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Limit Load (limit + load)

Distribution by Scientific Domains

Engineering	55%

Selected Abstracts

Imperfection Sensitivity and Limit Loads of Spherical Shells under Radial Pressure

PROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2005
Jens Pontow
The evaluation of the imperfection sensitivity of shell structures and the estimation of their limit loads are widely discussed phenomena. The perturbation energy concept according to Dinkler et al. [1], [2] enables to assess the imperfection sensitivity of shell structures by means of an energy value, the perturbation energy. A buckling criterion may be developed from the comparison between the perturbation energy and experimental data. This paper focuses on the imperfection sensitivity and limit loads of spherical shells of revolution under radial pressure. The investigations include the influence of the meridional angle and different types of boundary conditions. By comparing the numerical results with the German design rule DIN 18800, critical values for the perturbation energy are derived to predict the limit loads. These critical values for the perturbation energy allow to judge whether the German design rule DIN18800 predicts the limit loads of spherical shells under external pressure with varying meridional angles and different boundary conditions with the same reliability in respect of the perturbation energy. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Numerical simulation of rotating bending process for U-tubes in heat exchangers

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 10 2009
H.-S. KIM
ABSTRACT Heat exchangers comprise thousands of tubes having U-shaped portions. Rotating bending method has been widely utilized to make U-bends. Although this method shows an excellent performance, cracks have been frequently detected in the U-bends due to residual stresses induced by bending. In this paper, the bending process is simulated based on elastic,plastic finite element analyses in order to investigate the magnitude and distribution of the residual stresses including the effects of operating pressure. Analyses results show that the residual stress increases as the radius of U-bend decreases and that operating pressure has a detrimental effect in terms of stress corrosion cracking at the intrados of U-bend. It is thought that these results can be utilized for the estimations of fracture mechanics parameters such as limit load, stress intensity factor and J-integral, prevention of the cracking, and establishment of the optimum inspection strategy for the heat exchanger tubes. [source]

Inclined standing contact fatigue

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 7 2003
B. ALFREDSSON
ABSTRACT An experimental method is presented, in which a sphere is repeatedly pressed against a surface with an inclined contact load. The method is a development of the normally loaded standing contact fatigue test. Experiments are performed for three inclination angles below the angle of friction and the results are compared to those of the normally loaded standing contact fatigue test. The influence of tangential load on endurance limit load, number of cycles to crack initiation, contact mark appearance and crack behaviour in the surface as well as in cut views are evaluated. The surface crack behaviour outside the contact mark is analysed based on the cyclic contact stresses in the test specimen. The trajectories of the largest principal stresses are followed in both the surface view and in the cut view on the symmetry plane. These stress trajectories are compared to the experimental crack results. The connection between the inclined standing contact fatigue cracks and surface distress micro-cracks is also discussed. [source]

Influence of anisotropy on a limit load of weld strength overmatched middle cracked tension specimens

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 5 2003
S. ALEXANDROV
ABSTRACT A plane-strain upper bound limit load solution for weld strength overmatched middle cracked tension specimens (M(T) specimens), is found. It is assumed that the weld material is isotropic, but the base material is orthotropic and its axes of orthotropy are straight and parallel to the axes of symmetry of the specimen. A quadratic orthotropic yield criterion is adopted. The solution is based on a simple discontinuous kinematically admissible velocity field and is an extension of the corresponding solution for the specimen made of isotropic materials. These two solutions are compared to demonstrate the influence of anisotropy on the magnitude of the limit load. [source]

On the investigation of shell buckling due to random geometrical imperfections implemented using Karhunen,Loève expansions

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2008
K. J. Craig
Abstract For the accurate prediction of the collapse behaviour of thin cylindrical shells, it is accepted that geometrical and other imperfections in material properties and loading have to be accounted for in the simulation. There are different methods of incorporating imperfections, depending on the availability of accurate imperfection data. The current paper uses a spectral decomposition of geometrical uncertainty (Karhunen,Loève expansions). To specify the covariance of the required random field, two methods are used. First, available experimentally measured imperfection fields are used as input for a principal component analysis based on pattern recognition literature, thereby reducing the cost of the eigenanalysis. Second, the covariance function is specified analytically and the resulting Friedholm integral equation of the second kind is solved using a wavelet-Galerkin approach. Experimentally determined correlation lengths are used as input for the analytical covariance functions. The above procedure enables the generation of imperfection fields for applications where the geometry is slightly modified from the original measured geometry. For example, 100 shells are perturbed with the resulting random fields obtained from both methods, and the results in the form of temporal normal forces during buckling, as simulated using LS-DYNA®, as well as the statistics of a Monte Carlo analysis of the 100 shells in each case are presented. Although numerically determined mean values of the limit load of the current and another numerical study differ from the experimental results due to the omission of imperfections other than geometrical, the coefficients of variation are shown to be in close agreement. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Kinematic modelling of shear band localization using discrete finite elements

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 4 2003
X. Wang
Abstract Modelling shear band is an important problem in analysing failure of earth structures in soil mechanics. Shear banding is the result of localization of deformation in soil masses. Most finite element schemes are unable to model discrete shear band formation and propagation due to the difficulties in modelling strain and displacement discontinuities. In this paper, a framework to generate shear band elements automatically and continuously is developed. The propagating shear band is modelled using discrete shear band elements by splitting the original finite element mesh. The location or orientation of the shear band is not predetermined in the original finite element mesh. Based on the elasto-perfect plasticity with an associated flow rule, empirical bifurcation and location criteria are proposed which make band propagation as realistic as possible. Using the Mohr,Coulomb material model, various results from numerical simulations of biaxial tests and passive earth pressure problems have shown that the proposed framework is able to display actual patterns of shear banding in geomaterials. In the numerical examples, the occurrence of multiple shear bands in biaxial test and in the passive earth pressure problem is confirmed by field and laboratory observations. The effects of mesh density and mesh alignment on the shear band patterns and limit loads are also investigated. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Convergence analysis and validation of sequential limit analysis of plane-strain problems of the von Mises model with non-linear isotropic hardening

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 3 2005
S.-Y. Leu
Abstract The paper presents sequential limit analysis of plane-strain problems of the von Mises model with non-linear isotropic hardening by using a general algorithm. The general algorithm is a combined smoothing and successive approximation (CSSA) method. In the paper, emphasis is placed on its convergence analysis and validation applied to sequential limit analysis involving materials with isotropic hardening. By sequential limit analysis, the paper treats deforming problems as a sequence of limit analysis problems stated in the upper bound formulation. Especially, the CSSA algorithm was proved to be unconditionally convergent by utilizing the Cauchy,Schwarz inequality. Finally, rigorous validation was conducted by numerical and analytical studies of a thick-walled cylinder under pressure. It is found that the computed limit loads are rigorous upper bounds and agree very well with the analytical solutions. Copyright © 2005 John Wiley & Sons, Ltd. [source]