Critical Deformation Research Articles

BIOMECHANICAL MODELING IN SURGICAL TREATMENT OF A PATIENT WITH TRUE LUMBAR SPONDYLOLISTHESIS

Objective. To assess the results of clinical approbation of individual finite-element biomechanical model of a patient’s spino-pelvic complex with subsequent modeling of the best option of surgical treatment. Material and Methods. A biomechanical modeling of changes in the sagittal profile of a patient with degenerative disease of the lumbosacral spine, bilateral spondylolysis, and unstable grade 2 spondylolisthesis of the L4 vertebra was performed. The developed biomechanical model made it possible to assess the characteristics of the stress-strain state of the spinal motion segments aroused due to development of the disease. Within the built biomechanical model of the patient’s spino-pelvic complex, a corrective operation was further modeled that assumed a preservation of harmonious profile of sagittal spino-pelvic relationships. Post-correction characteristics of the stress-strain state of spinal motion segments were studied and compared with preoperative parameters of the biomechanical model. Results. Using methods of biomechanics and computer modeling allowed to calculate the stress-strain state of the lumbosacral spine under static load for two options of fixation and intervertebral cage implantation at the L4–L5 level: four transpedicular screws (L4–L5 vertebrae) and six transpedicular screws (L3–L4–L5 vertebrae). The simulation results showed that neither metal implants, nor elements of the lumbosacral spine experienced critical stresses and deformations that could lead to the destruction and instability of the implant. Conclusion. The developed individual biomechanical finite-element solid model of the spine and pelvis allowed for biomechanical justification of prerequisites for the formation and further progression of degenerative changes in spinal motion segments associated with violations of the sagittal profile due to grade 2 spondylolisthesis of the L4 vertebra. The model built on the results of radiological examination biomechanically substantiated the best option of corrective spine surgery allowing to minimize stresses and deformations by choosing reasonable magnitude of correction of sagittal spino-pelvic parameters and configuration of transpedicular system.

Quantitative Assessment of the Bauschinger Effect in Magnesium Alloys with the Asymmetry Effect

Special features of the quantitative assessment of the Bauschinger effect in magnesium alloys with asymmetrical deformation behavior are considered. It is found that the Bauschinger effect is associated with the different contribution of detwinning to the overall deformation, and calculation of the quantitative parameters of this effect by stress and deformation criteria gives close results. In this case, the asymmetrical behavior of the magnesium alloys at strain and compression exerts similar influence both on stress of the initial plastic deformation (compressional yield strength) and on the contribution of the deformation detwinning to the overall plastic deformation. Parameters of the Bauschinger effect during condensation of the magnesium alloys are close to zero; i.e., in this case, the effect is hardly evident; and inelasticity, responsible for that, is associated with the special features of detwinning just under strain. Comparison of the Bauschinger effect for two alloys—industrial ZK30 and advanced ZE10 with the rare earth elements—counts in favor of the latter in all cases.

Ultimate State Evaluating Criteria of RC Structural Systems at Loss of Stability of Bearing Element

The paper deals with the deformation of reinforced concrete structural systems of multi-story buildings and structures under accidental impacts. One of these impacts is instantaneous removal of a bearing element of a system. Before this moment researches of survivability and resistance against progressive collapse of structural systems under such impacts were based on the strength criteria. At the same time instantaneous removal of structural element may be caused by loss of stability at evolutionary accumulation of corrosion damages or other physical impacts. That is why the deformation criteria of loss of stability of a structural system under accidental impacts are proposed in this paper. The energy approach and the mixed method of structural mechanics are applied to evaluate survivability and resistance against progressive collapse of a structural system at loss of stability of a bearing element. Two – level computational models are used to solve this problem. An example of calculation of 14-storey building under such impact in accordance to deformation criteria is presented. It is shown, that critical force, that lead the structural system to progressive collapse at evolutionary accumulation of damages is less then ultimate compressive force, which were calculated in accordance to strength criteria.

Droplet deformation, oscillation and detachment on a vibrating plate by a controlled airflow

AbstractIn this work, a detailed experimental study on the influence of fluid properties on the droplet behavior subjected to a shear flow and harmonic surface vibration is conducted. The experiments were executed in a rectangular channel and an acrylic channel wall was utilized to analyze the droplet wetting behavior. Both the effect of shearing mechanism induced by airflow and harmonic vibration induced by an electromagnetic shaker for droplet volumes in the range of 5−40 µl are studied here. Furthermore, the effect of fluid viscosities on the motion of droplets is analyzed for a wide range of water and glycerine mixture ratios. Experiments show that the critical bulk velocity at which the droplet movement begins is a function of fluid properties and droplet sizes. Increasing the droplet volume results in a decrease of the critical bulk velocity, while the droplet deformation increases. On the contrary, increasing the glycerine content of the liquid droplets results in an increase in both the critical bulk velocity and droplet deformation. The droplet movement can be categorized into three motion patterns based on experimental observations: (i) the droplet shape is largely retained with a small tail formation at the rear end, (ii) small droplets detach from the tail at rear end of the main droplet, (iii) the droplet deforms over its entire length resulting in forming of a film.

Study of the Plastic Formation in the Production of Thermoelectric Material Based on Bismuth Telluride

We carry out an experimental-theoretical study of the process of the equal-channel angular pressing (ECAP) to obtain a bismuth-telluride-based thermoelectric (TE) material. A brief review of the mathematical modeling of the ECAP process is given, and the effect of the design features and temperature of ECAP regimes on the formation of plastic is studied. The results of calculations of the thermally stressed state of the samples at different stages of the ECAP process are presented. The calculations for the ECAP process are carried out using the Lagrange finite element mesh. During the calculation, the mesh is adjusted to the geometry of the die, becoming rarer or finer depending on the magnitude of the plastic deformation to satisfy the specified calculation accuracy and the convergence of the iterative process. We discuss the results of an experimental study of the structure and properties of the samples obtained with the help of ECAP using various methods (X-ray diffractometry and scanning electron microscopy). The TE characteristics of the obtained materials are measured by the Harman method. Comparative methodological calculations of the ECAP process for a bismuth-telluride-based TE material with a change in the parameters determining the formation of grains are performed (the critical plastic deformation as a function of temperature and the power-law dependence of the rate of this deformation). This allowed us to adjust the design model of the ECAP process using the grain size measurements in the TE material. The results of the calculation of the process of grain formation at different temperatures of plastic molding are presented and compared with the experimental data. The practical result of this research is the improved geometry of the die punch and the validated technological regimes of plastic deformation, which allowed obtaining samples with high TE efficiency values.

Fracture mechanics of pile foundations on permafrost soils by the example of Norilsk

In Norilsk, more than 30% of the housing stock is in the state of severe disrepair. The analysis of possible causes of failures and deformations of pile foundations in the city of Norilsk is presented. The numerical calculation of the warming of permafrost soils is carried out. The thawing of these soils only due to climate warming cannot result in critical deformation of pile foundations.

Adjusted pile foundation construction for skyscrapers

The article considers the issues of using maximum of pile length by achieving pile limited equilibrium to satisfy all deformation criteria for the skyscrapers. In case the pile limited equilibrium is achieved while constructing, additional loads will transfer to the surrounding piles. The process can be stopped until the necessary number of piles reaches the limited equilibrium. To determine the real pile behavior in the condition of the limited equilibrium 45 static pile tests under the maximum load 120 000 kN applied in skyscrapers constructing process in Russia were summarized. Tests analysis makes it possible to estimate the value of the limited and residual skin friction for different soil conditions. FEM analysis results show the soil and foundation behavior in the process of piles part reaches the ultimate equilibrium. According to the researches result, the approach to the optimal pile foundation design was made. The sphere of its implementation and practical significance were also considered.

Labile technogenic geological system of the flooded Shevchenko salt mine (Ukraine)

This paper presents the analog ecological-mining-geological model of the labile technogenic geological system created at the Shevchenko flooded salt mine area within Artyomovsk rock salt deposit, which is the largest rock salt deposit in Europe. Description of all the system elements taking into account their interconnection and interaction are presented on the basis of the analytical processing and compilation of basic mining and geological data as well as the results of the long-term complex ecological-mining-geological monitoring.The paper describes both the geology of the mine area and the condition assessment of the mine including its shape, parameters, and layout. In addition, scientific interpretation of the mechanism of multi-act intrasystem destructive processes, which have been taking place in the last few decades are provided. Natural and technogenic factors determining the development of the created technogenic geological system (such as man-made karst and critical geomechanical deformations) are summarized and analysed. Predictive evaluation of the time-dependent deformation processes development has been carried out using theexisting methodology for assessing the geomechanical condition of the mined-out area of the salt massive. Correctness of the method for evaluation of stability of the unsupported workings system currently in use for the Artyomovsk rock salt deposit development has been confirmed. This work concerns the scientific problems of maintenance of the geo-ecological safety in the densely populated areas disturbed by underground salt mining. Hereinabove research results add information and analytical base to improve the deformation control system for ductile salt layers in various dynamic conditions of man-caused and natural loads. It is shown that such control is required for the aim of reduction of environmental risks and ensuring the safe operation of salt deposits, salt resources protection as well as infrastructure objects at the Earth’s surface nearby sites of modern salt mining activity.

Modified criterion for prediction of tunnel deformation in non-squeezing ground conditions

The strength factor-based criterion for tunnel deformation prediction proposed by Hoek in 2000 is reckoned to be the most practical criterion among the tunnel deformation criteria since 1980s. In view of the fact that Hoek’s criterion was obtained based on case studies under squeezing ground conditions, it has a limited range of applications, applicable mainly in squeezing tunnels. In this work, this criterion was modified by taking into consideration the conditions of eight unstable stations in three non-squeezing tunnels in Iran to amplify its application range. Relative displacements and strength factor (defined as a strength-to-stress ratio) were obtained in unstable stations first. Then, the parametric values were plotted on a Cartesian coordinate’s plane. By using the optimal regression line passing through all points, a criterion for prediction of tunnel deformation was proposed finally. A comparison made between the measured values and the ones predicted by the new criterion shows that the variance accounted for was 77% and the root mean square error was 2%, an acceptable accuracy and a small error implying the effectiveness of the new criterion in tunnel deformation prediction. In addition, the results show that the strength factor of 0.38 can be used to determine the boundary between squeezing and non-squeezing conditions; the behavior and type of failure of the tunnel would be predictable by use of the strength factor.

Modified-Weibull-stress-based evaluation of brittle fracture occurrence during earthquakes in steel members

Brittle fractures can originate from shallow surface cracks on welded parts of steel structures during earthquakes. Since the occurrence of such fractures is significantly influenced by the shape of the welded parts, the existing methods based on material testing cannot predict fractures. This study focused on a modified Weibull stress, which considers the processes of nucleation and propagation of microcracks at different depths, and demonstrated its applicability to the evaluation of brittle fracture initiation during earthquakes. The demonstration was implemented on three types of structural steel using low-temperature experiments and numerical stress analyses on crack tips. Additionally, the independency of the obtained critical modified Weibull stress from the initial crack depth, strain rate and prestrain was examined in the prediction of the critical crack-tip opening displacement. Finally, the relationship between the critical deformation of the beam-to-column connection of a steel bridge pier at the fracture time (in the case of a fracture originating from a shallow crack) and its weld toe radius was quantitatively evaluated as an example of actual use of the modified-Weibull-stress-based evaluation.

Molecular dynamics simulations of structural instability of fullerene family under tension force

ABSTRACTFullerene molecules are cage-like nanoscopic structures with pentagonal and hexagonal faces. In practical applications such as fullerene-reinforced nanocomposites (FRNCs), these structures may be subjected to tension force. In this research, we employ molecular dynamics (MD) simulation to compute the behaviour and deformation of different fullerene molecules, ranging from C60 to C2000, under tension force. To model the interactions between carbon atoms in the MD simulations, the adaptive intermolecular reactive bond order (AIREBO) force field is used. The displacement–force and the displacement–strain energy curves are obtained. It is observed that a new type of structural instability occurs in the fullerene molecules when the applied tension force increases. This abnormal structural instability in the fullerenes is investigated for the first time in the literature. The critical tensile forces and the corresponding mode shapes are determined for different fullerenes. The results indicate that the critical forces and deformations strongly depend upon the number of carbon atoms.

Breaking properties of neutron star crust

The strength of neutron star crust is crucial for modelling magnetar flares, pulsar glitches and gravitational wave emission. We aim to shed some light on this problem by analysing uniaxial stretch deformation (elongation and contraction) of perfect body-centered cubic Coulomb crystals, paying special attention to the inherent anisotropy of this process. Our analysis is based on the semi-analytical approach of Baiko and Kozhberov (2017), which, for any uniform deformation, allows one to calculate, in fully non-linear regime, critical deformation parameters beyond which the lattice loses its dynamic stability. We determine critical strain, pressure anisotropy and deformation energy for any stretch direction with respect to the crystallographic axes. These quantities are shown to be strongly anisotropic: they vary by a factor of almost 10 depending on the orientation of the deformation axis. For polycrystalline crust, we argue that the maximum strain for the stretch deformation sustainable elastically is 0.04. It is lower than the breaking strain of 0.1 obtained in molecular dynamic simulations of a shear deformation by Horowitz and Kadau (2009). The maximum pressure anisotropy of polycrystalline matter is estimated to be in the range from 0.005 to 0.014 $nZ^2e^2/a$, where $n$ is the ion number density, $Ze$ is the ion charge, and $a$ is the ion-sphere radius. We discuss possible mechanisms of plastic motion and formation of large crystallites in neutron star crust as well as analyse energy release associated with breaking of such crystallites in the context of magnetic field evolution and magnetar flaring activity.

Surface tension convection caused by free surface deformation in KTa1−xNbxO3 melts

Experiments on surface tension driven convection of high temperature potassium tantalate niobate (KTa1−xNbxO3, KTN) melts have been carried out in an in-situ observation system. There is a double loop axially symmetric vortex pattern. With the temperature increases, the convection can be transferred from one stable state to oscillatory state and then to another stable state. The oscillatory surface tension convection, which is related to the free surface deformation, can be characterized by the oscillatory main trunk and two unequal branches. The branches depress the large pressure gradient and compensate the return flow to stabilize the circular current. There is a linear decreasing relationship between the deformation angle θ and the oscillatory frequency f. For KTN melts with higher Nb content, the convective pattern is not various, but a smaller degree of deformation can occur accompanied by a weaker oscillation process. The values of critical deformation coefficient S parameter for both the onset and the offset of oscillations decrease with the increase of the content of Nb. The critical values of oscillation satisfy with Son · x ≈ 2.3 × 10−3 and Soff · x ≈ 4.0 × 10−3, respectively.

Analysis of the fatigue cracks development in crane girders and assessment of their residual life

The results of analysis of the residual life of crane girders with operational defects based on numerical studies of the stress-strain state, equations of limiting states, and kinetic dependences of the fatigue crack development, based on the criteria of deformation and fracture mechanics are presented. High level of wear of the fixed capital assets of engineering constructions and metal structures as well as operation of the facilities in beyond-design-basis terms contribute to origination of the emergency situations caused by damage accumulation. Crane girders operated under emergency conditions due to the fatigue cracks of different lengths present in the most dangerous zones of the beam wall with an eccentric application of crane load are studied. The results of the numerical experiment revealed the lines of tension intensity impact at the crack tip appeared at the upper zone of the wall at different values of the loading eccentricity attributed to the rail shift from the vertical axis of the beam. The dependence of the length of the fatigue crack and stress intensity in the crack tip on the number of load cycles of the beam is determined. To assess the bearing capacity of crane girders operated in emergency conditions, it is suggested to use the effective values of the stress intensity factors calculated for the specific loading conditions, taking into account the structural features of the beams, size of the fatigue cracks and their location in the crane girders. Proceeding from the results of analysis the diagrams which provide of the remaining residual life of crane girders with a crack are constructed. Using traditional methods of structure calculation for cyclic fracture toughness we developed and implemented the calculation algorithm for individual lifetime of the crane girders which includes the obligatory analysis of the stress-strain state of the crane girders with a crack at the upper zone of the wall.

Friday, September 28, 2018 4:05 PM–5:05 PM abstracts: tumor and deformity: 249. Cervical, thoracic and spinopelvic compensation after proximal junctional kyphosis: Does location of PJK matter?

BACKGROUND CONTEXT Proximal Junctional Kyphosis (PJK) can occur at any segment along the spine and yet, compensation mechanisms at levels proximal to an area of PJK have not clearly been characterized. Understanding compensation mechanisms may help in determining optimal level selection when performing revision surgery for PJK. PURPOSE Evaluate the difference in compensatory mechanisms between thoraco-lumbar and thoracic PJK. STUDY DESIGN/SETTING Retrospective review of prospective database. PATIENT SAMPLE A total of 369 patients out of 496 eligible (73.2%) for 2 years follow-up. OUTCOME MEASURES Radiographic alignment of the cervical and thoracic spine as well as pelvic orientation. METHODS PJK location was based on UIV location: LT (T8–L1) or UT (T1–7). Inclusion criteria were fusion >5 levels with the LIV being S1/Ilium. PJK was defined by Glattes criteria. Alignment parameters were compared between PJK patients separated by UIV Group. Correlation Analysis was made between PJK magnitude and global or cervical alignment within UIV group. Percentage of patient reach criteria for cervical deformity according to cSVA (>4cm) were calculated overall and within each subgroup. RESULTS There were 369 patients included in the analysis; mean age of 63, BMI 28 and 81% female, LT (n=193) versus UT (n=176). The rate of radiographic PJK was 49% and higher in the LT group (55% vs. 42%, p=.01). No significant differences were found in global alignment between PJK patients, with the exception of TK being larger for PJK patients (UT:−49.4 vs. −59.0, LT: −46.5 vs. −56.4; all p CONCLUSIONS PJK location results in different compensation mechanisms of the cervical and thoracic spine. The LT group compensates with an increase in PT and CL to maintain an acceptable cSVA. The UT group increases their CL to counter the increase in T1S but continues to have TS-CL mismatch with an elevated cSVA due to maximum compensation at the cervical level. As a result, increase in cSVA led to 40.3% of patients meeting criteria for CD with focal deformity located in the cervical spine. Future studies should investigate the surgical strategy to treat PJK depending on the location of the focal deformity.

Influence of Stress State on the Mechanical Impact and Deformation Behaviors of Aluminum Alloys

Under impact loading conditions, the stress state derived from the contact between the projectile and the target, as well as from the subsequent mechanical waves, is a variable of great interest. The geometry of the projectile plays a dertermining role in the resulting stress state in the targeted structure. In this regard, different stress states lead to different failure modes. In this work, we analyze the influence of the stress state on the deformation and failure behaviors of three aluminum alloys that are commonly used in the aeronautical, naval, and automotive industries. To this purpose, tension-torsion tests are performed covering a wide range of stress triaxialities and Lode parameters. Secondly, the observations from these static tests are compared to failure mode of the same materials at high impact velocities tests with the aim of analysing the role of stress state and strain rate in the mechanical response of the aluminum plates. Experimental impacts are conducted with different projectile geometries to allow for the analysis of stress states influence. In addition, these experiments are simulated by using finite element models to evaluate the predictive capability of three failure criteria: critical plastic deformation, Johnson-Cook, and Bai-Wierzbicki.

Methods for the Determination of Curvatures and the Difference Between the Slopes of Foundations as the Criteria of Deformation of the Basements of Buildings and Structures

We proved the identity of measurements of deformations of the bases of buildings and structures by using the methods of leveling and cyclic inclinometric methods. We present some recommendations concerning the determination of deformations of the bases of buildings and structures (settlements, curvatures of the bent section of the structure) according to the data of inclinometric of measurements of the slope angles of foundations instead of the leveling measurements under the condition of distant location of a permanent bench mark.

Normal Sections Calculation of Bending Reinforced Concrete and Fiber Concrete Elements

The basic principles of the normal sections calculation of reinforced concrete and fiber reinforced concrete bending elements are considered. In the article the power and deformation methods of calculation of reinforced concrete and fiber concrete elements of rectangular cross-section are presented. The deformation model of the calculation of reinforced concrete and fiber concrete elements is presented in the framework of the method of calculation resistance of the section. This method makes possible from the common methodological positions to perform calculations of reinforced concrete and fiber concrete elements. Namely, to select reinforcement and to determine the carring capacity. The proposed deformation model for calculating fiber concrete elements is based on generally accepted preconditions. A hypothesis of plane cross sections is accepted as fair. The deformation diagram of compressed concrete is described by a nonlinear function with established parametric points. Distribution of stresses in stretched concrete is taken rectangular with corresponding coefficients which are taken depending on the type of deformation diagram. Determination of the carring capacity of fiber concrete elements occurs under extreme deformation criteria. Two cases of destruction of the investigated elements are considered. The first case is the destruction due to the achievement of limiting deformations in the concrete of the compressed zone with the simultaneous achievement of the fluidity limit in the working reinforcement. The second case is the destruction due to the achievement of limiting deformations in the concrete of the compressed zone without reaching the fluidity limit in the working reinforcement. Both cases of calculation are reduced to one functional dependence. This avoids the delimitation of different calculation cases. The main no dimensional modifier is the mechanical coefficient of reinforcement. According to the developed method, examples of calculations of reinforced concrete, fiber reinforced concrete elements and fiber concrete elements with longitudinal reinforcement are executed. The possibility of a spread variant design of reinforced concrete and fiber concrete elements is shown.

Stability of steel columns stiffened by stays and multiple crossarms

A pre-stressed stayed steel column (PSSC) can effectively enhance the buckling behaviour of compression columns. In the past, researchers have primarily concentrated on examining the behaviour of PSSCs with single-bay crossarms. However, research focused on PSSCs with multiple crossarms is limited. This article aims to investigate the stability behaviour of PSSCs stiffened with multiple crossarms according to geometric analysis in conjunction with finite element (FE) studies. The results show that the critical buckling modes can be complicated due to the introduction of multiple crossarms. Critical buckling deformation similar to three half sine waves can be observed. It has also been demonstrated that interactive buckling can be ignored when determining the actual buckling strength of PSSCs stiffened by multiple crossarms, though it must be considered for PSSCs with single-bay crossarms. The effects of stay diameter and pretension in the stay have been separately investigated, and the results show that the buckling strength of a steel column can be obviously enhanced even if the pretension in stays is quite small, because the stiffness of the stays can be automatically activated by column deformation.

Deformation Characteristics and Texture Development of Biadded Cu-29Zn Alloys

Theories regarding texture transition mechanisms of brass alloys and its critical deformation level of when the change of texture transition occurs are still in debate. Previous observation showed that copper type texture dominantly formed at high temperature process whereas brass type texture tended to occur at low temperature. In contrast, another research observed the occurrence of copper type texture at low strain level while higher strain level resulted in brass type texture. Thus further research is needed to affirm one that well-satisfy the actual texture transition phenomenon. In this research, Cu-Zn-xBi alloys were produced by gravity casting process using pure Cu and Zn ingots with varied Bi addition of 0.2, 0.4, and 0.8 wt. %. As-cast samples were homogenized at 800 °C for 2 h in a muffle furnace. The samples were then cold-rolled with the level of deformation of 20, 40, and 70 %. Characterization includes chemical composition analysis, microstructure observation, hardness testing, and texture measurement. Results showed that addition of Bi prompted Bi-rich dispersoid phase which segregated inside the grain and along the grain boundary in globular forms. Slip was dominant at 20 % deformation level and its density increased with the addition of Bi. At 40 % deformation, twinning replaced slip as the predominant mechanism. The twin density increased with higher Bi content. Further deformation at 70% produced shear bands and flattened the Bi dispersoid phase. Greater Bi content induced the formation of shear band. At 40% deformation, pole figure images show the trend of copper type texture with orientation of {112} <111> with intensity of 7.92. This texture was formed by mechanical twinning during deformation process. At 70 % deformation, samples illustrated the combination of brass and Goss type texture at orientation of {110} <112> and {110} <001> due to the shear band.