Prolonged Loading Research Articles

Analysis of incidence of tibia stress fractures among the militaries

Аbstract. In the process of special training of military servicemen, various elements of the musculoskeletal system of a person are constantly exposed to mechanical loads of various frequencies, intensities and strengths. With such prolonged and shock loads characteristic of military personnel and athletes, permanent minor damage to the bones occurs, which over time can lead to impaired formation of bones and joints, up to the development of the disease. Violation of the motor reactions of the limb ultimately leads to the suppression of the mechanisms of social adaptation, physiological functions and aggravates the course of most diseases, decompensating processes that affect not only the quality of life, but also its duration. A very important point is that labor losses in military personnel during stress fractures can reach 6 months, which negatively affects the service, with a total duration of 12 months of military service. In this regard, questions arise about the advisability of such military servicemen in the army and further spending of budget funds for their maintenance. The stress fractures of long bones are analyzed on the example of fractures of the tibia. It has been established that the greatest number of injuries associated with stress fractures occur during combat training conducted in a special military uniform. A feature of the course of stress fractures is increasing pain in the limb. Among injured with tension fractures, 83,5% of the military did not do the sports before drafting, and physical activity that arose during the service was difficult or not tolerated.

Comparison of Multi-criteria Decision Making Methods for Selection of Handmade Carpets

ABSTRACT Selecting the best carpet from a set of available alternatives for a particular end-use situation is a difficult job because of association with multiple decision criteria. Three multicriteria decision-making (MCDM) methods, i.e., weighted sum model (WSM), weighted product model (WPM), and technique for order preference by similarity to ideal solution (TOPSIS) were used to evaluate the overall durability value of handmade carpets considering abrasion loss, compression recovery, thickness loss after dynamic loading, and thickness loss after prolonged heavy static loading as decision criteria. The weights of carpet properties (decision criteria) were determined by considering opinion of 10 domain experts. Abrasion loss, compression recovery, thickness loss after dynamic loading and thickness loss after prolonged heavy static loading received weights of 0.366, 0.186, 0.308, and 0.140, respectively. All the three MCDM methods yielded the same ranking for the first position. Moreover, WSM and WPM had complete agreement for the first seven positions. Rank correlation coefficient between WSM-WPM, WSM-TOPSIS, and WPM-TOPSIS are found to be 0.990, 0.943, and 0.973, respectively i.e. very high. Therefore, any one of these MCDM methods can be used for handmade carpet selection problem. Sensitivity analysis proved that the ranking produced by TOPSIS is quite robust in response to the change in weights of decision criteria.

Immediate Effect of Dynamic Cupping on Pain in Teachers with Mechanical Neck Pain: An Experimental Study

Background: Mechanical neck pain occurs due to prolonged loading on neck, poor posture, stress and changes in connective tissues. Cupping therapy is ancient medical treatment, which use suction on skin. Dynamic cupping gives combine effect of cupping and massage. Which relive muscle tension by increasing microcirculation. Aim: To find immediate Effect of dynamic cupping on pain in teachers with mechanical neck pain. Material and Method: 40 male and female teachers with mechanical neck pain were included in the study and treated with dynamic cupping. Numeric Pain Rating Scale and Pain Pressure Threshold were taken for pain intensity Measurement. Result: Paired t test was used for Intra group analysis. Significant difference was observed in pain intensity bychanges in score of in Numeric Pain Rating Scale and Pain Pressure Threshold (p< 0.05) immediately and after 280 minutes of treatment. Conclusion: Hence, we conclude that there is a significant reduction in pain after the treatment with dynamic cupping in teachers with mechanical neck pain. So, dynamic cupping can be used clinically in patients with mechanical neck pain.

ВЛИЯНИЕ ТЕМПЕРАТУРЫ И ДЛИТЕЛЬНОСТИ НАГРУЖЕНИЯ НА НЕСУЩУЮ СПОСОБНОСТЬ И ДЕФОРМАТИВНОСТЬ КЛЕЕНОЙ ДРЕВЕСИНЫ

The paper describes the problem of identifying the properties of a glue-wood beam in operation (with prolonged loading and variable temperature). Tests were carried out on model structures with prolonged transverse bending and constant temperature variations. During the tests, the values of stresses and deflections were recorded in a wide range of loads and temperatures. Stress diagrams are plotted for all investigated models. The results obtained showed that the presence of an adhesive layer significantly affects the bearing capacity and deformability of wood, which must be taken into account when designing wooden structures.

МЕТОД ПОСТРОЕНИЯ ДИАГРАММ-ИЗОХРОН ВЫСОКОПРОЧНОГО СТАЛЕФИБРОБЕТОНА И ЕГО МАТРИЦЫ

High-strength steel fiber concrete, made on the basis of fine-grained high-strength concrete, is a quite promising building material, in particular, for the construction of high-rise buildings and structures of increased massiveness. The introduction of steel fiber into the concrete matrix can significantly reduce the influence of such shortcomings of fine-grained concrete as increased fragility and explosive nature of fracture, and also positively affects the tensile properties of concrete. However, the widespread use of high-strength steel fiber concrete is currently limited, among other things, by the lack of an experimentally relied normative framework for this material. The proposed article aims to bridge this gap. Modern engineering trends are aimed at introducing into practice diagram methods of calculation based on real diagrams of material deformation under load. This article describes the technique of constructing isochron diagrams for fine-grained high-strength concrete and steel fiber concrete with disperse reinforcement in the amount of 1.5% by weight, made from Russian-made components. Isochron diagrams allow you to calculate the deformation of the material depending on the level of load at any time, including during prolonged loading. There have been made changes to the existing methodology, allowing to take into account the nonlinearity of both current and ultimate creep characteristics depending on the level of loading. The proposed theoretical dependences give good convergence with the experimental data.

Варикозная болезнь нижних конечностей в сочетании с Hallus valgus

Our research is dedicated to the combined pathology of musculoskeletal system – Hallux valgus with varicose veins of lower extremities that are common in the surgical practice. This study allowed us to estimate frequency of hallux valgus and varicose veins combined with each other and also to identify main factors that contribute to these diseases progression. Methods and principles of the research. To diagnose the combined pathology instrumental investigation (foot X-ray in two planes) was performed in 40 (36,7%) patients out of 109 that were under treatment in the surgical unit of the General Surgery department in “Private Healthcare Institution Clinical Hospital Russian Railways– Medicine”, Tyumen in 2019 and had varicose veins treated previously. A questionnaire was developed for conducting a sociological study. Results. The main reason of these diseases occurring is the congenital connective tissue defect and the veins wall weakening caused by the genetic predisposition. The acquired factors are: lifestyle and type of work (frequent and protracted static muscle load, wearing uncomfortable footwear), obesity. It is identified that the combined pathology (Varicose veins and Hallux Valgus) occur in every third patient, suffering from varicose veins. According to the results of the survey, 28 (70%) patients have genetic factors. Prolonged static load prevails among acquired factors, obesity takes the second position and it is diagnosed in 16 cases (11 women and 5 men). Conclusion. The frequency of these diseases occurring together was 36,7% in our study. Systemic approach allows to comprehensively assess various pathological changes in the blood and lymph circulation. “Combined pathology of musculoskeletal system” booklet was developed and implemented into the practical healthcare (among municipal polyclinics of Tyumen).

Wood moisture accounting in creep equations

Wood as a structural material differs from other materials used in construction and industry, high variability of its properties. This is due, among other things, to the action of various variable factors – moisture content, temperature, inclination of fibers and others. The influence of wood moisture is especially strong – as a result of moistening the strength of wood considerably decreases in comparison with durability in absolutely dry condition. In addition, wood is a significantly nonlinear structural material. Non-linearity is manifested both in short-term and prolonged loading. Research of wood in time can be divided into two directions: longterm durability of wood and creep of wood. Modern models of wood creep are based on linear theories. Analysis of experimental data of various researchers on wood creep, has shown that the area of linear creep is observed at rather low levels of loading. At medium and high levels of experimental loading the existing models of linear wood creep theory do not correspond to experimental data. All this points to the actuality of the development of methods of calculating wooden structures for creep (linear and nonlinear), taking into account the wood moisture.

Predicting plasticity‐controlled failure of glassy polymers: Influence of stress‐accelerated progressive physical aging

ABSTRACTThis study focuses on the prediction of long‐term failure of glassy polymers under static or cyclic loading conditions, including the role of stress‐accelerated progressive aging. Progressive physical aging plays a dominant role in a polymer's performance under prolonged loading conditions, and to obtain accurate predictions of failure, its effect has to be considered. First, the aging kinetics, as influenced by temperature and stress history, are studied extensively. Similar to an elevated temperature, the application of a stress (below the yield stress) activates the aging process, and as a result, the yield stress will evolve faster in time. The activation by stress appears to be limited; at some stress level, the activation stagnates and is followed by rejuvenation. This evolution is captured in a model by introducing a state parameter, which describes the thermodynamic state of the material and is directly linked to the yield stress. With the aging kinetics included in the model, an accurate prediction of the failure time for cyclic loading conditions is obtained. For static loading conditions, however, the effect of physical aging is overestimated because of the stagnation of the activation by stress. It appears that there are marked differences in the stress level where stagnation and subsequent rejuvenation occur for a cyclic or static load. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1300–1314

A synthetic bone insert may protect the lateral cortex and fixation plate following a high tibial osteotomy by reducing the tensile strains.

To determine the effectiveness of a synthetic bone insert on improving medial opening wedge high tibial osteotomy integrity in response to post-surgical cyclical loading. A medial opening wedge high tibial osteotomy, secured with a compression fixation plate, was performed on 12 cadaveric knee specimens that were randomised to either: (1) a synthetic insert condition (n = 6), in which a 9mm bio-absorbable wedge was inserted into the gap space; or (2) a plate-only condition (n = 6). Uniaxial strain gauges, placed on the lateral cortex and fixation plate, measured the strain response as the specimens were subjected to a staircase cyclical loading protocol; a sinusoidal waveform between 100 and 800N was applied and increased by increments of 200N every 5000 cycles until failure. Peak strains at failure were compared between conditions using a one-tailed independent samples t test. The strains from the fixation plate were significantly different between the insert and plate only conditions (p = 0.02), transitioning from a compressive strain with the wedge (mean [SD] = - 8.6 [- 3.6]µε) to a tensile strain without the wedge (mean [SD] = 12.9 [23]µε). The strains measured at the lateral cortex were also significantly affected by the inclusion of a synthetic bone insert (p = 0.016), increasing from - 55.6 (- 54.3)µε when the insert was utilised to 23.7 (55.7)µε when only the plate was used. The addition of a synthetic insert limited the tensile strains at the plate and lateral cortex, suggesting that this may protect these regions from fracture during prolonged loading.

Core-Shell Polymer-Based Nanoparticles Deliver miR-155-5p to Endothelial Cells

Heart failure occurs in over 30% of the worldwide population and most commonly originates from cardiovascular diseases such as myocardial infarction. microRNAs (miRNAs) target and silence specific mRNAs, thereby regulating gene expression. Because the endogenous miR-155-5p has been ascribed to vasculoprotection, loading it onto positively charged, core-shell poly(isobutylcyanoacrylate) (PIBCA)-polysaccharide nanoparticles (NPs) was attempted. NPs showed a decrease (p < 0.0001) in surface electrical charge (ζ potential), with negligible changes in size or shape when loaded with the anionic miR-155-5p. Presence of miR-155-5p in loaded NPs was further quantified. Cytocompatibility up to 100 μg/mL of NPs for 2 days with human coronary artery endothelial cells (hCAECs) was documented. NPs were able to enter hCAECs and were localized in the endoplasmic reticulum (ER). Expression of miR-155-5p was increased within the cells by 75-fold after 4 hours of incubation (p < 0.05) and was still noticeable at day 2. Differences between loaded NP-cultured cells and free miRNA, at days 1 (p < 0.05) and 2 (p < 0.001) suggest the ability of prolonged load release in physiological conditions. Expression of miR-155-5p downstream target BACH1 was decreased in the cells by 4-fold after 1 day of incubation (p < 0.05). This study is a first proof of concept that miR-155-5p can be loaded onto NPs and remain intact and biologically active in endothelial cells (ECs). These nanosystems could potentially increase an endogenous cytoprotective response and decrease damage within infarcted hearts.

EFFECTS OF DIABETES MELLITUS ON VISCOELASTICITY OF ULTRASTRUCTURES OF PERIPHERAL NERVES: THREE-DIMENSIONAL FINITE ELEMENT ANALYSES

Diabetes mellitus induces a variety of neuropathies and causes various symptoms. Understanding how diabetes affects mechanical properties of nerves is useful for preventing complications of diabetes mellitus such as the carpal tunnel syndrome. In a previous study, a two-dimensional hyper-viscoelastic finite element model (FEM) of the ultra-structures of normal rat sciatic nerves was developed using an optical coherence tomography (OCT) microscope and in vitro parallel compression tests. The main goal of this study was to extend the FEM from two to three dimensions and use it to explore hyper-viscoelasticity of ultra-structures of sciatic nerves of diabetic rats. A modification of the compression testing system to enhance OCT cross-sectional images of the nerve samples was also conducted. The results showed that the instantaneous shear moduli of the perineurium, epineurium, and endoneurium of the diabetic rat were all greater than those of the normal rats. Due to high instantaneous shear moduli and low percentage of relaxation, the diabetic nerve is prone to damage when subjected to prolonged mechanical loads.

Application of the Cervical Flexion Relaxation Ratio to Investigate the Impact of Torso-borne Load Redistribution

Students and military personnel often carry heavy torso loads (e.g. backpacks) which can lead to pain in the shoulders and back. To minimize pain associated with torso loads, load redistribution devices have been developed to off-load weight from the shoulders to the hip. Previous studies have used the cervical flexion relaxation ratio (cFRR), a measure of muscle activity between the extension and flexion phase of forward head motion, to correlate backpack loads with the potential of developing neck pain. PURPOSE: Using the cFRR, assess the impact of redistributing torso-borne loads and whether changes in cFRR are observed following prolonged load carriage. METHODS: Twelve volunteers walked at 1.34 m·s-1 at 0% grade for 40 min while wearing a torso-borne baseline load of 27 kg and two load distribution conditions to offload shoulder pressure. Flexible pressure sensors monitored pressure distribution at the shoulders and hips. To capture cFRR, bilateral EMG sensors with integrated tri-axial accelerometers were placed on the cervical erector spinae muscle bellies. EMG data were sampled at 2 kHz, demeaned, band pass filtered from 30 to 500 Hz, and full wave rectified. cFRR (Table 1) was measured pre-walk and post-walk and outcomes were submitted to repeated measures ANOVA based on load conditions, side of body and time. RESULTS: The average pressure measured at the shoulders for the baseline load (3.76 ± .90 kPa) was significantly higher than the two load distribution conditions (1.55± 1.68 kPa, p = .001; 1.72± 1.12 kPa, p < .0005, respectively). There were no main effects due to load condition or body side (p > .074). However, there was a significant main effect of time (p = .033). CONCLUSION: The load distribution equipment successfully shifted pressure from the shoulders to the hips, however this did not correlate with an improvement in cFRR. Changes in cFRR were observed pre- vs. post-walk indicating that the cFRR measure is sensitive to load carriage over time.Table 1: cFRR

Fatigue load mitigation in wind turbine using a novel anticipatory predictive control strategy

Wind energy has become a recent evolving source of renewable energy which needs an extensive exploration. The increased configuration of wind turbine instantaneously increases the structural loading of wind turbine components. The prolonged loading on structural components imposes a great impact on the lifetime of the wind turbine and reduces the feasibility of thinner rotor blade. These economical detriments due to the structural damage of turbine are dealt effectively by proposing an anticipatory preview-based control strategy for individual pitching of blades. The proposed multiple point model predictive controller with fuzzy logic switching, exploits the preview wind measurement from the light detection and ranging system which predicts the wind speed in advance. The utmost objective of the proposed controller is its optimized individual blade pitching to reduce the fatigue loads on the wind turbine components using the preview wind data. The blade root bending moment of individual blades and the tower fore-aft deflection which are chosen as the parameters of fatigue stress to be analyzed and controlled. The National Renewable Energy Laboratory’s Fatigue, Aerodynamics, Structures and Turbulence 5 MW baseline onshore wind turbine is used for validating the proposed controller in MATLAB simulation. The non-linear wind field is simulated using the TurbSim software, and the short-term and lifetime damage equivalent loads of the wind turbine for the simulated wind field is analyzed using the MLife software of the National Renewable Energy Laboratory. The proposed controller is compared with the typical model predictive controller and linear quadratic-based controller.

In-situ creep deformation of cold-sprayed aluminum splats at elevated temperatures

This study provides new insights into temperature-dependent splat sliding mechanisms in cold-sprayed deposit by mechanical investigations at length scales comparable to the splats. In-situ indentation of 6061 Al splat structure is performed inside a scanning electron microscope from room temperature up to 400 °C. Indentation at 176 °C, which is the standard heat-treatment temperature, is characterized by enhanced nanohardness (1.65 GPa) as compared to room temperature (1.37 GPa). This is associated with the precipitate formation and improved splat-bonding due to solid-state diffusion. Further enhancement of temperature results in softening, with nanohardness ~70 MPa at 400 °C. The elastic modulus of the splat structure is ~50% of the ‘bulk’ modulus at room temperature and is attributed to energy-dissipation due to splat-sliding activated during indentation. ‘Recovery Resistance’ is computed to quantify energy-dissipation, and a five-fold jump in dissipation is noticed from room temperature to 400 °C. The elasto-plastic zone under the indenter becomes larger with temperature and comprises of multiple splats. Hence, the splat-sliding is found to be enhanced at higher temperatures. Indentation creep investigations show the transition of deformation mechanism from purely plastic (material pile-up) at lower temperatures to non-plastic (crack propagation) at 400 °C. Creep stress-exponents are computed and correspond to solute drag (~3) and dislocation creep (~4–7) mechanisms. At 400 °C, stress-concentration along the splat interfaces is observed in the vicinity of the indenter, eventually leading to crack initiation, propagation and splat delamination due to prolonged loading. These observations highlight that splat interfaces play a vital role in determining the deformation behavior of cold-sprayed materials.

CRACK RESISTANCE OF CENTRIFUGAL-CAST STEAM P I P E S MADE OF STEEL 1 5 K h l M l F

Significance of assessing the characteristics of crack resistance of centrifugal-cast (CFC) tubes made of steel 15KhlMlF is substantiated. The characteristic features of the metal under study are considered along with the methodology of crack resistance tests. Three modifications of the metal of the CFC pipes in the initial state, that differ in the degree of developed segregational heterogeneity, and two modifications of the metal with almost the same degree of structural heterogeneity, which differ in the running time as a part of the operating equipment are studied. It is shown that a decrease in the intensity of the segregational damage of the metal structure has almost no effect on the level of the strength characteristics, but is accompanied by an increase in the plastic properties and toughness of the metal. We present the results of studying crack resistance of centrifugal-cast pipes (steel 15KhlMlF) under static, cyclic and prolonged static loading in conditions of high-temperature creep. It is shown that an increase in the degree of structural heterogeneity of the CFC steel adversely affects the characteristics of static crack resistance and cyclic crack resistance as well, but to a far lesser extent and has little if any effect on the crack resistance of the CFC steel at creep. Cyclic crack resistance slightly decreases with increase of the operating time of the metal in functioning pipelines, whereas the characteristics of the prolonged static crack resistance get worse significantly. It is shown that welded joints of the CFC pipelines have a substantially lower crack resistance under creep conditions compared to the base metal. Statistical processing of the experimental data is used to get kinetic diagrams of cyclic and prolonged static crack resistance of 15X1M1F CFC-steel in creep conditions. The results of practical applications of the obtained crack resistance characteristics of the metal of the CFC pipes are demonstrated with a focus on the problems of ensuring the reliable operation of the steam pipelines of thermal power plants at the end of their service lifetime.

Cross-limb dynamics of postural tremor due to limb loading to fatigue: neural overflow but not coupling.

Many experiments have shown independence of the index finger dynamics under bilateral postural tremor protocols. Here we investigated in young adults the dynamics of bilateral multidirectional postural tremor and forearm muscle activity under the progressively fatiguing conditions supporting an external weight to the point of induced postural failure. When no loads were applied, tremor in the vertical (VT) and mediolateral (ML) directions was similar with prominent peaks within 2- to 4-Hz and 8- to 12-Hz bandwidths. Contrastingly tremor in the anterior-posterior (AP) direction was characterized by a single peak between 0 and 2 Hz. Although no tremor coupling occurred cross limbs, strong within-limb coupling was found between ML and VT directions when no loads were applied (coherence range: 0.77-0.85), implying that these oscillations are related and likely derived from mechanical sources. Applying an external load to the index finger(s) led to significant increases in the amplitude of VT tremor and EMG activity within that limb but also caused increases in tremor directions not aligned with the gravitational vector (AP and ML). Significant increases in VT and ML tremor and EMG activity in the contralateral (unloaded) limb were also found when a single index finger was loaded; however, this bilateral increase did not align with increases in interlimb coupling (coherence <0.21). The effects of fatigue caused by prolonged loading were widespread, affecting tremor and muscle activity in both limbs through a combination of neural and mechanical mechanisms. The single- and dual-limb loading to fatigue increased neural overflow but not tremor coupling between the index fingers.NEW & NOTEWORTHY This study investigated bilateral multidirectional tremor under unloaded and loaded conditions. We found that tremor in the mediolateral and vertical directions within a limb were strongly coupled, a result not reported previously. Furthermore, when holding a weight to failure, tremor in all directions increased. Tremor also increased in the contralateral (unloaded) limb despite no interlimb coupling. This contralateral increase in tremor following loading a limb until fatigue is hypothesized to stem from motor-overflow effects.

Investigation of the unsteady creep of reinforced plates of nonlinearly inherited materials, taking into account the weakened resistance by transverse shear

The problem of inelastic bending deformation of plates is formulated using the idea of the method of time steps in rectangular Cartesian and cylindrical coordinate frames based on two versions of the Tymoshenko theory and taking into account plates weakened resistance to transverse shears during plane-cross reinforcement and. The mechanical behavior of the materials of the components of the composition is described by the nonlinear-hereditary Rabotnov’s creep theory. The bending behavior under creep conditions of ring plates made of D16T aluminum alloy and axisymmetrically reinforced along boron and spiral-circular trajectories by boron fibers is studied. It is shown that under short-term loading the classical theory is quite acceptable for calculating the mechanical behavior of such composite structures. Under prolonged loading in the creep process, transverse shear deformations actively and rapidly develop in the binder material of the plate. Therefore, taking into account the weakened resistance to transverse shear after calculating the creep of thin-walled reinforced structural elements is needed. The compliance of the reinforced plates under long-term loading predicted by the classical theory and the first version of the Tymoshenko’s theory is significantly less than that determined by the second version of the Tymoshenko’s theory. Therefore it is recommended to use the second version of the Tymoshenko’s theory for adequate calculations of the creep of the reinforced plates.

Spatial distribution of load induced soft-tissue strain in cattle claws

Claw disorders in dairy cattle have negative effects on both animal welfare and farm profits. One possible cause of claw disorders is the high mechanical load that cattle encounter when walking and standing on hard concrete floors. It is currently unclear how high mechanical loading leads to claw disorders and lameness. It is hypothesized that mechanical loading leads to compression of the soft tissue in the claws, which may directly or indirectly lead to tissue damage. Roentgen stereophotogrammetry in combination with CT-reconstruction was used to detect deformations in the distal hind limbs of dissected specimens of dairy cows under a range of loading regimens. The load was recorded in 3D using a force plate.Even at moderate load levels, such as during standing, the soft tissue layer was considerably compressed (>10% of the initial thickness), especially where the sole rests on the floor. Compression increases with increased and/or prolonged load. Most importantly, the location of areas of highest compression coincides with the locations where sole ulcers are most often found. These findings provide insight into the etiology of bovine claw disorders, and may contribute to solutions to reduce them.

Experimental study of the strength and durability of metal-composite high-pressure tanks

The results of unique experimental studies of the strength and service life of a metal-composite high-pressure tank are presented. The goal of the study is to analyze the fracture mechanisms and evaluate the strength characteristics of the structure. The methodology included tests of full-scale samples of the tank for durability under short-term static, long-term static and cyclic loading with internal pneumatic pressure. Generalized test results and data of visual measurements, instrumental and acoustic-emission control of deformation processes, accumulation of damages and destruction of full-scale tank samples are presented. Analysis of the strength and stiffness of the structure exposed to internal pneumatic pressure is presented. The types of limiting states of the tanks have been established experimentally. Change in the stress-strain state of the tank under cyclic and prolonged static loading is considered. Specific features of the mechanisms of destruction of a metal-composite tank are determined taking into account the role of strain of the metal liner. The calculated and experimental estimates of the energy potential of destruction and the size of the area affected upon destruction of the tank are presented. Analysis of test results showed that the tank has high strength and resource characteristics that meet the requirements of the design documentation. The results of the experiments are in good agreement with the results of numerical calculations and analysis of the stress-strain state and mechanisms of destruction of the metal-composite tank.

Rheological properties of mineral-cement mix with foamed bitumen with the addition of redispersible polymer powder

The main objective of the research presented in this article was the search for response concerning the influence of redispersible polymer powder (RPP) on the rheological properties (evaluation of the complex modulus and phase shift angle) of a mineral-cement mix with foamed bitumen (MCAS). Redispersible polymer powders are used in the construction industry as ingredients of mortar, cement concrete, plaster, adhesives and tile cement. However, literature related to an analysis of the influence of redispersible polymer powders on the properties of a mineral-cement mix with foamed bitumen (MCAS). The objective of the research was executed through the use of known identification methods in terms of rheological properties. The analysis of the complex modulus was conducted spanning linear viscoelasticity for deformation spanning 25 to 50 μstrain per PN-EN 12697-24 annex D. The test set-up assumes the determination of the complex modulus E* and the phase shift angle φ at the full sine wave for direct expansion and compression using cylindrical samples (DTC-CY). Using the redispersible polymer powder for MCAS can improve hydrophobic properties and limit rigidity, together with an improvement of the elasticity of the mineral-cement mix with foamed bitumen (MCAS). The increase of elasticity of the MCAS can be caused by a modification of the mineral matrix and a disclosure of interactions between the aggregate-cement and the polymer. In case of a recycled substructure, this phenomenon is significant due to the placement of the substructure in an arrangement of construction layers (increased humidification). Test results have shown a reduction of the complex modulus and the emergence of the effect of the polymer at high temperatures and after a prolonged load period.