Dart impact tester measures the toughness of packaging film.

Overview

Dart impact test is a common method to evaluate the resistance of packaging film materials under dynamic impact loads. This method determines the toughness of a material under impact by making a dart head of a specific mass fall freely from a predetermined height and impacting the clamped specimen. Toughness is defined here as the comprehensive ability of a material to absorb energy and resist fracture, which is essential for packaging materials to withstand unexpected shocks during actual transportation and storage.

Test principle and equipment

The drop dart impact testing machine is mainly composed of a release device, a dart head, a vertical conduit and a specimen clamping system. During the test, the dart head falls freely in the catheter, and its impact energy is determined by the mass of the dart head and the height of the fall, and the calculation formula is:
E = m × g × h
where E is the impact energy (unit: joule), m is the mass of the dart head (kg), g is the acceleration of gravity (9.81 m/s²), and h is the fall height (m). By adjusting the mass or height, the simulation of different impact energies is possible. The equipment is usually equipped with photoelectric or acoustic sensors to accurately determine whether a specimen has cracked.

Testing process

Before testing, the specimen should be clamped flat in a ring fixture to ensure that there is no wrinkle or pretension. The test environment is usually controlled under standard temperature and humidity conditions to reduce the impact of environmental fluctuations on the results. The mass of the dart head or the drop height is adjusted using an incremental or decreasing method until the impact energy is found that causes a 50% probability of rupture of the specimen, which is often reported as the impact strength of the material. A sufficient number of parallel tests should be performed on each sample to ensure the statistical reliability of the data.

Application:

The test results not only provide a single impact strength value, but also provide insight into material properties by analyzing rupture patterns such as ductile tears or brittle fractures. Higher impact strength values usually indicate that the material can better disperse stress and have better toughness under high-speed impact. This data can be used to guide the material selection, thickness design, and process optimization of packaging films, such as in food preservation packaging and industrial product protection, ensuring that the integrity of packaging is maintained during circulation.

Standards and specifications

There are a variety of relevant test standards in different regions and industries, and they may differ in specimen size, dart head geometry, clamping method, etc. The corresponding criteria should be selected according to the target market or customer requirements and clearly stated in the report. Here are some common criteria for reference:

Influencing factors and precautions

Test results are influenced by a variety of factors. Materials include resin type, molecular weight distribution, additives and film structure; the specimen involves thickness uniformity and whether there are stress concentration defects; The operation covers clamping strength, dart head cleanliness and ambient temperature and humidity. To ensure comparability of results, these conditions should be documented in detail in the test report. Regularly calibrating equipment using standard reference materials is also an important part of ensuring data accuracy.

Epilogue

The Dart impact test provides an intuitive and reproducible method for quantifying the toughness of packaging films. Through standardized testing and detailed data analysis, it can help production and R&D personnel evaluate material properties more scientifically, and promote the development of packaging materials in a more durable and economical direction. With the advancement of material technology, the testing methods themselves are also evolving, and it is of great significance to keep the standard updates and technical literature on them in order to maintain the advanced and relevant nature of the test.

References

1. Standard Test Method: ASTM D1709, Standard Test Method for Resistance of Plastic Films to Free Dart Impact.
2. Standard test method: ISO 7765-1, Determination of plastic films and sheets against free dart impact Part 1: Step method.
3. Technical Overview: Mechanical property testing technology for packaging materials, covering impact testing principles and application examples.
4. Instrument Operation Guide: Operation and maintenance manual for general drop dart impact testing machines, involving equipment calibration and common problem handling.