ASTM F320-21

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: F320 − 16 F320 − 21
Standard Test Method for
Hail Impact Resistance of Aerospace Transparent
Enclosures
This standard is issued under the fixed designation F320; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope
1.1 This test method covers the determination of the impact resistance of an aerospace transparent enclosure, enclosure
(windshield, canopy, window, lens cover, etc.), hereinafter called windshield, during hailstorm conditions using simulated
hailstones consisting of ice balls molded under tightly controlled conditions. This test shall also be used to meet hail test or
performance requirements that are specified by design or contract.
1.2 Units—The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical
conversions to SI units that are provided for information only and are not considered standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use. For specific hazard statements, see Section 7.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Terminology
2.1 Definitions:
2.1.1 damage, n—any modification in visual properties or integrity of a windshield as a result of hail impact including scratches,
crazing, delamination, cracks, penetration, or shattering.
2.1.2 ice ball, n—a frozen masssphere of water, with filler, that simulates a natural hailstone in weight, size, and toughness.
2.1.3 impact angle, n—the angle between the ice ball flight path and the target normal.
2.1.4 sabot, n—a plastic device for protecting carrier used to carry the ice ball while in down the launch tube. One type of sabot
(see Fig. 1) consists of a split polycarbonate rod containing a central cavity for holding the ice ball. Each sabot half is designed
to assure aerodynamic separation from the ice ball after ejectionexiting from the launch tube.
This test method is under the jurisdiction of ASTM Committee F07 on Aerospace and Aircraft and is the direct responsibility of Subcommittee F07.08 on Transparent
Enclosures and Materials.
Current edition approved April 1, 2016May 1, 2021. Published April 2016June 2021. Originally approved in 1978. Last previous edition approved in 20102016 as
F320 – 10.F320 – 16. DOI: 10.1520/F0320-16.10.1520/F0320-21.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F320 − 21
FIG. 1 Sabot Configuration
3. Summary of Test Method
3.1 The test method involves launching a series of ice balls of specified sizes at a sample windshield at a designated velocity and
angle and in a specified pattern. Requirements are specified for the ice ball, test specimen, procedure, and data acquisition. The
ice ball is photographed in flight to verify its integrity.
3.2 Requirements are specified for a particularan example apparatus and test procedure, but options are permitted for certain areas.
permitted. However, it must be possible to demonstrate demonstrated that the options used result in an ice ball impacting the test
panel with the same size, consistency, and velocity as with the specified apparatus and procedure. Following are areas where
options are allowed:
3.2.1 Ice Ball Mold Material.
3.2.2 Launcher—Any type of launcher is allowable as long as the iceball ice ball reaches the test specimen intact at the correct
speed. The use of sabots and sabot material and geometry are optional.
3.2.3 Method of Determining Ice Ball Integrity.
3.2.4 Ice Ball Speed Measurement, optional as long as accuracy standards are met.
3.2.5 Test Specimen Sizes—Those given are minimum.
3.2.6 Safety—Safety must satisfy the safety standards of the test facility being used.
4. Significance and Use
4.1 This test method shall be used to determine the hail impact resistance of windshields for acceptance, design, service, or
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research purposes. By couplingusing this method with the installed windshield angle and velocity of a specific aerospace vehicle,
design allowables, criteria, and tolerances can be established for that vehicle’s windshield.
5. Apparatus
5.1 The facilities and equipment required for the performance of this test procedure include a suitable firing range equipped with
an ice ball mold, a launcher, blast deflector, sabot trap, velocity measuring system, test specimen holder, and a camera with or
without strobe lights to verify ice ball integrity. Ancillary equipment required for this test includeincludes test specimen, ice balls,
sabots, and firing cartridges. An example facility is described below.
5.2 Firing Range—The firing range shall be a minimum of 9 by 18 ft (3 by 6 m) enclosed to contain flying debris and to exclude
unauthorized personnel.
5.3 Ice Ball Mold, two aluminum blocks with hemispherical cavities and vent holes for filling with water and for water expansion
during freezing.
5.4 Launcher, a variety of launchers are suitable as noted in 3.2.23.2.2. In addition to the powder gun described in this test method,
laboratories have also successfully utilized compressed gas compressed-gas gun launchers. An example of a powder gun launcher
is shown in Fig. 2, consisting of a barrel, breech, breech plug, and control. The barrel shall be made from high-quality AISI 4130
seamless steel tubing, or equivalent, in the annealed condition. The breech shall be made from AISI 4130 steel rod, or equivalent,
heat treated to a 160-160 to 180-ksi (1104-180 ksi (1104 to 1242-MPa)1242 MPa) ultimate tensile strength condition. The size of
cavity to be used in the breech depends on the desired test velocity (see Table 1). The breech plug, which locks the cartridge in
place and contains the firing pin, shall be made of 4340 steel heat treated to a 160-160 to 180-ksi180 ksi ultimate tensile strength
condition. The firing pin is actuated by a kinetic impact air piston. Control is accomplished by an electrically actuated air valve.
2 2
For a 100-psi (0.69-MPa)100 psi (0.69 MPa) air source, a 0.75-in.0.75 in. (4.84-cm (4.84 cm ) piston traveling 0.5 in. (13 mm)
is used.
5.5 Blast Deflector—Place a plate with a 4-in. (100-mm)4 in. (100 mm) diameter hole as shown in Fig. 3 between the sabot trap
and the first velocity measuring station. Then place a corrugated cardboard plate over the hole. This deflector is not required for
compressed gas compressed-gas gun systems.
5.6 Sabot Trap is made by placing two steel plates two to four ice ball diameters apart, centered on the flight path and located
FIG. 2 Launcher Design
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TABLE 1 PowerPowder Loads
Desired Veloc- Barrel Bore, in. Barrel Length, Cartridge Size, Powder Weight,
Powder Type
ity, ft/s (m/s) (mm) in. (m) caliber grains (g)
A
200 (60) 1.25 (32) 10 (0.25) 0.30 Bullseye 6 (0.39)
2.25 (57) 10 (0.25) 0.30 Bullseye 6 (0.39)
500 (150) 0.75 (19) 10 (0.25) 0.30 Bullseye 5 (0.32)
B
1.25 (32) 60 (1.52) 0.50 IMR 4227 40 (2.59)
2.25 (57) 60 (1.52) 0.50 Bullseye 30 (1.94)
2.25 (57) 10 (0.25) 0.30 Bullseye 12 (0.78)
1000 (300) 0.75 (19) 10 (0.25) 0.30 Bullseye 9 (0.58)
1.25 (32) 60 (1.52) 0.50 Bullseye 60 (3.89)
1.25 (32) 10 (0.25) 0.30 Bullseye 20 (1.30)
2.25 (57) 60 (1.52) 0.50 Bullseye 70 (4.54)
2000 (600) 0.75 (19) 60 (1.52) 0.50 Bullseye 35 (2.27)
1.25 (32) 60 (1.52) 0.50 Bullseye 70 (4.54)
2.25 (57) 60 (1.52) 0.50 Bullseye 150 (9.72)
A
The sole source of supply of the apparatus manufacturer known to the committee at this time is Hercules, Inc., 1313 North Market Street Wilmington, DE 19894-0001.
If you are aware of alternative suppliers, please provide this information to ASTM International Headquarters. Your comments will receive careful consideration at a meeting
of the responsible technical committee , which you may attend.
B
The sole source of supply of the apparatus manufacturer known to the committee at this time is duPont, Chestnut Run Plaza 705/GS38 Wilmington, DE 19880-0705.
If you are aware of alternative suppliers, please provide this information to ASTM International Headquarters. Your comments will receive careful consideration at a meeting
of the responsible technical committee , which you may attend.
FIG. 3 Blast Deflector
a minimum of 6 ft (1.82 m) from the launcher muzzle as shown in Fig. 4. This trap is not required for systems that utilize
aerodynamic separation of the sabot or other suitable mechanisms to ensure that the sabot does not impact the test article.
5.7 Velocity Measurement System—The break-screen velocity measurement There are multiple options for velocity measurement
including laser-photodetector systems, light-screens, high-speed photogrammetry, chronographs, and break screens. The essential
FIG. 4 Sabot Trap
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features of the velocity measurement system are that it be accurate and repeatable, not be triggered by small stray objects traveling
with the projectile, and not alter the flight path or damage the projectile. The system shall be accurate to 61 % or better.
Historically, the break-screen has been used and is described below. The break-screen velocity measurement method consists of
a set of screens, power supply, wiring, and counters. Three screens shall be made from a lightweight bond paper with an electrical
circuit painted on the paper by the silk screen process. The paint for the circuit shall be electronic grade electrical conducting
paint. Do not thin the paint. The break-screen shall be made with lines ⁄8 in. (3.2 mm) wide by 18 in. (460 mm) long as shown
in Fig. 5 giving a resistance of no more than 300 Ω. Fig. 6 shows the arrangement of components and gives the electronic circuit
to be used with the three screens. The system shall be accurate to 61 % or better. Laser-based photo detector systems and
high-speed-film-based systems are also acceptable, provided the accuracy is 61 %.
5.8 Test Specimen Holder—Use one of two types of test specimen holders. The one The test specimen holder shall be designed
to securely grip the perimeter of the panel with the impacted zone being unsupported. The test specimen holder shown in Fig. 7
is designed to hold an 18-18 by 18-in. (0.46-18 in. (0.46 by 0.46-m)0.46 m) test specimen that can be impacted at angles ranging
from 0 to 80° as detailed in Section 8. When testing a complete windshield, use edge restraints similar to the actual installation
and place the windshield in the proper orientation (see 9.2).
5.9 Ice Ball Integrity Camera—Verify ice ball integrity before impact by obtaining a photograph or high-speed video of the ice
ball in flight before impact. This is accomplished Still images are captured by illuminating the ice ball with a strobe light while
the ice ball is in the field of view of a camera lens. This synchronization can be obtained by using an open shutter with the strobe
triggered at the second with a velocity screen. The signal is split with part going to the velocity counters and part to a variable
time-delay generator. Using the estimated ice ball velocity, a time delay is selected so the ice ball will be in view of the camera
lens when the strobe is triggered.
5.10 Balance, for powdergunpowder and ice balls, capacity 0.2 lb (100 g), accuracy 61 % (1.0 g).61 %.
5.11 Clinometer or Protractor, to measure impact angle, accuracy 6 ⁄4 °.
5.12 Syringe, 100-cm100 cm , for puttinginjecting water into the ice ball mold.
6. Materials
6.1 Sabot—An effective injection molded sabot configuration is shown in F
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