R-Curve Generation and CTOD Evaluation Considering Maximum Crack Growth Size and Parabolic Crack Front

1994 ◽  
Vol 22 (1) ◽  
pp. 20 ◽  
Author(s):  
DR Petersen ◽  
S Bhattacharya ◽  
AN Kumar
Keyword(s):  
Crack Growth ◽  
Crack Front ◽  
Parabolic Crack ◽  
Maximum Crack

Comparison of DBEM and FEM Crack Path Predictions with Experimental Findings for a SEN-Specimen under Anti-Plane Shear Loading

2007 ◽  
Vol 348-349 ◽  
pp. 129-132 ◽  
Author(s):  
Roberto G. Citarella ◽  
Friedrich G. Buchholz
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Front ◽  
Crack Path ◽  
Shear Loading ◽  
Crack Growth Behaviour ◽  
3D Crack Growth ◽  
Corner Points ◽  
Experimental Findings

In this paper detailed results of computational 3D fatigue crack growth simulations will be presented. The simulations for the crack path assessment are based on the DBEM code BEASY, and the FEM code ADAPCRACK 3D. The specimen under investigation is a SEN-specimen subject to pure anti-plane or out-of-plane four-point shear loading. The computational 3D fracture analyses deliver variable mixed mode II and III conditions along the crack front. Special interest is taken in this mode coupling effect to be found in stress intensity factor (SIF) results along the crack front. Further interest is taken in a 3D effect which is effective in particular at and adjacent to the two crack front corner points, that is where the crack front intersects the two free side surfaces of the specimen. Exactly at these crack front corner points fatigue crack growth initiates in the experimental laboratory test specimens, and develops into two separate anti-symmetric cracks with complex shapes, somehow similar to bird wings. The computational DBEM results are found to be in good agreement with these experimental findings and with FEM results previously obtained. Consequently, also for this new case, with complex 3D crack growth behaviour of two cracks, the functionality of the proposed DBEM and FEM approaches can be stated.

Three-Dimensional Study of Fatigue Crack Growth in a Rotating Disc

2013 ◽  
Vol 3 (2) ◽  
pp. 45-62
Author(s):  
Eskandari Hadi ◽  
Nami Mohammad Rahim
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Front ◽  
Numerical Technique ◽  
Three Dimensional ◽  
Crack Orientation ◽  
Rotating Disc ◽  
Mesh Density ◽  
Three Dimensional Finite Element

The problem of fatigue-crack-growth in a rotating disc at different crack orientation angles is studied by using an automated numerical technique, which calculates the stress intensity factors on the crack front through the three-dimensional finite element method. Paris law is used to develop the fatigue shape of initially semi-elliptical surface crack. Because of needs for the higher mesh density and accuracy near the crack, the sub-modeling technique is used in the analysis. The distribution of SIF’s along the crack front at each step of growth is studied and the effect of crack orientation on the rate of crack-growth is investigated. The calculated SIF’s are reasonable and could be used to predict the probable crack growth rates in fracture mechanics analysis and can help engineers to consider in their designing and to prevent any unwanted failure of such components.

The Effect of Crack Growth Retardation when Comparing Constant Amplitude to Variable Amplitude Loading in an Aluminium Alloy

2014 ◽  
Vol 891-892 ◽  
pp. 948-954 ◽  
Author(s):  
Madeleine Burchill ◽  
Simon A. Barter ◽  
Michael Jones
Keyword(s):  
Growth Rate ◽  
Fatigue Life ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Growth Retardation ◽  
Crack Front ◽  
Constant Amplitude ◽  
Variable Amplitude ◽  
Growth Increments ◽  
Crack Growth Retardation

It has often been observed that the growth of short fatigue cracks under variable amplitude (VA) cyclic loading is not well predicted when utilising standard constant amplitude (CA) crack growth rate/stress intensity data (da/dN v DK). This paper outlines a coupon fatigue test program and analyses, investigating a possible cause of crack growth retardation from CA-only testing. Various test loading spectra were developed with sub-blocks of VA and CA cycles, then using quantitative fractography (QF) the sub-block crack growth increments were measured. Comparison of these results found that, after establishing a consistent uniform crack front using a VA load sequence, the average crack growth rate then progressively slowed down with the number of subsequent CA load cycles applied. Further fractographic investigation of the fracture surface at the end of each CA and VA sub-block crack growth, identified significant crack front morphology differences. Thus it is postulated that a variation or deviation from an efficient crack path is a driver of local retardation in short crack growth during CA loading. This may be a source of error in analytical predictions of crack growth under VA spectra loading that may need to be considered in addition to other potential effects such asless closure whilst cracks are small. For aircraft designers, using solely CA data for fatigue life predictions this may result in non-conservative estimates of total crack fatigue life, producing unexpected failures or an increased maintenance burden.

Closure Effect on Interaction of Two Surface Cracks Under Cyclic Bending

2010 ◽  
Author(s):  
Masanori Kikuchi ◽  
Yoshitaka Wada ◽  
Maigefeireti Maitireyimu ◽  
Hirotaka Sano
Keyword(s):  
Crack Growth ◽  
Crack Closure ◽  
Crack Front ◽  
Surface Crack ◽  
Specimen Surface ◽  
Surface Cracks ◽  
Paris Law ◽  
C Value ◽  
Closure Effect ◽  
Surface Crack Growth

Crack closure effect on interaction of two surface crack growth processes by fatigue is studied. At first, change of C value in Paris’ law along crack front of single surface crack is measured experimentally. It is shown that C value decreases near specimen surface. Crack closure effect is studied numerically for a surface crack by elastic-plastic cyclic analyses. It is found that closure effect appears more strongly near specimen surface than the maximum-depth point. By determining effective stress intensity factor including closure effect, it is shown that change of C value is equal to the change of closure effect along crack front. Using new C value considering closure effect, fatigue crack growth is predicted using S-FEM. It is shown that fatigue life and crack configuration agree well with experimental ones. Finally, interaction of two surface cracks is evaluated numerically, and it is shown that crack closure plays important role on the interaction of two cracks.

Automatic Fatigue Crack Growth

2009 ◽  
Author(s):  
S. C. Mellings ◽  
J. M. W. Baynham
Keyword(s):  
Fatigue Crack ◽  
Cyclic Loading ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Front ◽  
Initial Crack ◽  
Design Stage ◽  
Load Spectrum ◽  
Forensic Investigations ◽  
Crack Faces

One of the critical requirements of fatigue crack growth simulation is calculation of the remaining life of a structure under cyclic loading. This paper presents a method which predicts the remaining fatigue life of a part, and gives information on the eventual mode of failure. The path of a growing crack needs to be understood so that informed assessment can be made of the structural consequences of eventual fast growth, and the likelihood of leakage and determination of leakage rates. For these reasons the use of standard handbook solutions for crack growth is generally not adequate, and it is essential to use the real geometry and loading. The reasons for performing such simulation work include preventive investigations performed at the design stage, forensic investigations performed after failure, and sometimes forensic investigations performed during failure-when the results provide input to the planning of remedial work. This paper focuses on the 3D simulation of cracks growing in metal structures exposed to cyclic loading, and explains the techniques which are used. The loading might arise from transients of pressure or other mechanical forces, or might be caused by thermal-stress variations. The simulation starts from an initial crack which can be of any size and orientation. The relevant geometry of the cracked component is modelled, and the loading is identified using one or more load cases together with a load spectrum which shows how the loading cycles. The effects of the crack are determined by calculating stress intensity factors at all positions along the crack front (it would be called the crack tip if the modelling was performed in 2D). The rate and direction of crack growth at each part of the crack front are calculated using one of the available crack growth laws, together with appropriate material properties. The effects of such growth are accumulated over a number of load cycles, and a new crack shape is determined. The process is repeated as required. The use of multi-axial and mixed mode techniques allows the crack to turn as a result of the applied loading, and the resulting crack path is therefore a consequence of both the detail of the geometry and the loading to which the structure is subjected. Gas or other fluid pressures acting on the crack faces can have significant impact, as can the contact between opposing crack faces when a load case causes part of the crack to close.

Role of Crack Wake Toughening on Elevated Temperature Crack Growth in a Fiber Reinforced Ceramic Composite

1993 ◽  
Vol 115 (3) ◽  
pp. 273-280 ◽  
Author(s):  
Shantikumar V. Nair ◽  
Tsung-Ju Gwo
Keyword(s):  
Elevated Temperature ◽  
Crack Growth ◽  
Crack Front ◽  
Volume Fraction ◽  
Process Zone ◽  
Stable Crack Growth ◽  
Creep Process ◽  
Failure Behavior ◽  
Matrix Cracks ◽  
Presence And Absence

Theoretical models were developed to predict the nature of the elevated temperature failure behavior in composites containing bridged cracks both for the case where crack front creep is absent (brittle regime) and for the case where a frontal creep process zone is present (ductile regime). The nature of the thermally activated time-dependent bridging of matrix cracks was first briefly reviewed from an earlier study and then applied to the case where crack front creep was present. Stable crack growth was predicted both in the presence and absence of crack front creep after an initial delay period, or initiation, which depends on crack size and wake parameters, such as, fiber diameter, volume fraction and interface properties. The dependence of the initiation time and crack growth rates on flaw size and wake parameters as well as on composite microstructure was derived both for the presence and absence of crack front creep. The implications of the results for elevated temperature composite component design are discussed.

Fatigue Growth Prediction of Internal Surface Cracks in Pressure Vessels

1998 ◽  
Vol 120 (1) ◽  
pp. 17-23 ◽  
Author(s):  
X. B. Lin ◽  
R. A. Smith
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Front ◽  
Internal Surface ◽  
Pressure Vessels ◽  
Surface Cracks ◽  
Elliptical Shape ◽  
Set Of Points

Fatigue crack growth was numerically simulated for various internal surface cracks with initially either semi-elliptical or irregular crack fronts. The simulation was directly based on a series of three-dimensional finite element analyses from which the stress intensity factors along the front of growing cracks were estimated. The fatigue crack growth law obtained from small laboratory specimens was incrementally integrated at a set of points along the crack front, and a new crack front was then re-established according to the local advances at this set of points by using a cubic spline curve. This method enabled the crack shape to be predicted without having to make the usual assumption of semi-elliptical shape. Fatigue analysis results are presented and discussed for fatigue shape developments and deviations from the semi-elliptical shape, aspect ratio changes, stress intensity factor variations during crack growth, and fatigue life predictions. Some of the results were also compared with those obtained by two simplified methods based on one and two degree-of-freedom models, respectively.

Comparison of Computational Crack Path Predictions with Experimental Findings for a SEN-Specimen under Anti-Plane Shear Loading

2006 ◽  
Vol 324-325 ◽  
pp. 1109-1112 ◽  
Author(s):  
Friedrich G. Buchholz ◽  
Victor Teichrieb
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Front ◽  
Fracture Criterion ◽  
Shear Loading ◽  
Plane Shear ◽  
Crack Growth Behaviour ◽  
3D Crack Growth ◽  
Experimental Findings

In this paper the rather complex 3D fatigue crack growth behaviour in a SEN-specimen under anti-plane shear loading is investigated by the aid of the programme ADAPCRACK3D and by application of a recently developed 3D fracture criterion. It will be shown that the computationally simulated results of fatigue crack growth in the FE-model of the specimen are in good agreement with experimental findings for the development of two anti-symmetric cracks, which originate from the two crack front corner points, that is where the crack front intersects the two free side surfaces of the laboratory SEN test-specimens. Consequently, also for this case with a rather complex 3D crack growth of two anti-symmetric cracks, the functionality of the ADAPCRACK3D-programme and the validity of the proposed 3D fracture criterion can be stated.

The influence of mean stress on fatigue crack propagation in a quenched and tempered alloy steel

1977 ◽  
Vol 12 (2) ◽  
pp. 81-88 ◽  
Author(s):  
E H R Wade ◽  
G M C Lee
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Crack Front ◽  
Mean Stress ◽  
Free Surfaces ◽  
Front Profile ◽  
Crack Growth Rates

A series of tests are reported which support the proposal that fatigue crack growth rates are retarded by crack closure at low values of applied mean stress intensity. In particular, the evidence presented indicates that closure occurs most readily at the specimen's free surfaces. This leads to dramatic changes in crack front profile under certain loading conditions.

Comparison of Computational Crack Path Predictions with Experimental Findings for a Quarter-Circular Surface Crack in a Shaft under Torsion

2007 ◽  
Vol 348-349 ◽  
pp. 161-164 ◽  
Author(s):  
Friedrich G. Buchholz ◽  
J. Wiebesiek ◽  
M. Fulland ◽  
Hans A. Richard
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Front ◽  
Fracture Criterion ◽  
Circular Crack ◽  
Fe Model ◽  
Crack Growth Behaviour ◽  
3D Crack Growth ◽  
Experimental Findings

In this paper the rather complex 3D fatigue crack growth behaviour in a shaft with a quarter-circular crack under torsion is investigated by the aid of the programme ADAPCRACK3D and by application of a recently developed 3D fracture criterion. It will be shown that the computationally simulated results of fatigue crack growth in the FE-model of the shaft are in good agreement with experimental findings for the development of two anti-symmetric cracks, which originate from the two crack front corner points, that is where the crack front intersects the free surface of the cylindrical laboratory test-specimens. Consequently, also for this case with a rather complex 3D crack growth of two anti-symmetric cracks, the functionality of the ADAPCRACK3Dprogramme and the validity of the proposed 3D fracture criterion can be stated.

Sign in / Sign up

Export Citation Format

Share Document