ЖЕЛЕЗОБЕТОННЫЕ БАЛКИ С УЧЕТОМ РЕАКЦИИ РАСПОРА ПРИ КРАТКОВРЕМЕННОМ ДИНАМИЧЕСКОМ НАГРУЖЕНИИ

Dynamic impacts that became frequent lately cause large human and economic losses, and their prevention methods are not always effective and reasonable. The given research aims at studying the way of enhancing explosion safety of building structures by means of yielding supports. The paper presents results of numerical studies of strength and deformation property of yielding supports in the shape of annular tubes under static and short-term dynamic loading. The degree of influence of yielding supports was assessed taking into account three peculiar stages of deformation: elastic; elasto-plastic; and elasto-plastic with hardening. The methodology for numerical studies performance was described using finite element analysis with program software Ansys Mechanical v17.2. It was established that rigidity of yielding supports influences significantly their stress-strain state. The research determined that with the increase in deformable elements rigidity dependence between load and deformation of the support in elastic and plastic stages have linear character. Significant reduction of the dynamic response and increase in deformation time of yielding supports were observed due to increasing the plastic component. Therefore, it allows assuming on possibility of their application as supporting units in RC beams.

Design and calculation of steel concrete beams on yielding supports under dynamic loading requires considering the development of the thrust reaction that can lead to a significant increase in the bearing capacity and crack resistance of beams with yielding supports, which reduce the intensity of dynamic loading. Purpose : The aim of the work is to analyze the positive effectiveness of installing yielding supports in thrust conditionally flexible beams under intense dynamic loading. Methodology: The strength analysis of steel concrete beams at conditionally elastic deformation with thrust on yielding supports under the dynamic load. Numerical results are based on this method. Research findings : It is confirmed that the strength of flexible steel concrete beams with thrust directly depends on flexibility in the vertical direction. Value: The effectiveness is shown for yielding supports in flexible steel concrete structures with thrust under short-term dynamic loading.

The paper presents the results of a comprehensive experimental and numerical study of the destruction of reinforced beams made of concrete and fibroconcrete under short-term dynamic action. Experimental studies on were carried out on a copra rig. A short-term dynamic load on the beam was created with the help of a falling load weighing 450 kg from a height of 700 mm. In experiments, the magnitude of the dynamic load was determined using a force gauge sensor, linear displacement sensors were used to calculate linear displacements. Numerical modeling is carried out in a full three-dimensional dynamic formulation within the framework of the phenomenological approach of continuum mechanics with the explicit allocation of reinforcing elements. For the numerical solution, the finite element method is used, modified to solve dynamic problems. In the calculations, the impact of the load on the beam was replaced by an impulse. The dependence of the pulse on time was determined from the experiment. The effect of reinforcement on the deformation and destruction of the beam is investigated. The comparison of experimental and numerical results is carried out.

The aim of this paper is to give a brief overview of same field measuring techniques of soil properties under dynamic loading. Evaluation of determination of spring and dumper properties of dynamically loaded soil are presented. The methods of measuring basic parameters such as the spring constant and damping coefficient are given. The responses of the single mass system, supported by a linear spring and a viscous damper are investigated for vertical, sliding, rocking, and torsion vibrations. Dynamic plate loading tests are used for measuring soil properties in a wide range of independent variety of magnitudes of static and dynamic loads. Influences of static and dynamic loads on spring and damping behavior of soil are studied at the building site of Uglegorsk thermal power plant. For soil behavior of the embedded foundations the methods of analysis have been developed. The field method for determining properties of embedded plates under dynamic loads has performed on the sites with loam and sand. Free vertical and horizontal vibrations of the plates induced by the proper impact of mass. Experimental results of the dumping ratio and mass ratios measuring have shown.

Nucleus pulposus (NP) cell density is orchestrated by an interplay between nutrient supply and metabolite accumulation. Physiological loading is essential for tissue homeostasis. However, dynamic loading is also believed to increase metabolic activity and could thereby interfere with cell density regulation and regenerative strategies. The aim of this study was to determine whether dynamic loading could reduce the NP cell density by interacting with its energy metabolism. Bovine NP explants were cultured in a novel NP bioreactor with and without dynamic loading in milieus mimicking the pathophysiological or physiological NP environment. The extracellular content was evaluated biochemically and by Alcian Blue staining. Metabolic activity was determined by measuring glucose and lactate in tissue and medium supernatants. A lactate-dehydrogenase staining was performed to determine the viable cell density (VCD) in the peripheral and core regions of the NP. The histological appearance and tissue composition of NP explants did not change in any of the groups. Glucose levels in the tissue reached critical values for cell survival (≤0.5 mM) in all groups. Lactate released into the medium was increased in the dynamically loaded compared to the unloaded groups. While the VCD was unchanged on Day 2 in all regions, it was significantly reduced in the dynamically loaded groups on Day 7 (p ≤ 0.01) in the NP core, which led to a gradient formation of VCD in the group with degenerated NP milieu and dynamic loading (p ≤ 0.05). It was demonstrated that dynamic loading in a nutrient deprived environment similar to that during IVD degeneration can increase cell metabolism to the extent that it was associated with changes in cell viability leading to a new equilibrium in the NP core. This should be considered for cell injections and therapies that lead to cell proliferation for treatment of IVD degeneration.

Briquette coals with different cement contents are frequently used to study the coal body’s properties. In this study, the deformation and strength of briquette coal samples with 0, 5, 10, and 20% cement contents were experimentally and theoretically investigated using the acoustic emission (AE) characteristics monitored during the uniaxial compression tests. The results show that the uniaxial compression process of raw coal and briquette coal samples can be subdivided into compaction, elastic, plastic (yield), and brittle failure stages. With an increase in cement content, briquette coal samples undergo the elastic and plastic stages, and their postpeak stress drop rate gradually grows, and their plastic deformation is followed by brittle failure. The uniaxial compressive strength and elastic modulus of briquette coal samples show a linearly increasing relationship with cement content, while their Poisson’s ratio decreases gradually. During the uniaxial compression, raw coal and briquette coal samples produce the AE signals. The overall AE signal of briquette coal samples is relatively low, and there are no obvious AE events in raw coal samples. The uniaxial compressive strength, elastic modulus, and Poisson’s ratio of briquette coal samples with a 20% cement content and their AE signal cumulative amplitude, count, and energy values are very close to the corresponding parameters of raw coal samples. Therefore, they can be used for simulating raw coal samples in laboratory tests.

Fracture frequency of all-ceramic crowns during dynamic loading in a chewing simulator using different loading and luting protocols

Determination of mode I dynamic fracture toughness of IM7-8552 composites by digital image correlation and machine learning

Based on an analysis of the National Automotive Sampling System (NASS) database from calendar years 1995-2000, over 30,000 fractures and dislocations of the knee-thigh-hip (KTH) complex occur in frontal motor-vehicle crashes each year in the United States. This analysis also shows that the risk of hip injury is generally higher than the risks of knee and thigh injuries in frontal crashes, that hip injuries are occurring to adult occupants of all ages, and that most hip injuries occur at crash severities that are equal to, or less than, those used in FMVSS 208 and NCAP testing. Because previous biomechanical research produced mostly knee or distal femur injuries, and because knee and femur injuries were frequently documented in early crash investigation data, the femur has traditionally been viewed as the weakest part of the KTH complex. However, the relative risk of hip injuries to the risks of knee and thigh injuries in frontal crashes of late-model vehicles suggests that this may not be the case. This study investigated the frontal-impact fracture tolerance of the hip in nineteen tests performed on the KTH complexes from sixteen unembalmed human cadavers. In each test, the pelvis was rigidly fixed by gripping the iliac wings with the thigh-to-pelvis angle set to correspond to a standard automotive-seated posture. A dynamic load was applied to the knee along the axis of the femur at loading rates that are representative of knee-to-knee bolster impacts in frontal crashes. Rigidly fixing the pelvis minimizes inertial effects along the KTH complex, which results in similar force levels along the KTH complex. Consequently, in these tests, the weakest part of the KTH complex failed first. All seventeen fixed pelvis tests that produced usable data resulted in acetabular fractures at an average applied force of 5.70 kN (sd = 1.38 kN). The lack of injuries to the femoral shaft and distal femur in these tests indicates that the tolerance of the hip is less than that of the femur under frontal-impact loading. To further explore the tolerance of the femur relative to the hip, thirteen uninjured knee/femur specimens from seven cadavers previously used in hip tolerance tests were dynamically loaded. In these tests, the head of the femur was supported in a fixed "acetabular cup" to minimize inertial effects, and load was applied at the knee along the axis of the femur. All of these tests resulted in femoral neck fractures. Two tests also resulted in fractures to the femoral shaft. The average tolerance of the femoral neck from these tests is 7.59 kN (sd = 1.58 kN), which is significantly higher (p < 0.05) than the tolerance of the acetabulum. These results suggest that the mid and distal portions of the femur have a higher tolerance under these loading conditions than the pelvic and femoral portions of the hip.

A Novel Fluid Structure Interaction Experiment to Investigate Deformation of Structural Elements Subjected to Impulsive Loading

Insight into the localized strain effect on micro-galvanic corrosion behavior in AA7075-T6 aluminum alloy

The role of dislocation walls for nanoindentation to shallow depths

Study of the role of velocity fluctuations in processes of energy exchange between mesoscopic and macroscopic scale levels represents an important stage in the development of our knowledge about the shockwave behavior of heterogeneous materials. In the case of dynamic deformation, the concept of mesoparticle has much wider meaning as applied to quasistatic processes, in which mesoparticles are specific structural defects such as dislocation groups, vortex structures, shear bends, and other structural formations of scale 0.1‐10 μ m [1]; they represent field structures, the only distinct feature of which is the presence of a velocitycorrelated group of medium points. This means that a mesoparticle is a space formation, the internal points of which have identical or close velocities. The lifetime of these structures is determined by the duration of the dynamic deformation process. Each mesoparticle, as a separate structural formation, has its own overall velocity. In a heterogeneous medium, a dynamically deformed structure is characterized by velocity scattering. Therefore, mesoparticle velocity fluctuations can remove a considerable part of momentum and energy transferred to the medium. According to recent experiments [2], the generally accepted opinion that 90% of plastic work is immediately transformed into heat is erroneous. It is found that, in the microsecond range of dynamic loading, only 30‐ 35% of plastic work is transformed into heat, while the rest of the work is spent on the formation of the mesostructure. The main mechanism of structure formation is large-scale velocity fluctuations, the quantitative characteristic of which is the standard deviation of the mesoparticle velocities. Analysis of the experimental data on shock loading of materials reveals two regimes of energy exchange between mesoscales and macroscales of dynamic deformation—smooth or evolutional and catastrophic regimes. The latter regime implies that the mean particle velocity decreases suddenly at a certain strain rate, while the standard deviation of velocities increases. This statement was verified by impact tests of two sets of 30XH4M steel targets subjected to different thermal treatments. As an example, Fig. 1 shows the time profiles of the mean velocity and standard deviation of velocities as obtained upon plane impact loading of two targets with velocities of 324 and 320 m/s. The profiles were recorded using a two-channel velocity interferometer [3]. Although the impact velocities are close to each other in these experiments, the time profiles of the mean velocity and standard deviation of velocities are significantly different. In the first case, the mean velocity increases gradually up to 310 m/s, while in the second case, the break of the mean velocity occurs at a velocity of 160 m/s (point B in Fig. 1b). The behavior of the standard deviation of velocities is opposite: its increase rate is much higher in the second case. The second case corresponds to the catastrophic regime of energy exchange between the mesoscale and macroscale. To deduce a criterion for the transition from the evolutional to catastrophic regime of energy exchange between the mesoscopic and macroscopic scales of dynamic deformation, we consider the one-dimensional propagation of an elastoplastic wave in a medium characterized by mesoscopic velocity fluctuations. The equations of momentum and mass conservation have the form

In this paper, we use ABAQUS finite element numerical analysis software to theoretically study the damage model of the expanded head anti-floating anchor rod under tension in pulverized clay. The results show that: 1) the mode of anchor rod under tension damage is related to the burial depth ratio L1/D2, when L1/D2≤2, the anchor rod undergoes shallow burial damage; when L1/D2≥6, the anchor rod undergoes deep burial damage; when 2&lt;L1/D2&lt;6, the anchor rod undergoes mixed damage. 2) When the burial depth of anchor rod L1 is greater than 6m, the ellipse formed by the maximum principal stress cloud around the anchor rod is roughly 4D1 in height and 5D1 in width. 3) When the anchor is in the elastic stage, the load-displacement curves of shallowly buried anchor, transitional anchor, and deeply buried anchor are sloped straight lines with the same slope; after the anchor enters the plastic stage, the slope of the load-displacement curves decay at different rates for anchor rods with different burial depths. 4) The tensile damage of the deeply buried anchor rod roughly goes through the elastic stage, the plastic zone formation stage, the plastic zone soil strengthening, and the range expansion stage.

Strength and Deformability Models of Cellular Structure Shells at Static and Short-Term Dynamic Loading