DETERMINATION OF PLANE STRAIN

FRACTURE TOUGHNESS(K I C )

EXPERIMENT NO.8

M E 2 1 8 : S O L I D M E C H A N I C S L A B O R A T O R Y

B A T C H : A 8

0 7 0 1 0 0 4 2 - 0 7 0 1 0 0 4 6

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D E T E R M I N AT I O N O F P L A N E S T R A I N F R AC T U R E

T O U G H N E S S ( K I C ) EXPERIMENT NO.8

AIM

To determine KIC of the given material experimentally.

APPARATUS

1. Jewelers’ saw.

2. Vernier scale.

3. Mechanical extensometer.

4. CT specimen (compact tension).

THEORY

KIC is known as the plain strain fracture toughness of the material. It depends on the material only and is theoretically independent of the size, geometry and loading. For a CT specimen,

KIC=PQ.f(a/w)/(B.W1/2) Where, PQ is the critical load, a is the crack length, B,W are the specimen dimensions.

The required dimensions of the CT specimen are shown in the next page.

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PROCEDURE

The CT specimen is ensured to have the required dimensions. This CT specimen is applied with increasing load on by using a mechanical extensometer. The corresponding graph is plotted. A 5% secant line is drawn intersecting the curve at PQ. This can be used to calculate the value of KIC.

GRAPH

Load (N)

000

1000

2000

3000

4000

5000

6000

7000

8000

9000

Machine Extension (mm)0.0 1.0 2.0 3.0 4.0

Preload

Metals, Tensile Setup

Gauge Length:

Area:

100.0 mm

About 10.0 mm x 5.00 mm

A8 KIC

CALCULATIONS

Dimensions of the CT specimen: a=2.6cm,W=5.2cm, B=1.2cm Starting point for slope calculation: (0.46464, 962.37); End point:(1.1342, 5852.5). Slope of pcmod line=7303.5 Slope of 5% secant line=0.95*7303.5=6938.3 Hence, the equation of secant line: y=962.37+7303.5*(x-0.46464) Thus, the intersection of the secant line with the curve is (1.3128, 6840.6) Hence, PQ=6840.6 f(a/W)=9.659 for a CT curve with a/W=0.5 Now, KIC=P.f(a/W)/(B.W1/2) =6840*9.659*1000/(5.20.5*1.2) =24.143*106 Pa.m0.5 Thus, KIC=24.143 MPa√m.

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RESULT

The value of KIC of the given CT specimen of aluminum alloy is 24.143 MPa√m.

PRECAUTIONS

1. Check the dimensions of the CT specimen to be precise.

2. Avoid parallax error.

3. Make the notch in the correct manner as required by the experiment.

4. Adjust the extensometer properly and make up for the zero error.

DETAILS OF STUDENTS

Table 2.1

ROLL NUMBER NAME

07010042 Repaka Jyoti Swaroop

07010043 Sharath Chandra Pawar

07010044 Puvvada N V Prudhvi Teja

07010045 J G M V Pramod

07010046 Vishnu Narayanan Suresh