Grain Size: The Fabric of (Brittle) Fracture of Polycrystals

Armstrong, R.D.

doi:10.1016/b978-0-08-022146-5.50019-1

Cited by 5 publications

(6 citation statements)

References 28 publications

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“…However, the true fracture stresses were reduced at smaller grain sizes to correct for an increased plastic strain preceding fracture, thus producing a relatively low value of k C {ε = 0} ≈ 80 MPa mm 1/2 . The value compares with k C ≈ 104 MPa mm 1/2 (and σ 0C ≈ 350 MPa) as given by Madhava [17] in a comprehensive compilation of grain-size-dependent σ C measurements, including (lower) intercrystalline failure stresses and (higher) post-yield cleavage measurements (see [18]). The issue relates importantly to the question of whether yielding would always precede fracturing, as will be discussed.…”

Section: Introductionmentioning

confidence: 99%

Material grain size and crack size influences on cleavage fracturing

Armstrong

2015

Phil. Trans. R. Soc. A.

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A review is given of the analogous dependence on reciprocal square root of grain size or crack size of fracture strength measurements reported for steel and other potentially brittle materials. The two dependencies have much in common. For onset of cleavage in steel, attention is focused on relationship of the essentially athermal fracture stress compared with a quite different viscoplastic yield stress behaviour. Both grain-size-dependent stresses are accounted for in terms of dislocation pile-up mechanics. Lowering of the cleavage stress occurs in steel because of carbide cracking. For crack size dependence, there is complication of localized crack tip plasticity in fracture mechanics measurements. Crack-size-dependent conventional and indentation fracture mechanics measurements are described also for results obtained on the diverse materials: polymethylmethacrylate, silicon crystals, alumina polycrystals and WC-Co (cermet) composites.

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Section: Introductionmentioning

confidence: 99%

Material grain size and crack size influences on cleavage fracturing

Armstrong

2015

Phil. Trans. R. Soc. A.

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“…Deformation behaviors of a large scaled bulk nc aluminum have been analyzed with mechanism-based properties of stacking fault energy and twinability. 11,12,17) …”

Section: Introductionmentioning

confidence: 99%

“…1) Especially, nanocrystalline (nc, the grain size below 100 nm) metals generally exhibit alternative deformation mechanisms depending on ultrafine crystalline (ufc, the grain size in the range from 100 nm to 500 nm) or microcrystalline (mc, the grain size above 500 nm) metals; [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] plastic deformation by means of intragranular slip becomes to lose its significance. For ufc and mc metals, yield stress follows the Hall-Petch relationship; 2,3) greater stress is concentrated near the adjacent grains due to the presence of multiple pile-up dislocations, leading that as the grain size increases, yield stress decreases.…”

Section: Introductionmentioning

confidence: 99%

Positive Deviation from a Hall-Petch Relation in Nanocrystalline Aluminum

2009

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The grain size dependence of yield stress has been investigated for nanocrystalline (nc) bulk aluminum produced by hot extrusion of ballmilled powders. The Hall-Petch slope is positively deviated as the grain size is reduced below 60 nm. For the specific grain size range from 60 nm down to 48 nm, structural analyses and estimation of deformation mechanism exhibit that perfect dislocation emission critically governs deformation of nc aluminum, since the inherent aluminum properties of high stacking fault energy and low twinability can not afford any other deformation modes.

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“…(7), the quantity in square brackets is Petch's relationship for the cleavage fracture stress [22]. A compilation of cleavage fracture stress measurements was reported at ICF4 [53]. At constant plastic zone size, as appears to generally obtain in engineering fracture mechanics tests, a Hall-Petch type of dependence is obtained for K Ic .…”

Section: The Bilby-cottrell-swinden Model Of Crack Growthmentioning

confidence: 99%

Sir Alan Cottrell and the dislocation mechanics of fracturing

Armstrong

2014

Strength, Fracture and Complexity

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Sir Alan Cottrell led the transformation of metallurgy from an observational science to analytical description. The following ditty, written for an analysis of the influence of polycrystal grain size on mechanical strength properties, could very well have been inspired by subliminal guidance from Cottrell:The physically-weaker mortals are supported With stronger materials, needfully, more so every day. How so, you say -by brain power exhorted To restrict the role that cracks and dislocations play!The following account is an honoring contribution in recognition of the great man's leading researches on one of several materials-based topics that he led: the dislocation mechanics of fracturing.

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Grain Size: The Fabric of (Brittle) Fracture of Polycrystals

Cited by 5 publications

References 28 publications

Material grain size and crack size influences on cleavage fracturing

Material grain size and crack size influences on cleavage fracturing

Positive Deviation from a Hall-Petch Relation in Nanocrystalline Aluminum

Sir Alan Cottrell and the dislocation mechanics of fracturing

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