| 1. |
- Alfredsson, Bo, et al.
(författare)
-
Initiation and Growth of Standing Contact Fatigue Cracks
- 2000
-
Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 65:1, s. 89-106
-
Tidskriftsartikel (refereegranskat)abstract
- In the standing contact fatigue test an indenter subjects a case hardened test specimen to a stationary but pulsating contact load. Two crack types appearing in the test specimen are investigated. The ring/cone cracks are surface cracks that circumvent the contact area, whereas the lateral cracks are horizontal sub-surface cracks. The initial crack lengths are determined for both crack types. Actual crack paths from experiments are evaluated numerically. For each crack tip position, stress intensity factors are determined from J(1) and J(2) integrals. The stress intensity ranges are compared to criteria for fatigue crack propagation rate and direction. As the cracks propagate, they orient in the direction with mode II loading close to zero.
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| 2. |
- Bjerkén, Christina, PhD, 1962-, et al.
(författare)
-
A numerical method for calculating stress intensity factors for interface cracks in bimaterials
- 2001
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier. - 0013-7944 .- 1873-7315. ; 68:2, s. 235-246
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a method For obtaining the complex stress intensity factor (or alternatively the corresponding energy release rate and mode mixity) for an interface crack in a bimaterial using a minimum number of computations. A crack closure integral method for homogeneous materials developed by Rybicki and Kanninen has been modified to include mismatch in material properties. This was achieved directly from the nodal forces at the crack tip and the displacements near the tip as obtained from a finite element analysis using only four-node constant strain elements. Numerical calculations for tensile and mixed mode loading showed good agreement with results from corresponding analytical solutions. The main advantages of this method are that it is straightforward and easy to use and that the number of calculations needed to obtain the stress intensity Factors can be held to a minimum. (C) 2000 Elsevier Science Ltd. All rights reserved.
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| 3. |
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| 4. |
- Faleskog, Jonas, et al.
(författare)
-
A probabilistic model for cleavage fracture with a length scale - parameter estimation and predictions of stationary crack experiments
- 2004
-
Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 71:1, s. 57-79
-
Tidskriftsartikel (refereegranskat)abstract
- This study presents a large experimental investigation in the transition temperature region on a modified A508 steel. Tests were carried out on single-edge-notch-bend specimens with three different crack depth over specimen width ratios to capture the strong constraint effect on fracture toughness. Three test temperatures were considered, covering a range of 85 degreesC. All specimens failed by cleavage fracture prior to ductile tearing. A recently proposed probabilistic model for the cumulative failure by cleavage was applied to the comprehensive sets of experimental data. This modified weakest link model incorporates a length scale, which together with a threshold stress reduce the scatter in predicted toughness distributions as well as introduces a fracture toughness threshold value. Model parameters were estimated by a robust procedure, which is crucial in applications of probabilistic models to real structures. The conformity between predicted and experimental toughness distributions, respectively, were notable at all the test temperatures.
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| 5. |
- Hakami, H., et al.
(författare)
-
Shear fracture energy of Stripa granite : Results of controlled triaxial testing
- 1990
-
Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 35:4-5, s. 855-865
-
Tidskriftsartikel (refereegranskat)abstract
- We have performed controlled triaxial experiments on Stripa granite in a 'nearly stiff' environment. This means that, before the commencement of loading, an initial confining pressure was 'locked' in the pressurizing chamber of the triaxial vessel. During the axial loading of the sample, the confining pressure was unavoidably increased, opposing largely the 'free' expansion of the sample due to overall microcracking. Further increase in confining pressure beyond the peak load resulted from the dilation of the formed shear fracture, during shear displacement. Under triaxial testing condition a reasonable assumption is that the shear fracture in the specimen is a consequence of pure shear (mode II) state of stress prevailing in the sample, in the vicinity of a 'bandlike' zone, from which the shear fracture propagated. Under this assumption and by the relevant fracture mechanics approach incorporating the 'slip weakening' model, shear fracture energy of Stripa granite was estimated. The results were compared with those estimated through controlled triaxial experiments at constant confining pressure, recently reported by other workers. Also, the influence of the testing method described here on the process of laboratory failure of rock in shear is discussed.
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| 6. |
- Hoffelner, W., et al.
(författare)
-
A fracture mechanics analysis of ultrasonic fatigue
- 1982
-
Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 16:3, s. 365-371
-
Tidskriftsartikel (refereegranskat)abstract
- The method of ultrasonic fatigue finds increasing interest in materials science. Especially, fatigue crack growth rates near the threshold stress intensity range, Δ”K0, can be determined with this method in reasonable times providing no frequency and corrosion effects exist. But for an accurate application of this technique it is necessary to improve the testing systems and also the determination of the dynamic cyclic stress intensity range, Δ”K. In this paper, fatigue crack growth experiments at ultrasonic frequencies with different mean stresses and also the calculation of the dynamic stress intensity range with finite elements are treated. On this basis fatigue crack growth curves at room temperature of the alloys Hastelloy X and IN 800 were measured and compared with results obtained at low frequencies. No significant influence of frequency could be found in these materials.
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| 7. |
- Jernkvist, Lars-Olof
(författare)
-
Fracture of wood under mixed mode loading : II. Experimental investigation of Picea abies
- 2001
-
Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 68:5, s. 565-576
-
Tidskriftsartikel (refereegranskat)abstract
- An experimental investigation of mixed mode I/II fracture in Norway spruce (Picea abies) is presented. Mixed mode fracture is studied in two principal crack systems, RL and LR, in which the crack planes extend along and across the wood fibres, respectively. The investigation shows that onset of mixed mode cracking can be predicted with a very simple fracture criterion in both these crack systems. However, the applicability of the fracture criterion to cross-fibre cracks is limited to configurations, in which the crack tip T-stress, i.e. the non-singular stress acting parallel to the crack plane, is low.
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| 8. |
- Jernkvist, Lars-Olof
(författare)
-
Fracture of wood under mixed mode loading : I. Derivation of fracture criteria
- 2001
-
Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 68:5, s. 549-563
-
Tidskriftsartikel (refereegranskat)abstract
- A mixed mode I/II fracture criterion applicable to cracks oriented both along and across the fibres in wood is derived within the framework of linear elastic fracture mechanics. The use of a common fracture criterion for both types of cracks is made possible by the fact that cracks in wood generally propagate along the fibres, irrespective of both the original crack orientation and the degree of mode mixity. The derived criterion is simple, and contains a single material dependent fracture parameter. The applicability of the fracture criterion to spruce (Picea abies) is experimentally validated in part two of the paper
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| 9. |
- Jivkov, Andrey
(författare)
-
Fatigue corrosion crack extension across the interface of an elastic bi-materia
- 2004
-
Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 71:7, s. 1139-1153
-
Tidskriftsartikel (refereegranskat)abstract
- In this work crack propagation in a bi-material composed of a thin elastic layer ideally bonded to a large elastic substrate is studied. A flaw is assumed existing on the surface of the layer. Cracks nucleate from the flaw and propagate through the bi-material. The cracks have realistic geometrical shapes, where the crack tip is an integral part of the crack surface. Thus the crack propagation is associated with a crack surface evolution. Material loss due to corrosion of the crack surface is the physical ground for the evolution. A controlling mechanism for the surface advancement is the rupture of a brittle corrosion-protective film, which is continually building-up along the corroding surface. The rate of surface evolution is a function of the degree of protective film damage, caused by the surface straining. This leads to a moving boundary formulation, for which a numerical solution is proposed. Fatigue loading is considered as a suitable way to maintain crack evolution at a constant peak load level. Under the assumed model, the cracks always pass the interface. The elastic mismatch is shown to influence the growth rate variation around the interface. Crack extensions are presented as functions of the elastic mismatch and as functions of the initial flaw size. It is shown how the results can be used in designing bi-material systems. A typical morphology evolution of a crack passing through an interface with a weak-stiff transition is presented. An example of fatigue corrosion fracture is offered, which shows that the crack morphology of the model resembles the one observed in reality. It is concluded that the realistic crack geometry is an effective concept and the moving boundary formulation could be a very successful tool for simulating realistic crack propagation.
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| 10. |
- Jivkov, Andrey, et al.
(författare)
-
Strain-driven corrosion crack growth : A pilot study of intergranular stress corrosion cracking
- 2002
-
Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 69:18, s. 2095-2111
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Tidskriftsartikel (refereegranskat)abstract
- This work proposes a model for corrosion driven crack growth. The model poses a moving boundary problem, where a chemical attack removes material from the body. The rate of the chemical attack is a function of the strain along the body surface. No crack growth criterion is needed for the analysis. A finite strain formulation is used and the material model is assumed hyperelastic. The problem is stated for a large body, containing a large crack. A low frequency cyclic loading is considered. Thus, corrosion is assumed to dissolve material with a rate approximately proportional to the strain rate. The problem is solved using finite element method based program, enhanced with a procedure handling the moving boundary. Parametric studies are performed for a series of different initial shapes of the near-tip region. Presented results show that the crack growth rate is largely dependent on the initial crack geometry. For a set of initial shapes and load levels steady-state conditions of growth are achieved, while for the others the cracks show tendency to branch.
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| 11. |
- Lorentzon, M., et al.
(författare)
-
A path independent integral for the crack extension force of the circular arc crack
- 2000
-
Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 66:5, s. 423-429
-
Tidskriftsartikel (refereegranskat)abstract
- A path independent integral expression for the crack extension force of a two-dimensional circular arc crack is presented. The integral expression, which consists of a contour and an area integral, is derived from the principle of virtual work. It is implemented into a FEM post-processing program and the crack extension force is calculated for a circular are crack in a linear elastic material. Comparison with exact solutions by Cotterell and Rice for the effective elastic stress intensity factor shows acceptable accuracy for the numerical procedure used
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| 12. |
- MackAldener, M., et al.
(författare)
-
Analysis of crack propagation during tooth interior fatigue fracture
- 2002
-
Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 69:18, s. 2147-2162
-
Tidskriftsartikel (refereegranskat)abstract
- Tooth interior fatigue fracture is a failure mode that is initiated as a fatigue crack in the interior of the tooth of a gear. TIFF cracks have been observed in case hardened idler gears. A fracture mechanical analysis of a TIFF crack is performed utilising FEA. A 3D TIFF crack is modelled at a position in the tooth that corresponds with an observed crack surface. The different material properties in the case and the core, determined by mechanical testing, are considered, as well as the residual state of stress due to case hardening. Various crack lengths are analysed to estimate crack propagation both into the core and into the case. The following results have been found: A TIFF crack initiated slightly under the case layer will propagate into the case layer where it stops. . The main crack propagation will take place in the core. . The crack propagation is only a small portion of the total life (order of 10(5) cycles). . After reaching the case layer the TIFF crack eventually deflects toward the tooth root and the upper part of the tooth falls off. The crack deflection is due to redistribution of contact loading. Several gear teeth pairs are simultaneously in contact and the cracked tooth is loaded less than the uncracked during this stage of life.
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| 13. |
- Månsson, Tomas, et al.
(författare)
-
Closure effects on fatigue crack growth rates at constant and variable amplitude loading
- 2004
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 71:10-sep, s. 1273-1288
-
Tidskriftsartikel (refereegranskat)abstract
- Accurate measurements of fatigue propagation rates after single and during repetitive overloads were performed. It was shown that plastic deformations in the crack tip region and in the crack wake cause crack closure that is of major importance for crack growth rates. The consequences of this for methods to determine certain material properties are discussed. An improved method to measure closure free propagation rate data was utilised. The possibilities and shortcomings of compliance methods to determine crack closure levels are pointed out. The relevance of using DeltaK(I,eff) = K-I,K-max - K-I,K-lim, where K-I,K-lim possibly could be interpreted as the crack closure level was investigated and is discussed. A method to predict average crack propagation rates at block loadings consisting of well-defined load cycles of different amplitudes and R-factors was suggested. Three-dimensional effects after overloads were observed. These observations confirmed that the crack closure behaviour also depends on geometry of the specimen.
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| 14. |
- Nilsson, Fred L., et al.
(författare)
-
Growth of surface cracks under constant and variable amplitude loading
- 2004
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 71:12, s. 1725-1735
-
Tidskriftsartikel (refereegranskat)abstract
- Fatigue crack growth experiments were performed on surface cracked tensile specimens of Inconel 718 at 400 degreesC. The loading was carried out at constant as well as at variable amplitude. The experimental results for the mean growth rate were compared with predictions based on data obtained from testing of compact tension specimens. Both nominal data as well as data corrected from measured crack closure were used in the predictions. The corrected data provided much better predictions than the nominal ones indicating that the level of crack closure during the testing of the surface cracked specimens was much lower than in compact tension specimens.
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| 15. |
- Ohlsson, Ulf, et al.
(författare)
-
Fracture energy and fatigue strength of unreinforced concrete beams at normal and low temperatures
- 1990
-
Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 35:1-3, s. 195-203
-
Tidskriftsartikel (refereegranskat)abstract
- Results are presented from tests where the fracture energy and the fatigue strength have been determined for unreinforced concrete beams. The tests were performed at temperatures between +20 and −35°C with concrete with compressive strength varying between 25 and 100 MPa.
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| 16. |
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| 17. |
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| 18. |
- Ribeiro-Ayeh, Steven, et al.
(författare)
-
Strength prediction of beams with bi-material butt-joints
- 2003
-
Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 70:12, s. 1491-1507
-
Tidskriftsartikel (refereegranskat)abstract
- Failure of bi-material interfaces is studied with the aim to quantify the influence of the induced stress concentrations on the strength of the interfaces. The suggested approach is applied to a specimen configuration where two different materials are butt-joined to form a two-material beam. Strength predictions for different interface bias are made and verified in experiments where a polymer foam material is joined with members of either aluminium or Plexiglas.The predictions are made using a simple point-stress criterion in combination with highly accurate finite element calculations. The point-stress criterion was known from earlier work to give accurate predictions of failure at cracks and notches but had to be slightly modified to become applicable for the studied configurations. Both the strength and the cross-over from local, joint-induced failure to global failure were predicted with reasonable accuracy.
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| 19. |
- Rustan, Agne
(författare)
-
Importance of using joints to achieve scaled fragmentation in magnetite concrete used for sublevel caving blast models
- 1990
-
Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 35:1-3, s. 425-438
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Tidskriftsartikel (refereegranskat)abstract
- Model scale tests have been undertaken to find a model material which can give scaled fragmentation in sublevel caving blast models where the purpose is to study the swelling and fragmentation of the burden when blasted against waste rock and also to study the gravity flow of the blasted burden when being discharged into the drift. To achieve a wished Rosin Rammler distribution of the blasted material in the blasted model, it was shown necessary to introduce weakness plans of different size and stochastic orientation in the model material. Crushed microscopic glass plates or coarse magnetite grains were used for that purpose with success
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| 20. |
- Schon, J., et al.
(författare)
-
Numerical and experimental investigation of a composite ENF-specimen
- 2000
-
Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 65:4, s. 405-433
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Tidskriftsartikel (refereegranskat)abstract
- An extensive numerical and experimental investigation has been carried out regarding fracture mechanical properties for the end notch flexure (ENF) specimens. Static and cyclic properties were studied for different interfaces and for several graphite/epoxy composites. State of the art numerical analyses are described and experimental results are interpreted in terms of usefulness for applications to real structures. The FEM results were compared with beam models and it was found that for the specimen with a zero interface the beam models were acceptable whereas for the specimens with non-zero interface they did show a large error. Numerically, it was found that the effect of friction lowers the energy release rate by a few percent. Experimental results showed that for specimens with non-zero interfaces the delamination crack changed interface. (C) 2000 Elsevier Science Ltd. All rights reserved.
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| 21. |
- Stehn, Lars, et al.
(författare)
-
Orientation effects on the fracture of pond (S1) ice
- 1995
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Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 51:3, s. 431-435
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Tidskriftsartikel (refereegranskat)abstract
- The influence of structural anisotropy on the fracture toughness of S1 type freshwater ice was investigated by fabricating and testing three different fracture geometries from a single ice core. The ice was tested at - 16°C using the Chevron Edge Notch Round Bar in Bending (CENRBB), a Chevron Notched Tension (CNT) specimen and the Semi-Circular Bend (SCB) specimen. By this procedure, a complete anisotropic apparent fracture toughness (KQ) characterization is possible from one core. The specimens can be prepared with very little machining. This approach is therefore suitable for both field and, as in this work, laboratory studies. Three models are presented for computation of the stress-intensity-factor expressions for these specimens. There is a wide scatter in the KQ results and the apparent fracture toughness was higher for cracks perpendicular, than for cracks parallel, to the c-axis and the columnar grains. Possible explanations for this ambiguous behavior are discussed in terms of the microstructural influences and specimen size effects.
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| 22. |
- Talreja, Ramesh
(författare)
-
Fatigue reliability under multiple-amplitude loads
- 1979
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 11:4, s. 839-849
-
Tidskriftsartikel (refereegranskat)abstract
- method to determine the fatigue of structures subjected to multiple-amplitude loads is presented. Unlike the more common cumulative damage methods, which are usually based on fatigue life data, the proposed method is based on tensile strength data. Assuming the Weibull distribution for the initial tensile strength and the fatigue life, the probability distributions for the residual tensile strength in both the crack initiation and the crack propagation stages of fatigue are determined. The method is illustrated for two-amplitude loads by means of experimental results obtained by testing specimens of a structural steel and is shown to be more accurate than the Palmgren-Miner cumulative damage method
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| 23. |
- Talreja, Ramesh
(författare)
-
On fatigue life under stationary Gaussian random loads
- 1973
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 5:4, s. 993-1007
-
Tidskriftsartikel (refereegranskat)abstract
- Load parameters for a stationary Gaussian random load are taken as the location, scale and shape parameters of its power spectrum. The centre frequency of a power spectrum is proposed as a measure of fatigue life. A fatigue life function, formulated in terms of the load parameters, is evaluated from the test results obtained by fatigue testing a structural steel under six different power spectral shapes. The concept of a shape operator is employed to correlate fatigue lives under different power spectral shapes.
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| 24. |
- Talreja, Ramesh
(författare)
-
On fatigue reliability under random loads
- 1979
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 11:4, s. 717-732
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Tidskriftsartikel (refereegranskat)abstract
- We consider the problem of estimating the probability of survival (non-failure) and the probability of safe operation (strength greater than a limiting value) of structures subjected to random loads. These probabilities are formulated in terms of the probability distributions of the loads and the material strength. For the material strength, the Weibull distribution is assumed, the parameters of which are estimated by a statistical analysis of the experimental tensile strength of steel specimens subjected to different periods of random loads. The statistical analysis shows that, with the application of random loads, the initial homogeneous distribution of strength changes to a two-component distribution, reflecting the two-stage fatigue damage. In the crack initiation stage, the strength increases initially and then decreases, while an abrupt decrease of strength is seen in the crack propagation stage. The consequences of this behaviour on the fatigue reliability are discussed
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| 25. |
- Talreja, Ramesh
(författare)
-
Stiffness properties of composite laminates with matrix cracking and interior delamination
- 1986
-
Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 25:5-6, s. 751-762
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Tidskriftsartikel (refereegranskat)abstract
- Two modes of damage in composite laminates are considered: the intralaminar damage (matrix cracking) and the interlaminar damage (interior delamination). Using a vectorial representation of damage as internal variables in a phenomenological theory, relationships between the overall stiffness properties and the intensity of damage in the individual modes are determined. These relationships show that the intralaminar damage reduces all elastic moduli for a general orientation of the damage entities (cracks) and changes the initial orthotropic symmetry of a laminate. The interlaminar damage, however, does not change the symmetry but reduces the moduli. Predictions of the elastic moduli changes are compared with experimental results, showing excellent agreement
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| 26. |
- Tang, C.A., et al.
(författare)
-
Crack propagation and coalescence in brittle materials under compression
- 1998
-
Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 61:3-4, s. 311-324
-
Tidskriftsartikel (refereegranskat)abstract
- Two particular cases concerning crack propagation and coalescence in brittle materials have been modeled by using the rock failure process analysis code, RFPA2D, and the results have been validated by reported experimental observations. Firstly, axial compression of numerical samples containing a number of large, pre-existing flaws and a row of suitably oriented smaller flaws are simulated. It has been confirmed that under axial compression, wing-cracks nucleate at the tips of the pre-existing flaws, grow with increasing compression, and become parallel to the direction of the maximum far-field compression. However, coalescence of the wing-cracks may be in either tensile mode or shear mode, or a combination of both modes. The numerical results show qualitatively a reasonably good agreement with reported experimental observations for samples with similar flaw arrangements. The numerical results demonstrate that, with a confining pressure, the crack growth is stable and stops at some finite crack length; whereas a lateral tensile stress even with a small value will result in an unstable crack growth after a certain crack length is attained. Secondly, failure mode in a sample containing inhomogeneities on grain scale has also been simulated. The results show that the failure mode strongly depends on the mechanical and geometric properties of the grains and inclusions
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| 27. |
- Varias, A.G., et al.
(författare)
-
Temperature and constraint effects on hydride fracture in zirconium alloys
- 2000
-
Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 65:1, s. 29-54
-
Tidskriftsartikel (refereegranskat)abstract
- The fracture of hydrides in zirconium alloys is under consideration. According to the present boundary value problem, a hydride platelet lies ahead of a semi-infinite crack, along the crack plane. The surrounding material is elastic-plastic zirconium alloy. The platelet is either continuous or split into two parts, connected by a ductile matrix ligament. At distances from the crack tip, which are large compared to the hydride and the plastic zone size, the K-T field is applied and mode I, plane strain and contained yielding conditions prevail. Hydride platelet failure initiation and growth is simulated by using a de-cohesion crack growth model and the stress intensity factor, which causes fracture, is estimated at various temperatures as well as under various constraint conditions. Comparison of the calculated temperature effect on toughness with the experimental one is satisfactory. Fracture toughness decreases with T-stress. This effect is attributed to the interaction of the K-T field with hydride expansion, during precipitation. The reduction becomes more important at elevated temperatures and moderates the benefits on fracture toughness, caused by temperature increase. In addition to the detailed finite element results, analytical estimates on fracture toughness are presented, based on a cohesive zone model
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| 28. |
- Wang, T.C., et al.
(författare)
-
Stress state in front of a crack perpendicular to bimaterial interface
- 1998
-
Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 59:4, s. 471-485
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Tidskriftsartikel (refereegranskat)abstract
- Using a dislocation simulation approach, the basic equation for a crack perpendicular to a bimaterial interface is formulated in this paper. A novel expansion method is proposed for solving the problem. The complete solution for the problem, including the T stress ahead of the crack tip and the stress intensity factors are presented. The stress field characteristics are analyzed in detail. It is found that ahead of the crack tip and near the interface the normal stress, perpendicular to the crack plane, σx, is characterized by the K fields and the normal stress σy is dominated by the K field plus T stress in the region of 0 < r/b < 0.4 for 6/ao≤0.1, where b is the distance from the crack tip to the interface
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| 29. |
- Zang, Weilin, et al.
(författare)
-
An Integral-Equation Method For Piece-Wise Smooth Cracks In An Elastic Half-Plane.
- 1989
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 32:6, s. 889-897
-
Tidskriftsartikel (refereegranskat)abstract
- A boundary integral equation method for piece-wise smooth cracks in an elastic half-plane is presented. Both internal and surface cracks have been considered. The numerical formulation is based on an element description of the unknown dislocation densities along the crack line. Crack line kinks are treated by an introduction of double nodes at each kink. Numerical test examples are presented and compared, either to existing solutions, or to own finite element calculations. Excellent agreements were obtained for all cases.
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| 30. |
- Alam, Md. Minhaj, et al.
(författare)
-
Influence of defects on fatigue crack propagation in laser hybrid welded eccentric fillet joint
- 2011
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 78:10, s. 2246-2258
-
Tidskriftsartikel (refereegranskat)abstract
- Fatigue cracking of laser hybrid welded eccentric fillet joints has been studied for stainless steel. Two-dimensional linear elastic fracture mechanics analysis was carried out for this joint geometry for four point bending load. The numerical simulations explain for the experimental observations why the crack propagates from the lower weld toe and why the crack gradually bends towards the root. Lack of fusion turned out to be uncritical for the initiation of cracks due to its compressive stress conditions. The linear elastic fracture mechanics analysis has demonstrated in good qualitative agreement with fatigue test results that lack of fusion slightly (<10%) reduces the fatigue life by accelerating the crack propagation. For the geometrical conditions studied here improved understanding of the crack propagation was obtained and in turn illustrated. The elaborated design curves turned out to be above the standard recommendations.
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| 31. |
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| 32. |
- Alfredsson, K. Svante, et al.
(författare)
-
Stability of beam-like fracture mechanics specimens
- 2012
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier. - 0013-7944 .- 1873-7315. ; 89, s. 98-113
-
Tidskriftsartikel (refereegranskat)abstract
- Test specimens used to determine the interlaminar strength of composites as well as the strength of adhesive layers are known to occasionally suffer from instability. Thus, even though the experiments are performed under controlled load-point displacement, the experiments are terminated prematurely by unstable crack propagation. Often there exists a critical crack length which must be exceeded in order to obtain stable crack propagation. In this paper, a general method to assess the stability of beam-like fracture mechanics specimens is developed. Both systems subjected to a single load and the more general situation with several independent loads are treated. A simple formula is derived for the critical crack length for one-parameter loading. The only parameter necessary as input is the compliance of the un-cracked specimen. For the case of non-proportional loading, stability is determined by studying the eigenvalues of a symmetric matrix. Other findings quantified in the paper are the effect of orthotropy, the influence of a flexible interphase layer and the influence of the compliance of the loading device.
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| 33. |
- Andersons, Janis, et al.
(författare)
-
Statistical model of the transverse ply cracking in cross-ply laminates by strength and fracture toughness based failure criteria
- 2008
-
Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 75:9, s. 2651-2665
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Tidskriftsartikel (refereegranskat)abstract
- Cross-ply laminate subjected to tensile loading provides a relatively well understood and widely used model system for studying progressive cracking of the transverse ply. This test allows to identify material strength and/or toughness characteristics as well as to establish relation between damage level and the composite stiffness reduction. The transverse ply cracking is an inherently stochastic process due to the random variability of local material properties of the plies. The variability affects both crack initiation (governed by the local strength) and propagation (governed by the local fracture toughness). The primary aim of the present study is elucidation of the relative importance of these phenomena in the fragmentation process at different transverse and longitudinal ply thickness ratios. The effect of the random crack distribution on the mechanical properties reduction of the laminate is also considered. Transverse ply cracking in glass fiber/epoxy cross-ply laminates of the lay-ups [02/902]s, [0/902]s, and [0/904]s is studied. Several specimens of each lay-up were subjected to uniaxial quasistatic tension to obtain crack density as a function of applied strain. Crack spacing distributions at the edge of the specimen also were determined at a predefined applied strain. Statistical model of the cracking process is derived, calibrated using crack density vs. strain data, and verified against the measured crack spacing distributions.
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| 34. |
- Andreasson, Eskil, et al.
(författare)
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Micro-mechanisms of a laminated packaging material during fracture
- 2014
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Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 1873-7315 .- 0013-7944. ; 127, s. 313-326
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Tidskriftsartikel (refereegranskat)abstract
- The micro-mechanisms of fracture in a laminate composed of an aluminium foil and a polymer film are considered in this study. The laminates as well as the individual layers, with and without premade centre-cracks, were tensile tested. Visual inspection of the broken cross-sections shows that failure occurs through localised plasticity. This leads to a decreasing and eventually vanishing cross-section ahead of the crack tip for both the laminate and their single constituent layers. Experimental results are examined and analysed using a slip-line theory to derive the work of failure. An accurate prediction was made for the aluminium foil and for the laminate but not for the freestanding polymer film. The reason seems to be that the polymer material switches to non-localised plastic deformation with significant strain-hardening. (C) 2014 Elsevier Ltd. All rights reserved.
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| 35. |
- Biel, Anders, et al.
(författare)
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Effects of constitutive parameters on the accuracy of measured fracture energy using the DCB-specimen
- 2008
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Ingår i: Engineering Fracture Mechanics. - : Elsevier. - 0013-7944 .- 1873-7315. ; 75:10, s. 2968-2983
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Tidskriftsartikel (refereegranskat)abstract
- Several methods exist to estimate the fracture energy for adhesive joints using the double cantilever beam specimen and linear elastic fracture mechanics. Since the mechanical properties of all adhesives are non-linear, errors are generated. By use of an exact solution experiments are simulated. These are evaluated with eight different methods. The influence of the constitutive parameters is systematically studied. This influence is small for most methods. The error due to the choice of evaluation method is considerably larger. One of the commonly used methods gives accurate results; the error is less than 3%. However, most methods yield substantial errors.
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| 36. |
- Birgisson, Björn, et al.
(författare)
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Determination and prediction of crack patterns in hot mix asphalt (HMA) mixtures
- 2008
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Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 75:3-4, s. 664-673
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a comparison between predicted and measured crack patterns developing in hot mix asphalt (HMA) mixtures during common fracture tests. A digital image correlation (DIC) System was applied to obtain displacement/strain fields and for detecting crack patterns. The resulting cracking behavior was predicted using a displacement discontinuity boundary element method to explicitly model the microstructure of HMA. The predicted fracture initiation and crack propagation patterns are consistent with observed cracking behavior. The results imply that fracture in mixtures can be modeled effectively using a micro-mechanical approach and that crack propagation patterns can be captured using the DIC System.
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| 37. |
- Bjerkén, Christina, et al.
(författare)
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A study of the influence of grain boundaries on short crack growth during varying load using a dislocation technique
- 2004
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Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 1873-7315 .- 0013-7944. ; 71:15, s. 2215-2227
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Tidskriftsartikel (refereegranskat)abstract
- The propagation of short cracks in the neighbourhood of grain boundaries have been investigated using a technique were the crack is modelled by distributed dislocation dipoles and the plastic deformation is represented by discrete dislocations. Discrete dislocations are emitted from the crack tip as the crack grows. Dislocations can also nucleate at the grain boundaries. The influence on crack growth characteristics of the distance between the initial crack tip and the grain boundary has been studied. It was found that crack growth rate is strongly correlated to the dislocation pile-ups at the grain boundaries. (C) 2004 Elsevier Ltd. All rights reserved.
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| 38. |
- Bjerkén, Christina, et al.
(författare)
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Simulation of corrosion fatigue crack growth under mixed-mode loading
- 2008
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Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 1873-7315 .- 0013-7944. ; 75:3-4, s. 440-451
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Tidskriftsartikel (refereegranskat)abstract
- The kinking of a corrosion crack due to mixed-mode fatigue loading is studied using an adaptive finite element procedure. The rate of material dissolution is assumed to be proportional to the stretching of the corroding surface. The dissolution of material is governed by a corrosion law, where no criterion is needed for neither crack growth nor growth direction. The problem is treated as a general moving boundary problem. The kink angles are found to be in very good agreement with results for sharp cracks using criteria reported in the literature.
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| 39. |
- Bjerkén, Christina
(författare)
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The influence of biaxial loading on branching of a dissolution driven stress corrosion crack
- 2010
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Ingår i: Engineering Fracture Mechanics. - : Elsevier. - 0013-7944 .- 1873-7315. ; 77:11, s. 1989-1997
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Tidskriftsartikel (refereegranskat)abstract
- Stress corrosion cracking occurs due to the synergistic interaction between mechanical load and corrosion reactions. In this study, branching during anodic dissolution driven crack growth is studied using an adaptive FE procedure. The crack has an inherent blunt tip due to the dissolution, and the growth is treated as a moving boundary problem with a strain-assisted evolution law. Simulations are performed with different degrees of load biaxiality. It is found that increasing biaxiality promotes branching. No conditions for when branching takes place are found. Crack growth rates for branches are investigated, and it is found that, after an initial acceleration, constant growth rates can be reached, as well as decreasing speed and eventual arrest. The influence of T-stresses and perturbations sensitivity are discussed.
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| 40. |
- Boåsen, Magnus, et al.
(författare)
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A generalized probabilistic model for cleavage fracture with a length scale - Influence of stress state and application to surface cracked experiments
- 2019
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Ingår i: Engineering Fracture Mechanics. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0013-7944 .- 1873-7315. ; 214, s. 590-608
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A probabilistic model for the cumulative probability of failure by cleavage fracture with a material related length scale is further developed in this study. A new generalized effective stress measure is proposed, based on a normal stress decomposition of the stress tensor, capable of describing a state of normal stress in the range from the mean stress to the maximum principal stress. The effective stress measure associated with a material point is evaluated from the stress tensor averaged over the material related length scale. The model is shown to be well capable to predict both the fracture toughness at loss of both in-plane and out-of-plane constraint by model application to two different datasets from the open literature. The model is also shown to be well capable of predicting the probability of failure of discriminating experiments on specimens containing semi-elliptic surface cracks. A comparison where the master curve methodology is used to predict the probability of failure of the experiments is also included.
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| 41. |
- Boåsen, Magnus, et al.
(författare)
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Analysis of thermal embrittlement of a low alloy steel weldment using fracture toughness and microstructural investigations
- 2022
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Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 262
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Tidskriftsartikel (refereegranskat)abstract
- A thermally aged low alloy steel weld metal is investigated in terms of its fracture toughness and microstructural evolution and compared to a reference. The main purpose of the study is to investigate the effects of embrittlement due to thermal ageing on the brittle fracture toughness, and its effects on the influence of loss of crack tip constraint. The comparison of the investigated materials has been made at temperatures that give the same median fracture toughness of the high constraint specimens, ensuring comparability of the low constraint specimens. Ageing appears to enable brittle fracture initiation from grain boundaries besides initiation from second phase particles, making the fracture toughness distribution bimodal. Consequently, this appears to reduce the facture toughness of the low constraint specimens of the aged material as compared to the reference material. The microstructure is investigated at the nano scale using atom probe tomography where nanometer sized Ni-Mn-rich clusters, precipitated during ageing, are found primarily situated on dislocation lines.
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| 42. |
- Bremberg, Daniel, et al.
(författare)
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Automatic crack-insertion for arbitrary crack growth
- 2008
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Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 75:3-4, s. 404-416
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Tidskriftsartikel (refereegranskat)abstract
- A crack-insertion tool for automatic non-planar crack propagation calculations is under development. The final volume mesh of the cracked structure is achieved by a new approach. The cracked structure boundary is modelled as a discretized skin. A tube-like domain enclosing the crack-front is traced and filled with hexahedral elements while the remaining cracked structure is meshed with tetrahedral elements. The two separate meshes are finally connected by linear MPC equations. Results show that the method works very well for curved crack shapes in complex structures.
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| 43. |
- Busse, Christian, 1989-, et al.
(författare)
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Prediction of crystallographic cracking planes in single-crystal nickel-base superalloys
- 2018
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Ingår i: Engineering Fracture Mechanics. - : Elsevier. - 0013-7944 .- 1873-7315. ; 196, s. 206-223
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Tidskriftsartikel (refereegranskat)abstract
- The inherent anisotropy of single-crystal nickel-base superalloys brings many difficulties in terms of modelling, evaluation and prediction of fatigue crack growth. Two models to predict on which crystallographic plane cracking will occur is presented. The models are based on anisotropic stress intensity factors resolved on crystallographic slip planes calculated in a three-dimensional finite-element context. The developed models have been compared to experiments on two different test specimen geometries. The results show that a correct prediction of the crystallographic cracking plane can be achieved. This knowledge is of great interest for the industry and academia to better understand and predict crack growth in single-crystal materials.
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| 44. |
- Cadario, Alessandro, et al.
(författare)
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Fatigue growth of short cracks in Ti-17 : experiments and simulations
- 2007
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Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 74:15, s. 2293-2310
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Tidskriftsartikel (refereegranskat)abstract
- The fatigue behaviour of through thickness short cracks was investigated in Ti-17. Experiments were performed on a symmetric four-point bend set-up. An initial through thickness crack was produced by cyclic compressive load on a sharp notch. The notch and part of the crack were removed leaving an approximately 50 mu m short crack. The short crack was subjected to fatigue loading in tension. The experiments were conducted in load control with constant force amplitude and mean values. Fatigue growth of the short cracks was monitored with direct current potential drop measurements. Fatigue growth continued at constant R-ratio into the long crack regime. It was found that linear elastic fracture mechanics (LEFM) was applicable if closure-free long crack growth data from constant K-1max test were used. Then, the standard Paris' relation provided an upper bound for the growth rates of both short and long crack.The short crack experiments were numerically reproduced in two ways by finite element computations. The first analysis type comprised all three phases of the experimental procedure: precracking, notch removal and fatigue growth. The second analysis type only reproduced the growth of short cracks during fatigue loading in tension. In both cases the material model was elastic-plastic with combined isotropic and kinematic hardening. The agreement between crack tip opening displacement range, cyclic J-integral and cyclic plastic zone at the crack tip with Delta K-1 verified that LEFM could be extended to the present short cracks in Ti-17. Also, the crack size limits described in the literature for LEFM with regards to plastic zone size hold for the present short cracks and cyclic softening material.
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| 45. |
- Cadario, Alessandro, et al.
(författare)
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Fretting fatigue crack growth for a spherical indenter with constant and cyclic bulk load
- 2005
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Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 72:11, s. 1664-1690
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Tidskriftsartikel (refereegranskat)abstract
- Fatigue growth of edge cracks subjected to non-proportional fretting loads was investigated experimentally and numerically. The cracks were produced during fretting experiments with a spherical contact between two alpha + beta titanium alloys. Constant normal load was combined with cyclic tangential load and constant or cyclic bulk load. Crack propagation was detected during the experiments by strain gauges on the specimen surface and acoustic emission measurements. A parametric crack growth description procedure was used to model fatigue growth of the three-dimensional fretting cracks that were loaded with multiaxial and non-proportional stresses from the fretting contact. The predicted crack growth lives and crack shapes agreed with the experimental results. A crack path prediction based on the maximum principal value of the stress range tensor Delta sigma(ij) was evaluated.
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| 46. |
- Cao, Ri-hong, et al.
(författare)
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Failure and Mechanical Behavior of Transversely Isotropic Rock under Compression-Shear Tests : Laboratory Testing and Numerical Simulation
- 2021
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Ingår i: Engineering Fracture Mechanics. - : Elsevier. - 0013-7944 .- 1873-7315. ; 241
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Tidskriftsartikel (refereegranskat)abstract
- The failure and mechanical behavior of transversely isotropic rock are significantly affected by the original bedding planes. Until now, few studies have been performed to investigate the influence of the geometrical and mechanical parameters of the bedding planes on the fracture characteristics of transversely isotropic rocks under planar shear fracture loading conditions. For this purpose, experimental and numerical compression-shear tests on double-notched specimens are conducted to investigate the fracturing characteristics of transversely isotropic rock under planar shear fracture loading. The experimental study that focuses on the influence of bedding plane inclination on fracture load, fracture pattern and AE evolution, and six inclination angles is conducted in this study. Based on the flat joint contact model (for the rock matrix) and smooth joint contact model (for the original bedding plane) in PFC2D (particle flow code), the microscale fracturing process of transversely isotropic rock with different inclinations is simulated and analyzed. The results show that the inclination has an important influence on the fracture load and fracture pattern, and the maximum and minimum fracture loads are obtained for specimens with inclination angles of 30° and 60°, respectively. Moreover, the strength and spacing of the original bedding planes also play an important role in fracture loads. Higher bedding plane strength and wider bedding plane spacing result in higher fracture loads. In addition, with a moderate inclination angle, transversely isotropic rock with higher bedding plane strength tends to form cracks that cut through the rock matrix. However, with the decrease in the bedding plane strength, more fractures form along the bedding planes.
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| 47. |
- Carlberger, Thomas, et al.
(författare)
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An explicit FE-model of impact fracture in an adhesive joint
- 2007
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Ingår i: Engineering Fracture Mechanics. - : Elsevier. - 0013-7944 .- 1873-7315. ; 74:14, s. 2247-2262
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Tidskriftsartikel (refereegranskat)abstract
- Dynamic fracture of an adhesive layer in a structure is analysed. The structure represents some specific properties of an automotive structure and is simple enough to allow for closed form solutions obtained by the method of characteristics. These solutions are compared to results of explicit FE-analyses. The FE-solutions agree with the closed form solutions. Damage is included in the FE-model. Three constitutive models of the adhesive layer are used. It is shown that an amplification of the strain rate is achieved in the adhesive layer. It is also shown that an artificially increased flexibility of the adhesive in an aluminium structure gives only minor influences of the general behaviour. In some load cases, the adhesive layer will experience repeated loading/unloading. It is shown that in these cases an explicit FE-analysis with a “large” time step is more prone to give immediate rupture. Thus, the method is conservative.
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| 48. |
- Carlsson, Jenny, 1984-, et al.
(författare)
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Crack dynamics and crack tip shielding in a material containing pores analysed by a phase field method
- 2019
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Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 206, s. 526-540
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Tidskriftsartikel (refereegranskat)abstract
- Many naturally occurring materials, such as wood and bone, have intricate porous micro-structures and high stiffness and toughness to density ratios. Here, the influence of pores in a material on crack dynamics in brittle fracture is investigated. A dynamic phase field finite element model is used to study the effects of pores with respect to crack path, crack propagation velocity and energy release rate in a strip specimen geometry with circular pores. Four different ordered pore distributions are considered, as well as randomly distributed pores. The results show that the crack is attracted by the pores; this attraction is stronger when there is more energy available for crack growth. Crack propagation through pores also enables higher crack propagation velocities than are normally seen in strip specimens without pores (i.e. homogeneous material), without a corresponding increase in energy release rate. It is further noticed that as the porosity of an initially solid material increases, the crack tip is increasingly likely to become shielded or arrested, which may be a key to the high relative strength often exhibited by naturally occurring porous materials. We also find that when a pore is of the same size as the characteristic internal length then the pore does not localise damage. Since the characteristic internal length only regularises the damage field and not the strain end kinetic energy distributions, crack dynamics are still affected by small pores.
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| 49. |
- Carlsson, Jenny, 1984-, et al.
(författare)
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Simulating fracture in a wood microstructure using a high-resolution dynamic phase field model
- 2020
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Ingår i: Engineering Fracture Mechanics. - : Elsevier. - 0013-7944 .- 1873-7315. ; 232
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Tidskriftsartikel (refereegranskat)abstract
- As a simplified model, wood can be considered as consisting of hollow cells held together by a weaker middle lamella. We use a high-resolution finite element model, endowed with a phase field model for brittle fracture to model such a structure. The micro-structured discretised materials, with and without middle lamella, differ significantly from a homogenous continuum reference in terms of damage patterns. There is also significant difference between the models with and without middle lamella, since damage localises in the weaker middle lamella, which underlines the importance to include the middle lamella in mechanical analyses. At increased loading velocity, the damage becomes scattered over a larger region ahead of the crack tip, indicating that dynamic effects affect the crack behaviour and that dynamics need to be taken into consideration when loading rates are high or when crack propagation is unstable.
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| 50. |
- Chen, Bin, et al.
(författare)
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Element-removal global digital image correlation for accurate discontinuous deformation field measurement in fracture mechanics
- 2023
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Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 290
-
Tidskriftsartikel (refereegranskat)abstract
- We propose an element-removal (ER) global digital image correlation (DIC) method to improve the measurement accuracy of discontinuous deformation fields, such as crack propagation. The occurrence of cracks in materials or structures inevitably deteriorates the tracking accuracy, and, consequently, the strain field accuracy obtained by regular subset and global DIC. The proposed ER-global-DIC algorithm iteratively identifies and removes all the elements covering the crack, during the updating of displacement fields. In the remaining elements, the continuous shape function is applicable for accurate deformation measurement. In principle, although elements that contain the cracks are removed, the algorithm preserves the same number of nodes since the nodes are retained by the remaining elements. Synthetically deformed images based on analytical discontinuous displacement fields validate the effectiveness and accuracy of the proposed method. The ER-global-DIC is further applied to measure the discontinuous displacement fields containing a crack deflection, generated from a finite element model with a cohesive zone model. The results demonstrate the potential of the proposed method for discontinuous deformation measurement on advanced materials, e.g., fiber-reinforced composites.
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