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Examining composite materials with the scanning electron microscope
Abstracts of journals Compiled by Dr H. A. Barker, I. Bell, B. Gill and R. Warren, Department of Metallurgy and Materials Technology, University of Surrey, Guildford, England GENERAL
A simple continuua model of a layered composite material
Examining composite materials with the scanning electron microscope
Davis, L. W. and Long, J. R. Metals
Engineering Quarterly, Vol 12, No I, p 38 (Feb 1972) T h e advantages of using scanning electron microscopy in studies of composite materials are discussed, partmularly for magnifications between 100X and 200>(. T h e techniques are illustrated with examples taken from studies of composites of aluminium and titanium alloys reinforced with boron or Borsic fibres. Gradients in composite materials
]3ever, M.
B. and
Duwey,
P. E.
Materials Science and Engineering, Vol 10, No 1, p I (July 1972) In this review paper, the properties and behaviour of composites which have gradients in composition and structure are examined theoretically and the reported and potential applications of such materials are discussed. It is noted that compositional and structural gradients affect composite properties on both a local and a large scale. Influence of the shape of dispersed particles on the elastic behaviour of composite materials
Rossi, R. C., Cost, J. R. and Janowski,
K. R. Journal of the American Ceramic Society, Vol 55, No 5, p 234 (may 1972) T h e Young's modulus of MgO with up to 5 vol% of graphite inclusions was determined as a function of the volume fraction and the shape of the inclusions, which were in the form of fibres, plates or spheres. T h e measured values of modulus were in very good agreement with the predictions of a model which allowed for the orientation and shape of inclusions. T h e results demonstrated that the effec~ of shape can be significant. Non-destructive determination of fatigue crack damage in composites using vibration tests
Dibenedetto, A. T., Gauchel, J. V. Thomas, R. L. and Barlow, J. W.
Journal of Materials, Vol 7, No 2, pp 211-215 (June 1972) T h e vibrational responses of glass~-einforced epoxy and polyester laminates were studied at various levels of fatigue crack damage. Changes in Youn.g's modulus and damping capaoty were correlated with the extent of this damage. T h e damping was particularly mnsitive to debonding of the matrix and fibres. It is suggested that this may be a potential non-destructive testing method.
284
COMPOSITES November 1972
King, J. L. Journal of Strain Analysis,
Vol 7, No 2, p 146 (April 1972) A mathemaucal model of a material consisting o f alternate layers of material of high a n d low eIastic modulus is developed and treated as a continuum in order to derive an equation for its behaviour when loaded in one direction only. It is shown that this governing equation can be reduced to the Laplace equation and after consideration of solutions for the stress distribution round a crack and in a tensile specimen, it is concluded that the model is likely to be useful in any studies of conditions at the tip of a crack or at the root of a notch. Strain energy release rates for turning cracks
Harrison, N. L. Fibre Science and
Technology, Vol 5, No 3, p 197 (July
1972)
T h e ratio of strain energy release rates, which is a function of the relative values of the elastic constants of the material in different directions, has an important effect on the direction of propagation of a crack. T h e value of this ratio, which is also a function of the mode of stressing of the crack, was determined experimentally for unidirectional gap and theoretically by means of a method involving finite element analysis for a range of materials from elastically isotropic to extremely anisotropic. I't is concluded that a crack is more likely to propagate across the fibres in a highly anisotropic material than in an isotropic composite. Theory of photoelusticity for birefringent filamentary composites
Bert, C. W. Fibre Science 6" Tech-
nology, Vol 5, No 3, p 165 (July 1972) T h e theory of Bhagavantam concerning photoelasticity for the orthorhombic crystal system forms the basis of an explanation of the anisotropic behaviour of filamentary composites in which the fibres were of small diameter and in which both fibres and matrix were birefringent. It is suggested that transmission photoelasticity could be used to study glass/epoxy composites but for boron/epoxy, and other composites which contain non-transparent constituents, the reflective technique is recommended. Two-dimensional lattice orientation and three-dimensional erystallinity in carbon fibres
Ergun, S. Nature (Phys Sci), Vol 238, No 87, pp 137-139 (Aug 1972)
X-ray diffraction has shown that carbon fibres produced from polyacrylonitrile and 'Thornel 50' carbon fibre possess a degree of threedimensional crystallinity; that is the normals to the layers are not truly randomly orientated. Certain speculations concerning the connection between layers are also made.
METAL MA TRICES Discussion of 'Fabrication of composites by diffusion processing' and authors' reply
Agrawal, B. K. and Ramakrishnan, P.
Metallurgical Transactions, Vol 3. No 6, pp 1663-1664 (June 1972) Referring to the paper by Darroudi. Vedula and Heckel (Metallurgical
Transactions, Vol 2, p 325, 1971) a description is given of the preparation of composites of aluminium reinforced with mckel fibres which involved hotpressing a combination of nickel wires and aluminium powder. T h e extent of the reaction between the phases depended on the hot-pressing conditions. These could be controlled to give optimum bonding between the phases and consequently optimum composite strength. T h e optimum strength was found to be in agreement with the rule of mixtures. In their reply, the authors of the article pointed out that the aim of their work on AI-Ni composites had been to produce composites in which the different phases were in chemical equilibrium (i.e. A1,Ni in AI) r~ither than composites with maximum strength. Effect of thermotrausport upon offeutectic composite growth in Sn-Pb alloys
Verhoeven, J. D., Warner, J. C. and Gibson, E. D. Metallurgical Trans-
actions, Vol 3, No 6, p 1437 (June 1972) Experiments on the growth of offeutectic Sn-Pb composites showed that considerable segregation of Pb occurred in tile initial portions of the ingot. It is demonstrated theoretically that this effect can be attributed to thermotransport. T h e magnitude of the effect increases with the value of G/R, where G is the temperature gradient and R the growth rate. T h e effect is particularly significant in offeutectic growth studies because high values of G/R are necessary if dendrite formation is to be avoided. Etude th~orique et experimentale du couplnge thermoelastique dans les plaques composites (in French)
Chailleux, A and Ferte, J. P. Fibre
Science and Technology, Vol 5, No 3, # 173 (July 1972) T h e results of a theoretical and experimental study of the behaviou~ of boron-alumininm composites subjected to a uniform increase in temperature are presented and discussed. The thermal expansion characteristics of symmetric and antisymmetric cross-ply composites are
A simple continuua model of a layered composite material
Examining composite materials with the scanning electron microscope
Davis, L. W. and Long, J. R. Metals
Engineering Quarterly, Vol 12, No I, p 38 (Feb 1972) T h e advantages of using scanning electron microscopy in studies of composite materials are discussed, partmularly for magnifications between 100X and 200>(. T h e techniques are illustrated with examples taken from studies of composites of aluminium and titanium alloys reinforced with boron or Borsic fibres. Gradients in composite materials
]3ever, M.
B. and
Duwey,
P. E.
Materials Science and Engineering, Vol 10, No 1, p I (July 1972) In this review paper, the properties and behaviour of composites which have gradients in composition and structure are examined theoretically and the reported and potential applications of such materials are discussed. It is noted that compositional and structural gradients affect composite properties on both a local and a large scale. Influence of the shape of dispersed particles on the elastic behaviour of composite materials
Rossi, R. C., Cost, J. R. and Janowski,
K. R. Journal of the American Ceramic Society, Vol 55, No 5, p 234 (may 1972) T h e Young's modulus of MgO with up to 5 vol% of graphite inclusions was determined as a function of the volume fraction and the shape of the inclusions, which were in the form of fibres, plates or spheres. T h e measured values of modulus were in very good agreement with the predictions of a model which allowed for the orientation and shape of inclusions. T h e results demonstrated that the effec~ of shape can be significant. Non-destructive determination of fatigue crack damage in composites using vibration tests
Dibenedetto, A. T., Gauchel, J. V. Thomas, R. L. and Barlow, J. W.
Journal of Materials, Vol 7, No 2, pp 211-215 (June 1972) T h e vibrational responses of glass~-einforced epoxy and polyester laminates were studied at various levels of fatigue crack damage. Changes in Youn.g's modulus and damping capaoty were correlated with the extent of this damage. T h e damping was particularly mnsitive to debonding of the matrix and fibres. It is suggested that this may be a potential non-destructive testing method.
284
COMPOSITES November 1972
King, J. L. Journal of Strain Analysis,
Vol 7, No 2, p 146 (April 1972) A mathemaucal model of a material consisting o f alternate layers of material of high a n d low eIastic modulus is developed and treated as a continuum in order to derive an equation for its behaviour when loaded in one direction only. It is shown that this governing equation can be reduced to the Laplace equation and after consideration of solutions for the stress distribution round a crack and in a tensile specimen, it is concluded that the model is likely to be useful in any studies of conditions at the tip of a crack or at the root of a notch. Strain energy release rates for turning cracks
Harrison, N. L. Fibre Science and
Technology, Vol 5, No 3, p 197 (July
1972)
T h e ratio of strain energy release rates, which is a function of the relative values of the elastic constants of the material in different directions, has an important effect on the direction of propagation of a crack. T h e value of this ratio, which is also a function of the mode of stressing of the crack, was determined experimentally for unidirectional gap and theoretically by means of a method involving finite element analysis for a range of materials from elastically isotropic to extremely anisotropic. I't is concluded that a crack is more likely to propagate across the fibres in a highly anisotropic material than in an isotropic composite. Theory of photoelusticity for birefringent filamentary composites
Bert, C. W. Fibre Science 6" Tech-
nology, Vol 5, No 3, p 165 (July 1972) T h e theory of Bhagavantam concerning photoelasticity for the orthorhombic crystal system forms the basis of an explanation of the anisotropic behaviour of filamentary composites in which the fibres were of small diameter and in which both fibres and matrix were birefringent. It is suggested that transmission photoelasticity could be used to study glass/epoxy composites but for boron/epoxy, and other composites which contain non-transparent constituents, the reflective technique is recommended. Two-dimensional lattice orientation and three-dimensional erystallinity in carbon fibres
Ergun, S. Nature (Phys Sci), Vol 238, No 87, pp 137-139 (Aug 1972)
X-ray diffraction has shown that carbon fibres produced from polyacrylonitrile and 'Thornel 50' carbon fibre possess a degree of threedimensional crystallinity; that is the normals to the layers are not truly randomly orientated. Certain speculations concerning the connection between layers are also made.
METAL MA TRICES Discussion of 'Fabrication of composites by diffusion processing' and authors' reply
Agrawal, B. K. and Ramakrishnan, P.
Metallurgical Transactions, Vol 3. No 6, pp 1663-1664 (June 1972) Referring to the paper by Darroudi. Vedula and Heckel (Metallurgical
Transactions, Vol 2, p 325, 1971) a description is given of the preparation of composites of aluminium reinforced with mckel fibres which involved hotpressing a combination of nickel wires and aluminium powder. T h e extent of the reaction between the phases depended on the hot-pressing conditions. These could be controlled to give optimum bonding between the phases and consequently optimum composite strength. T h e optimum strength was found to be in agreement with the rule of mixtures. In their reply, the authors of the article pointed out that the aim of their work on AI-Ni composites had been to produce composites in which the different phases were in chemical equilibrium (i.e. A1,Ni in AI) r~ither than composites with maximum strength. Effect of thermotrausport upon offeutectic composite growth in Sn-Pb alloys
Verhoeven, J. D., Warner, J. C. and Gibson, E. D. Metallurgical Trans-
actions, Vol 3, No 6, p 1437 (June 1972) Experiments on the growth of offeutectic Sn-Pb composites showed that considerable segregation of Pb occurred in tile initial portions of the ingot. It is demonstrated theoretically that this effect can be attributed to thermotransport. T h e magnitude of the effect increases with the value of G/R, where G is the temperature gradient and R the growth rate. T h e effect is particularly significant in offeutectic growth studies because high values of G/R are necessary if dendrite formation is to be avoided. Etude th~orique et experimentale du couplnge thermoelastique dans les plaques composites (in French)
Chailleux, A and Ferte, J. P. Fibre
Science and Technology, Vol 5, No 3, # 173 (July 1972) T h e results of a theoretical and experimental study of the behaviou~ of boron-alumininm composites subjected to a uniform increase in temperature are presented and discussed. The thermal expansion characteristics of symmetric and antisymmetric cross-ply composites are