Comparison of Fracture and Fatigue Properties of Clad 7075-T6 Aluminum in Monolithic and Laminated Forms

Alic, J. A.; Archang, H.

doi:10.4271/750511

Cited by 8 publications

(8 citation statements)

References 13 publications

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“…3 are at marked variance with previous tests on similar laminate systems for which the loading was fully-reversed ( R = -1 ) 4-point plane bending [7,81. In bending fatigue, both 8-and 22-layer laminates gave higher S-N curves than monolithic, clad, 7075ST6, with the 22-layer laminates superior to those having 8 layers.…”

Section: Unriotched Specimenssupporting

confidence: 67%

“…To investigate this possibility, a number of unnotched bending fatigue tests were run on monolithic specimens cut from the same plate as that used for the present axial loading tests. These new bending tests gave fatigue lifetimes substantially greater than for the plate used in the earlier comparisons [7] and also greater than for any of the laminates tested earlier in bending. This result, together with the previous discussion comparing Fig.…”

Section: Unriotched Specimensmentioning

confidence: 73%

“…Tests were conducted using axial loading on both notched and unnotched specimens, otherwise similar to to those previously tested in bending fatigue [7,8]. For fatigue lifetime tests on the relatively small specimens used, it was anticipated that improvements in fatigue resistance would result from the tendency of cracks to form at different locations in the various layers, with a consequent isolation of the initial damage to one or a few laminae.…”

Section: Introductionmentioning

confidence: 99%

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Axial Fatigue of Adhesively-Bonded Laminates

Alic¹

1979

Fat Frac Eng Mat Struct

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Abstract-Fatigue tests with axial tension loading ( R = 0.1) have been performed on aluminum alloy laminates having 8 and 22 layers. The laminates were similar to those previously reported for bending fatigue, having 7075-T6 layers joined by Hysol EA 9410 epoxy. Both unnotched and notched ( K , = 2.42) specimens were tested.Fatigue lifetimes for both 8-and 22-layer laminates were significantly less than Tor monolithic specimens tested for comparison, the differences increasing as the maximum stress decreased. This was true for both the notched and unnotched tests and is the reverse of the trends previously found in bending. While the unexpected inferiority of laminates in tension fatigue appears to be at least partially a result of material variability, it is also evident that changing the type of loading can have unpredictable effects on the comparative fatigue performance of laminates. For both unnotched and notched laminates, different layers continued to crack at different locations, demonstrating the uncoupled nature of the fatigue process in the various layers.

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Section: Unriotched Specimenssupporting

confidence: 67%

Section: Unriotched Specimensmentioning

confidence: 73%

Section: Introductionmentioning

confidence: 99%

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Axial Fatigue of Adhesively-Bonded Laminates

Alic¹

1979

Fat Frac Eng Mat Struct

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“…16). As in bend i ng [13], lami nates tested under axial loading tended to break at different locations along the specimen gage length in different l ayers , thus confirming the earlier conclusion of substantial decoupling of the fatigue processes in the various layers . There was , however , a tendency for cracks to originate at the junction between the 3 in.…”

supporting

confidence: 71%

“…In bending fatigue , both 8-and 22-layer laminates gave higher S-N curves than monolithic (clad ) 7075-16, with the 22-layer laminates superior to those having 8 l ayers [13,14] . This is the reverse of the trends shown in Fig.…”

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confidence: 99%

Fatigue in Adhesively Bonded Laminates.

Alic¹

1977

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Stable crack growth in adhesively bonded aluminum alloy laminates

Alic

1975

Int J Fract

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Fabricating relatively thick sheets or plates by bonding together a number of thin layers has considerable potential for improving fracture toughness. This is because of the well-known size effect which leads to high values of the so-called plane stress fracture toughness K at thicknesses which are relatively small in high strength materials [~]. Laminated composites in which the crack front is perpendicular to the plane of the laminae, Fig. i, can take advantage of this effect; these have been termed crack-divider laminates [2]. To achieve high fracture toughness in such a laminate, the layers must be able to fracture independently of one another.A simple way of ensuring sufficiently low interlayer strengths is to use adhesive bonding [3,4].Because the achievement of maximum toughness in a laminate of high-strength material requires the use of thin layers which will typically exhibit considerable slow crack growth under increasing load, it is desirable to examine crack growth resistance or K R curves [5] for such laminates in preference to simple values of K at instability. This allows comparisons to be made among va~rious . c specimen sizes and types; the use of K_ curves is the most rational way of trying to find that thickness whic~ will offer the highest fracture toughness for a given material.In this work K_ curves have been determined for laminates of clad R 7075-T6 aluminum and compared to those for monolithic specimens having a similar total metal thickness.The specimen preparation and testing procedure have been described elsewhere [4]. Briefly, the laminates consisted of 8 layers, each 0.033 in thick, bonded with an epoxy adhesive, the bond layers being about 0.0035 in thick. Monolithic specimens for comparison were machined from a 0.256 in thick clad plate. The ordinary tensile properties of the laminated and solid materials were comparable, as shown in Table I. All fracture testing was done using compact tension specimens, Fig. I, which were pre-cracked by low-level fatigue cycling.The crack mouth opening displacement was measured during the final loading to failure using a conventional clipon displacement gage. The load-displacement trace obtained was then analyzed using a procedure suggested by Sullivan and Stoop [6]. This method relies upon an independently derived crack length-displacement calibration.The resulting K R curves are shown in Fig. 2. Good consistency was found among the various specimens tested, which showed a considerable range in slow crack growth, Aa, prior to instability.This behavior is caused primarily by differences in the initial crack lengths. The values of K at instability show the expected increase with crack extension, Aa. Inspection.of the fracture surfaces of the laminates, Fig. 3, indicates that crack growth does proceed independently in the Int Journ of Fracture II (1975)

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Comparison of Fracture and Fatigue Properties of Clad 7075-T6 Aluminum in Monolithic and Laminated Forms

Cited by 8 publications

References 13 publications

Axial Fatigue of Adhesively-Bonded Laminates

Axial Fatigue of Adhesively-Bonded Laminates

Fatigue in Adhesively Bonded Laminates.

Stable crack growth in adhesively bonded aluminum alloy laminates

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