Critical Deformation Research Articles

A modified Park-Ang model for seismic damage assessment of recycled aggregate concrete-filled square steel tube columns

This paper focuses on the seismic damage assessment mechanism of recycled aggregate concrete-filled square steel tube (RACFSST) columns via the seismic test results of 95 RACFSST column structures. Based on the dual criteria of deformation and energy, with consideration of the mechanical characteristics of RACFSST column structures, a modified Park-Ang model for seismic damage assessment of RACFSST columns was proposed by introducing the modified dissipation factor. The quantitative index of the performance-based seismic design of RACFSST columns was established, and the criteria of the damage performance level of RACFSST columns under different failure states were proposed. The results show that the modified Park-Ang damage model can reflect the seismic damage evolvement rule of RACFSST columns well. The seismic damage degrees of RACFSST columns can be divided into basically intact (D=0–0.02), slightly damaged and moderately damaged (D=0.02–0.41), severely damaged (D=0.41–0.98) and collapsed (D=0.98–1.00). Under the probabilistic reliability of 84.13%, the interlayer displacement angle limit of RACFSST columns at the corresponding five seismic performance levels were using normally (D<1/150), using temporarily (D=1/150), using after repair (D=1/100), hardly ensuring life safety (D=1/50) and preventing collapse (D=1/35). The seismic damage assessment basis for RACFSST columns under different performance levels is made clearly by controlling the damage threshold.

Mechanical compression characteristics of rapeseed based on continuous damage theory

In the process of mechanised sowing and harvesting, the damage and fragmentation of rapeseed are often caused by multiple contacts. The expansion of micro-defects and the accumulation of fusion damage in rapeseed can lead to fragmentation. To explore the law of mechanical damage of rapeseed, an elastoplastic model was established by Hertz contact mechanics. Combined with the continuous damage theory, the evolution equation of compression damage was established, and the accumulation method of compression damage was clarified. Three kinds of commercial seeds were taken as the experiment material. A single compression crushing test was carried out to verify the correctness of the elastoplastic model but multiple compression crushing tests were carried out to explore the damage accumulation process and method. The results show that the elastoplastic model can better fit the relationship between force and deformation during compression. The critical damage deformation δ d is equal to critical elastoplastic deformation δ s . When the deformation is more significant than 15 ± 2% of the diameter, the plastic deformation of rapeseed occurs. When the deformation is < δ d , the rapeseed will not be broken during the 30 cycles of equal displacement compression. When the deformation is > δ d , the damage leads to the decrease of the effective elastic modulus. With the increase of the compression deformation, the damage to the rapeseed intensified, resulting in the rapeseed being more easily broken. The research can provide a theoretical basis for designing structure and parameters in mechanised sowing and harvesting for rape. • An elastoplastic model for rapeseed was established by Hertz contact mechanics. • The evolution equation of compression damage for rapeseed was established. • The accumulation method of compression damage was clarified. • The damage leads to the decrease of the effective elastic modulus of rapeseed.

Моделирование критических локальных деформаций коры растущего дерева при ветровой нагрузке

The interaction between wind loads and forest plantations has been fairly well understood. A large amount of valuable scientific and practical information has been obtained and published so far in this field. There are some known data on wind load damage to plantations, its effect on their growth, and the ability of forest plantations to reduce wind speed and force. Nevertheless, the issues of wind impact on both individual trees and forested areas remain relevant. Analysis of the literature and Internet resources showed that the research has left out the issue of the wind load impact on the grown wood quality. Multi-year observations and a wind rose created using these observations enable the determination of the prevailing wind strength and direction for each area. Knowing the features of the wind load impact on the quality of timber after logging, it is possible to predict the percentage of the yield of commercial and low-quality wood, and to purposefully influence this parameter in plantation forest growing by setting out the planting material in accordance with these data. The article shows the developed method for theoretical estimation of the probability of occurrence of critical bark deformations in the compressed zone, which appears when bending a growing tree due to wind load. Classical studies of the critical state of compressed rods on an elastic base were used as the theoretical basis of the method. A part of growing tree bark plays the role of a rod, while cambium and other living cells between the bark and the trunk wood play the role of the elastic base. A correlation simple enough for practical application is proposed in order to obtain quantitative estimates. Adequacy of the modeling results is confirmed by their consistency with the experimental data. The application of the developed methodology is shown on the examples.

Deformation and critical dynamic stress for compacted volcanic ash subjected to monotonic and dynamic loads

Volcanic ash is widespread in volcanic areas and is considered as a potential construction material. Therefore, volcanic ash can be used as subgrade material when building highways and railways in volcanic areas. However, there is limited research on the critical dynamic stress as well as deformation characteristics of volcanic ash under dynamic load. The Global Digital System (GDS) monotonic triaxial tests and dynamic triaxial tests are presented in this paper to quantify the critical dynamic stress as well as deformation characteristics of volcanic ash subjected to monotonic and dynamic loads. The critical dynamic stress and deformation of volcanic ash are affected by stress level, water content and dynamic stress amplitude. Under monotonic loads, the strength of volcanic ash decreases with increasing water content and increases with increasing confining pressure. The deformation of volcanic ash exhibits strain softening behavior which is enhanced with increasing water content and weakened with increasing confining pressure. According to the shakedown theory, the patterns of accumulative plastic strain for the volcanic ash under different dynamic stress amplitudes are classified into three categories, named plastic shakedown, plastic creep, and incremental collapse. This study redefines the shakedown limits for volcanic ash based on the shakedown theory. The adoption of new shakedown limits provides more accurate descriptions of deformation characteristics at different stress levels, water contents and dynamic stress amplitudes. Based on the new shakedown limits, this paper presents empirical models for the calculation of critical dynamic stress for volcanic ash shakedown limits using regression analysis. As a contribution to the literature and potential engineering applications, the proposed models may provide theoretical significance for the subgrade state evaluation.

Instability-induced patterns and their post-buckling development in soft particulate composites

In this paper, we investigated elastic instabilities in soft particulate composites under finite strains. Through our numerical analysis, we find distinct instability modes developing in the composites upon the critical deformation level. In particular, fully predetermined by its initial geometry, the microstructures transform into (i) strictly doubled periodicity, (ii) seemingly non-periodic state, or (iii) longwave pattern. The latter may give rise to highly ordered domain formations. We analyze the various mechanisms leading to the development of the different instability modes and specifically focus on the seemingly non-periodic one. We illustrate the distinct features of their corresponding eigenmodes obtained from the Bloch-Floquet analysis. We further employ the quasi-convexification analysis and examine the energy landscapes of the soft composites developing the different instability modes. Finally, we examine the development of the predicted instability modes in the post-buckling regime. We find that, depending on the characteristic critical wavenumber, the post-buckling patterns can significantly diverge from those predicted by the Bloch-Floquet analysis. In the post-buckling regime, the instabilities may develop into various scenarios: from a combination of different repeating inclusion sets to disordered, seemingly chaotic patterns.

Dynamic fracture regimes forinitially prestressed elastic chains.

We study the propagation of a bridge crack in an anisotropic multi-scale system involving two discrete elastic chains that are interconnected by links and possess periodically distributed inertia. The bridge crack is represented by the destruction of every other link between the two elastic chains, and this occurs with a uniform speed. This process is assumed to be sustained by energy provided to the system through its initial configuration, corresponding to the alternating application of compression and tension to neighbouring links. The solution, based on the Wiener–Hopf technique and presented in Ayzenberg-Stepanenko et al. (Ayzenberg-Stepanenko et al. 2014 Proc. R. Soc. A 470, 20140121 (doi:10.1098/rspa.2014.0121)) is used to compute the profile of the medium undergoing failure. We investigate when this solution, representing the steady failure process, is physically acceptable. It is shown that the analytical solution is not always physically applicable and can be used to determine the onset of non-steady failure regimes. These arise from the presence of critical deformations in the wake of the crack front at the sites of the intact links. Additionally, we demonstrate that the structural integrity of the discrete elastic chains can significantly alter the range of speeds for which the bridge crack can propagate steadily.This article is part of the theme issue ‘Wave generation and transmission in multi-scale complex media and structured metamaterials (part 2)’.

Application of Alternative Methodology to Select the Optimum Design of TCU Carrier Using FEA

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;The transmission control unit is used in automobile domain, to control the automatic transmissions. TCU is associated with mechanical parts like Housing, Carrier, Hydraulic Plate etc. In this case, TCU carrier is mounted on hydraulic plate using a dowel pin to locate it accurately. During servicing of the TCU, Carrier with dowel pin is subjected to high displacement which leads to huge plastic deformation &amp;amp; failure of the carrier. A study was required using Finite Element Analysis for a series of designs to evaluate their structural stability and to recommend the best possible design. ANSYS tool is used for the simulation. During this study, when conventional method of reckoning stresses and strains as a criterion of comparison was adopted, it involved a tedious process &amp;amp; required many numbers of iterations. Despite plenty of iterations, it may not be possible to conclude the exact force at which the carrier fails or the max displacement it can withstand. The other reason to look for an alternative method is, the development team expectations about the structural stability of the carrier considering operating conditions is contradicting with the strains observed with conventional method. So, there was a need to develop alternative method to evaluate the carrier strength. Hence, stiffness criterion is obtained as a solution. Series of designs are compared based on stiffness &amp;amp; deformation criterion for loads ranging from operating load of 3 mm to maximum displacement load of 6 mm. The simulation results through this stiffness method obtained are also validated with testing results and accuracy of results is observed. This study using stiffness method helped us in selection of best possible carrier design suitable for maximum displacement load without any failure. Cost of testing for around 6 designs is reduced by using FEA and optimum design is also obtained.&lt;/div&gt;&lt;/div&gt;

A simplified approach for predicting the non-linear critical speed of railway tracks

When trains approach the railway track-ground critical speed ground deformations are amplified, potentially exceeding the linear-elastic strain range in the supporting earthworks. This leads to non-linear soil behavior which can be difficult to model due to high computational cost and the need for detailed characterization of soil properties. As a solution, for the first time this research presents a simplified methodology to calculate the non-linear critical speed of track-ground structures. The methodology uses a novel semi-analytical approach that combines dispersion curves with a simplified linear equivalent model. Using the approach, a track-ground static strain field is first calculated, and then converted into a dynamic one using a non-dimensional dynamic amplification function, independent of the elastic properties of the soil. The result allows the non-linear critical speed to be calculated using static simulation results which are relatively straightforward to generate. The methodology is validated using a 3D non-linear Hardening Soil-small (HSSmall) numerical model and then a parametric study is used to compare results for both concrete slab and ballasted tracks. The results show the proposed approach is a reliable tool for predicting the non-linear critical speed.

Stable Regional Reference Frame for Reclaimed Land Subsidence Study in East China

This study implemented a stable Regional Reference Frame in Shanghai, East China (called SHRRF), using seven years of continuous GNSS observations from the Shanghai Continuously Operating Reference System stations (SHCORS) to examine reclaimed coast–land subsidence. A well−distributed core station network suitable for regional applications was derived. The instantaneous station coordinates and seven frame parameters (translations, rotations, and scale) were estimated at each epoch through minimum constraint during the process of aligning SHRRF to the International Terrestrial Reference Frame (ITRF14). The average root mean square error (RMSE) of all stations under SHRRF was within 1.5 mm horizontally and 5 mm vertically for most epochs. Simultaneously, compared with the ITRF14 solutions, the average RMSE for each site at all epochs was reduced by ~30% horizontally and ~10% vertically. A temporal consolidation settlement model of the reclaimed soil under self−weight was established by combining a geotechnical−derived model with high precision permanent GNSS vertical solutions under SHRRF. The model indicates that ~50% of settlements occurred within 3.6 years, with the whole subsidence time being 46 years. SHRRF provides a precise regional reference frame for use in many East China geophysical applications besides reclaimed coast–land settlement including hydrologic loading, microplate motions, and critical structure deformation monitoring.

Experimental and simulation analysis of bubble deformation in foaming polypropylene

This paper investigates the bubble deformation in bubble growth using a self-made in situ visual injection molding device. The results show that the deformation degree of independent bubbles is kept within 0.015. Under the frame rate of 25 frames per second (FPS), it is found that adjacent bubbles with the same average diameter simultaneously pass through the deformation critical point, while adjacent bubbles with different average diameters can’t pass through the critical deformation point at the same time. The interaction in the process of adjacent bubble growth is simulated by finite element software, radial migration of bubbles is suppressed, the hoop stretch of bubbles is enhanced, and the deformation sequence of adjacent bubbles is determined by bubble radius and bubble pressure. On the basis of the bubble influence zone model and the bubble deformation model, a bubble deformation response model is established, used to reflect adjacent bubbles’ deformation response speed.

Prediction of the stress-strain state and stability of the front of tunnel face at the intersection of disturbed zones of the soil mass

The article presents a numerical solution of the spatial elastic-plastic problem of determining the stability of the tunnel face soils at the intersection of disturbed zones of the soil mass. The relevance of the study is related to the need to take into account the zones of disturbed soils when assessing the face stability to calculate the parameters of the support. Based on the finite element method implemented in the PLAXIS 3D software package, the construction of a finite element system "soil mass-disturbance-face support" and modeling of the intersection of the disturbed zones of the soil mass were performed. To assess the condition of soils, deformation and strength criteria are taken. The deformation criterion is expressed by the value of the calculated displacement of the tunnel contour in the face, and the strength criterion - by the safety coefficient until the maximum values of the stress state are reached according to the Coulomb–Mohr criterion. The results of the study are presented in the form of histograms of the safety coefficient dependences on the distance to the disturbance at different bending stiffness of the face support structure, as well as the isofields of deformation development. The parameters of rockfall formation in the face zone at the intersection of zones of disturbed soils were determined. The local decrease in strength and deformation properties in the rock mass along the tunnel track should be taken into account when assessing the stability of the tunnel face and calculating the parameters of the support. Within the framework of the constructed closed system, a qualitative agreement of the simulation results with the case of a collapse in the face during the construction of the Vladimirskaya-2 station of the St. Petersburg Metro was obtained.

The RED criterion for fatigue life assessment of metals under non-proportional loading

In the present paper, a novel criterion for fatigue life assessment of engineering components under multiaxial low-cycle fatigue regime is proposed. The criterion, named Refined Equivalent Deformation (RED) criterion, allows to take into account, when the load is non-proportional, the fatigue strength decrease experimentally observed for those metals sensitive to non-proportionality. The criterion is applied to two different metals (304 stainless steel and 6061 aluminum alloy) characterised by different non-proportional sensitivities. The accuracy of such a criterion is compared with those of other criteria available in the literature.

DETERMINING THE FORM OF ERROR DISTRIBUTION OF GEODETIC MEASURING

Industrial equipment is a dynamic system and has deformations not only during installation but also during operation. Under the influence of variable load and displacement of the center of gravity, the soil under the foundation settles unevenly, and accordingly, the equipment deforms unevenly, which is a threat to the equipment, the greater the load corresponds to more subsidence. Separation of partial deformations from full is important for determining the elements of straightening equipment for its uninterrupted and trouble-free operation. The presence of significant total deformation does not affect the performance of the equipment. The most critical deformations are partial deformations. Absolute vertical deformations are calculated as the difference in sediment between adjacent sediment marks, which are fixed on the equipment in the same measurement cycle.Comparing the values of deformations with the allowable technical conditions, decide on the need for straightening and adjustment of equipment. The accuracy of installation is characterized by a tolerance of 0.1÷0.5 mm on the relative position of the equipment, which is conjugate mounted at a distance of several tens or hundreds of meters. For installation of the equipment with such accuracy carry out special geodetic works with use of methods and technical means of measurements specially developed for this purpose in geodesy, metrology and mechanical engineering.

The Influence of the Performance Parameters of Bimetal Composite Pipe on the Forming Efficiency

In order to solve the problem of low efficiency in the mechanical drawing process of bimetal composite pipe, a dynamic model of the forming process of bimetal composite pipe is established based on the principle of virtual work and the elastic-plastic deformation criterion. The influence of the material properties of the inner pipe and the outer pipe on the forming success rate is studied. The residual stress of the inner pipe and the outer pipe after forming is taken as the main evaluation object, and the elastic modulus and yield of the material are systematically analyzed The influence of strength on residual stress. The results show that the ratio of the elastic modulus of the inner tube to that of the outer tube is more than 0.6 times of the yield strength when the bimetal composite tube is formed, and the materials with large elastic modulus and small yield strength of the inner tube and small elastic modulus and large yield strength of the outer tube should be selected as far as possible. At last, the theory of material parameter proportion for the successful forming of inner tube and outer tube is put forward. The research conclusion is reasonable and universal, which provides a scientific basis for the selection of composite tube materials, and has engineering practical significance for improving the forming efficiency of bimetal composite tube.

PHENOMENOLOGICAL CRITERIA OF DESTRUCTION

The paper reviews the known deformability criteria, which have become widespread to assess the probability of failure in both monotonic and nonmonotonic plastic deformation. The most widely used methods of assessing plasticity, in which the dependence of plasticity on the stress state scheme is described by plasticity diagrams. The plasticity diagram is an experimental dependence of the ultimate deformation on the stiffness index of the stress state. In most works, this dependence is represented by a flat curve. The plasticity of metals depends on many factors, namely the nature of the metal and the thermomechanical parameters of the process. With cold plastic deformation, the main factor influencing plasticity is the stress state and the law of its change during loading. To quantify the impact of stress state on the probability of failure using failure criteria. Under the destruction is understood the appearance of macrocracks, which leads to irreparable damage to the product. A common disadvantage of the known deformation criteria, which are common to assess the probability of failure in both monotonic and nonmonotonic plastic deformation is that the subintegral functions of these criteria are based on the hypothesis that the effect of stress state on plasticity is described by the plasticity diagram and the influence of load history – flat trajectories. Due to the fact that the plasticity diagrams cover a rather narrow class of stress states, in applied theories of deformability there is no single approach to estimating the value of the used plasticity resource in the processes of metal forming. From the performed research it follows that at present there are almost very few works in which the dependence of plasticity on the history of loading is described by spatial trajectories. Therefore, the question of the destruction criteria remains open and relevant.

A criterion for when an emulsion drop undergoing turbulent deformation has reached a critically deformed state

Turbulent breakup in emulsification devices is a dynamic process. Small viscous drops undergo a sequence of oscillations before entering the monotonic deformation phase leading to breakup. The turbulence-interface interactions prior to reaching critical deformation are therefore essential for understanding and modeling breakup. This contribution uses numerical experiments to characterize the critically deformed state (defined as a state from which breakup will follow deterministically, even if no further external stresses would act on the drop). Critical deformation does not coincide with a threshold maximum surface area, as previously suggested. A drop is critically deformed when a neck has formed locally with a curvature such that the Laplace pressure exceeds that of the smallest of the bulbs connected by the neck. This corresponds to a destabilizing internal flow, further thinning the neck. Assuming that the deformation leads to two spherical bulbs linked by a cylindrical neck, the critical deformation is achieved when the neck diameter becomes smaller than the radius of the smallest bulb. The role of emulsifiers is also discussed.

Deformation and initial breakup morphology of viscous emulsion drops in isotropic homogeneous turbulence with relevance for emulsification devices

This study uses numerical experiments to investigate initial breakup morphology for conditions similar to those experienced in an emulsification device (e.g., a high-pressure homogenizer) (Reλ = 33, We = 1–30, μD/μC = 22, ρD/ρC = 0.9, D/η = 22). Results show breakup consisting of two phases: and ‘oscillatory phase’ where the drops are periodically deforming and relaxing, followed by a ‘critical deformation phase’ where the drop deforms continuously until initial breakup. Large drops (We ≥ 13) go directly to the breakup phase and are highly deformed in multiple direction before bursting. Smaller drops (3 ≤ We ≤ 5) are less likely to go directly to the critical deformation phase and more likely to never reach it before exiting the device. These drops break by the formation of a single filament, creating two large fragments and a number of smaller satellites. Several turbulent structures contribute to critical deformation.

Transient Effect of Random Loads on Reinforced Cement Concrete Building on RCC Building with Staad Pro. V8i

Abstract. Dynamic load is one which changes with time quickly in comparison to the structure's natural frequency. If it varies quickly, the activity must be determined with a dynamic analysis. Explosive loads and impact loads are transients, or loads that are applied dynamically as one-half cycle of high amplitude. This transient load is applied only for a specific and typically short period of time in the case of blast loads typically less than one-tenth of a second. The response of the engineering structural building due to the reason of periodic load RCC building structure has been severely damaged, collapse and develop cracks. Bomb blast is the best example for impulsive load. To determine the response of a G+3 RCC building model in STAAD Pro subjected to triangular, rectangular and sinusoidal impulsive force for 0.5 seconds with maximum magnitude of 100kN. Effect of such loads on front, roof and side portion of the building studied. Observe that the critical deformations obtained on the front and roof portion of building. Effect of deformation along height of building was parabolic in nature with maximum deflection at top floor of building. It was also noted i.e sufficient reinforcement should be provided in beam, columns and slabs to impart ductility to the building against impulse loads.There is more demand for construction of high buildings due to increasing urbanization and population.

Cluster Hardening Effects on Twinning in Mg-Zn-Ca Alloys

Twinning is a critical deformation mode in Mg alloys. Understanding deformation twinning (DT) is essential to improving mechanical properties of Mg alloys. To address the experimentally observed conspicuous hardening effects in Mg-1.8Zn-0.2Ca alloys, interactions between the {10–12} twin boundaries (TBs) and solute clusters in Mg-Zn-Ca alloys were examined via molecular dynamics (MD) simulations. We find that the Zn/Ca-containing clusters show different hindering effects on TBs and an increment in the applied shear stress of 100 MPa is required to accomplish the interaction between the boundary and the cluster with Ca content &gt; 50 at%. The cluster hardening effects on twinning are positively correlated to the Ca content and the size of the clusters in Mg-Zn-Ca alloys.

ANALYSIS OF TEST EQUIPMENT FOR INVESTIGATION OF MATERIALS UNDER A STRONG LOAD APPLICATION

An analysis of publications on this topic. It is established that in most literature sources the work of wood is shown only in the ascending branch of deformation, which is a false statement. The method of experimental studies of alder and spruce wood by axial compression along the fibers with a short-term load at standard humidity (by increasing displacements) is presented. The age of the wood was about 40 years. Experimental studies of such samples were performed on a modern STM- 100 test machine. 18 samples with a cross section of 30x30x120 mm were tested. Based on the experiment, complete deformation diagrams “stress σc - strain uc” were constructed and the main parameters were established: critical and residual strains, as well as their corresponding stresses. It is established that both diagrams have an ascending and descending branch, ie they work in both pre-critical and super-critical stages of work.&#x0D; The average critical deformations of alder wood uc,0,d = 0,00397, as well as the corresponding maximum stresses fc,0,d = 35,6 MPa, and spruce wood - uc,0,d = 0,00421 (fc,0,d = 38.1 MPa).&#x0D; Also, the average residual deformations for alder wood uc,fin = 0.277, and the corresponding stresses σc,fin = 3.9 MPa; for spruce wood uc,fin = 0.212, and stress - σc,fin = 3.6 MPa. &#x0D; It is confirmed that deciduous and coniferous wood at standard humidity has an ascending and descending branch, ie works in the subcritical and supercritical stages of work.&#x0D; In the future it is necessary to conduct such experimental studies for other deciduous and coniferous species. In the future, determined mechanical characteristics experimentally, it is necessary to propose methods for finding and theoretical, which will give a complete picture of such materials.