Patent Application
20170292815
The present disclosure generally relates to methods, compositions, articles and systems for impulse reduction. In particular, embodiments relate to methods, compositions, articles and systems for absorbing, reflecting, and cancelling portions of shockwaves and fireballs.
Traditionally, measures including barriers such as steel, concrete, dirt, or gravel, have been used as the primary protection against explosions for assets, including, but not limited to, a person, infrastructure, vehicle, or combinations thereof. Infrastructure may be any infrastructure. For example and without limitation, infrastructure may include buildings, bridges, military installations, refineries, public works infrastructure (e.g., wastewater treatment facilities), utilities infrastructure (e.g., electrical substation), or oilfield infrastructure. Vehicles may be any land, air, or sea based vehicle. For example and without limitation, vehicles may include cars, trucks, tanks, aircraft, ships, or boats. While such traditional measures may provide adequate protection against ballistic projectiles, fireballs and shockwaves, hereinafter referred to collectively as resulting from explosions, may propagate through such barriers. Impulse from pressure waves (which may include shockwaves and fireball waves), the integral of force of the pressure wave over the time in which it acts, may be a significant source of damage. To provide additional protection against pressure waves, certain traditional blast protection systems having increased strength, mass, or number and direction of angles have to deflect or absorb impulse, thereby reducing the force absorbed by the asset.
The present disclosure provides for a method. The method includes providing an article having an impact side and an asset side and exposing the impact side of the article to a plurality of pressure waves, the pressure waves having a plurality of pressure wave frequencies. The method also includes reflecting at least one composite harmonic of a portion of the pressure wave frequencies and reducing an amplitude of a portion of the pressure waves.
The present disclosure further provides for a multilayer article. The multilayer article has an impact side and an asset side. The multilayer article includes layers arranged successively. The multilayer article includes a first layer, where the first layer of the article has a density ranging from 0.02 g/cc to 0.05 g/cc. The first layer may be a rubber. The multilayer article also includes a second layer. The second layer has a density higher than the first layer. The density of the second layer ranges from 0.25 g/cc to 0.43 g/cc. The second layer may be an insulator. The multilayer article includes a third layer. The third layer has a density higher than the first layer and the second layer. The density of the third layer ranges from 0.4 g/cc to 0.5. The third layer may be concrete.
The present disclosure also provides for a method. The method includes providing an article comprising multiple layers, wherein each layer is mechanically coupled with adjacent layers of the article. The article has an impact side and an asset side that is opposite the impact side. From the impact side to the asset side, each successive layer has a density that is greater than a density of the adjacent layer that is closer to the impact side. The method also includes receiving at least one pressure wave on the impact side of the article, wherein the at least one pressure wave includes a plurality of frequencies. In addition, the method includes reflecting at least one harmonic with the article, thereby reducing an amplitude of the at least one pressure wave. The method also includes absorbing at least a portion of the at least one pressure wave with the article.
The disclosure further includes an article having multiple layers. Each layer is mechanically coupled with adjacent layers of the article. The article has an impact side and an asset side that is opposite the impact side. From the impact side to the asset side, each successive layer has a density that is greater than a density of the adjacent layer that is closer to the impact side.
The present disclosure may be understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features may not be drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.
A detailed description will now be provided. The following disclosure includes specific embodiments, versions and examples, but the disclosure is not limited to these embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the disclosure when the information in this application is combined with available information and technology. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.
Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents. Further, unless otherwise specified, all compounds described herein may be substituted or unsubstituted and the listing of compounds includes derivatives thereof.
Further, various ranges and/or numerical limitations may be expressly stated below. It should be recognized that unless stated otherwise, it is intended that endpoints are to be interchangeable. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.).
As used herein, “fireball” refers to flame in the shape of a ball or other shape generated by an explosion. A fireball has wave characteristics including a frequency and amplitude.
As used herein, an “explosive” is a reactive substance that, upon ignition, causes a sudden, almost instantaneous, release of gas, heat, and pressure. An explosive may be categorized by the speed at which it expands. For example and without limitation, a “high explosive” may be an explosive at which a blast front moves faster than the speed of sound through a medium. A “low explosive” may be an explosive at which the blast front moves slower than the speed of sound through a medium.
As used herein, “shockwave” refers to a major change of pressure in a narrow region traveling through a medium, for example, air, caused by an explosion moving faster than sound. For purposes of this disclosure, a “major change in pressure” may be a change between 1 psi and 1,000,000 psi, or between 10 psi and 100,000 psi. “Narrow region” refers to a time between 1 microsecond and 1 millisecond, or between 1 millisecond and 100 milliseconds.
As used herein, a “blast” refers to a chemically initiated, thermally induced shock wave. A “blast front” may be the leading edge of the shock wave.
As used herein, the term “brisance” refers to the rapidity with which an explosion reaches its peak pressure, i.e., the shattering capability of a high explosive, determined mainly by its detonation pressure.
As used herein, “oxygen balance OB %” indicates the degree to which an explosive can be oxidized. If an explosive molecule contains just enough oxygen to form carbon dioxide from carbon, water from hydrogen molecules, all of its sulfur dioxide from sulfur, and all metal oxides from metals with no excess, the molecule is said to have a zero oxygen balance. The molecule is said to have a positive oxygen balance if it contains more oxygen than is needed, and a negative oxygen balance if it contains less oxygen than is needed. The sensitivity, strength, and brisance of an explosive may be dependent upon oxygen balance and may approach their maxima as oxygen balance approaches zero.
Without being bound by theory, a blast life cycle for a chemical-based explosive includes the steps of: 1) mixture; 2) ignition; 3) fireball; 4) shockwave; 5) impulse; and 6) repetition of steps 3-5 until the blast has decayed. “Mixture” refers to the mixture of explosive and oxygen for creating a blast. Following mixture, ignition may occur to create the blast. A fireball may then result from the ignition of the mixture. A fireball may propagate through a medium, such as air. In certain embodiments, the fireball may include unignited explosive, such that as the fireball propagates through an oxygen-containing medium such as air, the unignited explosive mixes with the oxygen and ignites. Thus, as the fireball propagates through the oxygen-containing medium, oxygen within the oxygen-containing medium may be reduced in the area through which the fireball has propagated.
Again, without being bound by theory, if of sufficient power, the fireball may generate a shockwave. Impingement of the shockwave on the asset may result in blast impulse, i.e., force of the blast integrated over the time of the blast. In certain blasts, multiple fireballs and shockwaves may be formed during the blast, each of which may result in blast impulse on the asset.
In certain embodiments of the present disclosure, an article may be employed to reduce blast force from a pressure wave resulting from an explosion from reaching the asset, thereby reducing the blast impulse on the asset. In certain embodiments, the article may reduce load and peak load on the asset from the pressure wave. As used herein, “load” refers to the force exerted by a pressure wave, and “peak load” refers to the highest force exerted by the pressure wave throughout the duration of pressure wave.
In certain embodiments, reduction of the blast force in an unconfined area may be measured in terms of “scaled distance” by assessing the blast force in terms of a net explosive quantity (NEQ) of trinitrotoluene (TNT). NEQ is the total mass of contained explosive substance. Explosion vents, blast walls, window damage, vehicle damage and injury thresholds may be estimated, and test results may be used for these estimations, using NEQ-to-volume ratio for an open space calculation, such as those performed by ConWep. In certain embodiments, the article may reduce the NEQ of the explosive and propellants by at least 10%, or at least 50%, or at least 70%, or at least 90%. For example, the article may reduce the NEQ by at least 70% compared to when the fireball had not impacted the article.
In some embodiments, the article may be directional. For instance, the article may have an impact side and an asset side. In these embodiments, the impact side of the article is adapted to receive the blast, including any pressure waves resulting from the blast. The asset side of the article is the side of the article opposite from the impact side and is adapted to face the asset to be protected. In certain embodiments, the article includes only a single layer. In other embodiments, the article may include multiple layers adhered together. When the article includes multiple layers, the individual layers may be the same or different. The individual layers may be selected, for instance, based on the threat anticipated.
The pressure wave that impacts the article may include a plurality of pressure wave frequencies. These frequencies may range from, for instance and without limitation, 0.1 Hz to 10,000 Hz, or from 1 Hz or less to 1000 Hz. The article may reflect a composite harmonic of a portion of the pressure wave frequencies, as shown in
When the article is a single layer, different pressure wave frequencies may be reflected by the article as the pressure wave reaches different depths of the article. In certain embodiments, the pressure wave frequencies reflected as a function of depth of the article may be in ascending order, i.e., lower frequency pressure waves are reflected by the article towards the impact side of the article with higher frequency pressure waves reflected as the pressure wave proceeds through the article to the asset side.
When the article includes multiple layers, the portion of the pressure wave frequencies reflected may be the same or different for each layer. In some embodiments, the pressure wave frequencies may be reflected in ascending order, i.e., the layer nearest the blast side of the article may reflect the lowest pressure wave frequencies with each layer closer to the asset side of the article reflecting successively higher frequencies.
The composite harmonic reflected of the portion of pressure wave frequencies may be a composite harmonic of, for instance, 100 Hz. Composite harmonics reflected by the article may include hundreds of composite harmonics, including, for instance, first through eighth composite harmonics, or a third and fourth harmonic. In embodiments where the article is a single layer, composite harmonic frequencies reflected may be in ascending order from blast side to asset side. Where the article is composed of multiple layers, each of the layers may reflect the same or different composite harmonics. In embodiments where the article is composed of multiple layers, composite harmonic frequencies reflected may be in ascending order by layer from blast side to asset side. As one of ordinary skill in the art with the benefit of this disclosure will recognize, reflection of the composite harmonic by the article may reduce the impulse of the pressure wave by reducing the force that is transferred to the asset.
Further, as will be appreciated by one of skill in the art with the benefit of this disclosure, the reflection of the composite harmonic may interfere with the pressure wave by cancelling frequencies of the pressure wave, as shown in
In certain embodiments, in addition to reflecting a composite harmonic of the pressure wave and cancelling the frequencies of the pressure wave, the article may absorb certain frequencies of the pressure wave, as shown in
In certain embodiments, the article may reduce or prevent frequencies ranging from 1 Hz to 150 Hz, or 1 Hz to 200 Hz, or 1 Hz to 500 Hz, or 1 Hz to 800 Hz, or 1 Hz to 1,000 Hz, or 1 Hz to 1,200 from propagating through the article and impacting the asset. Without being bound by theory, frequencies from 1 Hz to 1,000 Hz may have the potential to cause more damage to the asset than frequencies less than 1 Hz or greater than 1,000 Hz. In certain embodiments, the article may be “tuned,” i.e. manufactured to reflect certain ranges of frequencies by changing materials of construction or thicknesses of layers, such as in multilayer articles.
In certain embodiments, detonation of an explosive may form one or more ballistic projectiles. For example and without limitation, the ballistic projectile may be shrapnel or a bullet. In certain embodiments, the article may reduce the velocity of the ballistic projectile, capture the ballistic projectile, or change the trajectory of the ballistic projectile.
In certain circumstances, the distance between the article and the blast is further than the distance propagated by the fireball, but within the distance propagated by the shockwave.
In certain embodiments, article 20 is a panel having a thickness ranging from ¼ inch to 24 inches, or from 1 inch to 12 inches, or from 2 to 3 inches. In some embodiments, article 20 is a panel with a weight of from 1 to 30, or 5 to 10 pounds per square foot of panel. For example and without limitation, article 20 may be a 2 to 3 inch thick panel that weighs 5 to 10 pounds per square foot of panel. While article 20 is depicted in
In certain embodiments, asset 22 is armored and article 20 is supplemental to existing armor of asset 22. Existing armor of asset 22 may include, but is not limited to, steel, concrete, dirt, gravel and/or distance from explosive 24. In certain embodiments, asset 22 is not armored, with the exception of article 20. In some embodiments, asset 22 may be adhered, welded, or bolted to article 20. For example and without limitation, article 20 (e.g., panel) may be mechanically coupled with a building or vehicle.
If asset 22 is a living asset, such as a person or an animal, article 20 may reduce the risk of injury and death for asset 22 by reducing impulse and/or peak load exerted on asset 22. If asset 22 is a non-living asset, article 20 may reduce the risk of damage or destruction of asset 22 by reducing impulse and/or peak load exerted on asset 22. In some embodiments, use of article 20 may reduce impulse on asset 22 by at least 5%, by at least 10% or an amount ranging from 10% to 50% in comparison to impulse on asset 22 when article 20 is not located between explosive 24 and asset 22. In some embodiments, use of article 20 may reduce peak load on asset 22 and acceleration of asset 22 by up to 95% or between 10% and 95% in comparison to peak load on and acceleration of asset 22 of up to 95%, or 10% to 95% when article 20 is not located between explosive 24 and asset 22. In some embodiments, such as when asset 22 is a vehicle, use of article 20 may reduce a jump height of asset 22 by at least 5%, 10%, or between 5% and 50% in comparison to jump height of asset 22 when article 20 is not located between explosive 24 and asset 22. As used herein, “jump height” refers to a height at which asset 22 (e.g., a vehicle) is lifted from a surface (e.g., the ground) upon impact of portion of shockwave 10a. Impact test results are determined in accordance with SAE J211 Rev. July 2007, which is incorporated herein by reference in its entirety.
In explosive circumstance 18a, upon detonation of explosive 24, fireball 26 may form, as shown in
In explosive circumstance 18b as shown in
The fireball wave that impacts the article may include a plurality of fireball wave frequencies. These frequencies may range from, for instance and without limitation, 1 Hz or less to 1000 Hz or more. The article may reflect a composite harmonic of a portion of the fireball wave frequencies, as shown in
As further depicted in
In certain embodiments, in addition to reflecting a composite harmonic of the fireball wave, cancelling the frequencies of the fireball wave, and quenching the fireball, the article may absorb certain frequencies of the fireball wave as shown in
In certain circumstances, the distance between the article and the blast is within the distance propagated by the fireball.
In certain embodiments, article 20 may be impacted by multiple shockwaves and/or fireball waves. In some embodiments, a shockwave or fireball wave may create holes or “channels” in the article. Without being bound by theory, later impacting shockwaves and/or fireball waves may impart more force into the channels formed in the article than other portions of the article, thereby increasing the efficiency of the article in reducing blast impulse.
In certain embodiments, article 20 may be formed from a single layer. In some embodiments, where article 20 is formed from a single layer, the composition of article 20 is uniform, with a substantially constant density. In other embodiments where article 20 is a single layer, the composition of article 20 is not uniform and the density of article 20 varies from impact side 30 to asset side 32 of article 20. For instance, the variation in density from impact side 30 of article 20 to asset side 32 of article 20 may range from 0.01 g/cc to 20 g/cc, or from 0.03 g/cc to 10 g/cc, or from 0.25 g/cc to 1 g/cc. In some embodiments, the density of article 20 may increase (e.g., incrementally or continuously) from impact side 30 to asset side 32. Without being bound by theory, it is believed that relatively higher densities will reflect and absorb relatively higher frequencies, and relatively lower densities will reflect and absorb relatively lower frequencies. Again, without being bound by theory, it is believed that, in embodiments where article 20 has an increasing density from impact side 30 to asset side 32, article 20 will absorb, reflect, cancel, and dissipate frequencies of pressure waves in ascending order of frequency.
In certain embodiments, a single article 20 may be used to provide protection to asset 22. In other embodiments, multiple articles 20a-20f may be used to provide protection to asset 22, as shown in
In certain embodiments, as shown in explosive circumstance 18d of
Absorption of energy of pressure wave 15 by a layer may result in destruction or damage of the layer. For example and without limitation, absorption of energy of pressure wave 15 by a layer may puncture the layer, rupture the layer, increase the temperature of the layer, ignite the layer, or combinations thereof. Where article 20 includes multiple layers, the destruction or damage of each layer may be progressive, i.e., the layer closest to the impact side of the article may be destroyed or damaged first, followed by the next-most layer. Further, where article 20 includes multiple layers, not all layers may be destroyed or damaged.
Each of layers 28a-28f of article 20 may be the same or different. In certain embodiments, successive layers may increase in density; density ranges of successive layers may overlap. Without being bound by theory, it is believed that layers having relatively higher densities will reflect and absorb relatively higher frequencies, and layers having relatively lower densities will reflect and absorb relatively lower frequencies. In such embodiments, article 20 absorbs, reflects, cancels, and dissipates frequencies of pressure wave 15 in ascending order of frequency. While each successive layer may reflect and absorb frequencies that are higher than frequencies reflected and absorbed by the adjacent layer that is closer to impact side 30, in some embodiments there is overlap between the frequencies absorbed, reflected, cancelled, and dissipated by adjacent layers. In some embodiments, successive layers may increase in strength, including, but not limited to examples such as tensile strength, puncture resistance, tear resistance, and compressive resistance; strengths of successive layers may overlap.
In certain embodiments, at least some energy of pressure wave 15 is dissipated within article 20. For example and without limitation, at least some energy of pressure wave 15 may be dissipated within article 20 as a result of internal reflection and/or scattering of pressure wave 15 within article 20. In some embodiments, article 20 exhibits fire resistance, preventing or reducing the ability of a fire to propagate from impact side 30 through asset side 32. In some embodiments, article 20 exhibits insulation properties.
Examples of suitable compositions for use in layers 28a-28f of article 20 include, but are not limited to, concrete, synthetic or natural rubbers, neoprene, polyolefins (e.g., polyethylene, polypropylene), ceramic composites, metal foams (e.g., aluminum foam), polymer foams, thermoplastic composites, and fiber composites.
In certain embodiments, first layer 28a may reflect at least some frequencies of impinging pressure wave 15. In certain embodiments, first layer 28a may have a density of between 0.02 g/cc to 0.05 g/cc or around 0.03 g/cc. In some embodiments, first layer 28a may have a thickness of between 0.15 inches and 0.5 inches, or between 0.2 inches and 0.3 inches, or about 0.25 inches
In some embodiments, first layer 28a may exhibit elasticity. For example and without limitation, first layer 28a may contain a synthetic or natural rubber. In certain embodiments, first layer 28a may be composed at least in part of neoprene or a blend of neoprene with other rubbers. In some embodiments, the neoprene blend may be foamed. An aspect of neoprene may be that it reflects the energy of pressure wave 15 very quickly, i.e., for example, less than 10 milliseconds, prior to rupture.
In certain embodiments, second layer 28b may have a density of between 0.1 g/cc to 0.5 g/cc, or between 0.25 g/cc to 0.43 g/cc. In certain embodiments, second layer 28b may have a thickness of between 0.25 inches and 0.75 inches, between 0.4 inches and 0.6 inches, or approximately 0.5 inches.
In some embodiments, second layer 28b may be an insulator. Second layer 28b may absorb heat. For example and without limitation, when pressure wave 15 impacts article 20, at least some energy of pressure wave 15 may be transformed into thermal energy, increasing a temperature of one or more portions of article 20. Second layer 28b may function as an insulator to at least some thermal energy absorbed into article 20 from impact with pressure wave 15. For example and without limitation, second layer 28b may contain metal foam. The metal foam may be aluminum foam. An aspect of aluminum foam may be that it reflects the energy of pressure wave 15 quickly, i.e., less than 10 milliseconds, prior to rupture, as well as absorbing oscillations and heat.
In certain embodiments, third layer 28c may have a density of between 0.4 g/cc to 0.5 g/cc, or between 0.42 g/cc to 0.45 g/cc. In certain embodiments, third layer 28c may contain concrete. Aspects of concrete may be that it reflects, absorbs, and approximately evenly distributes heat and waves.
In certain embodiments of the present disclosure, the combination of first layer 28a, second layer 28b, and third layer 28c may reflect pressure wave frequencies ranging between 0.1 Hz to 175 Hz, or between 1 Hz and approximately 100 Hz.
In certain embodiments, fourth layer 28d may have a density of between 0.6 g/cc to 0.9 g/cc, or between 0.7 g/cc to 0.8 g/cc, or about 0.78 g/cc. In certain embodiments, fourth layer 28d may contain polypropylene thermoplastic, for instance, an ultra-high molecular weight polypropylene thermoplastic, such as a thermoplastic composite. In certain embodiments, fourth layer 28d may provide ballistic protection for asset 22, reducing the velocity of or diverting a ballistic projectile.
In certain embodiments, fifth layer 28e may have a density of between 0.8 g/cc to 1.1 g/cc, or between 0.9 g/cc to 1.0 g/cc, or about 0.97 g/cc. In certain embodiments, fifth layer 28e may contain a polyethylene thermoplastic, for instance, an ultra-high molecular weight polyethylene thermoplastic, such as a thermoplastic composite. In certain embodiments, fifth layer 28e may provide ballistic protection for asset 22 as well as provide structural support for article 20.
In certain embodiments, sixth layer 28f may have a density of between 1.2 g/cc to 1.7 g/cc, or between 1.4 and 1.5 g/cc. In certain embodiments, sixth layer 28f may contain a fiber composite.
Each layer of article 20 may be mechanically coupled to adjacent layers of article 20. Mechanical coupling of adjacent layers may be accomplished by any suitable method known to those skilled in the art. In some embodiments, mechanical coupling of adjacent layers may be accomplished by adhering adjacent layers to one another. For example, and without limitation, an adhesive suitable for adhering adjacent layers to one another is a urethane adhesive.
Article 20 may include adhesive layer 50 coupled to sixth layer 28f or adhered to asset 22 or a frame (not shown). Adhesive layer 50 may be a liquid butyl or butyl self-adhesive tape.
As shown in
In a particular embodiment of multilayer article 20 consistent with that depicted in
The disclosure having been generally described, the following examples show particular embodiments of the disclosure. It is understood that the example is given by way of illustration and is not intended to limit the specification or the claims. All composition percentages given in the examples are by weight.
A series of articles in the form of flat panels may be each, separately, subjected to pressure waves caused by explosion of an explosive that formed a fireball. Impulse of the portion of the pressure wave that propagates through the articles are to be measured using load cells to be placed on an asset on the opposite side of the articles as the explosive. The measured impulse of the pressure waves that propagated through the articles may be found to be reduced by at least 5% in comparison to the measured impulses of equivalent pressure waves without the articles being placed between the explosive and the load cells.
An article in the form of a flat panel will be placed between an asset with a load cell and an explosive, and subjected to pressure waves caused by explosion of the explosive that formed a fireball. Load will be measured by the load cells throughout the pressure wave. The measured peak load of the pressure wave that propagates through the article will be found to be reduced by 10% to 95% in comparison to the measured peak load of an equivalent pressure wave without the article being placed between the explosive and the asset.
An article in the form of a flat panel will be placed between an asset with an accelerometer and an explosive, and subjected to pressure waves to be caused by explosion of the explosive to form a fireball. Acceleration of the asset will be measured with the accelerometer. The measured acceleration of the asset will be found to be reduced by 10% to 95% in comparison to the measured acceleration of the asset without the article being placed between the explosive and the asset.
An article in the form of a flat panel will be placed between a vehicle and an explosive, and subjected to pressure waves caused by explosion of the explosive to form a fireball. The jump height of the vehicle will be found to be reduced by at least 5% in comparison to the measured jump height of a vehicle without the article being placed between the explosive and the vehicle.
An article in accordance with the present disclosure was exposed to a blast. Force on the article was measured using load cells. The results of the measurement versus time on the article is depicted in
Depending on the context, all references herein to the “disclosure” may in some cases refer to certain specific embodiments only. In other cases it may refer to subject matter recited in one or more, but not necessarily all, of the claims. While the foregoing is directed to embodiments, versions and examples of the present disclosure, which are included to enable a person of ordinary skill in the art to make and use the disclosures when the information in this patent is combined with available information and technology, the disclosures are not limited to only these particular embodiments, versions and examples. Other and further embodiments, versions and examples of the disclosure may be devised without departing from the basic scope thereof and the scope thereof is determined by the claims that follow.
This application is a non-provisional application which claims priority from U.S. provisional application No. 62/321,449, filed Apr. 12, 2016, which is incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62321449 | Apr 2016 | US |
