On the Extent of Dominance of Asymptotic Elastodynamic Crack-Tip Fields. Part 2. Numerical Investigation of Three-Dimensional and Transient Effects

1988 ◽  
Author(s):  
Sridhar Krishnaswamy ◽  
Aares J. Rosakis ◽  
G. Ravichandran
Keyword(s):  
Numerical Investigation ◽  
Three Dimensional ◽  
Crack Tip ◽  
Transient Effects ◽  
Crack Tip Fields

On the Extent of Dominance of Asymptotic Elastodynamic Crack-Tip Fields: Part I—An Experimental Study Using Bifocal Caustics

1991 ◽  
Vol 58 (1) ◽  
pp. 87-94 ◽  
Author(s):  
Sridhar Krishnaswamy ◽  
Ares J. Rosakis
Keyword(s):  
High Speed ◽  
Dynamic Stress ◽  
Dynamic Stress Intensity Factor ◽  
Three Dimensional ◽  
Crack Tip ◽  
Mode I ◽  
Transient Effects ◽  
Crack Tip Fields ◽  
Optical Configuration ◽  
Point Bend

The question of the domain of dominance of mode I asymptotic elastodynamic crack-tip fields is investigated experimentally for the cases of dynamically loaded stationary cracks as well as dynamically propagating cracks. The experiments reported are on three-point bend specimens loaded dynamically using a drop-weight tower. An optical configuration leading to a bifocal high-speed camera is proposed. This is used in conjunction with the method of caustics to obtain apparent dynamic stress intensity factor measurements simultaneously from two different regions around the crack tip. The results of this study indicate that three-dimensional and transient effects necessarily have to be taken into account in the interpretation of dynamic fracture experiments.

Fracture Mechanics of Thin Plates and Shells Under Combined Membrane, Bending, and Twisting Loads

2005 ◽  
Vol 58 (1) ◽  
pp. 37-48 ◽  
Author(s):  
Alan T. Zehnder ◽  
Mark J. Viz
Keyword(s):  
Fracture Mechanics ◽  
Plate Theory ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Crack Tip ◽  
Thin Plates ◽  
Element Analysis ◽  
Crack Tip Fields ◽  
Plates And Shells ◽  
Membrane Bending

The fracture mechanics of plates and shells under membrane, bending, twisting, and shearing loads are reviewed, starting with the crack tip fields for plane stress, Kirchhoff, and Reissner theories. The energy release rate for each of these theories is calculated and is used to determine the relation between the Kirchhoff and Reissner theories for thin plates. For thicker plates, this relationship is explored using three-dimensional finite element analysis. The validity of the application of two-dimensional (plate theory) solutions to actual three-dimensional objects is analyzed and discussed. Crack tip fields in plates undergoing large deflection are analyzed using von Ka´rma´n theory. Solutions for cracked shells are discussed as well. A number of computational methods for determining stress intensity factors in plates and shells are discussed. Applications of these computational approaches to aircraft structures are examined. The relatively few experimental studies of fracture in plates under bending and twisting loads are also reviewed. There are 101 references cited in this article.

On the Extent of Dominance of Asymptotic Elastodynamic Crack-Tip Fields: Part II—Numerical Investigation of Three-Dimensional and Transient Effects

1991 ◽  
Vol 58 (1) ◽  
pp. 95-103 ◽  
Author(s):  
Sridhav Krishnaswamy ◽  
Ares J. Rosakis ◽  
G. Ravichandran
Keyword(s):  
Three Dimensional ◽  
Crack Tip ◽  
Experimental Results ◽  
Mode I ◽  
Transient Effects ◽  
Adequate Description ◽  
Crack Tip Field ◽  
Drop Weight ◽  
The Impact ◽  
Laboratory Specimen

In Part I of this paper, the question of the extent of dominance of the mode I asymptotic elastodynamic crack-tip field (the KdI-field) was studied experimentally. Here, the results of two and three-dimensional elastodynamic finite element simulations of the drop-weight experiments are reported. The load records as obtained from the impact hammer and supports of the drop-weight loading device were used as boundary tractions in the numerical simulations. For the laboratory specimen studied, the results of the simulations indicate that the asymptotic elastodynamic field is not an adequate description of the actual fields prevailing over any sizeable region around the crack tip. This confirms the experimental results of Part I which showed that three-dimensional and transient effects necessarily have to be taken into account for valid interpretation of experimental results.

Elastic-plastic J-Tz dominance in bending and tension loadings

2019 ◽  
Vol 10 (5) ◽  
pp. 644-659
Author(s):  
Feizal Yusof ◽  
Karh Heng Leong
Keyword(s):  
Crack Length ◽  
Power Law ◽  
Crack Front ◽  
Three Dimensional ◽  
Crack Tip ◽  
Content Type ◽  
Elastic Plastic ◽  
Crack Tip Fields ◽  
Out Of Plane ◽  
Crack Tip Stress

Purpose Crack tip stresses are used to relate the ability of structures to perform under the influence of cracks and defects. One of the methods to determine three-dimensional crack tip stresses is through the J-Tz method. The J-Tz method has been used extensively to characterize the stresses of cracked geometries that demonstrate positive T-stress but limited in characterizing negative T-stresses. The purpose of this paper is to apply the J-Tz method to characterize a three-dimensional crack tip stress field in a changing crack length from positive to negative T-stress geometries. Design/methodology/approach Elastic-plastic crack border fields of deep and shallow cracks in tension and bending loads were investigated through a series of three-dimensional finite element (FE) and analytical J-Tz solutions for a range of crack lengths ranging from 0.1⩽a/W⩽0.5 for two thickness extremes of B/(W − a)=1 and 0.05. Findings Both the FE and the J-Tz approaches showed that the combined in-plane and the out-of-plane constraint loss were differently affected by the T-stress and the out-of-plane size effects when the crack length changed from deep to shallow cracks. The conditions of the J-Tz dominance on the three-dimensional crack front tip were shown to be limited to positive T-stress geometries, and the J-Tz-Q2D approach can extend the crack border dominance of the three-dimensional deep and shallow bend models along the crack front tip until perturbed by an elastic-plastic corner field. Practical implications The paper reports the limitation of the J-Tz approach, which is used to calculate the state of three-dimensional crack tip stresses in power law hardening materials. The results from this paper suggest that the characterization of the three-dimensional crack tip stress in power law hardening materials is still an open issue and requires other suitable solutions to solve the problem. Originality/value This paper demonstrates a thorough analysis of a three-dimensional elastic-plastic crack tip fields for geometries that are initially either fully constrained (positive T-stress) or unconstrained (negative T-stress) crack tip fields but, subsequently, the T-stress sign changes due to crack length reduction and specimen thickness increase. The J-Tz stress-based method has been tested and its dominance over the crack tip field is shown to be affected by the combined in-plane and the out-of-plane constraints and the corner field effects.

Fracture Analysis of Cracks in Orthotropic Materials Using ANSYS®

2006 ◽  
Author(s):  
A. O. Ayhan ◽  
A. C. Kaya ◽  
A. Loghin ◽  
J. H. Laflen ◽  
R. D. McClain ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Crack Tip ◽  
Transversely Isotropic ◽  
Fracture Analysis ◽  
General Purpose ◽  
Orthotropic Materials ◽  
Displacement Fields ◽  
Crack Tip Fields ◽  
Regular Manner ◽  
Orthotropic Properties

A methodology for performing two and three-dimensional fracture analyses in orthotropic materials using ANSYS software (“ANSYS”) is presented. The methodology makes use of analytically known crack tip fields in orthotropic materials and is implemented into a general purpose ANSYS macro. The ANSYS analysis, which takes into account the material orthotropy is performed in a regular manner by including the quarter point elements near the crack front. Then, in the post-processing module, the developed macro is run to associate the crack tip displacements with the orthotropic crack tip displacement fields to compute the mixed-mode stress intensity factors. Numerical examples are also presented that demonstrate application and validation of the procedure. These examples include an edge crack in an orthotropic strip and a surface crack in a transversely isotropic plate. The results show how the orthotropic fracture results may differ from those of isotropic fracture analysis. It is also shown that this difference can be dramatically big when the stress analysis is done using the orthotropic properties, whereas the fracture calculations are performed considering the crack tip fields for a crack in an isotropic material.

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