Why composites? 13 ponents in existing products and the use in new products that are made possible by the new materials.Direct substitution of a ceramic or composite part for a metal part is not likely to take full advantage of the superior properties and design flexibility of advanced materials.Substitution of conventional structural metals such as steel and aluminum alloy by composites is highly unlikely. Because of their low cost and manufacturability,these metals are ideally suited for applications in which they are now used.On the other hand,the metal industry has responded to the potential of direct substitution by developing new alloys with improved pro- perties,such as high-strength,low-alloy steel and aluminum- lithium.According to this assessment,significant displacement of metals could occur in four potential markets:aircraft,automobiles, containers and constructions. In the choice of material substitution,a variety of factors need to be taken into account.Compton and Gjostein (1986)analyzed the weight saving and cost for material substitution for ground trans- portation.Weight reduction that can be achieved in designing a part by substituting a light-weight material for a conventional one depends critically on the part's function.A unit volume of cast aluminum weighs 63%less than an equal volume of cast iron.Cast iron,however,is stiffer than cast aluminum.Therefore if a hypothetical cast-aluminum part is to be as stiff as a cast-iron one, more aluminum would have to be used and the weight saving would be reduced to 11%.If equal loading carrying capacity is required in the hypothetical aluminum part,the weight saving would be 56%. (In actual design situations the weight saving offered by the substitution of aluminum for cast iron ranges from 35 to 60%.) Similarly,aluminum and fiber-reinforced plastics are much lighter than mild (ordinary)steel by volume.The weight savings,however, are much smaller if equal stiffness or equal collapse load and bending stiffness (a measure of structural strength)is needed. High-strength steel is no lighter by volume than mild steel,nor is it stiffer.Where structural strength is the main concern,however, high-strength steel does offer a weight saving:18%in the example discussed by Compton and Gjostein. In terms of innovative designs and new products based upon advanced composites,the automotive industry undoubtedly pro- vides an excellent paradigm.The use of polymer matrix composites for primary body structures and chassis/suspension systems is under evaluation by the major automobile manufacturers.The potential advantages of using composites are:weight reduction and resulting
Why composites'? 13 ponents in existing products and the use in new products that are made possible by the new materials. Direct substitution of a ceramic or composite part for a metal part is not likely to take full advantage of the superior properties and design flexibility of advanced materials. Substitution of conventional structural metals such as steel and aluminum alloy by composites is highly unlikely. Because of their low cost and manufacturability, these metals are ideally suited for applications in which they are now used. On the other hand, the metal industry has responded to the potential of direct substitution by developing new alloys with improved properties, such as high-strength, low-alloy steel and aluminumlithium. According to this assessment, significant displacement of metals could occur in four potential markets: aircraft, automobiles, containers and constructions. In the choice of material substitution, a variety of factors need to be taken into account. Compton and Gjostein (1986) analyzed the weight saving and cost for material substitution for ground transportation. Weight reduction that can be achieved in designing a part by substituting a light-weight material for a conventional one depends critically on the part's function. A unit volume of cast aluminum weighs 63% less than an equal volume of cast iron. Cast iron, however, is stiffer than cast aluminum. Therefore if a hypothetical cast-aluminum part is to be as stiff as a cast-iron one, more aluminum would have to be used and the weight saving would be reduced to 11%. If equal loading carrying capacity is required in the hypothetical aluminum part, the weight saving would be 56%. (In actual design situations the weight saving offered by the substitution of aluminum for cast iron ranges from 35 to 60%.) Similarly, aluminum and fiber-reinforced plastics are much lighter than mild (ordinary) steel by volume. The weight savings, however, are much smaller if equal stiffness or equal collapse load and bending stiffness (a measure of structural strength) is needed. High-strength steel is no lighter by volume than mild steel, nor is it stiffer. Where structural strength is the main concern, however, high-strength steel does offer a weight saving: 18% in the example discussed by Compton and Gjostein. In terms of innovative designs and new products based upon advanced composites, the automotive industry undoubtedly provides an excellent paradigm. The use of polymer matrix composites for primary body structures and chassis/suspension systems is under evaluation by the major automobile manufacturers. The potential advantages of using composites are: weight reduction and resulting
14 Introduction fuel economy;improved overall quality and consistency in manu- facturing;lower assembly costs due to parts consolidation;lower investment costs for plant,facilities,and tooling;improved corro- sion resistance;and lower operating costs.The major barriers to the large-scale applications of composites are the lack of high-speed, high-quality,low-cost manufacturing processes;uncertainties re- garding crash integrity and long-term durability;and lack of adequate technologies for repair and recycling of polymer compos- ite structures.According to Compton and Gjostein,glass fiber reinforced composites are capable of meeting the functional re- quirements of the most highly loaded automotive structures.Candi- date fabrication methods include resin transfer molding,compres- sion molding,and filament winding.Among these methods,resin transfer molding seems the most promising,although none of these methods can satisfy all of the production requirements at this time. There is no doubt that the large-scale adoption of polymer matrix composites for automotive structures would have a major tech- nological impact on the fabrication and assembly of automobiles. Fig.1.6.Temperature capabilities of polymer,metal and ceramic matrix materials.(After Mody and Majidi 1987,with permission from the Society of Manufacturing Engineers.) Polymer matrix Metal matrix Ceramic matrix composites composites composites >2000 1500 1400题 ainjeiadwal 1200 1000 650 600 300 350 230 wnisauzeW sKol[e-adns apiu uoorl!S uoqI
14 Introduction fuel economy; improved overall quality and consistency in manufacturing; lower assembly costs due to parts consolidation; lower investment costs for plant, facilities, and tooling; improved corrosion resistance; and lower operating costs. The major barriers to the large-scale applications of composites are the lack of high-speed, high-quality, low-cost manufacturing processes; uncertainties regarding crash integrity and long-term durability; and lack of adequate technologies for repair and recycling of polymer composite structures. According to Compton and Gjostein, glass fiber reinforced composites are capable of meeting the functional requirements of the most highly loaded automotive structures. Candidate fabrication methods include resin transfer molding, compression molding, and filament winding. Among these methods, resin transfer molding seems the most promising, although none of these methods can satisfy all of the production requirements at this time. There is no doubt that the large-scale adoption of polymer matrix composites for automotive structures would have a major technological impact on the fabrication and assembly of automobiles. Fig. 1.6. Temperature capabilities of polymer, metal and ceramic matrix materials. (After Mody and Majidi 1987, with permission from the Society of Manufacturing Engineers.) u Polymer matrix composites 300 X 8. - 3 ei m smal S T3/imi Pol) u "55 cd "7-1rmoi the Z Metal matrix composites 1000 600 Ceramic matrix composites >2000- 1500 I 1 1200 £ £ E ^ D 3 3 O 3OI 1 -5 ^ H g. a •= .a .a .a R E S E < ^3 ™ — c ^ =
Why composites? 15 Another technological aspect that motivates the use of fiber composites pertains to the demand of an elevated temperature en- vironment (Steinberg 1986).Temperature capabilities of polymer, metal and ceramic matrix materials are shown in Fig.1.6 (Mody and Majidi 1987).The demand for high-temperature applications of composites is best exemplified by the need for aerospace materials. The U.S.goals for subsonic,supersonic and hypersonic flight and for space explorations require alloys and composites with superior strength,light weight and resistance to heat.According to Stein- berg,the evolution of aircraft has required continual improvements in materials because increased speed raises the heating of the skin from friction with the air and increased power raises the tempera- ture of the engine.Figure 1.7 shows the changes in skin tempera- tures from aircraft of the 1930s to the proposed Orient Express which is a transatmospheric craft capable of cruising at great speed in space.The skin materials have progressed from wood and fabric to advanced alloys of aluminum,nickel and titanium and graphite fiber reinforced polymer composites. Figure 1.8 shows the changes in engine temperature from engines cooled by water to those of scramjets.The need for composites in engine components can be understood from the evolution in engine Fig.1.7.Evolution of aircraft skin temperatures.(From 'Materials for Aerospace',Steinberg).Copyright C(1986)by Scientific American,Inc. All rights reserved. Skin temperatures 1930s trainer 50°C Second World War fighter 90°C 1980s interceptor 430C Space Shuttle 1090°C Orient Express 1650°C 500 1000 1500 2000 2500 Temperature (C)
Why composites? 15 Another technological aspect that motivates the use of fiber composites pertains to the demand of an elevated temperature environment (Steinberg 1986). Temperature capabilities of polymer, metal and ceramic matrix materials are shown in Fig. 1.6 (Mody and Majidi 1987). The demand for high-temperature applications of composites is best exemplified by the need for aerospace materials. The U.S. goals for subsonic, supersonic and hypersonic flight and for space explorations require alloys and composites with superior strength, light weight and resistance to heat. According to Steinberg, the evolution of aircraft has required continual improvements in materials because increased speed raises the heating of the skin from friction with the air and increased power raises the temperature of the engine. Figure 1.7 shows the changes in skin temperatures from aircraft of the 1930s to the proposed Orient Express which is a transatmospheric craft capable of cruising at great speed in space. The skin materials have progressed from wood and fabric to advanced alloys of aluminum, nickel and titanium and graphite fiber reinforced polymer composites. Figure 1.8 shows the changes in engine temperature from engines cooled by water to those of scramjets. The need for composites in engine components can be understood from the evolution in engine Fig. 1.7. Evolution of aircraft skin temperatures. (From 'Materials for Aerospace', Steinberg). Copyright © (1986) by Scientific American, Inc. All rights reserved. 1930s trainer Second World War fighter 980s interceptor Space Shuttle Orient Express Skin 50°C 90°C r — temperatures 1 430°C 1 090°C 1650°C 1 1 1 1 500 1000 1500 Temperature (°C) 2000 2500
16 Introduction performance.According to Steinberg,the thrust delivered by a big jet engine for transport and cargo aircraft has increased about six fold over the past 30 years,approaching 294000 newtons (66000 pounds)now.During the same period the weight of the engine has increased by a factor of only two or three.The thrust-to-weight ratio of the military aircraft may approach 15:1 by the year 2000.The performance of jet engines has been made possible partially with improvements in turbine blades.It is predicted that with the further improvements in blades and other aspects of aircraft propulsion,a typical propulsion system in the year 2000 will be likely to contain about 20%each of composites, steel,nickel and aluminum,15%titanium,2%ordered alloys (aluminides,e.g.titanium-aluminum or nickel-aluminum)and 1% ceramics (Steinberg 1986). Clark and Flemings (1986)have also examined the present and future material systems for meeting the engine operating tempera- ture requirements.In Fig.1.9 the lowest band on the graph indicates the temperature increase that has been achieved so far through improvements in nickel-based super-alloys,the standard turbine material.It is believed that in the coming decades alloy turbine blades made of metal strengthened by directional crystal structures,and blades protected by a coating of ceramics or special Fig.1.8.Evolution of aircraft engine temperatures.(From 'Materials for Aerospace'Steinberg).Copyright C(1986)by Scientific American,Inc. All rights reserved. Engine temperatures First World War water-cooled 150C 1930s air-cooled 300°C Fan-jct 600C Turbojet 1090°C Scramjet 1930°C 500 1000 1500 2000 2500 Temperature (C)
16 Introduction performance. According to Steinberg, the thrust delivered by a big jet engine for transport and cargo aircraft has increased about six fold over the past 30 years, approaching 294 000 newtons (66 000 pounds) now. During the same period the weight of the engine has increased by a factor of only two or three. The thrust-to-weight ratio of the military aircraft may approach 15:1 by the year 2000. The performance of jet engines has been made possible partially with improvements in turbine blades. It is predicted that with the further improvements in blades and other aspects of aircraft propulsion, a typical propulsion system in the year 2000 will be likely to contain about 20% each of composites, steel, nickel and aluminum, 15% titanium, 2% ordered alloys (aluminides, e.g. titanium-aluminum or nickel-aluminum) and 1% ceramics (Steinberg 1986). Clark and Flemings (1986) have also examined the present and future material systems for meeting the engine operating temperature requirements. In Fig. 1.9 the lowest band on the graph indicates the temperature increase that has been achieved so far through improvements in nickel-based super-alloys, the standard turbine material. It is believed that in the coming decades alloy turbine blades made of metal strengthened by directional crystal structures, and blades protected by a coating of ceramics or special Fig. 1.8. Evolution of aircraft engine temperatures. (From 'Materials for Aerospace' Steinberg). Copyright © (1986) by Scientific American, Inc. All rights reserved. First World War water-cooled 1930s air-cooled Fan-jet Turbojet Scramjet Engine temperatures 150°C <00°C 1 I 1090°C ••j;^j" -~ ;<m 1 1 1 1 1930°C 1 500 1000 1500 Temperature (°C) 2000 2500
Trends and opportunities 17 alloys,will allow an increase in turbine-inlet temperatures.How- ever,ultimately,the demand for very-high-temperature material can only be met by ceramic matrix composites and carbon-carbon composites. 1.4 Trends and opportunities Kelly (1987a&b),in a recent outline of the trends in materials science and processing,examined the status of fiber composites.It was concluded that the development of this field has been mainly driven by the aerospace industry.This development has contributed to the growth of a relatively small body of new science which related the colligative properties of fiber composites to the properties of the individual components.There have been interesting combinations of properties not hitherto available in single phase materials,for example,a negative thermal expansion and a negative Poisson's ratio.However,there have not been large non-linear synergistic effects.There is perhaps not much new science of the colligative properties of composites.However,in Kelly's view,the studies of design of fiber composites are critical for Fig.1.9.Rise in the operating temperature of jet engines with time. (From 'Advanced Materials and Economy'Clark and Flemings).Copy- right C(1986)by Scientific American,Inc.All rights reserved. 1600 1500 Ceramic matrix composites 1400 1300 Thermal-barrier coatings 1200 1100 Directional metal structures 1000 900 Conventionally cast super-alloys 800 1960 1970 1980 1990 2000 2010 Year
Trends and opportunities 17 alloys, will allow an increase in turbine-inlet temperatures. However, ultimately, the demand for very-high-temperature material can only be met by ceramic matrix composites and carbon-carbon composites. 1.4 Trends and opportunities Kelly (1987a&b), in a recent outline of the trends in materials science and processing, examined the status of fiber composites. It was concluded that the development of this field has been mainly driven by the aerospace industry. This development has contributed to the growth of a relatively small body of new science which related the colligative properties of fiber composites to the properties of the individual components. There have been interesting combinations of properties not hitherto available in single phase materials, for example, a negative thermal expansion and a negative Poisson's ratio. However, there have not been large non-linear synergistic effects. There is perhaps not much new science of the colligative properties of composites. However, in Kelly's view, the studies of design of fiber composites are critical for Fig. 1.9. Rise in the operating temperature of jet engines with time. (From 'Advanced Materials and Economy' Clark and Flemings). Copyright © (1986) by Scientific American, Inc. All rights reserved. U 2L o 1600 1500 Ceramic matrix composites Directional metal structures Conventionally cast super-alloys 1970 1980 1990 Year 2000 2010