: soil texture (percentage of sand, silt, and clay particles), salinity (electrical conductivity), pH, sodium adsorption ratio, soil porosity, and bulk density and the output was soil hydraulic conductivity. Correlation coefficient, root mean square error (RMSE), mean bias error (MBE), and Nash–Sutcliffe efficiency (NSE) were used to evaluate the models and compare them. Based on evaluation criteria the best performance was obtained for random forest (RF) (R = 0.89, RMSE = 0.53, mean absolute error (MAE) = 0.54, and NSE = 0.72). Following RF, the SVM with (R = 0.69, RMSE = 1.32, MAE = 0.69, and NSE = 0.48) performed better than LSSVM model.

Effect of artificially induced microcracks near the rock surface on granite fragmentation performance under heating treatment

Various novel assisted drilling technologies enhance rock fragmentation performance by introducing microcracks on the rock surface to weaken rock strength. However, the quantitative relationship between artificially induced microcracks and rock fragmentation characteristics is not clear. In this study, we induced artificial microcracks of varying degrees on the rock surface through one-dimensional heat conduction. With the aid of the fluorescent resin, we visualized the microcrack patterns and quantitatively assessed the artificially induced microcracks. Subsequently, we performed quasi-static indentation tests on granite samples containing microcracks to establish the quantitative relationship between microcracks and rock fragmentation performance. The results indicate that the release of crystal water within the temperature range of 200 °C–300 °C is the primary factor leading to a significant increase in microcracks. Load drop signals correlate with the propagation of microcracks, including the competitive interactions between mechanically induced microcracks and artificially induced microcracks. Artificially induced microcracks require a certain initial length to continue propagating under mechanical stress, and excessively short microcracks are detrimental to subsequent propagation. A higher density of microcracks implies a more complex microcrack network, facilitating the merging of cracks to form rock chips under smaller mechanical loads. The consistency between the length density and number density of microcracks in influencing the crater parameters reflects their equal importance in affecting rock fragmentation performance. These findings could help determine the extent of rock weakening by artificially induced microcracks and reveal the mechanisms of rock fracture behavior influenced by microcrack, holding significant implications for the optimization of the process parameters of various assisted rock drilling techniques.

222.2: Drop in peripheral blood Epstein-Barr virus nucleic acid loads after post-transplant lymphoproliferative disorders associates with better 5-year event-free survival: results from the multicenter PTLD-MSMS study.

222.2: Drop in peripheral blood Epstein-Barr virus nucleic acid loads after post-transplant lymphoproliferative disorders associates with better 5-year event-free survival: results from the multicenter PTLD-MSMS study.

Tensile and low-cycle fatigue failure of carbon fiber reinforced aluminium laminates

Fiber metal laminates (FMLs) have emerged as advanced materials for engineering applications due to their high strength-to-weight ratio. This study aims to understand the mechanical response and failure mechanisms of carbon-fiber reinforced aluminium laminates (CARALL) under monotonic and cyclic loading, specifically uniaxial tensile and low-cycle fatigue (LCF) conditions. CARALL, fabricated with alternating (3/2) layers of AA2024-T3 and unidirectional carbon fiber composite, exhibits superior ultimate tensile strength (UTS) compared to AA2024-T3 sheets, with a distinctive three-zone stress-strain curve. The first zone shows elastic strain in both the aluminium alloy and laminate. The second zone features elastic strain in the laminate and plastic strain in the aluminium alloy. In the third zone, surface modifications enhance adhesion, leading to a sudden load drop due to fiber fracture or delamination. Fractographic analysis indicates no significant necking in the laminate, contrasting with the ductile failure of AA2024-T3. The carbon fiber layer exhibits a pure brittle fracture with visible delamination at the interphase of carbon fiber layer and aluminium alloy sheet. Under LCF conditions, the laminate’s cyclic stress response remains stable, with fatigue cracks initiating in the aluminium layers but mitigated by the carbon fibers, leading to cyclic softening. High-magnification images reveal striation marks and transverse micro-cracks in the aluminium, highlighting the complex interaction between aluminium and carbon fiber layers during fatigue.

Atomistic insight of deformation mechanisms and mechanical characteristics of nano-scale silver (100) using nanoindentation

This work aims to utilize the widely adopted nanoindentation technique to explore the deformation behavior and mechanical characteristics of nanocrystalline silver (Ag) materials. Molecular Dynamics simulations were conducted to understand the material behavior at the nanometer scale. In this simulation, the effect of indentation velocity and indentation depth on defect formation and hardness during nanoindentation of Ag specimens was analyzed and discussed in detail. The results show that the deformation behavior of the Ag specimen was affected by different indentation velocities. These phenomena were confirmed by analyzing the load-displacement curve, which indicates elastic deformation by the appearance of a linear load-displacement at low indentation velocities. In contrast, plastic deformation was found by the presence of intensified serration in the load-displacement relationship at higher indentation velocities. In these cases, the hardness showed little variation when the indenter velocity was increased from 5 m/s to 10 m/s, whereas a significant increase in hardness was observed when the indentation velocity was further increased to 20 m/s. Importantly, the progression of load-displacement curves during nanoindentation demonstrates the occurrence of minor and major load drops, corresponding to an increase in indentation depth from 0.5 nm to 2 nm respectively. These findings were elucidated through dislocation extraction analysis (DXA), which revealed that a minor load drop at low indentation depths is attributed to the nucleation of an amorphous structure, while a major load drop at higher indentation depths is associated with the expansion of dislocation nucleation. Consequently, the hardness increased significantly as the indentation depth increased. This research, provides insight into atomistic investigation and offers guidelines for designing materials with excellent mechanical properties using nanoindentation.

Local buckling behavior and reinforced mechanisms of short circular timber columns confined with bamboo scrimber

Developing sustainable high-performance bamboo scrimber (BS) as structural and reinforcing materials is significant. BS was used as reinforcing material to increase ancient timber columns' load-bearing capacity and safety via a damage-free strengthening method. The BS panels were fastened to the surface of the wooden columns by spaced steel strips. The spacing of the steel strips was the important factor in balancing the appearance of the confined reinforced timber columns with maximizing the strength of the confined panels. In this study, eight short circular wooden columns reinforced with BS with varying spacing of steel strips were fabricated and tested under axial compression. Each specimen's damage characteristics, load-carrying capacity performance, and strain coordination were analyzed and compared. The reinforcement method has a significant effect, and the reinforcement system of all specimens provides an additional load-bearing capacity of more than 48.3 % with about 38 % increase in cross-section area. The load-bearing capacity decreases significantly with increasing the spacing of steel strips. When the steel strips' distance is more than 363 mm (the corresponding slenderness ratio is 41), the confined panel showed significant buckling behavior from the beginning of loading. In contrast, the confined panels of the other circular reinforced timber column showed buckling and load drop only near the peak load, which takes full advantage of the strength of the BS material. The strain growth trends of the confined panels and core column were similar, although the strain of the confined panels' bending offsets some of the compressive strain, which was evidence that they were synergistically stressed under axial compression. The part of confined slats between the steel strips was intercepted as a compression bar, and the commonly used equation for the load-bearing capacity of a flexible bar was introduced. Various flex rod equations based on material properties were calculated and compared to the test results. The calculations showed that the buckling equation suggested by Euler and CSA086-19 had the best agreement with BS materials with similar proportional limits and ultimate strength. BS as a flex rod was suggested with a slenderness ratio not exceeding 32, and a general equation for calculating the steel strip spacing considering the material thickness was proposed for construction reference.

Prediction of the dynamic pressure drop of filter media loaded with water mists based on the deposited droplet mass distributions and pore network model

Predicting the pressure drop of a filter is necessary, especially regarding the jump in the dynamic pressure drop of a filter without pre-filters when clogged by rain or fog droplets. However, the efficient prediction method for the pressure drop in cylinder filters loading with water mists in the pore network faces limitations due to the high requirements for microscopic images of materials and the need to consider for the increasing holding droplet capacity of filters. In this study, a systematic method that takes into account the distributions of the deposited droplet mass within the water-absorbed filter medium layers in the pore network model (PNM) was developed. The pore geometry and distributions were determined from 2D microstructure images, and the dynamic deposited droplet mass and water-absorbing capacity of fibers were combined with the changing saturation to optimize the PNM for calculating the dynamic pressure drop of the filter media. Specifically, the empirical equation of the self-defined equivalent single fiber filtration efficiency (ESFFE) describes the relationship between the changing single fiber filtration efficiency and the deposited droplet mass. The optimized PNM is suitable for predicting the behavior of bibulous wood cellulose fiber filter media. The dynamic pressure drop shows a slight increase before surging, following the typical “channel and jump” model. Although the calculations deviate slightly from the experimental results with 25 % deviations, this systematic method effectively predict the jump in pressure drop of the tested filter medium. Therefore, this systematic method for predicting pressure drop of filters holds promise in anticipating unsafe pressure drop jumps in filters installed in coastal areas.

Auxetic lattice reinforcement for tailored mechanical properties in cementitious composite: Experiments and modelling

This study uses additively manufactured polymeric auxetic lattice as reinforcement to develop cementitious composites with improved ductility and energy absorption characteristics. The compression performance of plain mortar along with reinforced specimens was experimentally investigated using auxetic lattices with different Poisson’s ratio. Experimental results indicate that auxetic lattices fabricated from ABS polymer exhibit lower strength and stiffness than concrete, and therefore the load-bearing capacity of lattice reinforced mortar decreases with progress in compression. Nevertheless, ductility improvement was observed due the presence of auxetic lattices. The maximum ductility improvement was approximately 100 % and 200 % at 15 % and 50 % drop in peak load respectively. The failure pattern and energy absorption capability of lattice-reinforced concrete composites (LRCC) specimens were also affected by the auxetic design and it’s negative Poisson's ratio, as the highest energy absorption at failure is nearly eight times higher than the plain mortar. The finite element results corroborated by experiments elucidate the role auxetic reinforcement in LRCC at different volume fractions. The findings suggest that the peak stress, ductility, Young's modulus, and energy absorption capacity of LRCC can be effectively tailored for various applications by tuning the auxetic lattice (reinforcement) properties.

Decoding load or selection in visuospatial working memory?

Flexible updating of information in Visual Working Memory (VWM) is crucial to deal with its limited capacity. Previous research has shown that the removal of no longer relevant information takes some time to complete. Here, we sought to study the time course of such removal by tracking the accompanying drop in load through behavioral and neurophysiological measures. In the first experimental session, participants completed a visuospatial retro-cue task in which the Cue-Target Interval (CTI) was manipulated. The performance revealed that it takes about half a second to make full use of the retro-cue. In a second session, we sought to study the dynamics of load-related electroencephalographic (EEG) signals to track the removal of information. We applied Multivariate Pattern Analysis (MVPA) to EEG data from the same task. Right after encoding, results replicated previous research using MVPA to decode load. However, especially after the retro-cue, results suggested that classifiers were mainly sensitive to a selection component, and not so much to load per se. Additionally, visual cue variations, as well as eye movements that accompany load manipulations can also contribute to decoding. These findings advise caution when using MVPA to decode VWM load, as classifiers may be sensitive to confounding operations.

The effect of axial–torsion coupling on the compressive collapse behavior of Kresling tubes

The coupled axial compressive and torsional response of thin-walled tubes, having Kresling geometric units in series, with hollow hexagonal cross-sections of similar wall thickness, is studied. The tubes are fabricated using multi-jet fusion technology with Polyamide-12 (PA12) material. Each tube is compressed under displacement-controlled quasi-static loading with roller boundary conditions to eliminate any reaction torque being induced in the tube. The tube’s deformation response is characterized by an initial load rise followed by a drop in the load past a load maximum. This load drop is caused by localized collapse within a single Kresling unit. The collapse mechanism is accompanied by relative rotation between the ends of the Kresling unit, indicating the presence of compression-twist coupling. After local densification in the collapsed Kresling unit is attained, the load rises and attains a peak followed by a second load drop causing the other Kresling unit to collapse. Finite Element (FE) simulations show that the nonlinearity of the material response influences the onset of the collapse of the Kresling unit. Results from the present study will be helpful in tailoring the geometry of the Kresling unit cells to attain desired energy absorption or to “tune” the end-displacement vs. rotation response of the structure.

Investigating the effectiveness of concentric welded anchor rods in column base plate connections: A numerical and experimental study

This study presents a new strategy for column base plate connections, which involves the utilization of welded anchor rods positioned concentrically beneath the base plate, in alignment with the connected column. The objective was to remove the eccentricity between the anchor rods and the column, thereby excluding the base plate from the load-transferring chain. A numerical study was performed to compare the cyclic behavior and uplift response of the proposed connection with conventional column base connections. Additionally, different weld types were investigated to connect the anchor rods to the base plate, and their efficiency was evaluated based on a comprehensive dataset of nine tests on equivalent base-plate T-stub connections with different base-plate thicknesses, anchor-rod strengths, and anchor-rod diameters. The numerical results showed that using welded anchor rods could remove the pinching from the hysteresis loops, as the anchor rods can effectively resist cyclic loads in both compression and tension. Furthermore, removing the eccentricity between the anchor rods and the column enhanced the uplift stiffness by approximately 31 %. The experimental results indicated that the failure mode was the fracture of anchor rods for all specimens, while the other components remained elastic. The specimens with high-strength anchor rods showed a brittle failure accompanied by a sudden drop in load, which coincided with the fracture of anchor rod in the softened heat-affected zone. All developed weld types successfully withstood the ultimate tensile strength of anchor rods upon fracturing.

A reliability-based design against post-buckling load drop in spherical shell cap with stochastic imperfections

Elastic buckling is a critical design consideration for deep spherical shell caps. Significant reduction is observed in the experimental critical load from the linearized eigen-buckling analysis, for reasons extensively discussed in the past and relooked recently through the energy barrier concepts. The Knock Down Factors (KDFs) were proposed to account for such a reduction. The highly conservative KDFs constitute the lower bound of a large experimental dataset; that can be reconciled by nonlinear stability analysis of the imperfect shell. This study models the KDFs as Uncertain-but-Bounded (UBB) variables to present a Reliability-Based Design (RBD) for spherical shell caps having random geometric imperfections in radius (R) and thickness (t). The RBD furnishes the pertinent design variables ((R/t) ratio and the dome height-to-base radius (H/r0) ratio) for a target reliability index (β) and the respective KDFs. A metamodelling approach is employed to reduce the computational burden of the proposed RBD for a thin spherical shell cap having zero-mean, stationary, homogeneous, gaussian stochastic geometric imperfections. The Riks algorithm is employed in the commercial code ABAQUS for the finite element-based nonlinear stability analysis of shells. The KDFs and the reliability bounds are presented for varying degrees of imperfections. Remarkably, the margin of conservatism in the KDFs is shown to be narrowed down by incorporating the dependency on (H/r0).

Study of different heterocycles showing significant anti-severe acute respiratory syndrome 2 activity in vitro and in vivo.

With the emergence of severe acute respiratory syndrome-related coronavirus (SARS-CoV-2), antiviral drug development has gained increased significance due to the high incidence and potentially severe complications of the resulting coronavirus infection. Heterocycle compounds, acting as antimetabolites of DNA and RNA monomers, rank among the most effective antiviral drugs. These compounds' antiviral effects on various SARS-CoV-2 isolates, as found in existing data collections, form the basis for further research. The aim of this study was to examine the possible antiviral effect of some originally synthesized heterocyclic compounds. The main methods were cell culturing, cytotoxicity assay, qRT-PCR assay, tissue and blood cells analysis, and micro-computed tomography (micro-CT) imaging. In both in vitro and in vivo conditions, the elimination of SARS-Cov-2 occurred significantly earlier after administration of the compounds compared to the control group. In hamsters, the primary symptoms of coronavirus disease disappeared following administration of heterocycle compounds. Using delta and omicron strains of the SARS-CoV-2 virus, newly created heterocycle compound analogs dramatically reduced SARS-CoV-2 multiplication, resulting in a drop in viral RNA load in the supernatant under in vitro conditions. Improvements in pathological manifestations in the blood, bone marrow, and internal organs of hamsters demonstrated that heterocycle compounds inhibited SARS-CoV-2 replication both in vitro and in vivo.