Development of a Macrostructural Model for Studying the Combined Effects of Plasticity and Roughness Induced Crack Closure PDF Download
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Author: Justin Mandel Crapps Publisher: ISBN: Category : Alloys Languages : en Pages :
Book Description
A weight function based modified strip-yield model is adapted to include the mode I effects of roughness induced crack closure. The weight function methodology is verified for arbitrary mixed mode loading conditions under load levels experienced in fatigue crack growth. A rough crack geometry is simulated as a sine wave fitted to a sawtooth defined by an asperity angle and period. Additional mode I crack closure due to mode II sliding of crack faces is calculated and incorporated into the strip-yield model by lengthening and shortening the crack face elements. Simulations of fatigue crack growth using the newly developed model are examined via a design and analysis of computer experiments. The effects of model parameters are identified. Combined roughness and plasticity induced crack closure for long cracks is studied.
Author: Justin Mandel Crapps Publisher: ISBN: Category : Alloys Languages : en Pages :
Book Description
A weight function based modified strip-yield model is adapted to include the mode I effects of roughness induced crack closure. The weight function methodology is verified for arbitrary mixed mode loading conditions under load levels experienced in fatigue crack growth. A rough crack geometry is simulated as a sine wave fitted to a sawtooth defined by an asperity angle and period. Additional mode I crack closure due to mode II sliding of crack faces is calculated and incorporated into the strip-yield model by lengthening and shortening the crack face elements. Simulations of fatigue crack growth using the newly developed model are examined via a design and analysis of computer experiments. The effects of model parameters are identified. Combined roughness and plasticity induced crack closure for long cracks is studied.
Author: N. Chen Publisher: ISBN: Category : Crack closure Languages : en Pages : 17
Book Description
A 2-D analytical model of the combined effects of plasticity-induced crack closure (PICC) and roughness-induced crack closure (RICC) has been developed. A zigzag crack growth path was employed to simulate surface roughness. The two opposing fatigue crack surfaces were translated by the mixed-mode displacement occurring near the deflected crack tip. This translation caused a mechanical interference of the opposing crack surfaces as the crack closed, that is, caused RICC. The gradual transition from RICC- to PICC-dominated crack closure was handled naturally by this model. The influence of the geometrical features of the surface roughness, R-ratio, and the cyclic load range on RICC were examined using the PICC-RICC model. The effect of microstructure on the RICC was examined. Despite the simple, 2-D nature of the model, it predicted the trends of experimental data on near-threshold crack growth behavior reported in the literature.
Author: National Aeronautics and Space Administration (NASA) Publisher: Createspace Independent Publishing Platform ISBN: 9781721572359 Category : Languages : en Pages : 32
Book Description
The results of an analytical closure model that considers contributions and interactions between plasticity-, roughness-, and oxide-induced crack closure mechanisms are presented and compared with experimental data. The analytical model is shown to provide a good description of the combined influences of crack roughness, oxide debris, and plasticity in the near-threshold regime. Furthermore, analytical results indicate that closure mechanisms interact in a non-linear manner such that the total amount of closure is not the sum of closure contributions for each mechanism. Newman, John A. and Riddell, William T. and Piascik, Robert S. Langley Research Center NASA/TM-2003-211755, NAS 1.15:211755, L-18207, ARL-TR-2774
Author: National Aeronautics and Space Administration (NASA) Publisher: Createspace Independent Publishing Platform ISBN: 9781721572137 Category : Languages : en Pages : 34
Book Description
A fatigue crack closure model is developed that includes interactions between the three closure mechanisms most likely to occur at threshold; plasticity, roughness, and oxide. This model, herein referred to as the CROP model (for Closure, Roughness, Oxide, and Plasticity), also includes the effects of out-of plane cracking and multi-axial loading. These features make the CROP closure model uniquely suited for, but not limited to, threshold applications. Rough cracks are idealized here as two-dimensional sawtooths, whose geometry induces mixed-mode crack- tip stresses. Continuum mechanics and crack-tip dislocation concepts are combined to relate crack face displacements to crack-tip loads. Geometric criteria are used to determine closure loads from crack-face displacements. Finite element results, used to verify model predictions, provide critical information about the locations where crack closure occurs. Newman, John A. and Riddell, William T. and Piascik, Robert S. Langley Research Center NASA/TM-2003-212402, L-18279, NAS 1.15:212402, ARL-TR-2959
Author: J. C. Newman Publisher: ISBN: Category : Fracture mechanics Languages : en Pages : 26
Book Description
An assessment of the plasticity-induced crack-closure concept is made, in light of the questions that have been raised on the validity of the concept, and the assumptions that have been made concerning crack-tip damage below the crack-opening stress. The impact of using other crack-tip parameters, such as the cyclic crack-tip displacement, to model crack-growth rate behavior was studied. Crack-growth simulations, using a crack-closure model, showed a close relation between traditional [delta]K[sub eff] and the cyclic crack-tip displacement ([delta][Dirac delta function][sub eff]) for an aluminium alloy and a steel. Evaluations of the cyclic hysteresis energy demonstrated that the cyclic plastic damage below the crack-opening stress was negligible in the Paris crack-growth regime. Some of the standard and newly proposed remote measurement methods to determine the "effective" crack-tip driving parameter were evaluated on middle-crack tension specimens. A potential source of the K[sub max] effect on crack-growth rates was studied on an aluminum alloy. Results showed that the ratio of K[sub max] to K[sub c] had a strong effect on crack-growth rates at high stress ratios and at low stress ratios for very high stress levels. The crack-closure concept and the traditional crack-growth rate equations were able to correlate and predict crack-growth rates under these extreme conditions.
Author: JC. Newman Publisher: ISBN: Category : Constraint Languages : en Pages : 17
Book Description
An assessment of the plasticity-induced crack closure concept is made, in light of some of the questions that have been raised on the validity of the concept, and the assumptions that have been made concerning crack-tip damage below the crack-opening stress. The impact of using other crack-tip parameters, such as the cyclic crack-tip displacement or cyclic crack-tip hysteresis energy, to model crack-growth rate behavior was studied. Crack-growth simulations using the modified Dugdale crack closure model showed a close relation between traditional ?Keff and the cyclic crack-tip displacement (??eff) for an aluminum alloy and a steel over a wide range in stress ratios. Evaluations of the cyclic hysteresis energy demonstrated that the cyclic plastic damage below the crack-opening stress was negligible in the Paris crack-growth regime. Some of the standard and newly proposed remote measurement methods to determine crack-opening stresses and the "effective" crack-tip driving parameter were evaluated from crack-growth simulations made on middle-crack tension specimens. Here, analyses were conducted under both constant-amplitude and single-spike-overload conditions. A potential source of the Kmax effect on crack-growth rates was studied at high stress ratios and at high stress levels for an aluminum alloy. Results showed that the ratio of Kmaxto Kc had a strong effect on crack-growth rates at high stress ratios and at low stress ratios for very high stress levels. The crack-closure concept and the traditional crack-growth rate equations were able to correlate and predict crack-growth rates under these extreme conditions.
Author: Justin Mandel Crapps
Author: Justin Mandel Crapps
Author: N. Chen
Author: Nong Chen
Author: National Aeronautics and Space Administration (NASA)
Author: National Aeronautics and Space Administration (NASA)
Author: James C. Newman (Jr.)
Author: J. C. Newman
Author: JC. Newman
Author: John A. Newman
Author: