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Metal matrix composites: Property optimisation and applications
Conference report Metal Matrix Composites: Property Optimisation and Applications London, UK, 8-9 November 1989 Organized by: The Institute of Metals This was the second conference organized by The Institute of Metals on metal matrix composites (MMC). It attracted approximately 170 delegates, with Europe being well represented. Such an attendance highlights the combination of academic interest and commercial development that this class of material continues to receive. Although the venue was essentially filled to capacity, the conference staff dealt with the 'domestic arrangements' in a very efficient manner and the whole event went very smoothly. The conference was sub-titled 'Property Optimisation and Applications' but it was the first topic that was the subject of the majority of the papers. Little emerged on current or imminent applications of these materials, although it was clear that much work is being done to put the technology in place that is required for future applications. Of course, many developments would not be expected to be publicized until after their completion, so we still await a detailed appreciation of where these materials will really be used. The technical sessions were divided into a review of applications in automotive and aerospace, followed by five sessions divided into the topics detailed below. There were 30 presentations in all and it can honestly be said that they were of a high standard. There was also a poster session to cover work that could not be fitted into the time available. It would not be appropriate to cover all the papers here and the following is just a selection. A full list of the papers presented can be found at the end of the report. For the sake of brevity, the name of the author making the presentation is given in the text; the co-authors are given in the list at the end. The opening session consisted of two reviews on applications: P.E. Irving (GKN Technology) dealt with the automotive industry while D. Charles (BAe) discussed aerospace. With regard to automotive, it was pointed out that the cost environment tends to militate against the introduction of MMC, since there is little or no premium associated with weight saving. Many of the other benefits thought to be offered by MMC can be difficult and expensive to quantify. Nevertheless, examples can be identified where use of MMC could lead to improved performance or an overall cost saving and this was discussed, using pistons, connecting rods and propeller shafts as examples. D. Charles then presented a considerably more positive view with regard to aerospace usage, where there is perceived to be a considerable potential for significant use by the year 2000. After outlining the potential in aeroengines, the author gave a detailed discussion of airframe applications, illustrated by reference to
feasibility studies at BAe. Whilst many applications are based on the mechanical properties, others such as guidance components will utilize the unusual physical properties that can be obtained. The competition from other materials was then emphasized and the resultant cost targets for MMC were discussed. The second session was entitled 'Case Studies' and it contained five papers on a wide variety of topics. C. Baker (Alcan) outlined the Duralcan route to particulate MMC and described the properties achieved to date. A plant with 12 000 tons capacity is expected to come on stream in 1990. A summary of the applications for the material revealed that, amongst the various aerospace components described, an investment cast gimball mounting was in production. Several automotive products were also under active evaluation but sporting goods were identified as the sector for initial volume applications, and light-weight MMC bicycle frames are expected to appear in 1990. Two further papers considered aerospace applications. C.J. Peel (RAe) considered the general scope of particulate MMC usage for air-frames, emphasizing that the fatigue crack growth and toughness properties required optimization, since current levels were likely to limit service use. K.S. Broad (BAe) then gave a detailed description of the design, fabrication, NDE and testing of various particulate and fibre-reinforced MMC components. A keel longeron tube in extruded particulate was identified as an attractive application. Jeffrey (Alcan) then addressed the problems of die wear encountered when extruding particulate MMC. Clearly, the die lives achieved will have a strong influence on the cost of extruded MMC parts and a detailed description was given of the performance of the die materials investigated in the search for material with the required combination of wear resistance and toughness. Finally, Mykura (Cray) described the design and manufacture of a fibre-reinforced automotive connecting rod. Further development was required in order to reduce the cycle time if mass production was to be achieved but it was also considered that MMC would allow a radical new design to be developed. The second technical session, on Manufacturing and Processing, consisted of seven papers: two were on particulate MMC and the remainder on fibre-reinforced materials. Amongst these, Borradaile (Norske Hydro) described the secondary processing of particulate MMC using conventional, low-cost casting technology. Essentially he presented a positive view of what could be achieved; in some instances it was even possible to turn problems into an advantage. For example, settling of the ceramic particles was held to improve the wear
COMPOSITES. MAY 1990 263
resistance of horse-shoes on the face that required the wear resistance. Miller (BP) gave an account of the optimization of the properties of extruded particulate composites based on their powder metallurgy route. It was held that the properties (stiffness, strength and ductility) meet the targets set by the air-frame manufacturers. Ward-Close (RAe, Farnborough) then described the virtues of a coated fibre process for the production of titanium matrix material reinforced with continuous fibres. The fibre distribution achieved was so good that the speaker felt the need to point out that the micrographs were real and not an idealization. The session on ‘Interfaces’ attracted four papers. Detailed metallographic studies of the interfaces were described by Reeves (University of Cambridge), for SIC particulate reinforced titanium MMC as manufactured by both the vacuum plasma spray and powder metallurgy routes, and by Fox (Imperial College), on ICI alumina fibre reinforced Al-Mg and Al-Li composites produced by melt infiltration. Hughes (Alcan) discussed the interfaces obtained in SIC and B,C particulate reinforced 2618 and 8090 matrices, as manufactured by the Co spray process. The interfaces in the Sic materials were generally clean but this was not the case for the B,C. Tensile properties were then related to the apparent interfacial strength, with good tensile strength being associated with the occurrence of broken particles, whilst low values occurred if the particles pulled out. Further work is required to develop an overall understanding. Johnson (Imperial College) reported on studies of the reaction kinetics between SIC particulate and molten Al and Al-Si. This reaction has, of course, considerable importance for composites fabricated by the molten metal route or subsequently processed by this route. The fourth session, on ‘Deformation’, comprised six papers on a variety of topics. Clyne (University of Cambridge) described the dimensional changes that were observed to occur under thermal cycling of a whisker-reinforced Mg-Li composite and discussed the reasons for these changes in terms of the internal residual stresses caused by thermal expansion mismatch. There followed papers on finite element based micromechanical modelling of continuous fibre MMC and on re-crystallization and texture development in particulate MMC. The final paper in the session, by Humphries (Imperial College), explored the use of conventional metallurgical modelling to predict the strength of particulate composites through characterizing the effect of such variables as work hardening, and grain and precipitation strengthening. The models were then employed to predict the experimental results obtained for model Al-SIC particulate composites, with fair agreement between experiment and theory. The final session, ‘Failure’, covered fundamental fatigue and fracture studies on MMC. Six papers were presented, the majority again considering the particulate. Knowles (University of Cambridge) discussed the fatigue crack growth rate and fracture toughness of 809O/SiC particulate material, finding the growth rates comparable to those reported for the matrix alloy at low and intermediate AK, with crack growth in the composite occurring essentially through the matrix. 264 COMPOSlTES . MAY 1990
The presence of residual quenching stresses was observed, which had a marked influence on the resultant crack front shape. Lloyd (Alcan), in investigating the reasons for the low tensile ductility of particulate MMC, concluded that cracked particles were not the reason for low ductility and suggested that the role of clusters of particles requires further investigation. The other two papers considered the appropriateness of fracture toughness test standards to MMC (Roebuck, NPL) and the micromechanical modelling of tensile strength (Mummery, Oxford). Blom (R.I.T., Stockholm) reported short and long crack work on Saffil-reinforced Al-Mg material. Early short crack growth was found to occur along the fibre/matrix interface before the crack started to grow as a dominant crack. Considerable crack closure was observed, due to the irregularity of the crack path. The single paper on continuous fibre composites, by Guild (QMC, London) considered the finite-element modelling of the composite behaviour in compression. Altogether a successful event and I look forward to the next in the series. N.J. Hurd
Papers presented OPENING SESSION Applications of MMC’S in the automotive industry, P.E. Irving and N.J. Hurd (GKN Technology L td, Wolverhampton) Metal matrixcomposites-readyfortake-off? D. Charles (British Aerospace Plc, Bristol) SESSION ONE-CASE STUDIES Properties and applications of particulate reinforced aluminium MMC’S, P.L. Morris and C. Baker (A/can International Ltd, Banbury) Progress towards the optimisation of particulate reinforced composites for aerospace applications, C.J. Peel, R. Moreton and S.M. Flitcroft (RoyalAerospace Establishment, Farnborough) Design, manufacture and test of representative metal matrix composite aircraft components, K. Broad (British Aerospace, Commercial Aircraft Ltd, Bristol) Extrusion of metal matrix composites: choice of die materials, P.W. Jeffrey, R.W. Hains, P.L. Morris and C. Jowett (A/can International Ltd, Ontario, Canada) The production of afibre reinforced aluminium connecting rod using theCray Process, N. Mykura and I.A. Strange (Cray Advanced Materials Ltd, Yeovil) SESSION TWO- MANUFACTURING/PROCESSING Production and properties of continuously reinforced titanium alloy MMC , C.M. Ward-Close and P.G. Partridge (RoyalAerospace Establishment, Farnborough) ‘Rapidly’ solidified safimax fibre reinforced MMC’s, Q. Li and G. McCartney (Liverpool University) and A.M. Walker (ICI Advanced Materials Group, Runcornj The secondary processing of particulate reinforced aluminium composites, J.B. Borradaile (Hydra Aluminium as, Havik Norway) High temperature joining of fibre reinforced aluminium alloys, N.J. Lindsay and V.D. Scott (University ofBath) and R.L. Trumper (ARE Holten Heath, Poole) Extrusion processing of aluminium alloy base metal matrix composites.T. Bryant, S.P. Derham and W.S. Miller (British Petroleum Research International, Sunbury-on- Thames) and A.E.J. Forno (NationalPhysicalLaboratory, Teddington)
Some microstructural features of interest in squeeze-cast SIC fibre aluminium composites, X. Dumant and G. Regazzoni (Pechiney Research Centre, Voreppe, France)
Texture development in aluminium alloy-SiC metal matrix composites, A.W. Bowen (RoyalAerospace Establishment, Farnborough) and F.J. Humphreys (ImperialCollege, London)
Drilling of fibre reinforced aluminium, L. Cronjager and D. Meister (Universitat Dortmund, lnstitut fur Spanende Fertigung, Dortmund, FRGJ
Microstructure and strength of powder blended AI-SIC composites, N. Hansen, Y.L. Liu and H. Lilholt (Rise National Laboratory, Roskilde, Denmark) and C.Y. Barlow (University of Cambridge)
SESSIONTHREE - INTERFACES
Modelling the microstructure and mechanical behaviour of particulate composites, F.J. Humphreys (imperial College, London)
Some effects of interfacial reaction layers in SIC particulatereinforcedtitanium,A.S. Reeves, W.M. St0bbsandT.W. Clyne (University of Cambridge) and H. Dunlop (Pechiney Research Centre, Voreppe, France) The interaction between liquid aluminium and particulate silicon carbide in AI-SIC MMC’S, P.K. Johnson, H.M. Flower and D.R.F. West (Imperial College, London) Microstructure-property relationships in spray deposited aluminium - SIC metal matrix composites, I.R. Hughes, A.J. Owen, S.A. Court and J. White (Alcan International Ltd, Banbury) TEM characterisation of fibre-matrix interfaces in Al alloy based MMC , S. Fox, D.R.F. West and H.M. Flower (Imperial College, London) SESSION FOUR - DEFORMATION Stress relaxation and strain ratchetting in whisker-reinforced Ma-Li allovs, CM. Warwick, J.F. Mason andT.W. Clvne (University of Cambridge) Micromechanical modelling of metal matrix composites using finite element analysis, M.R. Wisnom (University of Bristol) Factors affecting recrystallization in fibrous and particulate MMC ’S, R.A. Shahani and T.W. Clyne (University of Cambridge)
SESSION FIVE - FAILURE Fatigue and fracture of an aluminium - silicon carbide composite, D.M. Knowles and J.E. King (University of Cambridge) and C.W. Brown (British Petroleum International, Sunbury-onThames) Long and short fatigue crack growth and overload effects in Al 0 shortfibre reinforced AI-ZMg alloy, A.F. Blom, H.L. Groth (The Royallnstitute of Technology, Stockholm, Sweden), A. Melander, S. Preston and S. Savage /Swedish Institute for Metals Research, Stockholm, Sweden) Fracture toughness test procedures for particulate metal matrix composites, B. Roebuck and J.D. Lord (National Physical Laboratory, Teddington) The influence of microstructure on the compressive failure of metal matrix composites, F.J. Guild and P.J. Hogg (Queen Mary College, London) and D. Green (University of Bristol) The micromechanisms of fracture in particle reinforced metal matrix composites, P. Mummery and B. Derby (University of Oxford) Deformation and fracture in particulate reinforced Al composites, D.J. Lloyd IA/can International Ltd, Kingston, Ontario, Canada)
NDT International contains l l
infernational the independent journal of nondestructive testing
l
NDT international covers l l
NDT International provides a unique package of information on research and development in nondestructive testing methods and their industrial applications for quality assurance of raw materials, manufacturing products and structures.
Butterworths
Refereed research papers, state-of-the-art surveys, technical notes and case studies News and reviews of new equipment and services, industrial developments, conferences, exhibitions and publications NDT info - the fullest serially published survey of literature and patents in the field
l l l
Detection, sizing and characterization of materials inhomogeneities Measurement of component and defect dimensions Evaluation of material properties Assessment of integrity and strength of in-service structures Condition monitoring of operating plant
NDT International Published bimonthly ISSN 0308-9126 For a sample copy and further information contact Geraldine Hills at Butterworth Scientific Ltd, PO Box 63, Westbury House, Bury Street, Guildford, Surrey GU2 5BH, UK. Telephone 0483 300966 Telex 859556 SCITEC G
COMPOSITES . MAY 1990 265
feasibility studies at BAe. Whilst many applications are based on the mechanical properties, others such as guidance components will utilize the unusual physical properties that can be obtained. The competition from other materials was then emphasized and the resultant cost targets for MMC were discussed. The second session was entitled 'Case Studies' and it contained five papers on a wide variety of topics. C. Baker (Alcan) outlined the Duralcan route to particulate MMC and described the properties achieved to date. A plant with 12 000 tons capacity is expected to come on stream in 1990. A summary of the applications for the material revealed that, amongst the various aerospace components described, an investment cast gimball mounting was in production. Several automotive products were also under active evaluation but sporting goods were identified as the sector for initial volume applications, and light-weight MMC bicycle frames are expected to appear in 1990. Two further papers considered aerospace applications. C.J. Peel (RAe) considered the general scope of particulate MMC usage for air-frames, emphasizing that the fatigue crack growth and toughness properties required optimization, since current levels were likely to limit service use. K.S. Broad (BAe) then gave a detailed description of the design, fabrication, NDE and testing of various particulate and fibre-reinforced MMC components. A keel longeron tube in extruded particulate was identified as an attractive application. Jeffrey (Alcan) then addressed the problems of die wear encountered when extruding particulate MMC. Clearly, the die lives achieved will have a strong influence on the cost of extruded MMC parts and a detailed description was given of the performance of the die materials investigated in the search for material with the required combination of wear resistance and toughness. Finally, Mykura (Cray) described the design and manufacture of a fibre-reinforced automotive connecting rod. Further development was required in order to reduce the cycle time if mass production was to be achieved but it was also considered that MMC would allow a radical new design to be developed. The second technical session, on Manufacturing and Processing, consisted of seven papers: two were on particulate MMC and the remainder on fibre-reinforced materials. Amongst these, Borradaile (Norske Hydro) described the secondary processing of particulate MMC using conventional, low-cost casting technology. Essentially he presented a positive view of what could be achieved; in some instances it was even possible to turn problems into an advantage. For example, settling of the ceramic particles was held to improve the wear
COMPOSITES. MAY 1990 263
resistance of horse-shoes on the face that required the wear resistance. Miller (BP) gave an account of the optimization of the properties of extruded particulate composites based on their powder metallurgy route. It was held that the properties (stiffness, strength and ductility) meet the targets set by the air-frame manufacturers. Ward-Close (RAe, Farnborough) then described the virtues of a coated fibre process for the production of titanium matrix material reinforced with continuous fibres. The fibre distribution achieved was so good that the speaker felt the need to point out that the micrographs were real and not an idealization. The session on ‘Interfaces’ attracted four papers. Detailed metallographic studies of the interfaces were described by Reeves (University of Cambridge), for SIC particulate reinforced titanium MMC as manufactured by both the vacuum plasma spray and powder metallurgy routes, and by Fox (Imperial College), on ICI alumina fibre reinforced Al-Mg and Al-Li composites produced by melt infiltration. Hughes (Alcan) discussed the interfaces obtained in SIC and B,C particulate reinforced 2618 and 8090 matrices, as manufactured by the Co spray process. The interfaces in the Sic materials were generally clean but this was not the case for the B,C. Tensile properties were then related to the apparent interfacial strength, with good tensile strength being associated with the occurrence of broken particles, whilst low values occurred if the particles pulled out. Further work is required to develop an overall understanding. Johnson (Imperial College) reported on studies of the reaction kinetics between SIC particulate and molten Al and Al-Si. This reaction has, of course, considerable importance for composites fabricated by the molten metal route or subsequently processed by this route. The fourth session, on ‘Deformation’, comprised six papers on a variety of topics. Clyne (University of Cambridge) described the dimensional changes that were observed to occur under thermal cycling of a whisker-reinforced Mg-Li composite and discussed the reasons for these changes in terms of the internal residual stresses caused by thermal expansion mismatch. There followed papers on finite element based micromechanical modelling of continuous fibre MMC and on re-crystallization and texture development in particulate MMC. The final paper in the session, by Humphries (Imperial College), explored the use of conventional metallurgical modelling to predict the strength of particulate composites through characterizing the effect of such variables as work hardening, and grain and precipitation strengthening. The models were then employed to predict the experimental results obtained for model Al-SIC particulate composites, with fair agreement between experiment and theory. The final session, ‘Failure’, covered fundamental fatigue and fracture studies on MMC. Six papers were presented, the majority again considering the particulate. Knowles (University of Cambridge) discussed the fatigue crack growth rate and fracture toughness of 809O/SiC particulate material, finding the growth rates comparable to those reported for the matrix alloy at low and intermediate AK, with crack growth in the composite occurring essentially through the matrix. 264 COMPOSlTES . MAY 1990
The presence of residual quenching stresses was observed, which had a marked influence on the resultant crack front shape. Lloyd (Alcan), in investigating the reasons for the low tensile ductility of particulate MMC, concluded that cracked particles were not the reason for low ductility and suggested that the role of clusters of particles requires further investigation. The other two papers considered the appropriateness of fracture toughness test standards to MMC (Roebuck, NPL) and the micromechanical modelling of tensile strength (Mummery, Oxford). Blom (R.I.T., Stockholm) reported short and long crack work on Saffil-reinforced Al-Mg material. Early short crack growth was found to occur along the fibre/matrix interface before the crack started to grow as a dominant crack. Considerable crack closure was observed, due to the irregularity of the crack path. The single paper on continuous fibre composites, by Guild (QMC, London) considered the finite-element modelling of the composite behaviour in compression. Altogether a successful event and I look forward to the next in the series. N.J. Hurd
Papers presented OPENING SESSION Applications of MMC’S in the automotive industry, P.E. Irving and N.J. Hurd (GKN Technology L td, Wolverhampton) Metal matrixcomposites-readyfortake-off? D. Charles (British Aerospace Plc, Bristol) SESSION ONE-CASE STUDIES Properties and applications of particulate reinforced aluminium MMC’S, P.L. Morris and C. Baker (A/can International Ltd, Banbury) Progress towards the optimisation of particulate reinforced composites for aerospace applications, C.J. Peel, R. Moreton and S.M. Flitcroft (RoyalAerospace Establishment, Farnborough) Design, manufacture and test of representative metal matrix composite aircraft components, K. Broad (British Aerospace, Commercial Aircraft Ltd, Bristol) Extrusion of metal matrix composites: choice of die materials, P.W. Jeffrey, R.W. Hains, P.L. Morris and C. Jowett (A/can International Ltd, Ontario, Canada) The production of afibre reinforced aluminium connecting rod using theCray Process, N. Mykura and I.A. Strange (Cray Advanced Materials Ltd, Yeovil) SESSION TWO- MANUFACTURING/PROCESSING Production and properties of continuously reinforced titanium alloy MMC , C.M. Ward-Close and P.G. Partridge (RoyalAerospace Establishment, Farnborough) ‘Rapidly’ solidified safimax fibre reinforced MMC’s, Q. Li and G. McCartney (Liverpool University) and A.M. Walker (ICI Advanced Materials Group, Runcornj The secondary processing of particulate reinforced aluminium composites, J.B. Borradaile (Hydra Aluminium as, Havik Norway) High temperature joining of fibre reinforced aluminium alloys, N.J. Lindsay and V.D. Scott (University ofBath) and R.L. Trumper (ARE Holten Heath, Poole) Extrusion processing of aluminium alloy base metal matrix composites.T. Bryant, S.P. Derham and W.S. Miller (British Petroleum Research International, Sunbury-on- Thames) and A.E.J. Forno (NationalPhysicalLaboratory, Teddington)
Some microstructural features of interest in squeeze-cast SIC fibre aluminium composites, X. Dumant and G. Regazzoni (Pechiney Research Centre, Voreppe, France)
Texture development in aluminium alloy-SiC metal matrix composites, A.W. Bowen (RoyalAerospace Establishment, Farnborough) and F.J. Humphreys (ImperialCollege, London)
Drilling of fibre reinforced aluminium, L. Cronjager and D. Meister (Universitat Dortmund, lnstitut fur Spanende Fertigung, Dortmund, FRGJ
Microstructure and strength of powder blended AI-SIC composites, N. Hansen, Y.L. Liu and H. Lilholt (Rise National Laboratory, Roskilde, Denmark) and C.Y. Barlow (University of Cambridge)
SESSIONTHREE - INTERFACES
Modelling the microstructure and mechanical behaviour of particulate composites, F.J. Humphreys (imperial College, London)
Some effects of interfacial reaction layers in SIC particulatereinforcedtitanium,A.S. Reeves, W.M. St0bbsandT.W. Clyne (University of Cambridge) and H. Dunlop (Pechiney Research Centre, Voreppe, France) The interaction between liquid aluminium and particulate silicon carbide in AI-SIC MMC’S, P.K. Johnson, H.M. Flower and D.R.F. West (Imperial College, London) Microstructure-property relationships in spray deposited aluminium - SIC metal matrix composites, I.R. Hughes, A.J. Owen, S.A. Court and J. White (Alcan International Ltd, Banbury) TEM characterisation of fibre-matrix interfaces in Al alloy based MMC , S. Fox, D.R.F. West and H.M. Flower (Imperial College, London) SESSION FOUR - DEFORMATION Stress relaxation and strain ratchetting in whisker-reinforced Ma-Li allovs, CM. Warwick, J.F. Mason andT.W. Clvne (University of Cambridge) Micromechanical modelling of metal matrix composites using finite element analysis, M.R. Wisnom (University of Bristol) Factors affecting recrystallization in fibrous and particulate MMC ’S, R.A. Shahani and T.W. Clyne (University of Cambridge)
SESSION FIVE - FAILURE Fatigue and fracture of an aluminium - silicon carbide composite, D.M. Knowles and J.E. King (University of Cambridge) and C.W. Brown (British Petroleum International, Sunbury-onThames) Long and short fatigue crack growth and overload effects in Al 0 shortfibre reinforced AI-ZMg alloy, A.F. Blom, H.L. Groth (The Royallnstitute of Technology, Stockholm, Sweden), A. Melander, S. Preston and S. Savage /Swedish Institute for Metals Research, Stockholm, Sweden) Fracture toughness test procedures for particulate metal matrix composites, B. Roebuck and J.D. Lord (National Physical Laboratory, Teddington) The influence of microstructure on the compressive failure of metal matrix composites, F.J. Guild and P.J. Hogg (Queen Mary College, London) and D. Green (University of Bristol) The micromechanisms of fracture in particle reinforced metal matrix composites, P. Mummery and B. Derby (University of Oxford) Deformation and fracture in particulate reinforced Al composites, D.J. Lloyd IA/can International Ltd, Kingston, Ontario, Canada)
NDT International contains l l
infernational the independent journal of nondestructive testing
l
NDT international covers l l
NDT International provides a unique package of information on research and development in nondestructive testing methods and their industrial applications for quality assurance of raw materials, manufacturing products and structures.
Butterworths
Refereed research papers, state-of-the-art surveys, technical notes and case studies News and reviews of new equipment and services, industrial developments, conferences, exhibitions and publications NDT info - the fullest serially published survey of literature and patents in the field
l l l
Detection, sizing and characterization of materials inhomogeneities Measurement of component and defect dimensions Evaluation of material properties Assessment of integrity and strength of in-service structures Condition monitoring of operating plant
NDT International Published bimonthly ISSN 0308-9126 For a sample copy and further information contact Geraldine Hills at Butterworth Scientific Ltd, PO Box 63, Westbury House, Bury Street, Guildford, Surrey GU2 5BH, UK. Telephone 0483 300966 Telex 859556 SCITEC G
COMPOSITES . MAY 1990 265