Bulging Process Research Articles

Active interface bulging in Bacillus subtilis swarms promotes self-assembly and biofilm formation

Microbial communities such as biofilms are commonly found at interfaces. However, it is unclear how the physical environment of interfaces may contribute to the development and behavior of surface-associated microbial communities. Combining multimode imaging, single-cell tracking, and numerical simulations, here, we found that activity-induced interface bulging promotes colony biofilm formation in Bacillus subtilis swarms presumably via segregation and enrichment of sessile cells in the bulging area. Specifically, the diffusivity of passive particles is ~50% lower inside the bulging area than elsewhere, which enables a diffusion-trapping mechanism for self-assembly and may account for the enrichment of sessile cells. We also uncovered a quasilinear relation between cell speed and surface-packing density that underlies the process of active interface bulging. Guided by the speed-density relation, we demonstrated reversible formation of liquid bulges by manipulating the speed and local density of cells with light. Over the course of development, the active bulges turned into striped biofilm structures, which eventually give rise to a large-scale ridge pattern. Our findings reveal a unique physical mechanism of biofilm formation at air-solid interface, which is pertinent to engineering living materials and directed self-assembly in active fluids.

Cryogenic Failure Behaviors of Al–Mg–Si Alloy Tubes in Bulging Process

Abstract Cryogenic medium pressure forming has been developed to form the complex-shaped tubular components, in which the needed shape and tube diameter directly determine the complex evolution of biaxial stress in bulging process. The superposition of biaxial stress and cryogenic temperature complicates the deformation behaviors, especially for the final fracture and bulging limit, which determine the forming quality of components. Therefore, the effects of tube geometry on failure orientation and fracture strain of Al–Mg–Si alloy tubes under cryogenic biaxial stress were elucidated, by utilizing cryogenic free bulging with different length–diameter ratios. The failure orientations and corresponding damage modes under different bulging geometric conditions were revealed. The influence mechanism of tube geometry and temperature on the failure mode was analyzed theoretically. A fracture model was established to predict the fracture strain in cryogenic bulging. The failure mode changes from circumferential cracking to axial cracking with the decreasing length–diameter ratio, owing to the stress sequence reversal induced by the significant nonlinearity of the stress path under a small length–diameter ratio. The failure mode can inverse under a larger length–diameter ratio of 1.0 at −196 °C because of the enhanced nonlinearity, which is promoted by the improved plasticity at cryogenic temperature. The established model based on the more accurate assessment of hardening ability during deformation can accurately predict the fracture strain with an average deviation of 10.6% at different temperatures. The study can guide deformation analysis and failure prediction in the cryogenic forming of aluminum alloy tubular parts.

The Pairing Analysis Improvement of Magnetized Structure in Electromagnetic Bulging Process in Case of Tube with Field Shaper

The Pairing Analysis Improvement of Magnetized Structure in Electromagnetic Bulging Process in Case of Tube with Field Shaper

Determining the hot forming limits of titanium alloy sheet under different strain paths by constant equivalent strain rate hot gas bulging tests

This study aims to determine the hot forming limit diagram (FLD) of titanium alloy sheet using constant equivalent strain rate hot gas bulging tests. A novel method was proposed to calculate pressure-time curves under different strain paths, ensuring that the equivalent strain rate during hot deformation remains constant. The key of this method is the development of a VUMAT material subroutine that accurately reflects anisotropic hardening and r-value evolution, and the pressure loading curves under different strain paths were determined by coupling with the VUAMP amplitude subroutine embedded with a PID control algorithm. Based on dies with different cavity structures and unbonded double-layer samples, the FLDs of TA32 titanium alloy sheet under linear and nonlinear strain paths were obtained by carrying out hot gas bulging tests at 800 ℃ with a strain rate of 0.001 s-1. The results demonstrate that the proposed approach is applicable for determining the pressure-time curves under various complex strain paths, and it is experimentally verified that the equivalent strain rate of the sample apex is maintained near the target value during the bulging process. Furthermore, the significant effects of anisotropy and strain path change on the forming limits were quantitatively analyzed. The developed method is not only beneficial for testing the hot biaxial mechanical properties of materials, but also useful for controlling the strain rate during the hot forming of complex thin-walled components to improve the formability of materials.

Quenched Residual Stress Reduction in Pentagon-Curved Aluminum Alloy Forgings Using the Bulging Process.

Quenched residual stress in pentagon-curved forgings (PCGs) often leads to severe deformation during subsequent machining operations. This study aims to mitigate the quenched residual stress in PCGs through the implementation of the bulging method. The edge distance ratio (e/D), a geometric characteristic of PCGs, is defined and considered in the established thermo-mechanical model, which incorporates the effects of quenched residual stress. Increasing e/D resulted in amplified maximum internal stresses and surface stresses. To address this issue, a bulging finite element (FE) model was developed to effectively alleviate the quenched residual stress. The stress reduction in surface stress and internal stress was qualified using average stress reduction (Ra) and peak stress reduction (Rp), respectively. Notably, stress reduction exhibited an inverse relationship with e/D, indicating that decreasing e/D yields greater stress reduction. Furthermore, an overall stress reduction assessment was conducted for different bulging ratios, revealing that the stress reduction increased as the bulging ratio increased. A comprehensive comparison of different bulging ratios highlighted 2% as the most optimal bulging ratio for stress reduction in PCGs. X-ray diffraction measurement and the contour method were employed to determine surface stress and internal stress, respectively. The experimental results were in agreement with the simulation outcomes, validating the high accuracy of the FE model.

A one-dimensional model for axisymmetric deformations of an inflated hyperelastic tube of finite wall thickness

We derive a one-dimensional (1d) model for the analysis of bulging or necking in an inflated hyperelastic tube of finite wall thickness from the three-dimensional (3d) finite elasticity theory by applying the dimension reduction methodology proposed by Audoly and Hutchinson (2016). The 1d model makes it much easier to characterize fully nonlinear axisymmetric deformations of a thick-walled tube using simple numerical schemes such as the finite difference method. The new model recovers the diffuse interface model for analyzing bulging in a membrane tube and the 1d model for investigating necking in a stretched solid cylinder as two limiting cases. It is consistent with, but significantly refines, the exact linear and weakly nonlinear bifurcation analyses. Comparisons with finite element simulations show that for the bulging problem, the 1d model is capable of describing the entire bulging process accurately, from initiation, growth, to propagation. The 1d model provides a stepping stone from which similar 1d models can be derived and used to study other effects such as anisotropy and electric loading, and other phenomena such as rupture.

Theoretical Analysis and Verification on Plastic Deformation Behavior of Rocket Nozzle Using a Novel Tube Upsetting-Bulging Method

The rocket nozzle is one of the core components to ensure the safe flight of rockets. To overcome the problems of multi-step forming, the occurrence of defects, and severe plastic deformation in traditional technology, a novel forming method named tube upsetting-bulging (TUBG) is put forward. With the support of internal pressure, a tube is deformed with an upsetting and bulging process at the same time. The tube is thickened at the small end and thinned at the large end. A nozzle with sharply varying diameters can be obtained. A theoretical model of TUBG that considers wrinkles and rupture is built. The influence factors of internal pressure during TUBG are discussed. Experiments and simulation works are conducted to analyze the plastic deformation process of TUBG. Results show that mechanical properties and geometrical parameters have an obvious influence on critical internal pressure. The proposed theoretical model can be used to predict a forming zone without wrinkles, rupture, and severe strain values. A well-formed nozzle can be obtained using the predicted forming zone, which verifies the correctness of the theoretical analysis. It can be found that TUBG is a novel potential method to fabricate rocket nozzles with high efficiency and quality without defects.

Analysis of expansion performance and parameter sensitivity of solid expandable tubular with thread joint

During the expansion process of the threaded joint of the solid expandable tubular (SET), the thread meshing performance and sealing performance will deteriorate, which seriously hinders the development and application of the SET. In this paper, established the force analysis model of different threads in the bulging process and analysis the finite element model of thread. The meshing performance of φ108 mm × 7 mm SET joints made of 20G steel with three types of thread expansion is analyzed. The most suitable parameter range was obtained by optimizing the five thread parameters such as bearing surface angle, guide surface angle, taper, tooth depth and tooth pitch. The results show that the rectangular and trapezoidal threads are deformed seriously during expansion, and the connection of rectangular and trapezoidal threads is easy to cause the seal failure of the SET system; The effects of various thread parameters on the Mises stress and contact pressure distribution were analyzed. It was found that the Mises stress of the first turn of the special skew trapezoidal thread was the highest, and the Mises stress distribution was high at two ends and low at the middle, with the maximum difference of 160 MPa and the contact pressure distribution was high at two ends and low at the middle, with the maximum difference of 200 MPa. The research results provide technical support for obtaining the SET thread with good meshing performance after expansion.

Determination of the Plastic Stress–Strain Relationship of a Rupture Disc Material with Quasi-Static and Dynamic Pneumatic Bulge Processes

Rupture discs, manufactured using a hydraulic or pneumatic bulge process, are widely used to protect vessels from over-pressuring. The stress–strain relationship of the material in the bulge process plays a major role in understanding the performance of rupture discs. Moreover, both the theoretical analyses and numerical simulations of rupture discs demand a reliable stress–strain relationship of the material in a real bulge process. In this paper, an approach for determining the plastic stress–strain relationship of a rupture disc material in the bulge process is proposed based on plastic membrane theory and force equilibrium equations. Pressures of compressed air and methane/air mixture explosions were used for the bulge pressure to accomplish the quasi-static and dynamic bulge processes of tested discs. Experimental apparatus for the quasi-static bulge test and the dynamic bulge test were built. The stress–strain relations of 316L material during bulge tests were obtained, compared, and discussed. The results indicated that the bulge height at the top of the domed disc increased linearly with an increase in bulge pressure in the quasi-static and dynamic bulge processes, and the effective strain increased exponentially. The rate of pressure rise during the bulge process has a significant effect on the deformation behavior of disc material and hence the stress–strain relationship. At the same bulge pressure, a disc tested with a larger pressure rise rate had smaller bulge height and effective strain. At the same effective stress at the top of the domed disc, discs subjected to a higher pressure rise rate had smaller effective strain, and hence they are more difficult to rupture. Hollomon’s equation is used to represent the relationship between the effective stress and strain during bulge process. For pressure rise rates in the following range of 0 (equivalent to quasi-static condition), 2–10 MPa/s, 10–50 MPa/s, and 50–100 MPa/s, the relation of stress and strain is σe = 1259.4·εe0.4487, σe = 1192.4·εe0.3261, σe = 1381.2·εe0.2910, and σe = 1368.4·εe0.1701, respectively.

Effect of non-uniform pressure on sheet formability in the bulging process of magnetorheological fluid pressure

Effect of non-uniform pressure on sheet formability in the bulging process of magnetorheological fluid pressure

Superplastic characteristics and forming of LZ91 Mg-Li alloy sheet

Magnesium-lithium (Mg-Li) alloys, due to their high specific strength, have great potential in the modern aviation industry. The superplastic characteristics, microstructure evolution, mechanical properties, and forming process of LZ91 Mg-Li alloys at 200°C–300°C were studied in this paper. Tensile tests show that the optimal elongation of tensile specimens is 812.6% at 300°C under a strain rate of 5 × 10−4 s−1. The flow stress of the material increases with strain during the high-temperature tensile testing due to the grain coarsening . Meanwhile, low dislocation densities were observed during tension, which is not sufficient for dynamic recrystallisation to occur. The finite element method is used to investigate the forming schemes of a narrow-mouth box component. Finally, this component was manufactured by the powder pressure bulging process at 300°C experimentally.

Improved formability of HMGF components by preforming in an upset bulging process

Hot Metal Gas Forming (HMGF) is a well-established combination of a profile hydroforming operation and an in situ hardening process. Roof rails and camshafts are typical applications. A significant limitation of the component geometry is the strain-related material thinning. In the polar coordinate system of the tube-shaped parts, the strain can be divided into circumferential and longitudinal portions. To achieve higher expansion ratios in circumferential direction, a longitudinal compression is necessary. In a conventional, non-tempered process setup this is achieved by an axial feeding movement during the forming operation. Under tempered conditions, in particular by friction coefficients well above 0.3, this is no longer possible in a controlled process. Anyhow, a beneficial material pre-distribution is required to enlarge the circumferential strain before material failure occurs. In the proposed preforming operation, the longitudinal compression is achieved by offset bulging. Based on aspect ratios between initial diameter, wall thickness, initial length and compression stroke, a specific, controlled wave pattern is achieved on the specimen. Subsequently, the semi-finished parts undergo the HMGF process in an austenitisation, transfer, forming and quenching procedure. By means of continuous, finite element based simulation and related model calibration in experimental trials, a significant increase in geometric complexity is achieved.

Application of laser barcode technology to sheet metal parts identification

Purpose: In the development of ideas for Industry 4.0, information about the element production cycle has become more and more important. Knowledge of the subsequent forming processes, determination of the machine on which the process has been carried out and of the type and wear of the tool, leads to smart production management, which plays an increasingly important role in the metal forming industry. To meet the current expectations for these challenges, an advanced technology needs to be introduced for monitoring the manufacturing processes by deploying flexible solutions. This technology must include, but not be limited to, identifying and tracking the product using laser marking. Design/methodology/approach: Laser marking allows a permanent mark in the form of a barcode to be applied to the sheet metal surface. Commonly used marking methods and the condition of the sheet metal surface can affect the marking contrast. This paper presents a concept for recording individual stages of sheet metal forming and determination of the impact of the laser marking technology on the contrast of the applied barcode. To ensure accurate control of the deformation stages, the bulging process of the spherical dome has been used as an example. Findings: Analysis of the influence of laser marking method on the barcode recognition accuracy can contribute to the development of smart management of the production process according to the idea of Industry 4.0. Research limitations/implications: A large plastic deformation has been applied to the sheet metal surface and no limitation in a barcode reading process (using vision scanning technology) was indicated. Also, the geometry deformation (different angle view of the CCD camera) of the barcode image has introduced no additional problems with a barcode reading. Originality/value: The optimal parameters of a laser marking technique for barcode marking, which are critical for the material that is subjected to metal forming operations that deform it, have been studied. The results shows that traceability is an attractive solution for tracking technological data in the production chain for a single-shaped product. Keywords: manufacturing control, laser marking, vision analysis, sheet metal forming, barcode quality. Category of the paper: Technical paper.

Relationship between pulsed laser energy and fracture mode in multiple-pulse laser shock bulging process

Relationship between pulsed laser energy and fracture mode in multiple-pulse laser shock bulging process

MoS2/Graphene Photodetector Array with Strain-Modulated Photoresponse up to the Near-Infrared Regime.

MoS2, an emerging material in the field of optoelectronics, has attracted the attention of researchers owing to its high light absorption efficiency, even as an atomically thin layer. However, the covered spectra of the reported MoS2-based photodetectors are restricted to the visible range owing to their electronic bandgap (∼1.9 eV). Strain engineering, which modulates the bandgap of a semiconductor, can extend the application coverage of MoS2 to the infrared spectral range. The shrinkage of the bandgap because of the tensile strain on MoS2 enhances the photoresponsivity in the visible range and extends its sensing capability beyond its fundamental absorption limit. Herein, we report a graphene/MoS2/graphene metal-semiconductor-metal photodetector (PD) array with a strain-modulated photoresponse up to the spectral range of the near-infrared (NIR). The MoS2 PD array on a flexible substrate was stretched in the biaxial direction to a tensile strain level of 1.19% using a pneumatic bulging process. The MoS2-based line-scanning system was implemented by digitizing the output photocurrent of the strained MoS2 linear array with a low-noise complementary metal-oxide-semiconductor (CMOS) readout integrated circuit (IC) and successfully captured vis-NIR images in foggy conditions. Therefore, we extended the application of the MoS2 PD array to the NIR regime and demonstrated its use in real-life imaging systems.

Analytical model for local bulging failure of mini-BRBs with circular restraint tubes

This paper proposes an analytical model for predicting local bulging failure of mini-BRBs with circular restraining tubes. The mini-BRB consists of a quasi-triangular core bar and an external circular restraining tube, and bulging of the tube can occur due to thrust of the inner core bar buckling in high-order mode. To analyze the mechanism of bulging, 4 specimens were designed with restraining tubes of different thicknesses, and strain gauges were attached to external surfaces of tubes to record strain distribution and development during the bulging process. An analytical model was established to obtain the lateral thrust versus bulging depth relationship, and a criterion was proposed to define the bulging resistance of circular tube. Numerical analysis was conducted and the results of which were employed to modify theoretical bulging resistance. Finally, based on experiment results, a performance-based design criterion with a safety factor considering the estimated maximum lateral thrust and the bulging resistance of tube was proposed to prevent premature local bulging failure.

Reduction of Residual Quenching Stresses in 2A14 Aluminum Alloy Tapered Cylinder Forgings via a Novel Cold Bulging Process

This study combined finite element method (FEM) simulations and physical experiments to develop a novel cold bulging process, with the aim of studying and mitigating the quenching residual stresses in 2A14 tapered cylinder forgings. The samples underwent cold bulging at different ratios (0–4.0%) to evaluate the residual stress reduction performance (via the hole-drilling strain-gauge method) and the improvements in their mechanical properties. The FEM simulation and experimental results revealed that our proposed cold bulging process reduced the quenching residual stresses by up to 85–87%. The density and uniformity of the precipitated phases increased along with the extent of cold bulging, as confirmed by transmission electron microscope (TEM) observations. Furthermore, compared to the unprocessed samples, the tensile and yield strengths, and elongation of the samples with 3% cold bulging were significantly enhanced (65 MPa, 55 MPa, and 1.7%, respectively).

Effect of magnetic field on tension–tension side of forming limit diagram in sheet metal forming using a magnetorheological fluid

Sheet flexible-die forming using a magnetorheological (MR) fluid, which can change the mechanical property of flexible-die during the forming process, has become an innovative technology with great application potential in manufacturing thin-walled complex components. Although it has been proved that using an MR fluid as a flexible-die can improve the sheet formability, there is still a lack of in-depth understanding and systematic research. In this paper, the bulging process using elliptical dies with six kinds of ellipticities was adopted to achieve different strain paths and obtain the tension-tension side of forming limit diagram (FLD). Experiments using three kinds of MR fluids and four magnetic field conditions were conducted to systematically study their effects on the tension–tension side of FLD. The effect of the magnetic field on the fracture pattern of the specimen and its mechanism were also discussed. Results showed that magnetic particle content and magnetic field condition have a comprehensive impact on the forming limit diagram. When an MR fluid with a magnetic particle content of 20% is used, the forming limit under different magnetic field conditions has little difference. When the magnetic particle content increases to 30%, the forming limit curve gradually increases with increasing magnetic flux density. But when it reaches 43%, the forming limit curve increased first and then decreased with the increase of magnetic flux density. Besides, the extended FLD of the Al1060-O sheet was established, in which the conventional forming limit diagram is expanded to consider the influence of the magnetic field condition. These results can provide guidance in the parameter selection of magnetic flux density and magnetic particle content in sheet flexible-die forming using an MR fluid.

Investigation of the bulging mechanism of C/SiC coating through in situ optical observation and numerical simulation

Carbon fibre-reinforced silicon carbide composites (C/SiC) are a type of high-temperature structural ceramics that can be widely applied in aerospace, hypersonic aircraft, and military fields. However, the practical application of such materials in some complex high-temperature environments is still limited owing to drawbacks such as the bulging problem. In this study, the bulging of a C/SiC coating in a high-temperature wind tunnel is investigated. The surface data of specimens in the high-temperature arc wind tunnel were obtained using optical visualisation equipment, and the entire process of the formation of coating bulges, and their evolution and fusion is illustrated. Then, a fully coupled thermal fluid-solid simulation model is established, and the influence of defects on the internal heat transfer of materials is analysed. Further, the thermal fluid-solid coupling simulation technology is also used to analyse the bulging process of the coating to understand the mechanism of chemical reactions in defects between the coating and substrate. This work can serve as a guide for the screening and improvement of the material coating process.

Experimental and numerical analysis on bulge forming process of GH4738 thick-walled ring

Ring rolling technology is widely used in the production of GH4738 aerospace rings, but the ring produced by ring rolling often has the phenomenon of uneven stress and unqualified strength. To solve these problems, the thick-walled ring bulge forming technology was proposed. In this paper, a 3D-coupled thermo-mechanical FE model of the GH4738 rectangular ring bulging process was developed, which is verified to be in good agreement with the experimental process. Based on this model, the thermal parameter distribution and evolution of GH4738 rectangular ring during the bulging process were investigated systematically. Then, the evolution of the minimum bulging displacement (BD) required for rings with the change of ring size was obtained by comparing the stress distribution of rings during the bulging process in seven cases. All these provide a theoretical basis for the selection of optimal BD in practical production. Finally, the influence of the bulging process on the microstructure and mechanical properties of GH4738 alloy ring was analyzed by experimental means, and it was verified that the bulging process can play a good role in improving the strength of the ring from the perspective of the average geometrically necessary dislocation (GND) density. The experimental results indicate that with the increase of BD, the grain size of the ring does not change that much, but the average GND density increases gradually, and the yield strength and tensile strength of the ring increase significantly.