EFFECT OF PLOUGHING SPEED ON THE DEVELOPMENT OF STRESS ON THE

STEYR TRACTOR LIFT SYSTEM ON SANDY LOAM SOIL

BY

SULE, S1 AND J. S. JATAU2

1 AGRICULTURAL ENGINEERING DEPT, FEDERAL POLYTECHNICBAUCHI

2 MECHANICAL ENGINEERING PROGRAMME, A.T.B.U, BAUCHI

ABSTRACT The effects of ploughing speed on the development of

stress on the Steyr tractor stabilizers and brackets on a

sandy loam soil were investigated using strain gauges. It

was found that stress on these parts of the three-point

linkage system increased with speed of ploughing. The use of

a modified ‘U’ bolt was found to reduce the stress.

INTRODUCTION Technical objects, like other material objects

undergo changes with time. As a rule these changes lead to

degradation of the object and sometimes to its destruction

(Otmianowski, 1983). Otmianowski (1983) stated that most of

the agricultural machines are exposed to the harmful effect

of the environment both during work as well as the time of

storage between seasons. Furthermore, accelerated wear of

many of the parts and mechanisms exist as a result of

impurities from dust and soil. The author also stated that

many dynamic factors such as ploughing resistance act upon

the machines during work of the tillage implements.

Ploughing resistance depends not only on the type of soil

and its bulk density but also on the soil moisture content,

stony nature of the soil, amount of roots of past crops and

other factors which change within the same farmland. In the

case of harvesting machine, the dynamic loading depends on

the mass of the handled material in unit time. All

agricultural machines that work on the farm are exposed to

the dynamic effect of undulating terrain as well as rolling

friction on both loose soil and bed-like farmland,

(Otmianowski, 1983). These factors all contribute to the

development of stress on the agricultural machine elements

which may lead to breakdowns.

Stress (σ) is defined as the effect of force or load acting

on a unit area of a body. Mathematically stress is defined

as below:

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Stress,

where:

P = force or load acting on a body.

A = cross sectional area of the body

A body that is subjected to a load and hence stress

will undergo deformation. This deformation per unit length

is known as strain. This deformation may eventually bring

about the failure of the body. By failure it is not meant

actual breaking of the material. Some machine parts are said

to fail when they have plastic deformation.

Strain,

where: = change in length of the body

= original length

Solid materials respond to external forces, such as

tension, compression, torsion, bending, and shear by elastic

deformation (that is, the material returns to its original

size and form when the external force is lifted), permanent

deformation, or fracture (Microsoft Encarta, 2006).

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Tension is a pulling force that acts in one direction; an

example is the force in a cable holding a weight. Under

tension, a material usually stretches, returning to its

original length if the force does not exceed the material's

elastic limit. Under larger tensions, the material does not

return completely to its original condition, and under even

greater forces the material ruptures.

Compression is the decrease in length that results from the

application of pressure. When a material is subjected to a

bending, shearing, or torsional (twisting) force, both

tensile and compressive forces are simultaneously at work.

When a rod is bent, for example, one side of it is stretched

and subjected to a tensional force, and the other side is

compressed.

Creep is a slowly progressing, permanent deformation

that results from steady force acting on a material.

Microsoft Encarta (2006) stated that materials subjected to

high temperatures are especially susceptible to this

deformation. The gradual loosening of bolts, sagging of long

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span cables, and the deformation of components of machines

and engines are all noticeable examples of creep.

Microsoft Encarta (2006) and Kelly (2007) defined

fatigue as the progressive, localised, and permanent

structural damage that occurs when a material is subjected

to cyclic or fluctuating strains at nominal stresses that

have maximum values less than (often much less than) the

static yield strength of the material. The resulting stress

may be below the ultimate tensile stress, or even the yield

stress of the material, yet still cause catastrophic

failure.

Khurmi and Gupta (2002) stated that machine parts are

sometimes subjected to loads with impact thus producing

impact stress. A mechanical or physical shock is a sudden

acceleration or deceleration caused, for example, by impact

(Kelly

, 2007).

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When designing machine parts, it is desirable to keep

the stress lower than the maximum or ultimate stress at

which failure of the material takes place. This stress is

known as the working stress, design stress, safe or

allowable stress. Ultimate stress is defined as the largest

stress obtained by dividing the largest value of the load

reached in a test to the original cross-sectional area.

Working or design stress (Ws) is therefore expressed

as:

or

In case of ductile materials for example, mild steel

where the yield point is clearly defined, the factor of

safety is based upon the yield point stress (Chwiej , 1979).

During ploughing or in general tillage

operations, some kinds of load exist on the tractor three-

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point linkage system. This load produces stress on the

system which may be destructive. The objective of this work

is to verify the effect of speed on the development of

stress on some parts of the three-point linkage system of

the Steyr tractor on a sandy loam soil, reduce the stress if

necessary and recommend an optimum ploughing speed.

METHODS

The following materials were used in this experiment: A

fifty by thirty meters portion of land (measured out of the

irrigation plot of the Agricultural Engineering Department

of the Federal Polytechnic, Bauchi), four digital

multimeters, strain gauges, 9V batteries, resistors, cables,

Steyr 768 tractor and a metering tape, Sand paper,

detergent, water and glue.

The surfaces of the stabilizer shafts and

brackets were properly cleaned using abrasive materials,

detergent and water. They were left to dry after which the

strain gauges were carefully attached using the glue. They

were pressed firmly and allowed to dry after which they were

soldered and wired with the resistors of 47Ω each. Double

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strain gauges were used. Figure 1 shows the circuit diagram

of the electrical wiring. The portion of land described

above was collected for analysis. The soil type was

determined using the method of soil type analysis (Michael,

1990). Other properties such as soil moisture content, bulk

density were determined. The speeds of ploughing were varied

using the hand throttle .The ploughing depth was also fixed

using the depth controller.

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Vi

Vo

SG

SG RR

R

Fig. 1 Circuit Diagram for the Single Strain Gauge

Connection

Where:

R = external resistance of gauges

Vo = voltage output

Vi = input voltage.

SG = Strain gauge

The measurements were first taken with the original Steyr

‘U” bolt (plate I) in place and latter the modified “U” bolt

(plate II) was fitted for comparative measurements.

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Plate I

Steyr U-Bolt

Plate II Modified ‘U’

Bolt

The soil test showed the soil type as sandy loam

soil. During the ploughing, the stresses on the brackets and

on the stabilizer shafts were converted to voltages and read

on the digital multimeters as the output voltages. Using the

following relationships, these voltages were converted to

stress (N/m2).

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According to Kurtz et al (1984), when two gauges are used,one as a dummy,

Where Vo = Voltage out Vi = Voltage in

RESULTS AND DISCUSSION Measurements were taken on the effect of speed on

stress development on both the brackets and the stabilizers

at 13.3%MC while ploughing was done at the depth of 20cm and

the width of 1m.

It was observed that stress increased with increase

in speed of ploughing. However the increases on the right

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side of the lift system were observed to be substantially

higher than those on the left side. The maximum stress

(39N/m2) measured during the experiment is taken as the

working stress. This working stress 39N/m2 is greater than

the calculated working stress of the material (14N/m2), it

shows that there are chances of occasional increases of

stress as a result of stumps and non- uniformity of

farmlands. The presence of stumps and none uniformity of

farmlands are some of the causes of shock stress on the

Steyr lift system which is very destructive to the system

tillage. This contributes to the failures of the right

brackets and the axle of the Steyr tractor.

The graphs on figures 2 to 5 show the effect of

speed on stress development on brackets and stabilizers.

This increase of stress with speed agrees with Kamal et al,

(1999). On this soil, increase of ploughing speed above

7.0km/hr is seen to produce a sharp increase in stress on

both brackets and stabilizers. The use of the modified ‘U’

bolt is seen to reduce the stress from 39N/m2 to 3N/m2. The

modified ‘U’ bolt absorbed impact shocks leading to the

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reduction of stress that could have otherwise be

destructive.

y = 3.642x2 - 48.084x + 194.93R2 = 0.9667

y = 2.1987x2 - 29.225x + 99.984R2 = 0.9996

0

10

20

30

40

50

60

70

0 2 4 6 8 10Speed [km /hr]

Stress on Righ

t Bracket [N

/mm2]

Steyr 'U' BoltM odified 'U' BoltPoly. (Steyr 'U' Bolt)Poly. (M odified 'U' Bolt)

Fig. 2 Effect of Speed of Ploughing on Stress Development onthe Right Bracket (Sandy Loam Soil of 13.3%M.C at 20cmdepth of ploughing)

y = 4.0327x2 - 51.245x + 175.22R2 = 0.9968

y = 1.2621x2 - 16.434x + 55.606R2 = 0.9982

051015202530354045

0 2 4 6 8 10Speed [km /hr]

Stress on Left Bracket [N/mm2]

Steyr 'U' BoltM odified 'U' BoltPoly. (Steyr 'U' Bolt)Poly. (M odified 'U' Bolt)

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Figure 3 Effect of Speed of Ploughing on Stress Developmenton the Left Bracket (Sandy Loam Soil of 13.3%M.C at 20cmdepth of ploughing)

y = 0.9971x2 - 8.4566x + 19.754R2 = 0.9738

y = 1.1778x2 - 14.395x + 46.212R2 = 0.9991

0

5

10

15

20

25

30

0 2 4 6 8 10Speed [km /hr]

Stress on Righ

t Stab. [N

/mm2]

Steyr 'U' BoltM odified 'U' BoltPoly. (Steyr 'U' Bolt)Poly. (M odified 'U' Bolt)

Figure 4 Effect of Speed of Ploughing on Stress Developmenton the Right Stabilizer (Sandy Loam Soil of 13.3%M.C at20cm depth of ploughing)

y = 2.8554x2 - 38.766x + 137.11R2 = 0.9717

y = 1.0579x2 - 13.468x + 45.451R2 = 0.9979

0

5

10

15

20

25

0 2 4 6 8 10Speed [km /hr]

Stress on Left Stab. [N/mm2]

Steyr 'U' BoltM odified 'U' BoltPoly. (Steyr 'U' Bolt)Poly. (M odified 'U' Bolt)

Figure 5 Effect of Speed of Ploughing on Stress Developmenton the Left Stabilizer (Sandy LoamSoil of 13.3%M.C at 20cm depth of ploughing)

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CONCLUSSIONIncrease of speed of ploughing with the Steyr ‘U’ bolt on

the Steyr tractor, brings about an increase of destructive

stress on the lift system and the axle.

RECOMMENDATIONIn order to avoid the breakdown of the Steyr tractor

stabilizer brackets and the axle, it is recommended that the

modified ‘U’ bolt is adopted for use on the Steyr tractor

and ploughing speed on this land is kept below 7.0km/hr.

REFERENCESKamal, A.R., Odesanmi, 0.0. and Onwualu, A.P. (1999). Effectof Speed and Depth of Cut on Draught and Power Requirementof a Disc Plough. Research and information bulletin of NCAMVol.1.

Kelly,M.S (2007) Fatigue. www.wikipedia.org

Khurmi R. S. and J. K .Gupta (2002). A Text Book of MachineDesign. Eurasia Publishing House. New Delhi.

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Kurtz, G Lester Thompson, Paul Claar (1984). Design ofAgricultural Machinery. John Willy and Sons, New York. Pp77-111.

Chwiej, M (1979). Maszynoznastwo Ogolne. PanstwoweWydawnictwo Naukowe, Warszawa.

Microsoft Encarta (2006) Microsoft corporation

Michael A. M. (1990). Irrigation — Theory and practice.Vikas Publishing House PVT Ltd, New Delhi. pp.448-584.

Otmianowski, T. (1983). Procesy Odnowy Maszyn Rolniczych.PWRiL. Warszawa.

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