Bulging Deformation Research Articles

Slt, MltD, and MltG of Pseudomonas aeruginosa as Targets of Bulgecin A in Potentiation of β-Lactam Antibiotics.

The interplay between the activities of lytic transglycosylases (LTs) and penicillin-binding proteins (PBPs) is critical for the health of the bacterial cell wall. Bulgecin A (a natural-product inhibitor of LTs) potentiates the activity of β-lactam antibiotics (inhibitors of PBPs), underscoring this intimate mechanistic interdependence. Bulgecin A in the presence of an appropriate β-lactam causes bulge deformation due to the formation of aberrant peptidoglycan at the division site of the bacterium. As Pseudomonas aeruginosa, a nefarious human pathogen, has 11 LT paralogs, the answer as to which LT activity correlates with β-lactam potentiation is important and is currently unknown. Growth of P. aeruginosa PAO1 strains harboring individual transposon-insertion mutants at each of the 11 genes for LTs, in the presence of the β-lactam antibiotic ceftazidime or meropenem, implicated the gene products of slt, mltD, and mltG (of the 11), in bulge formation and potentiation. Hence, the respective enzymes would be the targets of inhibition by bulgecin A, which was indeed documented. We further demonstrated by imaging in real time and by SEM that cell lysis occurs by the structural failure of this bulge. Upon removal of the β-lactam antibiotic prior to lysis, P. aeruginosa experiences delayed recovery from the elongation and bulge phenotype in the presence of bulgecin A. These observations argue for a collaborative role for the target LTs in the repair of the aberrant cell wall, the absence of activities of which in the presence of bulgecin A results in potentiation of the β-lactam antibiotic.

The mechanical analysis of flexible die drawing for spherical parts based on weight function

With the development of sheet metal forming technology and the increase in the application of spherical shell parts, flexible male die drawing technology has become one of the research hotspots because of its merits on strong applicability and ability to significantly increase the forming limit of the sheet. As a new type of flexible male die drawing process, solid granule medium forming (SGMF) has been rapidly developed in recent years. During the granule medium drawing process, there is a significant reduction in the thickness of the sheet metal in the female die in addition to the flange deformation. Thus, the stress state and the required forming force during the sheet metal forming process are very different from those during the conventional drawing. Taking the deformation process of the spherical shell parts as research object, the stress state of the spherical shell and the pressure of the granule medium were studied between the single drawing deformation and the single bulging deformation. On this basis, the stress model, pressure model, and required forming force model of the spherical shell parts in the granule medium drawing process were established with the drawing weight and bulging weight. Theoretical analysis, experiments, and FEM-DEM numerical simulations were employed to study the deformation of the spherical shell parts. The results show that the mechanical model based on the weight function theory can accurately reflect the stress state of the spherical shell parts during SGMF and can fully reveal the sheet metal deformation mechanism during SGMF. In addition, the theoretical analysis model established in this paper provides necessary theoretical support for the selection of equipment for SGMF process in practical application.

Failure analysis of 304H stainless steel convection tube serviced in an ethylene cracking furnace

Abstract The failure of a convection tube used in an ethylene cracking furnace after service for >6 years was analyzed by various characterizing techniques. Cracks were found on the second convection tube located under the straight tube section. Severe bulging deformation was found around the cracking area. Stereoscopic inspection revealed that the main crack has penetrated through the tube wall, while a circumferential crack network was formed on the failed tube surface. Chemical composition analysis confirmed that the failed tube material belong to the 304H stainless steel family. SEM analysis on the fractured surface showed that the cracking mechanism was mainly intergranular brittle fracture. Microstructure observation found that grains within the cracked area experienced severe growing compared with intact area. Besides, more coarsened chromium carbides distributed within grains and along grain boundaries around cracked area, where voids were also occurred at grain boundaries. Based on the above inspection and analysis, the crack of the convection tube were confirmed to be caused by the localized overheating. The root cause for such localized overheating may due to inadequate steam flow and uneven heat distribution within the convection tube during service.

Analysis of the off-corner subsurface cracks of continuous casting blooms under the influence of soft reduction and controllable approaches by a chamfer technology

In the current study, the morphology of the off-corner subsurface cracks located on the cross section of continuous casting bloom under a soft reduction operation was observed. A 3D thermo-mechanical model was adopted to calculate the temperature history, bulging deformation and stress distributions in the reduction region, and then to analyze the formation of the off-corner subsurface cracks under the influence of soft reduction. The results showed that the off-corner subsurface cracks can be formed under the influence of the extensive stress fields which develop in the cracking temperature range, especially located on the loosed side of the bloom corner region. Adjusting the chamfer angle and chamfer length can decrease stress concentration and bulging deformation to minimize the risk of off-corner subsurface cracks during the soft reduction operation.

Analysis of Stress-strain Characteristics of Geogrid Reinforced Crushed Gravel

To study the stress-strain characteristics of reinforced cushion with multi-layer geogrids, a new calculation method was proposed. Based on hyperbolic model, the reinforced cushion was regard as a nonlinear elastomer. The effect of reinforcing geogrids was considered as an equivalent additional pressure and included into the gravel skeleton. Considering the friction effect between geogrids and crushed gravel, the calculation method of stress-strain relationship and shear strength of the reinforced crushed gravel was deduced through definite integral. The proposed method was verified by triaxial tests and the calculated results were in good agreement with the measured data. Furthermore, the key parameters influencing the shear strength, such as the total number of geogrids, the geogrids spacing and the corresponding position, were quantified through sensitivity analysis. The effects of the key parameters on the stress-strain relationship of reinforced cushion were determined. It is shown that the ability of reinforced body to resist bulging deformation is great improved by geogrids. The key parameters are the confining pressure and the total number of geogrids. With the increase of the total number and the confining pressure, the shear strength of the reinforced body increases; but the shear strength is less affected by its location. The research results can provide reference for practical projects.

Analysis on morphology and stress concentration in continuous casting bloom to learn the formation and propagation of internal cracks induced by soft reduction technology

ABSTRACTThe crack formation and propagation were analysed according to actual internal crack morphology and the finite element model simulation of stress concentration. The results showed that most cracks were distributed along the transverse and the longitudinal section of the bloom. Distinct differences between these two major types of cracks were found in dimension and inclination, which were owing to different local stress concentrations. In the longitudinal section of the bloom, shear stress was concentrated in the brittle temperature region, which led to the formation of initial cracks and subsequently cracks propagation. Meanwhile, the maximum tensile stress occurred at the edge between the brittle temperature region and surrounding material, which resulted in crack formation and propagation along the transverse section of the bloom. This phenomenon was due to the obvious bulging deformation of the solidified shell induced by soft reduction.

Atomic-Scale Structure and Stress Release Mechanism in Core-Shell Nanoparticles.

Core-shell nanoparticles find applications in catalysts, sensors, and theranostics. The full internal 3D atomic structure, however, cannot be resolved by current imaging and diffraction techniques. We analyzed the atomic positions and stress-release mechanism in a cubic Au-Pd core-shell nanoparticle in approximately 1000 times higher resolution than current experimental techniques using large-scale molecular dynamics simulation to overcome these limitations. The core-shell nanocube of 73 nm size was modeled similarly to solution synthesis by random epitaxial deposition of a 4 nm thick shell of Pd atoms onto a Au core of 65 nm side length using reliable interatomic potentials. The internal structure reveals specific deformations and stress relaxation mechanisms that are caused by the +4.8% lattice mismatch of gold relative to palladium and differential confinement of extended particle facets, edges, and corners by one, two, or three Au-Pd interfaces, respectively. The three-dimensional lattice strain causes long-range, arc-like bending of atomic rows along the faces and edges of the particle, especially near the Au-Pd interface, a bulging deformation of the Pd shell, and stacking faults in the Pd shell at the corners of the particle. The strain pattern and mechanism of stress release were further characterized by profiles of the atomic layer spacing in the principal crystallographic directions. Accordingly, strain in the Pd shell is several times larger in the extended facets than near the edges and corners of the nanoparticle, which likely affects adsorption, optical, and electrochemical properties. The findings are consistent with available experimental data, including 3D reconstructions of the same cubic nanoparticle by coherent diffractive imaging (CDI) and may be verified by more powerful experimental techniques in the future. The stress release mechanisms are representative for cubic core-shell nanoparticles with fcc structure and can be explored for different shapes by the same methods.

Axial impact compressive behaviors of a novel 3-D integrated multilayer fabric reinforced composite tubular structures

Axial impact compression often leads to delamination in laminated composite tubes. A novel 3D fully integrated multilayer tubular fabric invented by authors can eliminate the delamination. This fabric is in tubular form with several layers of crimp-free in-layer yarns oriented at prescribed orientations, fully interlocked by a set of through-layers yarns, which often are made of the same type of fibers as the in-layer yarns. We investigated axial impact compressive behaviors of carbon/epoxy composite circular tubes with reinforcement of the 3D integrated multilayer tubular fabrics. Four different levels of impact energies, i.e., 20 J, 30 J, 40 J and 50 J, were set in tests. The load-displacement curves have been obtained and the damage morphologies have been photographed. The tested results were compared with those in finite element analyses (FEA) with a microstructure model. The tubes were in bulging deformation, resin crack and yarn breakage. We found that the selection of winding yarn is more important to improve axial compressive strength. For the tube designing, the high strength polymer fibers such as polyester fibers could be used for the winding yarns. While high stiffness and strength fibers, such as carbon fibers, must be used for the axial yarns.

High-temperature creep constitutional model of Q460E steel and effect of creep on bulging deformation of continuous casting slab

Mechanical properties and creep behavior of Q460E continuous casting slab were studied by means of uniaxial tensile tests on a Gleeble-3800 thermomechanical simulator from 1000 to 1100 °C. The high-temperature creep constitutional equation was derived based on experimental data. The parameters in the equation were calculated by using the regression analysis inverse-estimation method. The experimental curves in the primary and secondary creep stages are fitted well. A three-dimensional elastic–plastic and creep finite element model was proposed in order to investigate the bulging deformation of slab and the bulging deformation at the beginning position of bending segment on the slab continuous casting machine was computed accurately. The results indicate that the maximum bulging deformation appears at the geometric center of the slab. The maximum value of the bulging deformation obtained by the elastic–plastic analysis is 1.301 mm. Considering the creep effect, the deformation increases to 1.827 mm which is about 1.4 times the value obtained by the elastic–plastic analysis. The calculation of bulging deformation using the elastic–plastic creep model is more reliable and accurate.

Bulging intervertebral disc: an asymptotic elasticity solution

A bulging intervertebral disc (IVD) occurs when pressure on a spinal disc damages the once healthy disc, causing it to compress or change its normal shape. In medicine, most attention has been paid clinically to diagnosis of and treatment for such problems, which little effect has been made to understand such issues from a mechanics perspective, i.e., the bulging deformation of the soft IVD induced by excessive compressive load. We report herein a simple elasticity solution to understand the bulging disc issue. For simplicity, the soft IVD is modeled as an incompressible circular composite layer consisting of an inner nucleus and outer annulus, sandwiched between two vertebral segments which are much stiffer than the IVD and can be treated as rigid bodies. Without adopting any assumptions regarding prescribed displacements or stresses, we obtained the stress and displacement fields within the composite layer when a certain compressive stain is applied via an asymptotic approach. This asymptotic approach is very simple and accurate enough for prediction of the bugling profile of the IVD. We also performed finite-element modeling (FEM) to validate our solutions; the predicted stress and displacement fields inside the composite are in good agreement with the FEM results.

Microstructure evolution and mechanical properties of flash butt-welded Inconel718 joints

Microstructural evolution and mechanical properties of the Inconel718 alloy subjected to flash butt welding are investigated in this work. A gradient structure without welding defaults in a heat-affected zone (HAZ) is formed on the base material (BM) because of a thermal gradient and strain gradient. A gradient of the grain size results from a decrease in the recrystallization degree from the welding seam (WS) to the coarse-grained zone (CGZ). In addition, dissolution of the γ″ and γ′ phases occurred after temporary flashing, and this is mainly responsible for the lower ductility and strength (hardness) in the HAZ. However, formation of GB carbides and their coarsening account for the decrease in impact toughness in WS and adjacent zones. Meanwhile, a double-necking phenomenon during loading is attributed to the coarse carbides in WS and to large grains in the CGZ. Despite a decrease in ductility, the welding joint exhibits sufficient formability during roundness correction and bulging deformation. This work provides a new understanding of the good properties that the flash butt-welded Inconel718 alloy has, and this is expected to be applicable for other superalloys.

Numerical Simulation of Bulging Deformation for Wide-Thick Slab Under Uneven Cooling Conditions

In the present work, the bulging deformation of a wide-thick slab under uneven cooling conditions was studied using finite element method. The non-uniform solidification was first calculated using a 2D heat transfer model. The thermal material properties were derived based on a microsegregation model, and the water flux distribution was measured and applied to calculate the cooling boundary conditions. Based on the solidification results, a 3D bulging model was established. The 2D heat transfer model was verified by the measured shell thickness and the slab surface temperature, and the 3D bulging model was verified by the calculated maximum bulging deflections using formulas. The bulging deformation behavior of the wide-thick slab under uneven cooling condition was then determined, and the effect of uneven solidification, casting speed, and roll misalignment were investigated.

In situ synchrotron radiation X-ray diffraction studies on molecular aggregation structure of nylon 12 films during bulge testing.

It is desirable to establish a method for evaluating mechanical properties, such as modulus and strength, of micrometer and sub-micrometer thick polymer films. Bulge tests, where bulge deformation is imposed on films by the pressure of an inert gas, are suitable for satisfying this demand. However, very few studies on polymer films exist in the literature. In this study, bulge testing equipment for in situ synchrotron radiation wide-angle X-ray diffraction (WAXD) measurements is designed and used to study the relationship between the molecular aggregation structure and the mechanical properties of a crystalline nylon 12 (Ny12) film during bulge testing. Isothermally crystallized and quenched Ny12 films exhibited stress-strain curves similar to those obtained by conventional uniaxial elongation. In situ WAXD measurements during bulge testing revealed that the lattice extension of the crystallites is clearly dependent on crystallinity. Concretely, crystallites in the isothermally crystallized film show higher elastic properties than those in the quenched one. The results of the molecular aggregation structure, including the crystal structure and the amorphous chain surrounding the crystallites, of the films during bulge deformation firstly obtained in this study must be useful for designing toughened polymer films.

Microstructure and mechanical properties of AZ31 magnesium alloy thin-walled circular tube after localized bulging deformation

Microstructure and mechanical properties of AZ31 magnesium alloy thin-walled circular tube after localized bulging deformation

Finite element simulation of bulge deformation for slab continuous casting

This paper aims to provide an investigation of the bulge deformation rules by using finite element analysis software, ABAQUS/Standard. A three-dimensional thermo-mechanical coupling model, considering the dynamic contact between the slab and rolls, has been established to study the temperature and bulge deformation distributions of the slab over the casting process. The simulated results of temperature profile were compared with the measured temperatures during the continuous casting process, the results of which showed a high agreement. Moreover, the bulge deformation rules of the slab were investigated systematically, especially at the thickness direction of the cross section which is the bulge deformation of the slab on the narrow side. A wave motion was found in the bulge deformation on the wide side of the slab cross section due to the joint effect of the ferrostatic pressure and the roller supporting force. The bulge deformation on the narrow side without the constraint from the roller support was cumulative, which was greater than the recovery count and compensated the bulge deformation on the wide side. In addition, the influences of various casting process parameters on bulge deformation were studied systematically in this paper. The results showed that bulge deformation on the narrow side and the wide side both increased with an increase in casting speeds and roll pitch. The method of fixed-gap and variable-diameter was suggested to be applied in the manufacture process in order to reduce the bulge deformation.

A new analytical model for the low-velocity perforation of thin steel plates by hemispherical-nosed projectiles

Abstract Ballistic experiments were conducted on thin steel plates that are normally impacted by hemispherical-nosed projectiles at velocities higher than their ballistic limits. The deformation and failure modes of the thin steel plates were analyzed. A new method was proposed according to the experimental results and the perforation phenomenon of the thin steel plates to determine the radius of the bulging region. In establishing this new method, a dynamic method combined with the plastic wave propagation concept based on the rigid plastic assumption was adopted. The whole perforation process was divided into four consecutive stages, namely, bulging deformation, dishing deformation, ductile hole enlargement, and projectile exit. On the basis of the energy conservation principle, a new model was developed to predict the residual velocities of hemispherical-nosed projectiles that perforate thin steel plates at low velocities. The results obtained from the theoretical calculations by the present model were compared with the experimental results. Theoretical predictions were in good agreement with the experimental results in terms of both the radius of the bulging region and the residual velocity of the projectile when the strain rate effects of the target material during each stage were considered.

Characterizing the Viscoelastic Properties of Hydrogel Thin Films by Bulge Test

In this work, we carried out bulge test for quantifying the viscoelastic properties of poly (vinyl alcohol) (PVA) thin films with custom-developed apparatus. A viscoelastic bulge deformation (VBD) model based on the elasticity–viscoelasticity correspondence principle and spherical cap equation is established to describe the bulge deformation of polymeric thin films. The VBD model can be used to determine the time-dependent modulus by bulge test for polymeric films. Uniaxial compressive relaxation test and PRONY series fitting method are used to define the constitutive parameters of the VBD equations. We presented two types of VBD models in frequency domain under linear loading and step loading conditions. Through inverse Laplace transformation, the proposed VBD model can effectively predict the bulge deformation of PVA hydrogel thin film. Numerical simulations are also conducted to validate the VBD model under step loading conditions. This work provides a methodology to characterize the viscoelastic properties of polymeric films by bulge test.

Research and Application of Parametric Modeling Technology for Human Body Based on OpenGL

This paper aims to build the human body models based on the belly shape features. We use NURBS surface to build the human body models, and control vertex in the surface to deform. Based on the OpenGL, the integral deformation of the height and width of the whole human body model was carried out. Specifically, girth, radial and bulging deformation was accomplished on the area of belly. Finally, we get the human body models with different belly shape, which is of significance.

Bearing Capacity of the New Composite Foundation with Discrete Material-Concrete Compound Piles

In order to solve the bulging deformation and fracture at the top of widely used gravel piles in treating ground consolidation, a new, optimized composite foundation form was proposed. The composite foundation was constructed using discrete materials and concrete piles. Additionally, various parameters of this new composite foundation were analyzed, including foundation forms, construction technologies, bearing mechanism and failure mode. By applying cavity expansion theory, the Vesic cavity spreading pressure of the discrete material-concrete pile is solved as a polar axis symmetric problem on the basis of Mohr–Coulomb yield criterion. Then the computing formula for the ultimate bearing capacity of the discrete materials-concrete pile is elicited when the internal friction angle of soil in the piles is φ = 0 and φ ≠ 0. Finally, the ultimate bearing capacity value of the composite foundation is acquired through analytic calculation and numerical simulation. Finally, it is found that the calculation result is 14.4% lower than that of the simulated result, which is within the acceptable accuracy range and therefore proves the accuracy of the analytic calculation method for bearing capacity of the new composite foundation.

Study on analysis methods of post-buckling bulging deformation behavior of bellows subjected to internal pressure

Study on analysis methods of post-buckling bulging deformation behavior of bellows subjected to internal pressure