MODULUS OF RUPTURE & BREAKING STRENGTH OF CERAMIC TILES [IS-13630-PART-6]

Objective

Determination of modulus of rupture and breaking strength of a whole tile by means of three point loading, the central point being in contact with the glazed surface of the tile.

Apparatus

• Drying oven having capacity of 110±5⁰C
• Recording gauge – Accurate to 2%
• Two support cylindrical rods – These rods are made up of metal and the part of the rod which will be in contact with the test specimen must be covered with rubber having required hardness. One of theses two rods should be slightly pivotable and the other one should be slightly rotatable about its own axis. The dimension of the rods and the thickness of the rubber covering the metal rod should be as per table-1.

• Central cylindrical rod – The construction of this rod is same as that of support rod and it should be slightly pivotable.

The dimension of the rods and the thickness of the rubber covering the metal rod should be as per table-1.

Table – 1
Diameter of Rods, Thickness of Rubber and Length
Dimension of Tile (mm)	Diameter of Rod (d), in mm	Thickness of Rubber (t), in mm	Overlap of Tile Beyond the edge supports (l), in mm
≥ 95	20	5	10
< 95 ≥ 48	10	2.5	5
< 48 ≥ 18	5	1	2

 

Procedure for Sample Preparation

1. Each sample consists of 7 or 10 no’s of test specimens depending upon their dimension. (see the table-2)

Table-2
Dimension of Tile (mm)	Minimum number of Test Specimen
≥ 48	7
< 48 ≥ 18	10

2. Preferable whole tile should be tested to find the accurate test result. But if the length of any tile is more than 300 mm or if it is non rectangular in shape, then cut it, so that it fits in the testing machine.
3. Dry the cut specimens in the oven maintained at a temperature of 110±5⁰C until it attains constant mass.

Test Procedure

1. Place a test specimen on two support rods with the glazed surface facing upward. It should be placed in such a way so that the specimen projects by the length ‘l’ (as given in tbla-1) beyond each support rod.

Note: For extruded tiles, place the tiles so that the projecting ribs are at right angles to the support rods. For all other rectangular tiles the greater side is at right angle to the support rods.

2. Position the central rod on the glazed surface of the test specimen and make sure that it is equidistance between the two support rods.

Note: If the tile has relief surfaces, then place a 2^nd layer of rubber of appropriate thickness (as given in table-1), on the central rod.

3. Apply the load evenly in such a way as to obtain a rate of increase of stress of 1±2 N/mm²/s.
4. Record the load (F) when the specimen breaks.
5. Continue the steps 1 to 4 for all the test specimens in a sample.

Calculation of Test Result

Average breaking strength and average modulus of rupture is calculated by averaging five acceptable test results.

A test is said to be acceptable if the specimen breaks within a central portion of length equivalent to the diameter of the central rod.

If there are fewer than five acceptable results, a second sample is tested consisting double the number of tile and then a minimum of ten acceptable result is required to calculate the average value.

The breaking strength is calculated using following formula.

S = FL / b

Where,

S = Breaking strength, in N

F = Load required to break the tile, in N

L = Centre to centre length between two support rods, in mm

b = Width of the tile, in mm

The modulus of rupture is calculated using following formula.

δ = 3FL / 2bh²

Where,

δ = Modulus of Rupture, in N/mm²

F = Load required to break the tile, in N

L = Centre to centre length between two support rods, in mm

b = Width of the tile, in mm

h = Minimum thickness of the test specimen measured after the test along the broken edge, in mm

Report

The test report should contain the following

• Description of the tile
• Number of test specimens
• Values of d, t, l, L & F
• Modulus of rupture and breaking strength of each test specimen.
• Average modulus of rupture and breaking strength.

Reference

IS: 13630 (Part-6) – ceramic tiles – methods of tests, sampling and basis for acceptance [Part 6 – determination of modulus of rupture and breaking strength]