We use cookies to give you the best experience possible. By continuing we’ll assume you’re on board with our cookie policy

# Theory of Impact Test Essay Sample

The whole doc is available only for registered users OPEN DOC

Get Access

## Theory of Impact Test Essay Sample

The impact toughness (AKA Impact strength) of a material can be determined with a Charpy or Izod test. These tests are named after their inventors and were developed in the early 1900’s before fracture mechanics theory was available. Impact properties are not directly used in fracture mechanics calculations, but the economical impact tests continue to be used as a quality control method to assess notch sensitivity and for comparing the relative toughness of engineering materials. The two tests use different specimens and methods of holding the specimens, but both tests make use of a pendulum-testing machine. For both tests, the specimen is broken by a single overload event due to the impact of the pendulum. A stop pointer is used to record how far the pendulum swings back up after fracturing the specimen. The impact toughness of a metal is determined by measuring the energy absorbed in the fracture of the specimen. This is simply obtained by noting the height at which the pendulum is released and the height to which the pendulum swings after it has struck the specimen .

The height of the pendulum times the weight of the pendulum produces the potential energy and the difference in potential energy of the pendulum at the start and the end of the test is equal to the absorbed energy. Since toughness is greatly affected by temperature, a Charpy or Izod test is often repeated numerous times with each specimen tested at a different temperature. This produces a graph of impact toughness for the material as a function of temperature. An impact toughness versus temperature graph for a steel is shown in the image. It can be seen that at low temperatures the material is more brittle and impact toughness is low. At high temperatures the material is more ductile and impact toughness is higher. The transition temperature is the boundary between brittle and ductile behavior and this temperature is often an extremely important consideration in the selection of a material. In this test the specimen is positioned across the lowest point in the path of a striker mounted at the end of a pendulum.

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. In the Izod impact test, the test piece is a cantilever, clamped upright in an anvil, with a V-notch 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. 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.

When the results of a number of tests performed in different temperatures are plotted, ductile-to-brittle transition curves, may be obtained. As the temperature is reduced through the transition range, the fracture surface changes from one having a ‘fibrous’ or ‘silky’ appearance with much distortion at the sides, to one of completely crystalline appearance with negligible distortion. There is a strong correlation between the energy absorbed and the proportion of the cross-section which suffers deformation in fracture, and the fracture surface is frequently described in terms of the percentage of its area which is crystalline in appearance. Typical fracture appearances with crystallinity increases as the temperature is reduced.

We can write a custom essay

Order an essay

## You May Also Find These Documents Helpful

Impacts throughout US government

Federalism, a theory by which political power is divided between a national government and state governments, each having their own area of jurisdiction has impacts throughout US government. It has proved to be significant due to many consequences of Federalisms of law, and has increased the idea of regionalism. However, in recent years the significance of Federalism has been reduced by the growth in the...

Impact of Globalization

Impact of Globalization on Bengaluru Impact of Globalization on Bengaluru In the last two decades Globalization has been an integral part of India’s progress. One of the biggest impacts of globalization has been on IT (Information Technology) industry. IT industry flourished rapidly in India due to highly educated and literate workforce. Metropolis cities started developing at faster pace due to IT industry. Why Bengaluru? Bengaluru,...

Impact on my life

It’s taken me seventeen years to realize how much of an impact my brother has truly had on my life. I never really realized that one person can have a lasting effect in your decisions and the way you perceive life. This person can be very inspirational and even more so if it is someone close to you or a relative. In my case, it...

The Other Wes Moore: The Impact of...

The Other Wes Moore: The Impact of Family Many people would say we are all just products of our environment. For two young boys from Baltimore, this could not be truer. In “The Other Wes Moore: One Name, Two Fates,” written by Wes Moore, two fatherless, young boys growing up in the same neighborhood with the same name, end up on two entirely different paths...

Technology Appropriation Impact of a new road...

New developments keep arising every day which have got different impacts on the lives of people who live in the area where there is new development. The introduction of a new road in Bibera on the pygmies, Bagyeli varies from the economic impacts, social and even political impacts. Roads are known to open up areas for more development activities and cause a lot of changes...

### Essays 64,739

300+
Materials Daily
100,000+ Subjects
2000+ Topics
Free Plagiarism
Checker
All Materials
are Cataloged Well

Sorry, but copying text is forbidden on this website. If you need this or any other sample, we can send it to you via email.

Sorry, but only registered users have full access

immediately?

Become a member

Thank You A Lot!

Emma Taylor

online

Hi there!
Would you like to get such a paper?
How about getting a customized one?

Can't find What you were Looking for?