Plastics Quality Control and the Role of Impact Testing

Characterizing materials is necessary to ensure performance and quality. Hence, material testing is playing a key role in modern manufacturing.

The characteristics of different materials can be determined using a variety of tests, of which the most critical are impact tests.

Impact Tests

Impact tests are employed to measure the toughness of a specific material. In a pendulum impact test, the impact force is measured by striking the sample with a swinging arm. The degree of deformation of the sample is then measured after the impact to determine its toughness.

A material's toughness is a characteristic of its ability to absorb energy in the event of plastic deformation. Brittle materials exhibit low toughness due to their ability to endure the small amount of plastic deformation.

A material’s impact value can also vary with temperature. The impact energy of a material normally decreases at lower temperatures as it becomes more brittle at these temperatures.

Impact Testing in Plastics Quality Control

Plastics are increasingly being used in a myriad of industries, including the automotive industry. As a result, the demand for accurate testing is ever increasing to evaluate the performance of a wide range of plastics under different environmental conditions.

Impact testing can be used to assess the ability of a polymer to resist fracture, a key concern for the automotive industry. Characterization is necessary because the addition of colorants and other treatments to a polymer compound may change its impact properties.

Impact testing is being performed across the supply chain, from resin manufacturers to compounders and processors. They ensure the quality at the batch level using pendulum impact testers.

There are different types of impact tests available, of which the two major types of pendulum impact tests are Izod and Charpy. Izod tests, developed by ASTM, are widely utilized in the North American region, while Charpy tests are more typically utilized in other geographic regions.

The Izod Impact Test

Izod impact testing is an ASTM standard procedure that generally involves the use of a notched sample to measure impact energy.

The Izod impact test is different from the Charpy impact test wherein the sample is secured in a cantilevered beam configuration rather than a three-point bending configuration.

The Charpy Impact Test

The Charpy impact test is also referred as the Charpy V-notch test. In this standardized high strain-rate test, the amount of energy absorbed by a material during fracture is measured. From this absorbed energy, the given material’s notch toughness is determined.

Impact Testing Solutions from Zwick

Zwick/Roell, a provider of hardware and software solutions for material characterization, has developed a suite of impact testing solutions specially designed to meet the integrity and reliability demanded by plastics customers.

Zwick has designed its HIT pendulum impact testers line (Figure 1) with reduced vibration in the pendulum rod, thereby achieving the highest levels of accuracy in testing.

The Zwick equipment is also engineered for high throughput and dependability.

Figure 1. HIT Izod

According to Zwick’s Plastics Industry Manager, Florian Liebert, intelligent features like automatic pendulum identification ascertain consistency in test procedures and decrease changeover times between tests. The automated specimen feeding feature of the Zwick equipment is shown in Figure 2.

Figure 2. HIT Automated Specimen Feeding

Building on its vast experience in performing impact testing on many different plastics, Zwick has developed a specialized measurement and control software named the ZwicktestXpert II software, which automatically inputs the capacity value of the pendulum and thus eliminates this input value as a likelihood source of test error.

With the testXpert software, Zwick’s HIT pendulum impact testers can provide complete traceability of the testing process.

Conclusion

Ergonomic design, reliability and accuracy are standard aspects of HIT pendulum impact testers. Zwick’s instruments deliver outstanding performance due to their novel features such as superior vibration damping and pendulum coding.

HIT pendulum impact testers also have intelligent features like automatic recognition of the pendulum and subsequent test value selection according to the relevant standard.

Tool-free pendulum change and ergonomic design make the Zwick equipment user friendly and enable reduced changeover time between tests, concluded Liebert.

About Zwick USA

For over 150 years the name of Zwick Roell has stood for outstanding technical expertise, innovation, quality and reliability in materials and component testing. Our customers’ confidence in us is reflected in our position as world-leaders in static testing and the significant growth we are experiencing in fatigue strength testing systems. The figures tell the same story: in the 2011 the company achieved incoming orders of €185m.

With innovative product development, a comprehensive range and worldwide service, this family concern supplies tailor-made solutions for the most demanding research and development and quality assurance requirements in over 20 industries. With over 1100 employees, a production facility in Ulm, Germany, additional facilities in America and Asia plus agencies in 56 countries worldwide, the Zwick brand name guarantees the highest product and service quality.

This information has been sourced, reviewed and adapted from materials provided by Zwick USA.

For more information on this source, please visit Zwick USA.

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