Obvious Deformation Research Articles

Dynamics of a bubble in a liquid fully confined by an elastic boundary

In order to investigate the dynamics of a bubble in a liquid fully confined by an elastic boundary, which are used for applications and research of cavitation bubbles in botanical and biomedical sciences, we establish a related numerical model by the boundary element method. The boundary is defined as an interface between two liquids with different densities to simulate the environment of biological tissue efficiently. Our numerical model is validated thanks to the results of an available related experiment and the calculations of a confined corrective Rayleigh–Plesset equation. Then, we focus on the dynamics of a non-spherical bubble caused by relative position of the bubble and confinement. The results show that the confinement can lead to a rapid oscillation of a bubble, and a jet will be generated along the eccentric direction because of the accumulation of high pressure and disturbance on one side of the spherical confinement. Furthermore, elastic modulus of the boundary, size of the confinement, and eccentric position of the bubble in the confinement are considered in this paper. The amplitude and cycle of a bubble oscillation will decrease with the increase of the elastic modulus and decrease of the size of the confinement. What's more, eccentricity leads to a strong restriction on the bubble surface near the boundary and obvious non-spherical deformation of the elastic boundary. The study can contribute to understandings and applications of cavitation bubbles in expulsion of spores, plant cell wall broken, thrombolysis, and other related botanical and biomedical fields.

3D DEM simulation of initial anisotropy in dredger fill soft soil

The initial anisotropy has a significant effect on the mechanical properties of the soft soil. Based on the initial anisotropy of the particles, the mechanical characteristics are analysed from a microscopic view, and the micro-macro relationship of the soil is established. According to the particle morphology of soft soil, the discrete element method is used to construct the flaky particle clusters, and seven sets of samples with different initial deposition angles are established for consolidation and undrained triaxial simulation tests. The results show that the strength of the sample decreases first and then increases with the increase of the deposition angle. When the deposition angle is 0°, the flaky particles mostly appear in a nearly horizontal suspension, and the sample has the largest shear strength. The distribution of the contact force chain formed by the particles in the shearing process is also related to the deposition angle. Different deposition angles form displacement fields of different shapes. When the deposition angles are 45° and 60°, there are obvious deformation displacement bands. At the same time, the initial deposition angle affects the particle coordination number. The higher the sample strength corresponding to the lowest average coordination number of particles. The contact normal anisotropy coefficient is related to the strain hardening and strain softening characteristics in the shearing process. The increase in the contact normal anisotropy coefficient shows the characteristics of hardening, and the smaller the contact normal anisotropy coefficient shows the characteristics of softening.

Three-Dimensional Linear Restoration of a Tunnel Based on Measured Track and Uncontrolled Mobile Laser Scanning.

Traditional precision measurement adopts discrete artificial static observation, which cannot meet the demands of the dynamic, continuous, fine and high-precision holographic measurement of large-scale infrastructure construction and complex operation and maintenance management. Due to its advantages of fast, accurate and convenient measurement, mobile laser scanning technology is becoming a popular technology in the maintenance and measurement of infrastructure construction such as tunnels. However, in some environments without satellite signals, such as indoor areas and underground spaces, it is difficult to obtain 3D data by means of mobile measurement technology. This paper proposes a method to restore the linear of the point cloud obtained by mobile laser scanning based on the measured track center line. In this paper, the measured track position is interpolated with a cubic spline to calculate the translations, and the rotation parameters are calculated by combining the simulation design data. The point cloud of the cross-section of the tunnel under the local coordinate system is converted to the absolute coordinate system to calculate the tunnel line. In addition, the method is verified by experiments combined with the subway tunnel data, and the overall point error can be controlled to within 0.1 m. The average deviation in the horizontal direction is 0.0551 m, and that in the vertical direction is 0.0274 m. Compared with the previous methods, this method can effectively avoid the obvious deformation of the tunnel and the sharp increase in the error, and can process the tunnel point cloud data more accurately and quickly. It also provides better data support for subsequent tunnel analysis such as 3D display, completion survey, systematic hazard management and so on.

Stretch-induced shear deformation in periodic soft networks

The bio-inspired periodic network design with unit lattice constructed by wavy filamentary microstructures displays potential applications in the fields of bio-integrated devices and tissue engineering, due to its reproduction of the J-shaped mechanics curve that typically observed in biological soft materials. An obvious macroscopic shear deformation can be induced during the uniaxial tension of such kind of periodic soft network materials, which is an important issue for practical application, since that mechanical matching between the network material and target biological tissue is essential for conformal adhesion, while such unusual shear behavior is rarely observed in conventional biological materials. For quantitative evaluation, a theoretical model for nonlinear mechanics of periodic soft network materials is developed and then validated by finite element analysis (FEA) and experiments. The results present a hook-shaped characteristic curve for the shear deformation, whose mechanism is explained via the analysis of microscopic deformation of lattice structure. Based on this model, several factors are taken into account to investigate their effects on the shearing behavior, including horseshoe geometrical parameters, interconnect configuration and lattice topology. The results could provide potential guidelines for the design and optimization of such periodic soft network materials.

Alteration in micro-mechanical characteristics of wellbore cement fracture surfaces due to fluid exposure

The stiffness of wellbore cement fracture surfaces was measured after exposing to the advective flow of nitrogen, silicone oil, and medium sweet dead crude oil for different exposure periods. The test specimens were extracted from fractured cement cylinders, where the cement fracture surfaces were exposed to the different fluids up to 15 weeks. A nanoindenter with a Berkovich indenter tip was used to measure load-indentation depth data, which was used to extract the elastic modulus (E) and nano-hardness (H) of the cement fracture surfaces. A reduction in the elastic modulus compared with an unexposed specimen were observed in all the specimens. Both elastic modulus and nano-hardness for the specimens exposed to silicone oil were lower than specimens exposed to nitrogen gas and varied with the period of exposure. The elastic modulus and nano-hardness of the specimens exposed to crude oil were the lowest with a significant decrement with the exposure period. The frequency distribution of the nanoindentation measurements shows that the volume-fraction ratio of the two types of cement hydrated nanocomposites for both the unexposed and test specimens is about 70:30%. Phase transformation beneath the indenter is observed for all of the specimens, with more obvious plastic deformation in specimens exposed to crude oil. Analytical measurements (SEM, EDS, FT-IR, and XRD) on exposed cement fracture surfaces reveal different levels of physical and chemical alteration that are consistent with the reduction in stiffness measured by nanoindentation. The study suggests that cement stiffness will decrease due to crude oil exposure, and the fracture will be sensitive to stress and pore pressure with time.

Precision cutting of epoxy resin board (ERB) by ultraviolet (UV) nanosecond laser ablation with consideration of hazardous gas protection

Mechanism and processing technology of ultraviolet (UV) nanosecond laser precision cutting of epoxy resin board (ERB) were investigated based on by-products analysis and orthogonal experiment. Interactions between UV nanosecond laser and ERB was studied, and by-products generated during laser cutting process were analyzed. Among them, gaseous by-products such as CO and benzene were potentially toxic. Under premise of cutting off ERB (0.5 mm thick), minimum seam width (75 ± 3 µm) was obtained at laser cutting parameters combination of 4.04 W - 1000 mm/s – 8 (cutting times). Meanwhile, there was no obvious burr and thermal deformation of the seam. Overall, UV nanosecond laser is a viable process for precision cutting of ERB, but protective measures must be taken during the process.

Study on the Influence of Close Distance Construction of Urban Tunnel on the Existing Station

In the construction of the tunnel passing through the existing structure at an ultra-close distance, the existing structure will produce obvious deformation. It is very important to understand the deformation characteristics of the existing upper structure at different positions, especially to ensure the safety of the upper structure and improve the effectiveness of tunnel construction. In this study, the double-line tunnels of Qingdao Metro Line 4 passing under the Cuobuling station were taken as the engineering background, and a detailed 3D numerical model was established. This study comprehensively considered the on-site construction process, including grouting hardening, stress release of the excavated rock mass, grouting pressure and so on. The influence of tunnel excavation on the ground settlement was compared with or without a station structure, and the result was fitted with an empirical formula. Finally, the deformation of the station structure due to the excavation of the double-line tunnels was analyzed. The results of the analysis were as follows: (1) In the presence of the station structure, the excavation of the tunnels had a significant impact on the surface settlement. (2) The settlement of the sidewall caused by the excavation of the left-line tunnel was greater than that of the right-line tunnel, and the settlement at the junction of the sidewall and the bottom plate was smaller than that at other positions of the sidewall. (3) Compared with the roof and middle slabs, the floor of the station was more susceptible to the influence of tunnel excavation. Overall, the research could provide guidance and reference for similar double-line tunnels through existing stations.

Structural monitoring and analyses on the stability and health of a damaged railway tunnel

In this paper, a study of stability and health of a newly-built railway tunnel is presented. The field test was implemented to monitor the secondary lining due to the significant cracking behaviors influenced the stability and health of the tunnel structure. Surface strain gauges were installed for monitoring the status of crack openings, and the monitoring outputs demonstrated that the cracks were still in the developing stage. Additionally, adjacent tunnel and poor condition of surrounding rock were identified as the causes of the lining cracking by systematically characterizing the crack spatial distribution, tunnel site and surrounding rock conditions. Reconstruction of partial lining and reconstruction of the whole secondary lining were designed as the maintenance projects for different cracking regions based on the construction feasibility. For assessing the health conditions of the reinforced lining, embedded strain gauges were set up to continuously measure the strain and the internal force of the reconstructed structures. For the partially reconstructed lining, the outputs show the maximum tensile elongation is 0.018 mm during 227 days, which means the structure has no obvious deformation after maintenance. The one-year monitoring of fullsection was implemented in the other two completely reconstructed cross-sections by embedded strain gauge. The outputs show the reconstructed secondary lining has undertaken the pressure of surrounding rock with the time passing. According to the calculated compressive and tensile safety factors, the completely reconstructed lining has been in reliable and safe condition during the past year after reinforcement. It can conclude that the aforementioned maintenance projects can effectively ensure the stability and health of this tunnel.

Research on Large Deformation Mechanism and Countermeasures of Shallow Buried Soft Rock Tunnel with Abundant Water

In view of the obvious deformation characteristics of shallow buried soft surrounding rock tunnels affected by excavation disturbance, this article takes a Tunnel as the engineering background and combines the geological conditions of the tunnel to carry out on-site monitoring and analysis of surrounding rock deformation after tunnel excavation. The deformation after excavation has the characteristics of fast deformation speed, long duration and large deformation. In addition, the excavation position and step have an important influence on the settlement of the vault and the convergence of the surrounding rock. The settlement of the vault and the convergence of the surrounding rock caused by the excavation of the upper and middle steps account for 61.16% and 63.34% of the total deformation respectively. Through the analysis of large deformation and collapse phenomenon, it is known that the large deformation mechanism in the cave mainly includes soft rock plastic flow and progressive loosening expansion. The soft rock plastic flow caused phenomena such as side wall bulging, top pressure and steel arch distortion, and the progressive loosening and expansion caused the collapse of the tunnel face and surface cracks. Finally, according to the principles of the New Austrian Method, temporary support (transverse bracing + vertical bracing) + grouting anchor pipe + spray-mixing coordinated support was used to construct the pipe shed at the same time, and the support was optimized, the leading small conduit was encrypted, and added Measures such as temporary invert and lock-foot anchor pipe have successfully dealt with the large deformation section of the collapse, and the treatment effect is good, which can provide reference and reference for similar projects.

Failure analysis on 304 stainless steel tube of semi water gas preheater in coal chemical plant

A semi water gas preheater of coal chemical plant suffered a serious leakage failure, and a large numbers of fracture cracks were found on the tube bundles. A series of failure investigation including chemical composition, tensile strength, metallographic inspection and corrosion deposits have been conducted to identify the root cause of failure. It can be found that the cracks were initiated from the outer wall of the tube whose morphology was branched pattern. Macro observation showed that the ends were even and no obvious plastic deformation existed. With the scanning electron microscopy (SEM) attached energy dispersive spectroscopy (EDS) analysis, it can be concluded that the surface of the crack area is covered by a thick layer of corrosion products with high sulfur and oxygen content. Therefore, the reason of the fracture may be that the ambient temperature at the lower tubesheet is rapidly quenched to below the dew point temperature when the two gas mediums are exchanging heat energy. The dew point condensation of the shift gas on the outer wall of the tube forms a wet hydrogen sulfide environment, which leads to the typical sulfide stress corrosion cracking (SSCC). By the way, some recommendations have been proposed to avoid the occurrence of the similar failure again. Considering that this kind of cracks failure in heat exchanger tubes caused by single sulfide medium is seldom reported in previous research, this paper provides essential reference for improving the safety maintenance management of similar equipment.

Tailored Bonded Interfacial Intermolecular Entanglement of Polyethylene/Ultrahigh-Molecular-Weight Polyethylene Blends: Enhancing Miscibility, Reinforcement, and Friction Reduction

For achieving a well-miscible and highly enhanced polyethylene/ultrahigh-molecular-weight polyethylene (PE/UHMWPE) blend, which is an important blend for polyolefin materials with wide applications, tailored bonded interfacial intermolecular entanglement between the two phases was innovatively constructed via a facile reactive melt process through reaction between epoxy and carboxyl groups grafted onto polymer chains. The UHMWPE phase with obvious decreasing size and distribution was tightly embedded in a PE matrix, and the interfacial transition area increased dramatically, leading to forming a homogeneous and miscible blend. Meanwhile, the viscoelasticity and molecular entanglement density were improved remarkably, indicating an enhanced interfacial intermolecular diffusion, and a tight and robust dual network structure with covalent linkage and intermolecular entanglements was constructed in the blend. Obvious deformation with regular striation and many pulling-out UHMWPE fibrils were observed on an impact-fractured surface, and mechanical strength/toughness of the blend was remarkably enhanced. Furthermore, the wear rate and the friction coefficient were reduced significantly, and the worn surface presented smooth and flat features, confirming highly improved mechanical and tribological properties of the blend. This work provided a facile method to fabricate an enhanced PE/UHMWPE blend with application potential.

The first magnetically controlled growing rod (MCGR) in the world \u2013 lessons learned and how the identified complications helped to develop the implant in the past decade: case report

BackgroundThe first magnetically controlled growing rod (MCGR) was implanted in 2009. Since then multiple complications have been identified that have helped drive the development of the MCGR and its surgery. The aim of this report is to illustrate how identified complications in the first MCGR helped with developments in the past decade and to report a unique failure mechanism with stud fracture close to the barrel opening.Case presentationA 5-year old girl with a scoliosis of 58.5 degrees at T1–9 and 72.8 degrees at T9-L4 had a single MCGR inserted and anchored at T3–4 and L3–4. At postoperative 13 months the MCGR was noted to have lost of distraction between lengthening episodes due to unrestricted turning of the internal magnet. To prevent further loss of distraction, an external magnet was placed outside the skin to prevent the magnet from turning back. The overall balance was suboptimal and after the rod was fully distracted, proximal junctional kyphosis occurred. Subsequently, the MCGR was modified with an internal keeper plate to prevent loss of distraction and a dual set of these rods were implanted when the patient was 9 years old. Extension proximally to C7-T1 was done to manage the proximal junctional kyphosis. Her spinal balance improved and distractions continued. She subsequently developed add-on below and the piston rod was not aligned with the actuator. The lumbar spine was also observed to have autofusion. She subsequently had final fusion surgery performed at the age of 15 from C7-L4 leaving a residual tilt below to avoid fusion to the pelvis. The final extracted rod on the left side indicated the “crooked rod sign” on X-ray and rod dissections revealed a new failure mechanism of stud fracture close to the barrel opening. Body fluids and tissue may infiltrate the rod despite no obvious deformation or fractures resulting in hastened wearing of the threads.ConclusionsThere are various complications associated with MCGRs that are related to rod design and surgical inexperience. Repeated rod stalling is not recommended with potential stud fracture and “crooked rod sign”. Rotor stalling and thread wearing which indicates rod failure still require solutions.

Oxidation damage and interfacial failure of dissimilar metal welds containing ferritic heat resistant steels

The ex-service steam tubes containing dissimilar metal weld (DMW) between high Cr ferritic steel T91 and austenitic stainless steel TP347H and the ex-service steam tubes containing DMW between low Cr ferritic steel G102 and austenitic stainless steel TP347H were obtained from coal-fired thermal power plants in China, and their microstructures at the nickel-based weld metal (WM)/ferritic steel interfaces and oxidation characteristics were investigated. After operating for 15,000 h at steam temperature of 541 °C and steam pressure of 17.5 MPa, a G102/TP347H DMW failed along the WM/G102 steel interface, which was a dangerous premature failure mode without obvious plastic deformation. This interfacial failure was attributed to the interaction between oxidation and cracking along the interface, where fracture appeared to be related with the strain concentration at the interface. Oxide notch along the WM/G102 steel interface was the precursor of premature interfacial failure of DMW involving G102. For the DMW involving high Cr ferritic steel T91, ferritic steel side could form a Cr-rich passive film during service and thus would not be further oxidized after operating for 67,000 h at steam temperature of 541 °C and steam pressure of 3.5 MPa. It was concluded that oxidation played a more important role in failure of these DMWs, and retarding the development of oxidation and avoiding the interfacial oxide notch would dramatically improve the service performance of steam tubes containing DMWs.

Study on the Dynamic Response of Landslide Subjected to Earthquake by the Improved DDA Method

Majiagou landslide, a major ancient landslide in Three Gorges Reservoir region, is located in the high earthquake area of southwest China. The 2013 Badong earthquake caused an obvious deformation of landslide monitored by the sliding inclinometer. A strong earthquake may induce the reactivation of ancient landslide. So, it is necessary to research the seismic dynamic response of Majiagou landslide. For this purpose, discontinuous deformation analysis (DDA), improved by introducing the artificial joint and viscous boundary, is applied in this study. The displacements at monitoring points caused by Badong earthquake are calculated and compared with the field data, verifying the numerical method and model. Further, a strong earthquake with the peak acceleration of 1 g is assumed to act on the landside, the initiation and evolution process of landslide is simulated, and the movement features of landslide are discussed. The dynamic failure of landslide and the local amplification of seismic wave can be embodied, indicating that the improved DDA provides an alternative approach for analyzing the seismic dynamic response of jointed rock.

Time-dependent damage mechanism of rock deterioration under freeze–thaw cycles linked to alpine hazards

The unique natural environment of the alpine terrains along the Tianshan highway has led to the frequent occurrence of hazards. The typical hazards in this area, such as sliding collapse, have obvious time-dependent deformation characteristics, and the extreme climatic change causes rock mass deterioration under freeze–thaw cycles, which serves as an important factor that indirectly triggers hazards, while the relationship between the time-dependent characteristics of hazards and the damage characteristics of rock mass deterioration triggering hazards remains uncertain. A series of microscopic examination and macroscopic mechanical experiments were conducted on quartz sandstone from the Tianshan highway to study the mechanism. The experimental results show that the cyclic freeze–thaw action changed the microstructure of quartz sandstone and weakened its mechanical performance. The weakening effect on the long-term mechanical characteristics is much more remarkable than that on the short-term characteristics, and the failure modes become more complicated after long-term loading. Based on the experimental phenomenon, the mechanism was analyzed, and a new constitutive model was established to reflect the long-term mechanical characteristics of rock with freeze–thaw cycles and predict the deformation of an unstable rock mass during collapse. These results can provide a reference for alpine hazard prevention.

Integrated modeling of motion decoupling and flexure deformation of carrier in transfer alignment

In airborne distributed inertial measurement system, there are complex working environment and obvious structural deformation regards to the carrier, which make the research of transfer alignment technology more complicated. Considering the influence of dynamic deflection and coupled motion, the integrated transfer alignment model of decoupled and flexed deformation is established in the paper, which is based on the requirement of high precision navigation information at the sub antenna of airborne earth observation system. On the one hand, combined with Fiber Bragg Grating (FBG) sensor to measure the deflection of the aircraft wing, a general deflection model of the aircraft wing is established, and the accuracy of the model is verified by finite element analysis. On the other hand, the traditional airborne transfer alignment regards the motion of the carrier and the dynamic deformation of the carrier as uncorrelated motion, but there is a strong coupling between them in practice. In the paper, based on the geometric relationship between them, the coupling is solved, and the system error equation is updated. The feasibility and accuracy of the proposed transfer alignment model are verified by semi physical simulation experiments. The results show that the proposed model is faster and more accurate than the traditional transfer alignment model.

Design and application of hydro-mechanical coupling test system for simulating rock masses in high dam reservoir operations

A meter-level direct shear test system and a true triaxial test system were designed by placing the traditional test apparatus into sealed cabins subjected to high water pressure. The influences of three-dimensional seepage water pressure on the shear and compression deformation of rock mass in Xiluodu Hydropower Station were studied. The test results showed that the changes in water pressure caused obvious shear deformation of the interlayer dislocation zone and tensile deformation and reduction in the triaxial compression strength of the fractured rock mass. The effect of water pressure on shear displacement and tensile displacement had a hysteresis effect. This was consistent with deformation data collected through field monitoring. The deformation mechanism in the reservoir valley was the coupling of the stress and seepage fields caused by reservoir impoundment. The effective stress was reduced, the mechanical parameters were weakened, and the change of the initial stress field led to the slightly overall shear slip and tensile deformation of the bank slope.

Improving plain and fretting fatigue resistance of A100 steel using ultrasonic nanocrystal surface modification

In this study, ultrasonic nanocrystal surface modification (UNSM) was used to improve plain and fretting fatigue properties of A100 steel. Results showed that an obvious plastic deformation layer was induced in A100 steel, and the martensite microstructure was remarkably refined. In addition, surface compressive residual stress after UNSM treatment was enhanced to 1700 MPa due to the severe lattice distortion. The increased surface hardness and the presence of beneficial compressive residual stresses after UNSM treatment significantly enhanced the plain/fretting fatigue resistance of A100 steel by retarding fatigue crack nucleation and propagation.

Design Optimization and Manufacturing of Bio-fixed tibial implants using 3D printing technology

To obtain high performance (matching, mechanical properties, and biocompatibility) of personalized biomechanical fixation-type tibial implants, three-dimensional reconstruction was performed using a combination of reverse and positive methods. The implant design was optimized using a topological optimization method, the shape-optimized B-unit structure was filled, and the performance was evaluated for implants prepared by direct forming technology of Selective Laser Melting (3D Printing). The results show obviously reduced weight of the tibial implant, increased stress and displacement, yet with a more uniform distribution. The mechanical properties of the tibial implant were lower than those of the B-units, the weight was lighter, and the stress distribution was more uniform. The surface of the tibial implants prepared by SLM appeared clean and bright, the metal texture was good, the structure between the porous struts was clear, the surface had low powder adhesion, the lap joint was good, and no obvious warping deformation or forming defects were observed. The results of this study provide a foundation for the direct application of high performance personalized biofixation implants.

Random generation of asphalt mixture mesostructure and thermal–mechanical coupling analysis at low temperature

To further study the damage mechanism of asphalt mixture during ice crystal frost heaving force and to provide reference and suggestions for the prevention and research of frost damage of asphalt pavement in severe cold areas. Taking AC-13 asphalt mixture as an example, this study uses Matlab to establish a random delivery model of irregular aggregates and uses ANSYS to conduct a thermal–mechanical coupling analysis of asphalt mixtures with different porosity and temperatures. Results show that the numerical model can be used for the microstructure analysis of asphalt mixtures. Moreover, in a low temperature environment of −5 °C to −25 °C, the moisture in the void will freeze sharply within 60 s and eventually reach the same temperature value as the matrix. In the three-way constrained displacement field, the frost heave force generated by ice crystals causes the largest and most obvious deformation on the surface of the specimen. In addition, due to the interaction of the aggregate surface, the asphalt components are reorganized. Under the extreme condition of −25 °C, the stress value in the bonding surface reaches the maximum 33.07 MPa, which is three times that of asphalt mortar under the same conditions. It shows that under the same strain, the bonding surface reaches the allowable stress earlier than the asphalt mortar and fails. Therefore, this study not only provides a quantitative expression for the frost heave damage of ice crystals but also reveals the influence of ice crystals on the macroscopic properties of asphalt mixture from a meso level.