The Process of Plastic Impact Testing and Impact Sample Preparation for Plastics
A brief history of plastics impact testing
To detect material behaviors at high deformation speeds, impact testing is employed. Pendulum impact testers, high-speed testing equipment, and drop weight testers are all used to determine how plastics behave under impact loading.
In the past, choosing between drop weight and pendulum impact testers appeared straightforward. After all, the material, customer desire, and end-use application requirement were the only factors that mattered. Traditional testers are indispensable, reasonably priced, and trustworthy.
Yet, other studies assert that the reproducibility and accuracy of these straightforward conventional tests are poor. However, there is a solution to these limits, and it comes in the form of new instrument modifications.
Moreover, there has been a push to replace Izod impact reporting with the Charpy test, a pendulum impact technique that is popular in Europe. The car industry, which wants to support efforts for worldwide standardization, is the main force behind the shift.
The Charpy and Izod Tests
The Charpy and Izod tests, which were developed, cleared the path for impact testing of plastics.
In 1900, the Charpy impact test was invented by Georges Augustin Albert Charpy. In the end, it was thought to be a very well-liked test for determining the relative toughness of materials. The thing that people enjoyed the most was how affordable it was. Because it is affordable, it is readily available.
This impact test evaluates a typical notched specimen and calculates the energy it has absorbed. It does this by shattering as a result of an impact load. The test measures the notch sensitivity and impact toughness of engineered materials such as composites, polymers, metals, and ceramics.
The dimensions of a typical Charpy impact test specimen are 55 mm x 10 mm x 10 mm, with a notch drilled into a larger dimension. It entails holding the specimen firmly at both ends on a pendulum arm and striking it with a hammer. The notch should be opposite where the hammer strikes.
The precise amount of energy absorbed by the specimen is measured by monitoring the pendulum arm’s motion reduction. High strain rates caused by pressurization or impact, stress concentrators like voids, notches, cracks, and low temperatures are important elements that affect material toughness.
The Izod impact test was named after the English engineer Edwin Gilbert Izod. The Charpy impact test and this test are comparable. At low temperatures, it is also used to evaluate materials.
To perform the Izod impact test, a specimen must be cut into a round or square portion with one, two, or three notches that are each 70 mm x 15 mm x 3 mm in size. This test also includes striking and swinging down the specimen while it is safely maintained vertically by a pendulum with a predetermined weight at the end of the arm.
The amount of energy lost by the pendulum reveals the force of the hit. To determine this energy loss, the pendulum’s loss of height during its swing is measured. Impact strength, according to academics, is the propensity of polymer composites to withstand a high-energy impact without fracturing or breaking.
They even claimed that the characteristics of individual fibres utilized for interlaminar, interfacial, and hybridization adhesion between the matrix and the fibre in hybrid composites and fibre-reinforced polymer composites have a significant impact on such materials’ impact properties.
Impact testing types (Charpy and Izod)
When evaluating the durability or impact strength of materials, the Charpy and Izod impact tests are both highly regarded methods. Essentially, they are measurements of the total amount of energy that a substance can absorb.
This energy absorption is directly connected to how brittle the material is. Brittle materials include, for example, glass and ceramics. As a result, they absorb less energy than ductile materials like copper and aluminium.
Understanding a material’s energy absorption characteristics is crucial since it may be used to estimate how much plastic deformation it can withstand before failing catastrophically. It’s also crucial to keep in mind how these two impact testing approaches differ and overlap.
Test of Charpy Influence
The Charpy impact test, which was first employed in 1900, is still among the most used ways to conduct impact tests today. It is favoured mostly due to how simple it is to create samples and get findings.
A weighted pendulum is dropped from a specific height during a Charpy impact test to make contact with the selected specimen. The height of the pendulum before and after it was cracked, as well as the difference between the two readings can be used to conclude that this substance would then absorb energy.
The specimen is positioned horizontally on the device. The machine is typically a 55 mm x 10 mm x 10 mm bar with a notch drilled onto its face. This notch is positioned to face away from the pendulum and is either U-shaped or V-shaped. It aids in both encouraging the fracture and concentrating the tension.
Even when it is as cold as -45°F, a Charpy impact test can be performed at both decreased and ambient temperatures. Usually, it is completed in accordance with EN 10045-1, ISO 148, ASTM E23, and ASTM A370. The ISO 179 and ASTM D6110 tests, which are typically conducted on metals, can also be carried out on polymers and plastics.
Test of Izod Impact
Edwin Gilbert Izod first presented the test procedure in 1903. The Charpy impact test is very similar to this one in terms of both the test setup and the specimen design.
On the other hand, there are certain distinctions, such as the specimen orientation, which is fastened onto the apparatus vertically with the notch facing the pendulum. The specimen is then struck by the pendulum at a certain location above this notch.
The Charpy and the Izod impact tests have a number of differences in addition to their many similarities. One of these variations is the ability to use either metallic or plastic specimens for the Izod impact test.
The standard size of plastic samples is a bar with the following dimensions: 64 mm x 12.7 mm x 3.2 mm (V-shaped). Whereas metallic samples often come in the form of a circular, 11.42mm by 127mm bar with one to three machined V-shaped notches. The most common Izod impact test methodologies are ASTM D256, ISO 180, and ASTM E23.
Which Should You Use, Then?
In the end, the choice of impact testing type depends on the goal. Product design, material characterisation, quality control, inspecting incoming material, and R&D are a few of the things that need to be taken into account.
The plastics that are covered by the ISO, ASTM, and other standards, however, are specifically mentioned. For instance, the ASTM D1709 standard can be used to test thin films, whereas ISO 6603-2 or ASTM D3763 can be used to test the polycarbonate used in automotive parts.
In essence, the Charpy impact test is generally utilised on metals while the Izod impact test can be performed on both metals and plastics. Thus, choose Izod if you’re looking for a plastic impact tester.
Yet, this does not rule out the possibility of Charpy impact testing for plastics. To find out a material’s ductility, toughness, and ductile-brittle transition temperature, do a Charpy impact test. The sensitivity of plastic specimens with notches can also be determined similarly.
Whereas Izod impact testing uses simply a V-notch, Charpy impact testing uses both a V-notch and a U-notch. The specimen must be placed horizontally and with the notch facing away from the pendulum while conducting Charpy impact testing. The specimen, on the other hand, must be placed upright and with the notch facing the pendulum when an Izod impact test is being conducted.
Whereas the upper tip of the sample is the striking point for Izod impact testing, the centre of the sample is the striking point for Charpy impact testing. Although EN 10045-1, ISO 148, and ASTM E23 are frequently used requirements for Charpy impact testing, ISO 180, ASTM D256, and ASTM E23 are frequently used specifications for Izod impact testing.
Impact Testing System Features
An impact testing system must have an appropriate specimen as well as supports and anvils. To effectively take the blow of a moving object with sufficient energy to break the specimen, it must be placed in the right place. A tool to gauge the amount of energy this fractured specimen has absorbed should also be present.
Charpy and Izod impact tests are most frequently conducted on rubber and plastic specimens using the Class J Automated Impact and Izod Impact Testing system. Tensile impact pendulum and fixtures are used in this test. It can also be applied to plastic sheets and films. It now offers extremely cost-effective configurations to meet Izod tests from 1J to 22J and Charpy tests from 1J to 50 J thanks to the substantially optimized design.
High resolution, energy losses, touch screen display, centre alignment, replaceable pendulum, larger test area, anvils, and supports are some of its standout characteristics.
