dissertation global and local fracture properties of metal matrix ...

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J [kN/m] J [kN/m] J [kN/m] 8 6 4 2 0 8 6 4 2 0 8 6 4 2 0 Section 7 0 0,4 0,8 1,2 1,6 ∆a [mm] a) 0 0,4 0,8 1,2 1,6 ∆a [mm] b) 0 0,4 0,8 1,2 1,6 ∆a [mm] c) Fig. 7.6. The J-integral resistance curves for the MMC: a) in the as-fabricated condition; b) after 4 ECAP passes; c) after 7 ECAP passes 89
Section 7 between the Rtot and the slope of the J-∆a curve was derived dJ η ≈ R d( ∆ a) b 90 tot , (7.11) where η is the pre-factor in the J-evaluation formula and b the ligament length b = W-a [70]. The Rtot data, calculated by Eq. 7.11 in the region from ∆a = 0.2 mm up to ∆astab, are listed in Table 7.2, as well. A significant increase of the Rtot-values with increasing homogeneity of the particle distribution is observed: the Rtot-value of the MMC after 7 ECAP passes is higher than the Rtot-value of the as-fabricated material by a factor of 2. As was shown in [50], for the flat fracture region, Rtot is determined by the plastic strain energy to form the micro-ductile fracture surface and the energy spent below the fracture surface. 7.4.3. The effect of ECAP on the fracture surface morphology A different morphology of the fracture surfaces of tested disk compact specimens is revealed. In Figure 7.7a, the pre-fatigued region and the fracture surface in front of the crack tip for the specimen from the as-fabricated MMC is shown. A vast amount of particle clusters on the fracture surfaces as well as on the pre-fatigued region is seen. Regions with relative homogeneous particle distribution on the fracture surface can be also observed. In Figure 7.7b, an image of the broken particle cluster is given at higher magnification. One can see that there is no matrix between the alumina particles in clusters. On the contrary, the fracture surface of the specimen after 7 ECAP passes looks more homogeneous (Fig. 7.7c). Typical micro-ductile mechanism of fracture prevails, a few particle clusters on the fracture surface are observed. Almost no particle clusters can be found on the pre-fatigued region. Voids are initiated by a particle/matrix decohesion mechanism. In Figure 7.8, corresponding pictures from both halves of the broken specimen from the MMC after 7 ECAP passes are given. It is clearly seen, that most of particles are observed only on a single half of the broken specimen. Some of them are marked by arrows: the position of the particle on the half of the broken specimen, where the particle is observed, is marked by solid arrow; whereas the other dimple initiated by this particle on the other half of the broken specimen by a dashed arrow.
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MONTANUNIVERSITÄT MONTANUNIVERSIT
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TABLE OF CONTENTS 1. Introduction 5
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7.4.4. The effect of ECAP on the lo
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Section 1 The main results of this
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Section 2 2.2. The influence of the
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Section 2 high strength, fine reinf
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Section 2 etched to mark the inclus
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Section 2 (4.) The specimen prepara
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Section 3 Fig. 3.1. The digital ele
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height [µm] height [µm] 10 0 -10
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Section 3 Fig. 3.5. The observation
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Section 3 3.3.2. The determination
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Section 3 The Eshelby tensor does n
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equivalent stress Section 3 Fig. 3.
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Assume σ m eq Calculate matrix sec
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Section 4 Table 4.1. Chemical compo
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4.1.1.3. Fracture mechanics tests S
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Section 4 Fig. 4.4. A view of a com
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Section 4 Table 4.3. Mechanical pro
Page 39 and 40: εfr [%] εfr [%] N 16 12 8 4 0 150
Page 41 and 42: Section 4 4.2. The effect of the he
Page 43 and 44: Section 4 It should be noted that n
Page 45 and 46: CODi [µm] 40 30 20 10 0 Section 4
Page 47 and 48: Section 4 Table 4.4. Results of the
Page 49 and 50: CODi [µm] COD i [µm] CODi [µm] 2
Page 51 and 52: Cast MMCs 10%-RT 10%-8h 10%-24h 10%
Page 53 and 54: COD vi [µm] COD vi [µm] CODvi [µ
Page 55 and 56: CODvi [µm] CODvi [µm] 80 60 40 20
Page 57 and 58: Section 4 Table 4.6. The values of
Page 59 and 60: σ p max [MPa] σ p max [MPa] σ p
Page 61 and 62: σ p max [MPa] σ p max [MPa] 1200
Page 63 and 64: σ interf max [MPa] σ interf max [
Page 65 and 66: Section 4 4.5. The relation between
Page 67 and 68: Section 4 Table 4.9. Conditions for
Page 69 and 70: Ln(Ln(1/(1-F σ))) Ln(Ln(1/(1-F σ)
Page 71 and 72: Section 5 diameter of 2…8 µm and
Page 73 and 74: MnS-inclusion r θ MnS-inclusion Se
Page 75 and 76: σ interf [MPa] σ interf [MPa] σ
Page 77 and 78: Section 6 where n is the number of
Page 79 and 80: Ji [kN/m] J i [kN/m] 25 20 15 10 5
Page 81 and 82: Section 7 7.2. A model by Tan and Z
Page 83 and 84: Section 7 its initial length, li. O
Page 85 and 86: 1 µm Section 7 5 µm Fig. 7.3. A s
Page 87 and 88: Section 7 a) b) c) Fig. 7.4. Micros
Page 89: Section 7 It is important that no p
Page 93 and 94: Section 7 Fig. 7.8. The fracture su
Page 95 and 96: 10 z [mm] 5 -10 -15 Section 7 0 -20
Page 97 and 98: Section 7 Table 7.3. Data on measur
Page 99 and 100: 8. Summary Section 8 This work deal
Page 101 and 102: Section 8 The effect of the homogen
Page 103 and 104: Table 9.1. Data on stress for Speci
Page 113 and 114: Table 9.11. Data on stress for Spec
Page 119 and 120: Table 9.17. Results of the stereoph
Page 121 and 122: 1 2 1 2 3 3 4 5 6 5 9 119 7 7 8 9 6
Page 123 and 124: 8 9 10 6 10 122 11 12 13 14 11 12 1
Page 125 and 126: 9 10 11 12 13 124 50 µm Fig. 9.6.
Page 127 and 128: 1 2 1 2 3 3 4 4 126 5 5 6 9 7 50 µ
Page 129 and 130: 1 1 2 2 3 4 3 4 5 5 128 6 7 6 7 50
Page 131 and 132: Fig. 9.12. Fracture surface with ma
Page 133 and 134: 1 2 3 1 2 3 4 5 6 7 8 9 10 4 5 132
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Fig. 9.22. Fracture surface with ma
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Fig. 12.36. Fracture surface of the
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[14] Lewandowski JJ, Liu C, Hunt WH
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[42] Rice JR, Rosengren GF. Plane s
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[70] ASTM E1820-01, “Standard Tes
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