Bulging Distortion of Austenitic Stainless Steel Sheet on the Partially Penetrated Side of Non-Penetration Lap Laser Welding Joint

Non-penetration laser welding of lap joints in austenitic stainless steel sheets is commonly preferred in fields where the surface quality is of utmost importance.However,the application of non-penetration welded austenitic stainless steel parts is limited owing to the micro bulging distortion that occurs on the back surface of the partial penetration side.In this paper,non-penetration lap laser welding experiments,were conducted on galvanized and SUS304 austenitic stainless steel plates using a fiber laser,to investigate the mechanism of bulging distortion.A comparative experiment of DC01 galvanized steel-Q235 carbon steel lap laser welding was carried out,and the deflection and distortion profile of partially penetrated side of the sheets were measured using a noncontact laser interferometer.In addition,the cold-rolled SUS304 was subjected to heat holding at different temperatures and water quenching after bending to characterize its microstructure under tensile and compressive stress.The results show that,during the heating stage of the thermal cycle of laser lap welding,the partial penetration side of the SUS304 steel sheet generates compressive stress,which extrudes the material in the heat-affected zone to the outside of the back of the SUS304 steel sheet,thereby forming a bulge.The findings of these experiments can be of great value for controlling the distortion of the partial penetrated side of austenitic stainless steel sheet during laser non-penetration lap welding.

Analysis of bulging process of aluminum alloy by overlapping sheet metal and its formability

The influences of strength coefficient K, work hardening exponent n and thickness t of the overlapping sheet on bulging process are analyzed based on hardening material model. Also, bulging experiments are carried out by taking the aluminum alloy LF21 as formed sheet metal, and selecting overlapping sheet with different thicknesses and material properties, by which accuracy of the above analysis result is verified in the aspects of geometric shape, thickness distribution and limit bulging height. The results show that higher strength coefficient K, larger work hardening exponent n and proper thickness of the overlapping sheet are helpful to improve the formability and forming uniformity of formed sheet metal.

Viscous warm pressure bulging process of AZ31B magnesium alloy with different ellipticity dies

Based on the bulging principle of different ellipticity dies, the methyl vinyl silicone rubber with excellent thermal stability and heat transfer performance was chosen as the viscous medium. The finite element analysis and experiments of viscous warm pressure bulging （VWPB） of AZ31B magnesium alloy were conducted to analyze the influence of different ellipticity dies on the formability of AZ31B magnesium alloy. At the same time, based on the grid strain rule, the forming limit diagram （FLD） of VWPB of AZ31B magnesium alloy was obtained through measuring the strain of bulging specimens. The results showed that at the temperature range of viscous medium thermal stability, the viscous medium can fit the geometry variation of sheet and generate non-uniform pressure field, and as the die ellipticity increases, the difference value of non-uniform pressure reduces. Meanwhile, according to the FLD, the relationship between part complexity and ultimate deformation was investigated.

DETERMINATION OF PRESSURIZING CURVE AND COMPUTER CONTROL OF THICKNESS THINNING FOR SUPERPLASTIC BULGING

This paper proposes the assumption that the flow with viscous friction is the stretch of part of the sheet that lies along the walls of a die during the process of superplastic bulging according to superplastic flow equation and geometrical model of bulging of a sheet into a long trapezoid groove or truncated cone, by introducing the friction-factor P which describes the friction effect on the process. Also, the paper proposes the method of controlling thickness nonuniformity and develops the equipment which for uniform thickness of bulging, is automatically controlled with a computerl it also analyzes the important innuence of lubrication on thickness distribution of bulging materials. By the assumption, the relationship between bulging pressure and time is obtained in bulging of a sheet into the groove and cone, and p-t curve of multi-mould-cavity complicated bulging is discussed based on the analysis of single-mould-cavity bulging characteristics.

Ballistic performance of spherical fragments penetrating PCrNi3MoV target plates

PCrNi3MoV steel is a medium-carbon,low-alloy quenched and tempered steel that finds its applications in military gun barrels due to the high wear resistance and ablation resistance.To study the penetration and failure modes of PCrNi3MoV plates impacted by tungsten spheres,tungsten spheres of various diameters(5 mm,8 mm,and 10 mm)were used to impact PCrNi3MoV steel plates with thicknesses of 6 mm,9 mm,and 14 mm.The penetration performance of the spheres was analyzed for different velocities,and the ultimate penetration velocity of the plate was obtained.It was found that the primary failure modes of the PCrNi3MoV plate were compression pitting failure and shear failure.Using the dimensional analysis method,a relationship between the bulge height of the steel plate and the fragment velocity,an equation for the ultimate penetration velocity,and a relationship between the target penetration energy and the fragment velocity were obtained.Then,a projectile-target action index was proposed to describe the process of tungsten spheres with different velocities impacting target plates.The results suggested that under the same thickness of the target plate,a larger-diameter fragment required more kinetic energy to obtain the same ultimate penetration effect as a smaller-diameter fragment.The equations obtained through dimensional analysis predicted values that agreed well with experimental values,indicating that these equations can be applied to engineering applications.

Low Surface Brightness Galaxies Selected by Different Model Fitting

We present a study of low surface brightness galaxies(LSBGs) selected by fitting the images for all the galaxies inα.40 SDSS DR7 sample with two kinds of single-component models and two kinds of two-component models(disk+bulge):single exponential,single sersic,exponential+deVaucular(exp+deV),and exponential+sérsic(exp+ser).Under the criteria of the B band disk central surface brightness μ_(0,disk)(B)≥22.5 mag arcsec^(-2) and the axis ratio b/a> 0.3,we selected four none-edge-on LSBG samples from each of the models which contain 1105,1038,207,and 75 galaxies,respectively.There are 756 galaxies in common between LSBGs selected by exponential and sersic models,corresponding to 68.42% of LSBGs selected by the exponential model and 72.83% of LSBGs selected by the sersic model,the rest of the discrepancy is due to the difference in obtaining μ_(0) between the exponential and sersic models.Based on the fitting,in the range of 0.5≤n≤1.5,the relation of μ_(0) from two models can be written as μ_(0,sérsic)-μ_(0,exp)=-1.34(n-1).The LSBGs selected by disk+bulge models(LSBG_(2)comps) are more massive than LSBGs selected by single-component models(LSBG_1comp),and also show a larger disk component.Though the bulges in the majority of our LSBG_(2)comps are not prominent,more than 60% of our LSBG_(2)comps will not be selected if we adopt a single-component model only.We also identified 31 giant low surface brightness galaxies(gLSBGs) from LSBG_(2)comps.They are located at the same region in the color-magnitude diagram as other gLSBGs.After we compared different criteria of gLSBGs selection,we find that for gas-rich LSBGs,M_(*)> 10^(10)M_⊙ is the best to distinguish between gLSBGs and normal LSBGs with bulge.

Recent progress in hair follicle stem cell markers and their regulatory roles

Hair follicle stem cells(HFSCs)in the bulge are a multipotent adult stem cell population.They can periodically give rise to new HFs and even regenerate the epidermis and sebaceous glands during wound healing.An increasing number of biomarkers have been used to isolate,label,and trace HFSCs in recent years.Considering more detailed data from single-cell transcriptomics technology,we mainly focus on the important HFSC molecular markers and their regulatory roles in this review.

Solution of rectangular bar forging with bulging of sides by strain rate vector inner-product

Abstract：ools. The effective strain rate for for determining the total pressure developed during forging of a rectangular bar forging with bulging was expressed in terms of four-dimensional strain rate vector. The inner-product of the vector was termwise integrated and summed. The integral mean value theorem was applied to determining the ratio of the strain rate components and the values of direction cosine of the vector and then an analytical solution of stress effective factor was obtained. The compression experiments of pure lead bar were performed to test the accuracy of the solution. The optimized results of total pressure by golden section search were compared with those of the indicator readings of the testing machine. It indicates that the optimized total pressures are 2.60%-10.14% higher than those measured. The solution is available and still an upper-bound solution.

Effect of electromagnetic bulging on fatigue behavior of 5052 aluminum alloy

The effect of electromagnetic bulging on the fatigue behavior of the5052aluminum alloy was investigated throughtensile-tensile fatigue testing.The intriguing finding is that the bulged specimens exhibited enhanced fatigue strength as depicted bymaximum stress vs the number of cycles until failure(S-N)curves,by comparison with these original aluminum alloys.Althoughthe fatigue process of the original and budged alloys follows the same mechanism with three distinct steps,namely,crack initiation ata corner of the tested samples,stable crack propagation with typical fatigue striations and finally catastrophic fracture with dimplefractographic features.The typical crack propagation rate vs stress intensity factor range(da/dN-ΔK)curves derived from thespacing of striations reveal a lower crack propagation rate in the bulged specimens.The enhancement of fatigue strength inelectromagnetically bulged aluminum alloy is further rationalized in-depth on the basis of strain hardening and dislocation shieldingeffect.

Numerical Simulation of Magnetic Pressure in Tube-electromagnetic Bulging with Die

Calculation of magnetic pressure is the basis of application of electromagnetic forming (EMF). This paper carries out a numerical simulation of magnetic pressure under the influence of die by means of finite element method. The analysis model of electromagnetic bulging with die is created by using ANSYS, and the distribution of magnetic pressure acting on the tube and the die is obtained. The differences between EMF and other technologies and the effect of die on tube formability are analyzed. The die has important influence upon the calculation accuracy. The simulating conclusions with different discharge energy and current frequency are verified through the technologic tests. The distribution of magnetic pressure acting on the tube agrees well with the measurements of the deformed tube.

SIMUUTION OF ELECTROMAGNETIC TUBE BULGING BASED ON LOOSE COUPLING METHOD

A loose coupling method is used to solve the electromagnetic tube bulging. ANSYS/ EMAG is used to model the time varying electromagnetic field with the discharge current used as excitation, in order to obtain the radial and axial magnetic pressure acting on the tube, the magnetic pressure is then used as boundary conditions to model the high velocity deformation of tube with DYNAFORM, The radial magnetic pressure on the tube decreases from the center to the tube end, axial magnetic pressure is greater near the location equal to the coil height and slight in the other region. The radial displacement of deformed workpicces is distributed uniformly near the tube center and decreases from the center to the end; Deformation from the location equal to coil height to the tube end is little. This distribution is consistent with the distribution of radial pressure; Effect of the axial magnetic pressure on deformation can be ignored, The calculated results show well agreements with the experimental results.

Analytical Solution for Three-dimensional Forging Taking into Account Bulging of Sides by Mean Yield Criterion

Currently, for some complex plastic deformations, the analytical solution can not be obtained by using Mises yield criterion, because Mises yield criterion is nine dimensions, the velocity field is complex, and the solving methods are not innovative. Corresponding solutions of these problems are that yield criterion is linearized to reduce the variable numbers, and the velocity field and the solving methods are reasonably simplified, respectively. In this paper, a new linear yield criterion--mean yield（MY） criterion and inner-product of strain rate vector are used to analytically solve 3D forging taking into account bugling of sides. The velocity field is expressed as a vector in three dimensions, and rotation and divergence are applied to confirm that the velocity field is kinematically admissible. Then, the corresponding strain rate tensor of the velocity field is transformed into principal one by making the determinant of coefficients of the tensor cubic equation be zero. By using MY criterion, the plastic power is term by term integrated and summed according to inner-product of strain rate vector. An upper bound analytical solution is obtained for the forging, and verified by a pure lead press test. The test result turns out that the total pressure calculated by MY criterion is higher by 2.5%-15% than measuring value. In addition, a measuring formula of bulging parameter （a） is proposed, but the values of a measured by the formula are lower than those optimized by the golden section search. The total pressure calculated by MY criterion is compared with the ones by twin shear, Trasca yield, and Mises yield criterion. The comparing result shows that the total pressure calculated by MY criterion is slightly higher than the mean value of that by twin shear and Trasca yield criterion, and lower than that by Mises yield criterion, but more close to that by Mises yield criterion compared with that by other two. The proposed analytical solving methods can be effectively used to other complex plastic deformation, simplifying the solving process and obtaining the reasonable results.

Structure parameters and function of hydraulic elastic bulging roller

The fundamental principle and method of the determining of structure parameters for the hydraulic elastic bulging roller were discussed. The relationship among crown of roller, hydraulic pressure and thickness of roller sleeve was studied. Aluminum was chosen as experimental material to accomplish the dynamic load experiment. The hydraulic elastic bulging roller exerts good effect on shape control and therefore has a broad application prospect in engineering. [

Fracture prediction in non-isothermal viscous pressure bulging of aluminum alloy sheet using ductile fracture criterion

The failure of AA3003 aluminum alloy sheet metal was predicted for non-isothermal viscous pressure bulging (VPB). Utilizing the coupled thermo-mechanical finite element method combined with ductile fracture criterion, the calculations were carried out for non-isotherm VPB at various temperatures and the influences of the initial temperature of viscous medium on failure mode of bulge specimens were investigated. The results show that the failure modes are different for the non-isothermal VPB with different initial temperatures of viscous medium. For the non-isothermal VPB of AA3003 aluminum alloy sheet with initial temperature of 250 ℃, when the initial temperature of viscous medium ranges from 150 to 180 ℃, the formability of sheet metal can be improved to a full extent. The validity of the predictions is examined by comparing with experimental results.

Hydraulic bulging process with axial feedings and strain field of U-shaped metal bellows

Based on the traditional hydraulic bulging process,an improved hydraulic bulging process with axial feeding in the bulging process was proposed.The finite element simulation and experiment of bellows formed by the traditional and improved hydraulic bulging processes were conducted.The grid strain measurement system analysis results of strain and wall thickness distribution of the metal bellows,obtained from simulation and experiment,show that the maximum thinning rates of the wall thickness under the traditional and improved processes were 15%and 10%,respectively.And the wall thickness distribution of the metal bellows formed with improved process was more uniform.The strain values from the root to crown of the waveform increased gradually.However,the strain values were smaller than those of traditional process due to the axial feeding of the improved process in bulging process.

Bulging in incremental sheet forming of cold bonded multi-layered Cu clad sheet: Influence of forming conditions and bending

Bulge is a defect that causes geometrical inaccuracy and premature failure in the innovative incremental sheet forming (ISF) process. This study has two-fold objectives:(1) knowing the bulging behavior of a Cu clad tri-layered steel sheet as a function of forming conditions, and (2) analyzing the bending effect on bulging in an attempt to identify the associated mechanism. A series of ISF tests and bending analysis are performed to realize these objectives. From the cause-effect analysis, it is found that bulge formation in the layered sheet is sensitive to forming conditions in a way that bulging can be minimized utilizing annealed material and performing ISF with larger tool diameter and step size. The bending under tension analysis reveals that the formation of bulge is an outgrowth of bending moment that the forming tool applies on the sheet during ISF. Furthermore, the magnitude of bending moment depending upon the forming conditions varies from 0.046 to 10.24 N·m/m and causes a corresponding change in the mean bulge height from 0.07 to 0.91 mm. The bending moment governs bulging in layered sheet through a linear law. These findings lead to a conclusion that the bulge defect can be overcome by controlling the bending moment and the formula proposed can be helpful in this regards.

Finite Element Analysis and Experiment on Viscous Warm Pressure Bulging of AZ31B Magnesium Alloy

Aiming at overcoming the low plasticity of magnesium alloy at room temperature, we researched viscous warm pressure bulging（VWPB） of AZ31B magnesium alloy based on the excellent thermal stability of viscous medium under the warm forming condition. The potential improvements of plastic deformation ability and forming quality of AZ31B magnesium alloy are expected with the aid of thermal characteristics of viscous medium. During bulging process the velocity field variation and pressure stress field distribution of viscous medium are observed at different temperatures through which the effect of temperature on the mechanical property of viscous medium and AZ31B magnesium alloy are analyzed. The results show that the formability of AZ31B magnesium alloy increases first and then decreases as the temperature increases and it is the best at 200 ℃. On the other hand, the viscous medium which can build non-uniform pressure stress field also exhibits a good flow property at elevated temperature, and it is helpful to improving the formability of AZ31B magnesium alloy.

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.

Analysis and Simulation of Superplastic Sheet-Metal Bulging by Finite Element Method

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NUMERICAL SIMULATION AND EXPERIMENT OF CAVITY GROWTH DURING SUPERPLASTIC BULGING OF MAGNESIUM ALLOY ZK60

Numerical simulation and experimental studies on cavity growth were carreed out dur-ing the bulging process of saperplastic magnesium Alloy. A three--dimensional rigid-viscoplastic finite element program has been developed and applied to predict the cav-ity radiusand volume fraction of cavity growth. The final prediction on the cavityradius and volume fraction distribution was exhibited as colorful shade pictures. Theexperimental studies wereperformed under similar conditions to the numerical oneand provided for quantitativecomparison. According to the metallography observation,the radius and volume fraction of cavity growth was quantitative achieved by usingProfound--Iron & steel software. The numerical results were in reasonable quantita-tive agreement with the experiment.