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Патент USA US2405590

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ug.. 13, 1946.
3 Sheets-Sheet 1
Filed March 8, 1940
F/G. 5
2l 22 *20
Wl? MA 50N
E3, 1946,
Filed March 8, 1940
FIG, /5
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5 sheets-sheet s
,51 .
Patented Aug. 13, Y1946
~ 2,405,590
Warren I’. Mason, West Orange, N. J., assignor to
Bell Telephone Laboratories, Incorporated,
New York, N. Y., a corporation of New York
Application March 8, 1940, Serial No. 322,865 i
16 Claims.
(Cl. 109-81)
shield a layer of springs the compliance of which
This invention relates to detonation shields for
protection against explosions.
cooperates with the mass of the sand and the
The principal object of the invention is to pro
tect a vessel, shelter or other object against det
other elements to produce the desired attenua
tion. The springs may be provided by corrugated
onation waves resulting from the explosion of a
torpedo, mine, depth charge, bomb or the like.
Other` objects are to increase the effectiveness
and decrease the Weight and cost of detonation
A further object is to armor a vessel against
the effects oi explosions Without decreasing its
When an explosive such, for example, as
trinitrotoluene is set ofi it sends out in all di
rections a wave of very high pressure which
travels somewhat faster than the velocity of
soundl at steady frequencies in the medium and
sheet metal or they may be of the coil type or
any other suitable type.
When used for the protection of a vessel or
other water craft the detonation shield prefer
ably covers the entire hull to a point above the
Water line. If desired the backing plate of the
shield may constitute part of the outer plate of
the hull. Corrugated metal partitions may be
used to form bulkheads. The various layers may
be so proportioned that the shield will ñoat in
15 water and will, therefore, not decrease the buoy
ancy of a vessel when applied thereto. This is
a particularly important feature when the shield
is to be added to an unarmored vessel already
20v Also in accordance with the invention two
layers of metal and an interposed layer of sand
or other dissipative granular material may be
proportioned in thickness to provide a shield of
minimum weight per unit area for protection
attenuates as sound waves do inversely with
distance. When the medium is air, and to a
large extent when the medium is Water, the dam
age is caused chiefly by this high pressure wave.
The more rapidly the explosive burns, the more
destructive the wave becomes. In accordance
with the invention there is provided an eiîec
tive detonation shield designed in accordance 25 against a detonation wave set up by the explosion .
of a charge of given weight. This feature .is of
with the principles of acoustic and mechanical
importance when the shield is used for a vessel
wave filter theory. The shield comprises one or
because it is usually desirable to keep the Weight
more portions for attenuating the components
of the armor at a minimum relative to the pro
of high frequencies in the detonation Wave and
in tandem therewith one or more portions for 30 tection afforded.
The principles of the invention may also be ap
attenuating the components of low frequencies.
plied in the design of the Walls and roof of a
The shield is therefore very effective in dissipat
bomb-proof structure such, for example, as an
ing all of the energy of the detonation wave to
air raid shelter. In this application all of the
such an extent that the wave is rendered harm
less to the object protected.
35 supporting layers may be metal plates, all may
be reinforced concrete or part may be of one
A dissipative granular material such,` for ex
type and part of the other. One or more inter
ample, as sand or gravel is capable of dissipat
posed layers of sand or similar material are also
ing the large amount of energy associated With
used and, in the preferred embodiment, a layer
a detonation wave. Such material offers an at
tenuation which is high even for low frequencies 40 of springs.
The nature of the invention will be more fully
and increases rapidly with an increase in fre
understood from the following detailed descrip
quency. The shield, therefore, comprises one or
tion and by reference to the accompanying draw
more layers of this type of material, included
especially for attenuating the high frequencies
ings, of which
Fig. 1 is a cross-sectional view of the hull of a
The sand or other material may be held between 45
vessel to which a detonation shield in accordance
layers of metal plates or reinforced concrete.
with the invention has been applied;
The sand is more effective if confined in cells of
Fig. 2 is a cross-sectional view of one form
comparatively small cross-sectional area. Such
of the detonation shield using a single layer of
cells may be formed by partitions between the
50 dissipative granular material and a layer of
The low frequency energy not suñiciently at
Figs. 3, 4 and 5 are respectively a cross-sec
tenuated by the sand is still further reduced by
tional view, a side View and a top View of a frag
means of a mechanical filter which offers addi
ment of another form of the shield comprising
tional attenuation at these frequencies. Such a
ñlter may be provided by incorporating in the 55 two layers of dissipative granular material;
Figs. 6, 7 and 8 are respectively a cross-sec
the size of the charge to be protected against
tional View, a side view and a top view of a frag
and the physical properties of the various layers.
ment of another form of the shield employing a
The dimensions given are merely representative,
Fig. 6 is a cross~sectional view of anotherY form
cellular construction;
Figs. 9, 10 and 11 are respectively a. cross
sectional view, a side view and a top View of a
fragment of a shield similar to the one shown
of the shield which is similar to the one shown
in Fig. 3 except for the addition of the parti
tions 28 which extend from the front plate I6
in Figs. 3, 4 and 5 kexcept that the corrugated
nearly to the iirst intermediate plate I8 to di
metal springs have been replaced by coil springs;
vide the> spaceinto cells. For most eiïectlve re
Fig. 12 is a sectional View of a bomb-proof 10 sults the individual cells thus formed should have
shelter with walls and roof constructed in ac
acomparatively small cross-sectional area, pref
erablynot exceeding one square inch. Fig. 7 is
cordance with the invention;
Fig. 13 is a plan View of the shelter shown' in
a side view taken along the line 1_1 of Fig. 6
Fig. 12;
8: is a» top view taken along the line
0f 'Fìg.
Figs. 14, 15 and 16 are cross-sectiQnalwiews.of'
diiîerent forms of the walls androof -of" the shel
Elshows.~ another modification of the shield
ter shown in Figs. 12 and 13;
of Fig. 3 inwhich coil springs 21 replace those
Fig. 17 is a diagrammatic representation' of an
'of the corrupted metal type. Fig. 10 is a side
elemental layer of dissipative granular material;
View taken. along the line iii--lü of Fig. 9 and
Fig. 18 is an equivalent electrical circuit for
Fig. 11 is a top view taken along the line II--I I.
the layer shown in Fig. 17 used in explaining the
It will be understood, of course, that the coil
springs 21 may also be substituted for those of
Fig. 19 shows curves giving the attenuation of
sandV for detonation waves of various average
pressures plotted against frequency; and
Fig. 20 shows representative curves giving the
ratio of the initial energy to the energy at any
the corrugated metal type shown in Figs. 2> and
6. Also the space between the plates I6 and I8
25 in Figs. 2, 3 `and 9 may be divided into cells by
means of partitions such as 2S shownin Figs. 6,
7 and 8.
point >for a> detonation wave passing through a>
The principles of the invention may also be
layer of sand.
applied to a bomb-proof structure such, for ex
Fig. 1 shows one form of a detonation shield 30 ample, as the air raidshelter shown in Fig, v12,
I2y in accordance'with the >invention applied to
which is an elevation` partly cut away, and Fig..
the hull I3V of'a vessel toprotect the vessel from
13 which is a plan View. A bomb 28 is shown
a mine I4. The shield Vpreferal?ily covers the er1
approaching the shelter. As illustrated, the
tire submerged portionof the hull and extends
for aA short distance above the water line I5.
As lshown to a larger 'scale> inthe cross-section
al View of Fig. 2', the shield lí'comprisesan outer
metal plate i6, a layer-pf sand, gravel or> otherv
dissipative granular material4 I1, an’intermedi'ate
metal plate i8, a layer of corrugatedV metal
springs "IviLand a metal-backing Vplate 20. As
shown in Fig. l theÍ backing plate 20.7may form
part of the outerV plate of the hullof the vessel.
The shield l2 mayl be madefwaterètight and the
thicknesses of the layersV so proportioned Ythat
theY shield asa whole willhave‘approximatelyVV
the samefaverage. density as water. T’Jnderfthese`
conditions thev shield will float in water. Such
a shield may, therefòre, beV attached tota Vessel`
shelter has a circular floor p_lan and aconical
roolf. The walls 3û_and the roof SI have the
construction shown in4 greater detail in the cross
sectional View of Fig. 14 comprising an outer
metal plate 33, two intermediate metal Vplates 35
and 31, a metal backingplate 39, anouter layer
of sand 34 between the plates 33 and 35, an i11
ner layer of sand 38 between the plates 31 and
35 and a layer of corrugated metal springs 35 be
tween the intermediate plates 35 andriìl.Y The
ñoor lili is placed several feet below the ground
level 4Iand the rood? is. supported by a heavy,
central Ysteel column >¿I2 which has a concrete cap
43. Thewallis Seton a concrete foundation 44
and the central column has a concrete footing,
£5. The shelter;V has an entrance whichmay be
without decreasing the buoyancy of they Vessel.
50 closed by the door ‘1B-'having beveled sides and
Fig. 3 shows a cross-sectional viewfcf anotherY
a ladderl ¿i1-is ¿provided to facilitate ingress and
formof detonation shield for the protectionof
thehull of a Yvessel in the. manner shownin Fig.
Asapmodificationyof the'wall construction of
1.- The shield of` Fig. B» issimilar to the one
Fig, 14~ one or; more ofgthe metal platesmay be
shown in'Fig. 2 except that a second intermedi-`replaced by layers of concrete, preferably rein
ate metal plate 2ll and a second- layer of'sand
forced with steel mesh. As shown in the cross
or similar material 22 are includedfin'. order "to,
sectional viewotFigi. 1_5,v for example, the outer
give added protection. Asshown more clearly, i'n
plate 33„thaintermediateplate 31 and theback
Fig'. 4, a side View taken along. the line ¿L4-Lof
ingplate 39' may be replaced, respectively, by the
Fig. 3 and in Fig. 5, a top View taken along. the 60 i reinforced. concrete layers MLM and 42. Under
linee-5, vertical partitions such as 23, 2l and
certain circumstances it may be desirable >to re
25'may be included between adjacent. metal
place-.all .oit thesteel plates by` layers of concrete,
plates to divide the various layers of thel shield
as showninFig. 16; The construction shown in
into separate water-tight compartments. These
Fig. 16 isr the same as-thatshown in Fig. l5 ex
partitions are preferably made of corrugated
cept that the intermediate plate 35v is replaced
metal so as not to restrict the movement ofthe
by a layer ofïconcrete 43'.
plates relative to each other. The shield will
Suggested thicknessesfor the' various layers of
have substantially the sameavërage density as
inches thick and the distance >between the plates
thewall lshown inFig. 14 arev one inch for each
ofthe plates 33 and 35; one-half inch for each
of theplates 31 and 39, eight inches for each of
the» layersof sand 311e> and 38V and'a spacing of
ißaland 2i forming the spring> compartment is
two feet. As explained hereinafter,` these dimen
between the-two intermediate plates. In Fig. 16
sions may, of course, be altered,`_,depending upon
. each of the concrete layersAD andv4l3- may be
water if the outer plate I6 hasa thickness of 5/8
inch, each of the plates I8, 2D and 2l hasla thick,
ness of two inches, each layer of sand is .eight
eight inches »forA the. spring> compartment formed
thickness Z is given in terms of the above-defined
two inches thick and each of the other concrete
quantities by the following equation:
layers may be one inch thick. These dimensions
are, of course, to be taken only as representa
tive, and may be altered within wide limits to suit
particular circumstances. The springs 36 in Figs.
14, 15 and 16 are shown as made of corrugated
metal but it is to be understood that coil springs,
The values to be used for M, C, Rv and RH de
such as 21 in Fig. 9, or springs of any other suit
pend both upon the material employed and the
able type, may be substituted therefor in any of
10 pressure to which it is subjected. For sand the
these figures.
attenuation in napiers per centimeter plotted
The principles on which the invention is based
against frequency for detonation waves having
will now be considered briefly. The pressure dia
average pressures of 300, 1000, 2500, 10,000 and
gram of a detonation wave shows a very sharp
25,000 pounds per square inch is shown by the
increase in pressure withtime followed by a rapid
solid line curves 50, 5|, 52, 53 and 54, respectively,
decrease as the energy is communicated to the
Vsurrounding medium. A'Fourier analysis of this Y of Fig. 19.VV TheY attenuation is roughly propere.. .
tional to frequency, and is higher for the lower
pressure wave shows that a large part of the en
pressures because the effect of friction becomes
ergy is carried by quite high frequencies. 'I‘here
greater. At the lower pressures the resistance
fore, in order to dissipate the energy a medium
is required which will provide high attenuation 20 due to hysteresis accounts for a larger part of
the loss while at the higher pressures the viscous
at high frequencies. A layer of loose particles
resistance is more important. Attenuation char
of a dissipative granular material such as sand
acteristics for other materials and for other pres
or gravel has been found to be the cheapest and
sures may be obtained by making the appropri
most satisfactory for this purpose.
The attenuating properties of sand or other 25 ate substitutions in the above equation.
. If the sand is confined to cells of comparatively
similar material may be investigated most con
veniently by a consideration of its equivalent
electrical circuit. Fig. 1’7 represents an end View
of an elemental layer of sand assumed to be cen
trally located in a completely filled, long, open 30
ended tube of large cross-sectional area. On one
surface the layer of sand is acted upon by a uni
small cross-sectional area, as shown in Figs. 6, 7
and 8, the attenuation will be increased at all
frequencies and for all pressures. The equivalent
circuit for this case is the same as that shown
in Fig. 18 except that a resistance must be added
in series with each mass
formly distributed force F1 which represents the
pressure exerted by a detonation wave traveling
through the sand from one end of the tube to 35
to take account of the viscous resistance which
the other. The movement of the layer is resisted
opposes the translation of the elemental layer as
on the other side by a force Fz exerted by the
a whole. The magnitude of the added resistance
succeeding layers of sand but the layer may be
is directly proportional to the square of the per
displaced to the new position indicated by the
40 imeter of the cross-section of the cell and in
dotted lines.
versely proportional to the area. The dotted
Fig. 18 represents diagrammatically the equiv
curves 55 and 56 of Fig. 19 give the attenuation
alent T-network for the layer of sand of Fig. 17
frequency characteristics for sand confined in
under the conditions set forth. The series arms
a pipe of one-half inch inside diameter for aver
of the network consist of two equal reactances
age pressures, respectively, of 1000 and 25,000
pounds per square inch. At the lower pressures
the added attenuation is small. At the higher
pressures, however, a comparison of curves 54
each representing half of the mass of the layer
and 5S shows that the increase in attenuation
of sand. The interposed shunt branch comprises
is considerable, especially at the lower frequen
a compliance C which is the compliance (inverse
cies. In practice it is found desirable to keep the
of stiffness) of the layer of sand, a resistance Rv
cross-sectional areas of the cells comparatively
which represents the viscous resistance of the
small, preferably under one square inch.
sand and is constant with frequency and a sec
It should be pointed out that the energy at
ond resistance
tenuation of a detonation wave by a layer of sand
which is inversely proportional to the frequency
is not the same as the pressure attenuation. This
is due to the fact that, as shown by the curves
of Fig. 19, the sand offers higher pressure at
tenuation to the higher frequencies than to the
60 lower frequencies. Therefore, as the wave travels
through the sand the higher frequencies are ab
sorbed, leaving the lower frequencies as the pre
dominant ones.
and represents the hysteresis resistance due to
the fact that sand after compression will not re
turn to its original volume. In the equivalent
electrical circuit of Fig, 20 the symbol for in
ductance is used for M/2 and the symbol for
capacitance is used for C because in the mechani
cal analogy mass corresponds to inductance and
compliance corresponds to capacitance. For sim
ila1` reasons the resistance symbol is used for
RH/ w and Rv.
The attenuation A in napiers per centimeter
Also, since a pressure wave of
lower frequency lasts for a longer time, it delivers
more energy to the backing plate and hence the
energy attenuation is less than the pressure at
tenuation. It follows then that, as the predomi
nant frequencies are progressively lowered, a
thicker and thicker layer of sand is required to
effect a given energy reduction.
The facts just discussed are illustrated by the
curves of Fig. 20, which give the ratio of the
initial energy to the energy at any point for a
detonation wave traveling through a layer of
for a layer of dissipative granular material of 75 sand, the thickness of which is gi@ by the
abscissas. The solid line curve 58' relates tothe y
wave set up by the explosion of a 40G-pound
charge of trinitrotoluene. It will be noted that
the curve rises slowly- up to about the three
inch point, then rises sharplydfrom there to
about the twelve-inch point, above which it
gradually ilattens out. It is apparent that for
this type of explosion a three-inch layer of sand
is not very effective in the matter of energy re
duction, but a twelve-inch layer effects a re
duction of over 800, while an additional nine
inch layer reduces the energy by less than 200.
For lighter charges the predominant frequencies
are higher and a thinner layer of sand is re
quired for a given energy reduction. The dotted
curve 59, for example, relates to a two-gram
charge of lead azide. The curve is of the same
. type as is curve 58 but the steeply rising por
tion now falls between the one-inch and three
oiî frequency. The compliance (inverse of. stiff
Y ness)r of thesprings. may be soY chosen with re.
spect to. the massV of the layer of- sand lv'l' and
the plates i6 and I3 that the ñlter will have a
cut-oli .below 10,0 cycles per second and will,
therefore, effectively attenuate most of. the re
maining energy.
VWhat is claimed is:
l. A detonation shield comprising an. outer
plate, a backing plate, a first intermediate plate,
a second intermediate plate, a layer of dissipa
tive granular material between said outer platev
andsaid ñrst intermediate plate, alayer of springs
between said twoV intermediate plates, and a
second layer of dissipative granular material be
tween said second> intermediate plate and said>
backing plate.
2. A detonation shield in accordance with claim
l in which said dissipative granular material is
inch points. In practice, therefore, the layer> 20 sand.
of sand is usually made between two and twelve
3. A detonation shield in accordance with claim
1 in which said plates are made of metal.
lies between four and nine inches.
4. A detonation shield in accordance with claim
It will now be pointed out how a detonation
1 in which one of said plates is made of concrete.
shield of minimum weight per unit area may be 25
5. A detonation shield in accordance with claim
constructed. It is assumed that the shield com
1 in which one of said plates is made of metal
prises two layers of metal plates with an inter
and another of said plates is made of concrete.
vening layer of sand and is t0 be used to pro
6. A detonation shield in accordancewith claim
tect a vessel against a torpedo containing a 4m0
1 in which said dissipative granular material is
poundV charge of trinitrotoluene. The forward 30 sand and the thicknesses of said layers are so
plate is made thick enough to stop the motion
proportioned that said shield as a whole has an
of the torpedo and set oif‘ the charge. The
average density approximately equal to the den
energy in the resultant detonation wave will be
sity of water.
transmitted through the forward plate without
7. A detonation shieldin accordance with claim
much reduction but, as it passes through the 35 1 in which said springs are 4made of corrugated
layer of sand,_it will be reduced in accordance
inches in thickness, and the preferred thickness
with curve 58 of Fig. 20.
The backing plate
8. A detonation shield in accordance with
must then be made of sui‘licient thickness to
claim 1 in which the space between two of said
absorb the residual energy withoutl rupture.
plates is divided into a number of water-tight'
The question is, how thick to make the layer 40 compartments.
of sand. As already pointed out, a thickness
9. A detonation shield in accordance with
of from two to twelve inches will usually be
claim 1 in which all of the spaces between said
chosen. Over most of this range the energy
plates are divided into> water-tight compart
ratio curve is rising steeply and it will be i'ound
that a given weight of sand will have greater» 45
10. A detonation shield in accordance with
energy absorbing power than will the same
claim 1 in which the space occupied by said dissi
weight of armor plate. As the thickness of the
pative granular material is divided into cells
layer of sand is increased, the thickness of the
each _of comparatively small cross-sectional area.
backing plate can be decreased and the reducl1. A detonation shield in accordance with
tion in the weight of the backing plate will be 50 claim 1 in which said dissipative granular mate
greater than the increase in the weight ofthe
rial is sand and the space occupied by said sand
sand. However, somewhere near the upper end
is divided into» cells yeach of comparatively small
of this range, when the curve starts to flatten
cross-sectional area.
out, there will be found a point whererincreasing
12. A detonation shield in accordance with
the thickness of the sand will add just as muchA 65 claim 1 in which the space occupied by said dis
weight as is saved by the reduction in the thick
sipative granular material is divided into cells
ness of the backing plate. The location of thiseach of comparatively small cross-sectional area
point will determine the optimum thickness of
and the space between said two intermediate
the layer of sand for a minimum weight per unit
plates is divided into a number of water-tight
area for the shield as a whole. The thickness
thusdetermined for the layer of sandl depends,> 60 compartments.
13. A detonation shield in accordance with
of course, upon the size of the explosive charge,
claim l in which said springs are made of cor
the physical characteristics of the metal plates.
rugated metaLthe space occupied by said dis
and the properties` of the sand or other dissipa
tive granular material used. If the thickness 65 sipative granular material is divided into cells’
of the layer of sand is further increased, the
each of comparatively small cross-sectional area
added weight of the sand willfbe greater than
and the space between said two intermediate
the saving of metal in the backing plate.
plates is -divided into a number of water-tight
AS already pointed out, sand or similar mate
rial is especially effective in attenuating high
le. A detonation shield in accordance with
frequencies. A low frequency Apulse may, how
claim 1 in -which said plates are made of metal,
ever, get through the layer of sand. 'Ilo-further
said springs aremade of corrugated metal, the
attenuate the low frequencies a layer of springs,
space occupied by said dissipative granular ma
such as I9 in Figs. 1 and 2, is added to provide
terial is divided intocells each of comparatively
a low-pass mechanical ñlter section -with low cut 75 small. cross-sectional area and the?space between
said two intermediate plates is divided into a
number of Water-tight compartments.
15. A detonation shield in accordance with
claim 1 in which said plates are made of metal,
said springs are made of corrugated metal, said
dissipative granular material is sand, the space
occupied by said sand is divided into cells each
claim 1 in which said plates are made of metal,
said springs are made of corrugated Inet-al, said
dissipative granular material is sand, the space
occupied by said sand is divided into cells each
having a comparatively small cross-sectional
area and the space between said two intermediate
plates is divided into a number of water-tight
compartments, said shield as a whole having an
having a comparatively small cross-sectional area
average density approximately equal to the den~
and the space between said two intermediate
plates is divided into a number of water-tight l0 sity of water.
16. A detonation shield in accordance with
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