An improved boundary element formulation for calculating stress intensity factors: Application to aerospace structures

1987 ◽  
Vol 22 (4) ◽  
pp. 203-207 ◽  
Author(s):  
M H Aliabadi ◽  
D P Rooke ◽  
D J Cartwright
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Boundary Element ◽  
Stress Intensity Factors ◽  
Crack Tip ◽  
Stress Fields ◽  
Element Formulation ◽  
Intensity Factors ◽  
Singular Stress ◽  
Singular Stress Field

In order to compute stress intensity factors accurately, the standard boundary element method is modified to take explicit account of the singularity in the stresses at a crack-tip. The known expansion terms of the crack tip displacement and stress fields are subtracted to remove the numerical difficulties associated with the representation of a singular stress field at the crack-tip. Hence the accuracy of calculation is much improved, without appreciably increasing the amount of computation involved. Furthermore, the stress intensity factor is directly obtained as a part of a solution and no extrapolations are required. The improved formulation is applied to a configuration, which is representative of a part of the wing in a civil transport aeroplane. This configuration consists of a pair of circular cut-outs (supply ports) near to which smaller holes exist; these small holes are particularly susceptible to cracking.

Use of automated photoelasticity to determine stress intensity factors of bimaterial joints

2005 ◽  
Vol 40 (8) ◽  
pp. 785-800 ◽  
Author(s):  
B Zuccarello ◽  
S Ferrante
Keyword(s):  
Stress Intensity ◽  
Stress Field ◽  
Stress Intensity Factors ◽  
External Loading ◽  
Intensity Factors ◽  
Singular Stress ◽  
Full Field ◽  
Basic Law ◽  
Singular Stress Field ◽  
Element Approach

A new systematic experimental procedure has been developed to obtain the stress intensity factors governing the singular stress field that occurs near the intersection between the interface and free edges of bimaterial joints. A preliminary theoretical study of the singular stress field is carried out by the well-known Airy stress function method. The obtained stress laws are properly combined with the basic law of photoelasticity in order to define a procedure that permits the zone dominated by the singularity to be located and the stress intensity factors (SIFs) to be computed on the basis of full field data provided from automated photoelasticity. In particular, a systematic error analysis is used to determine the model zone where the experimental data have to be collected in order to obtain accurate SIF evaluation. As an example, the proposed method is applied to determine the SIFs of various aluminium/ PSM-1 specimens under different external loading conditions using Fourier transform photoelasticity. The experimental results have been compared to those obtained by an independent procedure, based on a boundary element approach, in order to validate the accuracy of the proposed procedure.

Evolution of Tenacity in Mixed Mode Fracture – Volumetric Approach

2020 ◽  
Vol 22 (4) ◽  
pp. 931-938
Author(s):  
O. Zebri ◽  
H. El Minor ◽  
A. Bendarma
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Stress Intensity Factors ◽  
Mixed Mode ◽  
Local Stress ◽  
Critical Stress Intensity Factor ◽  
Mixed Mode Fracture ◽  
Intensity Factors ◽  
Singular Stress

AbstractIn fracture mechanics most interest is focused on stress intensity factors, which describe the singular stress field ahead of a crack tip and govern fracture of a specimen when a critical stress intensity factor is reached. In this paper, stress intensity factors which represents fracture toughness of material, caused by a notch in a volumetric approach has been examined, taking into account the specific conditions of loading by examining various U-notched circular ring specimens, with various geometries and boundary conditions, under a mixed mode I+II. The bend specimens are computed by finite element method (FEM) and the local stress distribution was calculated by the Abaqus/CAE. The results are assessed to determine the evolution of the stress intensity factor of different notches and loading distances from the root of notch. This study shows that the tenacity is not intrinsic to the material for all different geometries notches.

Effects of the Length of Carbon Nanotube (CNT) in CNT Reinforced Composites

2006 ◽  
Vol 324-325 ◽  
pp. 855-858
Author(s):  
Q. Wang ◽  
X. F. Sun ◽  
Kimihiro Ozaki
Keyword(s):  
Fracture Toughness ◽  
Carbon Nanotube ◽  
Stress Intensity ◽  
Stress Field ◽  
Stress Intensity Factors ◽  
Reinforced Composites ◽  
Intensity Factors ◽  
Singular Stress ◽  
Singular Stress Field

In this paper, the strength of the singular stress field near the ends of the CNTs in composites was analyzed to clarify the effects of the CNT length on stress filed in the CNT reinforced composites when studying the fracture toughness. The singular stress field was separated into two types of singularities, symmetric and skew-symmetric, near the ends of CNTs according to the deformation and loading types. The stress intensity factors of the singular stress field were calculated for these two types of singularities. The effects of the CNT length in CNT reinforced composites on these stress intensity factors were investigated.

An Experimental Investigation of the Crack Tip Stress Intensity Factors in Plates Under Cylindrical Bending

1962 ◽  
Vol 84 (4) ◽  
pp. 542-546 ◽  
Author(s):  
Fazil Erdogan ◽  
Ozcan Tuncel ◽  
Paul C. Paris
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Stress Intensity Factors ◽  
Crack Tip ◽  
Tensile Tests ◽  
Critical Value ◽  
Intensity Factors ◽  
Cylindrical Bending ◽  
Crack Tip Stress

This experimental study was undertaken to investigate the validity of the theory based on the crack tip stress intensity factors to explain the fracture of thin cracked plates subjected to static bending moments. Plexiglas sheets were used as specimens and the loading was pure cylindrical bending. The results indicate that there is in fact a critical value of the stress intensity factor at which the crack starts growing. It was found that, while in static tensile tests the crack growth was unstable, in the case of bending, the external load (here, the bending moment) which starts the crack growing is not sufficient for the complete fracture of the plate if it is maintained constant. That is, when the critical value of the stress intensity factor is reached, the crack starts growing on the tensile side of the plate whereupon the crack tip takes a triangular shape and the system again becomes stable. In order to make the crack grow further, a considerable increase in the load is required.

Parametric Study of Stress-Intensity Factors in Bonded Composite Stringer Panels

1987 ◽  
Vol 109 (1) ◽  
pp. 36-39
Author(s):  
C. A. Bigelow
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Integral Equations ◽  
Stress Intensity Factors ◽  
Parametric Study ◽  
Crack Tip ◽  
Algebraic Equations ◽  
Intensity Factors ◽  
Variable Theory

Stress-intensity factors are determined for an infinite cracked orthotropic sheet adhesively bonded to an orthotropic stringer. Since the stringer is modeled as a semi-infinite sheet, the solution is most appropriate for a crack tip located near a stringer edge. Both adherends are treated as homogeneous, orthotropic media which are representative of many fiber-reinforced composite materials. The complex variable theory of elasticity was used to obtain a set of integral equations describing the problem. The integral equations are replaced by an equivalent set of algebraic equations, which are solved to obtain the shear stress distribution in the adhesive layer. From these adhesive stresses, the stress-intensity factors are found. A parametric study is conducted to determine the sensitivity of the system to material properties and specimen configuration. Unless the crack tip is very close to or under the stringer, the stress-intensity factor is approximately that of the unstiffened sheet. However, as the crack propagates beneath the stringer, the stress-intensity factor decreases significantly. Increasing the stringer stiffness or the adhesive stiffness also decreases the stress-intensity factor.

scholarly journals Application of J2 Integral Method in Calculating Complicated Stress Intensity Factors on Three-dimensional Components

2021 ◽  
Vol 293 ◽  
pp. 02012
Author(s):  
Long. Li ◽  
Yousheng. Deng ◽  
Liqing Meng ◽  
Lingtao Li ◽  
Yunfang Zheng
Keyword(s):  
Stress Intensity ◽  
Stress Intensity Factors ◽  
Integral Method ◽  
Three Dimensional ◽  
Crack Tip ◽  
Stress Fields ◽  
Experimental Result ◽  
Intensity Factors ◽  
Corner Crack ◽  
Crack Tips

In this paper, a technique to determine complicated stress intensity factors on three-dimensional components, which based on the conservation law and the elementary mechanics is proposed, it only needs the geometric relationship between multiple singular stress fields from the crack section, and obtaind the relationship between the stress at different crack tips. In the expression of the stress intensity factor K, K is proportional to the stress σ at the crack tip, and we can get the supplementary equation of between different stress fields K according to the ratio of the stress at the crack tip, then use the J-integral method to calculate the stress intensity factors of different stress fields. In order to verify the feasibility of this method, a cracked R-fluted shells model was constructed. Under the action of the bending moment, the corner crack propagation is simulated through the reserved corner crack, and two crack tips with different stress fields are generated during the simulation. The experimental result indicates that the proposed method is effective for cracked R-fluted shells. It is also shown that the method has universal applicability for solving complex stress intensity factors on three-dimensional components.

Determination of Stress Intensity Factors for an Interfacial Crack in a Bi-Material by Digital Photoelasticity

2004 ◽  
Vol 1-2 ◽  
pp. 139-146
Author(s):  
M. Ravichandran ◽  
K. Ramesh
Keyword(s):  
Stress Intensity ◽  
Stress Field ◽  
Stress Intensity Factors ◽  
Interfacial Crack ◽  
Intensity Factors ◽  
Singular Stress ◽  
Singular Stress Field ◽  
Digital Photoelasticity ◽  
Least Squares Approach

The main sources of error in the determination of stress intensity factors (SIFs) for an interface crack in a bi-material by conventional photoelasticity are the measurement of the positional co-ordinates of the data point and the fringe order. In the present work, use of two digital photoelasticity methods for collecting these data is discussed. SIFs are evaluated using constant radius method and a least squares approach based on the singular stress field equation. The need for developing a multi-parameter stress field solution for evaluating SIF is highlighted.

Boundary Element Analysis of Interface Cracks

2005 ◽  
Author(s):  
A. R. Hadjesfandiari ◽  
G. F. Dargush
Keyword(s):  
Stress Intensity ◽  
Boundary Element ◽  
Stress Intensity Factors ◽  
Stress Singularity ◽  
Dissimilar Materials ◽  
Quadrature Formulas ◽  
Element Formulation ◽  
Intensity Factors ◽  
Element Analysis ◽  
Crack Problems

A new boundary element formulation is developed to determine the complex stress intensity factors associated with cracks on the interface between dissimilar materials. This represents an extension of the methodology developed previously by the authors for determination of free-edge generalized stress intensity factors on bimaterial interfaces, which employs displacements and weighted tractions as primary variables. However, in the present work, the characteristic oscillating stress singularity is addressed through the introduction of modified weighting functions and corresponding numerical quadrature formulas. As a result, this boundary-only approach provides extremely accurate mesh-independent solutions for a range of interface crack problems. A number of computational examples are considered to assess the performance of the method in comparison with analytical solutions and previous work on the subject.

Stress Intensity Factors of an Infinite Solid with Two Cavities having a Crack Emanating from the Cavity under Tension

2004 ◽  
Vol 261-263 ◽  
pp. 669-674
Author(s):  
Hironobu Nisitani ◽  
T. Teranishi ◽  
K. Fukuyama
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Stress Intensity Factors ◽  
Crack Tip ◽  
The Body ◽  
Intensity Factors ◽  
Simple Method ◽  
Circumferential Crack ◽  
Crack Tip Stress

It is important to know the stress intensity factor of a circumferential crack emanating from the cavity, because in some cases the fatigue strength of metals is affected by the existence of an internal cavity or an inclusion. Recently a method for calculating the highly accurate values of stress intensity factors was proposed by H. Nisitani, based on the usefulness of the stress values at a crack tip calculated by FEM. This method is called the crack tip stress method. In this study, the crack tip stress method is applied to the problem of an infinite solid having two cavities with a circumferential crack emanating from the cavity subjected to tension. The accuracy of the crack tip stress method was discussed based on some values obtained by the body force method. Moreover, a simple method for calculating the stress intensity factor of this problem was presented.

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