Severance of polycarbonates and polycarbonate laminates with linear shaped charge

Abstract

The present invention involves a method for severance of materials made of polycarbonate, polycarbonate laminate and acrylic/polycarbonate laminate, such as the materials from which many of today's military aircraft canopies are manufactured. A method of severing a section of an aircraft canopy so as to allow aircrew egress is necessary for aircrew safety. Past severance methods focused on fracturing materials using the shock waves created by explosive charges placed on, near or in the canopy material. These methods are effective for fracturing canopies manufactured from acrylic type materials, however, they are not reliable in severing polycarbonate type materials.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to severing materials, such as an aircraft canopy made from polycarbonate, polycarbonate laminate or acrylic/polycarbonate laminate, with an explosive charge.

BACKGROUND

[0002] Most military aircraft contain an ejection seat that allows the pilot to escape the aircraft while in flight. When an ejection seat is jettisoned from the cockpit of an aircraft, it must pass through the region occupied by the transparent canopy of the aircraft. In instances where the canopy is not jettisoned prior to the ejection seat firing, the ejection seat must be capable of blasting entirely through the canopy. To reduce the risks to the pilot or other aircraft occupant attendant to forcing the-ejection seat through the canopy, canopy fracture systems have been provided to fracture the canopy and better clear a path for the ejecting occupant so as to minimize bodily impact with the canopy.

[0003] Canopy fracture systems have been effective at removing portions of canopies that are made from fragilizing materials, such as cast or stretched acrylic. Fragilizing materials are those that may be caused to shatter into a significant number of pieces on application of sufficient pressure or explosive force. These systems utilize a mild detonating charge (MDC) or linear shaped charge (LSC) placed on, in or near the transparency which, upon detonation, creates shock waves that fracture the canopy. With fragilizing canopies, such as those made from cast or even stretched acrylic, it is not necessary to fully sever the material in order to defeat its structural integrity.

[0004] Many high performance aircraft utilize polycarbonate in their canopies instead of acrylic. Polycarbonate is a nonfragilizing material, meaning that it does not shatter on application of explosive force. With polycarbonate, it is absolutely necessary to fully sever the material because fracturing to complete the break is very unreliable. Because polycarbonate has a relatively low melt point and because cutting the material generates considerable heat there also exists a potential for resealing behind the cut if the severance is not complete.

[0005] U.S. Pat. No. 5,170,004 teaches an explosive device wherein a nearly incompressible transmitting medium is placed between the explosive device and an aircraft canopy. The function of the transmitting medium is to transmit the shock wave, produced upon detonation, to the canopy with a minimum of dissipation. This device is effective on fragilizing canopies but has not been successful with thicker non-fragilizing canopies made from monolithic polycarbonate, polycarbonate laminates or acrylic/polycarbonate laminates.

[0006] U.S. Pat. No. 5,780,763 teaches a method of fracture wherein explosive cords are placed in parallel grooves on the tipper surface of a canopy and simultaneously detonated to create overlapping shock waves. This method is apparently capable of breaking a 0.75 inch thick polycarbonate in the laboratory at ambient temperature or below, but is unreliable at elevated temperatures on the order of 165° Fahrenheit or above. This method, however, requires two charges, grooves to be cut in the material and also utilizes shock waves which are not reliable on polycarbonate materials.

[0007] U.S. Pat. No. 5,954,296 also relates to an aircraft canopy fracture system. The 296 patent claims a canopy with a severable region shaped so as to inhibit passage of the severable region back through the canopy after severance. The 296 patent also refers to the use of a LSC to sever a polycarbonate canopy.

[0008] All documents, including other patents and references, referred to in this document are hereby incorporated by reference in their entirety, although no documents are admitted to render any of the claims unpatentable either alone or in combination with any other references known by the applicant.

[0009] The prior art also does not adequately deal with the problems of providing for severance around the corners of the severable portion of the target or for routing a charge over the top of another charge.

[0010] It is therefore an object of this invention to provide a severance method which severs materials such as polycarbonate, polycarbonate laminates or acrylic/polycarbonate laminates that cannot be severed by existing methods except by use of excessive amounts of explosive charge or by placing the charge inside the material to be fractured, thereby degrading the material's structural integrity.

[0011] It is another object of this invention to provide a severance method that allows for a minimum amount of explosive charge to sever a given thickness of material at high and low temperature extremes.

[0012] It is further an object of this invention to provide a severance method that allows for severance around corners and through intersecting portions of the explosive charge.

SUMMARY OF THE INVENTION

[0013] The present invention is a method for severing a non-fragilizing material such as polycarbonate with a linear shaped charge (“LSC”). Previous methods of polycarbonate, polycarbonate laminate or acrylic/polycarbonate laminate severance were either ineffective, or required imbedding explosive charges into the canopy itself. The prior art relies on the use of shock waves to fracture aircraft canopies. These methods, however, are not effective or reliable on canopies made from non-fragilizing materials such as polycarbonate, polycarbonate laminate or acrylic/polycarbonate laminate. The present invention discloses a method of using the cutting face of the explosive charges to sever a material such as polycarbonate, instead of relying on unreliable shock waves. Because the severance method of this invention is more effective and more reliable than previous severance methods, a lesser amount of explosive charge is required to effect target severance. In the case of a polycarbonate aircraft canopy target, the present invention's severance method provides pilots with a lower exposure to explosion back blast and noise.

[0014] An LSC is placed in proximity to the material to be severed at a distance sufficient to generate an explosive cutting face or “jet” adequate for cutting the target thickness. The LSC is held in place and at the sufficient distance by a retainer that surrounds the back of the charge. The retainer is adhered or attached to the target, again maintaining the appropriate distance between the charge and the target. Upon detonation, the charge severs the target. The charge and retainer may be tooled to provide for effective severance with minimum explosive force around corners. The present invention also provides for various methods of charge intersection, crossover and detonation transfer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 is a side view of an explosive charge of the present invention attached to a target that is to be severed.

[0016] FIG. 2 is a side view of an explosive charge of the present invention after detonation severing the target material.

[0017] FIGS. 3 a -d are tables showing performance test results of varying grain sizes of various LSCs on polycarbonates of varying thickness.

[0018] FIG. 4 is a depiction of a polycarbonate laminate and its target thickness.

[0019] FIG. 5 is a depiction of a severance pattern disclosed in U.S. Pat. No. 5,954,296.

[0020] FIG. 6 is a depiction of the crossover method of laying one LSC over another.

[0021] FIG. 6 a is a depiction of a side view of the crossover method.

[0022] FIG. 6 b is a depiction of a side view of the crossover method where a portion of the sheathing on the lower length of LSC has been cut away.

[0023] FIG. 6 c is a depiction of a side view of the crossover method where a solid anvil is placed under the lower length of LSC to aid in detonation transfer.

[0024] FIG. 7 is a depiction of the invention's method of piggy-backing where one LSC comes up over a lower piece of LSC and rides the same line of severance for a given distance.

[0025] FIG. 7 a is a side view of the piggyback method.

[0026] FIG. 8 is a depiction of the mitered joint method with four intersecting pieces of LSC.

[0027] FIG. 8 a is a side view of the miter method.

[0028] FIG. 9 is a depiction of the miter method joining two lengths of LSC at a right angle.

[0029] FIG. 9 a is side view of the miter method used at a right angle.

[0030] FIG. 10 is a depiction of transferring LSC detonation through a crossover or intersection in the LSC utilizing a booster charge.

[0031] FIG. 10 a is a depiction of transferring LSC detonation through a crossover or intersection in the LSC utilizing an explosive transfer charge encased in a manifold.

DETAILED DESCRIPTION

[0032] Referring to the drawings by reference numbers, FIG. 1 shows a linear shaped charge (“LSC”) 10 of the present invention in position on the target. The LSC is of a strength sufficient to sever a target, such as an aircraft canopy transparency, made from polycarbonate, polycarbonate laminate or acrylic/polycarbonate laminate.

[0033] The LSC 10 includes an explosive core 11 and a sheath 12. The best results are obtained when the LSC is shaped like a chevron with the opening facing and parallel to the target 13. There is open space between the LSC and the target. The LSC is surrounded by a retainer 14 that is attached to the target by some form of adhesive. The retainer attaches the LSC to the target such that the LSC is offset from the target by a distance 15 that allows the LSC to generate an explosive blast of sufficient strength to sever the target. FIG. 2 shows the present invention at the moment of explosion severing a target.

[0034] In a preferred embodiment the retainer is made from rubber and attached to the canopy with an epoxy or other adhesive. The retainer not only serves to hold the LSC in place at an appropriate distance from the canopy, it also acts to attenuate the back blast and noise from the explosion to protect the aircrew (in the case of a canopy target). The retainer may also be made from a other type rubber products, an epoxy composite or other compounds and still achieve satisfactory results.

[0035] LSC sheathing is made of metal, typically tin, lead, aluminum, silver or copper. For severance of polycarbonates, tin, lead and silver are preferable, but silver is rarely used due to high material costs. Testing was performed using PBXN-5/Lead, PBXN-5/Tin, HNS/Lead and HNS/Tin LSC of varying coreloads. Some of those test results are set forth in FIG. 3. This testing revealed that a lead sheath is slightly more effective for severing polycarbonates than a tin sheath. Both are effective, however, and because of the hazards of working with lead, a tin sheath is the preferred embodiment. A tin sheath is slightly more effective than a lead sheath in severing aluminum. Testing also determined that PBXN-5 powder is superior to HNS powder.

[0036] Because of the lack of success with previous canopy fracturing and severance methods in polycarbonate canopies, a great deal of testing was performed to determine the proper LSC coreload and stand off necessary to sever a set thickness of polycarbonate. In the present invention the coreload and stand-off necessary to sever polycarbonates of varying thickness is disclosed. As would be expected, the thicker the polycarbonate to be severed, the greater the coreload required. The LSC is more effective if setoff a certain distance from the target. A tabular representation of the test results achieved on varying polycarbonate thicknesses with varying LSC coreload, powder sheathing, back ups and stand-off is set forth below:

		IDENTIFICATION
TEST #	SOURCE	INFORMATION	NOTES	Back Up	Thickness	Penetration
1	UDRI	Dow-Calibre 300-6, ¾″, #4	12 gr/ft HNS/Lead, RTV, No Stand-Off(SO),	retainer	0.75	.045/broke
			Parallel Beam, Broke
2	UDRI	Dow-Calibre 300-6, ¾″, #2	20 gr/ft RDX/Lead, RTV, No SO, Parrallel Beam, Broke	retainer	0.75	broke
3	UDRI	Dow-Calibre 300-6, ¾″, #9	12 gr/ft HNS/Lead, RTV, No SO, Bottom Clamped,	retainer	0.75	0.05
			.05 Imp., B-U
4	UDRI	Dow-Calibre 300-6, ¾″, #12	21 gr/ft CH6/Al, 0.090 SO, 0.275 Penetration,	TMD	0.75	.15/break
			Cracked Through
5	UDRI	Dow-Calibre 300-6, ¾″, #14	21 gr/ft CH6/Al, No SO, 0.180 Penetration, Some	TMD	0.75	.180/break
			cracking
6	UDRI	Dow-Calibre 300-6, ¾″, #15	21 gr/ft CH6/Al, No SO, RTV filled, Little Penetration	TMD	0.75	0.075
8	UDRI	Dow-Calibre 300-6, ¾″, #3	40 gr/ft PBXN5/Lead, .180 SO, inside radius-straight, cut	rubber	0.075	broke
33	Texstar	Coated In C678, Out C992, {fraction (5/16)}″	12 gr/ft, HNS/Tin, 0.125 SO, some pen, all melted,	rubber	0.312	0.19
			no cut
34	Texstar	Coated In C678, Out C992, {fraction (5/16)}″	12 gr/ft, PBXN-5/Tin, 0.160 SO, Cut	rubber	0.312	cut
35	Texstar	Coated In C678, Out C992, {fraction (5/16)}″	12 gr/ft, PBXN-5/Tin, .160 SO, 90° Angle, Cut	paper	0.312	0.3
			except angle
36	Texstar	Coated In C678, Out C992, {fraction (5/16)}″	12 gr/ft, PBXN-5/Tin, .160 SO, unrestrained, Cut	paper	0.312	cut
37	Texstar	Coated In C678, Out C992, {fraction (5/16)}″	12 gr/ft, HNS/Tin, 0.125 SO, Unrestrained, Cut	paper	0.312	cut
38	Texstar	Coated In C678, Out C992, {fraction (5/16)}″	15 gr/ft, HNS/Tin, 0.125 SO, cut	rubber	0.312	cut
39	Texstar	Coated In C678, Out C992, {fraction (5/16)}″	12 gr/ft, PBXN5/Tin, 360° sep test, cut & broke	rubber	0.323	cut
49	Texstar	Coated In C678, Out C992, ⅜″	12 gr/ft, PBXN-5/Tin, 0.160 SO, Nearly Severed	paper	0.375	0.18
50	Texstar	Coated In C678, Out C992, ⅜″	12 gr/ft, HNS/Tin, 0.125 SO, cut	rubber	0.375	cut
51	Texstar	Coated In C678, Out C992, ⅜″	15 gr/ft, HNS/Tin, 0.125 SO, cut	rubber	0.375	cut
52	Texstar	Coated In C678, Out C992, ⅜″	12 gr/ft, PBXN5/Tin, 0.130 SO, remelted + D73	rubber	0.375	cut
53	Texstar	Coated In C678, Out C992, ⅜″	12 gr/ft, HNS/Lead, 0.130 SO, remelted	rubber	0.375	cut
54	Texstar	Coated In C678, Out C992, ⅜″	15 gr/ft, PBXN5/Tin, .15 SO, 360° 2″ R Bend-
			sep. test, cut except
			joint	rubber	0.375	not joint
65	Texstar	Coated In C678, Out C992, ½″	15 gr/ft, PBXN-5/Tin, 0.160 SO, some penetration,	paper	0.5	0.35
			mostly melted
66	Texstar	Coated In C678, Out C992, ½″	15 gr/ft, PBXN-5/Lead, 0.160 SO, melted but not	paper	0.5	0.41
			severed
67	Texstar	Coated In C678, Out C992, ½″	15 gr/ft, PBXN-5/Lead, 0.160 SO, unrestrained,	paper	0.5	0.41
			some pen, melted
68	Texstar	Coated In C678, Out C992, ½″	15 gr/ft, PBXN-5/Tin, 0.160 SO, unrestrained	paper	0.5	0.445
69	Texstar	Coated In C678, Out C992, ½″	15 gr/ft, PBXN5/Lead, 90 deg bend, 0.150 SO, close	paper	0.5	cut/not bend
70	Texstar	Coated In C678, Out C992, ½″	15 gr/ft, PBXN5/Tin, 90 deg bend, 0.150 SO,	paper	0.5	cut/.36
			shattering, close
71	Texstar	Coated In C678, Out C992, ½″	15 gr/ft, PBXN5/Lead, 200 deg F., 0.150 50, remelted	rubber	0.5	cut/remelted
72	Texstar	Coated In C678, Out C992, ½″	15 gr/ft, PBXN5/Tin, 200 deg F., 0.150 SO, unteth,	paper?	0.5	cut
			hanging thread
73	Texstar	Coated In C678, Out C992, ½″	15 gr/ft, PBXN5/Lead, −65° F., 0.150 SO, cut	rubber	0.5	cut
74	Texstar	Coated In C678, Out C992, ½″	15 gr/ft, PBXN5/Tin, −65° F., 0.160 SO, cut	rubber	0.5	cut
75	Texstar	Coated In C678, Out C992, ½″	20 gr/ft, PBXN-5/Lead, unteth, cut	rubber	0.5	cut
76	Texstar	Coated In C678, Out C992, ½″	20 gr/ft, PBXN-5/Tin, unteth, cut	rubber	0.5	cut
77	Texstar	Coated In C678, Out C992, ½″	20 gr/ft, PBXN-5/Tin, unteth, some penetration, S curve,	rubber	0.5	cut/.45
			not cut
78			20 gr/ft, PBXN-5/Lead,.145 SO, ″S″turn, not	rubber	0.55	cut/.45
			cut in bends
79	Texstar	Coated In C678, Out C992, ½″	15 gr/ft, PBXN-5/Tin, 90° turn, 0.145 SO, restrained,	rubber	0.5	0.32
			2″ radius
80	Texstar	Coated In C678, Out C992, ½″	15 gr/ft, PBXN-5/Lead, 90° turn, 0.145 SO, restrained,	rubber	0.5	cut/99%
			2″ radius
81	Texstar	Coated In C678, Out C992, ¾″	30 gr/ft, PBXN-5/Lead, unrestrained, .175 SO, cut	paper	0.75	cut
82	Texstar	Coated In C678, Out C992, ¾″	30 gr/ft, PBXN-5/Tin, unrestrained, .175 SO,	paper	0.75	0.54
			.540 pen, cracked
83	Texstar	Coated In C678, Out C992, ¾″	30 gr/ft, HNS/Lead, 0.150 SO, .480 pen, some cracking	paper	0.75	0.48
84	Texstar	Coated In C678, Out C992, ¾″	30 gr/ft, HNS/Tin, 0.120 SO, unteth, .440 pen	rubber	0.75	0.44
85	Texstar	Coated In C678, Out C992, ¾″	30 gr/ft, PBXN5/Lead, 0.150 SO, −70° F., Cut	rubber	0.75	cut
86	Texstar	Coated In C678, Out C992, ¾″	30 gr/ft, PBXN5/Lead, 0.150 SO, 200° F.,	rubber	0.75	cut
			untethered, cut
87	Texstar	Coated In C678, Out C992, ¾″	30 gr/ft, PBXN5/Lead, 0.182 SO, 200° F., restrained, cut	rubber	0.75	cut
88	Texstar	Coated In C678, Out C992, ¾″	30 gr/ft, PBXN5/Lead, 0.182 SO, 200° F.,	rubber	0.75	cut
			unrestrined, cut
105	NSWC	MX2054-920415, 0.500	.530 thick, 15 gr/ft PBXN5/Lead, .150 SO, Nearly	rubber	0.53	0.5
			severed
106	NSWC	MX2054-920415, 0.500	.530 thick, 20 gr/ft PBXN5/Lead, .150 SO, 90° bend, cut	rubber	0.53	cut
109	Pilkington	0.250 × 36 × 60	12 gr/ft, 815525-2 (Min/Max), RTV, No SO, No Cut,	no SO	0.25	0.12
			cracked thru
110	Pilkington	0.250 × 36 × 60	12 gr/ft, 815525-2 (Min/Max), RTV, No SO, Scored,	no SO	0.25	cut/melted
			cut & melted
111	Pilkington	0.250 × 36 × 60	12 gr/ft, 815525-2 (Min/Max), No SO, No cut	no SO	0.25	.05/cracking
112	Pilkington	0.250 × 36 × 60	12 gr/ft, 815525-2 (Min/Max), No SO, No cut	no SO	0.25	.04/melting
113	Pilkington	0.250 × 36 × 60	12 gr/ft, 815525-2 (Min/Max), 0.110 SO, Use CH	rubber	0.25	cut
			825252, Cut
114	Pilkington	0.250 × 36 × 60	12 gr/ft, 815525-2 (Min/Max), 0.110 SO, Use CH	rubber	0.25	cut
			825252, Cut
116	Pilkington	0.250 × 36 × 60	12 gr/ft, HNS/Tin, 0.110 SO, Use CH 825252, Cut	paper	0.25	cut
118	Pilkington	0.250 × 36 × 60	12 gr/ft, PBXN-5/Tin, 0.110 SO, Use CH 825252(?), Cut	paper	0.25	cut
119	Pilkington	0.250 × 36 × 60	12 gr/ft, HNS/Lead, 0.110 SO, 200° F., Cut	rubber	0.25	cut
120	Pilkington	0.250 × 36 × 60	12 gr/ft, HNS/Lead, 0.110 SO, RTV Filled, Poor	rubber	0.25	0.025
			Performance
125	Pilkington	0.312 × 36 × 60	12 gr/ft, HNS/Lead, 0.110 SO, No Cut	rubber	0.312	.28/pen
126	Pilkington	0.312 × 36 × 60	12 gr/ft, HNS/Lead, 0.145 SO, No Cut	rubber	0.312	0.22
127	Pilkington	0.312 × 36 × 60	15 gr/ft, HNS/Lead, 0.145 S.O., Cut	rubber	0.312	cut
128	Pilkington	0.312 × 36 × 60	15 gr/ft, PBXN-5/Lead, 0.145 SO., Cut	rubber	0.312	cut
129	Pilkington	0.312 × 36 × 60	12 gr/ft, PBXN-5/Tin, 0.110 SO, Use CH 825252, Cut	paper	0.312	cut
			but Remelted
141	Pilkington	0.350 × 36 × 60	15 gr/ft, HNS/Lead, 0.145 S.O., Cut	rubber	0.312	cut
142	Pilkington	0.350 × 35 × 60	15 gr/ft, PBXN-5/Lead, 0.145 SO., Cut	rubber	0.312	cut
143	Pilkington	0.350 × 36 × 60	15 gr/ft, PBXN-5/Tin, 0.145 SO., Cut	paper	0.35	cut
167	Texstars	0.310 Ply Laminate	12 gr/ft PBXN5/Tin, .15 SO, Gap Test, Gap did	rubber	0.312	cut/not jnt
			not break
173	Sierracin	0.375 Ply Laminate	15 gr/ft HNSILead, 0.145 SO, Cut	rubber	0.375	cut
174	Sierracin	0.375 Ply Laminate	15 gr/ft PBXN-5/Lead, 0.145 SO, Cut	rubber	0.375	cut
175	Sierracin	0.375 Ply Laminate	15 gr/ft PBXN-5/Tin, 0.145 SO, Cut	paper	0.375	cut
176	Texstars	0.375 Ply Laminate	12 gr/ft PBXN5/Tin, .070 SO, Untethered, butted	rubber	0.375	cut/not jnt
			joint, cut, not joint
177	Sierracin	0.375 Ply Laminate	12 gr/ft, PBXN-5/Tin, 0.070 SO, Cut joint	rubber	0.375	cut jont
178	Sierracin	0.375 Ply Laminate	12 gr/ft, PBXN-5/Tin, 0.150 SO, cut 1 end,	rubber	0.375	0.305
			.235 pen other end
181	Sierracin	0.500 Ply Laminate	15 gr/ft HNS/Lead, 0.145 SO, No Cut, .310 Penetration	rubber	0.5	0.31
182	Sierracin	0.500 Ply Laminate	15 gr/ft PBXN-5/Lead, 0.145 SO, Cut	rubber	0.5	cut
183	Sierracin	0.500 Ply Laminate	20 gr/ft HNS/Lead, 0.145 SO, No Cut, .450 Penetration	rubber	0.5	0.45
184	Sierracin	0.500 Ply Laminate	20 gr/ft PBXN-5/Lead, 0.145 SO, Cut	rubber	0.5	cut
185	Sierracin	0.500 Ply Laminate	15 gr/ft PBXN-5/Lead, 0.145 SO, Cut but remelted	rubber	0.5	cut
186	Sierracin	0.500 Ply Laminate	15 gr/ft PBXN-5/Lead, 0.145 SO, 200° F., Cut	rubber	0.5	cut
187	Sierracin	0.500 Ply Laminate	15 gr/ft PBXN-5/Lead, 0.145 SO, −65° F., Cut	rubber	0.5	cut
188	Sierracin	0.500 Ply Laminate	15 gr/ft PBXN-5/Tin, 0.145 SO, Cut but remelted	paper	0.5	cut
189	Sierracin	0.750 Ply Laminate	25 gr/ft HNS/Lead, 0.145 SO, No Cut, ˜0.420	rubber	0.75	0.42
			Penetration
190	Sierracin	0.750 Ply Laminate	30 gr/ft HNS/Lead, 0.145 SO, No Cut, ˜0.450	paper	0.75	0.45
			Penetration
191	Sierracin	0.750 Ply Laminate	20 gr/ft PBXN-5/Lead, 0.145 SO, No Cut, ˜0.450	rubber	0.75	0.4
			Penetration
182	Sierracin	0.750 Ply Laminate	25 gr/ft PBXN-5/Lead, 0.145 SO, No Cut, ˜0.550	rubber	0.75	0.55
			Penetration
193	Sierracin	0.750 Ply Laminate	30 gr/ft PBXN-5/Lead, 0.165 SO, Cut	paper	0.75	cut
194	Sierracin	0.750 Ply Laminate	30 gr/ft PBXN-5/Tin, 0.145 SO, No Cut, ˜0.550	paper	0.75	0.55
			Penetration
195	Sierracin	0,750 Ply Laminate	15 gr/ft PBXN-5/Lead, 0.145 SO, ˜0.440 Penetration	paper	0.75	0.44
196	Sierracin	0.750 Ply Laminate	30 gr/ft PBXN-5/Lead, 0.165 SO, Cut Partially	paper	0.75	0.7
197	NSWC-IH	0.500 0910108-06	15 gr/ft PBXN-5/Lead, 0.145 SO, 90 deg, 1 of 90's	none	0.5	0.46
			not cut
198	NSWC-IH	0.500 0910108-06	15 gr/ft PBXN-5/Tin, 0.145 SO, 90 deg, some pen.	none	0.5	0.4
			not cut
199	NSWC-IH	0.500	15 gr/ft, PBXN-5/Tin, 0.145 SO, some pen, all melted,	paper	0.5	0.42
			no cut
200	NSWC-IH	0.500	15 gr/ft, PBXN-5/Lead, 0.145 SO, remelted		0.5	.46/cut
205	Sierracin	0.750	30 gr/ft, PBXN-5/Tin, 0275 SO, ˜.550 Pen., Crack &	paper	0.75	0.55
			Melt, No Cut
206	Sierracin	0.750	30 gr/ft, PBXN-5/Lead, 0.250 SO, ˜.650 to Cut, No	paper	0.75	.675/cut
			Sep. remelted
207	WPAFB	0.750	40 gr/ft, HNS/Lead, 0.150 SO, cut, unrestrained	rubber	0.75	cut
208	WPAFB	0.750	40 gr/ft, HNS/Tin, 0.190 SO, .480 pen, unrestrained	rubber	0.75	0.48
209	WPAFB	0.750	40 gr/ft, PBXN5/Lead, 0.200 SO, cut, unrestrained	rubber	0.75	cut
210	WPAFB	0.750	40 gr/ft, PBXN5/Tin, 0.230 SO, cut, unrestrained	rubber	0.75	cut
213	Texstar	Coated In C678, Out C992, ½″	15 gr/ft, PBXN5/Lead, 90 deg bend, 0.150 SO, cut/0.48	paper/-	0.53	.48/cut
			penetration
214	Texstars	Coated In C678, Out C992, ½″	25 gr/ft, HNS/Tin, 0.150 SO, restrained, −65° F., cut	rubber	0.54	cut
215	Texstars	Coated In C678, Out C992, ½″	25 gr/ft, HNS/Tin, 0.150 SO, Broke, 0.475 Pen	rubber	0.54	0.475
216	Texstars	Coated In C678, Out C992, ½″	15 gr/ft, PBXN5/Lead, 0.150 SO, 200° F.,	rubber	0.54	cut
			Unrestrined, Cut
217	Texstars	Coated In C678, Out C992, ½″	15 gr/ft, PBXN5/Lead, 0.150 SO, restrained, cut	rubber	0.54	0.5
218	Navy	1/2″, MX2054-920415	20 gr/ft PBXN5/Tin, 0.185 SO, 90° bend, 2″ R,	rubber	0.5	cut
			untethered, cut
220	Texstars	1/2″, Coated In C678, Out C992	17.5 gr/ft PBXN5/Tin, 185 SO, 90° bend, 2″ R, not cut	rubber	0.53	0.22
221	Texstars	0.740 Laminated, special	40 gr/ft PBXN5/Lead, 0.200 SO, Cut	rubber	0.74	cut
222	Sierracin	0.500 Inch	20 gr/ft PBXN5/Lead, 0.15 SO, 90° bend, 2″ R, 200° F.,	rubber	0.5	cut
				cut
223	Sierracin	0.500 Inch	20 gr/ft PBXN5/Lead, 0.15 SO, 90° bend, 2″ R, −65° F.	rubber	0.5	cut
224	Sierracin	0.500 Inch	15 gr/ft PBXN5/Lead, 0.15 SO, untethered, cut	rubber	0.5	cut
225	Sierracin	0.500 Inch	15 gr/ft PBXN5/Lead, 0.15 SO, tethered, cut	rubber	0.5	cut
226	Sierracin	0.75 inch	30 gr/ft PBXN5/Lead, 0.15 SO, cut	rubber	0.75	cut
228	Texstars	0.50 inch	15 gr/ft PBXN5/Lead, 0.15 SO, 1/2″ RTV filled Apex,	rubber	0.5	not RTV
			not cut in RTV area
231	UDRI	0.75 inch	12 gr/ft PBXN5/Tin, 0.100 SO, .285 pen	rubber	0.765	0.285
232	UDRI	0.75 inch	15 gr/ft PBXN5/Tin, 0.100 SO, .36 pen	rubber	0.765	0.36
233	UDRI	0.75 inch	15 gr/ft PBXN5/Lead, 0.100 SO, .33 pen	rubber	0.765	0.33
234	UDRI	0.75 inch	17.5 gr/ft PBXN5/Tin, .100 SO, HMR-T98-1321, .320	rubber	0.765	0.32
			pen, cracking thru
235	UDRI	0.75 inch	17.5 gr/ft PBXN5/Tin, .100 SO, LMR-T98-1323, .32 pen	rubber	0.765	0.32
236	UDRI	0.75 inch	17.5 gr/ft PBXN5/Lead, .110 SO, HMR-T98-	rubber	0.765	0.3
			1322, .30 pen
237	UDRI	0.75 inch	17.5 gr/ft PBXN5/Lead, .110 SO, LMR-T98-1320,	rubber	0.765	0.31
			.31 pen
238	UDRI	0.75 inch	20 gr/ft PBXN5/Tin, 0.150 SO, .57 pen	rubber	0.765	0.57
239	UDRI	0.75 inch	20 gr/ft PBXN5/Lead, 0.110 SO, .4 pen	rubber	0.765	0.4
240	UDRI	0.75 inch	22.5 gr/ft PBXN5/Tin, .110 SO, HMR-T98-1321,	rubber	0.765	0.48
			.48 pen
241	UDRI	0.75 inch	22.5 gr/ft PBXN5/Tin, .110 SO, LMR-T98-1323,	rubber	0.765	0.45
			.45 pen, 99% broken
242	UDRI	0.75 inch	22.5 gr/ft PBXN5/Lead, .150 SO, HMR-T98-1322,	rubber	0.765	0.58
			.58 pen
243	UDRI	0.75 inch	22.5 gr/ft PBXN5/Lead, .100 SO, LMR-T98-1320,	rubber	0.765	0.37
			.37 pen
244	UDRI	0.75 inch	25 gr/ft PBXN-5/Tin, 0.190 50, .6 pen, cut	rubber	0.765	cut
245	UDRI	0.75 inch	25 gr/ft PBXN-5/Lead, 0.190 SO, .6 pen	rubber	0.765	0.6
246	UDRI	0.75 inch	30 gr/ft PBXN5/Tin, 0.190 SO, .60 pen, cut	rubber	0.765	cut
247	UDRI	0.75 inch	30 gr/ft PBXN5/Lead, 0.150 SO, 0.69 pen	rubber	0.765	0.69
248	UDRI	0.75 inch	40 gr/ft PBXN5/Tin, 0.200 SO, cut	rubber	0.765	cut
249	UDRI	0.75 inch	40 gr/ft PBXN5/Lead, 0.200 SO, Cut	rubber	0.765	cut
250	Navy	D910108-08	20 gr/ft PBXNS/Lead, 0.150 SO, 1/2″ RTV Block,	rubber	0.53	0.5
			no cut under RTV
251	Texstars	0.375 inch	15 gr/ft PBXN5/Tin, 0.15 SO, 360° turn butt	rubber	0.375	not at joint
			up with angle cut
252	Texstars	0.375 inch	15 gr/ft PBXN5/Tin, 0.15 SO, 360° turn with overlap	rubber	0.375	cut
253		0.75 inch	25 gr/ft PBXN5/Tin, 0.190 SO, partial cut then broke	rubber	0.75	cut
254		0.75 inch	30 gr/ft PBXN5/Tin, 0.190 SO, bent 120° but hanging.	rubber	0.75	cut-
255		0.75 inch	40 gr/ft PBXN5/Tin, 0.200 SO, 360° turn with	rubber	0.75	cut
			overlap, broke, but not a nice clean cut
256	Navy	D910108-08	15 gr/ft PBXN5/Tin, .150 SO, 360° turn with overlap,	rubber	0.53	0.4
			0.40 pen, cut overlap lsc off
257	Navy	D910108-08	20 gr/ft PBXN5/Lead, .180 SO, 360° turn with overlap,	rubber	0.53	0.4
			some pen. But most 0.40 +
258	Navy	D910108-08	25 gr/ft PBXN5/Lead, .180 SO, 360° turn with overlap,	rubber	0.53	cut
			mostly cut except overlap
259	Navy	D910108-08	15 gr/ft PBXN5/Tin, 150 SO, 360° turn with overlap,	rubber	0.53	0.37
			broke but only 0.37 pen.
260	Navy	D910108-08	15 gr/ft PBXN5/Tin, 150 SO, 360° turn with piggyback	rubber	0.53	0.35
			overlap, .36 pen.
261	Navy	D910108-08	20 gr/ft PBXN5/Lead, .150 SO, 360° turn with piggy-	rubber	0.53	cut/not over
			back overlap., did not cut overlap
262	Navy	D910108-08	25 gr/ft PBXN5/Lead, .150 50, 360° turn with piggy-	rubber	0.53	cut/not over
			back overlap, did not overlap
263	Navy	D910108-08	20 gr/ft PBXN5/Tin, Cross over, .150 SO. cut bottom	rubber	0.53	cut/not over
			LSC without detonating
264		.500 inch	15 gr/ft PBXN5/Tin, loop with mitered joint, .150	rubber	0.5	0.3
			SO, did not cut
265		.500 inch	15 gr/ft PBXN5/Tin, loop with mitered joint, .150	rubber	0.5	0.3
			SO, did not cut
266		.500 inch	25 gr/ft PBXN5/Tin, ″D″ shape with mitered	rubber	0.5	cut
			corners, .150 SO, Cut nicely
270	Sierracin	1.00 inch, 7 ply laminate	40 gr/ft PBXN5/Tin, 90° mitered angle, .180	rubber	1	cut
			SO, cut nicely cut
271	Texstars	.375 Coated.	12 gr/ft PBXN5/Tin, 0.070 SO, .300 pen	rubber	0.375	0.3
272	Sierracin	.500 Laminated	12 gr/ft PBXN5/Tin, .070 SO, cut	rubber	0.5	cut
273	Sierracin	.500 Laminated	15 gr/ft PBXN5/Tin, .070 SO, .360 pen	rubber	0.5	0.36
274	Navy	.500 cast	25 gr/ft PBXN5/Tin, .150 SO, ″O″ with T Mitered, Cut	rubber	0.5	cut
278	Sierracin	Laminated .448	12 gr/ft PBXN5/Tin, .070 SO, 90° bend, cut	rubber	0.448	cut
279	Sierracin	.448 Laminated	12 gr/ft PBXN5/Tin, .070 SO, 90° bend, cut	rubber	0.448	cut
280	Sierracin	.525 Laminated	15 gr/ft PBXN5/Tin, .150 SO, 900 bend, nearly	rubber	0.525	99% cut
			completely severed
281	Sierracin	.525 Laminated	12 gr/ft PBXN5/Tin, .150 SO, 200° F., 90°	rubber	0.525	0.36
			bend, did not cut
282	Sierracin	.525 Laminated	15 gr/ft PBXN5/Tin, .150 SO, 200° F., 90° bend, cut	rubber	0.525	cut
283	Sierracin	.448 Laminated	12 gr/ft PBXN5/Tin, .070 SO, 200° F., 90° bend, cut	rubber	0.448	cut

[0037] Previous methods of aircraft canopy fracturing and severance relied on the use of shock waves generated from an explosive charge. In order to facilitate shock wave transfer from the explosive charge to the target, U.S. Pat. No. 5,170,004 taught the use of a nearly incompressible medium placed between the charge and target. While this method is effective on acrylic and other fragilizing type materials, it is not reliable with polycarbonate, polycarbonate laminate or acrylic/polycarbonate laminates. With polycarbonate type materials, the use of a incompressible or other medium between the LSC and the target degrades rather than improves results. This is because polycarbonates are not easily fractured and therefore cutting using the explosive “jet” blast of the LSC is preferable to fracturing using shock waves. Because severance is preferable to fracturing, it is important that the area between the LSC and the target be clear of debris. This goes against the teaching of the 004 patent which taught the use of some form of nearly incompressible medium between the charge and the target in order to facilitate transmission of shock waves.

[0038] U.S. Pat. No. 5,780,763 taught a method of fracture wherein explosive charges are placed in parallel grooves cut in the upper surface of the material and simultaneously detonated to create overlapping shock waves. Again, because this method relies on shock waves which are unreliable to sever polycarbonate materials it is inferior to the present invention that uses the unimpeded explosive “jet” blast of the LSC to sever the material.

[0039] As revealed by the test results set forth above, the best severance results are obtained by use of a rubber back up, a PBXN-5 powder and a lead or tin sheath. Ideal set off was in the range of 0.100 to 0.300 inch for coreloads of 12 to 40 grains per foot.

[0040] Laminates of polycarbonate, acrylic, stretched acrylic and polyurethane can be severed with less overall energy than pure polycarbonate. The target thickness for the laminate is the total thickness from the LSC side through the final layer of polycarbonate or polyurethane. FIG. 4 shows the target thickness of a laminate. Any acrylic outside the final polycarbonate or polyurethane layer is easily shattered by the shock wave created by the LSC severing the polycarbonate. Acrylic layers between the LSC and the final layer or polycarbonate or polyurethane will act very much like the polycarbonate for the entire thickness.

[0041] Another shortcoming in the prior art was difficulty in safely severing polycarbonates and other materials around corners. To create a passageway for an ejecting or egressing aircrew it is necessary that the LSC circumscribe some pattern sufficient to allow egress. Severance problems arise when the LSC is bent around the corners of this pattern. These problems are attributable to at least two factors. First, in bending the LSC the coreload may be disbursed to less than an optimum strength, especially on the outside of the bend. Second, when the LSC and its retainer are bent around corners, the open end of the chevron may be shifted from parallel to the target surface. Optimal results are achieved when the open end of the chevron is parallel to the target surface and the explosive force is therefore perpendicular to that surface. Any alteration from parallel lessens the explosive force striking the target and impedes severance.

[0042] Therefore, in a preferred embodiment of this invention, bends in the LSC are gentle, with turn radii kept on the order of 2 inches or above. In this way the coreload of the LSC is kept consistent. Additionally, both the LSC and its retainer are tooled so as to keep the open end of the LSC chevron parallel to, and the apex of the chevron and resulting explosive force perpendicular to, the target. Through these methods, the full force of the explosive charge is expended directly on and perpendicular to the target. This allows severance with a minimum of coreload, thereby reducing noise and back blast.

[0043] The LSC must be placed on the target in a pattern that will effect severance of a portion of the target. In the prior art the LSC was not able to crossover another length of LSC. Instead the LSC would be bent around as it approached another length of LSC. FIG. 6 is a depiction of a LSC pattern on the severable portion of an aircraft canopy, as disclosed in the 296 patent discussed above. In FIG. 5 it can be seen that the charges must turn at sharp bends where it would be simpler, require less LSC and tooling, and avoid the degradation in performance associated with sharp bends if a length of LSC could simply intersect or crossover another length. This invention effects such intersections and crossovers in several ways.

[0044] FIG. 6 depicts one crossover method. A first length of LSC 20 is first run along the target. A second length of LSC 21, intersecting the first length, can then be run over the top of the first length. When a crossover method is utilized the second length of LSC must be detonated before the first. If the first length of LSC is detonated before the second length it will blow the second length off the target and greatly impede the severance capability of the second length of LSC. Additionally, the crossover must be designed so that upon detonation, the second length of LSC detonates the first length of LSC. If the second length of LSC merely severs the first length, without detonating it, the severing capability of the LSC will be again greatly reduced.

[0045] FIG. 6 a shows the second length of LSC 21 flattened over the first length of LSC 20. By flattening the second length of LSC 21 its cutting force is reduced and it will detonate, instead of sever, the first length of LSC 20. It may also be desirable to cut away some of the metal sheathing on the top of the first length of LSC to assist detonation by reducing the amount of metal sheathing that the second length of LSC must to detonate through in order to detonate the first length of LSC. FIG. 6b shows the crossover method wherein the first length of LSC 20 has part of its metal sheathing cut away 22 to facilitate its detonation by the second length of LSC 21. This may be especially important in higher coreload material.

[0046] Another method of ensuring detonation of the first length of LSC by the second length is to insert a solid material under the first length of LSC so that upon detonation of the second length of LSC the first length is forced against the solid material to assist in detonation transfer. FIG. 6c shows a solid anvil type object 22 placed under the first length of LSC 20. The anvil adds reliability to the detonation transfer, especially with higher coreload LSC severance.

[0047] A variation on the crossover method is shown in FIG. 7. In this method the second length of LSC 21 comes up on the first length of LSC 20 and rides the same line of severance for some given distance. This crossover method (referred to as a piggyback) not only avoids the sharp bend problem, it can also be used to add to the cutting capability of the first length of LSC and should be considered in areas of the target material that are thicker than other areas. In the piggyback method it is also important to fire the second length of LSC first. Firing the first length (the length closest to the target) first could result in blowing the second length off the target. FIG. 7a shows a side view of the piggy back method.

[0048] An additional method of routing LSC through intersections in a pattern is the mitered joint. FIG. 8 shows a four way mitered joint. The LSC is cut on the appropriate angle (i.e. 45°) to meet with another end of LSC that is similarly mitered. The joint is then joined with an adhesive. Appropriate adhesives include C-7/W and 5-minute epoxy. FIG. 8a depicts a crossview of the four way mitered joint. FIG. 9 shows a method of joining two lengths of LSC at a right angle. As with the crossover method, if one mitered joint is to ride over another it is important that the LSC closest to the target is not detonated until after the other length of LSC.

[0049] FIG. 10 shows another method of LSC intersection. In FIG. 10, a booster charge 30 is placed at the intersection of the adjoining lengths of LSC. The lengths of LSC abut to the booster charge that transfers detonation through the intersection. While booster charges have been used to transfer detonation in other mediums, they have not been utilized with LSC. FIG. 10a shows an LSC intersection where an explosive transfer charge powder, typically HNS or PBNX-5, 31 is enclosed in a manifold 32 that assists in transferring detonation. These methods do not provide for cutting under the booster or transfer charge but can provide for breaking at that point. Additionally, the manifold method is limited in use because the manifold becomes a projectile upon detonation if not retained. Therefore, in the case of aircraft transparency severance, the manifold method is limited to use on the sill of the aircraft, where it can be retained by a retainer mounted over the LSC and held to the aircraft's fuselage.

[0050] The retainer is not shown in the intersection figures, but those skilled in the art will recognize that a charge holder can be designed to take account of the LSC intersection or crossover.

[0051] The severance method of the present invention may be utilized in a system designed so as to be seated proximal to a sill portion of the aircraft and the system may include, in addition to the above-described arrangement for freeing a severable region of the canopy, one or more explosive charge positioned on or in close proximity to at least a portion of the sill and that will, on detonation, free substantially the entire transparent portion of the canopy from the aircraft. The present system also may be designed so as to selectively initiate either the detonation of the explosive charges mounted on or near the sill so as to sever substantially the entire transparent portion of the canopy or the severance of the smaller, severable region of the canopy. Detonation of the explosive charges mounted on or near the sill may be preferred over severing the severable region of the canopy in situations where the aircraft is on the ground or is otherwise not in flight and immediate egress from the cockpit is necessary.

[0052] The present severance method may also be designed so that the one or more explosive charges mounted on or near the sill detonate and free a large portion of the canopy from the aircraft simultaneous with the fracturing of the smaller, severable region to allow egress from the aircraft. Alternately, the present severance method may be used in a system to provide for the detonation of the one or more explosive charges mounted on or near the sill after the fracturing and severance of the smaller, severable region.

[0053] Various other details of the design and implementation of aircraft canopy fracturing systems will be apparent to those of ordinary skill in the art and, therefore, are not provided herein. Such details are in part provided in, for example, “A Systems Engineering Design Guide to Aircraft Explosive Canopy Fracturing”, December 1993, Teledyne Ryan Aeronautical, McCormick Selph Ordinance, the entire content of which is incorporated herein by reference.

[0054] Those of ordinary skill in the art also will appreciate that various changes in the details and arrangements of parts and materials which have been herein described and illustrated in order to teach the nature of the invention may be made by those skilled in the art. Any such modifications remain within the principle and scope of the invention as expressed in its claims.

Claims

1. A method of severing a polycarbonate or laminate of polycarbinate material comprising: selecting a severance site on said material; surrounding an linear explosive charge in a retainer such that the only area of said explosive charge not surrounded by said retainer faces said material; attaching said retainer to said material at a set distance (“stand off”) such that there is open space between said explosive charge and said material such that, upon detonation, said explosive charge generates an explosive cutting face or jet of sufficient strength to sever said material; and detonating said explosive charge.

2. The method of claim 1 wherein said retainer is made of silicone rubber.

3. The method of claim 1 wherein said explosive charge is a linear shaped charge with a V shaped cross section.

4. The method of claim 3 wherein said explosive charge has a metal sheathing of tin.

5. The method of claim 3 wherein said explosive charge has a metal sheathing of lead.

6. The method of claim 3 wherein said retainer and said explosive charge are tooled such that the open end of said V shaped cross section of said explosive charge is at all times parallel to said material.

7. The method of claim 3 wherein said linear shaped charge with a V shaped cross section is placed at a stand off in the range of 0.100 to 0.300 inches.

8. The method of claim 7 wherein said linear shaped charge with a V shaped cross section has a coreload in the range of 12 to 40 grains per foot.

9. The method of claim 7 wherein said polycarbonate or laminate of polycarbonate material is of a thickness on the order of 0.25+/−0.15 inches thick; and said linear shaped charge with a V shaped cross section is a PBXN-5 charge with a tin or lead sheathing and a charge on the order of 10 to 15 grains per foot.

10. The method of claim 7 wherein said polycarbonate or laminate of polycarbonate material is of a thickness on the order of 0.50+/−0.15 inches thick; and said linear shaped charge with a V shaped cross section is a PBXN-5 charge with a tin or lead sheathing and a charge on the order of 15 to 20 grains per foot.

11. The method of claim 7 wherein said polycarbonate or laminate of polycarbonate material is of a thickness on the order of 0.75+/−0.15 inches thick and said linear shaped charge with a V shaped cross section is a PBXN-5 charge with a tin or lead sheathing and a charge on the order of 30 to 40 grains per foot.

12. A method of severing a polycarbonate or laminate of polycarbonate material comprising: affixing a linear shaped explosive charge in proximity to said material whereby in so locating said explosive charge ensuring that all bends in said explosive charge have a radius of greater than or equal to 2 inches; and detonating said explosive charge.

13. A method of severing a pattern from a material comprising: placing a linear shaped explosive charge in proximity to said material to be severed about the pattern to be severed from said material such that said explosive charge intersects itself; and detonating said explosive charge.

14. The method of claim 13 wherein said explosive charge has a V shaped cross section.

15. The method of claim 14 wherein the intersecting portions of said explosive charge with a V shaped cross section are overlaid such that the portion of said explosive charge with a V shaped cross section that runs over top of the other intersecting portion of explosive charge with a V shaped cross section is deformed such that said V shape is flattened to eliminate the cutting force of that section of said explosive charge and instead provides for detonation of said other intersecting portion of explosive charge.

16. The method of claim 14 wherein the portion of said explosive charge with a V shaped cross section that is located closest to the material to be severed has a reduced thickness of metal sheathing at the point where the other portion of said explosive charge with a V shaped cross section overlays it.

17. The method of claim 14 wherein a solid material is placed between the portion of said explosive charge with a V shaped cross section that is located closest to said material to be severed and said material at the point where the other portion of said explosive charge with a V shaped cross section overlays it.

18. A method of detonation transfer between intersecting portions of linear shaped explosive charges comprising: placing a booster charge at the point of intersection between said intersecting portions of linear shaped explosive charges; and detonating said linear shaped explosive charges.

19. A method of detonation transfer between intersecting portions of linear shaped explosive charges comprising: placing an explosive transfer charge at the point of intersection between said intersecting portions of linear shaped explosive charges; enclosing said explosive transfer charge within a manifold; and detonating said linear shaped explosive charges.