- Email: [email protected]
Design with advanced composite materials
ConferencetepoK AVK (Reinforced Plastics) Conference Main:, Germany, 5-7 November 1990 The 23rd International AVK Conference (Reinforced Plastics Conference in Germany) was held November 5-7, 1990, in the Rheingoldhalle in Mainz, Germany. About 700 people had registered for the technical conference representing about 400 companies and scientific institutes concerned with composite materials. The two dozen exhibitors covered a wide range of subjects on composite materials and their applications. Most attendees were quite impressed with the exhibits, and in the following a few highlights shall be mentioned. BASF spotlighted their recent acquisition of fibre reinforced plastic parts used or prototypes in the automobile industry. Similar to BASF, Dynamit Nobel showed their ability of composite structures in this field. Besides some exhibitors of testing units, mainly rheometers, scientific institutes dominated the exposition. The German Plastic Institute (DKI), Darmstadt, presented its new materials database. The expositions of the Institute for Plastics Processing (IKV), Aachen, and the Southgerman Plastics Center (SKZ), Wiirzburg, focused on their involvement in the Composite Demonstration Centers, recently established by the German Ministry for Research and Development (BMFT). The conference itself was opened with an eulogy on Dr Kannebley in order to give him the AVK consolation prize. The following three or four presentations in section A gave a broad view of the problems connected to the future use of composite materials. Despite the opportunity to acquire knowledge and support for applying fibre reinforced materials, industry is currently worrying about
the costs. In addition, the time of industrial use of the most advanced composite technical part, the automotive leaf spring, is not in sight. An advancement in this area was presented by Mr Abelson from General Motors featuring the All Purpose Van (APV) in an impressive film performance. The APV contains a high volume of composite materials and is the first composite manufactured large series van which meets the high US-crash standards. Further presentations dealt with the simulation of tool-making for SMC products and the measuring of curing parameters using dielectric sensors, as Mr Gati from Tectra explained. A very interesting presentation was given by Mr Miiller from IKV focusing on the area of load application to highly stressed composite parts leading to an easy use design strategy. An important point within this meeting was the panel discussion on the subject ‘Means of disposal for GRP’ by Dr Kiinig of BASF, spotlighting the recycling problems connected to the increased application of glass tibre reinforced plastics. Concluding the conference, one has to say that the meeting was split between optimism shown by the industry currently using composite materials and a touch of sceptism hand in hand with the will to solve the problems on the part of the scientific composite institutes and demonstrations centres. The 24th International AVK Conference will be held in Berlin on September 12-14, 1991, and one will see what has happened in the field of composite materials from nowadays. Dip/.- Ing. Jens Schuster Institute for Composite Materials Ltd (IVW) University of Kaiserslautern Germany
Bookreviews Design with advanced composite materials Edited by L.N. Phillips The Design Council/Springer,
1989, f35.00
Mechanical behaviour and properties of composite materials - Volume 1
Fundamental principles of fiber reinforced composites K. Ashbee Technomic Publishing Co. Inc., 1989 ISBN O-87762-597-2, pp 372, SFr 150
Co. Inc., 1989
It is a sign of the increasing maturity of composite materials that not one but three books on the fundamentals of composites and designing with them are available for review.
Composites Manufacturing December 1990
261
C. Zweben, H.T. Hahn and T.W. Chou Technomic
Publishing
The first edited by and with contributions from Leslie Fatigue is treated from a mechanism rather than Phillips, who would I am sure not be offended to be called - materials viewpoint. It is clear that there are too many one of the founders of composites, is a down to earth materials and structures to give a comprehensive account book when compared with the clinical precision of some of the phenomenon. The aim is to borrow from the metals of the more theoretical texts available. Repeatedly the approach where possible - the points of first ply failure practical experience of the editor and contributors in and of yield both mark the boundary between elastic and handling real fibres, messy resins and composite artefacts, inelastic behaviour. The chapter deals with the longitudinal as distinct from computer printout and elasticity equations, fatigue and stress rupture of unidirectional composites, shines through the presentation. The editor puts composites while for multidirectional laminates the effects of in their cultural/historical setting. However, both here compression, notches, temperature, stacking sequence and elsewhere the book would have benefitted from a and the environment are discussed. The author then goes mention of more recent work on carbon fibre structure on to consider the behaviour of discontinuous fibre and a fuller account of the carbon fibre/resin interface reinforced material, lifetime prediction and data analysis. which plays such an important role in determining While a lot of data are presented, why is there so little composite behaviour. Also there is no need to use on compression fatigue and no mention of torsional Imperial units - the SI variety is much simpler. fatigue? Composites tend to be weak in both these modes Test methods and standards and their significance are of loading. still a contentious issue and the book reviews methods Finally there is a mathematical account of the applicable to the reinforcements and polymer matrices thermomechanical properties of 2D woven fabrics. as well as considering prepregs and the measurement of Omissions, which as far as I can judge are not treated in electrical and mechanical properties of composites. the later volumes, are the topics of thermal expansion Nevertheless a more extensive and critical overview and electrical and thermal conduction. This is puzzling would have been helpful. The essentially non-mathematical since many sophisticated uses of advanced composites account of bonding, mechanical fastening and repair is depend upon these parameters. Although well supplied masterly and would enable most of us to design a simple with references there is no index - presumably the reader but effective joint. Applications from aerospace to violins has to wait for this until volume six is completed. are detailed in a long chapter. Will the ‘Stradivarius’ of Probably most people familiar with strong materials the future turn out to be made of carbon fibres and epoxy have heard of Inglis and his treatment of the stresses in resin? I certainly hope so. The only thing missing from a-plate containing a crack or notch-after all it goes back this account are some statistics to show how extensive nearly 80 years. However, most books do no more than the market for composites already is and by how much quote the result, whereas in Fundamental Principles of it is expected to grow in the next decade or so. The final Fiber Reinforced Composites the derivation is explored. two chapters will disabuse the reader who thinks that This sets the level for the book. It is a refreshing, essentially academic, exploration of the materials science he/she can escape from mathematics in this book. Firstly there is a detailed treatment of the anisotropic properties of fibres and matrices. The treatment is analytical/ mathematical and unlike most publications on composites of laminates and sandwich members and failure criteria plus a brief flip through some micromechanical models. it contains worked examples and questions. An instructor’s manual is available, which I, for one, would certainly In the latter case the account of shear could have been better. Finally, damage, fracture and toughness maps are require if I were teaching the topic. considered in depth. The book is not a compendium of data but, as the title suggests, attempts to go back to basics and use these to The second book is volume one of the six-volume develop the science of composites. It is good to see Delaware Composites Design Encyclopedia. Volume one is references to some seminal papers - in one case going rather variable in quality. The introduction is marred by back nearly two centuries. More practical aspects are not mixing Imperial and metric units, it is stated that carbon omitted; there is a chapter on fabrication and another fibres are linear in their behaviour to failure and there is on joining, repair and adhesives. Even so the approach no mention of oriented polyethylene or ceramic fibres remains theoretical. The treatment of environmental nor of non-polymer matrices. However, this is more than effects is biased, but understandably so, towards the compensated for by a leisurely, lucid discussion of the author’s original work involving osmosis in composites. physical properties of composites. I was surprised to see nothing on the prediction of Considerable information on unidirectional, disconcomposite properties from those of the components, but tinuous fibre, randomly oriented 2~ fibres and balanced the freshness of the book elsewhere makes up for this. weave fabric composites is given. Through-thickness It is not possible to recommend one book over and properties, which are rarely measured or mentioned, are above the others since each is aimed at a different market. quoted as estimated percentages of the associated Any library with a worthwhile section on composites longitudinal figure, though the values for transverse should have all three. tension seem rather high in some cases. An illustration of the problems confronting the design engineer due to composites variability is that the in-plane shear and compression strengths for a widely used, unidirectional, carbon fibre composite gleaned from various sources N. L. Hancox show differences of over 100%. The favoured approach AEA Technology, to the problem of materials variability is to use a fixed Harwell Laboratory, UK property value that is lower than the mean.
262
Composites Manufacturing December 1990
the costs. In addition, the time of industrial use of the most advanced composite technical part, the automotive leaf spring, is not in sight. An advancement in this area was presented by Mr Abelson from General Motors featuring the All Purpose Van (APV) in an impressive film performance. The APV contains a high volume of composite materials and is the first composite manufactured large series van which meets the high US-crash standards. Further presentations dealt with the simulation of tool-making for SMC products and the measuring of curing parameters using dielectric sensors, as Mr Gati from Tectra explained. A very interesting presentation was given by Mr Miiller from IKV focusing on the area of load application to highly stressed composite parts leading to an easy use design strategy. An important point within this meeting was the panel discussion on the subject ‘Means of disposal for GRP’ by Dr Kiinig of BASF, spotlighting the recycling problems connected to the increased application of glass tibre reinforced plastics. Concluding the conference, one has to say that the meeting was split between optimism shown by the industry currently using composite materials and a touch of sceptism hand in hand with the will to solve the problems on the part of the scientific composite institutes and demonstrations centres. The 24th International AVK Conference will be held in Berlin on September 12-14, 1991, and one will see what has happened in the field of composite materials from nowadays. Dip/.- Ing. Jens Schuster Institute for Composite Materials Ltd (IVW) University of Kaiserslautern Germany
Bookreviews Design with advanced composite materials Edited by L.N. Phillips The Design Council/Springer,
1989, f35.00
Mechanical behaviour and properties of composite materials - Volume 1
Fundamental principles of fiber reinforced composites K. Ashbee Technomic Publishing Co. Inc., 1989 ISBN O-87762-597-2, pp 372, SFr 150
Co. Inc., 1989
It is a sign of the increasing maturity of composite materials that not one but three books on the fundamentals of composites and designing with them are available for review.
Composites Manufacturing December 1990
261
C. Zweben, H.T. Hahn and T.W. Chou Technomic
Publishing
The first edited by and with contributions from Leslie Fatigue is treated from a mechanism rather than Phillips, who would I am sure not be offended to be called - materials viewpoint. It is clear that there are too many one of the founders of composites, is a down to earth materials and structures to give a comprehensive account book when compared with the clinical precision of some of the phenomenon. The aim is to borrow from the metals of the more theoretical texts available. Repeatedly the approach where possible - the points of first ply failure practical experience of the editor and contributors in and of yield both mark the boundary between elastic and handling real fibres, messy resins and composite artefacts, inelastic behaviour. The chapter deals with the longitudinal as distinct from computer printout and elasticity equations, fatigue and stress rupture of unidirectional composites, shines through the presentation. The editor puts composites while for multidirectional laminates the effects of in their cultural/historical setting. However, both here compression, notches, temperature, stacking sequence and elsewhere the book would have benefitted from a and the environment are discussed. The author then goes mention of more recent work on carbon fibre structure on to consider the behaviour of discontinuous fibre and a fuller account of the carbon fibre/resin interface reinforced material, lifetime prediction and data analysis. which plays such an important role in determining While a lot of data are presented, why is there so little composite behaviour. Also there is no need to use on compression fatigue and no mention of torsional Imperial units - the SI variety is much simpler. fatigue? Composites tend to be weak in both these modes Test methods and standards and their significance are of loading. still a contentious issue and the book reviews methods Finally there is a mathematical account of the applicable to the reinforcements and polymer matrices thermomechanical properties of 2D woven fabrics. as well as considering prepregs and the measurement of Omissions, which as far as I can judge are not treated in electrical and mechanical properties of composites. the later volumes, are the topics of thermal expansion Nevertheless a more extensive and critical overview and electrical and thermal conduction. This is puzzling would have been helpful. The essentially non-mathematical since many sophisticated uses of advanced composites account of bonding, mechanical fastening and repair is depend upon these parameters. Although well supplied masterly and would enable most of us to design a simple with references there is no index - presumably the reader but effective joint. Applications from aerospace to violins has to wait for this until volume six is completed. are detailed in a long chapter. Will the ‘Stradivarius’ of Probably most people familiar with strong materials the future turn out to be made of carbon fibres and epoxy have heard of Inglis and his treatment of the stresses in resin? I certainly hope so. The only thing missing from a-plate containing a crack or notch-after all it goes back this account are some statistics to show how extensive nearly 80 years. However, most books do no more than the market for composites already is and by how much quote the result, whereas in Fundamental Principles of it is expected to grow in the next decade or so. The final Fiber Reinforced Composites the derivation is explored. two chapters will disabuse the reader who thinks that This sets the level for the book. It is a refreshing, essentially academic, exploration of the materials science he/she can escape from mathematics in this book. Firstly there is a detailed treatment of the anisotropic properties of fibres and matrices. The treatment is analytical/ mathematical and unlike most publications on composites of laminates and sandwich members and failure criteria plus a brief flip through some micromechanical models. it contains worked examples and questions. An instructor’s manual is available, which I, for one, would certainly In the latter case the account of shear could have been better. Finally, damage, fracture and toughness maps are require if I were teaching the topic. considered in depth. The book is not a compendium of data but, as the title suggests, attempts to go back to basics and use these to The second book is volume one of the six-volume develop the science of composites. It is good to see Delaware Composites Design Encyclopedia. Volume one is references to some seminal papers - in one case going rather variable in quality. The introduction is marred by back nearly two centuries. More practical aspects are not mixing Imperial and metric units, it is stated that carbon omitted; there is a chapter on fabrication and another fibres are linear in their behaviour to failure and there is on joining, repair and adhesives. Even so the approach no mention of oriented polyethylene or ceramic fibres remains theoretical. The treatment of environmental nor of non-polymer matrices. However, this is more than effects is biased, but understandably so, towards the compensated for by a leisurely, lucid discussion of the author’s original work involving osmosis in composites. physical properties of composites. I was surprised to see nothing on the prediction of Considerable information on unidirectional, disconcomposite properties from those of the components, but tinuous fibre, randomly oriented 2~ fibres and balanced the freshness of the book elsewhere makes up for this. weave fabric composites is given. Through-thickness It is not possible to recommend one book over and properties, which are rarely measured or mentioned, are above the others since each is aimed at a different market. quoted as estimated percentages of the associated Any library with a worthwhile section on composites longitudinal figure, though the values for transverse should have all three. tension seem rather high in some cases. An illustration of the problems confronting the design engineer due to composites variability is that the in-plane shear and compression strengths for a widely used, unidirectional, carbon fibre composite gleaned from various sources N. L. Hancox show differences of over 100%. The favoured approach AEA Technology, to the problem of materials variability is to use a fixed Harwell Laboratory, UK property value that is lower than the mean.
262
Composites Manufacturing December 1990