ISO/TR 13086-5:2022
(Main)Gas cylinders — Information for design of composite cylinders — Part 5: Impact testing of composite cylinders
Gas cylinders — Information for design of composite cylinders — Part 5: Impact testing of composite cylinders
This document provides information for the design of composite cylinders related to impact testing and service experience with impact, including: — low energy impact, which can result from events that can occur during handling or working around cylinders; — high energy impact, which can result from accidents during transportation, or impact by large objects with velocity; — drop impact, which can result from handling, where cylinders are dropped or tipped over; and — high velocity impact, which can result from high energy impact by a small object, such as gunfire, and demonstrates non-shatterability of the cylinder or tube. Where appropriate, field experience relevant to testing requirements is provided. NOTE Unless otherwise stated, the word “cylinder” refers to both cylinders and tubes.
Bouteilles à gaz — Informations relatives à la conception des bouteilles en matière composite — Partie 5: Essais d'impact sur bouteilles en matière composite
General Information
Standards Content (Sample)
TECHNICAL ISO/TR
REPORT 13086-5
First edition
2022-06
Gas cylinders — Information for
design of composite cylinders —
Part 5:
Impact testing of composite cylinders
Bouteilles à gaz — Informations relatives à la conception des
bouteilles en matière composite —
Partie 5: Essais d'impact sur bouteilles en matière composite
Reference number
© ISO 2022
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Low energy impact . 1
4.1 General . 1
4.2 Visible indications . 2
4.3 Concepts in standards . 2
4.3.1 General . 2
4.3.2 30 J impact level . 2
4.3.3 488 J impact level . 2
4.3.4 1 200 J impact level . 2
4.3.5 Consequences . 3
4.4 Test concepts . 3
5 High energy impact (accidents) . 4
5.1 General . 4
5.2 Visible indications . 4
5.3 Design influence . 4
6 Drop impact . 6
6.1 General . 6
6.2 Test scenarios . 6
6.3 Design influences . 7
7 High velocity impact.8
7.1 General . 8
7.2 Test parameters . 8
7.3 Test results analysis . 9
8 Failure considerations .10
9 Inspection and examination . .11
10 Field incidents.12
10.1 Bridge hit . 12
10.2 Rollovers. 13
10.3 Rollover with penetration .13
10.4 Vehicle collision .13
10.5 Forklift impact . 14
10.6 Other incidents . 15
11 Impact projects .15
12 Discussion .15
13 Summary .16
Annex A (informative) Low energy impact testing .17
Annex B (informative) Drop impact testing (low pressure liquified gas, up to 50 l) .19
Annex C (informative) Drop impact testing (high pressure) .20
Annex D (informative) High velocity impact testing .21
Annex E (informative) Alternative high velocity impact testing .22
Bibliography .24
iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 58, Gas cylinders, Subcommittee SC 3,
Cylinder design.
A list of all parts in the ISO/TR 13086 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
Introduction
This document considers how impact testing is carried out, why it is done in particular ways and the
relevance of various aspects (e.g. a cylinder drop, a flying element through the air, from what direction,
size, shape, weight, impact velocity, etc.; does the cylinder “fail” safe or blow into fragments with
associated pressure wave?).
This document only addresses cylinders, as a definition of all the associated equipment and its
interaction with the cylinders is difficult to assess. The designer can conduct some system level impact
tests, including drop, to assess valves, pressure release devices and other attached components.
It is recognized that there are differences between cylinders/tubes that are for general use (without
any requirements related to packaging and protection in service) and cylinders/tubes permanently
mounted in frames (which offer some differences in loading and protection). Impact testing of an
assembly can be different from testing a single, freestanding cylinder/tube.
This document addresses transportable cylinders, vehicle fuel containers and cylinders permanently
mounted in frames. It applies to all sizes of cylinders, and to carbon, aramid and glass fibre
reinforcements.
Drop testing of smaller cylinders is a requirement in some regulations, codes and standards. For serial
production of automotive cylinders, an adequate returnable packing material/method to protect
the cylinder during production and until mounted in the vehicle can be used. However, the drop of a
cylinder demonstrates a general resistance to impact, which improves safety.
In addition to providing an understanding of the background, an overview is provided of some standard
approaches to conducting tests.
v
TECHNICAL REPORT ISO/TR 13086-5:2022(E)
Gas cylinders — Information for design of composite
cylinders —
Part 5:
Impact testing of composite cylinders
1 Scope
This document provides information for the design of composite cylinders related to impact testing and
service experience with impact, including:
— low energy impact, which can result from events that can occur during handling or working around
cylinders;
— high energy impact, which can result from accidents during transportation, or impact by large
objects with velocity;
— drop impact, which can result from handling, where cylinders are dropped or tipped over; and
— high velocity impact, which can result from high energy impact by a small object, such as gunfire,
and demonstrates non-shatterability of the cylinder or tube.
Where appropriate, field experience relevant to testing requirements is provided.
NOTE Unless otherwise stated, the word “cylinder” refers to both cylinders and tubes.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 10286, Gas cylinders — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 10286 apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 Low energy impact
4.1 General
Low energy impacts can occur during normal service. Examples of this include dropping tools on the
cylinder, being hit by road debris, some bouncing when initiating or ending a lift by a crane, hoist, or
forklift, being hit by a forklift, or similar incidents. In some cases, low energy impact can leave visual
evidence of the impact or can require a cylinder to be removed from service.
4.2 Visible indications
Some impacts can be from contact with sharp objects, in which case there would likely be some
visual indication of surface damage, such as a cut or surface indentation. Other impacts can be from
blunt objects, which can result in some surface crazing, and either surface indentations or internal
delamination, or both, without necessarily leaving visible damage. Glass fibre composite reinforcement
with a translucent resin is more likely to show visible damage due to impact. Acoustic Emission Testing
(AET) or Modal Acoustic Emission (MAE) can be appropriate to assess damage if there is no visible
damage.
Low energy impact can cause some reduction in strength, but it is unlikely to result in a rupture when
the impact occurs or before the opportunity for inspection. Guidance on these issues is provided in
standards on visual inspection (see Clause 9).
4.3 Concepts in standards
4.3.1 General
There are some common low energy impact levels that are used in standards, including 30 J, 488 J and
1 200 J. These energy levels are based on typical events that can occur in service. Information related to
low energy impact testing is provided in Annex A.
4.3.2 30 J impact level
The 30 J impact level is based on impact from road debris, such as one that can impact a natural gas
or hydrogen fuel container mounted below a vehicle. The debris can, for example, be dislodged as a
wheel passes over it. This impact level is used in a test from an EU standard for liquid fuel containers
(i.e. gasoline or diesel), and subsequently applied to gaseous fuel containers. Impacts that can reach
this energy level, would, for example, include a granite stone about 40 mm in diameter hitting at about
95 km/h, or a cube of steel about 22 mm on a side hitting at about 95 km/h. This level of impact is
often considered as a means of evaluating protective coatings and is generally applied prior to chemical
exposure testing.
4.3.3 488 J impact level
The 488 J impact level is based on the energy from dropping a man-portable cylinder weighing about
27,3 kg from a height of about 1,8 m. This is viewed as the highest combination of weight and height that
can occur during transportation or installation by an individual. Such a drop can occur on any part of
the cylinder.
The 488 J energy level reasonably represents energy of a similar cylinder falling off a loading dock or
the bed of a transport vehicle. However, the energy level varies with the size of the cylinder. The impact
is unlikely to occur axially on the end boss in such a fall. Accordingly, as cylinder size increases, the
488 J energy level is maintained on the end and is intended to be representative of other loads that can
occur during handling, such as being hit by a forklift, or hitting an object while being transported by a
forklift.
The 488 J energy level has been effective as a means of assuring impact resistance in the field based on
safe responses to most incidents. There has also been some interest in testing to an impact energy level
that is higher, but still less than the energy level of a high velocity impact.
4.3.4 1 200 J impact level
The 1 200 J impact level, by one account, addresses a stone of approximately 650 g kicked up by or
falling off a vehicle travelling at 110 km/h in one direction, and impacting a cylinder going the opposite
direction at 110 k/h. Such a stone would be approximately 80 mm to 90 mm in diameter, while a cube
of steel with the same weight would be about 44 mm on a side. While this scenario is not as likely as
the two energy levels discussed above, the energy level represents an impact that can occur in service.
Transported cylinders generally have some protection from road debris, including the truck bed and
side walls.
4.3.5 Consequences
Some standards have adopted both the 488 J and 1 200 J impact levels, where passing the 488 J impact
is mandatory, and a warning label is applied if the 1 200 J impact results are not successful.
Some possible consequences of low energy impacts, following subsequent pressure cycling, include
crack growth, delamination, and liner leakage. While strength can be compromised by impacts, it does
not necessarily result in rupture of the cylinder.
While cracks can grow during pressure cycling, the pressure cycling can also serve to blunt some of the
stress concentration that results from the impact. In testing of cylinders with cut flaws, including deep
cut flaws, a full lifetime of cycles was applied, and in some cases, the burst pressure was higher after
[13]
cycling than without cycling . However, the performance of the cylinder after an impact depends on
factors such as the fibre type, fibre stress ratio, and construction. Performance dispersion within a
production batch can also affect the evaluation of cylinder performance drop due to impacts.
An impact can also result in delamination within the wall. If the construction is exclusively continuous
fibres, delamination between layers is not necessarily of consequence. In some cases, an intentional
delamination between layers has been part of a design as a means of improving cyclic fatigue life.
However, if localized reinforcements are included, such as dome caps or cloth inserts, and the localized
reinforcements delaminate from the wound layers, the structural response of the laminate can be
altered, and strength can be compromised.
An impact that causes cuts or broken fibres reduces the local stiffness of the laminate. This results in
greater local deformation during pressure cycling, which results in lower fatigue life in a metal liner,
and possibly leading to leakage of the cylinder contents.
4.4 Test concepts
The 30 J impact is generally applied in a test via a pendulum with a defined impacting mass and pivot
arm length. An alternative can be a weight dropped from a given height. Caution is advised when using
other methods to catch the impactor after the first impact, to avoid multiple impacts. The 488 J impact
is often applied to transportable cylinders in the form of a drop test, but can also be conducted using a
pendulum or dropped weight. The 1 200 J impact is also generally applied by a pendulum, but can also
be applied using a dropped weight or by an impactor in a horizontal orientation that is powered by a
pressurized gas.
The impact is based on equivalent energy, but consideration can be given to differences in momentum.
Using the example of the 30 J impact, the momentum of the stone or steel cube would be the same,
about 2,24 N·s. For a typical 30 J impact test, the mass is a steel pyramid of 15 kg, which would result
in an impact velocity of about 1,41 m/s, and a momentum of 21,2 N·s, or about 10 times that of the
possible field event. At this point, testing is based on energy, but it would be useful to understand how
momentum influences results.
The cylinder is subject to pressure testing following the impact. Most current standards require
pressure cycling. The upper cycle pressure generally is the working pressure. The number of cycles is
generally reflective of the number of pressure cycles that occur between inspections, although several
standards require the same number of cycles as the original cycle test. Some standards consider the
test successful if the cycling is completed without a rupture of the cylinder. Other standards generally
burst the cylinder after cycling, with a minimum pressure that can be, for example, 80 % of the original
design burst pressure.
5 High energy impact (accidents)
5.1 General
High energy impact can occur due to accidents for a vehicle transporting a cylinder, or using it as a
fuel container that can in some cases involve other vehicles. Examples of this include a single vehicle
hitting a bridge or other structure, dropping a cylinder that is being transported, or a similar incident.
A vehicle transporting a cylinder can be hit by another vehicle, such as an automobile, truck, or train,
where it is possible for the cylinder to be hit directly or caused to be ejected from the transporting
vehicle. A tube trailer, battery vehicle, or vehicle transporting a multiple element gas container (MEGC)
can run off the road and roll over. Prevention of roll-overs or other road accidents can be considered
when designing the tube trailer, battery vehicle, or MEGC. High energy impact can also result from
misuse of the cylinder.
5.2 Visible indications
High energy impact generally gives visual evidence of the impact if the cylinder physically contacts
another component. If there is visual evidence, it is likely to be rejected on this basis. Impact with
a sharp or small diameter component is more likely to show evidence of impact. If there is a known
impact, it is generally considered that the cylinder can be removed from service.
Impact with a flat component at high energy is also likely to show some indication of damage. In
some cases, impact from a flat component results in resin crazing and a noticeable loss in composite
properties, such as can be detected when the composite wall is tapped with a coin. It is also possible for
an impact with a relatively flat component to cause reversal of curvature of a cylinder, fracturing the
inner layers, without necessarily showing significant damage on the outer surface.
Cylinders have also been known to rupture during an impact event. At very high levels of energy, the
difference between a rupture and a progressive failure releasing gas can be negligible. However, it
is possible that a high energy impact by a relatively small structure will only result in a hole in the
cylinder and a release of contained gas.
The characteristics of the impacting body, of how impact energy is distributed into the composite wall,
and characteristics of the wall itself, affect results. Consideration of non-dimensional terms helps to
understand how laminate damage can occur. Comparing items such as diameter of the impacting body
to the wall thickness or cylinder diameter can show likelihood of penetration of the wall. Looking at the
load over the affected area, compared with the transverse compressive strength or the shear strength
of the laminate can show likelihood of penetration versus laminate crushing.
5.3 Design influence
Comparing the total energy of impact to reserve strength of the laminate, i.e. the difference between
energy contained at burst pressure versus energy contained when impacted, can give insight as to
whether the impact will result in simple damage, penetration, or rupture.
The location of a cylinder in a vehicle during an impact event has an effect on how much damage the
cylinder receives. Energy is absorbed by either the vehicle or the frame, or both, during the event, which
can offer some protection for the cylinder.
If the accident is such that the impact loading is only on a frame or container, and from the frame or
container into the cylinder through the end bosses, it is possible that there is no visible damage, or even
no damage, to the cylinder. In this case, AET or MAE can be required to assess if there is, in fact, any
damage sustained by the cylinder in the accident. If it can be confirmed that there is no damage, the
cylinder can safely remain in service.
The frame, container, or bundle structure is likely to absorb some of the energy through deflection or
deformation, providing additional protection for the cylinders. A standard that addresses both cylinder
design and frame design can offer information on design and testing that considers interaction of the
cylinder and frame. The designer of the packaging would be aware of potential impact threats, and at a
minimum conduct a failure modes and effects analysis (FMEA) to address possible concerns.
The pressure in the cylinder affects the level of damage incurred and the consequences. Pressure
adds stress to the composite reinforcement, but it also stabilizes the wall, limiting deformation when
impacted. Figure 1 shows cylinders with three diameters, each designed for four different service
pressures, with a radial load in the cylinder applied at zero pressure and service pressure.
Figure 1 shows that deflection is greater for unpressurized cylinders than pressurized cylinders, as the
pressure resists the impact load. Figure 1 also shows that larger diameter cylinders deflect less under
load, for a determined stress level, given that the wall is thicker if the service pressure is the same.
When pressurized after an impact at low pressure, the cylinder is more likely to have a lower burst
pressure than a cylinder impacted at a higher pressure, given the greater deflection, and greater risk of
damaged internal fibres, due to the impact loading.
The cylinder has an associated design margin of safety that allows some absorption of impact energy
without rupture. The combination of pressurization and design margin limits risk of rupture. If there is
a lower pressure in the cylinder, there is greater risk of damage, but the margin of safety is higher, and
the contained energy is lower. Therefore, even with high damage risk, the safety risk is acceptable due
to the reduced energy content. In any case, a cylinder with suspected damage would either be inspected
or removed from service, or both.
Key
1)
254 mm, no pressure X service pressure (bar )
508 mm, no pressure Y max displacement (mm)
1016 mm, no pressure
254 mm, service pressure
508 mm, service pressure
1016 mm, service pressure
1) 1 bar = 0,1 MPa = 105 Pa; 1 MPa = 1 N/mm
Figure 1 — Wall deflection under load versus diameter and contained pressure
The gas contents, i.e. whether it is compressed gas or liquified gas, have some influence on results of
an accident. If the vehicle carrying the cylinder is moving, the contained mass affects the dynamic
response of the cylinder and any framing. Depending on the level of the impact, the contained mass can
also limit deformation of the wall.
The cylinder construction also affects the level of damage incurred. A thicker wall is generally regarded
as more impact resistant. Lower strength materials result in a thicker wall. Glass fibre requires a higher
stress ratio, or safety factor, than carbon fibre, so a cylinder with glass fibre reinforcement is generally
regarded as more impact resistant.
The cylindrical section of the cylinder or tube is nominally the thickest part. The domes are generally
thinner, with the thinnest part adjacent to the cylindrical section, and increasing in thickness moving
towards the end boss.
Some cylinders are made using hybrid material construction, for example, using both carbon fibre and
glass fibre. This gains the advantage of the improved stress rupture characteristics of the carbon fibre,
and the advantage of a thicker wall by adding the glass fibre. Some hybrid construction intermixes the
carbon and glass fibres while winding, while others use interspersed layers of carbon and glass. Still
others use carbon fibre on the inside layers, and glass fibres on outer layers. Using fibres with different
modulus of elasticity also has some benefits with structural dynamics during high energy impact.
The impact energy in one impact incident was calculated to be in the range of 80 000 J to 100 000 J. The
energy level can be lower than this in some incidents, but it can be higher in others. As with low energy
impacts, a consideration of different momentum levels would be of interest.
High energy impact testing is generally not included in qualification testing of cylinders and tubes. High
energy impact is not common in the field, and the impact levels and means of application are varied.
These factors make it difficult to develop a meaningful test. However, the designer can consider some
impact testing outside the scope of the standards. This would serve to build knowledge on the impact
energy threshold leading to cylinder performance drop and corresponding damage criteria, for the
definition of adequate pre-fill (pass/fail) inspection criteria. Regardless of specific application, the
maximum impact energy is likely the same for any cylinder that is used in transportation.
The current impact tests, including drop, low energy impact, and high velocity impact, are considered
sufficient to address impact resistance of cylinders and tubes, such that a higher energy impact test is
not necessary. This is supported by field experience, given that in addition to the low level of incidence,
the consequences of these impact have not been such that a new qualification test is necessary.
Examples of known impact incidents are given in Clause 10.
6 Drop impact
6.1 General
Dropping of cylinders and tubes can occur during transportation, handling, and use. These drops can
occur in virtually any orientation, horizontal, vertical, or at an angle, although the orientation can be
somewhat controlled by the size and use of the cylinder.
A cylinder that is horizontal on a loading dock or transport truck can roll straight off the dock or truck
bed, resulting in a horizontal drop. If it rolls off where one end extends off the dock or truck bed before
the other, i.e. rolls off at an angle, then it is likely to be at an angle when it impacts the ground. A drop on
the end of a cylinder is most likely when carried by hand.
6.2 Test scenarios
The height of the drop is derived from likely scenarios in service. A drop height of 1,8 m is generally
used to reflect the maximum height of a loading dock or truck bed. This would also apply to a smaller
cylinder carried by hand. As cylinder size increases, the likelihood of impacting from a drop on the end
of the cylinder decreases. The vertical drop can be limited in energy or be replaced by a defined impact
on the end of the cylinder or tube.
Similarly, larger tubes are not likely to be transported or moved without the use of either handling
equipment or a cradle, or both, or support frame. In this case, the drop test can be replaced by an impact
test.
Cylinders are generally drop tested on a flat and level concrete surface. Drop testing in horizontal and
vertical orientations is relatively straightforward. A cylinder is required to bounce on the ground as
part of the horizontal test until it comes to rest. Damage is generally across the length of the cylinder,
but can be concentrated on the ends or localized build-up locations. A cylinder is required to bounce on
the ground as part of the vertical test until it comes to rest, but it is permissible to prevent the cylinder
from toppling over. Toppling brings an uncertainty to the vertical test, and tests areas outside of the
boss area. The 45° drop test is intended to address such areas. For large cylinders and tubes, it can be
necessary to adjust the angle of the cylinder to maintain the centre of gravity and a minimum distance
from the lower end to the ground. It is important to verify the angle prior to the drop.
6.3 Design influences
The 45° drop test (see Figure 2) tends to load mostly near the tangent area between the dome and the
cylindrical portion or the cylinder, or near areas where build-ups are applied. The 45° drop introduces
a rotational energy component into the test. When the first end hits the ground, the centre of gravity
is still moving downward. The rotational component from bounce of the first end can result in a higher
impact loading of the second end than the first end.
Figure 2 — 45° drop test
The impact energy depends on the mass of the cylinder, which is affected by its size, the materials of
construction, and the wall thickness. Response to the impact depends on the energy level, materials of
construction, and design features. Some cylinders use integral foam or foam covers in the dome area to
provide protection against drop impact. Other cylinders can use a build-up area in the cylinder so that
impact is reacted in that area. Higher safety margins or hybrid construction can be used to improve
performance.
There is some issue with reproducibility of drop tests. Precision in establishing the orientation of the
cylinder and precision in release of the cylinder without imparting spin are key factors. It is necessary
to exercise caution with these issues to reduce scatter. Even with the reproducibility issue, this test has
been effective as a test for demonstrating impact resistance.
The test is conducted without internal pressure, so there is no resulting stabilization of the wall during
the test. Experience has shown that dropping a cylinder when empty is more severe than when the
cylinder is pressurized. Annex C provides information related to drop testing of high-pressure cylinders.
Testing of small cylinders is sometimes conducted with water to simulate load and response of cylinders
containing liquified gases such as propane. However, this is not necessarily representative of the proper
weight, and it does not reflect that liquified gases would have pressure that would stabilize the cylinder
wall in a drop test, unless some pressure is added for the test. Annex B provides information related to
drop testing of low-pressure cylinders used for liquified gases.
Conformable containers are being developed for use in containing compressed natural gas or hydrogen
gas for use as a vehicle fuel. Carrying out a drop test in sufficient orientations ensures that the container
is impact resistant regardless of orientation.
7 High velocity impact
7.1 General
The high velocity impact test is often called the gunfire test. It serves two purposes:
a) assurance that the cylinder will not rupture when hit by a bullet of similar calibre and energy level;
and
b) assurance that the cylinder will not rupture when subjected to penetrating impact at high velocity
of similar energy level.
This is one of the few impact tests that are conducted under pressure during qualification. Pressure
during testing is necessary for high velocity impact, as it tests for non-shatterability under pressure.
A high velocity impact (gunfire) test was historically used on metal cylinders to confirm that ductility
was sufficient that they did not shatter and rupture during a high velocity impact. The high velocity
impact test was later applied to composite cylinders to similarly demonstrate they did not shatter and
rupture. Annex D provides information related to high velocity impact testing.
7.2 Test parameters
The test is generally conducted using a 7,62 mm (30 calibre) AP (armour piercing) bullet (see Figure 3).
The cartridge is generally 51 mm long, with a nominal muzzle velocity of 850 m/s. Actual muzzle
velocity depends on specific cartridge, barrel length, and other factors. The bullet has an energy of
about 3 500 J. Armour piercing rounds are used to ensure penetration and improve repeatability. Other
hardened bullets can be used, noting that the key factor is the capability to penetrate the cylinder
wall. If softer bullets are used, they would likely spread on impact, increasing the impact diameter, but
decreasing the likelihood of penetration. The intent is to demonstrate the cylinder does not rupture
when the wall is penetrated. It is generally not specified whether the bullet exits, or is captured by, the
cylinder.
Military applications often use larger calibre bullets or cuboid impactors with higher energy levels, but
commercial applications generally use the bullets and energy levels discussed above.
Figure 3 — Cartridge and bullet for high velocity impact (gunfire) test
The gunfire test originally defined the path of the bullet to be 45° to the perpendicular axis of the
cylinder (see Figure 4). More recently, the path of the bullet has been defined as perpendicular to the
longitudinal axis of the cylinder. This change has been made because it is more likely for the bullet to
penetrate as cylinder wall thickness increases, the bullet is less likely to ricochet, and it is easier to set
up the test.
Figure 4 — Gunfire test at an angle of 45°
7.3 Test results analysis
One factor in cylinder performance in this test is the dynamic response of the cylinder to the impact.
When the bullet hits, it deforms the shell, setting up stress and deformation waves in the cylinder. Some
of these waves are in-plane, others are out-of-plane. The construction of the cylinder, particularly the
fibre material, hybridization, wind angles, and thickness would affect these stress and deformation
waves. If the bullet penetrates the first wall, then hits the second wall such that the stress is additive,
the probability of the cylinder failing can be higher. This can be a basis to shoot the bullet at an angle
other than perpendicular to the axis.
As the wall thickness increases, which can be due to higher pressure or larger diameter, it becomes
more resistant to penetration, and is unlikely to hit the second wall with enough energy to be concerned
about the path of the bullet. Initially, when a bullet failed to penetrate the cylinder wall, multiple bullets
at one point were used to penetrate the wall, or a higher energy/calibre bullet was used. Experience
has shown that if the initial bullet did not penetrate, the cylinder would pass the test if more bullets or
higher energy/calibre bullet were used. Therefore, the criterion has been updated such that if the bullet
does not penetrate the cylinder, the test is deemed to be passed.
If the bullet does not penetrate the cylinder wall, the test setup would include a means to safely vent the
pressurized gas.
Historically there were some instances where very small cylinders were tested. The 7,62 mm bullet was
large compared with the diameter, such that enough of the cylinder wall was destroyed by the bullet for
the cylinder to be cut in half, which does not address the issue of rupture/not shattering. In such cases,
when the diameter is less than 120 mm, the round is reduced to 5,6 mm (22 calibre).
There has been some consideration for replacing the bullet, fired by a rifle, with a mechanism that fires
a bullet from an industrial test fixture instead of a rifle, or penetrates the cylinder with a rod of the
same diameter as the bullet and at the same energy level. Such a mechanism would not be considered
a firearm, even if fired using gunpowder. However, the rod can also be energized pneumatically,
hydraulically, or mechanically. Consideration can be given to whether the momentum of the bullet is
significant, and needs to be matched. Annex E provides information related to a bullet impactor or a
mechanical impactor that can be used in place of a bullet fired from a gun.
8 Failure considerations
The modes of failure of the cylinder and effects of failure would be considered when evaluating the
application and developing the operational controls. If failure occurs, the two likely failure modes would
be leak or rupture. Protection of the cylinder from impacts, and inspection after suspected impacts, are
a starting point for avoiding failures.
Consequences of a leak include:
— failu
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