PROCEDURE SHIP MATERIAL

8/7/2019 PROCEDURE SHIP MATERIAL

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OBJECTIVES OF TESTING

The mechanical testing of metals to be used in shipbuilding is carried out to assess and verify

that the properties of the metal are suitable for their intended purpose and match the specification

requirements. Hardness is the property of a material that enables it to resist plastic deformation,

usually by penetration. However, the term hardness may also refer to resistance to bending,

scratching, abrasion or cutting. The objectives of hardness testing are to identify the degree of surface

hardness which is the amount of resistance of a surface to abrasion or indentation.

Measurement of Hardness

Hardness is not an intrinsic material property dictated by precise definitions in terms of fundamental

units of mass, length and time. A hardness property value is the result of a defined measurement

procedure. Hardness of materials has probably long been assessed by resistance to scratching or

cutting. Relative hardness of minerals can be assessed by reference to the Mohs scale that ranks the

ability of materials to resist scratching by another material. Similar methods of relative hardness

assessment are still commonly used today. There are three principal standard test methods for

expressing the relationship between hardness and the size of the impression, these being Brinell,

Vickers, and Rockwell. For practical and calibration reasons, each of these methods is divided into a

range of scales, defined by a combination of applied load and indenter geometry.

Hardness Testing Methods

1. Rockwell Hardness Test

2. Rockwell Superficial Hardness Test

3. Brinell hardness Test

4. Vickers Hardness Test

5. Micro hardness Test

6. Mohs hardness Test

7. Scleroscope and other hardness testing methods
http://www.gordonengland.co.uk/hardness/rockwell_superficial.htmhttp://www.gordonengland.co.uk/hardness/brinell.htmhttp://www.gordonengland.co.uk/hardness/microhardness.htmhttp://www.gordonengland.co.uk/hardness/mohs.htmhttp://www.gordonengland.co.uk/hardness/scleroscope.htmhttp://www.gordonengland.co.uk/hardness/brinell.htmhttp://www.gordonengland.co.uk/hardness/microhardness.htmhttp://www.gordonengland.co.uk/hardness/mohs.htmhttp://www.gordonengland.co.uk/hardness/scleroscope.htmhttp://www.gordonengland.co.uk/hardness/rockwell_superficial.htm


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Applications in Shipbuilding Industry In Hardness Testing

It is carried out in order to assess and verify that the properties of the metal are

suitable for their intended purpose and match the specifications requirements. There are

several of tests performed and it includes our topic, hardness testing.

The main reason why hardness testing are required so are because to identify the

degree of surface hardness which is the amount of resistance of a surface to abrasion or

indentation.

Hardness can be measured by using hardness testing machine such as:

1. Brinell

2. Vickers

3. Universal hardness testing machine

A compressive force is applied to the surface of the metal by forcing a small steel ball

into the materials under a set load for a specified time (dwell time) and then measuring the

degree of indentation into its surface. The smaller the indentation produced the harder the

materials.

The hardness value is given as a Brinell hardness number that is either read from a Brinell

References Table or determined by calculation. HN equals the force used to produce the

indentation divided by the surface area of the indentation

Hardness number = Force used surface area of indentation

Or

Hardness Number = ___ __________Load______________

Area of curved surface of the indentation


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To calculate the area of curved surface of indentation use to represent the diameter of the

ball, and D the diameter of the indentation.

For more reliable results when using a Brinell hardness test, it is important to use a ball

diameter suitable for the thickness of material being tested. The thickness of the piece should

be at least eight times greater than the depth of the indentation. Brinell testing balls are made

of either hardened steel or carbide of fixed diameters of 1mm, 5mm or 10mm and these are

selected depending on the thickness of the test specimen.


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PROCEDURES

Brinell Hardness Testing

Prepare the Brinell hardness testing machine for use.

Obtain a suitable test specimen of the material requiring testing.

Select the appropriate diameter of ball (hardened or carbide) for the thickness of the

test specimen of a fixed and known diameter.

Set the required load on the dial.

Apply a preload by bringing the surface of the test piece in contact with the ball

penetrator.

Apply a predetermined amount of force to the surface of the test piece causing

indentation.

Hold the force for a predetermined amount of time before removal. Steel 30 seconds

while softer materials 60 seconds.

Measure the indentation using the microscope that reads in millimetres across twodiameters. Take several readings and average these out.

Using a Brinell reference table convert the averaged diameter measurements to a

Brinell Hardness Number. Or calculate the Brinell Hardness Number H, by using

the formula provided.

FIGURE 1


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Because of the relatively large indentation left in the surface of the material being

tested the Brinell test can be considered a destructive test because the indentation is

intrusive and permanently remains in the surface and a non-destructive test when the

indentation is tolerated or considered non-intrusive.

Types of materials:

Copper alloys Case hardened steel Zinc

Soft steel Cast iron Lead

Aluminium Aluminium andmanganese alloys

Aluminium alloys

Malleable iron Bearing metals

Steel Phosphor bronze

Hard cast iron Beryllium

Pearlitic malleable iron Copper

Titanium Malleable irons

Table 1: Types of material for Brinell testing.

Rockwell Hardness Testing

The depth of penetration of an indenter under certain arbitrary test conditions is

determined.

The indenter may either be a steel ball of some specified diameter or a spherical

diamond-tipped cone of 120 angle and 0.2 mm tip radius, called Brale. The type of

indenter and the test load determine the hardness scale (A, B, C).

A minor load of 10 kg is first applied, which causes an initial penetration and holds

the indenter in place.

Then, the dial is set to zero and the major load is applied.

Upon removal of the major load, the depth reading is taken while the minor load is

still on. The hardness number may then be read directly from the scale.


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The hardness of ceramic substrates can be determined by the Rockwell hardness test,

according to the specifications of ASTM E-18.

This test measures the difference in depth caused by two different forces, using a dial

gauge.

Using standard hardness conversion tables, the Rockwell hardness value is

determined for the load applied the diameter of the indenter, and the indentation

depth.

Vickers Hardness Testing

For those with extremely hard surfaces, the surface is subjected to a standard pressure

for a standard length of time by means of a pyramid-shaped diamond.

The indenter is pressed into the sample by an accurately controlled test force.

The force is maintained for a specific dwell time, normally 10 15 seconds.

After the dwell time is complete, the indenter is removed leaving an indent in the

sample that appears square shaped on the surface.

The size of the indent is determined optically by measuring the two diagonals of the

square indent.

The Vickers hardness number is a function of the test force divided by the surface

area of the indent. The average of the two diagonals is used in the following formula

to calculate the Vickers hardness.

HV = Constant x test force / indent diagonal squared

The constant is a function of the indenter geometry and the units of force and

diagonal.

The Vickers number, which normally ranges from HV 100 to HV1000 for metals, will

increase as the sample gets harder.


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Tables are available to make the calculation simple, while all digital test instruments

do it automatically. A typical Vickers hardness is specified as follows:

356HV0.5

- where 356 are the calculated hardness and 0.5 is the test force in kg.

The diagonal of the resulting indention is measured under a microscope and the

Vickers Hardness value read from a conversion table.


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Table 2: Hardness unit conversion table

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