What is Measured?

During the Izod impact test, the following quantities are measured:

• Initial height of the pendulum, $h_1$
• Height reached by the pendulum after fracturing the specimen, $h_2$
• Energy absorbed during fracture (directly indicated by the machine)
• Dimensions of the specimen at the notch

These measurements are used to determine the impact toughness of the material.

Why are the Calculations Required?

The measured quantities help determine the energy absorbed by the specimen during fracture.

The calculations enable determination of:

• Potential energy before impact
• Remaining potential energy after fracture
• Energy absorbed during fracture
• Impact toughness of the material

These properties indicate the resistance of the material to sudden impact loading.

Observation Table

Assume a standard Izod specimen with:

• Width = 10 mm
• Thickness below notch = 8 mm

Trial	Initial Height $h_1$ (m)	Final Height $h_2$ (m)	Energy Absorbed (J)
1	0.75	0.55	40
2	0.75	0.54	42
3	0.75	0.53	44

Sequential Calculations

1. Initial Potential Energy

$$PE_1=W h_1$$

2. Remaining Potential Energy

$$PE_2=W h_2$$

3. Energy Absorbed

$$E=W(h_1-h_2)$$

4. Impact Toughness

When required,

$$\text{Impact Toughness} = \frac{E}{A}$$

where

• $E$ = Energy absorbed
• $A$ = Cross-sectional area below the notch

Solved Numerical Example

Given

• Pendulum weight = 200 N
• Initial height = 0.75 m
• Final height = 0.55 m

Step 1

Initial potential energy

$$PE_1=200\times0.75=150\ \text{J}$$

Step 2

Remaining potential energy

$$PE_2=200\times0.55=110\ \text{J}$$

Step 3

Energy absorbed

$$E=150-110=40\ \text{J}$$

Therefore,

$$\boxed{E=40\ \text{J}}$$

Interpretation of Results

• Higher absorbed energy indicates greater impact toughness.
• Ductile materials absorb more energy before fracture.
• Brittle materials fracture after absorbing relatively little energy.
• The notch ensures fracture occurs at a predetermined location.

Result

The Izod impact test was performed successfully, and the impact toughness of the material was determined from the energy absorbed during fracture.