computational nano & micro mechanics laboratory ucla measurement of tungsten armor - ferritic...
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Computational Nano & Micro Mechanics Laboratory UCLA
Measurement of Tungsten Armor - Ferritic Steel Interfacial Bond Strength Using a Nanosecond Laser Source
Jaafar El-Awady, Sauvik Banerjee, Shahram Sharafat, Nasr Ghoniem and Vijay Gupta
Mechanical and Aerospace Engineering Department University of California Los Angeles, Los Angeles
ConfigurationConfiguration Bond StrengthBond Strength Measurement Method Measurement Method Reference Reference
Porcelain/Metal 8-12 ksi4 point flexural test (FEM
stress analysis)DeHoff, 1982
gold alloy and pure titanium bars/ dimethacrylate polymer-glass fiber
composite
10-35 MPa Push out test Villittu, 2003
Thin film polymer/ metalAs a function of strain energy release rate
10-25 J/m2
4 point bend test (Fracture mechanics approach)
Somerday, 2003
Zirconia composite coating/stainless steel
10-40 MPa Tension tester Kobyashi, 2004
Very strong and ultra thin film interfaces for device
applications
as high as 2.5 GPa !
Laser spallation technique Gupta, 2003
6ns-duration
Beam Splitter for Nd:YAG
Energymeter
Mirror
Convex Lens
Specimen Holder
SiO2
Substrate
CoatingHe-Ne laser
(Interferometer)
CTCR
T
Aluminum
Nd:YAG Laser
Continuum Corp.
Model: Precision II
1064nm wavelength
Al layer melts and rapidly expands, causing the sacrificial SiO2 layer to spall off and sending strong compressive stress waves through substrate into film layer Compressive waves are reflected as tensile waves from free surface of film and cause tensile failure at film/substrate interface
f
•Determine interface bond strength of W-armor/ferritic steels as a function of vacuum plasma spraying (VPS) parameters
•Establish lifetime for W-armor/steel interface bond as a function of number of thermal cycles induced by (a) laser, and (b) x-rays simulated pulses, and (c) RHEPP ion pulses: Develop low-cycle “SN curve” for W-armor delamination
•Determine failure mechanism of W-armor delamination: (a) interface fatigue crack nucleation/ propagation, and/or (b) surface crack nucleation and propagation to the interface
•Work will also includes microscopy and SEM of failed interfaces to determine failure mechanisms.
1mm
Laser=65mJ
Magnified pictures of Laser-spalled area (Laser energy = 65mJ):
Sample:
SummarySummary
• Tungsten has been chosen as the primary candidate armor material protecting the low activation ferritic steel first wall (FW) chamber
• The tungsten armor is less than 1-mm thick and is applied by vacuum plasma spraying (VPS)
• Interface bond strength between the W-armor and the substrate needs to be quantified in order to provide guidance for further R&D of the W-armor protected FW
WF82H
SteelFe7W6
W
F82H Steel
Bonding Tungsten to Low Activation Ferritic Steel(Romanoski et. al., Oak Ridge National Laboratory)
IntroductionIntroduction
Pull-Off Adhesion Tester(www.defelsko.com)
Schematic of Tension Tester (Kobayashi, Vacuum, 73, 2004)
Three-point bend test (NPL,UK)
Four-point bend test:Fracture Mechanics Approach (Somerday et. al., SNL, USA)
Methods of InterfaceMethods of InterfaceBond Strength MeasurementsBond Strength Measurements
Bond Strength Measurements for Different Bond Strength Measurements for Different ConfigurationsConfigurations
The Laser Spallation Interferometer ExperimentThe Laser Spallation Interferometer Experiment
x
S1Sn-1
Sn SN
hn-1 hn
f(t)
n
n
BackFace
FrontFace
The compressive load from the laser source can be related to the measured velocity of the front surface:
i
xvPxuPf NN
NN
,ˆ,ˆˆ 21
21
The stresses at any of the interfaces can be related to the applied compressive load from the laser source at the back face or in other words to the velocity of the front face as follows:
,ˆˆ,ˆ 21
21
21NNnn xv
i
Af
P
Ax
• Because of the short rise time of the stress pulse, an interfacial region of approximately 70 to 150 micrometers is stressed uniformly.
• High amount of Laser energy can be obtained by reducing the focus area
• The failure occurs at the weakest link in the region which is spanned by the coating, interface and the substrate material.
• Such a short pulse is able to invoke a rather local response from the interface such that minute structural and chemical changes are directly reflected in the measured strengths.
Failure in Cu(1400nm)/TiN(70nm)/Si System: (a) Failure inside Si (b) Failure at the interface
of Cu/Tin (Gupta et. al., UCLA, USA)
Properties of the materials:
Titanium: h = 200 m, = 4.5 g/cc, = 3.3 mm/s
Bone Tissue: h = 6 m, = 2 g/cc, = 6.0 mm/s
Compressive stress from laser sourceMaximum ≈ 1100 MPa
Calculated stress at interfaceMaximum tensile stress at failure ≈ 200MPa
Laser Energy = 65mJ
Determining Interfacial StressesDetermining Interfacial Stresses
Advantages of TheAdvantages of TheLaser Spallation TechniqueLaser Spallation Technique
Adhesion Strength Measurement Adhesion Strength Measurement