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New high modulus fibre
I COMPOSITES news I New high modulus fibre Warren K. Stratton of the Boeing Company, Philadelphia, USA, presented a paper at the SAMPE symposium, 21-23 April, on the evaluation of Du Pont's high modulus organic fibre PRD-49 type 1. Brief details about the fibre were given in the June issue of Composites (page 77). Du Pont list the following characteristics of the fibre : Organic filament (0.0004 in diameter) Low density (0'053 lb/in~; half that of aluminium) High modulus (23 million lbf/in2; 2.3Xaluminium) High strength (340000 lbf/in'; 5X aluminium) Potential low cost Usable to 4600F Chemically resistant Fire resistant (similar to Nomex) Handles and fabricates like glass fibre In January 1969, the Boeing Company and Du Pont entered into arn agreement to jointly evaluate PRD49-1 for use in aerospace applications. The work was conducted primarily by the Vertol Division and the Seattle Airplane Group. Composite specimens were made using an epoxy resin (Americaaa Cyanamid Company BP 907) and a 330-350°F cure. The average density of the cured composite was 0"055 lb/in 3. The data obtained indicated high fibre uniformity and that design strengths of 160000-175 000 lbf/in* and a design modulus of 1 2 - 1 3 X 1 0 ' lbf/in ~ should be attainable. Creep tests on PRD-49-1 composites showed that creep and creep rupture are similar to glass-fibre composites, and that there are no particular problems with PRD-49-1 composites. At a volume fraction of 60.9% fibre, the PRD-49-1 composite had a flexural strength of 81 300 lbf/in'~; a compressive strength in the range 33 000-50 000 lbf/,in'; and a shear strength of 76001bf/in ~. While the absolute compressive strength appears to be low, on a strength-to-weight basis PRD-49-1 composite compares favourably with other materials (eg 674 000- 940 000 in for PRD-49-1 / epoxy composite compared with 730 000 in for 7075-T6 aluminium). Fatigue data for PRD-49-1 composites show them to be about 26% better than S-glass at 10' cycles and equal to the boron produced during 1964-65. Du Pont tests have indicated that the erosion resistance and impact strength of PRD-49-1/epoxy composites is equal to or better than other composites. Since January 1969, the Boeing Company has used approximately 2001b of PRD-49-1 fibres to make a
number of engineering test and manufacturing development items. Fabricating experience has included resin-preimpregnated unidirectional tape, calendering resin-fibre into woven cloth, laminating laboratory test coupons, three 1/ll-scale CH-47 blades, and preliminary milling, sawing and turning tests. Several full-scale components have been fabricated, including radomes, antennas and blade boxes for the CH-47 helicopter and access doors for the BO-105 helicopter. Fabrication and test of a horizontal stabilizer for the BO-105 is nearing completion. A flight demonstration is tentatively planned for later this year. A spoiler for the Boeing 737 was built and tested in 1970, ~nd this provided a 14% weight reduction over the aluminium spoiler (compared with 15"3% for carbon-fibre composite). Aspects which require further research are the movement of fibres during cure and the negative coefficient of thermal expansion of PRD-49-1 (of carbon fibre). E. I. Du Pont de Nemours and Company Inc, 8111 Du Pont Building, Wilmington, Delaware 1989, USA
Self-lubricating bearings A liner material, Uniflon type R, for self-lubricating bearings with a friction rating of 0"06 (which the makers claim-is half that of any other material) has been developed in the USA by the North American Rockwell Group. T h e development is a result of work done for NASA by Rockwell who have granted sales rights in the UK, Europe and the Commonwealth to Rose Bearings, Saxilby (Baker Perkins Group). T h e British company is now incorporating the new material in their range of self-lubricating precision bearings. T h e composite type R material consists of a high strength fabric which has a coefficient of friction only slightly higher than PTrE. On this fabric is spread a mixture of PTF'E and a bonding matrix, with a low coefficient of friction. T h e makers say that the matrix is a polyallomer, ie, two polymers joined to produce a third with different properties: one polymer provides the necessary adhesion, the other provides elasticity. Type R bearings are designed to work at low surface speed. A typical dynamic application on a size 10 bearing (~in bore) gave a wear of 0.076 mm after 124 000 cycles when subject to a load of 74200N which gives a bearing pressure of 234.2 M N / m 2 when oscillated through -+-25 ° at 10 cycles per minute. T h e temperature range of type R is --75°C to 150°C.
These bearings have been used on various applications by many American aircraft companies, such as Boeing, Bell, General Dynamics, Lockheed and Douglas. Rose Bearings, Saxilby, Lincoln, UK
Stainless steel reinforcement for concrete Warm worked high strength stainless steel bar for reinforcing and fixing concrete sections is being produced by George Clarke of Sheffield under the name of Staifix. The bar, which is available in diameters of 10, 12, 16 and 20ram is ribbed to improve adhesion to the concrete matrix. Staifix is manufactured from Silver Fox 'Hi-proof' 316 Stainless Steel, a highly corrosion resistant steel of the 18/10/3 category produced by the Special Steels Division of the British Steel Corporation. T h e manufacturers list the following six advantages of Staifix : (1) High shear-stress/proof-stress ratio (80%) (reinforcement, pins, dowels, etc). (2) High limiting fatigue stress (cyclic stressed structural components, bridge hinge joints). (3) High strength and impact at subzero temperatures (cryogenic storage tanks). (4) High resistance to corrosion (chemical, industrial and marine environments). (5) High stress and low cover applications (cladding panels with substantial savings in weight). (6) Non-magnetic (laboratory, electrical generation applications). Because this steel is resistant to corrosion the covering of concrete can be as low as ½in (as compared with the usual 2in) and this can lead to weight savings of up to 40% on cladding panels, this weight saving in turn reduces the difficulties and costs of erection. Staifix has been used to provide the reinforcement and fixing of 1345 external concrete panels fitted to 500 dwellings in a development by Manchester Corporation at Moss Side. The largest panels are almost 20ft long and weigh 3½ tons. Well over a quarter of a million feet of Staifix is being used at a development consisting of over 1900 dwellings at Kidbrooke in South East London for the Greater London Council. Here Staifix is being used as reinforcement to form the load bearing rib fixtures on cladding panels where its high strength and corrosion resistant properties allow it to be positioned in a low concrete cover area. The Staifix bar bridges the gap between the main
CQMPQSITES Sentember 1971
135
number of engineering test and manufacturing development items. Fabricating experience has included resin-preimpregnated unidirectional tape, calendering resin-fibre into woven cloth, laminating laboratory test coupons, three 1/ll-scale CH-47 blades, and preliminary milling, sawing and turning tests. Several full-scale components have been fabricated, including radomes, antennas and blade boxes for the CH-47 helicopter and access doors for the BO-105 helicopter. Fabrication and test of a horizontal stabilizer for the BO-105 is nearing completion. A flight demonstration is tentatively planned for later this year. A spoiler for the Boeing 737 was built and tested in 1970, ~nd this provided a 14% weight reduction over the aluminium spoiler (compared with 15"3% for carbon-fibre composite). Aspects which require further research are the movement of fibres during cure and the negative coefficient of thermal expansion of PRD-49-1 (of carbon fibre). E. I. Du Pont de Nemours and Company Inc, 8111 Du Pont Building, Wilmington, Delaware 1989, USA
Self-lubricating bearings A liner material, Uniflon type R, for self-lubricating bearings with a friction rating of 0"06 (which the makers claim-is half that of any other material) has been developed in the USA by the North American Rockwell Group. T h e development is a result of work done for NASA by Rockwell who have granted sales rights in the UK, Europe and the Commonwealth to Rose Bearings, Saxilby (Baker Perkins Group). T h e British company is now incorporating the new material in their range of self-lubricating precision bearings. T h e composite type R material consists of a high strength fabric which has a coefficient of friction only slightly higher than PTrE. On this fabric is spread a mixture of PTF'E and a bonding matrix, with a low coefficient of friction. T h e makers say that the matrix is a polyallomer, ie, two polymers joined to produce a third with different properties: one polymer provides the necessary adhesion, the other provides elasticity. Type R bearings are designed to work at low surface speed. A typical dynamic application on a size 10 bearing (~in bore) gave a wear of 0.076 mm after 124 000 cycles when subject to a load of 74200N which gives a bearing pressure of 234.2 M N / m 2 when oscillated through -+-25 ° at 10 cycles per minute. T h e temperature range of type R is --75°C to 150°C.
These bearings have been used on various applications by many American aircraft companies, such as Boeing, Bell, General Dynamics, Lockheed and Douglas. Rose Bearings, Saxilby, Lincoln, UK
Stainless steel reinforcement for concrete Warm worked high strength stainless steel bar for reinforcing and fixing concrete sections is being produced by George Clarke of Sheffield under the name of Staifix. The bar, which is available in diameters of 10, 12, 16 and 20ram is ribbed to improve adhesion to the concrete matrix. Staifix is manufactured from Silver Fox 'Hi-proof' 316 Stainless Steel, a highly corrosion resistant steel of the 18/10/3 category produced by the Special Steels Division of the British Steel Corporation. T h e manufacturers list the following six advantages of Staifix : (1) High shear-stress/proof-stress ratio (80%) (reinforcement, pins, dowels, etc). (2) High limiting fatigue stress (cyclic stressed structural components, bridge hinge joints). (3) High strength and impact at subzero temperatures (cryogenic storage tanks). (4) High resistance to corrosion (chemical, industrial and marine environments). (5) High stress and low cover applications (cladding panels with substantial savings in weight). (6) Non-magnetic (laboratory, electrical generation applications). Because this steel is resistant to corrosion the covering of concrete can be as low as ½in (as compared with the usual 2in) and this can lead to weight savings of up to 40% on cladding panels, this weight saving in turn reduces the difficulties and costs of erection. Staifix has been used to provide the reinforcement and fixing of 1345 external concrete panels fitted to 500 dwellings in a development by Manchester Corporation at Moss Side. The largest panels are almost 20ft long and weigh 3½ tons. Well over a quarter of a million feet of Staifix is being used at a development consisting of over 1900 dwellings at Kidbrooke in South East London for the Greater London Council. Here Staifix is being used as reinforcement to form the load bearing rib fixtures on cladding panels where its high strength and corrosion resistant properties allow it to be positioned in a low concrete cover area. The Staifix bar bridges the gap between the main
CQMPQSITES Sentember 1971
135