Charpy Impact Test

Summary

The Charpy Impact Test is a standardized method used to measure the toughness of materials under impact loading and multiaxial stress states. It involves swinging a pendulum to impact a notched specimen to determine the amount of absorbed energy. This test highlights the differences in impact energy absorption between strain age plain carbon steel and normalized steel, demonstrating how material structures affect toughness and behavior under stress. It also explores how materials with different crystal structures respond to temperature changes, with certain materials maintaining ductility even at lower temperatures.

Highlights

• A pendulum impact testing machine is used to measure the toughness of materials. 🎯
• The test compares results between strain age plain carbon steel and normalized steel. ⚖️
• Strain age steel shows brittle behavior, absorbing only 13 joules, whereas normalized steel absorbs 182 joules. 🤔💡
• The test demonstrates how different materials react under varying temperatures and stress conditions. 🌐
• Materials with face-centered cubic structures retain their ductile behavior at low temperatures. 🌬️

Key Takeaways

• The Charpy Impact Test measures a material's toughness by assessing energy absorption during impact. ⚒️
• Strain age plain carbon steel absorbs less energy and exhibits brittle behavior, while normalized steel shows higher energy absorption and toughness. 📉➡️📈
• Materials with body-centered cubic structures show temperature-dependent toughness, unlike face-centered cubic structures which remain ductile at low temperatures. 🌡️❄️

Overview

The Charpy Impact Test is a fascinating and clever way to gauge the toughness of materials. Using a pendulum with a heavy hammer, the test demonstrates how different materials absorb energy when struck. By observing the pendulum's swing before and after hitting a specimen, one can see the energy dynamics at play — a true spectacle of physics and materials science!

In the test video, strain age plain carbon steel and normalized steel take center stage. The brittle nature of strain age steel is evident, absorbing only a mere 13 joules of energy, while the normalized steel, a true tough cookie, absorbs an impressive 182 joules. The divergence in impact energy absorption reveals the underlying differences in the materials' structures and mechanical properties.

Moreover, the video touches on the unique behaviors of different crystal structures under temperature variations. Materials with body-centered cubic structures have a transition in toughness, while those with face-centered cubic structures maintain their ductility even in the cold. This indicates the importance of choosing the right material for the right environmental conditions.

Chapters

• 00:00 - 00:30: Introduction to Charpy Impact Test The chapter introduces the Charpy impact test, which is a standardized method to measure the toughness of materials under impact loading and multiaxial stress conditions. It involves the use of a pendulum impact testing machine. The machine features a pendulum with a heavy weight at the end, lifted to a starting position as the initial step. The accuracy of the machine's adjustment is checked by the tester as part of the process.
• 00:30 - 01:00: Machine Calibration and Setup The chapter titled 'Machine Calibration and Setup' discusses the initial steps in preparing a machine for testing. The process ensures that a pendulum used in the testing is set to the correct starting position and that friction is adequately compensated. This preparation is verified by conducting a zero test without a test specimen. Once the zero test confirms the pendulum's accuracy, the machine is deemed ready for tests. The first test mentioned is on strain aging plain carbon steel, specifically S 235 grade, which has been machined for testing purposes.
• 01:00 - 02:00: First Test - Strain Aged Steel The chapter titled 'First Test - Strain Aged Steel' discusses the procedure of testing a specimen with a standardized size and shape, featuring a v-shaped notch. It describes how the tester places the specimen on a support in the lower part of a testing machine and uses a centering device to adjust its position precisely. Once all preparations and checks are complete, the test is ready to begin with a pendulum mechanism.
• 02:00 - 02:30: Principle of Measurement The principle of measurement involves using a pendulum that, when released, swings downwards to hit a specimen with its rounded hammer. The specimen absorbs some of the pendulum's energy, preventing it from reaching its original height on the opposite side. The absorbed energy by the specimen is measurable at the position of the Dragon Decatur, which, in this test, amounts to 13 joules. This process leverages the transformation of potential energy of the pendulum from its starting position.
• 02:30 - 03:00: Analysis of First Specimen The chapter explains the mechanics of a hammer pendulum used for analyzing a specimen. The initial potential energy is determined by the mass of the hammer (M) multiplied by gravitational acceleration (G) and the starting height (H). Upon release, the hammer swings down, impacting the specimen and rises to a new, lower height (h) at the first reversal point. At this point, the pendulum possesses only potential energy represented by M times G times small h. The chapter discusses how the energy absorbed by the specimen in the process can be calculated.
• 03:00 - 04:00: Second Test - Normalized Steel The chapter titled 'Second Test - Normalized Steel' discusses the notch impact energy, referred to as kV. The analysis involves observing the difference between two potential energies. The specimen examined exhibits minimal plastic deformation and has a mostly flat, slightly glittering fracture surface. These characteristics indicate that this type of steel can absorb only small amounts of notch impact energy, as it demonstrates predominantly brittle behavior. This behavior is attributed to strain aging, which limits the steel's ability to deform plastically under stress.
• 04:00 - 05:00: Temperature Effects on Impact Energy This chapter discusses the methodology and outcomes of a second test using a normalized steel specimen (s 235) to evaluate the impact of temperature on impact energy. The process involves placing the specimen on support, centering it, setting the drag indicator, and releasing the pendulum to measure the impact energy. The experiment is carried out under controlled safety measures to ensure accurate results.

Charpy Impact Test Transcription

• 00:00 - 00:30 the Charpy impact test the standardized Charpy impact test has been designed to measure the toughness of materials under impact loading and multiaxial stress state a pendulum impact testing machine is used to do so the pendulum on the machine has a heavy weight at the end this is lifted into the starting position in step one then the tester checks whether the testing machine has been adjusted accurately in order to do
• 00:30 - 01:00 this he turns the drag indicator downwards and releases the pendulum without a test specimen the drag indicator stops at position zero this proves that the pendulum has the correct starting position and that the friction is correctly compensated the machine is ready for the tests first test strain age plain carbon steel s 235 this is our test specimen it has been machined to
• 01:00 - 01:30 standardized size and shape with the characteristic v-shaped notch the tester places the specimen on a support in the lower part of the machine and adjusts its position with a centering device next he turns the drag indicator downwards again and checks that everything is prepared correctly perfect the test can begin the pendulum is
• 01:30 - 02:00 released it swings downwards and hits the specimen with its rounded hammer ping the specimen absorbs part of the pendulums energy so the pendulum doesn't reach the full height on the other side the amount of energy that has been absorbed by the specimen can now be read off at the position of the Dragon Decatur it only amounts to 13 joules in this test here is the main principle of the measurement in its starting position the pendulum only has potential energy
• 02:00 - 02:30 it is given by mass of the hammer M times gravitational acceleration G times starting height capital H after the pendulum has been released the hammer moves downwards hits the specimen and then only swings to height small H exactly at the first reversal point the pendulum again only has potential energy which is M times G times small H the energy that has been absorbed by the
• 02:30 - 03:00 specimen is called knotch impact energy kV it corresponds to the difference between the two potential energies the first specimen only shows very little plastic deformation a mostly flat slightly glittering fracture surface has been formed this is another important indication that this kind of Steel is only able to absorb small amounts of notch impact energy it shows mainly brittle behavior due to the strain aging
• 03:00 - 03:30 effect second test the second specimen has been made from normalized steel s 235 it is also placed on the support and centered the tester turns the drag indicator to its starting position rejects all safety measures and releases the pendulum this time the impact sounds
• 03:30 - 04:00 much deeper and richer an impressive energy of 182 joules has been absorbed by the specimen here the specimen did not break into two pieces instead it was pushed through the counter bearings under heavy plastic deformation in comparison with the strain H steel the normalized steel absorbs much more notch impact energy and behaves in a very tough manner the Charpy impact test is
• 04:00 - 04:30 not only carried out at room temperature materials with body-centered cubic crystal structure such as plain carbon Steel's show a characteristic s-shaped curve of the impact energy versus temperature in the so called upper shelf region the material absorbs a lot of energy and behaves in a tough manner at low temperatures in the lower shelf region only a small amount of impact energy is absorbed and brittle fractures occur
• 04:30 - 05:00 metallic materials with a face centered cubic crystal structure on the other hand to not experience a ductile to brittle transition these materials retain their ductile behavior towards low temperatures and are therefore well suited for low temperature applications