Analysis of numerical calculation of elastic-plastic shell collapse with growing instability

2020 ◽  
Author(s):  
А.S. Novoseltsev ◽  
A.V. Babkin
Keyword(s):  
External Surface ◽  
Stationary Problem ◽  
Explosive Loading ◽  
Surface Forces ◽  
Maximum Pressure ◽  
Plastic Shell ◽  
Explosive Load ◽  
Elastic Plastic ◽  
Time Of Application ◽  
Pressure Fall

The paper presents research of the collapse of the elastic-plastic shell under external surface forces simulating explosive loading by mathematical simulation using numerical methods. The problem was solved in two-dimensional curved geometries as a non-stationary problem of continuum mechanics. We applied the Wilkins Lagrangian method. The instability of the shell was initiated by harmonic surface perturbations on the outer or inner surfaces. The characteristics of the explosive loading were also changed: the maximum pressure, pressure fall time constant, and the time of application of the explosive load. The size of instability was determined by the deviation of the disturbed surface or the boundary of the jet-forming layer from the cylindrical one. We have established the parameters of the shell and the impulse loading on the shell, which affect most strongly the growth of instability during collapse.

Sliding Contact Analysis of Layered Elastic/Plastic Solids With Rough Surfaces

2001 ◽  
Vol 124 (1) ◽  
pp. 46-61 ◽  
Author(s):  
Wei Peng ◽  
Bharat Bhushan
Keyword(s):  
Surface Deformation ◽  
Rough Surfaces ◽  
Normal Load ◽  
Three Dimensional ◽  
Sliding Contact ◽  
Fast Fourier Transformation ◽  
Maximum Pressure ◽  
Asperity Contact ◽  
Elastic Plastic ◽  
Von Mises

A three-dimensional numerical model is presented to investigate the quasi-static sliding contact behavior of layered elastic/plastic solids with rough surfaces. The model is applicable for both single-asperity contact and multiple-asperity contacts. The surface deformation is obtained based on a variational principle. The surface and subsurface stresses in the layer and the substrate are determined with a Fast Fourier transformation (FFT) based scheme and von Mises and principal tensile stresses are computed accordingly. Contact statistics, such as fractional contact area, maximum pressure/E2 and relative meniscus force are predicted. The results are used to investigate the effect of the contact statistics on friction, stiction, and wear problems such as debris generation, brittle failure, and delamination of layered media. Optimum layer parameters are identified. It allows the specification of layer properties, according to the contact statistics, to reduce friction, stiction, and wear of materials. A normalization procedure is presented to apply the results on various combinations of surface roughness, material properties, and normal load.

Expansion/contraction of a spherical elastic/plastic shell revisited

2014 ◽  
Vol 27 (3) ◽  
pp. 483-494
Author(s):  
Sergei Alexandrov ◽  
Alexander Pirumov ◽  
Yeau-Ren Jeng
Keyword(s):  
Plastic Shell ◽  
Elastic Plastic

scholarly journals Mathematical model of the elastoplastic shell collapse, taking into account the possible development of the process instability

2019 ◽  
Author(s):  
А.S. Novoseltsev ◽  
A.V. Babkin
Keyword(s):  
Mathematical Model ◽  
External Surface ◽  
Numerical Study ◽  
Nonstationary Problem ◽  
Tangential Direction ◽  
Initial Time ◽  
Explosive Load ◽  
Adjustment Procedure ◽  
Elastoplastic Shell ◽  
The Mathematical Model

The mathematical model for the subsequent numerical study of the shaped charge liner collapse affected by external surface forces simulating an explosive load is presented. The basic liner was considered as an originally cylindrical compressible elastoplastic shell within the framework of a two-dimensional flat nonstationary problem of continuum mechanics. To ensure the rationality of the modeling and numerical calculation at the initial time the design fragment was discriminated in the liner by central beams. Deformation of the fragment being a part of the shell was taken into account by the boundary conditions of cyclic repeatability in the tangential direction. For numerical solving the well-known Wilkins Lagrangian method was used, which was refined in terms of the relations describing the mechanical behavior of an elastoplastic medium. Additionally, a self-developed grid adjustment procedure was used, excluding the appearance of highly elongated cells in the calculation. The instability of the shell deformation was initiated by harmonic surface perturbations, initially assigned on the outer or inner surfaces. The degree of instability was assessed by the deviation of the disturbed surface (or the boundary of the so-called stream-forming layer) from the cylindrical one. The used finite-difference algorithms are implemented in the form of appropriate calculation programs. A number of computational verification measures was performed proving the viability of the developed mathematical model and the possibility of its further use

Underground Space Construction by Explosive Loading in a Borehole

2007 ◽  
Vol 566 ◽  
pp. 185-190
Author(s):  
Kazuyoshi Tateyama ◽  
Shigeru Itoh ◽  
Hironori Maehara
Keyword(s):  
Laboratory Experiments ◽  
Explosive Loading ◽  
Borehole Wall ◽  
Underground Space ◽  
Explosive Load ◽  
Space Construction

In cases where a borehole has been dug in the ground and subjected to an explosive load, the soil around the borehole wall will be abruptly compressed and a cavity will then be created in the portion of the ground that is surrounded by the compressed soil wall. When this procedure is applied to the construction of tunnels or foundations, underground spaces can be created with minimum mucking and a thinner lining. The authors carried out some laboratory experiments in which small boreholes were expanded by blasting. The results of the experiments increase our knowledge and elevate the possibility of applying this procedure to underground space construction.

Cyclic Operation of Pressure Piping With γ Heating

1960 ◽  
Vol 82 (2) ◽  
pp. 447-451 ◽  
Author(s):  
K. R. Merckx
Keyword(s):  
Heat Generation ◽  
Reactor Core ◽  
Operating Conditions ◽  
Pressure Tube ◽  
Maximum Pressure ◽  
Residual Tensile Stress ◽  
Tube Surface ◽  
Elastic Plastic ◽  
Cyclic Operation ◽  
Test Reactor

An elastic-plastic analysis is developed for an internally cooled pressure tube with uniform heat generation. This analysis extends the method of calculating the location of the elastic-plastic boundary reported by Barrie [4] to account for the change in the plastic zone due to residual stresses which occur during cyclic operation. Numerical calculations are made for operating conditions expected to be encountered in a pressure tube in a loop through the Engineering Test Reactor Core. The numerical results show that the radius of the initial plastic boundary decreases during subsequent loading cycles. Also, for equal maximum pressure and volumetric heat generation, the total plastic strain per operational cycle on the inner tube surface and the residual tensile stress on the outer tube surface increase when the tube wall is thickened.

Impact of Intensity of Residual Stress Field Upon Re-Yielding and Re-Autofrettage of an Autofrettaged Thick Cylinder

2010 ◽  
Author(s):  
Anthony P. Parker ◽  
John H. Underwood ◽  
Edward Troiano
Keyword(s):  
Residual Stress ◽  
Stress Field ◽  
Hoop Stress ◽  
Bauschinger Effect ◽  
Numerical Study ◽  
Fatigue Cracks ◽  
Maximum Pressure ◽  
Residual Stress Field ◽  
Intensity Effect ◽  
Elastic Plastic

Re-autofrettage has been identified as a significant, cost-effective method to achieve higher re-yield pressure (RYP) and/or weight reduction in large caliber gun tubes. For a given overstrain, residual stress profiles for hydraulic and for swage autofrettage may differ significantly in their intensity. The simplest representation of this ‘intensity’ effect is the magnitude of the bending moment ‘locked in’ via the residual hoop stress. Hill’s analytical, plane strain, Von Mises, analysis predicts a larger ‘locked-in’ moment than does the equivalent open-end condition. By assuming a range of stress-field intensities (f) scaleing from 1.0 to 1.4 times that produced by open-end hydraulic autofrettage, it was possible to assess re-yield behavior following initial autofrettage via a generic numerical study. In cases where Bauschinger effect is absent, re-yield initiates at the original elastic plastic interface. This includes the ideal Hill distribution. When Bauschinger effect is present, re-yield for f ≤ 1.1 initiates at the bore and after further pressurization at the original elastic plastic interface within two zones. For f ≥ 1.2 the reverse is the case, with initial yield at the original elastic plastic interface and subsequently at the bore. RYP increases with increasing f up to f = 1.175 and then decreases significantly. This loss of RYP may be mitigated by hydraulic re-autofrettage. At f = 1.0 re-autofrettage increases RYP by 4%. At f = 1.4 RYP is increased by 19%. There are modest increases in safe maximum pressure as a result of re-autofrettage. RYP closely approaching re-autofrettage pressure is achievable for f ≥ 1.3. Within this range, re-autofrettage offers a significant benefit. Re-autofrettage also produces beneficial effects via increased bore hoop compressive stress, this increase varying from 20% for f = 1 to zero for f = 1.4. Such increased compression will benefit fatigue lifetime for fatigue cracks initiating at the bore. Conversely, tensile OD hoop stress increases, with increasing f, by a maximum of 6%.

Use of Magnetic Anisotropy Method for Assessing Residual Stresses in Metal Structures

2020 ◽  
Vol 854 ◽  
pp. 10-15
Author(s):  
Elena A. Krivokrysenko ◽  
G.G. Popov ◽  
Victor I. Bolobov ◽  
V.E. Nikulin
Keyword(s):  
Residual Stresses ◽  
External Surface ◽  
Calculated Data ◽  
Surface Layers ◽  
Metal Structures ◽  
Elastic Plastic ◽  
Compressive Stresses ◽  
Calibration Dependence ◽  
Proportional Relationship ◽  
Series Of Experiments

A series of experiments on measuring of difference between the main mechanical stresses (DPMS) was carried out using a mechanical stress scanner based on the magnetoanisotropic method. The magnitude of the DPMS is fixed when a magnetic field is induced on a carbon steel plate under uniaxial tension. A direct proportional relationship is shown between the magnitude of the DPMS signal recorded by the scanner and the magnitude of tensile stresses in the plate in the region of elastic deformation of steel. Measurement of the DPMS signal in the central part of similar plates previously subjected to elastic-plastic bending showed that positive values of the signal are fixed in the surface layers of the metal on the inside of the plate, which corresponds to tensile residual stresses, while the negative ones concentrate at the external surface, which corresponds to compressive stresses. A transverse incision on a curved plate from the inside leads to a decrease in the value of the signal of the DPMS, which indicates a decrease in the level of residual stresses in the metal. The values of the DPMS signal in the central part of the curved plate, recalculated using the established calibration dependence on the value of the residual stresses, were compared with the values of the stresses established by calculation, based on the Henki’s theorem on the unloading of an elastic-plastic body. A satisfactory convergence was obtained between the experimental and calculated data.

Accurate Determination of Plastic Collapse Loads From Finite Element Analyses

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
C. Doerich ◽  
J. M. Rotter
Keyword(s):  
Finite Element ◽  
Accurate Determination ◽  
Shell Structures ◽  
Collapse Mechanism ◽  
Plastic Shell ◽  
Plastic Collapse ◽  
Collapse Load ◽  
Plastic Limit ◽  
Elastic Plastic ◽  
Collapse Strength

When computational modeling is used to evaluate the true strength of an imperfect elastic-plastic shell structure, the current European standard on shell structures requires that two reference strengths are always determined: the linear bifurcation load and the plastic limit (plastic collapse) load. These two loads are used in more than one way to characterize the strength of all imperfect elastic-plastic systems. Where parametric studies of a problem are being undertaken, it is particularly important that these two loads are accurately defined, since all other strengths will be related to them. For complex problems in shell structures, it is not possible to develop analytical solutions for the plastic collapse strength, and finite element analysis must be used. Unfortunately, because a collapse mechanism often requires the development of very extensive plasticity involving large local strains, and the collapse load is simply at the end of a slowly rising load-deflection curve, it is sometimes difficult for the analyst to accurately determine this plastic collapse strength. This paper describes two methods, based on modifications of the Southwell plot, of obtaining very accurate evaluations of the plastic limit load, irrespective of whether a fairly complete plastic strain field has developed or not. These two methods allow plastic collapse limit loads to be reported with great precision.

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