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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: 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: 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: 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: N. Ranganathan Publisher: ISBN: Category : Block load tests Languages : en Pages : 25
Book Description
The fatigue crack growth behavior of the aluminum alloy 2024 is analyzed using the crack closure and an energy-based concept. The different test conditions studied include load ratio and environmental effects, crack growth retardation following a single overload, and crack propagation under block load tests. Crack opening loads using the compliance technique permit the effect of load ratio to be taken into account. After an overload, in the deceleration phase, the evolution of the crack opening load is not compatible with that of the crack growth rate. The measured crack opening levels under constant-amplitude loading conditions are comparable to those predicted under plane strain conditions for moderate ?K levels. It is shown that most of the effects usually attributed to closure can be successfully explained using energy concepts. In particular, it is shown that there exists a linear relationship between the crack growth rate and the energy dissipated per cycle at high growth rates, which is valid for both the environments studied, and it corresponds to a crack growth mechanism characterized by striation formation during each cycle. For lower growth rates a power law relationship can be proposed between these two parameters. The above-mentioned linear relationship holds also for the block loading conditions based on total energy dissipated per block. Certain experimental facts bring out the effect of closure on the energy dissipated. It is further shown that the possible existence of a mixed (Mode I and Mode II) mode crack opening at the crack tip has to be taken into account to correctly evaluate the energy dissipated near the crack tip.
Author: Kenneth Reifsnider Publisher: Woodhead Publishing ISBN: 012818261X Category : Technology & Engineering Languages : en Pages : 466
Book Description
Durability of Composite Systems meets the challenge of defining these precepts and requirements, from first principles, to applications in a diverse selection of technical fields selected to form a corpus of concepts and methodologies that define the field of durability in composite material systems as a modern discipline. That discipline includes not only the classical rigor of mechanics, physics and chemistry, but also the critical elements of thermodynamics, data analytics, and statistical uncertainty quantification as well as other requirements of the modern subject. This book provides a comprehensive summary of the field, suited to both reference and instructional use. It will be essential reading for academic and industrial researchers, materials scientists and engineers and all those working in the design, analysis and manufacture of composite material systems. - Makes essential direct and detailed connections to modern concepts and methodologies, such as machine learning, systems controls, sustainable and resilient systems, and additive manufacturing - Provides a careful balance between theory and practice so that presentations of details of methodology and philosophy are always driven by a context of applications and examples - Condenses selected information regarding the durability of composite materials in a wide spectrum of applications in the automotive, wind energy, civil engineering, medical devices, electrical systems, aerospace and nuclear fields
Author: NA. Fleck
Author: NA. Fleck
Author: Norman A. Fleck
Author: Wolf Elber
Author: N. A. Fleck
Author: R. Craig McClung
Author: Marcos Lugo
Author: James C. Newman (Jr.)
Author: 
Author: N. Ranganathan
Author: Kenneth Reifsnider