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ASTM D5420 Gardner falling weight impact test for flat rigid plastic

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ASTM D5420 Standard Test Method for Impact Resistance of Flat, Rigid Plastic Specimen by Means of a Striker Impacted by a Falling Weight (Gardner Impact)

ASTMD5420 measures the relative ranking of materials based on the energy required to crack or break a plastic sheet when struck by a falling weight (the "Gardner Impact" method).


Test Principle

The core principle is a free-falling weight impact. A specified weight is dropped from a predetermined height through a guide tube. The weight strikes a hardened steel striker, which then impacts the plastic specimen resting on a support plate.

The test utilizes the Bruceton Staircase Method (or Up-and-Down Method). Instead of testing all specimens at one height, the drop height is adjusted up or down based on whether the previous specimen passed (did not fail) or failed. This concentrates the testing around the threshold where 50% of the specimens are expected to fail, providing a highly precise estimate of the material's impact resistance using fewer samples. 


Test Equipment Required For ASTM D5420: 

Falling-Weight Tester

A Rigid base, 1.0m slotted guide tube, vertical mounting verified by spirit level.

ASTM D5420 Gardner falling weight impact test for flat rigid plastic

Weights (Masses)0.9 kg (2 lb), 1.8 kg (4 lb), or 3.6 kg (8 lb) steel rod weights.
Striker (tup)

A hardened steel striker with a rounded nose. The standard specifies two main diameters:

15.86 ± 0.10 mm (for Geometries GA, GB, GC)

12.70 ± 0.10 mm (for Geometries GD, GE)


Specimen Support Plates

A plate with a specific hole mounted under the specimen. The diameter of this hole changes based on the chosen geometry (ranging from 16.26 mm to 76.0 mm).

Measurement DevicesAccuracy of 1% of average specimen thickness for dimensional measurement.


Test Specimen Information

Size: Diameter/width at least 25 mm larger than the support plate hole; must lie flat on the support.

Thickness: Variation ≤5% within a sample; machining to reduce thickness variation is not allowed.

Quantity: 20 specimens for known mean-failure height; ≥6 extra for unknown starting height; as few as 10 for approximate results (higher deviation).

Condition: Free of cracks/imperfections (unless defects are test variables); tested in as-received condition.

Conditioning: Follow ASTM D618 Procedure A or E171; hygroscopic materials (e.g., nylon) use sealed dry-as-molded specimens.


Key Test Parameters:

ParameterDetails
Striker Diameter15.86 mm (GA/GB/GC); 12.70 mm (GD/GE)
Support Plate I.D.GA/GD:76.0 mm; GB:31.75 mm; GC/GE:16.26 mm
Impact Mass0.9 kg, 1.8 kg, 3.6 kg
Failure CriteriaVisible crack, shatter, through-puncture, brittle split, or loose chip
CalculationMean-failure height: 0+dh(A/N±0.5); Mean-failure energy: wf


Test Stipulations:

Specimen Requirements: No collapse into the support hole; bowed samples invalidate results.

Data Use: Results from different geometries cannot be directly compared; only for relative material ranking.

Base Fixing: Bases <375 lb must be bolted to concrete floors.


Test Procedures of ASTM D5420 Fall dart impact test: 

Conditioning: Specimens are conditioned (usually at 23°C and 50% RH) to stabilize their mechanical properties.

Measurement: The exact thickness of each specimen is measured.

Setup: The correct geometry (GA-GE) is selected, and the specimen is placed flat on the support anvil without clamping (unless specified).

Impact: The weight is raised to the desired height and released.

Evaluation: After impact, the specimen is removed and examined.

Failure Definition: A failure is defined as any crack, split, or hole visible to the naked eye under normal lighting. Permanent deformation (denting) alone is not considered a failure.

Staircase Progression: If the specimen fails, the next one is tested at a lower height. If it passes, the next is tested at a higher height. This continues until enough data points are collected around the 50% failure threshold.


Test Applications & Industry Fields

The ASTM D5420 is critical in any industry where rigid plastic sheets or parts are exposed to sudden impacts. Common fields include:

Construction & Building Products: Evaluating the durability of rigid PVC siding, window profiles, and panels (referenced by D4226).

Automotive: Testing interior and exterior plastic components.

Packaging: Assessing the puncture resistance of rigid plastic films or containers.

Consumer Goods: Manufacturing of durable goods, electronics casings, and protective equipment.


Related Standards

ISO 6603‑2

Instrumented puncture impact testing (for force–deflection curves)

ISO 7765‑1

ISO 7765-2

Falling‑dart impact for plastic films and thin sheets.
ASTM D1709Plastic film falling hammer impact test
ISO 6603-1Plastics - Determination of the punching properties of rigid plastics - Part 1: Non-instrumented impact test
JIS K 7211Plastics -- Determination of puncture impact behaviour of rigid plastics -- Part 1: Non-instrumented impact testing
ASTM D5628Falling dart impact resistance of rigid plastics (similar principles but different striker geometry).
ASTM D3763Standard Test Method for High Speed Puncture Properties of Plastics Using Load and Displacement Sensors
ASTM D1709Standard Test Methods for Impact Resistance of Plastic Film by the Free-Falling Dart Method
ASTM D7136Standard Test Method for Measuring the Damage Resistance of a Fiber-Reinforced Polymer Matrix Composite to a Drop-Weight Impact Event


Importance of the Test for Materials:

Core Mechanical Property: Impact resistance is critical for viscoelastic plastics; the test quantifies resistance to sudden impact, preventing in-service cracking/fracture.

Material Selection & Design: Provides data to rank materials and optimize formulations for real-world impact loads (drops, collisions).

Quality & Compliance: Ensures consistency in production, validates product safety, and supports compliance with industry specifications.

Failure Prediction: Identifies brittle/ductile failure modes to improve product durability and service life.

Related products and device

ASTM D5420 Rigid Plastic Falling Weight Impact Tester

XJB-30E Heavy duty frame falling dart impact testing machine mainly used to test plastic, film, or sheet thickness below 1mm, impact by falling dart, check the energy when 50% of test specimen broken. Conform with standard: ISO 7765-1, ASTM D1709

ASTM D5420 plastic free-falling weight impact tester

XJB-30A Falling dart impact tester mainly used to test plastic, film, or sheet thickness below 1mm, impact by falling dart, check the energy when 50% of test specimen broken. Conform with standard: ISO 7765-1, ASTM D1709, GB 9639.

Related Standard

ISO 6603-1 Rigid plastics falling dart puncture-impact test

ISO 6603-1 specifies falling-dart methods to measure the puncture‑impact performance of rigid plastics using only the 50% impact‑failure energy (E₅₀) threshold, without recording force–time or force–deflection curves.

ASTM D1709 Falling Dart Impact Resistance of Plastic Film

ASTM D1709: Standard Test Methods for Impact Resistance of Plastic Film by the Free-Falling Dart Method


ASTM D1709 test methods cover the determination of the energy that causes plastic film to fail under specified conditions of impact of a free-falling dart. This energy is expressed in terms of the weight (mass) of the missile falling from a specified height which would result in 50 % failure of specimens tested.

ISO 7765-1 Impact resistance by the free-falling dart method

ISO 7765-1:1988 Plastics film and sheeting — Determination of impact resistance by the free-falling dart method 

Part 1: Staircase methods


ISO 7765-1 and ASTM D1709 specifies methods for the determination of the energy, that causes plastics films and sheet less than 1 mm in thickness to fail under specified conditions of impact of a free falling dart from a specified height, that would result in failure of 50 % of the specimens tested. Two methods are described. Method A employs a dart with 38 mm diameter hemispherical head, dropped from a height of 0,66 m, and method B employs a dart with a 50 mm diameter hemispherical head dropped from a height of 1,50 m. The measurement technique is the staircase method.

Drop Dart Impact Resistance of Plastic Film ASTM D1709, ISO 7765

ASTM D5420-21 Gardner Impact Test: Frequently Asked Questions

Q1: What is the core purpose of ASTM D5420-21?

A: ASTM D5420-21 measures the impact resistance of flat, rigid plastic specimens using a falling-weight driven striker (Gardner impact). It calculates the mean-failure energy/height to rank materials by their ability to resist cracking, shattering, or puncture under sudden impact.


Q2: Why is the ASTM D5420 test critical for rigid plastic materials?

A:It quantifies a key mechanical property for plastics, which are viscoelastic and sensitive to impact loads.

It supports material selection, product design, and quality control for real-world drop/collision scenarios.

It standardizes impact testing to ensure consistent, comparable data across labs and manufacturers.

It identifies failure modes (brittle/ductile) to improve product durability and safety.


Q3: What does the 1% accuracy requirement for the micrometer mean in ASTM D5420?

A: The micrometer used to measure specimen thickness must have an accuracy of 1% of the average thickness of the test specimens. This ensures precise thickness measurement, as thickness variation directly impacts impact test results and data reliability.


Q4: What are the five geometries (GA–GE)?

A: They simulate different failure modes:

GeometryStriker DiameterSupport Hole DiameterFailure Mode
GA15.86 mm76.0 mmGeneral impact
GB15.86 mm31.75 mmClassic Gardner
GC15.86 mm16.26 mmPunch-shear
GD12.70 mm76.0 mmHigh-speed puncture
GE12.70 mm16.26 mmPVC building products

Q5: How is “specimen failure” defined in ASTM D5420?

A: Failure is any visually observable crack, split, complete shatter, through-puncture, brittle split, or loose chip under standard lab lighting. Permanent deformation alone is not failure; penetrating dye (e.g., gentian violet) may be used to detect incipient cracks in fiber-reinforced polymers.


Q6: Why use the Bruceton Staircase (Up-and-Down) test method?

A: This method concentrates testing near the mean-failure height, reducing the number of specimens needed while providing a precise estimate of 50% failure energy/height—far more efficient than testing at random heights.


Q7: How many test specimens are required for ASTM D5420?

A: 20 specimens are standard for known mean-failure height; ≥6 extra specimens if the starting height is unknown. As few as 10 specimens may be used for approximate results (with higher standard deviation).


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