Mostafa Shazly, David Nathenson, and Vikas Prakash

Case Western Reserve University, Cleveland, Ohio

Modeling of High-Strain-Rate Deformation,

Fracture, and Impact Behavior of Advanced

Gas Turbine Engine Materials at Low and

Elevated Temperatures

NASA/CR—2003-212194

May 2003
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Mostafa Shazly, David Nathenson, and Vikas Prakash

Case Western Reserve University, Cleveland, Ohio

Modeling of High-Strain-Rate Deformation,

Fracture, and Impact Behavior of Advanced

Gas Turbine Engine Materials at Low and

Elevated Temperatures

NASA/CR—2003-212194

May 2003

National Aeronautics and

Space Administration

Glenn Research Center

Prepared under Grant NAG3–2677
Available from

NASA Center for Aerospace Information

7121 Standard Drive

Hanover, MD 21076

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22100

This report contains preliminary

findings, subject to revision as

analysis proceeds.

The Propulsion and Power Program at

NASA Glenn Research Center sponsored this work.

Available electronically at http://gltrs.grc.nasa.gov

Acknowledgments

The authors would like to acknowledge financial support from NASA’s advanced aeropropulsion research

program through NASA Grant NAG3–2677. The authors would also like to thank Dr. Susan Draper of NASA GRC

and Andreas Venskutonis of Plansee, Austria, for providing the Gamma Met PX material used in the present study.

The authors would also like to thank Dr. J.M. Pereira for several helpful technical discussions. The authors

would also like to acknowledge the financial support from the National Science Foundation through grants

CMS–9908189 and CMS–0079458 in setting up part of the elevated temperature and

high-speed imaging facility at CWRU.
NASA/CR—2003-212194 1 

INTRODUCTION 

Advanced intermetallics, such as cast gamma titanium-aluminides ( γ -TiAl), are considered to be 

one of the leading candidate materials for aircraft propulsion systems. When compared with 

Ni-based superalloys, γ -TiAl alloys are known to have lower density, excellent hightemperature strength retention, high specific stiffness at elevated temperatures, and good 

oxidation and corrosion resistance. However, these alloys have low ductility and poor crackpropagation resistance. As a result, in contemplating the use of γ -TiAl in airfoils, the threat of 

high velocity particle impact has always been of considerable concern to designers. 

In view of the stringent safety requirements of modern aero-propulsion systems and our 

incomplete state of understanding of the fundamental mechanisms involved during deformation 

and fracture of γ -TiAl alloys under impact loading conditions, a three-year integrated 

experimental, analytical, and computational program of research is being conducted at CWRU. 

During the first two year time period the focus of the research work will be to better characterize 

the dynamic material behavior of γ -TiAl alloys under impact loading conditions. The dynamic 

material properties of interest include, (a) dynamic compressive and tensile strength as a function 

of strain rate ranging from 100 s-1 to 104 s

-1 and temperatures ranging from room to 900 °C, 

(b) dynamic fracture characteristics, including dynamic fracture toughness and ductile-to-brittle 

transition as a function of crack-tip loading rates, and (c) high-velocity particle-impact 

experiments to understand the initiation and spread of damage including micro- and macrocracking and development of spall in γ -TiAl. In these later experiments the variables of primary 

interest include energy (impact velocity), specimen thickness, hardness of the projectile, and test 

temperatures. 

Two full-time graduate students are directly involved on the project: Mostafa Shazly and 

David Nathenson. Mostafa Shazly has completed his MS and is working towards his Ph.D. while 

David Nathenson is currently working on MS and will continue on his Ph.D. 

Accomplishments during the first year: 

• Design and development of elevated temperature facility to conduct high-strain rate 

experiments at elevated temperatures. This high-temperature facility has been designed 

and built and integrated with the Split Hopkinson pressure bar apparatus to conduct 

elevated temperature high-strain-rate experiments on γ -TiAl in both compression and 

tension. To-date elevated temperature high-strain-rate tests on gamma Met PX have 

been conducted in compression and tension at strain rates varying from 100/s to 3000/s 

and temperatures ranging from room to 900 °C. 

• Design and development of gas-gun facility for accelerating 1/16 to 1/8 inch projectiles 

for conducting high-velocity particle impact experiments.

A more detailed description of the accomplishments during the first year is described next.

NASA/CR—2003-212194 3 

HIGH STRAIN RATE DEFORMATION OF GAMMA-MET PX 

AT ELEVATED TEMPERATURES 

Graduate Student: Mostafa Shazly 

Although the introduction of classical titanium alloys such as IMI-834 and Ti-1100, have allowed 

improvements in the efficiency of gas turbine engines by replacing nickel and iron base 

superalloys, they cannot still meet the requirements of high operating temperatures and high 

specific strength of modern air-breathing propulsion systems. This is because at temperatures 

over 600 °C the mechanical strength and creep behavior of titanium alloys becomes inadequate. 

Moreover, oxidation problems arise due to the formation of brittle oxide surface layer, which 

leads to premature fracture damage in fatigue. Also, these alloys are subject to “titanium fire” 

(a great problem for engine applications), a phenomenon that results from the low thermal 

conductivity of the metal and the very high heat of formation of TiO2 oxide (Young-Won Kim, 

1989; Djanarthany, Viala and Bouix, 2001). 

Gamma titanium aluminides (γ-TiAl) are targeted as a material substitute for superalloys 

(LeHolm, Clemens and Kestler, 1999) for critical propulsion components in the 600 to 900 °C 

temperature range. Compared with titanium alloys, they present several advantages such as 

higher elasticity modulus, lower density, better mechanical behavior with temperature and higher 

oxidation resistance by formation of a surface passive alumina layer. However, these properties 

come at the expense of tensile ductility, which is typically in the range of 1 to 3%. As a result 

these intermetallics show poor crack-propagation resistance, and in contemplating the use of 

γ -TiAl in airfoils the threat of high-velocity small particle impacts is of considerable concern to 

designers (Wright, 1993; Austin, Kelly and McAllister, 1997). The absence of plasticity at 

classical fabrication temperatures is also a source of difficulty, in particular, in rolling γ-TiAl into 

thin sheets or foils. 

Gamma based titanium aluminides have an aluminum level of 45-52 at.%. Within this regime, 

there are two phases of interest-- the γ-TiAl ordered phase with face center tetragonal (f.c.t) L10

crystal structure with alternating (002) planes of Ti and Al atoms (Lui and Stiegler, ; Young-Won 

Kim, 1989; Dimiduk et al., 1991; Kim and Dimiduk, 1991; Yamagushi, 1993; Recina, 2000; 

Djanarthany, Viala and Bouix, 2001), and ordered α2-Ti3Al phase with the DO19 hexagonal close 

packed (h.c.p) crystal structure. α2 -Ti3Al contains three linearly independent slip systems that 

account for dislocation motion on the basal {0001}, prism {1010}, and pyramidal {0221} planes 

(Lui and Stiegler, ). Pure γ remains ordered up to the melting point of 1440 °C, while the α2

transforms at around 1125 °C to a disordered h.c.p structure (Recina, 2000). Because they have 

slower diffusion rates than conventional titanium alloys, titanium aluminides feature enhanced 

high-temperature properties such as strength retention, creep and stress rupture, and fatigue 

resistance (Lui and Stiegler, ; Millett, Gray and Bourne, 2000). In improving the mechanical 

properties of gamma titanium aluminides, Plansee AG of Austria has developed new generation 

of gamma titanium called Gamma Met. Gamma Met is available in both sheet and rod forms. 

This product is unique, because it is suitable for both propulsion and airframe components. 

Moreover, Gamma Met has better rolling characteristics and improved post-rolling mechanical 

properties. It does not need the costly fabrication processes typically used for other intermetallic 

components. Shaping and forming can be carried out at relatively low temperatures to produce 

parts which are more uniform than those obtained with other methods. Components can be 

economically fabricated in normal production settings with the same equipment as that used for 

conventional titanium alloys. In summary the main advantages of γ-Met material are (a) γ-Met 
NASA/CR—2003-212194 4 

alloy is 15% lighter than titanium alloys and more than 50% lighter than superalloys, (b) it 

withstands temperatures that are approximately 300°C higher than those for titanium alloys, 

(c) its specific stiffness is approximately twice that of titanium alloys and superalloys (based on 

modulus normalized with respect to density), (d) it exhibits high acoustic attenuation due to high 

specific stiffness, and (e) fabrication costs associated with γ-Met alloys are potentially the same 

as for titanium alloys and superalloys (Venskutonis, 2000). 

In the past little work has been done in the area of high-strain-rate deformation of γ-TiAl at 

elevated temperatures. Maloy and Gray III (1996) studied the high strain rate properties of 

duplex microstructures of Ti-48Al-2Cr-2Nb in compression. Their study showed that Ti-48-2-2 

has a yield stress anomaly at approximately 600°C. However, in the work of Gardiner et al. 

(1997) on duplex microstructures of Ti-38.5Al-2.7Nb-2.6Mn, no yield-stress anomaly was 

observed. The material showed strain hardening at all levels of plastic strain and test 

temperatures. Moreover, thermal softening was observed as the test temperature was increased 

above the room temperature. In tests performed between 700°C and 800°C and at strain rates of 

approximately 2500 s-1, cracking and fracture was observed at macroscopic plastic strains of 0.32. 

However, at temperatures below 700°C and similar strain rates no macro- and/or micro- cracking 

was observed. 

Wang et al (1999a) studied the high-strain-rate tensile properties of both duplex and fully lamellar 

microstructures of Ti-47Al-1.5Cr-.5Mn-2.8Nb at room temperature. Contrary to the observations 

of Maloy and Gray III (1996), they showed that the strength of duplex microstructures of 

Ti-48-2-2 decreases with increasing strain rate. However, for fully lamellar microstructure the 

material showed increasing strength with increasing strain rates. In another work by Wang et al. 

(1999b) on nearly lamellar microstructures of Ti-47Al-2Mn-2Nb, the material was observed to 

show increasing strength with increasing strain rate. 

The objective of our present work is to understand the high-strain-rate compression behavior of 

Gamma Met PX alloy (developed by GKSS of Germany), at temperatures ranging from room to 

900 °C and strain rates ranging from quasi-static to 3500 s-1. The report describes the 

development of the SHPB and SHTB facilities to conduct the elevated temperature experiments 

and the results of high-strain-rate uniaxial compression/tension tests on Gamma Met PX. 

EXPERIMENTAL WORK 

MATERIAL

Gamma Met PX has a chemical composition of Ti-45Al-X(Nb, B, C). The material used in the 

present study was supplied by Plansee AG in the form of 1⁄2" rods. The material was VAR cast 

and then hot extruded above the alpha transus temperature. The extrusion ratio was 100:1 and the 

bars are in the as-extruded condition. Microstructural investigation, Figure 1, shows that the 

material consists of nearly lamellar microstructure. The nearly lamellar microstructure was 

chosen since it has been shown to provide these alloys with high strength and acceptable levels of 

ductility (Kim, 1989; Dimiduk et al., 1991; Kim and Dimiduk, 1991). 
NASA/CR—2003-212194 5 

Figure 1: Microstructure of the as received Gamma Met PX.

DYNAMIC COMPRESSION TESTS: SPLIT HOPKINSON PRESSURE BAR 

(SHPB) 

Typical screw driven or servo-hydraulic testing machines are routinely utilized to obtain 

mechanical properties of engineering materials at strain rates less than 

1s-1. High capacity servo-hydraulic testing machines with high speed valves, control, and data 

acquisition instrumentation, can be used during compression testing to achieve strain rates as high 

as 100 s-1. However, to achieve higher strain rates (as high as 10,000 s-1), a split Hopkinson 

pressure bar (SHPB) is commonly employed. The historical prospective and the development of 

SHPB can be found elsewhere (Follansbee, 1985; Kaiser, 1998; Gray, 2000). The classical SHPB 

consists of two long bars with high elastic limit, termed incident and transmitted bars 

respectively, sandwiching a small cylindrical specimen, and a striker bar as shown in Figure 2. 

The SHPB facility at CWRU comprises of striker, incident and transmitted bars that are made 

from 19.05 mm diameter maraging steel having nominal yield strength of 2500 MPa. The striker 

bar is approximately 0.508 m long and the incident and transmitted bars are 1.524 m long. The 

striker bar is accelerated using an air operated gas gun. A pair of strain gages (Measurements 

Group WK-06-250BF-10C) are strategically attached on each of the incident and transmitted bars 

and are used in combination with a Wheatstone bridge circuit connected with a differential 

amplifier (Tektronix 5A22N) and a digital oscilloscope (Tektronix TDS 420) to monitor the strain 

during the test. When the striker bar hits the incident bar, a compressive pulse travels along the 

incident bar, and called the incident wave i ε . When the incident pulse reaches the specimen/bar 

interface, a reflected pulse r ε , travels back along the incident bar and a transmitted pulse t ε ,

travels through the specimen to the transmitter bar. 

For determination of the dynamic flow characteristics of Gamma Met PX, cylindrical 

compression tabs (4.70 mm diameter by 2.35 mm thick) were machined from a 12.7 mm diameter 

bar. The relatively small size of the specimens allow a stress amplification (ratio of stress in the 

sample to stress in bar) of 16:1, which was found to be necessary to deform the Gamma Met PX 

alloy specimens at high strain rates in view of the high yield-stress of Gamma Met PX alloy. 

Prior to the tests the two lateral surfaces (faces) of the specimens were ground and lapped flat. 
NASA/CR—2003-212194 6 

For the room temperature experiments Molybdenum grease was applied liberally in order to 

prevent friction at the specimen/bar interface. 

Figure 2: Schematic of Split-Hopkinson Bar at Case Western Reserve University. 

The theory behind SHPB is based on one dimensional elastic wave propagation in slender bars. 

According to superposition of one-dimension wave and homogeneity of stress and strain in the 

specimen, the expressions for strain ε(t), strain rate ε (t), and stress σ(t) in the specimen are given 

as (Follansbee, 1985) 

0

() ( )

t

ε t d = ετ τ ∫  , (1) 

2 ( ) b r

s

C

t

l

ε

ε = , (2) 

( ) t

s

AE

t

A

ε

σ = , (3) 

where Cb, is the longitudinal wave speed of the stress wave in the bar, A is the cross sectional 

area, and E is the Young’s modulus of the bar, and ls and As are the length and cross sectional area 

of the specimen, respectively. 
NASA/CR—2003-212194 7 

HIGH TEMPERATURE TESTING SET-UP FOR SHPB

Determination of dynamic response of a material at elevated temperatures using the SHPB is a 

challenging task. This is primarily due to the fact that heating the specimen while in contact with 

the bars also results in heating the ends of the incident and transmitter bars. This leads to a 

temperature gradient in the two bars, which in turn affects the elastic modulus and the density of 

the pressure bars, both of which are known to vary with temperature. Thus, in order to obtain 

accurate stress-strain curves, a correction needs to be applied to the strain-gage signals to 

compensate for the temperature dependent longitudinal wave velocity and elastic modulus by 

estimating the temperature gradient in the bars. Another problem of heating the specimen alone 

and then bringing the bars in contact, is the cold contact time. As soon as the bars come in 

contact with the specimen, the specimen loses its temperature by heat conduction to the bars. 

Figure 3 shows a finite element simulation of heat conduction in the specimen and the bar 

assembly using the commercial FEM package ABAQUSTM (2001). The analysis shows that the 

temperature distribution within the specimen changes continuously as soon as the bars are 

brought in contact. 

Several approaches have been used in the past to alleviate these problems. Amongst them an 

approach based on mechanical devices is to bring the bars in contact with the specimen just 

before the arrival of the pulse at the specimen plane has found wide spread use (see for example 

Frantz et al. (1984) and Lennon and Ramesh (1998). However, controlling the time between 

bringing the bars in contact and the arrival of the pulse is critical and even with the smallest 

contact time the temperature along the specimen is not uniform as shown in Figure 3. Other 

methods include, the use of Inconel 718 bars in testing up to 600 °C, as they retain their elastic 

properties up to this temperature, and the use of long aluminum oxide bars in contact with the 

steel bars for testing up to 1500 °C (Follansbee, 1985). 

x (mm)

Temperature (oC)

0 0.5 1 1.5 2 2.5 0

100

200

300

400

500

600

700

800

900

1000

1.0511 m sec

5.1020 m sec

10.368 m sec

15.229 m sec

Specimen Bar

x

y

Output Bar

specimen

Input Bar

Figure 3: Temperature distribution in the specimen as a function of time 

after the specimen is brought in contact with the bars. 
NASA/CR—2003-212194 8 

The schematic layout of the high temperature tests set up at CWRU is shown in Figure 4. In 

addition to the conventional SHPB, two air-cooled infrared spot heaters are used as the heating 

elements. The IR spot heaters have a circular cut shield which concentrates the heat flux at the 

focal point (0.25 inch diameter) as high as 650 watts per square inch. In order to overcome the 

problem of cold contact times between the bars and the specimen and thus allow sufficient time 

for the movement of the bars, the specimen is sandwiched between two WC inserts and the 

assembly comprising the inserts and the specimen is heated to the desired test temperature. The 

WC inserts are impedance matched to the incident and the transmitter bars, and hence do not 

disturb the incident, reflected and the transmitted wave profiles. 

Figure 4: Schematic of the high temperature set-up used in the present investigation. 

Just prior to conducting the test, the insert-specimen-insert assembly is heated up to the desired 

temperature level (usually 50 to 100 °C higher than the test temperature), and then the bars are 

brought manually in contact with the assembly. The specimen is being held between the two 

inserts by thermocouple wires pre-deformed to a cup-shape. This allows a near free expansion of 

the specimen during the compression test. The cup-shaped wires are spot welded to a screw that 

move inside a T-shape copper tube. The T-shape copper tube supports the WC inserts and allows 

for precise alignment with the incident and transmitter bars, as shown in Figure 5. A 0.015” 

chromel-alumel wire is spot welded to the specimen to monitor the specimen temperature prior to 

the test. This allows testing to be carried out over the range from room to 1000 °C. For high 

temperature experiments, boron nitride was used as lubricant agent between the specimen-inserts 

interfaces as well as the inserts-bars interfaces. 

When the bars make contact with the specimen, the WC inserts loose heat to the bars while 

maintaining the specimen temperature at the desired level for a long enough time-period so as to 
NASA/CR—2003-212194 9 

allow the test to be conducted at nominally uniform temperature conditions within the specimen. 

A finite element model for the set-up is shown in Figure 6. From the plot we see that for a test to 

be conducted at 800 °C, an initial temperature of 900 °C of the specimen and the WC insert 

assembly allows approximately 6.5 seconds to conduct the experiment before a temperature 

gradient develops within the specimen. The temperature remains fairly uniform along the entire 

length of the specimen during this time interval. However, in actual tests longer times to conduct 

the experiments are available because of the presence of the high temperature lubricant layer 

between the WC inserts which essentially acts as a thermal barrier, and the fact that the IR spot 

heaters were left on until just prior to conducting the experiments. 

 

Figure 5: Details of insert-specimen-insert assembly used in the high temperature SHPB tests. 

DYNAMIC TENSILE TESTS: SPLIT HOPKINSON TENSION BAR (SHTB) 

Although the development of a method to test materials in tension under high strain rate (later 

called Split Hopkinson Tension Bar, SHTB) was introduced a decade later after the SHPB, the 

progress in using SHTB was very slow due to difficulties inherent in sample design, load 

application, and data interpretation. There are five arrangements which have been used to apply a 

tensile pulse to the specimen. The differences between them inherent in the load application, 

sample design, and bars arrangement. The historical prospective and the development of SHPB 

can be found elsewhere (Al Mousawi et al., 1997, Nicholas and Bless, 1991). 

 

Figure 7 shows a schematic of the layout of the SHTB at Case Western Reserve University. The 

SHTB consists of an air operated gas gun, incident bar, transmitted bar, projectile, momentum trap 

bar, shock absorber, and strain gage circuits to measure the strain signals on the bars. The gun barrel 

is a 75 mm diameter standard pipe and is 1.33 m in length. It contains a hollow projectile made of 

hardened 4340 steel. The projectile is equipped with two Teflon pistons and its inner surface, which 

rides on the incident bar, is honed. The incident and transmitted bars were made of hardened 4340 

steel with a RC of 55. The end step of the incident bar (transfer flange) was built by a welding 

process using 4340 electrodes and was machined to the required size prior to heat treatment. The 

specimens used in the study were solid bars with threaded ends and a tensile gage section, as shown 

in Figure 8. The dimensions of the specimen are similar to those employed successfully in the past 

for SHTB testing (Nicholas, 1981). The specimens were machined from Gamma Met PX bars, and 

a finish grinding operation was performed over the gage length. 
NASA/CR—2003-212194 10

x (mm)

Temperature (oC)

0 10 20 30 40 0

100

200

300

400

500

600

700

800

900

1000

.5373 sec

1.045 sec

3.074 sec

6.879 sec

Bar

WC Insert

Specimen

Input Bar Output Bar

WC Insert

Specimen

x

y

Figure 6: Temperature distribution in the specimen as a function of time. 

Note the specimen is sandwiched between two WC inserts. 

Prior to conducting the high strain rate experiment, the threaded ends of the specimen were 

screwed into the input and output metallic bars (these bars are designed to remain elastic during 

the test). To conduct the experiment the tubular projectile is fired to the right onto to the end step 

on the right end of the incident bar. A pre-determined gap is kept between the momentum trap 

bar and the transfer flange such that the end of the momentum trap bar and the face of the transfer 

flange come in contact once the desired duration of the tensile pulse is transferred to the incident 

bar through the transfer flange. This tensile pulse then travels towards the specimen, where it is 

partly transmitted into the transmission bar, and is partly reflected as compression back into the 

incident bar. In the experiments the impact velocity of the striker bar was varied so as to obtain 

strain rates ranging from 500s-1 to 1000s-1. For all experiments a pulse shaper was utilized on the 

impact end of the incident bar. A pair of foil strain gages (Measurements Group WK-06-250BF10C) are strategically attached on the incident while a pair of semiconductor strain gages 

(BLH SPB3-18-100-U1) are attached on the transmitted bar. These gages are used to record the 

local strains as the reflected or transmitted pulses pass. The magnitudes and timings of the pulses 

determine the stress and strain rates in the specimen. 
NASA/CR—2003-212194 11

HIGH TEMPERATURE TESTING SET-UP FOR SHTB

With regards to SHTB testing at elevated temperatures, very little previous work exists in the 

literature (see for example the work by Rosenberg et al., 1986). In the present investigation, in 

order to conduct the elevated temperature tests the ends of the incident and transmitted bars were 

replaced with impedance matched precipitation hardened Inconel 718 inserts (see Figure 9). The 

Inconel 718 inserts allow extension of the threaded specimen grips to high temperatures and 

impedance matching helps to avoid wave dispersion that may occur as a result of a change in 

mechanical impedance at the 4340 steel and Inconel 718 interface. The specimens were heated 

using induction heating technique by using a water cooled Hüttinger TIG 10/100 RF generator. 

This generator uses 3-phase 230-V power line and delivers a maximum power of 10 kW at 

100 kHz. The power is coupled to the specimen by using 0.125” copper tubing coils. In the 

present study, a coil of 0.5” inside diameter and .35” long (two round turns) was used. To avoid 

damaging the semiconductor strain gages (attached to the transmitted bar) by coil current, the coil 

was insulated from the bars by using ceramic pieces having 0.125” diameter and 0.5” long. The 

temperature of the specimen was monitored by thermocouple wires attached to the specimen 

surface. 

Figure 7: Schematic of Split Hopkinson Tension Bar at Case Western Reserve University. 
NASA/CR—2003-212194 12

 

Figure 8: Schematic showing the dimensions of the tensile specimen used 

in SHTB testing. Please note all dimensions are in inches. 

Figure 9: SHTB high temperature set-up used in the present investigation. 

EXPERIMENTAL RESULTS AND DISCUSSION 

DYNAMIC COMPRESSION TESTING

In order to understand the high strain-rate response of Gamma Met PX a series of dynamic 

compression tests were conducted using the SHPB facility at CWRU. In these experiments the 

impact velocity of the striker bar was varied so as to obtain strain rates ranging from 1000 s-1 to 

3500 s-1. For all experiments a copper pulse shaper was utilized on the impact end of the incident 
NASA/CR—2003-212194 13

bar. The pulse shaper aids in dispersing the relatively sharp front of the incident stress wave, and 

thus allows high-strain-rate experiments to be conducted at near constant strain rates. Also, the 

slowly rising incident pulse prohibits premature failure of the relatively brittle Gamma Met PX 

alloys, especially during the early part of stress wave loading. 

 

Figure 10 shows typical incident, transmitted and the reflected strain profiles obtained in typical 

low impact velocity experiment at room temperature conducted by utilizing a copper pulse 

shaper. As mentioned before, the transmitted pulse can be related to the strength of the specimen 

by using Eq. (3), while the reflected pulse is proportional to the strain rate in the specimen 

(Eq. (2)). The relatively long rise time in the incident pulse is a consequence of the copper pulse 

shaper. Along with the high-strain-rate tests quasi-static tests ( -2 10 /s ) were also conducted to 

facilitate comparison with the high strain rate data. These specimens were tested using a Shenck 

Pegasus hydraulic test rig equipped with a 100 kN load cell. The displacement of the samples 

was monitored using a commercial extensometer. 

Time (s)

Voltage (V)

0 0.0002 0.0004 0.0006 -0.1

-0.05

0

0.05

0.1

Strain gage signal from a typical dynamic compression test

on Gamma Met PX at Room Temperature

Incident pulse obtained by

using a copper pulse shaper

Reflected pulse

Transmitted pulse

Figure 10: Typical incident, reflected and transmitted strain profiles obtained 

from a high strain-rate SHPB experiment. 
NASA/CR—2003-212194 14

The results of a selected room temperature dynamic compression tests on Gamma Met PX as a 

function of strain rate are shown in Figure 11. Due to the relatively brittle nature of these alloys 

true strains of only 0.3 were obtained during the experiments. It is interesting to note the 

relatively strong strain-rate sensitivity of the alloy at all levels of plastic strain as the strain rate is 

increased from 0.01 s-1 to 3500 s-1. The yield stress of the alloy is approximately 1250 MPa at a 

strain rate of 0.01 s-1 and increases to 2250 MPa at a strain rate of 3500 s-1. Also, the dynamic 

compressive response shows strain hardening at all levels of strain rates employed in the tests. 

The test conducted at 3500 s-1 resulted in complete failure of the specimen in the form of small 

fragments. In all the other tests the dynamic compression is stable and does not lead to failure of 

the specimen. 

True Strain

Ture Stress (MPa)

0 0.1 0.2 0.3 0

250

500

750

1000

1250

1500

1750

2000

2250

2500

2750

3000

.01 s-1

1200 s-1

2150 s-1

3500 s-1

Dynamic compression SHPB tests

on Gamma Met PX at room temperaure

Fragmentation

End of pulse

Figure 11: Dynamic compressive response of Gamma Met PX 

at room temperature as a function of strain rate. 

Figure 12 shows the strain gage signals obtained from the dynamic compressive test which 

resulted in failure during dynamic compression (strain rate 3500 s-1). The incident pulse, the 

transmitted pulse and the reflected pulse signals are shown. A sudden drop in signal strength is 

observed in the transmitted pulse at approximately 400 μs. This fall in signal corresponds to a 

sudden loss in stress carrying capacity of the specimen. The fall in stress is accompanied by a 

corresponding jump in strain rate, which manifests itself as a sudden jump in the reflected strain 

pulse signal in the incident bar. After the sudden fall in stress, the strain gage signal in the 

transmitted bar rises again due to reconsolidation of the crushed specimen in compression. 
NASA/CR—2003-212194 15

Time (s)

Voltage (V)

0 0.0002 0.0004 0.0006 -0.15

-0.1

-0.05

0

0.05

0.1

0.15

Strain gage signal from a typical high velocity SHPB test

on Gamma Met PX at Room Temperature

Incident pulse obtained by

using a copper pulse shaper

Reflected pulse

Transmitted pulse

Catastrophic failure of the specimen

under dynamic compression

Figure 12: Typical strain gage signal obtained from a relatively high velocity SHPB test 

on Gamma Met PX showing the failure of the specimen in dynamic compression. 

Figure 13 shows four selected frames from a video of a typical high velocity dynamic 

compression test in which the failure of the Gamma Met PX specimen in dynamic compression 

was observed. The high speed video was created by an ULTRA 17 camera operating at 

150,000 frames per second. The exposure time for each frame is 30 ns. The first frame was 

acquired after approximately 60 μs of the arrival of the incident pulse at the specimen plane. The 

progression of damage can be clearly seen in Frame 8. By Frame 10 the dynamic compression of 

the fragmented specimen is complete and indicates the beginning of the re-consolidation phase of 

the fragmented specimen. 
NASA/CR—2003-212194 16

Frame 4 : 60 μs Frame 6 : 90 μs 

Frame 8 : 120 μs Frame 10 : 150 μs 

Figure 13: Shows four selected frames from a video of a typical high velocity dynamic 

compression test in which the failure of the Gamma Met PX specimen was observed. 

Figure 14 shows the dynamic response of Gamma Met PX obtained by the high temperature 

SHPB facility at CWRU. The dynamic behavior is shown at nominal strain rates of 1800 to 

2150 s-1, and temperatures ranging from room to 900 °C. The change in flow stress with 

temperature is negligible between room temperature and 400 °C. At test temperatures between 

600 and 800 °C the flow stress shows signs of thermal softening. Between 800 and 900 °C there 

is an accelerated drop in the measured flow stress suggesting that the brittle to ductile transition 

temperature (BDTT) is between 800 and 900 °C. However, the level of flow stress at 900 °C is 

still higher than those measured for other gamma alloys at the same temperature (Maloy and 

Gray, 1996; Gardiner et al., 1997). Notice that although the flow-stress levels show thermal 

softening with increasing temperatures the strain hardening changes very little over the entire 
NASA/CR—2003-212194 17

range of test temperatures. Moreover, the strain hardening exponent at elevated strain rates is 

lower than that observed for quasi-static strain rates at similar test temperatures. This is in 

contrary to what has been reported for Ti-48-2-2 with duplex microstructure (Maloy and Gray, 

1996), where the strain hardening rate increases with increasing the strain rate and remains 

constant over the whole temperature range. 

True Strain

Ture Stress (MPa)

0 0.1 0.2 0.3 0

250

500

750

1000

1250

1500

1750

2000

2250

2500

2750

3000

2150 s-1 (RT)

2000 s-1 (400 o

C)

1900 s-1 (600 oC)

1900 s-1 (700 o

C)

1800 s-1 (800 oC)

2100 s-1 (900 o

C)

Dynamic compression SHPB tests

on Gamma Met PX at elevated temperaures

Fragmentation

End of pulse (radially cracked)

Figure 14: Dynamic compressive response of Gamma Met PX at strain rates of 

1800 to 2150 s-1 and temperatures ranging from room to 900 °C. 

Figure 15 shows the dynamic response of Gamma Met PX at nominal strain rates of 3000 s-1 to 

3500 s-1 and at temperatures ranging from room to 900 °C. At these high strain rates complete 

fragmentation of the sample is observed to occur during dynamic compression at room, 700 °C, 

and 800 °C test temperatures. The specimen compressed at 900 °C shows higher ductility and 

does not fragment. Instead, radial cracking is observed on the specimen after the test. In 

comparison with Ti-38.5Al-2.7Nb-2.6Mn (Gardiner et al., 1997), Gamma Met PX fractures at 

lower plastic strain levels at the higher strain rates. However, Gamma Met PX does not fracture 

at temperatures up to 900 °C while tested at strain rates similar to those of Ti-38.5Al-2.7Nb2.6Mn, which was observed to fracture at temperatures of 700 °C and higher. These experiments 

clearly indicate the better ductility of Gamma Met PX with increasing temperature, especially at 

temperatures beyond 800 °C. Moreover, the alloy does not show any yield anomaly at 

temperatures up 900 °C, unlike other gamma alloys with similar aluminum content which show 

yield anomaly at 400 °C (Morris, 1994) or 600 °C (Maloy and Gray, 1996). 
NASA/CR—2003-212194 18

True Strain

Ture Stress (MPa)

0 0.1 0.2 0.3 0.4 0

250

500

750

1000

1250

1500

1750

2000

2250

2500

2750

3000

3500 s-1 (RT)

3250 s-1 (700 o

C)

3000 s-1 (800 o

C)

3500 s-1 (900 o

C)

Dynamic compression SHPB tests

on Gamma Met PX at elevated temperaures

Fragmentation

End of Pulse (radially cracked)

Figure 15: Dynamic compressive response of Gamma Met PX at strain rates of 

3000 to 3500 s-1 and temperatures ranging from room to 900 °C. 

DYNAMIC TENSILE TESTING

To understand the dynamic tensile behavior of Gamma Met PX, the material was tested under 

strain rate up 1000 s-1 and from room to 900 °C. A typical strain gage output for SHTB is shown 

in Figure 16. The results for selected room and elevated temperatures tests are shown in 

Figure 17. At room temperature the tensile behavior of the material is observed to be 

independent of the applied strain rate in the strain rate range 500s-1 to 1000s-1. However 

compared with Ti-47Al-1.5Cr-.5Mn-2.8Nb with duplex and fully lamellar microstructures (Wang 

et al., 1999a), and Ti-47Al-2Mn-2Nb with nearly lamellar microstructure (Wang et al., 1999b), 

gamma met PX shows higher strength at failure and similar levels of ductility at similar strain 

rates. Moreover, Gamma Met PX shows a drop in the yield stress as well as flow stress at all 

levels of plastic strain with increasing temperature. Also, the strain to failure is observed to 

increase at elevated temperatures. All specimens were observed to fracture in a brittle manner 

with the fracture surface remaining essentially normal to the loading direction. 
NASA/CR—2003-212194 19

Time (sec)

Input Bar signals (volt)

Transmitted Bar signals (volt)

0 0.00025 0.0005 0.00075 0.001 -0.1

-0.075

-0.05

-0.025

0

0.025

0.05

0.075

0.1

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Strain gage signals from a typical dynamic tensile test

on Gamma Met Px at room temperture

Incindet pulse Transmitted pulse

Reflected pulse

Figure 16: Typical Incident, reflected and transmitted strain profiles 

obtained from a high strain rate SHTB experiment. 

Engineering Strain

Engineering Stress (MPa)

0 0.005 0.01 0.015 0

250

500

750

1000

1250

1500

1750

2000

500 sec-1

1000 sec-1

1000 sec-1 (600 oC)

900 sec-1 (800 o

C)

800 sec-1 (900 o

C)

Figure 17: Dynamic tensile response of Gamma Met PX. 
NASA/CR—2003-212194 20

CONCLUSIONS 

An experimental technique is developed for obtaining thermo-mechanical data for a wide variety 

of materials in dynamic compression at strain rates ranging from 500 to 3500 s-1. The technique 

utilizes the use of infra red spot heating devices to heat the specimens, and is relatively simple 

and economical to integrate with an existing split-Hopkinson pressure bar facilities. For 

conducting elevated temperature high strain rate tests in tension, an induction coil heating system 

is utilized. The high heating rates inherent to the spot heating method and the induction coil 

heating system several of the annealing and ageing issues that are present in other types of 

furnace configurations are avoided. On the basis of the data obtained to this point, it is clear that 

these techniques are capable of accurately and repeatedly obtaining elevated temperature data at 

high-strain rates under both compression and tension. 

Using the elevated temperature facility, high-strain-rate thermo-mechanical data is presented for 

Gamma Met PX under both compression and tension loading conditions and at temperatures 

ranging from room to 900 °C. Under dynamic compression, the room temperature experiments 

show that Gamma Met PX is highly rate-sensitive and yield strength as high as 2.2 GPa is 

observed at strain rates of 3500 s-1. Also, at room temperatures, Gamma Met PX shows 

appreciable strain hardening at all levels of strain rates employed in the present study. At the 

elevated temperatures, Gamma Met PX continues to show rate-sensitivity of yield stress and flow 

stress. The alloy shows little or no thermal softening up to test temperatures of 600 °C and at all 

strain rates employed in the present investigation. However, at temperatures beyond 800 °C there 

is an accelerated drop in flow stress. For test temperatures from room to 800 °C and at strain 

rates in excess of 3000 s-1, the Gamma Met PX specimens are observed to pulverize consistently. 

However, at test temperatures in excess of 800 °C, the alloy shows better ductility and the failure 

mode changes from fragmentation to radial cracking. The material does not show any yield 

anomaly up to 900 °C. 

Under dynamic tension (strain rates in the range 500 and 1000 s-1), the room temperature tests 

show negligible strain-rate dependence on both yield stress and flow stress. Moreover, with an 

increase in test temperature from room to 900 °C, the material shows a drop in both yield stress 

and flow stress at all levels of plastic strains. However, the measured levels of failure strength 

and ductility are higher when compared to those measured for other gamma titanium aluminides, 

such as Ti-47Al-1.5Cr-.5Mn-2.8Nb and Ti-47Al-2Mn-2Nb, under similar test conditions. 

 
NASA/CR—2003-212194 21

DESIGN AND DEVELOPMENT OF HIGH SPEED 

PARTICLE IMPACT FACILITY 

Graduate Student: David Nathenson 

The problem of categorizing impact damage in brittle materials at elevated temperatures and high 

strain rates is of concern to the aircraft engine industry in their quest for lighter and stronger 

materials. To this end, a study is being conducted at Case Western Reserve University into the 

room temperature behavior of impacts on soda lime glass and high temperature investigations of 

impacts on other brittle materials of interest such as Gamma Met PX and silicon nitride. During 

the past year the initial phase of this project, the construction and evaluation of a projectile 

accelerator, was completed. 

 

The actual study consists of three phases. The first of these is evaluation of soda lime glass under 

high strain rate impact conditions, a material studied extensively under static indentation 

conditions. Particle impact velocity and specimen thickness are to be varied. This study will 

yield a comprehensive understanding of internal cracking patterns and stress conditions during 

dynamic impact. Secondly, examination of Gamma Met PX and silicon nitride subjected to high 

strain rate impacts at normal and elevated temperatures will occur. Finally, numerical simulation 

of the impacts will be conducted to facilitate theoretical modeling. The purpose of this study is to 

gain a comprehensive picture of the material, its stress fields, and the resulting cracking patterns. 

 

Studying these materials under dynamic impact conditions requires the creation of a mechanism 

to fire projectiles of variable sizes consistently at given velocities. Velocities of between 100 and 

300 meters per second are desired to simulate conditions of incoming particles with blades inside 

of rotating jet engines. Additionally, the front surface target specimen must be oriented to a 

precise angle to the path of the incoming projectile. The specimens that were chosen for the 

study are soda lime glass plates of 50mm square with thicknesses of 3, 5, 15, and 25.4 mm. The 

silicon nitride and Gamma Met PX specimens are disks with radii of two inches and thickness of 

1/8 of an inch. Also, the target must be surrounded with a chamber to contain the impact while 

allowing for observation of the impact and access for heating elements. 

PROJECTILE ACCELERATOR DESCRIPTION 

In order to accelerate the projectile to the desired velocity, it was decided to utilize an existing 

design for a split Hopkinson pressure bar firing chamber already in use in our laboratory. This 

design arrangement allows for a reservoir of high pressure air to build up in a chamber on both 

sides of a piston (Figure 1). A valve on the back side is then opened to atmosphere, causing the 

piston to pull back and open the breach. The remaining air in front of the piston then pushes the 

projectile down the barrel. This firing chamber is designed using one inch thick steel end pieces 

connected with twelve 5/8 inch diameter bolts to a flanged cylinder. PTFE gaskets seal these 

pieces. The piston is constructed of aluminum to reduce mass and has two o-rings to provide a 

seal along its outer rim. Two 1/16 inch diameter holes bored through the piston allow the 

equalization of pressure between the two sides of the piston during the pressure buildup stage. 

Filling and firing is accomplished by means of standard plumbing connections. 

The gun barrel was designed to use a 3/4 inch diameter sabot and carry it for four and a half feet. 

This system of sabot and projectile is more effective than using a smaller bore and only the 

projectile because with a cylindrical sabot, the projectile shape and size can be varied. 
NASA/CR—2003-212194 22

A three-quarter inch diameter, 1.5 inch long nylon sabot was chosen (Figure 2). When combined 

with the actual projectile, in this study a sphere of hardened chrome steel diameter one sixteenth 

of an inch, the combination masses about 115 grams. The barrel was honed at Commercial 

Honing and machined with a one inch NPT thread at one end to screw into the firing chamber. 

This connection, the “breach,” is used to load the projectile. In order to separate the sabot from 

the projectile, a “sabot stripper” consisting of a plate with a 7/16 inch through hole removes the 

sabot while allowing the projectile to continue unimpeded (Figure 3). The sabot stripper can 

accommodate particles of any shape and size smaller than 7/16 inches. 

The impact chamber contains the aforementioned sabot stripper as well as a target holding 

apparatus that allows for both angular and linear alignment (Figure 4). The target holder can 

articulate angularly around the vertical axis and around the horizontal axis perpendicular to the 

projectile motion using pivots. Linear alignment is carried out by means of screw locked slides 

that enable the target to be placed precisely in the path of the projectile. The target itself is held 

in a clamping arrangement that does not impede measurements from the side or from the rear 

(Figure 5). This device is shaped as a square c-section of metal. The specimen rests against the 

front of the c section and is supported by the base of the C-section. The back of the holder has a 

two inch diameter circle machined in it. This circle is used to observe the rear of the specimen. 

Side observations can also be made because the sides of the holder are open. In this way, the 

specimen is secured and properly aligned with the path of the projectile. A shelf is included for 

the placement of optical instruments. The side walls of the chamber are constructed of 1/2 inch 

steel to prevent shrapnel from escaping. The top, front, rear and portholes in the sides are made 

of clear shatterproof Lexan to allow for visual measurement techniques. 

Figure 1: Design of Firing Chamber. 
NASA/CR—2003-212194 23

Figure 2: Sabot and Projectile Design. 

Figure 3: Sabot Stripper Design. 
NASA/CR—2003-212194 24

Figure 4: Target Holder – Alignment Systems. 

Figure 5: Target Holder – Specimen Holding Section. 
NASA/CR—2003-212194 25

OBSERVATION METHODS 

Observations of the soda lime glass specimens will be made by four methods: crack pattern 

investigation by high speed camera, point-wise deformation investigation by VISAR 

interferometer and strain gauges, and full field deformation by coherent gradient sensing. These 

systems will be employed in tandem to measure the displacements and strains in the specimens. 

DRS Hadland provided a high speed camera that is used to capture the internal crack patterns 

during the impact. The Ultra 17 camera takes pictures at a rate of up to 150,000 frames per 

second. That is, one frame every 6.67 microseconds. This allows for comparison to static 

cracking patterns and the effects of stresses. The frame rate is adjustable to allow for the best 

capturing of the material behavior. The maximum imaging capacity is seventeen frames. This 

configuration provides a series of images of the changes in the material. 

The VISAR interferometer provided by Valyn International provides point measurements of the 

out of surface displacement on the rear surface of the specimen. The VISAR probe is used to 

take point measurements of both the point on the rear surface corresponding to the impact 

location (the on axis position), and at points off the axis but located at a specific radial distance 

from the axis. For multiple measurements of neighboring spaces, Valyn VIP provided a multibeam probe with space for up to seven points. Evaporation coating of the glass specimens 

provides a reflective surface for the laser beams. 

The Coherent gradient sensing provides full field curvature measurements of curvature which can 

be related to strains. This technique measures the full field of the back surface of the target. The 

Coherent Gradient Sensing method or CGS was developed by A.J. Rosakis [5]. CGS methods 

use a laser beam reflected off of the specimen surface and transmitted through a pair of gratings 

and a lens to produce an image. The beam picks up gradients in the surface curvature which 

cause fringes when the beams traveling through the gratings interfere with one another. 

Strain gauges give a measurement of stresses in both the front and rear surfaces. These stacked 

tee rosette gages, of type CEA-06-032WT-120, from Vishay Measurements Group, use two 

perpendicular gages placed one on top of the other in order to get the best point measurement 

available. These gages are made of constantan alloy with self temperature compensation, 

120 ohm resistance, and copper tabs for soldering. Placed upon all of the specimens at a radial 

position 5mm above the projected point of impact, these gages provide readings of strain very 

close to the impact location. 

With these methods, the state of the deforming material can be completely examined. The silicon 

nitride and the gamma Met PX specimens will use the same methods, except the internal cracking 

patterns can not be examined during the test due to the opaque nature of silicon nitride and 

Gamma Met PX. 

PROJECTILE VELOCITY CALIBRATION 

The completion of the projectile accelerator paved the way for commencement of the testing 

phase, but first, the observation system was used to provide a calibration of the loading pressure 

to firing velocity relationship. The velocity of both the sabot and the projectile were observed. A 

laser system was used to measure the sabot velocity following its exit from the gun barrel. Also, 
NASA/CR—2003-212194 26

the high speed camera was used to provide images of the moving projectile as it exited the sabot 

stripper. This data was then processed to yield the velocity of the sabot and projectile. 

The laser trigger for the camera provided by DRS Hadland is converted into a velocity 

measurement system by means of a pair of 5mm long cube beam splitters that create two parallel 

beams, which are projected across the path of the firing sabot. The beams are 5mm apart. This is 

done despite the slight drop in velocity caused when the impacting particle separates from the 

sabot at the sabot stripper because the one-sixteenth inch diameter particle is much more difficult 

to measure with a laser beam than the three quarter inch diameter sabot. The sabot passes 

through the two beams in sequence and the drop in intensity each time is recorded by means of a 

high speed photodiode (Figure 6). These drops in light intensity provide accurate velocity 

measurement. 

The high-speed camera is triggered by the above laser system when the first beam is blocked by 

the passage of the projectile. This laser then triggers the flash and the camera that is set to take 

exposures of ten nanoseconds duration at the highest frame rate of 150,000 frames per second. 

This camera takes seventeen pictures which is more than sufficient to establish the velocity. The 

first exposure begins after a delay determined by the distance between the laser velocity system 

and the specimen surface, allowing for the recording to commence well before the projectile hits 

the surface. The images from the camera with the flash backlighting the scene show clearly the 

projectile exiting the hole in the sabot stripper and hitting the specimen. 

A sequence of images taken during a typical impact event is shown in Figure 7. This figure is for 

projectile velocity of 205 m/s (150 psi). The images represent every third frame taken from the 

image sequence, thus the approximate time between pictures is 20 microseconds. As can be seen 

from the images, the impacts cause visible cracking patterns in the specimens and throw up much 

debris. It should be noted that the same specimens were impacted multiple times during the 

velocity testing, so cracks already existed prior to the impacts recorded in these sequences. 

Figure 6: Velocity Measurement System. 
NASA/CR—2003-212194 27

 

Figure 7: Images of 205 m/s (150psi) test on 5mm thick glass. Shown frames are 20μs apart. 

Times are after triggering of velocity measurement system. Note conical like behavior of crack. 

Calibration of a distance occurs by entering the measurement of an object on one of the frames. 

For this series, the width of the front prong of the specimen holder was used, whereas, for the 

actual experiments, a scale will be placed on the specimen. This distance, and the inter-frame 

time allows the camera’s dedicated computer to determine the velocity by selecting one point in 

space at two different times (two separate frames). This method yielded the curve for sabot and 

projectile velocity versus firing pressure (Figure 8). Measurements were taken at pressures of 

100, 150, 200, 250, 300, 350 and 400 pounds per square inch. As shown, velocities as high as 

290 meters per second have been reached. By curve fitting in Microsoft excel, it was determined 

that the best equations for velocity in terms of pressure were second order polynomials. These 

equations are listed as follows: 

2

s

2

2

p

2

p

v = - 0.0002 + 0.4778 P + 134.64

R 0.8779

v = - 0.002 + 1.4012 P + 57.451

R 0.8779

s

∗Ρ ∗

=

∗Ρ ∗

=

With these equations, the necessary pressure for any given velocity can be determined. These 

calculations paved the way for the first stage of experiments to commence. 

 160μs 180μs 200μs

 220μs 240μs 260μs
NASA/CR—2003-212194 28

Load Pressure vs Sabot & Projectile Velocity Plot

0

50

100

150

200

250

300

350

0 100 200 300 400 500

Load Pressure (psi)

Velocity (m/s)

Sabot Vel

Proj Vel

Poly. (Sabot Vel)

Poly. (Proj Vel)

Figure 8: Pressure versus Sabot and Projectile Velocity Calibration Curves. 

SUMMARY AND FUTURE WORK 

In order to examine the impacts of spherical steel projectiles on brittle materials a gas gun type 

system was assembled. The system utilizes compressed nitrogen to propel a nylon sabot down a 

4.5 foot barrel at speeds up to 300 m/s. Following impact with a sabot stripper, which removes 

the nylon sabot, the steel projectile impacts the specimen. This specimen, held and aligned by a 

target holder, is located inside of a protective impact chamber. Laser velocity measurements are 

taken of every experiment. Several instruments including a high speed camera, strain gages and 

laser systems record the strains and out of surface displacements of the specimens as well as the 

cracking patterns. 

The laser velocity measurement system and the high speed camera have provided a 

comprehensive picture of the relationship between the firing pressure of the chamber and the 

resulting velocity of the sabot and projectile. With this calibration curve, target velocities can be 

reached consistently. Also, in observing the velocities of sabot versus projectile, it can be seen 

that little to no energy is lost during the sabot stripping process. This means that the maximum 

amount of kinetic energy is retained by the projectile following the impact. 

Armed with this data, the primary experiments of the soda-lime glass phase are now 

commencing. Experiments utilizing the VISAR, strain gages, and the CGS method are 

underway. When completed, this data will serve as a basis for the testing of other brittle 

materials using the same methods. Specifically, this testing will provide a fundamental 

understanding of the process of dynamic impact which will be used in the experimental and 

numeric study of Gamma Met PX and silicon nitride. 
NASA/CR—2003-212194 29

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Unclassified Unclassified

Annual Contractor Report—2001–2002

Unclassified

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 AGENCY REPORT NUMBER

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National Aeronautics and Space Administration

Washington, DC 20546–0001

Available electronically at http://gltrs.grc.nasa.gov

May 2003

NASA CR—2003-212194

E–13797

WU–708–87–23–00

NAG3–2677

36

Modeling of High-Strain-Rate Deformation, Fracture, and Impact Behavior of

Advanced Gas Turbine Engine Materials at Low and Elevated Temperatures

Mostafa Shazly, David Nathenson, and Vikas Prakash

Gamma-met PX; High speed particle impact; Dynamic compression and tension

Unclassified -Unlimited

Subject Categories: 01 and 07 Distribution: Nonstandard

Case Western Reserve University

10900 Euclid Avenue

Cleveland, Ohio 44106

Project Manager, J. Mike Pereira, Structures and Acoustics Division, NASA Glenn Research Center, organization code

5930, 216–433–6738.

Gamma titanium aluminides have received considerable attention over the last decade. These alloys are known to have

low density, good high temperature strength retention, and good oxidation and corrosion resistance. However, poor

ductility and low fracture toughness have been the key limiting factors in the full utilization of these alloys. More recently,

Gamma-met PX has been developed by GKSS, Germany. These alloys have been observed to have superior strengths at

elevated temperatures and quasi-static deformation rates and good oxidation resistance at elevated temperatures when

compared with other gamma titanium aluminides. The present paper discusses results of a study to understand dynamic

response of gamma-met PX in uniaxial compression. The experiments were conducted by using a modified split

Hopkinson pressure bar between room temperature and 900 °C and strain rates of up to 3500 s–1. The Gamma met PX

alloy showed superior strength when compared to nickel based superalloys and other gamma titanium aluminides at all

test temperatures. It also showed strain and strain-rate hardening at all levels of strain rates and temperatures and without

yield anomaly up to 900 °C. After approximately 600 °C, thermal softening is observed at all strain rates with the rate of

thermal softening increasing dramatically between 800 and 900 °C. However, these flow stress levels are comparatively

higher in Gamma met PX than those observed for other TiAl alloys.