Crack layer analysis of fatigue fracture in a metastable titanium alloy

Mostafa, I.; Welsch, G.; Moet, A.; Chudnovsky, A.

doi:10.1016/0921-5093(89)90201-3

Cited by 6 publications

(5 citation statements)

References 12 publications

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“…This demonstrates the constancy of 7* and gives remarkable support for considering 7* as a material constant. In addition, the value of 7* obtained through CL analysis is in excellent agreement with the computed value of the specific energy of the slip lines which were recognized as the dominant toughening mechanism [20]. The dissipative coefficient r, on the other hand, has different values at different stress levels (Table II and Fig.…”

Section: Evaluation Of Fl and 7*supporting

confidence: 68%

“…Previous microscopical work on the fracture surface of fatigue-broken specimens of the same Ti-! 5-3 alloy showed that microcracking exists across the specimen's thickness [20]. Assuming that a microcrack lies on one plane, the total area of microcracks per unit volume in m2/m 3 was taken as the product of their total length, per unit area, multiplied by the thickness of the specimen.…”

Section: Mechanisms Of Crack Tip Damagementioning

confidence: 99%

“…lb). Therefore, the ERR was evaluated experimentally using the evolution of the load displacement curves [20,21]. Figure 8 shows the experimentally measured energy release rates for crack propagation under different applied stresses.…”

Section: Energy Release Ratementioning

confidence: 99%

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The specific enthalpy of fracture for beta Ti-15-3 alloy

1992

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Fatigue crack propagation (FCP) experiments were conducted on beta Ti-15-3 alloy under various loading conditions to examine the constancy of the specific enthalpy for fracture, advanced by the Crack Layer (CL) theory as a material parameter characteristic of its intrinsic toughness. The energy release rate and the irreversible work were determined from load-displacement curves during crack propagation. Microscopic and diffraction analyses were conducted to identify the damage mechanisms ahead of the crack tip. A damage zone whose geometry exhibited plane strain character at the initial stage of crack propagation was observed optically. The damage zone transformed into plane stress configuration when the crack reached half its critical length. Damage mechanisms involved slip lines and microcracking which is believed to ensue from intense accumulation of slip processes. The magnitude of microcracking became more weighty as the crack moved deeper into plane stress dominance. The damage preceding crack advance was quantitatively assessed as the 'crack resistance moment' which is the volume of transformed material per unit crack extension. Application of the CL theory to the data generated under a wide range of applied stress levels gave rise to a constant value of the specific enthalpy of fracture, 20 MJ/m 3. This value is in close agreement with the specific energy of slip lines computed from microstructural considerations.

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Section: Evaluation Of Fl and 7*supporting

confidence: 68%

Section: Mechanisms Of Crack Tip Damagementioning

confidence: 99%

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The specific enthalpy of fracture for beta Ti-15-3 alloy

1992

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“…Determination of the crack length by the compliance method is also uncertain due to the nonlinearity of the unloading curve and the increase in specimen compliance created by the damage zone ahead of the crack tip . These factors indicate the necessity of developing a plane strain fracture toughness test for thin specimens .Plane strain fracture has been previously obtained in very thin specimens by using low load fatigue conditions [4,5] . In this report, such a method to obtain plane strain fracture is combined with a modified Begley and Landes energy analysis technique [6] to deduce the critical energy release rate (J,,,) in thin polyethylene specimens .…”

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confidence: 99%

“…Plane strain fracture has been previously obtained in very thin specimens by using low load fatigue conditions [4,5] . In this report, such a method to obtain plane strain fracture is combined with a modified Begley and Landes energy analysis technique [6] to deduce the critical energy release rate (J,,,) in thin polyethylene specimens .…”

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confidence: 99%

Evaluation of J1C for thin polyethylene specimens

1991

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Fracture toughness testing of polymers is required to estimate the material's fracture resistance when used in load bearing structures . One of the most commonly used fracture toughness tests, the American Society for Testing and Materials (ASTM) standard E813 [1], which was developed for metals but is also used to test polymers, employs thick specimens to limit the amount of crack tip plasticity, and thus approach the plane strain condition . Testing under plane strain conditions represents the worst case scenario ; it yields a conservative fracture toughness estimate. Testing under plane stress conditions produces much higher fracture toughness values [2] . Design with conservative fracture toughness values is desirable, however, in some cases, obtaining the worst case scenario has resulted in the testing of polyethylene specimens that were 250 mm thick [3] .A serious limitation of this method is that polymeric components seldom approach the thickness of the test specimen . Because of these varied thicknesses, it is expected that major morphological differences, i.e., crystallinity changes, will exist between the test specimen and the real component . These differences may cause intrinsically different fracture behaviors . In addition, the cost and feasibility of molding large specimens, as well as testing complications related to the large specimen width, exclude many laboratories from using such a test . For example, in thick specimens, crack tunnelling creates difficulties in locating the crack tip . Determination of the crack length by the compliance method is also uncertain due to the nonlinearity of the unloading curve and the increase in specimen compliance created by the damage zone ahead of the crack tip . These factors indicate the necessity of developing a plane strain fracture toughness test for thin specimens .Plane strain fracture has been previously obtained in very thin specimens by using low load fatigue conditions [4,5] . In this report, such a method to obtain plane strain fracture is combined with a modified Begley and Landes energy analysis technique [6] to deduce the critical energy release rate (J,,,) in thin polyethylene specimens .Thin single edge notch (SEN) specimens, 100 x 27 x 2 mm, were machined from a larger block of high density polyethylene (HDPE) . After razor notching one edge of the specimens to to a depth of five millimeters, the specimens were fatigue loaded at 0 .5 Hz, using a sinusoidal wave form which cycled from 0 to 12.3 MPa ((Y.-45% (). Crack propagation was monitored with a travelling microscope, and load vesus displacement hysteresis loops were recorded on an analog plotter . mnt Journ of Fracture 48 (1991) R47

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