KULLIYYAH OF ENGINEERING MATERIALS TESTING LAB LAB MODULE: STRENGTH OF MATERIALS TITLE
IMPACT TESTING
DATE OF EXPERIMENT DATE OF REPORT SUBMIT LECTURER NAME GROUP NO. NO.
NAME
MATRIC NO.
MARKING CRITERIA
GIVEN MARK
1 2 NAME OF GROUP MEMBERS
3 4 5 6 7 NO.
LECTURER COMMENT
1
Objective (5% )
2
Theory (5% )
3
Apparatus (5%)
4
Procedures (5%)
5
Experiment Data (10%)
6
Analysis & Calculation (10%)
7
Discussion (20%)
8
Conclusion (10%)
9
Formatting & Tidy (10%)
10
Attendance (10%)
11
Leadership / Cooperation (10%)
TOTAL MARK (100%)
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1.0
OBJECTIVE
To determine the impact resistance properties of various metals. 2.0
THEORY
2.1 Brittle Fracture: Fracture in materials was widely investigated especially during the industrial revolution where extraction processes of iron and steels led to the wide-spread uses of iron and steels for structural and transportation applications, etc. However, metallurgy of iron and steels was not deeply understood, which resulted in improper utilization of materials. Moreover, with low engineering technology, defects were normally observed in jointed metals or assembled parts, which were the main problems leading to weakening and global failure of engineering structures during services. The well-known case has been the tragic failure of the Liberty ships and T-2 tankers. The Liberty ships built during the World War II appeared to have cracks along the welds resulting in fracturing into two halves as they were at the deck prior to services as pictured in figure 1. Brittle fracture has then been investigated in great details whereas ductile fracture was however studied in a lower extent due to its less deleterious effects. Since brittle fracture has been one of the most catastrophic types leading to losses of life and cost, study of brittle fracture especially in steels has therefore been on the main focus. Investigation into causes and factors affecting fracture behavior has been of great interest and solutions to its problems have also been cooperated.
F ile Photo: Liberty ship which was broken in two halves along the welds.
2.2 Pendulum Impact Test: In this test the specimen is positioned across the lowest point in the path of a striker mounted at the end of a pendulum as shown in Figure 1. The striker, having been initially lifted to a specific height h1, and then released, swings against the specimen and breaks it. The striker continues its swing to the other side of the specimen to a height h2. Clearly the difference between the two heights multiplied by the weight of the striker corresponds to the amount of energy that is absorbed in fracture.
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F igur e 1. Schematic of a conventional Pendulum Impact Tester
2.3 Izod Impact Test: In the Izod impact test, the test piece is a cantilever, clamped upright in an anvil, with a Vnotch at the level of the top of the clamp. The test piece is hit by a striker carried on a pendulum which is allowed to fall freely from a fixed height, to give a blow of 120 ft lb energy. After fracturing the test piece, the height to which the pendulum rises is recorded by a slave friction pointer mounted on the dial, from which the absorbed energy amount is read.
F igur e 2. Basic Principle of Izod Impact Test
2.4 Charpy Impact Test: The principle of the test differs from that of the Izod test in that the test piece is tested as a beam supported at each end; a notch is cut across the middle of one face, and the striker hits the opposite face directly behind the notch.
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F igur e 3. Basic Principle of Charpy Impact Test
2.5 Post-Fracture Analysis: When a specimen is tested, the energy that is transferred in the impact test may be absorbed in a few different ways: through elastic deformations, plastic deformations, hysteresis, friction, or inertia. In Charpy tests specifically, the most significant of these are elastic and plastic deformations, with plastic deformation usually accounting for the majority of the absorbed energy. The amount of energy required to achieve fracture is reliant on the ductility of the material, and the unknown proportion of work done in elastic deformation to work done in plastic deformation which necessitates the physical examination of each broken specimen. Postfracture visual analysis can provide information on what percent of the area was ductile during impact and what percent of area was brittle; this is shown by the break patterns displayed in the broken surfaces as seen in Figure 4 below.
Figure 4: Guide for Determining Percent Ductility
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Figure 5: Fracture surfaces of different materials. 3.0
APPARATUS
3.1 Specimens for Impact Testing, according to ASTM E23. Made of the following materials: 3.1.1. Brass 3.1.2. Mild Steel 3.1.3. Aluminum 3.1.4. Stainless Steel 3.1.5. Copper 3.1.6. Low carbon Steel 5
3.2 Micrometer or vernier caliper 3.3 Instron Impact Testing Machine 3.4 Microscope 3.5 Safety goggles (PPE)
F igur e 6. Dimensions and geometry of Impact Testing Specimens to ASTM E23
4.0
PROCEDURES
4.1. Examine standard Charpy impact specimens of 10 x 10 x 55 mm³ dimensions with a notch of 45⁰ angle and 2 mm depth located in the middle as shown in Figure 6. 4.2. Room temperature test is first carried out by placing the brass Charpy impact specimen on the anvil and positioning it in the middle location using a positioning pin where the opposite site of the notch is destined for the pendu lum impact (see Figure 3). 4.3.Raise the pendulum to a height corresponding to the maximum stored energy of 300J. 4.4.Release the pendulum to allow specimen impact. Safely stop the movement of the pendulum after swinging back from the opposite side of the machine. 4.5.When the pendulum is still, safely retrieve the broken specimen without damaging fracture surfaces. Record the absorbed energy in Table 1. 4.6.Study the fracture surface under a microscope and sketch the fracture surface according to Figure 5. 4.7.To determine the percent ductility of the fracture, examine the specimens after testing under a microscope, and compare their broken surfaces to those in Figure 4 to get a numerical value 4.8.Repeat the test at the same test conditions using mild steel, aluminum, stainless steel, copper, and low carbon steel.
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5.0
EXPERIMENT DATA Absorbed Impact Energy (J)
Material
Theoretical Value
Percent Ductility
Experiment Value
Brass
Mild Steel
Aluminum
Stainless Steel
Copper
Low carbon Steel
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Sketch of Fracture Surface
6.0
DATA ANALYSIS
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7.0
DISCUSSION
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8.0
Conclusion
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