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

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Section 3 Fig. 3.2. Corresponding stereo image pairs with profiles passed through a particle (the particle location is marked). MMC. The pre-fatigue regions (in the bottom part of pictures) and the regions of micro- ductile fracture can be clearly distinguished. From the DEMs of the corresponding regions, crack profiles are extracted perpendicularly to the pre-fatigue crack front. The profiles are drawn so that they cross an alumina particle in front of the crack tip. Sometimes, the paths have a zigzag shape to find easier the corresponding path on the second specimen half. In Figure 3.3a, the two corresponding profiles through an alumina particle of the specimen are arranged so that the moment of fracture initiation is depicted, i.e., the moment when the ligament between the first void in front of the tip and the blunted pre-crack fails. The upper profile (drawn as the red line) corresponds to the left-hand side of Figure 3.2, the lower profile (blue line) corresponds to the right-hand side. The location of the particle in the center of the void is marked. The critical crack tip opening displacement, CODi, which is a measure of the local fracture initiation toughness [50], can be determined: CODi = 17 µm. If the lower profile of Figure 3.3a is shifted vertically so that two profiles touch each other at the location of the marked particle, we get a sketch of the crack at the moment of void initiation (Fig. 3.3b) and the crack tip opening displacement at the moment of void initiation, CODvi, can be measured. For the considered particle, we get CODvi = 10 µm. Analogously to 17
height [µm] height [µm] 10 0 -10 -20 -30 10 0 -10 -20 -30 COD i =17µm Section 3 -60 -20 20 60 100 COD vi=10µm distance [µm] a) -60 -20 20 60 100 distance [µm] b) 18 r Θ particle Fig. 3.3. Crack profile through a particle in the cast Al6061-10%Al2O3 MMC: a) at the moment of fracture initiation; b) at the moment of void initiation at the particle location. the local fracture initiation toughness CODi (which can be transferred to critical values of the stress intensity or the J-integral), CODvi gives the resistance of the material against void initiation and, thus, it can be considered as a local “void initiation toughness” [54].
Page 1 and 2: MONTANUNIVERSITÄT MONTANUNIVERSIT
Page 3 and 4: TABLE OF CONTENTS 1. Introduction 5
Page 5 and 6: 7.4.4. The effect of ECAP on the lo
Page 7 and 8: Section 1 The main results of this
Page 9 and 10: Section 2 2.2. The influence of the
Page 11 and 12: Section 2 high strength, fine reinf
Page 13 and 14: Section 2 etched to mark the inclus
Page 15 and 16: Section 2 (4.) The specimen prepara
Page 17: Section 3 Fig. 3.1. The digital ele
Page 21 and 22: Section 3 Fig. 3.5. The observation
Page 23 and 24: Section 3 3.3.2. The determination
Page 25 and 26: Section 3 The Eshelby tensor does n
Page 27 and 28: equivalent stress Section 3 Fig. 3.
Page 29 and 30: Assume σ m eq Calculate matrix sec
Page 31 and 32: Section 4 Table 4.1. Chemical compo
Page 33 and 34: 4.1.1.3. Fracture mechanics tests S
Page 35 and 36: Section 4 Fig. 4.4. A view of a com
Page 37 and 38: 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
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1 µm Section 7 5 µm Fig. 7.3. A s
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Section 7 a) b) c) Fig. 7.4. Micros
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Section 7 It is important that no p
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Section 7 between the Rtot and the
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Section 7 Fig. 7.8. The fracture su
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10 z [mm] 5 -10 -15 Section 7 0 -20
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Section 7 Table 7.3. Data on measur
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8. Summary Section 8 This work deal
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Section 8 The effect of the homogen
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Table 9.1. Data on stress for Speci
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Table 9.11. Data on stress for Spec
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Table 9.17. Results of the stereoph
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1 2 1 2 3 3 4 5 6 5 9 119 7 7 8 9 6
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8 9 10 6 10 122 11 12 13 14 11 12 1
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9 10 11 12 13 124 50 µm Fig. 9.6.
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1 2 1 2 3 3 4 4 126 5 5 6 9 7 50 µ
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1 1 2 2 3 4 3 4 5 5 128 6 7 6 7 50
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Fig. 9.12. Fracture surface with ma
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1 2 3 1 2 3 4 5 6 7 8 9 10 4 5 132
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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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