Torsion bar, also referred to as torsion beam suspension or torsion spring suspension, is suspension system found in vehicles

Torsion Bar

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Introduction

Torsion bar, also referred to as torsion beam suspension or torsion spring suspension, is suspension system found in vehicles. The long metal bar has two ends in which one ends is firmly perpendicular manner to the bar, linked with the wishbone or the suspension arm axle. The bar gains a rotary secured into the chassis of a vehicle, while the other end terminates in a lever fixed in a motion along its axis due to the wheels vertical motion. However, the bar’s motion finds resistance from the bar’s torsion resistance. The material, diameter, and length of the bar effectively determine the bar’s spring rate (Miller 2007). These suspensions find applications in trucks, Dodge, SUV’s from Ford, and GM. Torsion bars have room for height compensation in order to adjust the ride height. However, excessive torsion bar results in a harsh ride if a bump the suspension system hits a bump prematurely. Therefore, ride quality and proper steering are factors dependent on the suspension system (Knowles 2011).

A

In selecting any material, it is necessary to put into consideration a number of factors including cost, performance, safety and regulation. As such, the material chosen for the task is high-carbon steel, which is a material that introduces elements of competitive edge, economy, operation stability, and success in the manufacture of the torsion bar. This steel has less than 2.11 % and more than 0.8% carbon in its composition. The material has a high level of wear resistance metal hardness. In addition, high-carbon steel sustains heavy loads and operates over a wide range of high temperatures. Moreover, high-carbon steel has a low thermal conductivity and expansion has indicated in table two.

Table 1: Mechanical properties of high carbon steel (Adapted from: Pacific Sintered Metals n.d).

High Carbon Steel

PSM Code F-244-S

Density G/CC 6.8/7.2

Yield strength PSI (A) 40,000

Ultimate tensile strength PSI(A) 57,000

Elongation % (A, B) 1.0

Impact strength Ft-Lbs (A, E) 5

Apparent hardness Rockwell (F) RB 70

Transverse rupture PSI (A) 100,000

Young’s modulus 106 PSI (A) 19

Equivalent MPIF specification F-0008-35

Table 2: High carbon steel properties (Adapted from: material science and engineering).

High Carbon Steel

Density 203 kgm-3 7.84

Thermal conductivity Jm-1K 46

Thermal expansion 10-6K-1 10.8

Young’s modulus GNm-2 210

Tensile strength MNm-2 800

% elongation 8

Using table two, the normal stress developed by high-carbon steel is

σ = E*ε = 210*8 =1,680 GNm-2

Where σ = Normal stress

E = Young’s modulus

ε = Elongation

Metal alloys have inherent small elements regarded as residual or trace elements, which originate from the raw materials (Claymont 2009). However, solid forms of these metal alloys have no constituents of hazardous materials. Therefore, high-carbon steel has no hazardous material in solid form. In spite of this, exposure of high-carbon steel to processes, such as burning, grinding and machining, makes the metal emit airborne contaminants that it contains. As such, the processes in which high-carbon steel undergoes need to take place in well-ventilated environments and respiratory protection and other measures need adoption.

Given that high-carbon steel is an alloy of carbon and steel, the cost of manufacturing and component is reduced to the maximum. High-carbon steel is a metal alloy that has a wide acceptance globally. As such, there are no regulations that limit the use of the metal alloy in the manufacture of torsion bars. The properties of high-carbon steel including hardness, high tensile strength and wear resistance make it a suitable material for the manufacture of torsion bar. Land Rover Discovery develops high-tension forces; as such, high carbon steel will form the best material for the manufacture of the torsion bar.

B

Since the selected material is new, there is a need of subjecting the material to several tests including tensile tests, impact strength test, hardness test, and heat treatment test. The material will first be subjected into a torsion-testing machine, which will aid in depicting the shear strength and shear modulus of the material. In the torsion-testing machine, the twist angle and torque produced by the material as it undergoes twisting will be recorded. Strain gauges will aid in the determination of Poisson’s ratio, young modulus, and shear modulus.

Hardness test is necessary, and it will be conducted by subjecting a sample of high-carbon steel into an indenter machine. The depth of indenter will infer the hardness test since the indenter has a calibrated dial gauge. Impact test will also be conducted to determine the impact strength of high-carbon steel. This will occur through striking a test sample with a measuring device pendulum. The amount of absorbed energy is then measured and recorded.

Heat treatment test will occur through subjecting samples of high-carbon steel into an electric furnace. The samples are expected to remain in the furnace until the temperature is approximately 850OC. At this temperature, the samples will have to be soaked for about two hours in this temperature. The samples soaked then are classified into three groups. One group remains in the air, and the other two groups are quenched in palm oil and water respectively. Quenched samples are tempered at a temperature of 200OC for one hour and allowed to cool in the air. ANSYS 5.4 software will play a key role in conducting finite analysis for the numerical study. The test samples will be modelled with reference to experimentally tested samples, and torque, as well as boundary conditions, applied to aid in obtaining torsion deflections. Theoretical and experimental analysis will then facilitate in the determination of the static behaviour of high-carbon steel.

The testing process will take place with reference to data obtained from the Land Rover Discovery manufacturer concerning the static and dynamic loads disseminated by the vehicle, as well as the maximum and minimum rotary speeds of the axle of the vehicle. This data will aid in devising a failure mechanism for the testing process. In this, the strength and load bearing capacity developed by high-carbon steel will be compared to the data. As such, if the high carbon steel collected data infer small values than Land Rover Discovery data, rejection will occur. On the other hand, if the high carbon data depicts high values than Land Rover Discovery data, acceptance will occur. In addition, theories of failure such as maximum stress theory, strain energy of distortion theory, and maximum shear stress theory will find application in failure analysis. The test data will further aid in design decisions. In this, various designs development will take place to create a room for selection of the most suitable design that yields the best results.

The testing process will end after the determination of the static behaviour of high-carbon steel. This testing regime adopted will aid in inferring the appropriateness of adopting high-carbon steel as a material for torsion bar. Given that Land Rover Discovery is a heavy vehicle that has potential of disseminating heavy loads, the tensile strength, impact strength and hardness test for high-carbon steel are necessary to evaluate the suitability of the material in torsion bar manufacture. Land Rover Discovery suspension system emits heat; thus, a need for heat treatment test for high-carbon steel. Static behaviour determination is crucial for high-carbon steel material for it helps in inferring the behaviour of the material at differing loads and rotary motion. Therefore, the testing regime will aid finding out whether high-carbon steel material is suitable for making the Land Rover Discovery torsion bar component.

C

If the torsion bar were being designed for A Smart for 2, the material selection would differ extensively. This occurs since A Smart for 2 vehicle develops minimal loads than a Land Rover Discovery. The material selection process will then focus on weight reduction of the vehicle since a heavy material may lead to addition of weight on the axle of the vehicle. The selection process will also focus on reduction of use of an excess material that may appear redundant on the vehicle suspension system. The testing process will focus on the ability of the selected material to sustain shock loads, and bear the dynamic, as well as the static forces developed by the vehicle.

A low-carbon steel metal alloy would be efficient to make the torsion bar for A Smart for 2 vehicle. This is because, unlike high-carbon steel, low-carbon steel is quite light in weight. This characteristic makes the metal easier to form and gives the metal a ductile nature. In addition, the metal is fairly in expensive in comparison to high-carbon steel. Moreover, the surface hardening can take place through carburizing process. Carburizing process occurs through subjecting the metal alloy to a carbon-rich atmosphere.

On the other, the selection process of the material for torsion bar for Pagani Zonda C9 will also differ. Pagani Zonda C9 is light sport vehicle; therefore, the vehicle needs a suspension system that will aid in attaining this weight. The material selection process will emphasize on obtaining strength, and lightweight for the vehicle. The testing procedure of the material selected for Pagani Zonda C9 would pay much attention to the ability of the material to sustain higher dynamic forces, being strong, and exhibit malleability properties.

A suitable material for making a torsion bar for this kind of vehicle is aluminium. Aluminium is a light metal that will aid in development of the necessary weight of the vehicle. Aluminium also has the inherent properties of being a very strong metal, which is malleable and ductile. As such, aluminium develops the necessary strength and weight of the suspension system of Pagani Zonda C9.

Bibliography

Claymont, 2009. Material Safety Data Sheet. Evraz Claymont Steel, Inc.

Knowles, D, 2011. Automotive Suspension & Steering System: Classroom Manual. The Fifth

Edition. Delmar, Cengage Learning.

Miller, J, 2007. Be Your Own Auto Repair Technician. Global Media.

Pacific Sintered Metals, n.d. High Performance Powdered Metal (PM) Iron and Carbon

Steels. Retrieved from: HYPERLINK “http://www.pacificsintered.com/iron.html” http://www.pacificsintered.com/iron.html

Ragham, V, n.d. Material Science and Engineering. The fourth edition.