The Experts below are selected from a list of 237 Experts worldwide ranked by ideXlab platform

J. Escuadra - One of the best experts on this subject based on the ideXlab platform.

  • Numerical modelling of cracking path in round bars subjected to cyclic tension and bending
    International Journal of Fatigue, 2013
    Co-Authors: Jesús Toribio, Juan-carlos Matos, Beatriz González, J. Escuadra
    Abstract:

    Abstract This paper shows the evolution of the surface crack front in round bars constituted of different materials (determined by the exponent m of the Paris Law), subjected to fatigue tension loading (with free ends) or fatigue bending loading. To this end, a numerical modelling is developed on the basis of a discretization of the crack front (characterized by a semi-elliptical shape) and the crack advance at each point perpendicular to such a front, computed according to the Paris-Erdogan Law and by using a three-parameter stress intensity factor (SIF). For each of the considered case the evolution of the semi-elliptical crack front is analysed, studying the variation of the crack aspect ratio a / b (defined as the ratio between the semi-axes of the ellipse which defines the crack front) against the relative crack depth a / D . The obtained results show that the dimensionless SIF values along the crack front are quite higher under tension loading than in the case of bending loading. Thus, the risk of catastrophic failure is higher in the case of tensile loading (in relation to the less dangerous bending situation) if a local fracture criterion (on the basis of the maximum local SIF K along the crack front) is used, considering that fracture takes place when K reaches the material fracture toughness K C .

  • 056 Modelling of Crack Path Evolution in Round Bars under Cyclic Tension and Bending
    2013
    Co-Authors: Jesús Toribio, Beatriz González, J. C. Matos, J. Escuadra
    Abstract:

    ABSTRACT. This paper shows the evolution of the surface crack front in round bars constituted of different materials (determined by the exponent m of the Paris Law), subjected to fatigue tension loading (with free ends) or fatigue bending loading. To this end, a numerical modeling was developed on the basis of a discretization of the crack front (characterized as an ellipse) and the crack advance at each point perpendicular to such a front, according to a Paris-Erdogan Law, using a three-parameter stress intensity factor (SIF). Each analyzed case was characterized by the evolution of the semielliptical crack front, studying the progress with the relative crack depth a/D of the following three key variables: (i) crack aspect ratio a/b (relation between the semiaxes of the ellipse which defines the crack front); (ii) maximum dimensionless SIF; (iii) minimum dimensionless SIF.

  • Aspect ratio evolution in corrosion-fatigue cracking of high strength steel bars
    2013
    Co-Authors: Jesús Toribio, Juan-carlos Matos, Beatriz González, J. Escuadra
    Abstract:

    This paper shows the evolution of the surface crack front in prestressing steel wires subjected to fatigue in air and to corrosion-fatigue in Ca(OH)2+NaCl. To this end, a numerical modelling was made on the basis of a discretization of the crack front (characterized with elliptical shape), considering that the crack advance at each point is perpendicular to such a front according to a Paris-Erdogan Law, and using a three-parameter stress intensity factor (SIF). Each analyzed case (a particular initial crack geometry) was characterized by the evolution of the semielliptical crack aspect ratio (relation between the semiaxes of the ellipse) with the relative crack depth. Introduction The fatigue behaviour of cold drawn eutectoid steel, frequently used as reinforcement in prestressed concrete, has received attention in the past, both in air [1] and in aggressive environments [2-6]. NaCl corrosion-fatigue affects the fatigue performance of high strength steel by increasing the crack growth rate in relation to its value in inert environment [3,4], this effect being even higher if the environment is constituted by Ca(OH)2+NaCl [5]. When cylindrical rods (bars, wires, shafts...) are used, transverse cracking by fatigue usually takes place in the form of surface cracks with semielliptical shape [7]. Growth of surface cracks in round bars due to fatigue can be modelled using different criteria, e.g., prediction of the 90o intersecting angle of the crack with the surface or the iso-K criterion along the crack front [8]. Another criterion is based on the crack growth according to the Paris-Erdogan Law [9] considering the crack advance perpendicular to the crack front, assuming elliptic geometry for the growing crack [10,11] or avoiding the shape hypothesis, i.e., allowing the crack to grow with any shape [12]. Material This paper studies the corrosion-fatigue crack propagation in prestressing steel wires (chemical composition: 0.82 %C, 0.60 %Mn, 0.18 %Si, 0.010 %P and 0.024 %S). Mechanical properties of the steel were obtained by Singh and Sanchez-Galvez [5] as follows: Young’s modulus E = 204.4 GPa, yield strength σY = 1430 MPa, ultimate tensile strength (UTS) σR = 1670 MPa and fracture toughness KIC = 119 MPam 1/2 . Fatigue tests were performed [5] under 1 Hz sinusoidal wave and R-ratio equal to 0.5 in both air and aggressive environment consisting of 1 g/l Ca(OH)2 + 1 g/l NaCl solution at free corrosion potential, and results were fitted to the Paris-Erdogan Laws [9] in the form: m d d a C K N   (1) obtaining the coefficients of the Paris Law for prestressing steel in both environments. With regard to Paris exponent m, experimental results were m = 2.27 for fatigue crack propagation in air and m = 0.70 in the case of Ca(OH)2+NaCl corrosion-fatigue, where a clear decrease in the m-exponent was observed in corrosion-fatigue in spite of the elevation of the curve via an increase of the C coefficient, from 1.78·10 -11 for fatigue crack propagation in air to 2.04·10 -8 in the case of Ca(OH)2+NaCl corrosion-fatigue (with the corresponding units for ΔK give in MPam 1/2 and da/dN in m/cycle). Numerical modelling To study how a crack propagates in the cross section of a round bar under tension cyclic loading, a computer program in Java language was developed to determine the geometrical evolution of the crack front. The basic hypotheses of the modelling consisted of assuming that the crack front can been modelled as an ellipse with centre on the bar surface [7] and the fatigue propagation takes place in a direction perpendicular to this crack front, following a Paris-Erdogan Law [9]. Every elliptical arc of the crack was divided in z segments with exactly the same length using the Simpson method to discretize the front. The point at the cylinder surface presents difficulties regarding the computation of the stress intensity factor (SIF) K because there is a plane stress state at the crack edge. After that, every single point was shifted according to Paris-Erdogan Law perpendicular to the front, so as to keep constant the maximum crack depth increment, Δa(max) ≡ max Δai. The advance of every front point, Δai, can be obtained from the maximum crack increment and the ratio of the dimensionless SIF Y,

  • Modeling of Surface Crack Advance in Round Wires Subjected to Cyclic Loading
    Journal of Astm International, 2012
    Co-Authors: Jesús Toribio, Juan-carlos Matos, Beatriz González, J. Escuadra
    Abstract:

    This paper shows the evolution of the surface crack front in round bars constituted of different materials (determined by the exponent m of the Paris Law), subjected to fatigue tension loading (with free ends) or fatigue bending loading. To this end, a numerical modeling was developed on the basis of a discretization of the crack front (characterized with elliptical shape) and the crack advance at each point perpendicular to such a front, according to a Paris-Erdogan Law, using a three-parameter stress intensity factor (SIF). Each analyzed case was characterized by the evolution of the semielliptical crack front, studying the progress with the relative crack depth a/D of the following three key variables: (i) crack aspect ratio a/b (relation between the semiaxes of the ellipse which defines the crack front); (ii) maximum dimensionless SIF; and (iii) minimum dimensionless SIF.

  • Environmentally-assisted fatigue crack growth in prestressing steel wires
    Materials Science, 2012
    Co-Authors: Jesús Toribio, Juan-carlos Matos, Beatriz González, J. Escuadra
    Abstract:

    We present the evolution of the surface crack front in prestressing reinforced-concrete steel wires subjected to fatigue in air and to corrosion fatigue in Ca(OH)_2 + NaCl. To this end, a numerical modeling was performed on the basis of discretization of the crack front (with elliptic shape) by considering that the crack advance at each point is perpendicular to the analyzed front according to the Paris–Erdogan Law and using a three-parameter solution for the stress intensity factor (SIF). Each analyzed case (a particular geometry of the initial crack) was characterized by the evolution of the aspect ratio of the semielliptic crack (ratio of the semiaxes of the ellipse) with the relative crack depth and by the variations of the maximum dimensionless SIF at the crack front.

János Lukács - One of the best experts on this subject based on the ideXlab platform.

  • Fatigue Crack Propagation Limit Curves for High Strength Steels and their Application for Engineering Critical Assessment Calculations
    Advanced Materials Research, 2014
    Co-Authors: János Lukács, Marcell Gáspár
    Abstract:

    There are different prescriptions containing fatigue crack propagation limit curves and rules for the prediction of the crack growth. The research work aimed (i) to determine fatigue crack propagation limit curves for high strength steels and their welded joints, based on the Paris-Erdogan Law; (ii) to use the determined limit curves for engineering critical assessment (ECA) calculations. Experiments were performed on different high strength steels and their welded joints; and the propagating cracks in the specimens represent the different possible locations of the real cracks in the structural elements. Fatigue crack growth tests were executed by ΔK-decreasing and constant load amplitude methods. The evaluation process consists of six steps, and by means of the selected values a statistical method can be proposed for determination of the limit curves. Engineering critical assessment calculations were performed on a welded structural element having crack like defects.

  • Fatigue crack propagation limit curves for metallic and non-metallic materials
    2013
    Co-Authors: János Lukács
    Abstract:

    There are different documents containing fatigue crack propagation curves and rules for the prediction of crack growth. The research work aimed to develop a new method for determination of fatigue crack propagation limit curves and determination of limit curves for different metallic materials (steels, austempered ductile iron, aluminium alloys) and their welded joints and non-metallic materials (ceramic, polymer, composite), under different loading conditions, based on statistical analysis of test results and the Paris-Erdogan Law. With the help of the characteristic values of threshold stress intensity factor range (∆Kth), two constants of Paris-Erdogan Law (C and n), fracture and fatigue fracture toughness (KIc and ∆Kfc) a new method can be proposed. The limit curves represent a compromise of rational risk and striving for safety.

  • Two Methods for Determination of Fatigue Crack Propagation Limit Curves and their Applicability for High Strength Steels
    2013
    Co-Authors: János Lukács
    Abstract:

    There are different documents containing fatigue crack propagation limit or design curves and rules for the prediction of crack growth. The research work aimed to characterise the fatigue crack propagation resistance of different steels using limit curves and determination of limit curves for different structural steels and high strength steels, and their welded joints, under different loading conditions, based on statistical analysis of test results and the Paris-Erdogan Law. With the help of the characteristic values of threshold stress intensity factor range ( Kth), two constants of Paris-Erdogan Law (C and n), and fatigue fracture toughness ( Kfc) two reliable methods – a simplified method and a two stages method – can be proposed. Our testing results were compared with the testing results can be found in the literature. The limit curves calculated by the new method represent a compromise of rational risk (not the most disadvantageous case is considered) and striving for safety (uncertainty is known).

  • Fatigue crack growth tests on type 321 austenitic stainless steel in corrosive environment and at elevated temperature
    Procedia Engineering, 2010
    Co-Authors: János Lukács
    Abstract:

    Abstract There are different documents and standards containing fatigue crack propagation limit or design curves and rules for the prediction of crack growth. The background of the curves and the calculations consist of two basic parts: statistical analysis of numerous fatigue crack propagation experiments and fatigue crack propagation Law. The research work aimed to measure basic data for limit curves on austenitic stainless steel (type 321), in corrosive environment and at elevated temperatures; and to determine the design curves based on statistical analysis of measured data and the Paris-Erdogan Law. Fatigue crack growth tests were performed on modified CT specimens in water solution (30 g CuSO4∗5H2O+10 g NaCl+3 g NaOH in 1000 ml water), at nominally 100 °C and 300 °C testing temperatures. The examinations were executed by constant load amplitude method, the stress ratio was R = 0 , 1 , and f = 20 Hz frequency was used during the whole tests. In order to study the hold time effect, fatigue crack growth tests were terminated and 3 hours hold time period was applied. The constants of the Paris-Erdogan Law were calculated and these values were compared with data can be found in the literature.

  • Fatigue Crack Propagation Limit Curves for Different Metallic and Non-Metallic Materials
    Materials Science Forum, 2009
    Co-Authors: János Lukács
    Abstract:

    There are different documents containing fatigue crack propagation curves and rules for the prediction of crack growth. The research work aimed to develop a new method for determination of fatigue crack propagation limit curves and determination of limit curves for different metallic materials (steels, austempered ductile iron, aluminium alloys) and their welded joints and non-metallic materials (ceramic, polymer, composite), under different loading conditions, based on statistical analysis of test results and the Paris-Erdogan Law. With the help of the characteristic values of threshold stress intensity factor range (∆Kth), two constants of Paris-Erdogan Law (C and n), fracture and fatigue fracture toughness (KIc and ∆Kfc) a new method can be proposed. The limit curves represent a compromise of rational risk and striving for safety.

Jesús Toribio - One of the best experts on this subject based on the ideXlab platform.

  • Numerical modelling of cracking path in round bars subjected to cyclic tension and bending
    International Journal of Fatigue, 2013
    Co-Authors: Jesús Toribio, Juan-carlos Matos, Beatriz González, J. Escuadra
    Abstract:

    Abstract This paper shows the evolution of the surface crack front in round bars constituted of different materials (determined by the exponent m of the Paris Law), subjected to fatigue tension loading (with free ends) or fatigue bending loading. To this end, a numerical modelling is developed on the basis of a discretization of the crack front (characterized by a semi-elliptical shape) and the crack advance at each point perpendicular to such a front, computed according to the Paris-Erdogan Law and by using a three-parameter stress intensity factor (SIF). For each of the considered case the evolution of the semi-elliptical crack front is analysed, studying the variation of the crack aspect ratio a / b (defined as the ratio between the semi-axes of the ellipse which defines the crack front) against the relative crack depth a / D . The obtained results show that the dimensionless SIF values along the crack front are quite higher under tension loading than in the case of bending loading. Thus, the risk of catastrophic failure is higher in the case of tensile loading (in relation to the less dangerous bending situation) if a local fracture criterion (on the basis of the maximum local SIF K along the crack front) is used, considering that fracture takes place when K reaches the material fracture toughness K C .

  • 056 Modelling of Crack Path Evolution in Round Bars under Cyclic Tension and Bending
    2013
    Co-Authors: Jesús Toribio, Beatriz González, J. C. Matos, J. Escuadra
    Abstract:

    ABSTRACT. This paper shows the evolution of the surface crack front in round bars constituted of different materials (determined by the exponent m of the Paris Law), subjected to fatigue tension loading (with free ends) or fatigue bending loading. To this end, a numerical modeling was developed on the basis of a discretization of the crack front (characterized as an ellipse) and the crack advance at each point perpendicular to such a front, according to a Paris-Erdogan Law, using a three-parameter stress intensity factor (SIF). Each analyzed case was characterized by the evolution of the semielliptical crack front, studying the progress with the relative crack depth a/D of the following three key variables: (i) crack aspect ratio a/b (relation between the semiaxes of the ellipse which defines the crack front); (ii) maximum dimensionless SIF; (iii) minimum dimensionless SIF.

  • Aspect ratio evolution in corrosion-fatigue cracking of high strength steel bars
    2013
    Co-Authors: Jesús Toribio, Juan-carlos Matos, Beatriz González, J. Escuadra
    Abstract:

    This paper shows the evolution of the surface crack front in prestressing steel wires subjected to fatigue in air and to corrosion-fatigue in Ca(OH)2+NaCl. To this end, a numerical modelling was made on the basis of a discretization of the crack front (characterized with elliptical shape), considering that the crack advance at each point is perpendicular to such a front according to a Paris-Erdogan Law, and using a three-parameter stress intensity factor (SIF). Each analyzed case (a particular initial crack geometry) was characterized by the evolution of the semielliptical crack aspect ratio (relation between the semiaxes of the ellipse) with the relative crack depth. Introduction The fatigue behaviour of cold drawn eutectoid steel, frequently used as reinforcement in prestressed concrete, has received attention in the past, both in air [1] and in aggressive environments [2-6]. NaCl corrosion-fatigue affects the fatigue performance of high strength steel by increasing the crack growth rate in relation to its value in inert environment [3,4], this effect being even higher if the environment is constituted by Ca(OH)2+NaCl [5]. When cylindrical rods (bars, wires, shafts...) are used, transverse cracking by fatigue usually takes place in the form of surface cracks with semielliptical shape [7]. Growth of surface cracks in round bars due to fatigue can be modelled using different criteria, e.g., prediction of the 90o intersecting angle of the crack with the surface or the iso-K criterion along the crack front [8]. Another criterion is based on the crack growth according to the Paris-Erdogan Law [9] considering the crack advance perpendicular to the crack front, assuming elliptic geometry for the growing crack [10,11] or avoiding the shape hypothesis, i.e., allowing the crack to grow with any shape [12]. Material This paper studies the corrosion-fatigue crack propagation in prestressing steel wires (chemical composition: 0.82 %C, 0.60 %Mn, 0.18 %Si, 0.010 %P and 0.024 %S). Mechanical properties of the steel were obtained by Singh and Sanchez-Galvez [5] as follows: Young’s modulus E = 204.4 GPa, yield strength σY = 1430 MPa, ultimate tensile strength (UTS) σR = 1670 MPa and fracture toughness KIC = 119 MPam 1/2 . Fatigue tests were performed [5] under 1 Hz sinusoidal wave and R-ratio equal to 0.5 in both air and aggressive environment consisting of 1 g/l Ca(OH)2 + 1 g/l NaCl solution at free corrosion potential, and results were fitted to the Paris-Erdogan Laws [9] in the form: m d d a C K N   (1) obtaining the coefficients of the Paris Law for prestressing steel in both environments. With regard to Paris exponent m, experimental results were m = 2.27 for fatigue crack propagation in air and m = 0.70 in the case of Ca(OH)2+NaCl corrosion-fatigue, where a clear decrease in the m-exponent was observed in corrosion-fatigue in spite of the elevation of the curve via an increase of the C coefficient, from 1.78·10 -11 for fatigue crack propagation in air to 2.04·10 -8 in the case of Ca(OH)2+NaCl corrosion-fatigue (with the corresponding units for ΔK give in MPam 1/2 and da/dN in m/cycle). Numerical modelling To study how a crack propagates in the cross section of a round bar under tension cyclic loading, a computer program in Java language was developed to determine the geometrical evolution of the crack front. The basic hypotheses of the modelling consisted of assuming that the crack front can been modelled as an ellipse with centre on the bar surface [7] and the fatigue propagation takes place in a direction perpendicular to this crack front, following a Paris-Erdogan Law [9]. Every elliptical arc of the crack was divided in z segments with exactly the same length using the Simpson method to discretize the front. The point at the cylinder surface presents difficulties regarding the computation of the stress intensity factor (SIF) K because there is a plane stress state at the crack edge. After that, every single point was shifted according to Paris-Erdogan Law perpendicular to the front, so as to keep constant the maximum crack depth increment, Δa(max) ≡ max Δai. The advance of every front point, Δai, can be obtained from the maximum crack increment and the ratio of the dimensionless SIF Y,

  • Modeling of Surface Crack Advance in Round Wires Subjected to Cyclic Loading
    Journal of Astm International, 2012
    Co-Authors: Jesús Toribio, Juan-carlos Matos, Beatriz González, J. Escuadra
    Abstract:

    This paper shows the evolution of the surface crack front in round bars constituted of different materials (determined by the exponent m of the Paris Law), subjected to fatigue tension loading (with free ends) or fatigue bending loading. To this end, a numerical modeling was developed on the basis of a discretization of the crack front (characterized with elliptical shape) and the crack advance at each point perpendicular to such a front, according to a Paris-Erdogan Law, using a three-parameter stress intensity factor (SIF). Each analyzed case was characterized by the evolution of the semielliptical crack front, studying the progress with the relative crack depth a/D of the following three key variables: (i) crack aspect ratio a/b (relation between the semiaxes of the ellipse which defines the crack front); (ii) maximum dimensionless SIF; and (iii) minimum dimensionless SIF.

  • Environmentally-assisted fatigue crack growth in prestressing steel wires
    Materials Science, 2012
    Co-Authors: Jesús Toribio, Juan-carlos Matos, Beatriz González, J. Escuadra
    Abstract:

    We present the evolution of the surface crack front in prestressing reinforced-concrete steel wires subjected to fatigue in air and to corrosion fatigue in Ca(OH)_2 + NaCl. To this end, a numerical modeling was performed on the basis of discretization of the crack front (with elliptic shape) by considering that the crack advance at each point is perpendicular to the analyzed front according to the Paris–Erdogan Law and using a three-parameter solution for the stress intensity factor (SIF). Each analyzed case (a particular geometry of the initial crack) was characterized by the evolution of the aspect ratio of the semielliptic crack (ratio of the semiaxes of the ellipse) with the relative crack depth and by the variations of the maximum dimensionless SIF at the crack front.

B. Muñoz-abella - One of the best experts on this subject based on the ideXlab platform.

  • Study of the propagation of concave semi-elliptical shaped breathing cracks in rotating shafts
    International Journal of Fatigue, 2019
    Co-Authors: P. Rubio, J. Bernal, L. Rubio, B. Muñoz-abella
    Abstract:

    Abstract When a cracked shaft rotates, the crack contained in it progressively opens and closes during a revolution. Accordingly, the behavior of the shaft becomes nonlinear. In this paper, the propagation of concave semi-elliptical shaped cracks contained in rotating shafts has been studied considering the nonlinear effect of the breathing crack. To study the propagation, we propose an integration algorithm based on the Paris-Erdogan Law which allows determining the crack shape evolution of concave breathing cracks in rotating shafts. The Stress Intensity Factor used by the algorithm to analyze the propagation has been computed using the four parametric expression for concave cracks proposed by the authors in a previous work. By now, it has not been found in the literature propagation studies of concave surface cracks in rotating shafts that consider the breathing mechanism of the crack.

  • Propagation of surface breathing cracks in shafts under quasi-static rotary bending
    Nonlinear Dynamics, 2017
    Co-Authors: P. Rubio, L. Rubio, B. Muñoz-abella
    Abstract:

    Due to cyclic loading conditions, cracks frequently appear in rotating machines. The propagation of fatigue cracks in shafts can provoke severe accidents with high risks of people. During the rotation of the cracked shaft, the crack opens and closes in what is called the breathing mechanism, and consequently the behavior of the shaft becomes nonlinear. In the present paper, the propagation of a semi-elliptical crack contained in a rotating shaft has been analyzed considering the nonlinear effect of the crack as the shaft rotates. To this end, an integration algorithm which allows obtaining the crack front evolution has been improved. This procedure uses the Paris-Erdogan Law to determine the advance at a few points along the crack front and uses the general expression proposed previously by the authors that gives the Stress Intensity Factor along the crack front of an elliptical crack in a rotating shaft in terms of the crack depth ratio, the crack aspect ratio, the relative position on the front and the angle of rotation. Several initial semi-elliptical surface crack geometries have been analyzed. For each geometry, the evolution of the crack front has been studied, analyzing the variation of the crack aspect ratio against the crack depth ratio. By the moment, no fatigue growth analyses of surface cracks in rotating shafts, taking into account the breathing mechanism and considering the nonlinear behavior of the shaft, have been found in the literature.

Andrea Carpinteri - One of the best experts on this subject based on the ideXlab platform.

  • Fractal Modelling of Kinked Cracks and its Implications for their Fatigue Propagation in Concrete
    2013
    Co-Authors: Andrea Carpinteri, Sabrina Vantadori, Andrea Spagnoli, Danilo Viappiani
    Abstract:

    Threshold condition and rate of fatigue crack growth appear to besignificantly affected by the degree of deflection of cracks. In this paper, the reduction ofthe fatigue crack growth rate for a so-called ‘periodically-kinked crack’ as compared tothat for a straight counterpart is quantified via the Paris-Erdogan Law modifiedaccording to some simple theoretical arguments. It is shown that such a reductionincreases as the value of the kinking angle increases. Then, a so-called ‘continuouslykinkedcrack’ (the kink length tends to zero) is considered and modelled as a self-similarinvasive fractal curve. Using the Richardson’s expression, the fractal dimension of thecrack is expressed as a function of the kinking angle. It is shown that the fatigue crackgrowth rate in the Paris range depends not only on the above fractal dimension and inturn on the kinking angle, but also on the crack length. Some experimental results relatedto concrete and showing a crack size effect on the fatigue crack growth rate are analysed.

  • Sickle-shaped cracks in metallic round bars under cyclic eccentric axial loading
    International Journal of Fatigue, 2009
    Co-Authors: Andrea Carpinteri, Sabrina Vantadori
    Abstract:

    Abstract In the present paper, the fatigue propagation of an initial sickle-shaped surface crack in a metallic round bar under eccentric axial loading acting perpendicular to the crack plane is examined. Firstly, the stress-intensity factor (SIF) along the crack front is determined through a three-dimensional finite element analysis and the one-quarter point displacement method, for different values of the loading eccentricity. Then, the fatigue behaviour of the cracked bar is numerically analysed by a step-by-step procedure based on the Paris–Erdogan Law. The results are plotted in terms of crack paths, intersection angle and crack depth evolution, by varying the loading eccentricity.

  • Influence of the crack morphology on the fatigue crack growth rate: A continuously-kinked crack model based on fractals
    Engineering Fracture Mechanics, 2008
    Co-Authors: Andrea Carpinteri, Sabrina Vantadori, Andrea Spagnoli, Danilo Viappiani
    Abstract:

    Abstract Threshold condition and rate of fatigue crack growth appear to be significantly affected by the degree of deflection of cracks. In the present paper, the reduction of the fatigue crack growth rate for a so-called ‘periodically-kinked crack’ as compared to that for a straight counterpart is quantified via the Paris–Erdogan Law modified according to some simple theoretical arguments. It is shown that such a reduction increases as the value of the kinking angle increases. Then, a so-called ‘continuously-kinked crack’ (the kink length tends to zero) is considered and modelled as a self-similar invasive fractal curve. The sequence of kinking angles in the crack is such that the fatigue crack path is ‘on average’ straight. Using the Richardson’s expression for self-similar fractals, the fractal dimension of the crack is expressed as a function of the kinking angle. It is shown that the fatigue crack growth rate in the Paris range depends not only on the above fractal dimension and in turn on the kinking angle, but also, in an explicit fashion, on the crack length. Some experimental results related to concrete and showing a crack size effect on the fatigue crack growth rate are analysed.

  • Part-through cracks in round bars under cyclic combined axial and bending loading
    International Journal of Fatigue, 1999
    Co-Authors: Andrea Carpinteri, Roberto Brighenti
    Abstract:

    Abstract Fatigue fracture mechanics concepts can usefully be applied to analyse the propagation of surface cracks in metallic round bars under cyclic combined axial and bending loading. A finite element analysis is carried out to determine the stress field in the case of an elliptical-arc part-through fLaw, the aspect ratio, α = a b , of which ranges from 0.0 to 1.2 (α = 0.0 corresponds to the straight front, while α = 1.0 represents the circular-arc front). The fatigue crack growth is numerically examined by means of a two-parameter model based on the Paris-Erdogan Law. The propagation paths for different material properties and loading conditions converge to an inclined asymptote in the diagram of α against ξ, where ξ is the relative crack depth of the deepest point on the crack front. Experimental data and theoretical fracture energy considerations reported in the literature validate the results obtained through the above model.

  • Fatigue growth of edge fLaws in cylindrical bars
    Strength of Materials, 1995
    Co-Authors: Andrea Carpinteri, C. Majorana
    Abstract:

    The behavior of an edge fLaw in a cylindrical bar under constant amplitude cyclic axial or bending loading is examined. In particular, the surface fLaw is assumed to be of elliptical-arc shape with aspect ratio a_el/b_el. The relative crack depth ζ of the fLaw's deepest point is equal to the ratio between the maximum crack depth a and the bar diameter D. The aspect ratio of the initial fLaw is made to vary from 0.0 (straight front) to 1.0 (circular-arc front), while the parameter a_el/a is assumed to be equal to a value between 1.0 and ∞. The fatigue crack growth is analyzed by means of the Paris-Erdogan Law, with the stress-intensity factor along the crack front obtained through a finite element analysis. It is concluded that the edge fLaws considered follow preferred propagation patterns which tend to converge to an inclined asymptotic plane in the diagram of a_ellb_el against a_el/a and Z