The Material And Process Requirements For Driving Shaft Engineering Essay

Based on my research, a drive shaft, driving shaft or propeller shaft is a mechanical component for transmitting torque and rotation that always used to connect other components of a drive train that cannot be connected directly because of distance or the necessity to allow for relative movement between them.

Besides that, drive shafts carrying an important role as carrier of torque in driveline application. They may be subject to torsion and shear stress, equivalent to the difference between the input torque and the load. Therefore, they need to be strong enough to bear the stress, whilst avoiding too much excess weight as that would in turn increase their inertia.

Drive shafts frequently incorporate one or more universal joints or jaw couplings, and sometimes a splinted join or prismatic join to allow for variations in the alignment and distance between the driving and driven components

Based on the functions that is discussed in previous, I understand that the material of drive shaft must be strong enough to bear the stress, light weight which in a position to decrease the overall automobile weight and therefore, increase their inertia at exactly the same time.

For the mechanical properties that required for drive shaft like the ability to reduce the losses in transmission, high tensile strength material, high torsional strength and light-weight. Therefore, I'd like to suggest that polymer matrix composite is more desirable as a chosen material that can be apply in driveline application.

1. 1 Design Factors

In the progress of my research in driveline application, I then found out that marketing considerations are paramount in the motor car industry. You will discover two factors get this to particular application attractive to the industry.

On the main one hand, vehicles are solid in the market place on claims of increased comfort, luxury and smoothness of operation. On the other hand, the maker is also seeking to provide the maximum performance with the minimum fuel consumption at the same time.

Thus, usually these two requirements are conflicting. For instance, a reduction in body panel thickness reduces mass therefore increases performance and fuel efficiency, but this change also increases internal noise. Therefore, some automobile industry has spend much modal in doing research and recently, they have an idea which using carbon fiber (polymer matrix composite) in drive shafts which in a position to contributes to obtaining both aims simultaneously.

The factors to be optimized in a shaft after meeting the essential operating requirements just outlined is mass, smoothness of ride and cost. It is because reducing mass is important:

To improve performance of vehicle and reduce fuel consumption.

To reduce un-sprung mass and so improve vehicle handling and ride.

To reduce the residual out of balance forces from rotating parts therefore further improve smoothness in use.

2. 0 Material Selection

Based on the study of different type of material of drive shaft or propeller shaft in driveline application, I have chosen polymer matrix composite as the material selection in driveline application.

2. 1 Introduction to Polymer Matrix Composite

Polymer Matrix Composite is the material comprising polymer matrix coupled with a fibrous reinforcing dispersed phase. Polymer matrix composites are very popular because of the low priced and simple fabrication methods.

Use of non-reinforced polymers as structure materials is bound by low degree of their mechanical properties such as tensile strength of one of the strongest polymers (epoxy resin) is 20000 psi (140 Mpa). In addition to relatively low strength, polymer materials posses low impact resistance as well.

Besides that, the reinforcement is commonly stiffer and better than the matrix providing stiffness and strength. Reinforcement is laid in a specific direction, within the matrix, so that the resulting material will have different properties in several directions. As example, composites have anisotropic properties. This characteristic is exploited to optimize the look and provide high mechanical performance where it is necessary.

2. 2 Design of a Composites Shaft

According to A. W. Thompson from Bristol Composite Materials Engineering Ltd, He has mentioned the two typical shafts hand and hand, one manufactured in steel and the other in composites as shown in Figure 1.

Figure 1 Composite Drive Shaft (Upper) with Steel Shaft

The illustration shows the simplicity of the look made possible by carbon fiber. The combination of high stiffness and low density in the composite allows an extended shaft to be made without reaching a critical whirling speed. The whirling speed of your rotating shaft is the speed at which it becomes unstable and defluxions occurs normal to the axis of rotation. The benefit in whirling speed is certainly as to allow most two piece steel shaft to be replaced with a single composite part.

Besides that, weight and cost are reduced by dispensing with the central universal joint and the associated bearing. Moreover, N. V. H (Noise, Vibration and Harshness) factors are improved by the consequent isolation of the passenger compartment from drive line vibration following deletion of the centre bearing from underneath the driver's seat. Further reductions in N. V. H are possible by modification to the orientations of the fibres in the properller shaft tube, which effect longitudinal and radial stiffness.

2. 3 Reason Selecting Polymer Matrix Composite as Material in Driveline Application

The basic attraction of polymer matrix composite materials for driveshaft application is that they be able to boost the shaft length, which is otherwise constrained by bending resonance. For many vehicles, a one piece composite shaft may replace a two piece steel shaft which simplifies both shaft and installation in the vehicle.

Besides that, by using fibre reinforced composites, you'll be able to arrange the fibre orientations in the tube so the bending modulus has a higher value (above 100Gpa) whilst the precise gravity is low (below 1. 6). This brings about a favourable specific bending modulus and an increased critical speed as well.

Figure 2 Critical Speeds for Automotive Propshaft

According to A. W. Thompson from Bristol Composite Materials Engineering Ltd, the relationship between shaft length and critical speed for tubes suited to automotive propshaft is illustrated in Figure 2.

The graph demonstrates, for a specific application in which a critical speed of 8000 rev/min is acceptable, the longest shaft possible out of steel is 1250 mm whereas a composite shaft of 1650 mm could be performed.

Thus, the utmost length for either shaft is reduced with respect to the compliance of the finish connections. For acceptable NVH (Noise, Vibration and Harshness), there must also be an satisfactory margin between vibration drivers and bending resonance of the shaft. Nevertheless, it is normally true that a composite shaft can be produced longer when compared to a steel shaft and that for automotive platforms where a two-piece steel shaft with centre support bearing is specified a one-piece composite shaft may be acceptable.

This fundamental material property advantage is a powerful technical driver for composite shafts, and substantial weight savings may be accomplished. One-piece shafts also simplify the design and engineering of the vehicle floor pan.

Therefore, based on explanation above, it is actually that I have chosen carbon fiber composite (one type of the polymer matrix composite) as the material for drive shaft and additional material properties will be discuss at length later as well.

2. 3. 1 Material Property of Carbon Fiber Composite (Polymer Matrix Composite)

According to Core Composites, Division of ROM Development Corporation's research, the material properties of Carbon Fiber Composite are as below:

Features

Benefits

Extremely High Stiffness

With a number of modulus available from standard 33 msi to ultra high modulus pitch over 125 msi carbon fiber has the highest specific modulus of all commercial reinforcing fibers.

High Tensile Strength

The strongest of most commercial reinforcing fibers in tension. Especially best for the strain skin on composite laminates.

Excellent Corrosion Resistance

Used in reinforcing concrete, carbon has good alkaline resistance as well as resistance to salt water and many other chemical environments.

Excellent Fatigue Properties

Used as an initial reinforcement for fatigue prone products such as helicopter and wind mill blades as well as offshore power and driveline application.

Excellent Compression Properties

Proper fiber sizing for the resin matrix selected can yield impressive compressive properties but this quality could be very difficult to measure with standard ASTM test methods and careful test specimen preparation is crucial to accomplish accurate result.

Low Coefficient of Linear Expansion

Carbon is an excellent tooling reinforcement for molds that will dsicover temperature and where parts need tight dimensional stability.

2. 3. 2 Composite Shaft Performance

According to the research that done by Tetsuyuki Kyono, Composites Development Center, Toray Composites (America), Inc. about the carbon fiber composites applications for auto industries, they may have mentioned about carbon fiber composite drive shaft having crush worthiness. Crash load produced during head collision can be absorbed by newly developed joining technology without adhesive between carbon fiber composite tube and steel adapter.

This technology can truly add safety value to passenger cars in addition such as weight and noise reductions. Therefore, the performance data of the composite shaft should be take consideration as you of the key section in finding the right material to use in driveline application.

Thus, they have got evaluated torque carrying capability as index of shaft performance. Among typical data has been shown in Figure 3. It is noted composite drive shaft performed as expected up to 150-C at static torsional ensure that you showed much better fatigue resistance than steel system shown as target.

Figure 3 Torsional Strength of Drive Shaft for 2000 Nm Class

In Figure 4, residual torque carrying capacities after exposure to various environments are shown in percentage compare with control data. As shown below has shown the reduction in performance of composite drive shaft is very minimal.

Figure 4 Residual Torsional Strength (%) after Environmental Testing

2. 3. 3 Proving Test

After the evident laboratory tests above to show static strength and stiffness, fatigues tests are essential as well. Carbon fibre has a great performance in fatigue and glass fibre is really as good as most metals.

A composite shaft has withstood 106 cycles of maximum torque in comparison with the 104 cycles typically required of any steel shaft. Shafts were fitted to cars to get road experience and demonstrate satisfactory operations. Such testing demonstrates that the component does work and meets all the standards required.

In this application, for instance, road use showed that:

Temperature resistance to underbody environment was satisfactory

Corrosion resistance (example: to salt spray had not been a problem)

Creep loading resistance was adequate

Resistance to flying stone damage was not a problem

End attachment strength was adequate

Shock load capability was adequate

Based on the proving test that has been done by A. W. Thompson, we knew that polymer matrix composites is suitable to be studied as material in driveline application such as making drive shaft or propeller shaft as well due to its attractive material properties and less expensive cost as well if equate to others material such as steel.

2. 3. 4 Crash Performance of Composite Propshafts

According to Dr Andrew Pollard, GKN Technology, Wolverhampton, UK, he stat that increasing public curiosity about safe vehicles is encouraging car manufacturers and their suppliers to create components and systems that will succeed in an accident (2). The propeller shaft in rear- and fourwheel- drive cars is good example of this.

Figure 5 Behaviour of Propeller Shafts in Frontal Crash

In a frontal crash, the propeller shaft transmits forces from the engine/gearbox unit to the trunk axle. Many vehicles today have a two-piece propeller shaft that can buckle at the centre bearing in any direction, depending on joint position at impact. Hence, it is nearly impossible to predict the axial force and the absorbed by the shaft in an accident.

This is illustrated in Figure 5, contrasted with the behavior of your propeller shaft with a precise axial collapse mode. The mark for crash-optimized propeller shafts is to attain a defined behavior of axial force and displacement during an impact and consequently manipulated energy absorption as shown in Figure 5.

3. 0 Manufacturing Process of Carbon Fiber

The process to make carbon fibers is part chemical and part mechanical. The precursor is drawn into long strands or fibers and then heated to a very temperature with-out and can are exposed to oxygen. Without oxygen, the fiber cannot burn. Instead, the temperature causes the atoms in the fiber to vibrate violently until the majority of the non-carbon atoms are expelled. This technique is named carbonization and leaves a fiber composed of long, and tightly.

The fibers are coated to safeguard them from damage during winding or weaving. The coated fibers are wound onto cylinders called bobbins.

The fibers are coated to protect them from damage during winding or weaving. The coated fibers are wound onto cylinders called bobbins. Moreover, the inter-locked chains of carbon atoms with only a few non-carbon atoms remaining.

Here is a typical sequence of functions used to form carbon fibers from polyacrylonitrile.

3. 1 Spinning

First: Acrylonitrile plastic powder is mixed with another plastic, like methyl acrylate or methyl methacrylate, and is also reacted with a catalyst in a typical suspension or solution polymerization process to form a polyacrylonitrile plastic.

Second: The plastic is then spun into fibers using one of the different methods. In a few methods, the plastic is blended with certain chemicals and pumped through tiny jets into a chemical bath or quench chamber where the plastic coagulates and solidifies into fibers. This is similar to the process used to create polyacrylic textile fibers. In other methods, the plastic mixture is heated and pumped through tiny jets into a chamber where in fact the solvents evaporate, leaving a good fiber. The spinning step is important because the internal atomic structure of the fiber is formed during this process.

Third: The fibers are then washed and stretched to the required fiber diameter. The stretching helps align the molecules within the fiber and provide the foundation for the forming of the tightly bonded carbon crystals after carbonization.

3. 2 Stabilizing

Forth: Prior to the fibers are carbonized, they have to be chemically altered to convert their linear atomic bonding to a far more thermally stable ladder bonding. That is accomplished by heating the fibers in air to about 390-590 F (200-300 C) for 30-120 minutes. This causes the fibers to get oxygen molecules from the air and rearrange their atomic bonding pattern. The stabilizing chemical reactions are complex and involve several steps, a few of which occur simultaneously. They also generate their own heat, which must be manipulated to avoid overheating the fibers. Commercially, the stabilization process runs on the variety of equipment and techniques. In a few processes, the fibers are drawn through a series of heated chambers. In others, the fibers pass over hot rollers and through beds of loose materials held in suspension by the flow of hot air. Some processes use heated air blended with certain gases that chemically accelerate the stabilization.

3. 3 Carbonizing

Fifth: After the fibers are stabilized, they can be heated to a temperature of about 1, 830-5, 500 F (1, 000-3, 000 C) for several minutes in a furnace filled up with a gas mixture that will not contain oxygen. Having less oxygen prevents the fibers from burning in the high temperatures. The gas pressure inside the furnace is kept higher than the outside air pressure and the points where the fibers enter and exit the furnace are sealed to keep oxygen from entering. As the fibers are heated, they start to reduce their non-carbon atoms, and also a few carbon atoms, in the form of various gases including water vapor, ammonia, carbon monoxide, carbon dioxide, hydrogen, nitrogen, while others. As the non-carbon atoms are expelled, the remaining carbon atoms form tightly bonded carbon crystals that are aligned more or less parallel to the long axis of the fiber. In some processes, two furnaces operating at two different temperatures are used to raised control the rate de heating during carbonization.

3. 4 Treating the Surface

Sixth: After carbonizing, the fibers have a surface that will not bond well with the epoxies and other materials found in composite materials. To give the fibers better bonding properties, their surface is slightly oxidized. The addition of oxygen atoms to the top provides better chemical bonding properties and also etches and roughens the surface for better mechanical bonding properties. Oxidation may be accomplished by immersing the fibers in a variety of gases such as air, skin tightening and, or ozone; or in a variety of liquids such as sodium hypochlorite or nitric acid. The fibers can be coated electrolytically by making the fibers the positive terminal in a bath filled up with various electrically conductive materials. The top treatment process must be carefully manipulated to avoid forming tiny surface defects, such as pits, which could cause fiber failure.

3. 5 Sizing

Seventh: After the surface treatment, the fibers are coated to protect them from damage during winding or weaving. This technique is called sizing. Coating materials are chosen to be compatible with the adhesive used to form composite materials. Typical coating materials include epoxy, polyester, nylon, urethane, as well as others.

Eight: The coated fibers are wound onto cylinders called bobbins. The bobbins are loaded into a spinning machine and the fibers are twisted into yarns of various sizes.

3. 6 Quality Control

The really small size of carbon fibers will not allow visual inspection as a quality control method. Instead, producing regular precursor fibers and closely controlling the manufacturing process used to turn them into carbon fibers controls the product quality. Process variables such as time, temperature, gas flow, and chemical composition are closely monitored during each stage of the production.

The carbon fibers, as well as the finished composite materials, are also at the mercy of rigorous testing. Common fiber tests include density, strength, amount of sizing, and more. In 1990, the Suppliers of Advanced Composite Materials Association established standards for carbon fiber testing methods, which are actually used throughout the industry.

3. 7 Health insurance and Safety Concerns

There are three regions of concern in the production and handling of carbon fibers: dust inhalation, skin irritation, and the effect of fibers on electrical equipment.

During processing, bits of carbon fibers can break off and circulate in the air by means of an excellent dust. Industrial health studies show that, unlike some asbestos fibers, carbon fibers are too large to be always a health hazard when inhaled. They can be an irritant, however, and people working in the area should wear protective masks.

The carbon fibers can also cause skin irritation, especially on the back of wrists and hands. Protective clothing or the use of barrier skin creams is preferred for people in an area where carbon fiber dust is present. The sizing materials used to coat the fibers often contain chemicals that can cause severe skin reactions, which also requires protection.

In addition to being strong, carbon fibers are also good conductors of electricity. As a result, carbon fiber dust can cause arcing and shorts in electrical equipment. If electrical equipment can't be relocated from the area where carbon dust is present, the gear is sealed in a cabinet or other enclosure.

4. 0 Fabrication Procedure for Driveshaft by using Polymer Matrix Composite

According to the project research that done by Alex Santiago from Texas A&M University Kingsville, he has discussed the fabrication procedure for drive shaft by using polymer matrix composite which is carbon fiber as main material.

As reference, the fabrication process by Alex has been taken for me to understand the hand make drive shaft by using carbon fiber in true to life. Thus, the following fabrication process is belonging to Alex from Texas University which will probably be worth to be taken as references in this topic discussion.

There are a number of things to consider when picking a fabrication method. Time is a major consideration. There may be short amount of time for fabrication, therefore the fabrication process should be quick. The fiber needs to be laid at specific angles to give the shaft certain characteristics. The weave patterns need to be tight and compact. Resin needs to be applied evenly. The shaft needs to be wound in ways such that the yokes can be easily attached. The easiest fabrication method for developing a hollow tube is filament winding. Filament winding is an automated process when a filamentary yarn in the form of tow is wetted by resin and uniformly and regularly wound about a rotating mandrel. The filament winder can be programmed to generate specific and tightly wound patterns.

To build a composite part on the winder, a winding pattern is needed, plus a mandrel, mold release, fiber, resin and hardener, a way to apply even pressure to the part and a curing procedure. The wind patterns were dependant on using Laminate Design software created by Dr. Larry Peel. After entering mechanical properties for the resin and tow, different wind angles and layers were tried in the Laminate Design software before driveshaft had the desired characteristics. Table 1 provides wind angle and its purpose.

The tow, resin and hardener, and adhesive will be the most critical components of the shaft. Each structural component must be carefully selected so the shaft has good mechanical properties. The tow that was found in the Laminate Design Software calculations was chosen because it is strong, light weight, and aerospace quality carbon fiber. Fiber used by the aerospace, although expensive, is rigorously quality controlled. It was decided that fiber would be uniform, therefore giving the driveshaft uniform properties.

The resin and hardener were chosen for a number of reasons. First, the resin is tough. The resin also has a high viscosity. High viscosity is desired because, with the wet winding process, is simpler to control the amount of resin being put on the tow. Wet winding will be discussed further along the way section. Another reason behind choosing this resin is its elongation at break. At 6% elongation at break, it is known that the resin will not be too brittle and that the wound shaft will have some flex for absorbing the shock between shifting gears. Finally this resin was chosen because of its high pot life. After mixing the resin and hardener, there's a little over two hours before it starts to gel. This is enough time to wind the whole shaft prior to the resin sets up.

The adhesive was chosen for a couple of reasons. Foremost, the adhesive also met the requirements for high tensile lap shear strength at room and elevated temperatures. At room temperature the adhesive has lap shear strength of 4, 200 psi. At 250 F the lap shear strength is 2, 300 psi. Also, the adhesive is aerospace grade, ensuring high quality.

Table 1 Wind Angles

4. 1 Mandrels

In order to produce the mandrel of an driveshaft, several derivations should have been through. Mandrels made of cardboard tubing and solid shafts were considered. These ideas were never fabricated because it would be hard to eliminate the mandrel from the wound tube. The resin would cause the cardboard mandrel to adhere to the shaft rendering it impossible to eliminate. A good shaft of steel or aluminum would be heavy, and expensive to set-up.

4. 1. 1 Mandrel 1

Firstly, it was made a decision to create a mandrel manufactured from steel muffler tubing which was split with a plasma cutter into four parts along its length. The theory was to wind the shaft, allow it cure, then dismantle the mandrel and remove the tube. Next, two pieces machined out of steel were created and mounted on the muffler tubing that allows the mandrel to be spun in the filament winder. One end is chucked into the winder the other end has a live center which spins on the center point. This mandrel didn't work because the mandrel pieces cannot be bolted to the machined ends in a way that these were square. This is due to the fact that the muffler tubing is cold rolled which means it is pre-stressed. After the tubing was put into four pieces, each piece bowed.

4. 1. 2 Mandrel 2

A second mandrel was created using muffler tubing that was split into two pieces. This mandrel was square when bolted into place. To keep the tension of the fiber from pulling the gap in the mandrel closed, three round, wooden pucks were evenly spaced through the center of the mandrel.

The second mandrel was used to make a practice drive shaft. The pucks were evenly spaced through the guts of the mandrel. Shrink wrap tape, which shrinks and applies pressure when heated, is wrapped round the mandrel in the areas where the pucks are. The tape applies pressure and keeps the pucks in an upright position as shown in Figure 6. After the pucks were occur place, a few dry runs were made with no resin. One pass of every fiber angle was wound.

Figure 6: Wooden Puck in Mandrel

Once the winding began, it became evident that there is not enough turn around room. When winding a composite part, there are four defined areas on the part. The entire part includes the head, the change, the useable shaft, and the tail. The winding layout is shown in Figure 6. The wind angle is the angle the fiber makes with the guts type of the mandrel. The 45 degree and 15 degree wind angles didn't have enough friction to adhere to the mandrel in the turnaround areas. The fiber commenced to slide and bunch up, leading to misalignment in the pattern.

Figure 6: Winding Layout

This created a new problem. To keep carefully the fiber from slipping, the turnaround area would have to be lengthened. The mandrel at its current length just fits in the curing oven, rendering it impossible to lengthen the mandrel. To ease this issue, two pieces of pipe, about one foot long each, were threaded in to the ends of the machined pieces as shown in Figure 7. Adding the extensions made more turn around area. These threaded pieces can be removed once the shaft is wound and the resin creates. If the extensions are removed the mandrel can certainly be placed in the oven to complete curing.

Figure 7 Mandrel Extensions

The wind patterns were tested again with the extended change room. The extensions and the change in diameter kept the fiber from slipping, and allowed for full uniform coverage by the fiber. The test patterns were removed, and resin and hardener were mixed and poured into the resin bath to start a practice shaft. The resin bath applies resin to the fiber before it is wound about the mandrel. The resin bath can be seen in Figure 8. A practice shaft was wound using the setup shown in Table 2. A practice shaft was wound for a few reasons. The practice shaft allowed testing of the wind patterns with the resin and the fiber together. Curing temperature and time could be observed. Dismantling the shaft can be attempted, and the shaft can be inspected for proper resin wet out, roundness, and overall strength.

Table 2 Practice Shaft Wind Pattern Setup

Figure 8 Resin Bath

This was an extremely difficult process. First, the material that wrapped over the finish caps had to be cut back to be able to expose the bolts holding it to the mandrel. Once this was accomplished we commenced removing the bolts. Resin had seeped in to the threads of a few of the bolts triggering those to stick. The top of one bolt was twisted off looking to get it out. This bolt was machined out. After the caps were removed the shaft didn't collapse as expected. The gap were the mandrel have been split had filled in with resin. A tubing cutter was used to cut the shaft into sections and then it was split in two with a band saw. A 2 foot piece was spared and slid off the shaft. The ridge left inside the shaft was 0. 125 inches deep. This created a stress riser that severely reduced the integrity of the shaft. It had been obvious that this mandrel had not been going to work.

4. 1. 3 Mandrels 3

Improving upon the mistakes on the prior mandrels, a new, one piece, mandrel was created from aluminum tubing. The tubing maintained a 2. 75 inch OD and was readily available. A 16 gauge 2. 75 OD tube was purchased. The tubing is normally made for turbo charger inlet ducting. A test piece was cut from the tube to be used for testing. The test piece was wet sanded with 2000 grit sandpaper. A silicone mold release compound was applied to the test shaft. 90 test patterns were wound onto the piece and cured at 250F for 15 hours.

We used an increased curing temperature in order to expand the aluminum mandrel while compacting the fiber. After curing was complete, we then positioned the test mandrel in the deep freeze that was -20F in order to shrink the aluminum tube. The test mandrel was removed from the freezer. The tube was impacted onto a block of wood while holding the fiber. The mandrel came out with no difficulty. This test was successful.

The third mandrel was fitted to the finish caps. The finish caps were then bolted to the mandrel. Figure 9 shows the final mandrel.

Figure 9 Final Mandrel of Driveshaft

5. 0 Conclusion

As conclusion, the potential for carbon fibre composites (one type of polymer matrix composite) in automotive drive shafts as a way of attaining substantial fat loss has long been recognized and has been demonstrated in small volume since 1988.

Finally, I feel that polymer matrix composites is the best option materials which can applied in driveline application and engineers should find cost effective applications on it to bring this applications to fruitful use within future.

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