University of Wisconsin-Platteville

INDS 3310 Metallurgy and Joining Processes

Axle Shaft Comparison Test

Lab Assignment #1

Performed By:

Taylor Last

Reported By:

Taylor Last

Date Performed: Spring 2011

Date Due: 5/19/11

Date Submitted: 5/19/11

Instructor: Prof. Kyle Metzloff, Ph.D. Grade__________

ABSTRACT

The purpose of this lab was to run metallurgical tests on three separate axle shafts out of front solid axle four wheel drive

vehicles. The first axle was a low carbon alloy steel Dana 60 axle, which had the largest diameter of the three. The next

two were both Toyota front axle shafts, one being a stock low carbon alloy steel, and the other being an aftermarket

chrome-molybdenum axle shaft. These tests would determine the structure, hardness and torsional strength of all three

shafts, uncovering their metallic composition. These aspects were found through execution of both destructive and non

destructive testing.

After observation through a microscope, and use of a hardness tester, grain structure and hardening methods were found

for all three samples. A torsion tester was also used to determine the failure point of all three axle shafts, given in ft/lbs.

After research and observation, it was found that the Dana 60 shaft was made of AISI 1040 steel with a carbon content

of around .4%, case hardened through carburization to form coarse martensite, and had the highest breaking point for

torque at 8149 ft/lbs, and the second highest strength for torque per square inch at 5579 ft/lbs per square inch. The stock

Toyota shaft was also made of AISI 1040 or similar steel with a carbon content around.3%, case hardened through

carburization to form coarse martensite, and had the lowest breaking point of 4902 ft/lbs, and the lowest strength for

torque per square inch at 3985 ft/lbs per square inch. The aftermarket Toyota shaft was made of AISI 4340 chrome-

molybdenum steel with a carbon content of around .43%, through hardened to fine martensite, and had the second

highest breaking point at 8075 ft/lbs, and the highest strength for torque per square inch at 6409 ft/lbs per square inch.

OBJECTIVES

The objective of this experiment was to use metallurgical tests to decide which of the three axle shaft samples ultimately

had the highest torsional strength. Next was to determine which shaft had the highest torsional strength per inch squared.

After destructive testing, failure analysis’ determined why each sample broke, caused by the alloying elements, heat

treating, and mechanical properties due to grain structure for each sample. Through hardness testing and microscopy,

the samples could also be assessed as to which shaft contains the best torsional properties. Torsional strength is one of

the only key factors, as the other main strength types; shear, tensile, and compressive strength, play little to no part on an

axle shaft closed inside a sealed housing, only making contact on the ends with its splines.

The reasoning behind this experiment is to prove that when putting bigger tires and more torque to a four wheel drive

vehicle, that the solution is not always a larger diameter axle shaft to prevent breaking, but a different metallic makeup

that will give the same properties of a larger shaft. It is common when building an off road Toyota vehicle to discard the

stock axle housing and axles and switch to a Dana 60 axle housing and axles to prevent axle breakage due to larger tires

and a more powerful drive train. This lab will prove that the stock Toyota axle housing can remain, and an upgrade to

chrome-molybdenum axle shafts can be used to gain the same strength as a stock Dana 60 axle shaft.

INTRODUCTION

AXLE SHAFT TYPES, AND GIVEN FACTORY PROPERTIES.

-Dana 60 Axle Shaft: The Dana 60 front axle shaft is a mass produced axle shafts usually made for heavy duty truck

applications. These axle shafts are made from AISI 1040 low alloy carbon steel and their diameter being 1.41”. The

heat treatment and grain structure of the Dana 60 axle shaft are not given properties.

-Toyota Axle Shaft: The Toyota front axle shaft being tested is found in Toyota Pickups from 1979-1985. This specific

specimen was taken out of 1985 Toyota Pickup. The diameter is 1.23”. The heat treatment, grain structure and alloy

type are not given properties

-Chrome Molybdenum Aftermarket Toyota Axle Shaft: This front axle shaft is an aftermarket replacement made by

Longfield Superaxles partnered with RCV Performance for the stock Toyota Pickup front axle shafts from 1979-1985.

These axle shafts are made from AISI 4340 chrome-molybdenum steel with a diameter of 1.255”. The heat treatment

and grain structure are not given properties.

HYPOEUTECTOID AND HYPEREUTECTOID STEELS

Steel can be categorized by the amount of carbon it retains. A hypoeutectoid steel is an alloy that contains less than .8%

carbon. Hypereutectoid steels are alloys that contain between .8% to 2% carbon. Graph 2 shows the percent of carbon

and where steel places on the hypo/hypereutectoid graph.

VARIATIONS OF GRAIN STRUCTURES IN STEEL

Graph 2 also shows the grain structure for different carbon steels at different temperatures. Austenite is a face centered

cubic iron created when pure iron is heated above 1666°F, formed from allotropic transformation If steel is to be

hardened, it must turn into a solid solution of austenite before cooled to become another grain structure. When cooled,

hypereutectoid steels can become cementite, which is a mixture of iron and carbon, known as iron carbide. This results

in a very hard, yet brittle steel. Hypoeutectoid steels that are quenched in oil or water become martensite. Martensite

has a needle like grain structure which forms when carbon does not fully diffuse from being cooled quickly. Ferrite is

the grain structure of pure carbon. When steel is slow cooled from austenite, pearlite is formed. Pearlite is a grain

structure of alternating layer of ferrite and iron carbide. Alloying elements also determine fine or coarse grain structures,

adding to different strength properties. (Neely, pgs. 424-435)

TORSIONAL FORCE

Torsion refers to “the twisting or wrenching of a body by the exertion of forces tending to turn one end about a

longitudinal axis, while the other is held fast or turned the opposite direction.” (Neely, pg. 439) Torsion is measured in

foot/pounds in standard units, and Newton/meters in metric units. Torsion is one of the four main strengths, along with

shear, compressive, and tensile strength.

AISI 4340 CHROME-MOLYBDENUM HIGH ALLOY STEEL

Component Elements Properties

Metric English Comments

Carbon, C 0.370 - 0.430 % 0.370 - 0.430 % Chromium, Cr 0.700 - 0.900 % 0.700 - 0.900 % Iron, Fe 95.195 - 96.33 % 95.195 - 96.33 % Manganese, Mn 0.600 - 0.800 % 0.600 - 0.800 % Molybdenum, Mo 0.200 - 0.300 % 0.200 - 0.300 % Nickel, Ni 1.65 - 2.00 % 1.65 - 2.00 % Phosphorous, P <= 0.0350 % <= 0.0350 % Silicon, Si 0.150 - 0.300 % 0.150 - 0.300 % Sulfur, S <= 0.0400 % <= 0.0400 %

******All other properties will vary upon methods of heat treatment and production. (Matweb.com)

AISI 1040 LOW ALLOY CARBON STEEL

Component Elements Properties

Metric English Comments

Carbon, C 0.370 - 0.440 % 0.370 - 0.440 % Iron, Fe 98.6 - 99.0 % 98.6 - 99.0 % Manganese, Mn 0.60 - 0.90 % 0.60 - 0.90 % Phosphorous, P <= 0.040 % <= 0.040 % Sulfur, S <= 0.050 % <= 0.050 %

******All other properties will vary upon methods of heat treatment and production. (Matweb.com)

HEAT TREATMENT OF STEEL FOR TORSIONAL STRENGTH

The desired properties of a steel shaft that must withstand torsional forces lead to a heat treated steel that has been

hardened to an extent to resist plastic deformation, but has also been treated to prevent brittleness that can lead to

premature fractures. A study done by Tafila Technical University shows different methods of heat treatment to a

chrome-molybdenum-vanadium alloy steel called D2, to better its torsional strength. The method that worked best for

giving this steel its desired properties was to heat and hold the steel above the A3 line of the iron-carbon phase diagram.

(Graph #3) This gave a homogenous solution of austenite. The shafts were then rapidly cooled in oil to give the steel a

martensitic structure. The shafts were then tempered at 1292°F for two hours, which reduced the hardness and yield

strength, but gained elongation properties and toughness. Austenizing the steel at the highest temperature of 1958°F, and

quenching in oil showed a 191% increase in torsional strength of the steel shafts. (Tafila Technical University)

This expirement is true to a steel with such alloying elements. Molybdenum greatly increases the hardenability of steels,

while also reducing the susceptibility of temper-brittleness. Chromium as an alloying element also increases

hardenability, while also improving corrosion resistance and machinability. (Neely, pgs. 113-119)

For low alloy steels, such as those found in the Dana 60 and the stock Toyota, such heat treating methods are not as

effective. Had these steel shafts been treated in the same way as a chrome-molybdenum shaft, fewer alloying element,

the structure formed would be a more coarse needle-like martensitic structure, which would increase brittleness. Instead,

for low alloy steel such as these, methods of case hardening are more commonly found, which cause the outer portion of

the shaft to harden, while the inside remains much more ductile, thus increasing toughness. Carburizing is a form of

surface hardening that occurs when carbon is introduced into a steel alloy at an elevated temperature. Hardness and

depth of case depend on time and temperature of carburization. (Neely, pg. 426)

PROCEDURE

I. TORSION TESTING OF AXLE SHAFTS

***All tests were performed by RCV Performance’s chief engineer.

1. Before testing the axle shafts for torsional strength, the correct adapters were chosen to fit the diameter and spline count

of each axle shaft. In this case, the 27 and 30 spline adapters were chosen. (Figure 4)

2. The chief engineer then returned the hydraulic cylinder back to the start position. (Figure 2)

3. Before placing the shafts in, a straight line was drawn down the shaft, so permanent axle twist could be seen.

4. The first adapter was put into the moving portion of the tester, and the corresponding end of the shaft was inserted.

(Figure 5)

5. The other adapter was then inserted, with the other end of the shaft going into the splines. This adapter was secured onto

the stationery portion of the tester. (Figure 6)

6. After a thorough check, the chief engineer started the machine. (Figure 1)

7. A computer constantly monitored the torsion strength put on the shaft in ft/lbs to the angle of degree it was turning

during the test. (Figure 3)

8. The three tests ranged from 3 minutes to 11 minutes.

9. Once the tests were complete the adapters were removed and the axle sections were removed

10. The data was collected and the broken sections were saved to be cut and mounted to look at under the microscope.

II. SECTIONING SAMPLES

1. Each sample obtained for observation had to be cut into smaller pieces for both mounting in plastic, and testing for

hardness.

2. To do this, the metallurgical cold chop saw was used. This was used as the constant flow of coolant on the abrasive disc

gave the sample a clean cut, without creating a heat affected zone. (Figure 7)

3. First, a quick check was performed to look for the abrasive wheel’s condition, excess cut-off dust and proper coolant

level.

4. The sample was placed into the vice, closing the jaws and fastening it with the vise lever.

5. The cut-off end was secured with a spring vise to prevent the piece from moving at high speeds.

6. The cover was then closed.

7. Next, while holding the saw handle, the on button was pressed. This prevents a kick-back while turning on the saw.

8. The sample was cut all the way through, using the handle to pull down the saw.

9. The sample was then taken out of the vise, and the cover was left open.

10. These steps were repeated twice for all three axle shaft specimens. (One for mounting in plastic and one for hardness

testing)

III. HARDNESS TESTING

1. All three axle shaft samples were tested for hardness at all areas of the shaft. (Inner hardness through outer hardness)

2. The hardness tester used was the digital readout hardness tester, using the Rockwell Hardness C scale, and the ball

indenter. (Figure 8)

3. The sample was placed on the flat surface of the moveable spindle.

4. Using the up/down buttons, the spindle was moved so that the sample was about 1/4” away from the indenter.

5. The green start button was then pressed and the tester automatically started the test and the result showed on digital

screen when completed.

***If the reading was below 20 Rockwell C, the Rockwell B tester was used subtracting 80 to get Rockwell C.

6. The sample was then placed on the flat surface of the moveable spindle of the B tester. (Figure 9)

7. First on the B tester, the hardness test lever was pulled forward toward the operator, locking into position.

8. The specimen was then placed on the flat surface of the moveable spindle.

9. Using the spindle raise/lower lever, the sample was lifted towards the indenter until it they touched.

10. The lever was then continued, rotating counter-clockwise until the pre-test pressure needle aligned with the black dot in

the twelve o’clock position.

11. The release lever was then pushed down.

12. The hardness test lever was then released, moving toward the back slowly. It is important to wait until this lever has

completely stopped moving which may take about 30 seconds.

13. The lever was then pulled back towards the front locking it in place. As this happened, the hardness number indicator

needle was then pointing to the correct Rockwell B number.

***Hardness tests were taken at multiple positions.

IV. MOUNTING THE SAMPLES FOR MICROSCOPY

14. The other three samples that did not receive hardness tests were then utilized, along with the two failed axle shaft

samples, to be mounted in plastic, which is necessary for polishing and viewing the grain structure under the microscope.

15. The automatic sample mounting unit was used for these samples. (Figure 10)

16. Before starting the machine, the sleeve and plunger were wiped free of leftover plastic, which later made it easier to slide

the plunger into the sleeve.

17. Next, the machine was preheated by turning the cool/heat knob to “heat.” This preheated for roughly ten minutes, until

the heat light turned off.

18. Once preheated, the pressure release knob was turned off, and the hydraulic press was move so it protruding out of the

top, using the up/down/neutral knob to “up,” then back to “neutral” once at desired height.

19. The sample was placed on the top surface of the press. The surface that was to be viewed was placed facing down.

20. The knob was then turned to down, and the pressure was released until the press dropped to the bottom.

21. Next, 350 mL of Bakelite Powder was poured into the top of the sleeve.

22. The plunger was then placed down the sleeve, and was tightened using the threads in a clock-wise direction. Once tight,

the plunger was turned 1/4 of the way counter clock-wise to make it easier to remove once mounting was completed.

23. The pressure release was then turned off, and the knob was set to up. The press was then automatically lifted until it

reached 4100 psi.

24. The timer knob was then set to 12 minutes.

25. After the heating period, the cool/heat knob was switched to cool, and the timer was reset for about 8 minutes.

26. After cooling, the pressure was released, and the knob was turned to “down.”

27. The plunger was then removed by turning counter clock-wise, and setting the press to “up” with the pressure release off,

pushing the plunger out, followed by the mounted sample.

28. The sample was then removed out of the top of the sleeve, and ready for polishing.

***This process was done to all three axle shaft samples, and the two failed axle shaft samples.

V. POLISHING THE MOUNTED SAMPLES

1. Due to the mounting of five samples, The automatic polisher with a capacity of four samples was used. (Figure 13)

2. The mounting tool was used to keep the four samples level for surfacing and polishing. (Figure 14)

3. The sample holder was placed in the tool, and fastened down.

4. Each sample was placed in an open spot. With pressure applied to keep the sample on the flat surface, the set screw was

tightened with an allen wrench. (Figure 15)

5. The first wheel used was the Cameo Platinum 1 wheel with water.

6. The sample holder was place under the spindle, and the center pin of the spindle was lowered into the center hole of the

holder, and the handle was turned clock-wise to put pressure on the spindle.

7. The settings were 25 lbs. of pressure at 150 rpm.

8. After samples were surfaced flat, with no facets visible, the nylon wheel was used to polish each sample.

9. The settings were 35 lbs. of pressure at 200 rpm with diamond lubricant. (Figure 17)

10. After all samples were polished, they were removed from the holder to be final polished.

11. Final polishing was done individually on each sample on the manual polisher. (Figure 16)

12. Pressure was placed with body weight and the micropolish with water was used. (Figure 18)

VI. ETCHING THE SAMPLES

1. Once the samples were polished, and all scratches removed, they were etched to better reveal the properties of the grain

structures. (Figure 20)

2. After polishing, the samples were cleaned with denatured alcohol and left to dry. (Figure 19)

3. For storage, the samples were placed in the desiccator to prevent contamination. (Figure 12)

4. Once dry, the samples were placed in the sink, and etched with “Nital,” or Nitric Acid. (Figure 21)

5. The Nital was placed in a dropper, administered quickly and evenly to all portions of the visible sample.

6. The Nital remained on the sample for about 20 seconds, or until the surface of the sample became cloudy.

7. Once etched for the proper amount of time, the Nital was rinsed off with the denatured alcohol.

8. Once dry, the samples were ready to view under the microscope.

VII. VIEWING THE SAMPLES UNDER THE MICROSCOPE.

1. The microscope was first turned on, and the viewing software “PaxCam” was opened.

2. A new folder was created to save all captured pictures from the microscope.

3. Each sample was first placed on a flat piece of metal with clay in between. The sample was then flattened with the press.

***This was necessary in order to focus in on all the surface of the sample evenly. (Figure 22)

4. The sample was then placed on the stage of the microscope. (Figure 23)

5. The tests began on the smallest optical zoom, which was the 100x zoom.

6. Using the coarse adjustment, the image of the sample was found.

7. The fine adjustment was then used to focus on the sample to view a clear picture.

8. Step #7 was used to view the sample up until the 1000x zoom.

9. Pictures were captured from each size zoom at all different areas of the sample.

10. White balance and exposure were adjusted to better view the sample.

DATA

Hardness Based on Position

Toyota Inner 16.1 HRC

Chromoly Inner 47 HRC

Dana 60 Inner 5.1 HRC

Toyota Middle 14.9 HRC

Chromoly Middle 47 HRC

Dana 60 Middle 55.9 HRC

Toyota Outer 60.7 HRC

Chromoly Outer 51.5 HRC

Dana 60 Outer 53.5 HRC

Angle in degrees

Stock ft/lbs

Chromoly ft/lbs

Dana 60 ft/lbs***

0 50 12 500

4 116 70 1381

8 210 350 2417

12 700 1100 3453

16 1458 2108 4489

20 2336 3179 5525

24 3149 4155 6215

28 4081 4932 6906

32 4439 5405 7251

36 4626 5744 7596

40 4741 6065 7942

44 4780 6408 8100

46 4786 6428 8149

50 4932 6604 52 4902 6704 56

6752

62

6974 64

7033

74

7294 82

7421

86

7570 90

7590

98

7739 112

7835

114

7827 120

7929

132

7995 140

8035

142

8075

Data Set #2: Torque Measurement Values

Data Set #1: Hardness Values in

Rockwell C

***Shafts torsion tested during experiment were

chrome-molybdenum and stock Toyota. Dana 60

data was provided by RCV Performance from

previous testing

RESULTS

Graph 1: Torque v. Angle Graph

CALCULATING TORSIONAL STRENGTH PER INCH SQUARED

-Dana 60 Failure-------------------------------- 8149 ft/lbs.

-Stock Toyota Failure-------------------------- 4902 ft/lbs.

-Chromoly Toyota Failure--------------------- 8075 ft/lbs.

-Dana 60 Radius-------------------------------- 1.41 in.

-Stock Toyota Radius-------------------------- 1.23 in.

-Chromoly Toyota Radius--------------------- 1.26 in.

EQUATION FOR CALCULATING TORQUE PER INCH SQUARED

FT/LBS ÷ AREA (AREA = πr^2)

Dana 60----------------------------------------- 8149 ft/lbs ÷ 1.41 in. = 5779 ft/lbs per inch squared

Stock Toyota----------------------------------- 4902 ft/lbs ÷ 1.23 in. = 3985 ft/lbs per inch squared

Chromoly Toyota------------------------------ 8075 ft/lbs ÷ 1.26 in. = 6409 ft/lbs per inch squared

RANKING OF STRONGEST MATERIAL FOR TORSIONAL STRENGTH

1. Chrome-Molybdenum-------------------6409 ft/lbs per inch squared

2. Dana 60 Steel-----------------------------5579 ft/lbs per inch squared

3. Toyota Steel------------------------------3985 ft/lbs per inch squared.

Graph 2: Iron-Carbon Phase Diagram with

Hypo/Hyper Eutectoid Steels

Graph 3: Hardness Graph

Graph 4: Martensite Percentage Graph

Hypereutectoid Steel Hypoeutectoid Steel

DISCUSSION

IMAGES OF DANA 60 CAPTURED ON MICROSCOPE

IMAGES OF STOCK TOYOTA CAPTURED ON MICROSCOPE

Figure 25.1: Toyota Edge

Martensite 1000x

Figure 25.2: Toyota Middle

Pearlite 1000x

Figure 25.3: Toyota Center

Pearlite 1000x

Figure 24.1: Dana 60 Edge

Martensite 1000x

Figure 24.2:Dana 60 Middle

Pearlite 1000x

Figure 26: Changes of Grain of Different

Areas of Carburized Steel

Figure 24.3: Dana 60 Center

Pearlite 1000x

RESULTS OF ANALYSIS FOR HARDENING METHODS OF DANA 60 AND STOCK TOYOTA

Given the Dana 60 is comprised of AISI 1040 steel, the pictures

taken show different grain structures of this medium carbon steel

which has a carbon content of .4% and an untreated hardness of

around 5 Rockwell C. In comparison to the Figure 26,which

shows the different grain structures at different points of steel case

hardened through carburizing, the pictures taken at different areas

appear similar. As seen in Figure 24.1, towards the edge of the

shaft shows a coarse, needle-like martensitic structure. Towards

the middle, there are variations of ferrite and pearlite, which are

common structures found in medium carbon steels that have been

heated prior and cooled slowly. (Figures 24.2&3)

The pictures of the stock Toyota(Figures 25.1-3) show very

similar characteristics to the Dana 60 pictures. From this, a

conclusion can be drawn that the steel used in these axles are also

AISI 1040 steel or similar. They also show the same signs of

being case hardened through carburizing, and are hypoeutectoid

steels. The stock Toyota steel shows a lower torsional strength

which means the carbon content is closer to .3% carbon.

IMAGES OF CHROME-MOLYBDENUM TOYOTA CAPTURED ON MICROSCOPE

Figure 27.3: Chromoly Center

Fine Martensite 1000x Figure 27.2: Chromoly Middle

Fine Martensite 1000x

Figure 27.1: Chromoly Edge

Fine Martensite 1000x

Figure 28: Coarse Martensite (Upper)

v. Fine Martensite (Lower)

RESULTS OF ANALYSIS FOR HARDENING METHODS OF CHROMOLY TOYOTA

As, fine martensite is present throughout the entire shaft,

it can be concluded that these shafts have been fully heat

treated, and not case hardened. As shown at the bottom

of Figure 28, the grain structure of the chrome-

molybdenum steel is fine needle-like martensite, which is

commonly found in heat treated high alloy steels. The

top of Figure 28, shows coarse needle-like martensite,

which is commonly found in heat treated low carbon

steels such as the AISI 1040 steel found in both the stock

Toyota and Dana 60 axles.

In viewing the through, fine martensitic structure of the

chromoly shafts, (Figures 27.1-3) it can be concluded

that these shaft have been through a heat treatment and

quench that will cause the martensitic structure. As

stated in the Introduction under the Heat Treatment of

Steel for Torsional Strength, These shafts most likely

received similar heat treatment methods. As these shafts

are made from AISI 4340, using data from matweb.com,

the carbon content is at .43%. These shafts were most

likely heated above the A3 line upwards of 1500°F for at

least an hour. At this point, the metal is completely

consisting of austenite steel. To gain hardness, the

samples were quenched in a medium such as water or oil

to create a martensitic composition. Had the sample

been annealed, or cooled slowly, pearlite would have

formed with a low hardness number. The average

hardness number of the final shafts is about 48 HRC.

After cooling, the hardness would be higher, which is

desirable to resist deformation, however the shaft would

also be very brittle, and susceptible to fracture. These

shafts were then most likely tempered for at least two

hours at a temperature of at least 1000°F. Most of the

hardness was retained, while taking away the brittleness

of the steel, and gaining the desirable property of

toughness.

IMAGES OF BROKEN CHROME-MOLYBDENUM TOYOTA CAPTURED ON MICROSCOPE IMAGES OF BROKEN STOCK TOYOTA CAPTURED ON MICROSCOPE

Figure 29.3: Chromoly

At Crack 1000x

Figure 29.2: Chromoly

At Break 500x

Figure 29.1: Chromoly

Near Break 1000x

Figure 29.6: Chromoly Broken

At Surface Outer 1000x Figure 29.5: Chromoly Broken

At Surface Center 1000x

Figure 29.4: Chromoly

At Crack 200x

Figure 30.1: Toyota

At Break 1000x Figure 30.2: Toyota

Near Break 1000x

Figure 30.3: Toyota

At Break 500x

Figure 30.6: Toyota Broken

At Surface Outer 1000x

Figure 30.5: Toyota Broken

At Surface Center 1000x

Figure 30.4: Toyota

Away From Break 1000x

RESULTS OF FAILURE ANALYSIS FOR DANA 60 AND STOCK TOYOTA

GRAPH INTERPRETATION

Graph 1 shows the torque applied to each of the three axle shafts up until their failure point on the Y axis, and twist in angle

of degrees on the X axis. One thing that is important to note is the curves of each line representing a shaft. While the line is

in a straight up direction, this represents the elastic deformation of the shaft. This means that the shaft will return back to its

original position after released. Once the lines stray to the right, this show plastic deformation, which means that the shaft

will be permanently deformed after released. It is important to note the elastic limits of the Dana 60 and Stock Toyota

compared to the chrome-molybdenum axle shaft. All three shafts have an elastic limit around 30 to 40 degrees, however the

difference is in plastic deformation before failure. The Dana 60 and stock Toyota shafts show to still have brittle properties,

as they reach 10 more degrees after the elastic limit is reached before failing. The chrome-molybdenum shaft turned another

96 degrees before failing. This shows more toughness, which is desirable in torsional applications.

Graph 3 shows the different areas of the shafts, and what their hardness values are in Rockwell C. Values that are marked as

“outer,” were tests taken from the shaft, closest to the edge without receiving a skewed reading. Values marked as “center,”

were tests taken at the very center point of the shaft. Values marked as “middle,” were tests taken from an area in between

the center point and the outer edge.

In Figures 29.1-6, The fine grain structure of the fine martensite shows very smooth breaks without cratering. The

crystalline structure is also very fine; however a crack can be seen which is most likely caused from the larger spread of

force acting against the torque to prevent failure.

While conclusions have been drawn that the stock Toyota and Dana 60 axle shafts are made of steel similar to AISI 1040

steel, it can also be concluded that both shafts failed from the same reasons, since no pictures of broken Dana 60 axles

were available. As seen in Figures 30.1-6, through 1000x magnification, the crystal structure is apparent, but also shows

large coarse fractures, which can be drawn from the fact that the martensitic and pearlite structures of both shafts have

very coarse grains, which are undesirable for all strength types, as they fracture much easier than fine grained structures.

In Figure 30.3, slip plains in the grain structure can also be seen, which means that between the martensite grains are

crystallographic planes that cause the grains to slide across each other when stress is applied. This is also a reasonable

explanation as to why this steel failed.

As seen in Figure 32, the chrome-molybdenum shaft shows a very smooth break across the whole area. This is due to a

through heat treatment of metal. Figure 31 shows a failed shaft from torsional forces. Microvoids are also visible, due to

coarse craters on the surface from coarse grain structure failures. Figure 33 is the stock Toyota shaft, showing some

signs of microvoids towards the center. It is also apparent where the shaft was hardened on the outside, as its failure

differed from that of the steel towards the middle that was pearlite steel.

While conclusions have been drawn that the stock Toyota and Dana 60 axle shafts are made of steel similar to AISI 1040

steel, it can also be concluded that both shafts failed from the same reasons, since no pictures of broken Dana 60 axles

were available. As seen in Figures 30.1-6, through 1000x magnification, the crystal structure is apparent, but also shows

large coarse fractures, which can be drawn from the fact that the martensitic and pearlite structures of both shafts have

very coarse grains, which are undesirable for all strength types, as they fracture much easier than fine grained structures.

In Figure 30.3, slip plains in the grain structure can also be seen, which means that between the martensite grains are

crystallographic planes that cause the grains to slide across each other when stress is applied. This is also a reasonable

explanation as to why this steel failed.

As seen in figure_____, the chrome-molybdenum shaft shows a very smooth break across the whole area. This is due to

a through heat treatment of metal. Figure__________, shows a failed shaft from torsional forces. Microvoids are also

visible, due to coarse craters on the surface from coarse grain structure failures. Figure_______is the stock Toyota shaft,

showing some signs of microvoids towards the center. It is also apparent where the shaft was hardened on the outside, as

its failure differed from that of the steel towards the middle that was pearlite steel.

Figure 33: Toyota

Broken At Surface

Figure 31: Images of Broken Shaft

Surfaces from Torsional Force

Figure 32: Chromoly

Broken At Surface

DATA LEGITIMACY

All data and pictures taken from all three shafts are deemed legitimate as they were all executed during and at the place of the

experiment. The only data that was not recorded at the time of the experiment was the torsion testing of the Dana 60 axle;

however this data came from a documented experiment by RCV Performance.

WHAT WORKED/ WHAT DIDN’T WORK

Almost all aspects of this experiment worked well with proper patience and skill. Polishing of the samples took longer than

expected, and some scratches remained on the sample; however, this did not skew any results, and grain structure was easily

visible. One section of the torsion testing did not work, as a metal key for a key slot broke while testing. This was fixed by

placing a replacement key and running the test again.

OBJECTIVES MET

The first objective of finding the torsional strength of each shaft was met. Also, finding the proportional torsional strengths

were also found through simple calculations.

The second objective of finding the heat treatment types of each steel, and alloy types were also determined through

mounting, polishing, etching, and viewing through the microscope.

With this knowledge, the third objective of analyzing the reasons for failure were also determined.

Finally, the fourth objective of overall performance of the Dana 60 axle and the chrome-molybdenum axle were determined,

and found to have close torsional strengths, with the chrome-molybdenum having a higher proportional torsional strength.

CONCLUSIONS 1. The steel used for the Dana 60 axles was comprised of AISI 1040 steel with a torsional failure rate of 5579 ft/lbs per

square inch and a carbon content of .4%. This steel was case hardened through carburizing, containing coarse, hard

martensite towards the edge, and a mixture of soft ferrite and pearlite towards the center

2. The steel used for the stock Toyota axles was comprised of AISI 1040 steel with a torsional failure rate of 3985 ft/lbs per

square inch and a carbon content of .3%. This steel was case hardened through carburizing, containing coarse, hard

martensite towards the edge, and a mixture of soft ferrite and pearlite towards the center.

3. The steel used for the aftermarket axles was comprised of AISI 4340 steel with a torsional failure rate of 6409 ft/lbs per

square inch and a carbon content upwards of .43%. This steel was fully heat treated above the A3 line creating hardened,

fine martensite throughout, then tempered to increase toughness and decrease brittleness.

4. While the Dana 60 axle shaft did not have the highest torsional strength per square inch, the larger diameter caused it to

break at the highest point of the three at 8149 ft/lbs. Following was the chrome-molybdenum shaft at 8075 ft/lbs. The

smallest failure value was the stock Toyota shaft at 4902 ft/lbs.

5. Case hardening of the Dana 60 and stock Toyota shafts proved to create a very coarse grain structure that gave torsional

strength to the shafts; however the shafts showed little plasticity, failing shortly after the elastic limit due to the brittleness of

coarse grains.

6. The chrome-molybdenum shafts created a fine grain structure that produced the best torsional strength and a large amount

of plastic deformation before failing, which makes AISI 4340 steel the best choice for high torsional force applications.

ACKNOWLEDGMENTS

I would like to use this section to thank everyone for their help and contributions towards my metallurgy experiment.

-I would like to give special thanks to my professor, Kyle Metzloff Ph.d. His knowledge and help both in and out of class,

along with usage of the lab made my experiment able to be completed.

-I would also like to give much thanks to John Frana and others at RCV Performance for taking the time to give me a plant

tour and break axle shafts on their torsion tester. This was one of the biggest parts of my experiment, and I would not have

been able to complete my project without the assistance and accommodation of John and his contributions to my project.

-I also thank Bobby Long of Longfield Superaxles for providing me with my first sample of his chrome-molybdenum axle

shaft, and his time was much appreciated.

-Lastly, I would like to thank Randy’s Ring and Pinion for providing me with the Dana 60 sample, and sending it quickly and

free of charge.

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