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IV national and I international meeting on composite materials
Conference report IV National and I International Meeting on Composite Materials Milano, 19-21 November 1980 Organized by: Centro Materiali
Compositi, Napoli
This meeting, held during the Hast '80 Exhibition, was attended by more than 120 delegates coming from both firms in the field of fibre and resin manufacture and research institutes of various countries. The conference was divided into the following sessions: •
composite materials properties
•
applications
•
design
•
fabrication and testing
•
properties, design, metallic composites
In the opening address Professor Crivelli-Visconti, Chairman of the Centro Materiali Compositi, underlined how the expansion of composite materials had received a considerable boost in recent years due to their unique combination of properties. The reduction of fibre production costs together with the need for lighter structures with improved mechanical properties has made a considerable contribution to this expansion. However, in addition to the positive aspects, there are many difficulties associated with the application of these materials because of their peculiar properties. Among the papers presented, in the session on 'properties', Sih's paper was concerned with an analytical study of the influence of coupled heat and moisture diffusion on the transient stresses in a graphite/epoxy composite plate. From this investigation it was shown that the most severe conditions occur when the temperature of the surface plate changes suddenly while the moisture concentration is held constant. The paper presented by Stellbrink examined the influence of damage, possibly sustained during utilization, on the fatigue behaviour and residual strength of CFRP laminates. Then Caprino emphasized some limitations of the classical fracture mechanic models in estimating the notch-resistance of composite laminates, in which the existance of a critical zone at the crack tip, depending on material only, is postulated. Then he discussed experimental results and showed how such a critical damage zone depends on stacking sequence and laminate thickness in addition to material and fibre orientation. Miyano et al presented an investigation on the time and temperature dependences of the flexural resistance of unidirectional CFRP laminates and the tensile strength of the epoxy resin. Their experimental results showed the considerable influence which the said parameters had on both the flexural resistance of CFRP and the tensile strength of matrix. Hognat then showed a curing cycle optimization in terms of temperature, pressure and time in order to obtain a composite with excellent mechanical properties. In the following session devoted to 'applications' the papers presented covered electronics (Donadoni), building and
164
testing of sailplanes (Kensche) and realization of pipes with continuous longitudinal structure (Roccotelli e Rotundi). An interesting work presented by Longoni was a theoretical/experimental investigation of the suitability of composite materials for the construction of diaphragms in loudspeakers. The applications of iron/cement composites were discussed by Barberio. One of the parameters that characterizes such a meterial, which is made of a steel wire mesh within a cement matrix, is a low value of fibre volume fraction (Vf) so that the material would be better classified as a reinforced cement, than a cement composite. The author showed how an iron/cement composite is well suited to the building of shell elements as in cupolas of various forms and the hulls of hydrofoils. The morning session on the second day covered 'design' with composite materials. After a general analysis of the problem of weight saving in the automotive industry, Campagna illustrated some possible applications of composites for structural elements. The author also presented an interesting investigation of the optimization in design of a transmission shaft. Two papers presented by Vinson and Mennicucci dealt with the problems with adhesively bonded joints. The former carried out research into polyimide adhesives which have shown a greater resistance to temperature than epoxy adhesives, while the latter discussed joints bonded with polyurethane and epoxy adhesives and the influence of environment on their shear and fatigue strengths. Then Kunio discussed the effect of local fibre distribution ahead of a crack on the fracture toughness and considered the effect due to the reinforcing fibres on the values of Ge and on the scattering of such values. The last paper of this session presented by Harrison and Bader was concerned with the influence of stacking sequence on the initial cracking strain and the subsequent development of damage in various CFRP laminates under monotonic and cyclic straining. The session devoted to 'fabrication and testing' was opened with a paper presented by Choudin et al which dealt with the as yet unsolved problems with mouled SMC like reliable quality and reproducibility. They studied the possibilities of improving homogeneity of moulded products using a composite reinforced with fibres cut from rovings together with continuous mat, explaining technological processes for both laboratory and industrial production. In the paper presented by Bader and Collins the influence of coupling agents together with the influence of processing variables on the interfacial bond stiffness, strength and failure behaviour of glass fibre-reinforced polyamide 6 was investigated. It has been shown that using silane agents both tensile and impact strengths improved by over 20%. Caneva et al discussed non-destructive control acoustic emis-
COMPOSITES . JULY 1981
sion, while Caputo and Giudice's paper was concerned with using photoelasticity to investigate the stress state of composite materials. Sprecher gave a survey of Flakeglass based coatings as corrosion resistant materials, while in the paper presented by Locardi et al hydrolytic etching behaviour on surface treated specimens of mica and glass microspheres was discussed. Finally, Equevin's paper reported research into the risks associated with handling glass fibres. Statistical investigations have shown that the carcinogenic activity of fibres is mainly dependent on their diameter, increasing rapidly for values below 1/am. As the smallest diameter fibre presently in use is about 5/am one may deduce that there are no serious threats to the worker's health. Minor inflammation of skin, and more rarely of eyes, are the only troubles that may occur. Nevertheless care should be taken to maintain a low concentration of fibres in work areas especially if low diameter (less than 3 pan) fibres are to be used. In the last session of the meeting Tsuldzoe discussed friction and wear properties of several composites made of various kinds of fibres and matrices. After a discussion on the validity of the law of mixtures used to calculate the friction coefficient he proposed a model of composite material wearing taking into account Young's modulus and interlaminar shear strength. Vargitl discussed pollution caused by styrene emission which is always present in resins. He showed that it is possible to make polyester resins with good mechanical properties and which produce only small quantities of styrene.
Strand G fibre are now delivering anew balsacore material...Corelite. We've extended our range of formers and core materials even more to include Corelite - end-grain, kilndried balsa blocks laminated to a glassfibre scrim. It is supplied in 48"x 18" sheets with standard thicknesses of3/~' V2;'s/~,and 3/4,making it easier to handle with less wastage in trimming.The blocks are only 1"square, so the material conforms easily to difficult mould contours and helps to eliminate voids. The consistent density and Lloyds approval also assures the manufacturer of a stable product to meet design and strength specifications. Cordite is available from our local branches throughout the country. For more information, contact our Head Office on 01-568 7191or telex your order on 8951065.
Eistra Brentway T r a d i n g Estate, Brenfford, M i d d l e s e x T W 8 8ER.
Sgubini's subject of research was concerned with elastic wave propagation in periodic composite materials, while Sharma's paper was dedicated to coupling in laminated plates. Two papers concerned with directionally solidified eutectic composites were presented. It has been widely demonstrated that these composites have very attractive properties. Nickel and cobalt base composites obtained by directional solidification could aid the solution of problems of high temperature corrosion and wear resistance. In the first paper presented by Taha a description of the microstructures obtained by directional solidification of a Co - W eutectic was given, while Mahallwy's paper was concerned with the influence of composition on the structure of directionally solidified A1-Ni- and A1-Ni-Cu composites.
DSST The Dual-Sensor Strain Transducer for ADVANCED COMPOSITE Materials Performance matched to Composite Materials, with data recorded through specimen fracture Simple Clothespin-like Attachment Uniaxial and Biaxial Strain measuring Models
Finally Vassillaros discussed the effects of a marine environment on corrosion, fatigue and stress corrosion cracking of metal-matrix composites. This conference, one of the last organized in 1980, aimed to highlight that development of composite materials which had been reported in the various meetings held previously in the year. The delegates paid only partial attention to these general aspects whereas the single subject areas were developed and followed carefully. The papers presented, coming from more than 13 different countries, together with the lively discussions which followed succeeded in presenting some of the most interesting aspects of composites research in the different countries. The proceedings will be published by Applied Science Publishers Ltd.
L Crivelli-Visconti
COMPOSITES . J U L Y 1981
Functional at up to 600°F Uniaxial Model
Two independent axial sensors for Simultaneous Average and Bending strain data recording Signal Conditioners with Sum-and-Difference functions to provide complete Strain Measuring Systems
measurements Technology, Inc. Precision Varionics Ltd.
3029 Greer Road
29-31 St. Pauls St. North Cheltenham Glos. GI_50 4AQ England (0242) 31488/9
Palo Alto, CA 94303 (415) 493-5876
165
Compositi, Napoli
This meeting, held during the Hast '80 Exhibition, was attended by more than 120 delegates coming from both firms in the field of fibre and resin manufacture and research institutes of various countries. The conference was divided into the following sessions: •
composite materials properties
•
applications
•
design
•
fabrication and testing
•
properties, design, metallic composites
In the opening address Professor Crivelli-Visconti, Chairman of the Centro Materiali Compositi, underlined how the expansion of composite materials had received a considerable boost in recent years due to their unique combination of properties. The reduction of fibre production costs together with the need for lighter structures with improved mechanical properties has made a considerable contribution to this expansion. However, in addition to the positive aspects, there are many difficulties associated with the application of these materials because of their peculiar properties. Among the papers presented, in the session on 'properties', Sih's paper was concerned with an analytical study of the influence of coupled heat and moisture diffusion on the transient stresses in a graphite/epoxy composite plate. From this investigation it was shown that the most severe conditions occur when the temperature of the surface plate changes suddenly while the moisture concentration is held constant. The paper presented by Stellbrink examined the influence of damage, possibly sustained during utilization, on the fatigue behaviour and residual strength of CFRP laminates. Then Caprino emphasized some limitations of the classical fracture mechanic models in estimating the notch-resistance of composite laminates, in which the existance of a critical zone at the crack tip, depending on material only, is postulated. Then he discussed experimental results and showed how such a critical damage zone depends on stacking sequence and laminate thickness in addition to material and fibre orientation. Miyano et al presented an investigation on the time and temperature dependences of the flexural resistance of unidirectional CFRP laminates and the tensile strength of the epoxy resin. Their experimental results showed the considerable influence which the said parameters had on both the flexural resistance of CFRP and the tensile strength of matrix. Hognat then showed a curing cycle optimization in terms of temperature, pressure and time in order to obtain a composite with excellent mechanical properties. In the following session devoted to 'applications' the papers presented covered electronics (Donadoni), building and
164
testing of sailplanes (Kensche) and realization of pipes with continuous longitudinal structure (Roccotelli e Rotundi). An interesting work presented by Longoni was a theoretical/experimental investigation of the suitability of composite materials for the construction of diaphragms in loudspeakers. The applications of iron/cement composites were discussed by Barberio. One of the parameters that characterizes such a meterial, which is made of a steel wire mesh within a cement matrix, is a low value of fibre volume fraction (Vf) so that the material would be better classified as a reinforced cement, than a cement composite. The author showed how an iron/cement composite is well suited to the building of shell elements as in cupolas of various forms and the hulls of hydrofoils. The morning session on the second day covered 'design' with composite materials. After a general analysis of the problem of weight saving in the automotive industry, Campagna illustrated some possible applications of composites for structural elements. The author also presented an interesting investigation of the optimization in design of a transmission shaft. Two papers presented by Vinson and Mennicucci dealt with the problems with adhesively bonded joints. The former carried out research into polyimide adhesives which have shown a greater resistance to temperature than epoxy adhesives, while the latter discussed joints bonded with polyurethane and epoxy adhesives and the influence of environment on their shear and fatigue strengths. Then Kunio discussed the effect of local fibre distribution ahead of a crack on the fracture toughness and considered the effect due to the reinforcing fibres on the values of Ge and on the scattering of such values. The last paper of this session presented by Harrison and Bader was concerned with the influence of stacking sequence on the initial cracking strain and the subsequent development of damage in various CFRP laminates under monotonic and cyclic straining. The session devoted to 'fabrication and testing' was opened with a paper presented by Choudin et al which dealt with the as yet unsolved problems with mouled SMC like reliable quality and reproducibility. They studied the possibilities of improving homogeneity of moulded products using a composite reinforced with fibres cut from rovings together with continuous mat, explaining technological processes for both laboratory and industrial production. In the paper presented by Bader and Collins the influence of coupling agents together with the influence of processing variables on the interfacial bond stiffness, strength and failure behaviour of glass fibre-reinforced polyamide 6 was investigated. It has been shown that using silane agents both tensile and impact strengths improved by over 20%. Caneva et al discussed non-destructive control acoustic emis-
COMPOSITES . JULY 1981
sion, while Caputo and Giudice's paper was concerned with using photoelasticity to investigate the stress state of composite materials. Sprecher gave a survey of Flakeglass based coatings as corrosion resistant materials, while in the paper presented by Locardi et al hydrolytic etching behaviour on surface treated specimens of mica and glass microspheres was discussed. Finally, Equevin's paper reported research into the risks associated with handling glass fibres. Statistical investigations have shown that the carcinogenic activity of fibres is mainly dependent on their diameter, increasing rapidly for values below 1/am. As the smallest diameter fibre presently in use is about 5/am one may deduce that there are no serious threats to the worker's health. Minor inflammation of skin, and more rarely of eyes, are the only troubles that may occur. Nevertheless care should be taken to maintain a low concentration of fibres in work areas especially if low diameter (less than 3 pan) fibres are to be used. In the last session of the meeting Tsuldzoe discussed friction and wear properties of several composites made of various kinds of fibres and matrices. After a discussion on the validity of the law of mixtures used to calculate the friction coefficient he proposed a model of composite material wearing taking into account Young's modulus and interlaminar shear strength. Vargitl discussed pollution caused by styrene emission which is always present in resins. He showed that it is possible to make polyester resins with good mechanical properties and which produce only small quantities of styrene.
Strand G fibre are now delivering anew balsacore material...Corelite. We've extended our range of formers and core materials even more to include Corelite - end-grain, kilndried balsa blocks laminated to a glassfibre scrim. It is supplied in 48"x 18" sheets with standard thicknesses of3/~' V2;'s/~,and 3/4,making it easier to handle with less wastage in trimming.The blocks are only 1"square, so the material conforms easily to difficult mould contours and helps to eliminate voids. The consistent density and Lloyds approval also assures the manufacturer of a stable product to meet design and strength specifications. Cordite is available from our local branches throughout the country. For more information, contact our Head Office on 01-568 7191or telex your order on 8951065.
Eistra Brentway T r a d i n g Estate, Brenfford, M i d d l e s e x T W 8 8ER.
Sgubini's subject of research was concerned with elastic wave propagation in periodic composite materials, while Sharma's paper was dedicated to coupling in laminated plates. Two papers concerned with directionally solidified eutectic composites were presented. It has been widely demonstrated that these composites have very attractive properties. Nickel and cobalt base composites obtained by directional solidification could aid the solution of problems of high temperature corrosion and wear resistance. In the first paper presented by Taha a description of the microstructures obtained by directional solidification of a Co - W eutectic was given, while Mahallwy's paper was concerned with the influence of composition on the structure of directionally solidified A1-Ni- and A1-Ni-Cu composites.
DSST The Dual-Sensor Strain Transducer for ADVANCED COMPOSITE Materials Performance matched to Composite Materials, with data recorded through specimen fracture Simple Clothespin-like Attachment Uniaxial and Biaxial Strain measuring Models
Finally Vassillaros discussed the effects of a marine environment on corrosion, fatigue and stress corrosion cracking of metal-matrix composites. This conference, one of the last organized in 1980, aimed to highlight that development of composite materials which had been reported in the various meetings held previously in the year. The delegates paid only partial attention to these general aspects whereas the single subject areas were developed and followed carefully. The papers presented, coming from more than 13 different countries, together with the lively discussions which followed succeeded in presenting some of the most interesting aspects of composites research in the different countries. The proceedings will be published by Applied Science Publishers Ltd.
L Crivelli-Visconti
COMPOSITES . J U L Y 1981
Functional at up to 600°F Uniaxial Model
Two independent axial sensors for Simultaneous Average and Bending strain data recording Signal Conditioners with Sum-and-Difference functions to provide complete Strain Measuring Systems
measurements Technology, Inc. Precision Varionics Ltd.
3029 Greer Road
29-31 St. Pauls St. North Cheltenham Glos. GI_50 4AQ England (0242) 31488/9
Palo Alto, CA 94303 (415) 493-5876
165