ASTM F320 Standard Test Method for Hail Impact Resistance of Aerospace Transparent Enclosures

The standard "ASTM F320 Standard Test Method for Hail Impact Resistance of Aerospace Clear Enclosures," developed by the American Society for Testing and Materials (ASTM), describes a test method for determining the impact resistance of an aerospace clear enclosure (such as a windshield, canopy, window, lens cover) under hailstorm conditions using simulated hailstones composed of molded ice pellets under strictly controlled conditions. This test should also be used to meet hail test or performance requirements specified by design or contract.

For the purposes of this standard, the following terms and definitions apply:

• Damage refers to any change in the visual characteristics or integrity of a windshield as a result of hail impact, including scratches, cracking, delamination, fissures, penetration or shattering.
• Ice ball refers to a frozen water sphere with filling that imitates a natural hailstone in terms of weight, size and hardness.
• Impact angle refers to the angle between the flight path of the ice ball and the target normal.
• A sabot is the plastic carrier used to transport the ice ball down the launch tube. One type of sabot consists of a split polycarbonate rod with a central cavity to hold the ice ball. Each sabot half is designed to ensure aerodynamic separation from the ice ball after it exits the launch tube.

The test method involves projecting a series of ice balls of specified sizes at a specified speed and angle, in a specified pattern, against a sample windshield. Requirements for the ice ball, test sample, procedure, and data collection are specified. The ice ball is photographed in flight to verify its integrity. Requirements for a sample apparatus and test procedure are specified, but options are permitted. However, the options used must be demonstrated to result in an ice ball of the same size, consistency, and speed as the specified apparatus and procedure. Options are permitted in the following areas:

• Ice ball mold material.
• Launcher. Any type of launcher is permitted, as long as the ice ball reaches the test specimen intact at the correct speed. The use of sabots and the sabot material and geometry are optional.
• Method for determining ice ball integrity.
• Ice ball speed measurement as long as accuracy standards are met.
• Test sample dimensions. Those given are minimum.
• Security must meet the security standards of the testing facility used.

This test method can be used to determine the hail impact resistance of windshields for acceptance, design, service, or research purposes. Using this method with the windshield angle and speed installed on a specific aircraft, design allowances, criteria, and tolerances for that vehicle's windshield can be determined.

The facilities and equipment required for this test procedure include a suitable shooting range equipped with an ice ball mold, launcher, blast deflector, sabot trap, velocity measurement system, test sample holder, and a camera with or without flash to verify ice ball integrity. Ancillary equipment required for this test includes the test sample, ice balls, sabots, and ignition cartridges.

The shooting range must be an enclosed area of ​​at least 3 m x 6 m to contain flying debris and keep out unauthorized personnel.

The ice sphere mold is two aluminum blocks with hemispherical cavities and ventilation holes for filling with water and for the expansion of the water during freezing.

A variety of launchers are suitable as specified in this standard. In addition to the powder gun described in this test method, laboratories have also successfully used compressed gas gun launchers. An example of a powder gun launcher is shown in the figure and consists of a barrel, bore, barrel plug, and check. The barrel should be made of high-quality AISI 4130 seamless steel pipe or equivalent in the annealed condition.

In aerospace applications, transparent enclosures such as aircraft canopies, windows, and other glass components are critical not only for visibility but also for ensuring structural safety. These enclosures must withstand a variety of environmental stresses. One of the most damaging is hail impact at high altitudes or speeds. The ASTM F320 standard provides a vital testing framework for evaluating how well transparent plastics used in aviation can withstand hail impacts.

This standard establishes a laboratory method for simulating and evaluating the performance of transparent plastic materials used in aerospace structures against the impact of hailstones. The objective is to determine the impact resistance, integrity, and durability of the materials under realistic conditions.

This standard is particularly important for:

• Aircraft cockpit windows and canopies
• Helicopter windshields
• Transparent domes, observation panels and radomes
• Unmanned aerial vehicles (UAVs) with sensor lenses or covers

The ASTM F320 standard method involves controlled laboratory procedures that mimic real-life hail conditions. Key elements of the test include:

• Test samples: Flat or curved clear plastic samples typically used in aerospace glazing systems. Materials include polycarbonate, acrylic, or laminated composites.
• Simulated hailstones: Artificial hailstones are made of ice and vary in size and mass depending on the test scenario. Common diameters range from 25 mm to 50 mm.
• Impact velocity: Hailstones are projected onto samples using air guns or similar devices to achieve the expected hail impact velocity at the cruising altitude and airspeed. Velocities can range from 30 to 120 m/s or more.
• Evaluation criteria: After impact, the material is examined for:
  • Fracture or penetration
  • Delamination or cracking
  • Loss of optical clarity
  • Residual strength

The test can be repeated at multiple locations or in different areas to simulate hailstorm conditions.

The aerospace industry requires highly reliable, lightweight materials that perform under extreme conditions. The ASTM F320 standard helps manufacturers and engineers:

• Selecting appropriate materials for aviation enclosures
• Evaluating safety performance in hail conditions
• Improving design for durability and long-term durability
• Meeting regulatory and certification requirements (e.g. FAA, EASA)

In short, the ASTM F320 standard promotes consistency, comparability, and repeatability in impact resistance assessment. This standard is a key standard for ensuring the safety and reliability of transparent aerospace enclosures against hail impact. It helps develop materials and systems that protect equipment and reduce in-flight hazards. As aerospace materials evolve, this standard continues to provide a benchmark for performance under some of nature's more unpredictable threats.

Our organization, which has been supporting businesses across all sectors for years through a wide range of testing, measurement, analysis, and evaluation activities, has a strong team of employees who closely follow global developments in science and technology and are constantly improving themselves. In this context, we also provide testing services in accordance with the ASTM F320 Standard Test Method for Hail Impact Resistance of Aviation Transparent Enclosures.