Impact Test Of Metal Speciman Lab Report CE

1. OBJECTIVE

-To evaluate the energy absorbing characteristics of metal materials at room temperature using the Charpy, Izod, and tension impact methods. -To observe the failure patterns and failure surface

2. ASTM REFERENCE

ASTM E 23 Standard Test Methods for Notched Bar Impact Testing of Metallic Materials

3. SIGNIFICANCE

This experiment provides fundamental knowledge on impact behaviour of materials, test procedure, impact testing machine and its working principal, impact specimens, failure patterns etc.

4. APPARATUS AND MACHINE

Digital pendulum impact testing machine

5. SPECIMENS

Charpy (simple beam specimens), Izod (cantilever specimens), Tension Impact specimens made of different metals.

6. THEORY

An impact test normally determines the energy absorb in fracturing a test piece under high speed loading. Toughness is often measured by impact testing rather than by load – deformation (stress vs. strain) curves.

An impact test is a dynamic test in which a selected specimen which is usually notched, is struck and broken by a single blow in a specially designed machine. Using an impact. Machine, the energy absorbed while breaking the specimen is measured

Dynamic Load is that load which varies with respect to time.

The major factors that affect the results of an impact test are:

(a)Velocity (b)Specimen (c)Temperature

Table 1: Features of different types of fracture

Ductile fracture

Brittle fracture

A mode of fracture characterized by the slow

A mode of fracture characterized by the

creak propagation which usually follows a

nucleation and rapid propagation of a crack, with

zigzag path alone planes where a maximum

little accompanying plastic deformation.

resolved shear stress has occurred.

A surface experiencing ductile fracture generally

Brittle fracture surfaces in crystalline materials

has a dull, fibrous appearance.

can be identified by the shiny, granular

appearance.

Example: Fracture of mild steel , aluminum,

Example: Fracture of cast iron, high carbon steel.

Table 2: Effect of angle of notch on energy of rupture of mild steel

Angle of notch (degree)

Sketch of specimen

Charpy impact value

0

22.1

30

24.4

45

23.1

90

25.9

120

41.8

150

66.2

180

63.1

In manufacturing locomotive wheels, coins, connecting rods etc. the components are subjected to impact (shock) loads. These loads are applied suddenly. The stresses induced in these components are many times more than the stress produced by gradual loading. Therefore, impact tests are performed to assess shock absorbing capacity of materials subjected to suddenly applied loads.

Impact tests provide information on the resistance of a material to sudden fracture where a sharp stress rise or flaw is present. In addition to providing information not available from any other simple mechanical test, these tests are quick and inexpensive. The data obtained from such impact test is frequently employed for engineering purposes.