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Developments in boron filaments
COMPOSITES news 1 Reinforcements other than glass/ fibre will be widely used by 1985, says the report. No one reinforcement stands out but boron fibres, carbon fibres and metal whiskers, such as aluminium oxide, are all mentioned as likely candidates. T h e final section of the report deals with other plastics materials, which one or more of the panelists considered would be important by 1985. Panelists were also asked to list typical uses and good and bad characteristics of these materials and to estimate properties of the material in 1985 on a scale of 1 to 'l (not acceptabl e to outstanding). T a b l e 3 lists the results for four of the thirty-nine materials given in the report. These f o u r - - boron/epoxy, carbon / epoxy, boron / polyimide, e a r b o n / p o l y i m i d e - - are likely to have a large effect on the composites industry, Predictions about the cost of carbon fibres give an estimated low price of $ 1 0 - 1 2 / l b as volume increases. T h e limitlngcost factor for boron is the tungsten core. Cheaper core material or improved processing could result in $50-75/Ib boron. Large quantities of these materials are expected to be in use by 1985. Selwyn Enzer, the author of the report, is to be complimented upon the depth and range of this study and on its clear presentation. T h e address of the Institute for the Future is Riverview Centre, ,Middletown, Connecticut 06457, USA.
Developments in boron filaments T w o companies in the USA manufacture boron filament - - Avc9 Systems Division and ~f~he H a m i l t o n Standard DivisiOn of the United Aircraft Corporation. UP till recently both companies sold the filament to tape producers like 3M Company; US Polymeric and W h i t t a k e r Corporation, who then manufactured 3 in wide boron-epoxy tape consisting of a monolayer of parallel boron filaments in a 'B' staged resin matrix. T h i s is the form in which it is sold to fabricators. Now Avco have started a new factory at Lowell, Mass., to produce their own tape using the machine and resin technology previously developed by Whittaker, who have left the busino6s. According to a recent report in the American magazine Business Week, Avco have now the capacity to produce 8000-10 000 lb of filament a year, or 15 000 lb of tape. This is still far short of H a m i l t o n Standard's reported 22 000 lb capacity. Borgn-epoxy composites are currently being used in the tails of the two new fighter a i r c r a f t - - t h e US
l"a~le 3 Predictions about composites other than GRP
Boron/ polyimide (Aerospace, aircraft erlcjines)
Carbon/ poly[mide IAircraft. aeraspace)
Material (typical uses suggested)
Boron/epoxy Carbon/epoxy (Aircraft, auto- (Aircraft, acremotive, build- space, autoing materials, motive, buildaerospace) ing materials)
Characteristics ( + ) assets (--) liabilities
(-I-) very high strength and stiffness, lightweight (--) cost, Flammability, Processability
(q--} very high ( + ) high temstrength and perature / oxistiffness, light- dative stability, weight strength, stiff(--) cost, flare- hess, l i g h t mobility weight (--) cost, labrication
(-I-) hightemperature / oxldative stability, high strength and stiffness, lightweight (--) cost, fabrication
Anticipated properties in 1985" Price Processabillty Tensile strength Stiffness Impact strength Useful temp. range Chemical resistance Flammability
2 2 3 -J3 -f3 2 3 I
2 2-3 3 qL 3 -12-3 2 3 I
2 1-2 3 -f3 Jr2 3+ 3 3
2 1-2 3 -l3 -f2-3 3 3 2-3
Likelihood of being in widespread use by 1985
45%
70%
s0%
s0%
Potential market by 1985 (million Ib/yr)
20
200
I0
200
* l - - n o t acceptable if indicated property is important to intended use 2--acceptable performance in this property: still suitable in most cases 3---outstanding in property indicated; among the best performers available
Navy's F-14 and the US A i r Force's F-15. Each use about 150-200 lb of boron per plane. At present the market demand is below 10000 lb per year which keeps the price of filament and tape up at about $290 per lb. At a conference held at the US T r a d e Centre in April Paul R. Hoffman, vice-president of Avco Systems Division, forecast that boron-composites would be totally cost-effective in two to three years and that the price of boron filament would have fallen to $50-75 per lb in about five years. Other aircraft applications of boroncomposites which have flown are the horizontal stabilizer of the F - I l l (30% weight saving over original component); the wing flap of the A4 (Skyhawk); the F4 (Phantom jet) rudder; a floor beam for the 707; the tail rotor of the $61 helicopter; and the C5A wing flap. Small parts containing boron have been flying since 1967. H a m i l t o n Standard supply boron filament i.n the following forms : (1) Boron filament, diameter either 0"0040 in or 0"0056 in; ultimate tensile strength 400000 lbf/in~; tensile modulus of elasticity 55 X 10 ~ l b f / i n 2.
(2) Borsic filament, diameter either 0.0042in or 0.0057in. This is boron filament coated with silicon carbide to prevent interaction between boron and metal matrices. It is stable at 11000C in air and. 600°C in aluminium. T h e uTs and modulus are the same as for the uncoated boron filament. (3) Borsical T M tape and broad goods with either 0.0042 in or 0.0057 in Borsic filament. These are monolayer composite materials composed of spaced parallel Borsic filaments interspersed with plasmas p r a y e d 6061 aluminium alloy and backed by aluminium foil. T h e material layer may be diffusion bonded (for 6061 aluminium, 0.001 in, backing foil) or braze bonded (for 713, 0"001 in, aluminium foil). Borsic-aluminium composites have the following typical properties : modulus (0"), 30)<10' l b f / i n = (0.0042 in), 33X106 l b f / i n z (0"0057 in); u'rs (00) 140 000-190 000 l b f / i n ' (0"0042 in); 170 000-210 000 l b f / i n ' (0"0057 in). T h e longitudinal strcngth to density and modulus to density ratios of the
COMPOSITES September 1971 133
[COMPOSITES news Borsic-aluminium system are inferior to those of the boron-epoxy system, but the transverse and shear moduli are better. Also the Borsic-aluminium composite retains its strength and modulus up to much higher temperatures than the boron-epoxy or boronpolyimide composites. T h e Borsicaluminium system has better stress rupture properties than the best titanium alloys up to 500°C and excellent resistance to fatigue damage. Borsic-aluminium composite has been used in the spool of J T 8 D turbine engine fan blades, giving a weight saving of 40% over the original titanium structure. T h e US Air l'orce is currently sponsoring research into developing supersonic fan blades in Borsic-aluminium. Borsic-aluminium is being developed for use in space re-entry vehicles. T h e payload adapter for the US Air Force P R I M E programme is four feet in diameter and weighs 7'). lb with boron-aluminium skins, stringers, door and bulkhead. A 40% weight reduction compared with the original monocoque design was achieved in what is at present the largest boronaluminium structure to have been fabricated and tested. Avco supply boron filament o[ 0'0040 in and 0"0056 in diameter, with a UTS of 500 0001bf/in ~ and a Young's modulus of 58X10Blbf/inL T h e i r boron-reinforced epoxy prepreg tape has the trademark of the Whittaker Corporation - - Rigidite 5505/4. Avco quote the following average mechanical properties for a laminate at room t e m p e r a t u r e - flexural strength, 260 000 l b f / i n ~, flexural modulus 30X1061bf/in ~. T h e tape is available in increments of ~-in to 3 in maximum or as broad goods in widths and lengths to meet customer requirements. It can be used for structures which perform at temperatures up to 420°F. Avco Systems Division, Lowell Industrial Park, Lowell, Mass. 01851, USA Hamilton Standard, Division of United Aircraft Corp, Windsor Locks, Connecticut 06096, USA
A composite pipeline for Alaska ? Transportation of the vast reserves of crude oil and natural gas found on Alaska's North Slope and in the north of Canada into Canada and the United States has still to begin. Quantities have been estimated at 65 000 million barrels of oil and 700 million million cubic feet of natural gas for the Prudhoe Bay and Canada's Northwest Territories alone. Delivery rates of about 2 million barrels of oil a d a y - - w h i c h is more than the total amount of oil used daily in C a n a d a -
134
COMPOSITESSeptember 1971
and of 1500 million cubic feet of natural gas are contemplated. At present, oil and gas pipeline projects estimated at more than 8000 million dollars are being planned, of which about five to six thousand million dollars will probably pass the planning stage. These basic facts about the enormity of this pipeline project were presented by Dr G. K. Korbacher of the Institute for Aerospace Studies, University of Toronto, at a symposium entitled 'The North Slope p i p e l i n e - steel or composite'. An 8 ft diameter pipe operating at less than 9001bf/in 2 pressure is envisaged and its total length would be of tile order of 1600 miles. A feasible design for such a pipe in composite materials would be a glassmat/wire-sheet reinforced epoxy resin covered by an insulating layer of semi-rigid polyurethane foam, generated on site. T h e entire pipe could be continuously fabricated by filament winding, tested and laid in the final position by one machine operated by a small nunabe'r of men. T h e wall thickness of the pipe would be approximately ~ in and fibre loading about 58 wt %. Axial strength would
be about 85 0 0 0 1 b f / i n ' and modulus about 5 X 10' lbf/in'. T h e material costs for a composite pipeline are about the same as for an analogous steel pipeline but the composite pipe offers the nonstructural advantages of corrosion resistance, insulation and on-site fabrication. Corrosion resistance is obviously necessary both from a cost and a safety aspect. Insulation is necessary to keep the oil at a temperature of 60~100°F, when it flows freely, when ambient temperatures down to --70°F can be expected, and also to prevent the thawing of permafrost. On-site fabrication of large pipes from composite materials is clearly feasible (eg the Drostholm machine featured in Composites, Vol ], No 6, p 330); steel pipe would have to be transported ready made to the site. T h e case for a composite pipeline in such an extreme environment has still to be proved and work is i'n progress on model pipe systems. T h e existing techniques for steel pipe building will not help here: entirely new concepts of engineering design and construction need to be evolved for composite materials.
Developments in boron filaments T w o companies in the USA manufacture boron filament - - Avc9 Systems Division and ~f~he H a m i l t o n Standard DivisiOn of the United Aircraft Corporation. UP till recently both companies sold the filament to tape producers like 3M Company; US Polymeric and W h i t t a k e r Corporation, who then manufactured 3 in wide boron-epoxy tape consisting of a monolayer of parallel boron filaments in a 'B' staged resin matrix. T h i s is the form in which it is sold to fabricators. Now Avco have started a new factory at Lowell, Mass., to produce their own tape using the machine and resin technology previously developed by Whittaker, who have left the busino6s. According to a recent report in the American magazine Business Week, Avco have now the capacity to produce 8000-10 000 lb of filament a year, or 15 000 lb of tape. This is still far short of H a m i l t o n Standard's reported 22 000 lb capacity. Borgn-epoxy composites are currently being used in the tails of the two new fighter a i r c r a f t - - t h e US
l"a~le 3 Predictions about composites other than GRP
Boron/ polyimide (Aerospace, aircraft erlcjines)
Carbon/ poly[mide IAircraft. aeraspace)
Material (typical uses suggested)
Boron/epoxy Carbon/epoxy (Aircraft, auto- (Aircraft, acremotive, build- space, autoing materials, motive, buildaerospace) ing materials)
Characteristics ( + ) assets (--) liabilities
(-I-) very high strength and stiffness, lightweight (--) cost, Flammability, Processability
(q--} very high ( + ) high temstrength and perature / oxistiffness, light- dative stability, weight strength, stiff(--) cost, flare- hess, l i g h t mobility weight (--) cost, labrication
(-I-) hightemperature / oxldative stability, high strength and stiffness, lightweight (--) cost, fabrication
Anticipated properties in 1985" Price Processabillty Tensile strength Stiffness Impact strength Useful temp. range Chemical resistance Flammability
2 2 3 -J3 -f3 2 3 I
2 2-3 3 qL 3 -12-3 2 3 I
2 1-2 3 -f3 Jr2 3+ 3 3
2 1-2 3 -l3 -f2-3 3 3 2-3
Likelihood of being in widespread use by 1985
45%
70%
s0%
s0%
Potential market by 1985 (million Ib/yr)
20
200
I0
200
* l - - n o t acceptable if indicated property is important to intended use 2--acceptable performance in this property: still suitable in most cases 3---outstanding in property indicated; among the best performers available
Navy's F-14 and the US A i r Force's F-15. Each use about 150-200 lb of boron per plane. At present the market demand is below 10000 lb per year which keeps the price of filament and tape up at about $290 per lb. At a conference held at the US T r a d e Centre in April Paul R. Hoffman, vice-president of Avco Systems Division, forecast that boron-composites would be totally cost-effective in two to three years and that the price of boron filament would have fallen to $50-75 per lb in about five years. Other aircraft applications of boroncomposites which have flown are the horizontal stabilizer of the F - I l l (30% weight saving over original component); the wing flap of the A4 (Skyhawk); the F4 (Phantom jet) rudder; a floor beam for the 707; the tail rotor of the $61 helicopter; and the C5A wing flap. Small parts containing boron have been flying since 1967. H a m i l t o n Standard supply boron filament i.n the following forms : (1) Boron filament, diameter either 0"0040 in or 0"0056 in; ultimate tensile strength 400000 lbf/in~; tensile modulus of elasticity 55 X 10 ~ l b f / i n 2.
(2) Borsic filament, diameter either 0.0042in or 0.0057in. This is boron filament coated with silicon carbide to prevent interaction between boron and metal matrices. It is stable at 11000C in air and. 600°C in aluminium. T h e uTs and modulus are the same as for the uncoated boron filament. (3) Borsical T M tape and broad goods with either 0.0042 in or 0.0057 in Borsic filament. These are monolayer composite materials composed of spaced parallel Borsic filaments interspersed with plasmas p r a y e d 6061 aluminium alloy and backed by aluminium foil. T h e material layer may be diffusion bonded (for 6061 aluminium, 0.001 in, backing foil) or braze bonded (for 713, 0"001 in, aluminium foil). Borsic-aluminium composites have the following typical properties : modulus (0"), 30)<10' l b f / i n = (0.0042 in), 33X106 l b f / i n z (0"0057 in); u'rs (00) 140 000-190 000 l b f / i n ' (0"0042 in); 170 000-210 000 l b f / i n ' (0"0057 in). T h e longitudinal strcngth to density and modulus to density ratios of the
COMPOSITES September 1971 133
[COMPOSITES news Borsic-aluminium system are inferior to those of the boron-epoxy system, but the transverse and shear moduli are better. Also the Borsic-aluminium composite retains its strength and modulus up to much higher temperatures than the boron-epoxy or boronpolyimide composites. T h e Borsicaluminium system has better stress rupture properties than the best titanium alloys up to 500°C and excellent resistance to fatigue damage. Borsic-aluminium composite has been used in the spool of J T 8 D turbine engine fan blades, giving a weight saving of 40% over the original titanium structure. T h e US Air l'orce is currently sponsoring research into developing supersonic fan blades in Borsic-aluminium. Borsic-aluminium is being developed for use in space re-entry vehicles. T h e payload adapter for the US Air Force P R I M E programme is four feet in diameter and weighs 7'). lb with boron-aluminium skins, stringers, door and bulkhead. A 40% weight reduction compared with the original monocoque design was achieved in what is at present the largest boronaluminium structure to have been fabricated and tested. Avco supply boron filament o[ 0'0040 in and 0"0056 in diameter, with a UTS of 500 0001bf/in ~ and a Young's modulus of 58X10Blbf/inL T h e i r boron-reinforced epoxy prepreg tape has the trademark of the Whittaker Corporation - - Rigidite 5505/4. Avco quote the following average mechanical properties for a laminate at room t e m p e r a t u r e - flexural strength, 260 000 l b f / i n ~, flexural modulus 30X1061bf/in ~. T h e tape is available in increments of ~-in to 3 in maximum or as broad goods in widths and lengths to meet customer requirements. It can be used for structures which perform at temperatures up to 420°F. Avco Systems Division, Lowell Industrial Park, Lowell, Mass. 01851, USA Hamilton Standard, Division of United Aircraft Corp, Windsor Locks, Connecticut 06096, USA
A composite pipeline for Alaska ? Transportation of the vast reserves of crude oil and natural gas found on Alaska's North Slope and in the north of Canada into Canada and the United States has still to begin. Quantities have been estimated at 65 000 million barrels of oil and 700 million million cubic feet of natural gas for the Prudhoe Bay and Canada's Northwest Territories alone. Delivery rates of about 2 million barrels of oil a d a y - - w h i c h is more than the total amount of oil used daily in C a n a d a -
134
COMPOSITESSeptember 1971
and of 1500 million cubic feet of natural gas are contemplated. At present, oil and gas pipeline projects estimated at more than 8000 million dollars are being planned, of which about five to six thousand million dollars will probably pass the planning stage. These basic facts about the enormity of this pipeline project were presented by Dr G. K. Korbacher of the Institute for Aerospace Studies, University of Toronto, at a symposium entitled 'The North Slope p i p e l i n e - steel or composite'. An 8 ft diameter pipe operating at less than 9001bf/in 2 pressure is envisaged and its total length would be of tile order of 1600 miles. A feasible design for such a pipe in composite materials would be a glassmat/wire-sheet reinforced epoxy resin covered by an insulating layer of semi-rigid polyurethane foam, generated on site. T h e entire pipe could be continuously fabricated by filament winding, tested and laid in the final position by one machine operated by a small nunabe'r of men. T h e wall thickness of the pipe would be approximately ~ in and fibre loading about 58 wt %. Axial strength would
be about 85 0 0 0 1 b f / i n ' and modulus about 5 X 10' lbf/in'. T h e material costs for a composite pipeline are about the same as for an analogous steel pipeline but the composite pipe offers the nonstructural advantages of corrosion resistance, insulation and on-site fabrication. Corrosion resistance is obviously necessary both from a cost and a safety aspect. Insulation is necessary to keep the oil at a temperature of 60~100°F, when it flows freely, when ambient temperatures down to --70°F can be expected, and also to prevent the thawing of permafrost. On-site fabrication of large pipes from composite materials is clearly feasible (eg the Drostholm machine featured in Composites, Vol ], No 6, p 330); steel pipe would have to be transported ready made to the site. T h e case for a composite pipeline in such an extreme environment has still to be proved and work is i'n progress on model pipe systems. T h e existing techniques for steel pipe building will not help here: entirely new concepts of engineering design and construction need to be evolved for composite materials.