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Author: Mehmet Gkhan Gken Publisher: LAP Lambert Academic Publishing ISBN: 9783838357911 Category : Languages : en Pages : 84
Book Description
In spite of the fact that the use of contact elements in modeling crack surface contact, and thus in modeling of crack closure is inherently natural, almost no effort to incorporate it in the finite element analysis of fatigue crack growth has been reported in the literature. The traditional method is based on placing truss elements on the crack surface nodes In this research contact elements are used to model crack surface contact and similar to mentioned method the determination of crack opening stress is accomplished by monitoring the state of contact elements during incrementally applied loading. Instead of determining crack opening stress of every load cycle, an algorithm that makes it possible to find crack opening stress at predetermined load cycle intervals is developed. With the developed algorithm it was possible to analyze crack closure behavior during a larger number of load cycles with less execution time. Due to simulation of relatively high number of load cycles, final stabilization of crack opening stress values after a subsequent decay in the initially "stabilized" opening stress values is observed.
Author: Mehmet Gkhan Gken Publisher: LAP Lambert Academic Publishing ISBN: 9783838357911 Category : Languages : en Pages : 84
Book Description
In spite of the fact that the use of contact elements in modeling crack surface contact, and thus in modeling of crack closure is inherently natural, almost no effort to incorporate it in the finite element analysis of fatigue crack growth has been reported in the literature. The traditional method is based on placing truss elements on the crack surface nodes In this research contact elements are used to model crack surface contact and similar to mentioned method the determination of crack opening stress is accomplished by monitoring the state of contact elements during incrementally applied loading. Instead of determining crack opening stress of every load cycle, an algorithm that makes it possible to find crack opening stress at predetermined load cycle intervals is developed. With the developed algorithm it was possible to analyze crack closure behavior during a larger number of load cycles with less execution time. Due to simulation of relatively high number of load cycles, final stabilization of crack opening stress values after a subsequent decay in the initially "stabilized" opening stress values is observed.
Author: Jeffrey David Skinner Publisher: ISBN: Category : Finite element method Languages : en Pages :
Book Description
[3] The finite element predicted opening levels were in all cases significantly lower than those reported experimentally, however, similar trends in both crack opening level profile along the crack front, and opening level variations with crack growth were shown.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
Elastic-plastic finite element analyses were performed to predict the crack opening level profiles in semi-elliptical surface cracks. A script was written to use the commercial finite element code ANSYS to predict opening levels in cracked geometries. The functionality of the scripts was verified by comparing predicted opening levels in two and three-dimensional center-cracked geometries to experimental results. In addition, a parameter study was performed in which various aspects of the modeling routine were modified. This included a mesh refinement study as well as a study into the effect of a strain hardening material. The main focus of the current research, however, is to compare finite element predicted opening levels with published opening levels determined experimentally. Due to the complexities and long run-times involved with these models, no attempt was made at growing the cracks from initial length to final length. Instead, discrete crack lengths at which experimental opening levels were published were instead used. Also, no attempt was made to predict the crack aspect ratio evolution. The finite element predicted opening levels were in all cases significantly lower than those reported experimentally, however, similar trends in both crack opening level profile along the crack front, and opening level variations with crack growth were shown.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
Finite element analyses are frequently used to model growing fatigue cracks and the associated plasticity-induced crack closure. Two-dimensional, elastic-perfectly plastic finite element analyses of middle-crack tension (M(T)), bend (SEB), and compact tension (C(T)) geometries were conducted to study fatigue crack closure and to calculate the crack opening values under plane-strain and plane-stress conditions. The loading was selected to give the same maximum stress intensity factor in both geometries, and thus similar initial forward plastic zone sizes. Mesh refinement studies were performed on all geometries with various element types. For the C(T) geometry, negligible crack opening loads under plane-strain conditions were observed. In contrast, for the M(T) specimen, the plane-strain crack opening stresses were found to be significantly larger. This difference was shown to be a consequence of in-plane constraint. Under plane-stress conditions, it was found that the in-plane constraint has negligible effect, such that the opening values are approximately the same for the C(T), SEB, and M(T) specimens. Next, the crack opening values of the C(T), SEB and M(T) specimens were compared under various stress levels and load ratios. The effect of a highly refined mesh on crack opening values was noted and significantly lower crack opening values than those reported in literature were found. A new methodology is presented to calculate crack opening values in planar geometries using the crack surface nodal force distribution under minimum loading as determined from finite element analyses. The calculated crack opening values are compared with values obtained using finite element analysis and more conventional crack opening assessment methodologies. It is shown that the new method is independent of loading increment, integration method (normal and reduced integration), and crack opening assessment location. The compared opening values were in good agreement with strip-yield.
Author: Marcos Lugo Publisher: ISBN: Category : Aluminum alloys Languages : en Pages :
Book Description
From its discovery, crack closure was recognized as a key aspect in understanding the fatigue crack growth process. Considering the condition of plane stress, a vast amount of research has been conducted experimentally, analytically, and numerically to understand the complex process of fatigue crack growth and crack closure. Nonzero crack opening stress values are routinely observed, and it seems that there is a general agreement regarding the incidence of the phenomenon under plane stress. However, investigations regarding crack closure under plane strain conditions are less abundant. Moreover, the existence of crack closure under the plane strain state of the stress has been questioned. The importance of accurate measurements of closure to predict adequately fatigue crack growth rates should not be underestimated. Models employed to predict fatigue crack growth rates rely on plasticity-induced crack closure concepts, and the validity of plasticity-induced crack closure depends on crack closure measurements. Crack closure measurements can be performed with Elber's Method, the ASTM standard (Compliance offset method), or it may be done alternatively by the compliance ratio (CR) or the adjusted compliance ratio method (ACR). In this research, a small scale yielding two-parameter modified boundary layer analysis is performed to study the occurrence of plasticity-induced fatigue crack closure under constant amplitude loading and plane strain conditions. A wide range of T-stresses and KI levels are considered in the finite element analysis with the purpose of exploring the behavior of the crack opening stress. Crack closure was observed for some values of T-stress. Other values of T-stress resulted in an absence of closure under steady state conditions. In addition, an elastic-plastic finite element model was used to simulate a growing fatigue crack with WARP3D software. The computed displacements were used to determine the effective stress intensity factor range [delta]Keff with the ASTM standard compliance offset approach, the (CR) method, and the (ACR) method. Finally, measurement location effects on ACR and the ability of ACR method to remove residuals stresses were investigated.
Author: E. Bednarz Publisher: ISBN: Category : Crack closure Languages : en Pages : 19
Book Description
Plasticity induced crack closure and its effect on the fatigue growth of short cracks is investigated numerically. A plane stress finite-element analysis is used to simulate a nonpropagating crack of length 65 ?m in a single-edge-cracked specimen under two stress levels and two values of stress ratio R. A comparison of results is then made with a propagating crack of an initial length of 25 ?m, which is allowed to grow to a final length of 65 ?m. R values of 0.1 and -1.0 with stress levels of 60 and 90% of the yield stress for the material are considered. The plastic zone size for each case studied is approximately equal to the initial crack length, which provides conditions characteristic of short cracks.
Author: NA. Fleck Publisher: ISBN: Category : Crack closure Languages : en Pages : 23
Book Description
An elastic-perfectly plastic finite-element analysis has been conducted of plasticity-induced crack closure under plane strain conditions. At a load ratio R ( = Kmin/Kmax) of zero, crack closure was observed in a center-cracked panel but not in a bend specimen. Crack closure in the center-cracked panel occurred for a transient period of growth as the crack evolved from the state of a stationary crack to the steady state of a growing fatigue crack. The influence of specimen geometry upon closure response was rationalized in terms of the "T-stress." This stress is the nonsingular constant second term in the near tip series expansion of the normal stress parallel to the crack plane. No closure was observed in the center-cracked panel for R ? 0.3. The crack opening response and plastic zone distribution of a growing fatigue crack were compared with those of a cyclically loaded stationary crack and a statically loaded tearing crack. Some of the features of the solution for the growing fatigue crack were similar to the solution for a stationary crack, while other features bore more resemblance to those of a tearing crack.
Author: Mehmet Gkhan Gken
Author: Mehmet Gkhan Gken
Author: Jeffrey David Skinner
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Author: 
Author: Marcos Lugo
Author: N. A. Fleck
Author: E. Bednarz
Author: 
Author: NA. Fleck
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