Plastic Falling Dart Impact Strength Testing: Standards, Methods, and Applications

Plastic falling dart impact strength testing is a critical quality control and material characterization method used to evaluate the impact resistance and toughness of plastic films, sheets, and molded products. This comprehensive guide covers the testing principle, applicable standards such as ISO 7765, ASTM D1709, and GB/T 9639, specimen requirements, test procedures, and practical applications across the packaging, automotive, and construction industries.

Technical Overview

Falling dart impact testing, also referred to as falling weight impact testing or drop impact testing, is a dynamic test method used to determine the energy required to cause failure of plastic materials under a concentrated impact load. During the test, a dart or weight with a specified hemispherical or conical striking head is dropped from a controlled height onto a clamped specimen, and the impact energy at failure is recorded.

Unlike pendulum-based impact tests such as Izod (ISO 180, ASTM D256) or Charpy (ISO 179), which use notched bar specimens, falling dart testing evaluates flat specimens under multi-axial stress conditions that closely simulate real-world impacts such as drops, knocks, and puncture events. This makes it particularly valuable for thin plastic films, rigid sheets, and finished components where notch sensitivity is not the primary concern.

Failure is typically defined as any visible crack, perforation, hole, or tear through the specimen, or in the case of instrumented testing, a measurable drop in the force–deflection curve. The results are expressed as impact failure energy in joules (J), failure mass in grams (g) or kilograms (kg), or as impact strength normalized by specimen thickness.

Testing Samples

Flexible Plastic Films and Sheets

Thin flexible films with thicknesses typically below 0.1 mm are the most common test materials for falling dart impact. These include polyethylene (LDPE, LLDPE, HDPE), polypropylene (PP, cast and biaxially oriented), PVC, PET, PA, and multi-layer laminates used in food packaging, agricultural films, and industrial bags. Specimens are usually cut into squares or discs large enough to cover the annular opening of the specimen holder.

Rigid and Semi-Rigid Plastic Sheets

Rigid plastic sheets and plates, such as those made from PVC, PMMA (acrylic), PC (polycarbonate), ABS, and filled thermoplastics, can be tested using heavier darts and modified support fixtures according to standards such as ASTM D5420 and ASTM D5628. These materials are commonly used in glazing, signage, appliance panels, and thermoformed products.

Molded and Machined Specimens

Injection-molded or compression-molded discs and plaques can be tested to evaluate the impact performance of specific resin grades, compound formulations, or processing conditions. This is useful during material development, supplier qualification, and comparative benchmarking.

Pipes, Fittings, and Finished Products

Sections of plastic pipes, fittings, containers, and other finished parts may be subjected to falling weight impact testing to verify resistance to handling damage and external impact loads, often as part of product certification and routine factory quality control.

Testing Items

Typical test items and reported results for plastic falling dart impact strength testing include:

• Impact failure energy (J) at a specified failure probability, commonly the 50% failure point
• Dart mass at failure (g or kg) under a fixed drop height
• Drop height at failure under a fixed dart mass
• Mean failure energy and standard deviation from statistical evaluation
• Ductile versus brittle failure mode classification
• Maximum force, deflection at maximum force, and total absorbed energy (instrumented methods)
• Puncture resistance of films and laminates
• Temperature-dependent impact behavior at low, ambient, and elevated temperatures

Testing Methods

Several standardized test methods exist, and the choice depends on the material type, thickness, and the information required. All methods condition specimens in a controlled laboratory atmosphere, typically 23 °C and 50% relative humidity, before testing.

Staircase Method (Bruceton Method)

The staircase method, described in ISO 7765-1 Method A, ASTM D1709 Method A, and GB/T 9639, increases or decreases the dart mass in fixed increments after each test depending on whether the previous specimen failed or passed. This rapid up-and-down procedure efficiently converges on the mass or energy corresponding to approximately 50% failure probability. It is the most widely used approach for routine quality control of plastic films.

Statistical Method (Probit Method)

The statistical method, covered by ISO 7765-1 Method B, tests groups of specimens at several fixed dart masses and uses statistical analysis to calculate the mean failure energy and its confidence interval at various failure probability levels (for example, 50% and 90%). Although more specimens are required, this method provides a more complete characterization of the failure energy distribution.

Instrumented Falling Weight Impact Test

Instrumented impact testing according to ISO 6603-2 and ASTM D3763 (also ASTM D5628 for non-instrumented setups) uses a dart equipped with a force transducer and high-speed data acquisition to record the complete force–time and force–deflection response. This method distinguishes between the force at yield, force at break, and energy absorbed up to specific events, providing detailed insight into ductile versus brittle failure behavior.

Rigid Plastics Impact Test

For rigid sheets and flat components, ASTM D5420 (Gardner-type falling weight) and ISO 6603-1 describe procedures using heavier strikers and defined support anvils. Test parameters such as dart geometry, support diameter, and drop height must always be reported because results from different geometries are not directly comparable.

Applications

Falling dart impact strength data support a wide range of engineering and commercial decisions:

• Material selection and grade comparison for packaging films, technical films, and rigid sheets
• Incoming resin inspection and supplier quality assurance in film extrusion and converting operations
• Verification of film toughness after additive loading, recycling content incorporation, or down-gauging initiatives
• Certification of pipes, fittings, and construction products against regulatory and industry requirements
• Validation of packaging performance for transport, storage, and drop scenarios in food, pharmaceutical, and consumer goods supply chains
• Research and development studies on temperature effects, aging, UV exposure, and environmental stress cracking
• Failure analysis and root cause investigation of cracked or punctured plastic components

FAQ

What is the difference between falling dart impact and Izod/Charpy impact testing?

Falling dart testing applies a multi-axial impact load to a flat, unnotched specimen and measures the energy needed to cause through-failure, making it well suited to films, sheets, and finished parts. Izod and Charpy tests apply a bending impact to a notched bar specimen and measure energy absorbed per unit of notch area, making them better suited to evaluating notch sensitivity and brittle fracture behavior of rigid molding materials.

Which standard should be selected for plastic film testing?

For flexible films, ISO 7765-1, ASTM D1709, and GB/T 9639 are the most commonly applied standards. Method A of ASTM D1709 (38.1 mm dart) and Method B (50.8 mm dart) cover different toughness ranges, while ISO 7765-1 offers both staircase and statistical options. The chosen dart geometry, support opening, and drop height must match the expected strength range of the material.

How is the falling dart impact result calculated and reported?

For staircase testing, the result is the dart mass at which approximately 50% of specimens fail, converted to impact energy using the equation E = m × g × h, where m is the mass, g is gravitational acceleration, and h is the drop height. For instrumented testing, energy values are integrated directly from the force–deflection curve. Reports should always include the standard used, specimen thickness, conditioning, dart geometry, and support configuration.

What factors influence falling dart impact test results?

Key influencing factors include specimen thickness and its uniformity, temperature and humidity conditioning, dart head diameter and geometry, drop height, support ring diameter, clamping pressure, and the operator's definition of failure. Consistent test parameters are essential for meaningful comparisons between materials or production lots.

Can finished products be tested instead of flat specimens?

Yes. Sections of pipes, containers, panels, and complete articles can be tested using adapted fixtures, provided the support and striking conditions are documented. Many accredited third-party laboratories offer custom falling weight impact setups to evaluate real components under realistic impact scenarios.