Long-term Static Loading Research Articles

Development of a Method for Determining the Residual Life of Structural Elements with Cracks Under the Action of Load and Corrosive Environment, as well as the Application of Corrosion Inhibitors to Enhance It

A developed method for determining the lifespan of structural elements with large-scale cracks of complex geometry under the influence of long-term static loads and corrosive environments. The method is based on an appropriate computational model, which relies on the first law of thermodynamics for the elementary act of local failure (crack propagation), some fundamental principles of physical chemistry, as well as the basic principles of fracture mechanics. The advantages of this method over existing ones are substantiated. The application of the method is demonstrated through examples involving the determination of the residual life of such structural elements as torsion and a pipe with small cracks made of 45KhN2MFA steel (tempered at 470 K and 725 K) under the influence of long-term static loading and distilled water. As the cracks are considered small, we have constructed a computational model in terms of deformation parameters, including a well-known counterpart in fracture mechanics, crack opening at the crack tip δt. At the same time, based on available experimental data from the literature, it is substantiated that the application of existing linear fracture mechanics methods in stress intensity factors KI for implementing the mentioned problems, the application of existing linear fracture mechanics methods is inappropriate. To determine the residual life of structural elements using this method, it is necessary to have kinetic diagrams in coordinates of the growth rate of small cracks and the crack opening at the crack tip, which means V ∼ δt. These diagrams are constructed here using the provided formulas for determining δt and diagrams are constructed here using the provided formulas and known experimental data for 45KhN2MFA steel under the influence of distilled water and static tension. Using the mentioned method, the residual lifespans of the torsion and the pipe were calculated under the influence of long-term static loading and distilled water. Additionally, the effectiveness of water solutions of well-known inorganic corrosion inhibitors on the residual lifespan of the mentioned structural elements was verified through calculations. It was found that the residual lifespan effectively characterizes the performance of corrosion inhibitors, which can be applied in engineering practice.

Determination of the Residual Life of a Plate with a System of Cracks Under the Action of Long-Term Static Load and Corrosive Environment

Determination of the Residual Life of a Plate with a System of Cracks Under the Action of Long-Term Static Load and Corrosive Environment

Experimental Study of the Nonlinear Behaviour of Deep-Sea Mooring Polyester Fibre Ropes

Abstract Mooring ropes are essential components of ships and offshore floating structures and they are subjected to cyclic axial loads. This study investigates the evolution of the full-cycle stiffness of fibre polyester ropes under long-term static and dynamic loading. First, the static stiffness characteristics of the ropes, including the rope elongation properties at different stages, shrinkage rates, and creep coefficients after an idle period, are examined under static loads; an empirical formula for static stiffness is established. Second, the dynamic stiffness characteristics of the ropes are investigated under cyclic loads that are typical of platform production operations. The stabilities of the structure under different tensions are compared; the effects of mean tension, tension amplitude, and load cycle on the dynamic stiffness of the ropes are analysed and an empirical formula is established to predict the dynamic stiffness during the engineering design phase. The results of this study can be helpful for the rational design of deep-sea taut-leg mooring systems because they present the evolution of the full-cycle stiffness characteristics of mooring ropes.

A variable loading and automatic control test device for carpet resilience measurement

In this study, a novel multifunctional carpet test device was proposed to overcome deficiencies of current technology, including manual operation error and fixed load. The newly developed test device can automatically perform short-term static loading, long-term static loading and thickness measurement on five samples, simultaneously. The application of the load is achieved by using pneumatic system elements and automation of the developed test device is obtained by a PLC (Programmable Logic Controller) software. The device was verified according to “trueness” and “precision” criteria via statistical analyses. As a result of trueness determination, the Mean Absolute Percentage Error (MAPE) values of the developed test device were between 0.001–0.023, in comparison to that of the traditional carpet thickness tester, which exhibits very close trend between two measurements. The precision analysis results revealed no significant difference in 95% confidence interval between developed test device and the carpet thickness tester. Moreover, the developed test device is capable for thickness loss test by brief moderate loading, prolonged heavy loading and carpet thickness measurement, following related international standards.

Mechanical reliability of monolayer MoS2 and WSe2

<h2>Summary</h2> Mechanical reliability reflects the survival (or equivalently, failure) probability of materials under loading and is critical for their long-term and device-scale applications. So far, the mechanical reliability of two-dimensional (2D) materials remains elusive and largely unexplored, especially in long-term loading conditions. Here, through more than 300 nanomechanical experiments and 1,200 molecular dynamics simulations, we evaluate the mechanical reliability of monolayer (1L) MoS₂ and WSe₂ under both monotonic tension and long-term static fatigue loading conditions. Weibull statistics reveal their mechanical reliability to resemble that of common engineering ceramics and soda-lime glass. We uncover that the observed low reliability results from the synergistic effect of thermal fluctuations, variations in defect configuration, and defect density. Finally, we establish that proof testing can be an effective approach to improve the mechanical reliability of 2D monolayers in practical applications.

Effect of moisture content on the time-dependent mechanical characteristics of loess

It is of great significance to study the time-dependent mechanical properties of loess, as they are closely related to loess landslides. The purpose of this study is to investigate the effect of moisture content on the time-dependent deformation, strength and failure behaviors of undisturbed loess specimens from Nangou in Yan'an city, Shanxi Province, China, via triaxial shearing tests and multi-loading triaxial creep tests. The tests revealed different failure modes and the corresponding strain–time loess responses, which depend on the long-term static load and moisture content. The higher the moisture content is, the more obvious the time dependence of loess and the longer the time to reach the stable stage. This effect is closely related to the weakening effect of water on interparticle cementation and friction between soil particles in loess. Compared with instantaneous shear, long-term shear induced by water weakens the strength of loess, mainly because the particles in soil can be fully adjusted over time. The microscopic shear process of loess is essentially a process of change in microstructure with water exposure, loading and time, but the shear processes of loess in different shear modes are different (i.e., long-term shear and instantaneous shear). This study provides a theoretical basis for engineering construction and geological disaster prevention in loess areas.

Comparison of solo and conventional ring yarns: effects on the compression characteristics of cut-pile carpets

Carpet manufacturers are continuously looking for new approach to improve the characteristics of their produced carpets in terms of appearance and durability. Material and structural parameters have a significant effect on the carpet compression properties. This study deals with characterization of the cut-pile carpets produced with Solospun pile yarns in comparison to Ring spun yarns. To this end, the acrylic pile yarns were produced in same linear density using a semi-worsted Solo- and Ring spinning systems. Both prepared pile yarns were used to produce machine-woven carpets in two different weft densities (1500 and 2000 yarns/m). Compression characteristics of the manufactured carpet samples under compression loading were evaluated. The findings revealed that the hairiness of Solospun yarn decreased by 24% and 41% for 3 and 6 mm hairs, respectively; while the yarn abrasion resistance increased by 39%. The results also revealed that the thickness loss (TL) under long-term static loading was vividly lower for the carpets produced from Solospun yarns, in comparison to Ring spun yarns. The compression characteristics such as compressibility, permanent deformation, compression energy and residual energy of the carpet samples made of the Solospun yarns were less than those made of conventional Ring spun yarns. Finally, using the Solospun yarns as carpet pile leads to higher useful life and pile recovery of the cut-pile carpets. Accordingly, these yarns are recommended to be applied in the carpet industry, instead of the Ring spun pile yarns.

Model for the Simulation of the Time-Dependent State in RC Elements

The paper presents an upgrade of the previously developed model for nonlinear 3D analysis of concrete structures extended with the possibility of simulation of the long-term effects (shrinkage and creep) under long-term static load. The origin model is based on the so-called multi-surface principle with modified Rankin criterion for dominant tensile influences (appearance and development of cracks) and the modified Mohr-Coulomb criterion for dominant compressive states (yielding and cracking of concrete). The material behaviour is described with elementary material parameters (modulus of elasticity, Poisson’s coefficient and uniaxial compressive and tensile strength of concrete) by standard tests. Sufficient accuracy along with a simple and effective description of the very complex behaviour of reinforced concrete structures, make this model advantageous. Creep and shrinkage are based on the procedure given by the fib Model Code 2010 and extended with a special extension for non-linear creeping. Two simple examples show the capabilities of the model, while a good agreement between numerical and experimental results indicates that the developed model can well describe long-term effects in reinforced concrete structures, and that the model is appropriate for standard engineering practice.

Maintenance and Inspection of Fiber-Reinforced Polymer (FRP) Bridges: A Review of Methods.

Fiber-reinforced polymers (FRPs) are materials that comprise high-strength continuous fibers and resin polymer, and the resins comprise a matrix in which the fibers are embedded. As the technique of FRP production has advanced, FRPs have attained many incomparable advantages over traditional building materials such as concrete and steel, and thus they play a significant role in the strengthening and retrofitting of concrete structures. Bridges that are built out of FRPs have been widely used in overpasses of highways, railways and streets. However, damages in FRP bridges are inevitable due to long-term static and dynamic loads. The health of these bridges is important. Here, we review the maintenance and inspection methods for FRP structures of bridges and analyze the advantages, shortcomings and costs of these methods. The results show that two categories of methods should be used sequentially. First, simple methods such as visual inspection, knock and dragging-chain methods are used to determine the potential damage, and then radiation, modal analysis and load experiments are used to determine the damage mode and degree. The application of FRP is far beyond the refurbishment, consolidation and construction of bridges, and these methods should be effective to maintain and inspect the other FRP structures.

Experimental and Numerical Study on Long-Life and Progressive Damage in Laminates in Open-Hole Compression Tests

The strength theory design accuracy of carbon fiber reinforced plastics (CFRP) composite structures are integral to CFRP composite structures product weights along with production costs. In order to further improve the CFRP composite structure strength theory design accuracy in this paper, it developed an ATM/SIFT analysis method by combining strain invariant failure theory (SIFT) and Accelerated testing methodology (ATM). The developed implementation scheme of ATM/SIFT includes: three parts of accelerating material strength test, component strength main curve characterization, structures life prediction, among which the material life prediction is achieved by using Python code to customize user material subroutines (VUMAT), through secondary development on the ABAQUS platform. Based on the developed ATM/SIFT method, it analyzed the compressive gradual failure mechanism and life of IM600/TDE-85 composite laminated plates open pore structures. Finally, it predicted the long-term static load compression life of IM600/TDE-85 composite laminate open-hole structures by using ATM/SIFT method and compared this prediction results with test results.

Assessment of the stepped isothermal method for accelerated creep testing of high-density polyethylene

Thermoplastic materials are increasingly used in demanding structural applications under, in some cases, long-term static loading over several decades. In this regard, the stepped isothermal method (SIM) with creep testing at stepwise increased temperature levels in combination with time-temperature superposition (TTSP) provides a very time efficient procedure for long-term creep characterization. In the present study, the creep behavior of an injection molded high-density polyethylene material (HDPE) was investigated by SIM in the thermally untreated state as well as after annealing.Due to experimental issues regarding the heating behavior of the specimens and non-linear viscoelastic behavior, particularly at elevated temperatures, bi-directional curve shifting was required in order to generate meaningful master curves for creep compliance. In a first step, an Arrhenius equation was used for the horizontal curve shifting, based on activation energies, determined in additional multi-frequency dynamic mechanical analysis (DMA). Continuous master curves were then obtained by empirical vertical shifting of the individual creep curve segments for the different temperature levels. In general, good agreement was observed between the resulting SIM master curves and the corresponding conventionally measured creep compliance curves at least for a time range up to 300 hours. Furthermore, significant differences in the creep tendency of the annealed material state compared to the thermally untreated condition revealed the distinct influence of the thermal history on the resulting creep behavior.

Sitting posture detection and recognition of aircraft passengers using machine learning

AbstractProlonged sitting in a fixed or constrained position exposes aircraft passengers to long-term static loading of their bodies, which has deleterious effects on passengers’ comfort throughout the duration of the flight. The previous studies focused primarily on office and driving sitting postures and few studies, however, focused on the sitting postures of passengers in aircraft. Consequently, the aim of the present study is to detect and recognize the sitting postures of aircraft passengers in relation to sitting discomfort. A total of 24 subjects were recruited for the experiment, which lasted for 2 h. Furthermore, a total of 489 sitting postures were extracted and the pressure data between subjects and seat was collected from the experiment. After the detection of sitting postures, eight types of sitting postures were classified based on key parts (trunk, back, and legs) of the human bodies. Thereafter, the eight types of sitting postures were recognized with the aid of pressure data of seat pan and backrest employing several machine learning methods. The best classification rate of 89.26% was obtained from the support vector machine (SVM) with radial basis function (RBF) kernel. The detection and recognition of the eight types of sitting postures of aircraft passengers in this study provided an insight into aircraft passengers’ discomfort and seat design.

Durability prediction of brittle rocks based on type-I crack extension theory

When subjected to long-term static loading, with the accumulation of damage and fracture, brittle rock would fails when the static loading is lower than the compressive strength of the rock, and the increasing of the static loading can generally shorten the time required for the brittle rock failure. To explore the relationship between the durability of the brittle rock and the applied static loading, in this paper, the propagation modes of the microcracks in brittle rock under the static loading in the subcritical crack growth stage are uniformly attributed to the tensile mode, and the total time required for microcrack propagation in the subcritical crack growth stage is chosen as the criterion for judging the durability index of brittle rock. Based on the Maxwell model, the local effective tensile stress that drives crack propagation is derived. The phenomenon of brittle rock exhibiting tensile failure under the compressive stress is preliminarily explained, and the corresponding requirements for this phenomenon to occur are also presented. A new expression of rock durability prediction with a clear physical meaning is established. The key parameter, i.e., the durability index “n” in the newly derived expression is obtained through fitting, and the relationship between the durability index and the rock type is preliminarily analysed. This study may provide an approach for preliminarily estimating the durability of brittle rock.

Limiting State of 25Kh1M1FA Steel Under Long-Term Static Loading at Elevated Temperatures

Limiting State of 25Kh1M1FA Steel Under Long-Term Static Loading at Elevated Temperatures

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 study is aimed at analyzing the fracture mechanisms and evaluating the strength characteristics of the structure. The technique 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. The generalized test results and data of visual measurements, instrumental and acoustic-emission control of deformation processes, accumulation of damage, and destruction of full-scale tank samples are presented. The strength and the stiffness of the structure exposed to internal pneumatic pressure are analyzed. The types of limiting states of the tanks are established experimentally. Variation in the stress-strain state of the tank under cyclic and prolonged static loading is considered. The specific features of the destruction mechanism of the metal-composite tank are determined with allowance for the role of the metal liner strain. The calculated and experimental estimates of the energy potential of destruction and the size of the area affected by destruction of the tank are presented. Analysis of the test results show that the tank has high strength and resource characteristics that meet the requirements of the design documentation. The experimental results are in good agreement with the results of the numerical calculations and analysis of the stress-strain state and destruction mechanisms of the metal-composite tank.

Computational Model for the Evaluation of the Service Life Of Fiber-Reinforced Concrete Structures Under Long-Term Static Loading

We propose a computational model for the evaluation of the service life of fiber-reinforced concrete structural elements subjected to long-term tension. The model is based on the first law of thermodynamics and a proposed idealized tensile stress-strain diagram of fibrous concrete. This model is used for the evaluation of the service life of a fiber-reinforced concrete plate containing a circular hole under the conditions of long-term bilateral tension.

Settlement of the base of clay soil under regime weighting

The aim of the article is the development of the theory of strength and deformation of clay soils under conditions of triaxial compression under combined alternating long-term static and cyclic loading. As a result of the research, new experimental data were obtained on the peculiarities of the stress-strain state of clay soils under triaxial compression under combined alternating long-term static and cyclic loading, as well as the development of base sediments of foundation models in laboratory conditions. The significance of the results obtained for the construction industry lies in the fact that experimental studies of determining the changes in the strength and deformability of clay soils under combined alternating long-term static and cyclic loading are necessary for the modernization of engineering methods for calculating sediments and the bearing capacity of foundations.

Experimental study on individual risk in crowds based on exerted force and human perceptions

Frequent and intense interactions between individuals inevitably occur in crowd disasters. Previous studies indicate that the primary risk evaluation parameters for individuals in crowds during these interactions are exerted force and its duration. In this study, a series of controlled laboratory experiments simulating static and fluctuant loads were conducted to obtain real-time exerted force data and the associated individual subjective feelings. An individual risk evaluation method is then established to assign a specific individual risk value to each data set of exerted force and its duration according to the individuals’ feelings. This method divides the range of risk value into three zones: comfortable zone, uncomfortable zone and crisis zone. The transition from an uncomfortable zone to crisis zone is not a single numerical value but a range that considers individual differences. The method presented in this paper can assist in developing pedestrian simulation models as well as managing crowd events. Practitioner summary: Accident surveys indicate that casualties and injuries usually occur under a long-term static load or heavy dynamic load. We tested human body extrusion experiments in four conditions, measured the real-time load intensity and duration of the individual’s action on the thoracic cavity during the mutual extrusion process, and an individual risk evaluation method has been established based on the force exerted on the body and its duration to prevent crowd disasters. Abbreviations: NIST: National Institute of Standards and Technology; IREM: individual risk evaluation method; CPR: cardiopulmonary resuscitation

Creep of Textile-Reinforced Composite Under Static and Cyclic Loads

The paper considers the creep of a textile-reinforced thermoplastic composite with a glass filler under the action of a combined short-term cyclic and long-term static tensile loads at room temperature. The investigations were carried out on glass-fabric-reinforced polypropylene specimens, which were made by autoclave molding. The creep of the composite was experimentally investigated under a cyclic load at different amplitudes. The creep kernel has been calculated from experimental data according to the Boltzmann superposition principle. Other creep models of materials have been analyzed based on data from a review. The laws governing the short-term creep of polypropylene under the action of a static load have been determined. A behaviorial model of the composite under investigation under the considered conditions is proposed. Numerical calculations have been made with the aid of the proposed model using experimental results taken from other works, and a good agreement between them has been established. The peculiarities of the creep of textile-reinforced polypropylene under the considered conditions have been determined. The range of application of the model has been determined.

Evaluation of the Residual Service Life of Main Pipelines with Regard for the Action of Media and Degradation of Materials

We proposed new procedures for the evaluation of the residual service life of main pipelines with surface cracks under the action of a long-term constant gas pressure in gas pipelines, a variable pressure in oil pipelines, hydrogenation, and soil corrosion. The degradation of the materials is taken into account. Since the time dependence of the degree of degradation is insignificant, it is analytically described by linear dependences. The energy approach is used to determine the residual service life of the pipes. The corresponding computational models (differential equations with initial and final conditions) are developed. For specific pipe materials (Kh52, Kh60, and Kh70 steels), the residual service life is computed under long-term static and variable loads, in the presence of hydrogenation and soil corrosion with regard for the degradation of the materials for 30 yr.