Influence of structural defects on the beneficial effect of autofrettage

A comprehensive numerical study has been carried out to investigate and to explore the impact of the presence of part through surface cracks of various size and orientation in a thick welded ferritic steel cylindrical vessel, on the beneficial effect of autofrettage loading. It is well known that autofrettage loading enhances the load carrying capacity of defect free pressure vessels. The results of this study suggest that in presence of cracks, the localised near crack tip residual stress fields interact with in service stresses and influence the enhancement in load carrying capacity of autofrettaged vessel. Furthermore it is concluded that depending on the crack/loading configuration the impact of crack presence on post-autofrettage performance of the vessel varies from noticeable in some cases to marginal in others to negligible for cases where the crack tip stress field is not significantly disturbed by the service loads

Elastic-plastic analysis of pressure vessels and rotating disks made of functionally graded materials using the isogeometric approach

An NURBS-based isogeometric analysis for elastic-plastic stress in a cylindrical pressure vessel is presented. The vessel is made of a ceramic/metal functionally graded material, i.e. a particle-reinforced composite. It is assumed that the material plastic deformation follows an isotropic strain-hardening rule based on the von Mises yield criterion. The mechanical properties of the graded material are modelled by the modified rule of mixtures. Selected finite element results are also presented to establish the supporting evidence for validation of the isogeometric analysis. Similar analyses are performed and solutions for spherical pressure vessel and rotating disk made of FGMs are also provided

Pre-bent shape design of full free-form curved beams using isogeometric method and semi-analytical sensitivity analysis

In this paper, isogeometric analysis (IGA) is employed to solve the problem of a curved beam with free-form geometry, arbitrary loading, and variable flexural/axial rigidity. The main objective of the study is to develop a unified approach for full free-from curved beam problems that can be integrated with a newly developed semi-analytical sensitivity analysis to solve pre-bent shape design problems. The required set of B-spline control points are calculated using an interpolation technique based on chord-length parameterization. The one-to-one correspondence is considered for parameters of the geometry, loading, and rigidity which is proven to have extreme importance. An IGA curved beam element is suggested based on the Euler-Bernoulli beam theory for the general curvilinear coordinate. The validity and effectiveness of the proposed formulation is confirmed by application to a variety of examples. Moreover, three shape optimization examples are taken into consideration. In the first two examples, the pre-bent shapes of spiral and Tschinhausen curved beams with free-form geometry under distributed loading are obtained. In the third example, the pre-bending problem of wind turbine blades is addressed as an industrial example.</p

Elasto-Plastic Stress Analysis in Rotating Disks and Pressure Vessels Made of Functionally Graded Materials

A new elastio-plastic stress solution in axisymmetric problems (rotating disk, cylindrical and spherical vessel) is presented. The rotating disk (cylindrical and spherical vessel) was made of a ceramic/metal functionally graded material, i.e. a particle-reinforced composite. It was assumed that the material's plastic deformation follows an isotropic strain-hardening rule based on the von-Mises yield criterion. The mechanical properties of the graded material were modeled by the modified rule of mixtures. By assuming small strains, Hencky's stress-strain relation was used to obtain the governing differential equations for the plastic region. A numerical method for solving those differential equations was then proposed that enabled the prediction of stress state within the structure. Selected finite element results were also presented to establish supporting evidence for the validation of the proposed approach

Examination of saturation coverage of polygons using random sequential adsorption algorithm

The goal of random sequential adsorption (RSA), a time-dependent packing method, is to create a regular or asymmetric covering of an empty space that can fit in the allocated space without overlapping. The density of coverage tends to reach a limit in the infinite-time limit. We attempt to estimate saturated packing of oriented 2-D polygons, including squares(4-sides), regular pentagons (5-sides), regular hexagons (6-sides), regular heptagons (7-sides), regular octagons (8-sides), regular nonagons (9-sides), regular decagons (10-sides), and regular dodecagons (12-sides), in this study. We obtained results that are consistent with previous, extrapolation-based studies1. We utilised the "separating axis theorem" to determine if there is overlap between arriving polygons and those that have previously been placed. Saturation as a lower limit is considered to have been reached when RSA addition becomes excessively slow, according to us.Comment: 12 Pages, 4 Figure

Analytical, experimental and numerical study of a graded honeycomb structure under in-plane impact load with low velocity

Given the significance of energy absorption in various industries, light shock absorbers such as honeycomb structure under in-plane and out-of-plane loads have been in the core of attention. The purpose of this research is the analyses of graded honeycomb structure (GHS) behaviour under in-plane impact loading and its optimisation. Primarily, analytical equations for plateau stress and specific energy are represented, taking power hardening model (PHM) and elastic–perfectly plastic model (EPPM) into consideration. For the validation and comparison of acquired analytical equations, the energy absorption of a GHS made of five different aluminium grades is simulated in ABAQUS/CAE. In order to validate the numerical simulation method in ABAQUS, an experimental test has been conducted as the falling a weight with low velocity on a GHS. Numerical results retain an acceptable accordance with experimental ones with a 5.4% occurred error of reaction force. For a structure with a specific kinetic energy, the stress–strain diagram is achieved and compared with the analytical equations obtained. The maximum difference between the numerical and analytical plateau stresses for PHM is 10.58%. However, this value has been measured to be 38.78% for EPPM. In addition, the numerical value of absorbed energy is compared to that of analytical method for two material models. The maximum difference between the numerical and analytical absorbed energies for PHM model is 6.4%, while it retains the value of 48.08% for EPPM. Based on the conducted comparisons, the numerical and analytical results based on PHM are more congruent than EPPM results. Applying sequential quadratic programming method and genetic algorithm, the ratio of structure mass to the absorbed energy is minimised. According to the optimisation results, the structure capacity of absorbing energy increases by 18% compared to the primary model

Random sequential adsorption of aligned regular polygons and rounded squares: Transition in the kinetics of packing growth

We study two-dimensional random sequential adsorption (RSA) of flat polygons and rounded squares aligned in parallel to find a transition in the asymptotic behavior of the kinetics of packing growth. Differences in the kinetics for RSA of disks and parallel squares were confirmed in previous analytical and numerical reports. Here, by analyzing the two classes of shapes in question we can precisely control the shape of packed figures and thus localize the transition. Additionally, we study how the asymptotic properties of the kinetics depend on the packing size. We also provide accurate estimations of saturated packing fractions. The microstructural properties of generated packings are analyzed in terms of the density autocorrelation function.Comment: 7 pages, 9 figure