Effects of Notch Radius, Test Temperature and Mixed Mode ...
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ABSTRACT A nano-structured Al 89 Gd 7 Ni 3 Fe 1 composite was processed by extruding atomized amorphous powders at different extrusion ratios (ER). The extruded composite contained fcc α-Al, intermetallic particles, and a small amount of τ 1 particles. The effects of changing the notch radius from fatigue pre-crack to 100 µm on mode I fracture toughness were studied at different test temperatures (e.g. 298K and 498K). The effects of mixed mode (I/II) loading using different offset ratios were also studied at these temperatures. Increasing the test temperature showed a significant effect on the fracture toughness for both mode I and mixed mode I/II conditions. Fracture surfaces were examined to reveal the nature of failure of such nano-structured Al composite materials at these loading conditions. Objectives: Determine the effects of notch radius and test temperature on the fracture toughness of the present materials. Determine the effects of mixed mode loading on the fracture toughness of nano- structured Al composite at room temperature (RT) and 498K. INTRODUCTION Nano-crystalline metallic materials and metal–matrix composites (MMCs) both provide unique, but different combinations of properties. Nano-crystalline metallic materials typically possess high yield strength, as predicted by the Hall–Petch relationship [1, 2]. Many techniques have recently been developed to produce tubes, wires, and disks with nano-scale features. MMCs possess attractive properties such as high specific stiffness, modulus, and strength, although their damage tolerance (i.e. toughness) is typically not high enough to permit their more widespread use. Combining the two concepts of MMCs and nano-crystalline materials in the form of nano-structured MMCs have the potential to provide combinations of properties not possible with conventional structural materials. Nano-structured MMC's (NMMC's) can be produced by ball milling, spray deposition, and laser deposition. The present work uses the consolidation and subsequent extrusion of amorphous metal powders to produce NMMC’s. EXPERIMENTAL Materials: Atomized amorphous Al 89 Ni 3 Gd 7 Fe 1 powders were placed inside an aluminum can and were extruded into rods of 15.9 mm diameter. The rods contained the extruded powder and a 2 mm thick Al ring. Hot extrusion of the amorphous powders produces an ultra-fine structure consisting of high volume fraction of nano-structured intermetallic particles (e.g. 100 nm thick), embedded in the aluminum matrix. Testing conditions: 3PB specimen: 100 µm and 450 µm notch root radius. Notched toughness, fatigue pre-cracked toughness. Test temperatures: 298K and 498K. ATS Inc. temperature controlled cabinet ±1K. MTS 20 Kip servohydraulic rig, MTS 458.20 controller, FTA control software. Specimens fatigue pre-cracked at 20 Hz, sinusoidal wave, load ratio (R) =0.1. Fatigue crack length measured with metallic foil KRAK© (KG-A05)-gages monitored by a Fractomat model 1288 crack measurement system. Mixed Mode: different offset ratio (2C/S) were studied 0.2, 0.5, and 0.67. Mixed mode I/II configuration. Ratio 2C/S controls the mode mixity. Fatigued Pre-cracked Samples ACKNOWLEDGEMENTS Pratt and Whitney Company for materials supply and partial support. HAH acknowledges The Fulbright Association for AY 2006/2007 grant at CWRU. Notched Samples RESULTS SUMMARY CONCLUSIONS Significant effects of notch radius on the facture toughness. Increasing test temperature increases the toughness. Increasing Mode mixity increases the fracture energy of nano-structured Al-composite, while decreasing the fracture energy of 2034 Al-alloy. Fractography shows locally ductile/ dimpled fracture surface. Dimple size increases with increasing test temperature (Mode I). Different fracture surface appearance for Mode I vs. Mode I/II. Changing the offset ratios changed the fracture surface appearance. REFERENCES 1. E.O. Hall, Proc. Phys. Soc. London, 1951, Sect. B 64, pp.747-753. 2. N.J. Petch, J. Iron Steel Inst., 1953, 174, pp. 25-28. 3. Kamat, S.V. and Hirth, J.P., Acta Materialia, 1996, 44(1), pp. 201–208. 4. Toughness of Nano-structured Metal Matrix Composites via Processing- induced Devitrification of Amorphous Aluminum Alloys”, Hala A. Hassan, John. J. Lewandowski, Mater. Sci. and Eng. A, 2008. 5. “High Cycle Fatigue Behavior of a Nano-Structured Composite Produced via Extrusion of Amorphous Al 89 Gd 7 Ni 3 Fe 1 Alloy Powders”, Adel El- Shabasy, Hala Hassan, J. J. Lewandowski, Mater. Sci and Eng. A, 2008. Effects of Notch Radius, Test Temperature and Mixed Mode Loading on the Toughness of a Nano-Structured Al Composite Hala A. Hassan 1 , Adel. M. El-Shabasy 1 , John J. Lewandowski 2 1 Dept. of Design and Production Eng., Faculty of Eng., Ain Shams University, Cairo, Egypt 2 Dept. of Materials Sci. and Eng., Case Western Reserve University, Cleveland, OH, USA Sample Configuration RESULTS Mixed Mode Fracture Energy Mode I Fracture Toughness Effects of Test Temperature and Notch Radius S C a 0 10 20 30 40 50 200 300 400 500 600 Temperature (K) Kq (MPam 1/2 ) Fatigue Pre-crack Notch radius=100 Notch radius=450 32-B µm µm 0 10 20 30 40 50 200 300 400 500 600 Temperature (K) Kq (MPam 1/2 ) Fatigue Pre-crack Notch radius=100 Notch radius=450 µm µm 40-B 0 10 20 30 40 50 200 300 400 500 600 Temperature (K) Kq (MPam 1/2 ) Fatigue Pre-crack Notch radius=100 Notch radius=450 41-B µ m µ m Significant effects of notch radius on toughness. Increase in test temperature increases toughness (except for 450 µm notch root radius). SEM FRACTOGRAPHY Mode I: T=298K, average dimple size=49µm Mode I:T=498K, average dimple size=80µm Increasing Mode mixity (I/II) initially increases the total fracture energy. Further increases in Mode mixity (I/II) decreases the total fracture energy 0 1 2 3 4 5 6 7 0.0 0.2 0.4 0.6 0.8 Offset ratio (2C/S) J total (kJ/m 2 ) T=298K T=498K Material Offset ratio θ K I K II K C , K eq J I J II J Total (MPam 1/2 ) (MPam 1/2 ) (MPam 1/2 ) kJ/m 2 kJ/m 2 kJ/m 2 Nano Al-composite (notch) 0 0 16 0 16 2.56 0 2.56 0.2 25 19.9 3.06 20 3.96 0.09 4.05 0.5 40 23 4.8 23.6-26 5.29 0.23 5.52 0.67 60 14.7 4.22 14.7-15.2 2.16 0.18 2.34 Nano Al-composite (FPC) 0 0 13 0 13 1.69 0.00 1.69 0.2 25 9.7 1.7 10 0.94 0.03 0.97 0.5 40 18.2 2.4 18.6 3.31 0.06 3.37 0.67 60 10 3.6 10.6 1.0 0.13 1.13 2034 Al-alloy [3] 0 37 0 37 17.8 0 17.8 13 35.2 5.1 35.57 16.1 0.34 16.44 26 33.7 9 34.88 14.76 1.06 15.52 53 28.9 18.4 34.26 10.86 4.4 15.26 Comparison between the nano-structured Al- composite and conventional Al-alloy under different Mode mixity (I/II) Fatigue pre-crack Mode I/II Mode I/II : T=498K, offset ratio=3/6 Mode I/II : T=498K, offset ratio=4/6 Different mixed mode fracture appearance for 3/6 vs. 4/6 offset ratios 0 1 2 3 0 10 20 30 40 50 60 Crack Deviation Angle (θ) J total /J IC T=298K (Notch) T=498K (Notch) T= 298K (Pre-cracked) T= 498K (Pre-cracked) 2034 Al-alloy (298K) [3] 0 1 2 3 4 5 6 7 0.0 0.2 0.4 0.6 0.8 Offset ratio (2C/S) J total (kJ/m 2 ) T=298K (FPC) T=498K (FPC)
Transcript of Effects of Notch Radius, Test Temperature and Mixed Mode ...
ABSTRACT
A nano-structured Al89Gd7Ni3Fe1 composite was processed by extrudingatomized amorphous powders at different extrusion ratios (ER). The extrudedcomposite contained fcc α-Al, intermetallic particles, and a small amount of τ1
particles. The effects of changing the notch radius from fatigue pre-crack to 100µm on mode I fracture toughness were studied at different test temperatures (e.g.298K and 498K). The effects of mixed mode (I/II) loading using different offsetratios were also studied at these temperatures. Increasing the test temperatureshowed a significant effect on the fracture toughness for both mode I and mixedmode I/II conditions. Fracture surfaces were examined to reveal the nature offailure of such nano-structured Al composite materials at these loading conditions.
Objectives:
Determine the effects of notch radius and test temperature on the fracturetoughness of the present materials.
Determine the effects of mixed mode loading on the fracture toughness of nano-structured Al composite at room temperature (RT) and 498K.
INTRODUCTION
Nano-crystalline metallic materials and metal–matrix composites (MMCs) bothprovide unique, but different combinations of properties.
Nano-crystalline metallic materials typically possess high yield strength, aspredicted by the Hall–Petch relationship [1, 2]. Many techniques have recentlybeen developed to produce tubes, wires, and disks with nano-scale features.
MMCs possess attractive properties such as high specific stiffness, modulus,and strength, although their damage tolerance (i.e. toughness) is typically nothigh enough to permit their more widespread use.
Combining the two concepts of MMCs and nano-crystalline materials in theform of nano-structured MMCs have the potential to provide combinations ofproperties not possible with conventional structural materials.
Nano-structured MMC's (NMMC's) can be produced by ball milling, spraydeposition, and laser deposition. The present work uses the consolidation andsubsequent extrusion of amorphous metal powders to produce NMMC’s.
EXPERIMENTALMaterials:
Atomized amorphous Al89Ni3Gd7Fe1 powders were placed inside analuminum can and were extruded into rods of 15.9 mm diameter. The rodscontained the extruded powder and a 2 mm thick Al ring. Hot extrusion of theamorphous powders produces an ultra-fine structure consisting of high volumefraction of nano-structured intermetallic particles (e.g. 100 nm thick), embedded inthe aluminum matrix.
Testing conditions:
3PB specimen: 100 µm and 450 µm notch root radius.
Notched toughness, fatigue pre-cracked toughness.
Test temperatures: 298K and 498K.
ATS Inc. temperature controlled cabinet ±1K.
MTS 20 Kip servohydraulic rig, MTS 458.20 controller, FTA control software.
Specimens fatigue pre-cracked at 20 Hz, sinusoidal wave, load ratio (R) =0.1.
Fatigue crack length measured with metallic foil KRAK© (KG-A05)-gagesmonitored by a Fractomat model 1288 crack measurement system.
Mixed Mode: different offset ratio (2C/S) were studied 0.2, 0.5, and 0.67.
Mixed mode I/II configuration. Ratio 2C/S controls the mode mixity.
Fatigued Pre-cracked Samples
ACKNOWLEDGEMENTS
Pratt and Whitney Company for materials supply and partial support.
HAH acknowledges The Fulbright Association for AY 2006/2007 grant at CWRU.
Notched Samples
RESULTS SUMMARY
CONCLUSIONS
Significant effects of notch radius on the facture toughness.
Increasing test temperature increases the toughness.
Increasing Mode mixity increases the fracture energy of nano-structured Al-composite, while decreasing the fracture energy of 2034 Al-alloy.
Fractography shows locally ductile/ dimpled fracture surface. Dimple size increases with increasing test temperature (Mode I).
Different fracture surface appearance for Mode I vs. Mode I/II.
Changing the offset ratios changed the fracture surface appearance.
REFERENCES
1. E.O. Hall, Proc. Phys. Soc. London, 1951, Sect. B 64, pp.747-753.2. N.J. Petch, J. Iron Steel Inst., 1953, 174, pp. 25-28.3. Kamat, S.V. and Hirth, J.P., Acta Materialia, 1996, 44(1), pp. 201–208.4. Toughness of Nano-structured Metal Matrix Composites via Processing-
induced Devitrification of Amorphous Aluminum Alloys”, Hala A. Hassan,John. J. Lewandowski, Mater. Sci. and Eng. A, 2008.
5. “High Cycle Fatigue Behavior of a Nano-Structured Composite Producedvia Extrusion of Amorphous Al89Gd7Ni3Fe1 Alloy Powders”, Adel El-Shabasy, Hala Hassan, J. J. Lewandowski, Mater. Sci and Eng. A, 2008.
Effects of Notch Radius, Test Temperature and Mixed Mode Loading on the Toughness of a Nano-Structured Al Composite
Hala A. Hassan 1, Adel. M. El-Shabasy 1, John J. Lewandowski 21 Dept. of Design and Production Eng., Faculty of Eng., Ain Shams University, Cairo, Egypt
2 Dept. of Materials Sci. and Eng., Case Western Reserve University, Cleveland, OH, USA
Sample Configuration
RESULTS
Mixed Mode Fracture Energy
Mode I Fracture Toughness
Effects of Test Temperature and Notch Radius
S
C
a
0
10
20
30
40
50
200 300 400 500 600
Temperature (K)
Kq
(MP
am1/
2 )
Fatigue Pre-crackNotch radius=100 Notch radius=450
32-B
µmµm
0
10
20
30
40
50
200 300 400 500 600
Temperature (K)
Kq
(MP
am1/
2 )
Fatigue Pre-crackNotch radius=100 Notch radius=450
µmµm
40-B
0
10
20
30
40
50
200 300 400 500 600
Temperature (K)
Kq
(MP
am1/
2 )
Fatigue Pre-crackNotch radius=100 Notch radius=450
41-B
µmµm
Significant effects of notch radius on toughness.
Increase in test temperature increases toughness (except for 450 µm notch root radius).
SEM FRACTOGRAPHY
Mode I: T=298K, average dimple size=49µm
Mode I:T=498K, average dimple size=80µm
Increasing Mode mixity (I/II) initially increases the total
fracture energy.
Further increases in Mode mixity (I/II) decreases the total
fracture energy
0
1
2
3
4
5
6
7
0.0 0.2 0.4 0.6 0.8Offset ratio (2C/S)
J tot
al (k
J/m
2 )
T=298KT=498K
Material Offset ratio θ KI KII KC, Keq JI JII JTotal
(MPam1/2) (MPam1/2) (MPam1/2) kJ/m2 kJ/m2 kJ/m2
Nano Al-composite (notch)
0 0 16 0 16 2.56 0 2.560.2 25 19.9 3.06 20 3.96 0.09 4.050.5 40 23 4.8 23.6-26 5.29 0.23 5.52
0.67 60 14.7 4.22 14.7-15.2 2.16 0.18 2.34
Nano Al-composite (FPC)
0 0 13 0 13 1.69 0.00 1.690.2 25 9.7 1.7 10 0.94 0.03 0.970.5 40 18.2 2.4 18.6 3.31 0.06 3.37
0.67 60 10 3.6 10.6 1.0 0.13 1.13
2034 Al-alloy [3]
0 37 0 37 17.8 0 17.813 35.2 5.1 35.57 16.1 0.34 16.4426 33.7 9 34.88 14.76 1.06 15.5253 28.9 18.4 34.26 10.86 4.4 15.26
Comparison between the nano-structured Al- composite and conventional Al-alloy under different Mode mixity (I/II)
Fatigue pre-crack
Mode I/II
Mode I/II : T=498K, offset ratio=3/6 Mode I/II : T=498K, offset ratio=4/6
Different mixed mode fracture appearance for 3/6 vs. 4/6 offset ratios
0
1
2
3
0 10 20 30 40 50 60Crack Deviation Angle (θ)
J tot
al / J
IC
T=298K (Notch)T=498K (Notch) T= 298K (Pre-cracked)T= 498K (Pre-cracked)2034 Al-alloy (298K) [3]
0
1
2
3
4
5
6
7
0.0 0.2 0.4 0.6 0.8
Offset ratio (2C/S)J t
otal (k
J/m
2 )
T=298K (FPC)
T=498K (FPC)
