Cyclic Accumulation Research Articles

Analysis of Speckle-Structure Images of Material Surface During Cyclic Loading Damage Accumulation Using Neural Networks

Analysis of Speckle-Structure Images of Material Surface During Cyclic Loading Damage Accumulation Using Neural Networks

Effect of thermal cycles on rock cliff deformation. Monitoring and interpretation

Climatic actions are one of the factors controlling the evolution of slopes, this paper is devoted to a specific effect, relatively little studied, related to the effect of climate-driven temperature changes on rock massif deformation. The particularity of the study is to focus on permeable rocks and Temperatures varying in a range which discards freeze/thaw effects. Research has been carried out in relation with the analysis of the real case of a limestone cliff located in the Périgord region, the massif was highly instrumented, results show a slow cyclic accumulation of deformations with time, essentially synchronic with thermal cycles. An advanced constitutive model, specifically developed to capture rock degradation due to the differential expansion of the main minerals composing the rock, has been developed. It has been calibrated on experimental results obtained in the laboratory on block samples tested in a climatic chamber for a long series (several months) of daily thermal cycles. Deformation and shear wave velocity were monitored during the test. Model shows a good agreement with laboratory measurements.

Viscoplastic cyclic degradation model for soft natural soils

Cyclic loading affects the long-term response of geostructures build on natural soils. Soft soils are particularly susceptible to the development of large deformations, induced by the repetitive nature of loading. A new viscoplastic cyclic accumulation model is presented, which is an hierarchical extension of the Creep-SClay1S model, to model the long-term permanent deformation resulting from undrained cyclic loading of natural soft clays. The cyclic cumulative strains are incorporated by means of an additional viscoplastic multiplier. This cyclic viscoplastic multiplier adds four additional model parameters that are derived from undrained cyclic triaxial tests. The model is calibrated using experimental data from undrained cyclic triaxial tests performed on high quality block samples of natural Onsøy clay, at different average shear stresses, shear stress amplitudes and loading periods. The accuracy of the proposed model is demonstrated by comparing the element level simulations with the experimental data. The applicability of the proposed model is further illustrated with a boundary value problem, where an embankment submitted to cyclic loading is simulated. The use of the new model enables the simulation of the response of cyclic loaded foundations on soft soils, where the serviceability limit state over a long period of time is governing the design.

Finite element simulation and experiment of a new ring constrained groove pressing for 5083 aluminum alloy based on cyclic stress state

A new severe plastic deformation process of ring wave repeated groove pressing based on cyclic stress state is proposed. Finite element simulation and process test are carried out on 5083 aluminum alloy sheet during ring wave repeated groove pressing. The deformation mechanism of the sheet and mechanical mechanisms of sheet performance optimization in the process of severe plastic deformation are analyzed. With severe plastic deformation, subjecting the sheet under repeated cycles of tensile stress and strain, compressive stress and strain, the cyclic accumulation of strain is realized, so that the fracture strength and elongation of the processed material are considerably improved. Compared with the original sheet, under the flattening temperature of 300°C and three passes of ring wave repeated groove pressing, the fracture strength and elongation increased by 10 and 75%, respectively.

Centrifuge testing on monotonic and cyclic lateral behavior of large-diameter slender piles in sand

The existing studies have been primarily focused on the lateral behavior of large-diameter stubby pile or small-diameter slender pile in sand, with little attention paid to large-diameter slender pile. This study presents a unique series of centrifuge tests on monotonic and cyclic lateral behavior of heavily instrumented large-diameter slender piles in medium dense sand. Two typical length to diameter ratios (L/D) are considered with the same length (L = 60 m) but different diameters (D = 4 and 6 m). It is found that the lateral behaviors of large-diameter slender pile, including its monotonic p-y response, cyclic accumulation of lateral displacement and cyclic stiffness evolution, are marginally different from those of small-diameter slender piles, but significantly deviate from the large-diameter stubby piles. This may suggest the longstanding argument of ‘diameter effect’ is relatively minor, while the lateral behavior of monopile in sand is more significantly governed by the relative pile-soil stiffness. The API (2011) non-conservatively predicts both stiffness and capacity of the large-diameter slender piles, leading to development of a new p-y formulation. These centrifuge testing results form a unique database to support development of new design methods for large-diameter slender piles, and to verify advanced numerical analyses involving cyclic models.

Analysis of Value Creation Process of Platform-driven Scientific and Technological Innovation Value Chain: the Perspective of Informationization

At present, the innovation environment of science and technology innovation platform is constantly changing, which has gradually changed from the situation of science and technology innovation among single elements to the information comparison among the whole innovation value chain. In this paper, science and technology innovation platform is divided into four types: pure research platform, industrial technology research platform, business incubation platform and public service platform. It deeply analyzes the informationization process of innovation value chain driven by science and technology innovation platform, including basic research, applied research, experimental development and commercialization. By analyzing the role of knowledge capital, technology capital, venture capital and other information resources in science and technology innovation platform, it explores the value flow among platforms. It is found that the stock capital and variable capital of scientific and technological innovation are not a transformation, but realize the increment and cyclic accumulation of income along the innovation chain step by step. The research expands the analysis scope of informatization theory, combs the value creation process of science and technology innovation platform, and contributes to risk avoidance and benefit distribution.

Cyclic shear characteristics of marine cement soil under stress path with bidirectional shear stress

Under seismic loading, marine soil experiences horizontal shearing in two directions with different shear directions and amplitudes. It is therefore of considerable practical relevance to study the deformation behavior of marine cement soil under bidirectional shear loading. In this study, a series of cyclic simple shear tests were carried out to investigate the undrained deformation behavior of marine cement soil. The cyclic strain, stiffness softening, and cyclic strength were found to be significantly related to the phase difference and cement content. Cyclic shear strain accumulation increases as the number of cycles increases, and the emergence of inflection on the shear strain curve can be considered a suitable failure criterion for cement soil. The turning strain decreases as the cement content increases, and the phase difference decreases. With a decrease in cement content and an increase in phase difference, the rate of cyclic degradation and development of shear strain significantly increased. It was observed that the cyclic strength of cement soil increases with the cement content and decreases as the phase difference decreases.

A Temperature-Dependent Model of Shape Memory Alloys Considering Tensile-Compressive Asymmetry and the Ratcheting Effect.

Tensile-compressive asymmetry and the ratcheting effect are two significant characteristics of shape memory alloys (SMAs) during uniaxial cyclic tests, thus having received substantial attention in research. In this study, by redefining the internal variables in SMAs by considering the cyclic accumulation of residual martensite, we propose a constitutive model for SMAs to simultaneously reflect tensile-compressive asymmetry and the cyclic ratcheting effect under multiple cyclic tests. This constitutive model is temperature dependent and can be used to reasonably capture the typical features of SMAs during tensile-compressive cyclic tests, which include the pseudo-elasticity at higher temperatures as well as the shape-memory effect at lower temperatures. Moreover, the proposed model can predict the cyclic mechanical behavior of SMAs subjected to applied stresses with different peak and valley values under tension and compression. Agreement between the predictions obtained from the proposed model and the published experimental data is observed, which confirms that the proposed novel constitutive model of SMAs is feasible.

Cyclic volumetric strain accumulation for sand under drained simple shear condition

Volumetric strain of a soil element surrounding the pile accumulated under the drained cyclic loading condition is one of major concerns in geotechnical engineering design. In this paper, twenty stress-controlled drained simple shear tests, with 5000 cycles on Fontainebleau sand have been carried out, which aims to investigate four factors influencing cyclic accumulation behaviour: initial void ratio, normal stress, cyclic shear stress ratio and average shear stress ratio. Based on results, the cyclic volumetric strain accumulation for each influencing factor is summarized, which is found highly sensitive to the cyclic shear stress ratio that a bigger magnitude (more than 0.2) leads to a larger degree of densification. In addition, a simple analytical model is then proposed accounting for these factors with seven parameters that can be directly calibrated from laboratory tests. Finally, the applicability of the model is examined by simulating the additional tests through an adoption of the parameters calibrated by the training tests.

Strain and filler ratio transitions from chains network to filler network damage in EPDM during single and cyclic loadings

Chains and filler network damage were investigated during single and multiple cycles on a series of vulcanized EPDM containing various filler contents. In both series of experiments, a strain and a filler ratio transitions for damage mechanisms were identified. For low filler content (≤40 phr), damage mechanisms mostly occur in the elastically active rubber network consistent with the chains network alteration theory associated with irreversible chains scission/bond breakage. For high filler content (>40 phr), a strain transition occurs with damage initially located in the elastically active rubber network, but subsequently localizes in the vicinity of the filler-filler network. This is ascribed to filler re-aggregation with strain, improving its load-bearing capacity, that may release the immobilized rubber formed by the chains that are occluded and bonded to fillers. During cyclic experiments, such reversible release involving loss of weak physical bonds and chains slippage yields in a progressive cavity closing with cyclic accumulation that prevents further irreversible damage of the elastically active rubber network.

Predicting the cyclic behaviour of suction anchors based on a stiffness degradation model for soft clays

Abstract The behaviour of suction anchors subjected to combined average and cyclic loads in soft clays is an essential consideration in their design. A new numerical computation method was developed based on a stiffness degradation model for soft clay that was proposed by performing a series of undrained cyclic triaxial tests and embedded in the ABAQUS software package by encoding the USDFLD subroutine and defining relevant field variables. The numerical method predicts the cyclic behaviour of suction anchors by coupling the elastic-perfectly plastic model with the Mohr-Coulomb yield criterion and the proposed stiffness degradation model that can reflect the stiffness degradation and the accumulation of plastic deformation of soils around the anchor during cyclic loading. The numerical method was verified by a comparison with the model test results of suction anchors subjected to combined average and cyclic loads in soft clays. The proposed method can predict the cyclic deformation as well as the bearing capacity and capture the nonlinearity, hysteresis and cyclic accumulation characteristics of the load-displacement responses of suction anchors in soft clays.

Дисбаланс мікро- та макроелементів волосся як діаґностичний критерій алопецій:досягнення, проблеми та перспективи

Aim. To analyze modern scientific approaches to using the achievements of bioelementology in the diagnosis and treatment of various forms of alopecia. Identifying unresolved issues in this area of research. Materials and Methods. Literature search in MEDLINE, Embase, TOXNET databases, specialized journals and thesis papers depositories in Ukraine, Russia and Belarus. The references cited in the identified papers were used as well. The publications period used in the search was 2007-2020. Results and Discussion. The content analysis of scientific literature sources, which highlight the results of studies of homeostasis of trace elements and major elements in the human body, proves the validity of using the data obtained for the diagnosis, treatment and prevention of alopecia. Introduction of modern analytical methods made it possible to expand both qualitative and quantitative characteristics of the content of elements in hair, and then to substantiate the use of the elemental composition of hair as a medical diagnostic criterion. In addition, the analysis of hair for the content of trace elements and major elements is considered a potentially safe, non-invasive diagnostic tool; the samples do not require special equipment for storage and have no shelf life restrictions. At the present stage, an active search for the relationship between the elemental status of hair and alopecia of various origins is being carried out. It was established that all forms of alopecia are characterized by a disturbance of the homeostasis of iron, zinc, copper, and selenium. In addition, the researchers emphasize the importance of excess hair lead and cadmium in alopecia areata, of silicon in diffuse alopecia and androgenetic alopecia, and reduced levels of manganese in all forms of alopecia. The scientific community discusses the implementation of modern analytical methods to determine the elemental composition of biological fluids. The most promising are the methods of determining elements in the organs and human biological fluids using inductively coupled plasma-atomic emission and mass spectrometry. Trace elements and major elements play an important, but not entirely clear role in hair follicles normal development and immune cells function. These studies were mainly concerned with exploring of the cyclic accumulation of mast cells and macrophages in the perifollicular connective tissue. Accordingly, the dyscrasia can represent a modified risk factor, the assessment of which requires further in-depth studies. Conclusions. The content analysis of the published results of the studies of trace and major elements composition of hair showed that with alopecia areata there is a decrease in the content of S, Zn, Se, Mn, Mn, and Fe, and an excess of Pb, Cd, Ni, Cu, Al, Hg; diffuse forms of alopecia are characterized by a deficiency in the content of S, Fe, K, Ca, Zn, Cu, and Se; with androgenetic alopecia in women, there is a decrease in the content of Mn, Zn, Se, Mg, Fe, in men - a decrease in the levels of Zn, Cu, Mn, Mg, and Se; and an increase in the content of Cu and Cr. In order to correct alopecia of various origins, it is necessary to determine the quantitative ratio of trace elements and major elements in the hair and to systematize the results obtained in monitoring studies to establish their reference values in conditions of various geochemical locations. Keywords: hair, alopecia, elemental homeostasis, microelementosis

Experimental investigation on electro-mechanically coupled cyclic deformation of laterally constrained dielectric elastomer

A series of electro-mechanically coupled cyclic tests at large deformation are carried out to characterize the cyclic deformation of a laterally constrained dielectric elastomer (DE) in this work. In the strain-controlled cyclic tests of the dielectric elastomer (e.g., VHB 4910 DE) with a constant or cyclic voltage, cyclic stress softening occurs and is influenced by the phase-angle difference between the applied cyclic strain and cyclic voltage. In the stress-controlled cyclic tests of VHB 4910 DE with a constant or cyclic voltage, ratchetting (a cyclic accumulation of inelastic strain) takes place; the ratchetting strain is considerably enhanced by applying higher voltage level, higher stress level and lower stress rate, and is also affected by the phase-angle difference between the applied cyclic stress and cyclic voltage. Moreover, the remarkable recovery of residual strain after the cyclic tests demonstrates that the cyclic stress softening and ratchetting of VHB 4910 DE mainly stem from the viscoelasticity. The comprehensive experimental observations are very useful to develop, calibrate and validate an electro-mechanically coupled constitutive model of dielectric elastomers.

Effects of urban sprawl on haze pollution in China based on dynamic spatial Durbin model during 2003–2016

Abstract As one of the undesirable outcomes in the process of urbanization and industrialization, haze pollution in China would undoubtedly be affected by urban sprawl. Hence, studying the effects of urban sprawl on haze pollution at the national level has great theoretical and practical meanings for the sustainable development of Chinese cities in the long run. Based on the panel data of 285 prefecture-level and above cities during 2003–2016, this paper has tried to employ a dynamic spatial Durbin model under the space-and-time fixed effect to analysis how haze pollution is affected by urban sprawl in China. The results revealed that the relationship between urban sprawl and haze pollution shows a U-shaped curve in large cities but an inverted U-shaped curve in small and medium-sized cities, which provides a clear evidence for the spatial shift risk of haze pollution caused by urban sprawl amongst different sizes of cities. Furthermore, the spatial and temporal dependences have significantly deteriorated the haze pollution in China, while the spatiotemporal dependence has to some extent inhibited the concentration of haze pollution, thus the effective control of haze pollution should rely on the joint governance in space and the cyclic accumulation in time simultaneously.

Dynamic characteristics of marine soft clay under variable phase difference and initial static shear stress

Under seismic loading, the soil layer is subjected to multidirectional cyclic shear stress with different amplitudes and frequencies because of the coupling of multiple shear waves and the soil element within a slope or behind a retaining wall is subjected to initial static shear stress before subjected to cyclic loading. Due to the complexity of seismic loading propagation, a phase difference exists between the initial static shear stress and cyclic shear stress. To investigate the influence of the phase difference and initial static shear stress on cyclic shear strain, cyclic modulus, and cyclic strength, a series of laboratory tests are performed on Wenzhou marine soft clay by multi-directional simple shear system, which can simulate the actual state better by controlling the horizontal cyclic stress in the x and y directions simultaneously. As the phase difference varies from 0° to 90°, the dynamic shear modulus increases and cyclic strain accumulation decreases with an increasing number of cycles. The shear strain increases with the initial shear stress.

Stiffness based technique to probe cyclic damage accumulation in micro-structurally graded bond coats via micro-beam bending tests

ABSTRACTThis paper highlights a novel technique to delineate the fatigue response of different regions within thin microstructurally graded platinum nickel aluminide bond coats. Notched clamped beam structures fabricated from distinct microstructural zones of these coatings are subjected to programmed cyclic bending using the nano-indentation system. A methodical approach is established herein to quantify the cyclic damage preceding crack pop-in by using the cyclic stiffness of the beam as an indicator to mark failure. Preliminary results from these tests show that there is a characteristic change in the stiffness of the beam before a crack pop-in event occurs and different regions within the coating show different stiffening characteristics. Factors affecting the measured stiffness such as offsets in the loading position and blunting of the notch tip have been estimated using the finite element method. A graded flow stress model has been proposed and implemented in FEM to quantify the local flow stress changes accompanying the measured rise in stiffness. Electron transparent foils lifted off from the notched region of the beam post-testing suggests that the cyclic stiffening of the beams occurs due to dislocation hardening in the plastically deformed region close to the notch tip. Toughening mechanisms active in the crack wake have thus been investigated and correlated to the measured cyclic stiffness.

Simplified simulation of the installation of vibro-piles in water saturated soil

This paper presents a novel and simplified approach to simulate the effects of the vibro-pile installation on the deformation of deep excavation shoring walls at high ground water levels. Although commonly-used finite element simulations provide acceptable predictions of the wall displacements caused by underwater excavations, anchor installation, or pit dewatering processes, they could not explain the unexpected large wall movements measured in different excavations during the vibro-pile installation stage. Previous dynamic finite element simulations of the vibro-installation of a single pile showed that after few cycles the effective stress in the soil surrounding the pile reduces almost near to zero. The soil region affected was called “the liquefaction zone”. Due to the waves emanating from the pile, the soil beyond the liquefaction zone is subjected to a (high-) cyclic loading, i.e. a large number of strain cycles with small amplitude. When the soil behavior is modeled with hypoplasticity or elastoplasticity, its response to these small strain amplitudes is nearly (hypo)elastic resulting in an erroneous accumulation of stress or strains, see Osinov (2017) [1]. Based on this observation, Osinov et al. (2015) [2,3] suggested that the accumulation effects caused by many cycles of small strain amplitude could explain the large wall displacements observed during the pile installation. Following this idea, in this paper we model the soil behavior with a combination of hypoplasticity (which can be applied to cycles of large strain amplitudes and monotonic paths) and the high cyclic accumulation (HCA) model, which is able to extrapolate the accumulation of stress/strain caused by a large number of cycles of small strain amplitude (ϵampl<10−3). The pile installation is not explicitly modeled, but its effects are incorporated in the numeric model by applying a field of cyclic strain amplitudes around each pile. Using this combined constitutive model and simulation technique, the behavior of the shoring of an excavation pit in Potsdamer Platz, in Berlin was simulated under quasi-static conditions in a finite element program. The obtained simulation results are in good agreement with the horizontal displacement of the diaphragm wall measured during the entire construction stages, including the underwater excavation and the pile installation.

Blind recognition of space time block code in MIMO systems

Space time block code (STBC) and vertical Bell layered space–time (VBLAST) signals are widely applied in multiple-input multiple-output (MIMO) systems, and one essential step in the signal interception process is to recognize STBC/VBLAST. As the STBC signal is correlated in time, it has a specific cyclic frequency in higher-order cyclic accumulation, while the VBLAST signal emitted from different antenna is uncorrelated. According to this property, this paper proposes a blind recognition approach for STBC/VBLAST signals based on fourth-order cyclic accumulation (FCC). The recognition process is divided into two steps. In the first step, we first establish the correlation choosing criteria that makes sure all correlations of STBC can generate a statistically cyclic sequence. The cyclic statistic then is estimated by combining the FCC with channel information that provides the peaks phase of the statistically cyclic sequence. The second step compares the estimated cyclic statistic with a detection threshold, which is obtained by given a probability of false alarms. The proposed approach avoids the need for any prior knowledge of the transmitted signal, and can work well in the lowly SNR by employing the advantages of FCC.

Cell cycle accumulation of the proliferating cell nuclear antigen PCN-1 transitions from continuous in the adult germline to intermittent in the early embryo of C. elegans

BackgroundThe proliferating cell nuclear antigen (PCNA or PCN-1 in C. elegans), an essential processivity factor for DNA polymerase δ, has been widely used as a marker of S-phase. In C. elegans early embryos, PCN-1 accumulation is cyclic, localizing to the nucleus during S-phase and the cytoplasm during the rest of the cell cycle. The C. elegans larval and adult germline is an important model systems for studying cell cycle regulation, and it was observed that the cell cycle regulator cyclin E (CYE-1 in C. elegans) displays a non-cyclic, continuous accumulation pattern in this tissue. The accumulation pattern of PCN-1 has not been well defined in the larval and adult germline, and the objective of this study was to determine if the accumulation pattern is cyclic, as in other cells and organisms, or continuous, similar to cyclin E.ResultsTo study the larval and adult germline accumulation of PCN-1 expressed from its native locus, we used CRISPR/Cas9 technology to engineer a novel allele of pcn-1 that encodes an epitope-tagged protein. S-phase nuclei were labeled using EdU nucleotide incorporation, and FLAG::PCN-1 was detected by antibody staining. All progenitor zone nuclei, including those that were not in S-phase (as they were negative for EdU staining) showed PCN-1 accumulation, indicating that PCN-1 accumulated during all cell cycle phases in the germline progenitor zone. The same result was observed with a GFP::PCN-1 fusion protein expressed from a transgene. pcn-1 loss-of-function mutations were analyzed, and pcn-1 was necessary for robust fertility and embryonic development.ConclusionsIn the C. elegans early embryo as well as other organisms, PCN-1 accumulates in nuclei only during S-phase. By contrast, in the progenitor zone of the germline of C. elegans, PCN-1 accumulated in nuclei during all cell cycle stages. This pattern is similar to accumulation pattern of cyclin E. These observations support the model that mitotic cell cycle regulation in the germline stem and progenitor cells is distinct from somatic cells, as it does not heavily rely on cyclic accumulation of classic cell cycle proteins.

Circadian clock-dependent and -independent posttranscriptional regulation underlies temporal mRNA accumulation in mouse liver

The mammalian circadian clock coordinates physiology with environmental cycles through the regulation of daily oscillations of gene expression. Thousands of transcripts exhibit rhythmic accumulations across mouse tissues, as determined by the balance of their synthesis and degradation. While diurnally rhythmic transcription regulation is well studied and often thought to be the main factor generating rhythmic mRNA accumulation, the extent of rhythmic posttranscriptional regulation is debated, and the kinetic parameters (e.g., half-lives), as well as the underlying regulators (e.g., mRNA-binding proteins) are relatively unexplored. Here, we developed a quantitative model for cyclic accumulations of pre-mRNA and mRNA from total RNA-seq data, and applied it to mouse liver. This allowed us to identify that about 20% of mRNA rhythms were driven by rhythmic mRNA degradation, and another 15% of mRNAs regulated by both rhythmic transcription and mRNA degradation. The method could also estimate mRNA half-lives and processing times in intact mouse liver. We then showed that, depending on mRNA half-life, rhythmic mRNA degradation can either amplify or tune phases of mRNA rhythms. By comparing mRNA rhythms in wild-type and Bmal1-/- animals, we found that the rhythmic degradation of many transcripts did not depend on a functional BMAL1. Interestingly clock-dependent and -independent degradation rhythms peaked at distinct times of day. We further predicted mRNA-binding proteins (mRBPs) that were implicated in the posttranscriptional regulation of mRNAs, either through stabilizing or destabilizing activities. Together, our results demonstrate how posttranscriptional regulation temporally shapes rhythmic mRNA accumulation in mouse liver.