Mechanics of Fatigue Crack Closure PDF Download
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Author: Wolf Elber
Publisher: ASTM International
ISBN: 0803109962
Category : Fracture mechanics
Languages : en
Pages : 671
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Book Description
Author: Wolf Elber
Publisher: ASTM International
ISBN: 0803109962
Category : Fracture mechanics
Languages : en
Pages : 671
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Book Description
Author: CD. Carman
Publisher:
ISBN:
Category : Crack closure
Languages : en
Pages : 8
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Book Description
Fatigue crack delay behavior at high stress ratio caused by single peak overloads was investigated in two thicknesses of 7475-T731 aluminum alloy. Crack closure was measured in middle crack tension specimens with a crack-tip opening displacement gage located one-half of the specimen thickness behind the crack tip. Five overload ratios from 1.23 to 1.5 were investigated. The stress ratio was 0.7. Closure measurements indicated no closure occurred before or throughout the overload plastic zone following the overload. This was further substantiated by comparing the specimen compliance following the overload with the compliance of a low R ratio test when the crack was fully open. Scanning electron microscope studies revealed that crack tunneling and possibly reinitiation of the crack occurred, most likely a result of crack-tip blunting. The number of delay cycles was greater for the thinner mixed mode stress state specimen than for the thicker plane strain stress state specimen, which is similar to low R ratio test results and may be due to a larger plastic zone for the mixed mode case.
Author: Y. Yamada
Publisher:
ISBN:
Category : Chronic fatigue syndrome
Languages : en
Pages : 17
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Book Description
Fatigue-crack-growth-rate tests on compact specimens have been made on a variety of materials (2024-T3, 2324-T39, 7050-T7451, 4340 steel, and Inconel-718) over a wide range in stress ratios from 0.1 to 0.9 (and 0.95 in some cases) and several Kmax test conditions. Test data has been generated from threshold to near fracture using the compression precracking constant amplitude or compression precracking load reduction test methods in the threshold regime; and constant-amplitude loading at higher rates. A remote back-face strain (BFS) gage was used to monitor crack growth and to measure crack-opening loads. Local strain gages were also placed along and slightly off (about one-half thickness) the anticipated crack path to measure crack-opening loads. Elber's load-against-reduced-strain method was used to determine crack-opening loads by means of visual inspection (equivalent to a 0 % compliance offset). For a particular material, the BFS and local strain gages produced essentially the same crack-opening loads at low stress ratio (R = 0.1) conditions. But at high stress ratios (R >= 0.7) and Kmax test conditions, the local gages produced significantly higher crack-opening loads than the BFS gage in the threshold and near-threshold regimes. Previous research had proposed that high stress ratios (R >= 0.7) and Kmax test conditions produce closure-free conditions based on crack-mouth-opening-displacement or BFS gages, and plasticity-induced crack-closure modeling. However, crack closure under high stress ratios (R >= 0.7) and Kmax test conditions is attributed to residual-plastic deformations, crack-surface roughness, and/or fretting-debris. From local crack-opening load measurements, the effective stress-intensity-factor range (DKeff) appears to be uniquely related to the crack-growth rate in the threshold and near-threshold regimes.
Author: R. Craig McClung
Publisher: ASTM International
ISBN: 0803126115
Category : Fracture mechanics
Languages : en
Pages : 487
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Book Description
Author: J. C. Newman
Publisher: ASTM International
ISBN: 0803126247
Category : Fatigue
Languages : en
Pages : 436
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Book Description
Annotation Contains 24 papers from the November, 1998 symposium of the same name, sponsored by the ASTM Committee E8 on Fatigue and Fracture, and presented by Newman and Piascik (both of the NASA Langley Research Center). The papers focus on such areas as fatigue-crack growth threshold mechanisms, loading and specimen-type effects, analyses of fatigue-crack-growth-threshold behavior, and applications of threshold concepts and endurance limits to aerospace and structural materials. Annotation copyrighted by Book News, Inc., Portland, OR.
Author: I. Soya
Publisher:
ISBN:
Category : Crack closure
Languages : en
Pages : 16
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Book Description
Fatigue crack propagation tests were performed on a high-strength steel with yield strength of 598 MPa under various stress ratios. A fatigue crack opening model, which contains both the effects of R and ?K, was investigated based upon the cyclic elasto-plastic finite-element analysis (FEA) and the fracture mechanics approach with the small-scale yielding concept. Assuming the existence of the residual deformation in the wake of a crack, the crack opening stress-intensity factor can be calculated as the value at which the fatigue crack opening displacement becomes zero. Using this model, how R and ?K affect U was investigated. The resultant formula for U contains two parameters, one for the plastic deformation at a crack tip, and the other for the oxide and the roughness in a fatigue crack. The effective stressintensity factor range, based on the measurements of crack opening loads, gives the same crack propagation behavior for various stress ratios. It is observed in experiments, however, that U depends on the stress ratio R and the stress-intensity factor range ?K. The model successfully explains the experimental results. The fatigue crack propagation behavior under various stress ratios is described by the formula with five parameters, which can be obtained with only one specimen. The predicted crack propagation rates and threshold stress-intensity factor range agreed with empirical results. Therefore, the formula derived from this model may be applied well to the evaluation of fatigue crack extension.
Author: J. C. Newman (Jr)
Publisher:
ISBN:
Category :
Languages : en
Pages : 36
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Book Description
Author: William T. Riddell
Publisher:
ISBN:
Category : Aluminum alloys
Languages : en
Pages : 24
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Author: T. Nicholas
Publisher:
ISBN:
Category : Composite materials
Languages : en
Pages : 16
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Book Description
In the present study, the fatigue crack growth behavior of a near-?, ?-processed titanium alloy, Ti-1100, was investigated with the objective of assessing the influence of crack closure and stress ratio on fatigue threshold. Measurement of the crack-opening load in single-edge tension [SE(T)] specimens was made by near-tip strain gage and DCPD methods. Fatigue threshold stress intensity ranges, ?Kth, determined under constant stress ratio and constant maximum stress intensity, variable stress ratio conditions indicate almost identical values for R above 0.5. It is postulated that while crack closure in the wake of the crack tip is responsible for the no-growth condition in the former case, lack of sufficient damage accumulation at the crack tip as a consequence of the formation of an insignificant reversed plastic zone and large planar slip band formations surrounding the crack tip appears to be responsible for no growth in the latter case. The use of an effective stress intensity based on closure data consolidates most of the threshold data, indicating the independence of the fatigue crack growth data to mean stress or R.
Author: F. K. Haake
Publisher:
ISBN:
Category : Gas-turbines
Languages : en
Pages : 120
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Book Description
