Homework L

ENGR 200: Materials of Engineering

Laboratory 4

Impact Test

I.OBJECTIVES

The goal of this experiment is to reinforce student’s understanding of the concept of “impact energy” and”ductile-to-brittle transition temperature” (DBTT) by investigating the effect of temperature and carbon content on the toughness of steel by means of a Charpy Impact Test.

II.INTRODUCTION

Materials can be classified as ductile or brittle depending on their ability to undergo plastic deformation before fracture. Toughness is a measure of amount of energy a material can absorb up till fracturing and it is a temperature – dependent property. Some materials, most notably steels, can exhibit ductile or brittle behavior dependent on the test temperature. Elevated temperatures promote ductile behavior and increase the toughness of steels.

In this experiment we will examine the effect of test temperatures and carbon content on the toughness of two different plain carbon steels by means of impact testing.

III. SAFETY PRECAUTION

Due to the dynamic nature of an impact test (Charpy Test) as shown in Figure 1(a), there are several potentially dangerous steps in this experiment, which include:

1. Handling cold specimens (at dry ice temperatures) and hot specimens (at 500oC) 2. Raising the Charpy pendulum hammer (~ 27.2 kg or 60 lbs) and locking it in place 3. Placing the specimen in the specimen holder after locking the hammer 4. Releasing the hammer from its locked position 5. Collecting fractured samples from test area before the pendulum hammer comes to a halt and

while the samples are still at very high or very low temperatures

It is MANDATORY to adhere to the following precautions at all time during this experiment

• DO NOT perform the test without explicit consent from the Instructor • Wear protective gears (goggles, gloves) at all time during the experiment, especially when

handling objects at extreme temperatures • Liquid nitrogen can cause serious damage to the skin and the eyes • Extremely cold steel specimen may shatter into high-speed fragments in all directions during test. • Work in pairs. Prior to test, one person should raise the pendulum hammer, lock it, and use both

hands to hold the hammer in place while the other person places the specimen in the specimen holder using a pair of tongs

 

 

• Always use tongs instead of bare hands to place the specimens in the specimen holder • Students should stand at least 3 feet (1 m) away from the test area, and NEVER stand in the same

line as the direction of pendulum swing when the pendulum hammer is in motion • The team running the test should give ample warning to the class before releasing the pendulum

hammer • After releasing the pendulum hammer, the team should step back and stay 3 feet (1m) away from

the test area • After the pendulum hammer has come to a complete halt, collect the fractured samples using the

pair of tongs – NEVER use bare hands to pick up fractured samples, they could be very sharp, and still be at very high or low temperatures, and could potentially cause damage to your skin.

IV. EXPERIMENTAL

Materials and Apparatus

1. Charpy impact specimens of steel • 3 pieces of 1018 (Cold Finished) steel • 3 pieces of 1045 (Cold Finished) steel • 3 pieces of 1095 ( Cold finished) steel

2. Tinius Olsen Impact Test Machine 3. Dry ice 4. 1 oven

 

Experimental Procedures

 

1. Class is separated into three teams 2. Three notched steel (1018, 1045 and 1095) samples will be provided to each of the three teams 3. Each team will subject all three specimens to the following temperature treatments before test:

Team 1: at dry ice temperature ( -78.5 oC) Team 2: at room temperature Team 3: at 500oC (heated for 10 minutes in an oven)

4.1 Charpy Test: Two team members should prepare the hammer by raising it to the pre-determined height and locking it in place. Zero out the scale if necessary. Move everyone away from the test area. 4.2 The third team member should wear protective gear, quickly extract the test specimen and place it in the Charpy slot for testing 4.3 Once cleared, release the hammer and record the energy absorbed (in ft-lb). 4.4 Collect the specimen fragments using a pair of tongs and place it on the floor

5 Repeat steps (4).

6 Visually examine the fracture surfaces

 

 

 

 

Figure 1: (a) An Impact tester. The difference between the initial and final heights of the pendulum hammer represents the amount of energy absorbed by the material during test. (b) The specimen is placed in a horizontal fashion on the specimen holder with the V-notch aligned to the direction of the knife edge.

V. DELIVERABLES FROM YOU

1. Lab Assignment: Please prepare answers to questions in (2) (see below) and submit a softcopy in PDF format to your instructor via email on designated date. Data collection sheet needs not be turned in.

2. Please include and discuss the following in your report:

a) Graph the energy absorbed (y-axis) versus temperature (x – axis) for 1018, 1045 and 1095 at all three temperatures on *one* scatter plot graph and label this as Figure 1. You may also do it on three scatter plot graphs for 1018, 1045 and 1095 respectively (if you don’t know how to do it on one ) – please label these graphs as Figure 1, Figure 2 and Figure 3

b) Photograph the fractured surfaces of *each of the nine specimens* and note whether the fracture is ductile, brittle or a combination of the two. [Please refer to Chapter 8.6].

*Please create a matrix like Table 1 below and insert your photo in the corresponding cell.

Table 1. Fracture surfaces of steel specimens at various test temperatures

Test Temperature

[oC]

1018 1045 1095

-78.5 (Dry Ice) Photo Photo Photo 20 (RT) Photo Photo Photo

500 Photo Photo Photo

 

 

c) Comment on the effect of carbon content on the energy absorbed, DBTT [Please refer to Chapter 8.6]

d) Comment on the correlation between the energy absorbed and the type of fracture

Keep your answers concise. Keep your sentences & paragraphs short. Use table or graph wherever

possible.

 

ENGR 200: Materials of Engineering

Laboratory 4

Data Sheet for Impact Test

Name:

Group Members:

Date:

Table 2. Data Collection Sheet (Steel Specimen)

Test Temperature

[oC]

1018 1045 1095

-78.5 (Dry Ice) 20 (RT)

500

 

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