The study of ultimate strength in notched cylinders subjected to axial compression

Abstract

Inclusion of various defects, e.g. imperfection or notches, in cylinders during their service life is expected and identifying of the load bearing capacity of the structure in the presence of those imperfection and damages are necessary. In the present paper, the plastic buckling of notched cylinders is studied experimentally and numerically for various groups of the cylinder dimensions. The study focuses on influences of various characteristics of notches, such as orientation, position and notch length on the buckling capacity of the cylindrical shells. In this direction, the amount of absorbed internal strain energy affected by inserting notch is calculated and compared with intact ones.

Introduction

Metal cylinders and tubes are common structural components that are utilized in various fields of engineering under different types of loading such as compression loading. Application in aggressive environments causes corrosion and material defects in the components. Thus, evaluation of a defective cylinder in terms of load tolerability and sustainability in its service life is a necessary task in this domain.

Up to now, some nonextensive researches have been developed to investigate the buckling behavior of notched cylinders under compression loading. El Naschie [1] conducted an analytical formulation to reach the Eigen value of the cracked cylindrical shells and finally he presented approximate results for local buckling and post buckling behavior of these cylinders under compression loading. Estekanchi and Vafai [2] investigated the influence of through notches on the buckling load of the cylindrical shells under axial loading. Considering the linear behavior of cylinders, their answers are divided into two groups each of which has been presented on the basis of one assumption about the notch edges: a group on the basis of constrained edges and the other on the basis of free edges. They showed that a careful mesh refinement at the notch tips will give reliable results in the finite element study of the notched plates and shells. Javidruzi et al. [3] studied vibration, buckling load and dynamic stability of the notched cylindrical shells under tension and compression loading of models with circumferential and longitudinal notches. Vaziri and Estekanchi [4] investigated the elastic buckling load of the notched cylinders under combined action of internal pressure and axial compression. They conducted a parametric linear Eigen value analysis of notched cylindrical shells to gain insight into the effect of notch type, size and orientation. The nonlinear buckling of thin cylindrical shells with longitudinal notches subjected to the axial loading was studied by Starnes and Rose [5], [6] and it was concluded that the non-linear interaction between in-plane stress resultants and the out-of-plane displacements near the notch significantly affects the buckling behavior of the shells.

On the other hand, the effect of an opening in the wall of thin-walled cylinders has been observed previously by other researches such as Jullien and Limam [7] about the influence of various shapes, sizes and locations of opening on the compressive load capacity of cylinders. In another work Han et al. [8] using experimental observations and numerical simulations including the nonlinear behavior of the material investigated the effect of created openings in the aluminum cylinders with various L/D ratios. They introduce the effect of same phenomenon on the load tolerability of the cylinder as a deteriorating factor by experimental observation but in some cases the inverse effect is reported by the researchers that can be a surprising point in the paper and must be made clearer in its justification. The main point in the study and comparison of the effect of openings with notches on the cylinder's performance is the probability of the contact between the notch edges and sensitivity of the load bearing capacity of the cylinder to this factor, whereas, in the investigation of openings the influence of this factor usually is disregarded based on experimental verifications. Paik et al. [9], [10] experimentally and numerically investigated the buckling behavior of the notched plates. They didn't discuss the variation of buckling load in presence of the notch but showed that the ultimate strength of the plates in presence of notch decreases and proposed a formula to predict the ultimate strength of the notched plates in tension and compression loadings. Brighenti [11], [12] investigated the effect of various characteristics of cracks such as length, orientation and location on the buckling load of rectangular plates under compression and tension loads and showed that notch creation on the plates can affect the buckling load of the simply supported plates considerably.

Herein the concern of the presented work is to investigate the nonlinear behavior of moderately thick cylinders through FE modeling based on experimental observations. The results show that assumption of the linear elastic behavior in analysis of the cylinders in large range of dimensions may result in great errors since the cylinder may experience yield stress prior to buckling stage.