Literature survey The literature survey is prepared by M.R. Alexander, J. Collins and A.J. Hosty of the University of Shefield, UK

GENERAL

Characterisation of face sheet/core shear fracture of composite sandwich beams Carlsson, L.A., Sendlein, L.S. and Merry, S.L. Journal of Composite Materials Vol 25 No 1 (1991) pp 101-116

The debonding behaviour of cored composite materials was discussed with applications in the marine industry in mind. A test method that subjects the bondline between the core and facesheets to a shear stress singularity was presented and studied analytically by laminated beam shear deformation theory. Also experi- mental data was determined from glass/poly- ester face sheets and balsa wood core sandwich beams. It was found that the bondline shear fracture toughness was intermediate between the corresponding interlaminar fracture tough- ness values for a britle graphite/epoxy and a ductile graphite/PEEK composite.

Damage evolution in laminated advanced composites Joshi, S.P. and Frantziskonis, G. Composite Structures Voll7 No 2 (1991) pp 127-139

This paper extends the theory for damage evolution in a single ply. Simultaneous damage evolution in individual plies, at different rates, is accounted for; reduction of the rate of damage growth in a ply due to deformational restrictions imposed by adjacent plies is implicit in the formulation. The theory is valid for any sequence ofexternal loading. However, unloading and cyclic loading cases are not considered in this paper. This is achieved by completely updating the material parameters in a ply that has reached a saturated damage state. This parameter updating is based on the identified damage mode at failure of the ply. Predicted results are compared with available experimental data for T300 graphite-epoxy. Further results that demonstrate the capabil- ities of the theory are also presented.

Design of composite straps Graff, E. and Springer, G.S. Composite SIructures Voll7 No 3 (1991) pp 187-211

This paper reports on a finite element computer code for calculating the stresses and strains in, and elongations of racetrack shaped composite straps loaded by two pins in tension. A procedure for estimating the failure loads of such straps is established using the results provided by the finite element method and the Tsai-Wu failure criteria. Tests were performed to confirm the stress analysis and the failure mode. Forty-three straps were made of either T300/976, T1000/081, Im6/081 graphite epoxy, K49/081 Kevlar epoxy, or S-2/081 glass-epoxy. The strains and failure loads of these straps were measured, and compared to the calculated strains and failure

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loads and were found to be in good agreement. Charts for the estimating failure loads of racetrack shaped straps are presented. Lastly, the design of composite straps loaded by two or more pins is discussed.

Dual vacuum stressing technique for holographic nondestructive testing of honeycomb sandwich panels Rao, M.V., Samuei, R. and Ramesh, K. NDT International Vo123 No5 (1990)~~ 267-282

This paper reported the application of holographic nondestructive testing to identifying the debond areas in flat honeycomb sandwich test coupons and large panels of aluminium facesheet with different adhesives. The details of the new vacuum stressing technique for non-destructive testing these materials was presented. The study undertaken showed the detectability of debonds to be independent of the facesheet material and film adhesive system used in manufacturing the panels.

Effect of processing parameters on compression moulded PMR-lS/C3K composites Farouk, A. and Kwon, T.H. Polymer Composites Vol 11 No 6 (1990) pp 379-386

The effect of processing parameters on final material properties was studied using a computer controlled compression moulder instrumented for data acquisition. The par- ameters varied were pressure, time of appli- cation of the pressure and crosslinking temperature. Pressure affected both void content and thickness, as did the time of pressure application. Increasing pressure had a non-linear effect on interlaminar shear strength (ILSS). Both late and early appli- cations of the pressure reduced ILSS. ILSS was plotted three dimensionally against thickness and void content to show that the same properties could be achieved by different processes.

The fatigue behaviour of composite laminates under various mean stresses Rotem, A. Composite Structures Vol 17 No 2 (1991) pp 113-126

In this paper a method is developed for predicting the S-N curve of a composite laminate which is subjected to an arbitrary stress ratio, R (minimum stress/maximum stress). The method is based on the measuring of the S-N behaviour of two distinct cases, tension-tension and compression-compres- sion fatigue loadings. Using these parameters, expressions are formulated that estimate the fatigue behaviour under any stress ratio loading. Experimental results from the testing of graphite/epoxy laminates, with various structures, are compared with the predictions.

Fibre composite bar for reinforced concrete construction Saadatmanesh, H. and Ehsani, M.R. Journal of Composite Materials Vol 25 No 2 ( 1991) pp 188-203

An experimental determination of the feasibility of GFRP bar reinforcement for concrete structures was reported in this paper. The mechanical behaviour of concrete beams reinforced with glass-fibre-reinforced-plastic bars was characterized by the load-deflection response to failure. Longitudinal (flexural) reinforcement and transverse (shear) reinforce- ment was investigated. The conclusion was that this alternative to steel reinforcement performed well.

Filament winding cylinders : I. Process model Lee, S.-Y. and Springer, G. Journal of Composite Materials Vol 24 No 12 (1990)

pp 1271-1298

A model was presented that describes the filament winding process. Process variables such as winding speed, fibre tension and applied temperature to thermal, chemical and mechanical behaviour of the composite cylinder and the mandrel. From this model a user friendly computer program was written which can be used to calculate the temperature in the cylinder and mandrel ; the degree of cure and viscosity in the cylinder; the fibre tensions and positions; the stresses and strains in the cylinder and mandrel ; and the void diameters in the cylinder. Analytical and experimental studies to validate this model are described in Part II Validation of the process model, pp 1299-1343. Examples of the use of this model are given in Part III Selection of the process variables, pp 1344-1366.

A finite element/control volume approach to mold filling in anisotropic porous media Bruschke, M.V. and Advani, S.G. Polymer Composites Vol 11 No 6 (1990) pp 398-405

Composite manufacturing processes such as reaction injection moulding and resin transfer moulding can be described as mould filling in anisotropic porous media (fibres). The process has been modelled using a finite element/ control volume method to predict the flow of a viscous fluid through a fibre network and is based upon Darcy’s law. The model can predict free surface flow for an arbitrary mould shape. Experimentally measured permeabilities were used to verify the accuracy of the model and it is compared with results for a Newtonian fluid in a rectangular mould with good agreement being exhibited.

Optimizing fibre wetout for composites manu- facturing Cercone, L. Polymer Composites Vol I2 No 2 (1991) pp 81-86

This paper describes the impregnation process

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during composites manufacturing and outlines the critical factors which can be optimized to improve properties. The critical factors were found to be: resin viscosity vs. temperature, fibre resin adhesion and impregnation of fibre bundles. Nip rollers for optimizing these factors were considered, as were changes in the process envelopes.

Optimum design of composite wing structures by a refined optimality criterion Liu, I-W. and Lin, C-C. Composite Structures Vol 17 No I (1991) pp 51-65

In this paper the authors describe the tech- niques for the optimization of composite wing structures. The refined optimality criterion in this paper is an algorithm combining a criterion based on the Kuhn-Tucker con- ditions and the technique of fully stressed design. The main advantages of this method are the generality of use, the efficiency in computation, and the capability of identifying automatically the set of critical constraints. Sensitivity analysis of constraints is based on the virtual load principle. This method is reported as being especially suitable for optimum design of large scale structures. A modular type computer program, is develope using the finite element method, refined optimality criterion, sensitivity analysis and Fortran- language. Numerical results for triple spar composite wing structures are presented.

Three-dimensional elastic-plastic analysis of lmainated composite plates Nanda, A. and Kuppasamy, T. Composite Structures Vol I7 ( 1991) pp 213-225

In this paper the authors present a three- dimensional finite element analysis of laminated composite plates using an elastic-plastic model for an anisotropic material. The constitutive model is simple and the material parameters involved are easily obtained from uniaxial test results. Results are presented for simply supported laminate plates for various (width/thickness) ratios. The influence of the hardening parameter on the load-deflection response and the spread of yield zones in the plates is studied.

A unified approach to progressive crushing of fibre-reinforced composite tubes Hull, D. Composites Science and Technolog? VoI 40 No 4 ( 1991) pp 377-421

In this paper the author summarizes the main features of progressive folding and progressive crushing in tubes subjected to axial com- pression, with particular reference to the geometry of the folded or crushed region and the force displacement response. A detailed account is given of the two main modes of progressive crushing, splaying and fragmen- tation, which occurs in tubes made from fibre reinforced composite materials. The main theme of this article is that the crush geometry and the force displacement response are interrelated and that the wide range of response are interrelated and that the wide range of material and testing variables which affect the crushing can be accounted for on this basis. A detailed description is given of the effect of fibre arrangement on progressive crushing in carbon fibre epoxy tubes, filament- wound angle ply glass fibre-polyester tubes and in plane random chopped fibre-polyester tubes. Transitions between splaying and fragmentation modes are identiified and related to the force displacement response.

METAL MATRICES

Study on the elfect of the surface treatment on the residual stress gradient in silicon carbide (Sic) reinforced aluminium metal matrix composites Lu, J., Miege, B., Flavenot, J.F. and Thery, S. Journal of Composite Technology and Research Vol I2 No 4 ( 1990) pp 232-238

Manufacturing processes such as machining, surface finishing, shot peening, etc. are known to cause residual stresses in materials. Their effect upon various Sic reinforced aluminium matrix composites were studied using a conventional hole drilling technique and X-ray diffraction which used the surface interatomic lattice spacing as a strain gauge. The former was found to give the mean stress in the two phases and the latter to separate matrix and reinforcement stresses. Results obtained were very similar.

RESIN MA TRICES

Analysis of fatigue delamination growth in carboresin specimens with central hole Beghini, M., Bertini, L. and Vitale, E. Composite Structures Vol 17 No 3 ( 1991) pp 257-274

This paper describes the damage evolution observed by the authors in carboresin specimens with a central hole subjected to cyclic tensile loading. Damage monitoring was conducted via a purpose-designed automatic ultrasonic scanning apparatus, whose responses were checked by using micrographical obser- vations. Observed delamination onset and growth are discussed with reference to the results of three dimensional finite element analysis. In particular, a model simulating the presence of delaminations and their partial closure through non-linear contact calculations is employed in order to calculate the distribution of the energy release rates along the delamination boundaries. The results indicate that the observed evolution of delamination may be explained by numerical models, provided that the closure effects are taken into account.

Effect of advancement on epoxy prepreg processing--A dielectric analysis Day, D.R. and Shephard, D.D. Polymer Composites Vol I2 No 2 ( 1991) pp 87-91

Thermoset materials can experience large variations in their cure and flow behaviour due to small variations in material. These effect properties and mould filling during manu- facturing. Microdielectric sensors were used to monitor the cure behaviour ofepoxy/glass and epoxy/carbon composites throughout the cure cycle from the initial point of flow to the solid state. Relationships between cure phenomena and process conditions were discussed.

The etfects of injection moulding on the mechanical behaviour of long-fibre reinforced pbt / pet blends Vu-Khanh, T., Denault, J., Habib, P. and Low, A. Composites Science and Technology Vol40 No 4 ( 1991) pp 423-435

Long fibre reinforced thermoplastics have received much attention for their processability.

However, fibre degradation presents a major problem. This work investigates the effect of injection moulding parameters on fibre degradation and fracture performance in pbt-pet blend/glass fibre composites. The influence of six parameters and their inter- actions are analysed, peak cavity pressure, holding pressure, back pressure, screw speed, melt temperature and barrel profile. The authors report that most of the parameters affect the properties of the composite. The influence of the composite microstructure, which is in turn controlled by the moulding process, on the rigidity, strength and toughness of the composite is also discussed.

Fibrelresin compatibility in glass/phenolic laminating systems Tavakoli, S.M., Avella, M. and Phillips, M.G. Composites Science and Technology Vol 39 No 2 (1990) pp 127-145

In this paper the authors describe the assessment of eight different commercial reinforcement mats w-ith a cold cure phenolic resin, BP cellobond J2027L. The assessments were made at three stages of manufacture: contact-angle measurements against liquid resin were used to determine compatibility at the layup stage. The influence of glass and glass finish upon the degree of resin cure achieved was assessed by differential scanning calorimetry, thus the authors say indicating compatibility at the curing stage. The integrity of the resulting laminate was assessed by measurement of interlaminar shear strength on boards produced by resin transfer mould- ing. Despite the appreciable disparity between these individual indicators, the authors show that they may be combined to give an overall assessment.

Laboratory-scale screening of mechanical properties of resins and composites: relevance to composites for aerospace applications Davies, M. and Moore, D.R. Composite Science and Technology Vol 40 No 2 ( 1991) pp 131-146

In this paper a procedure for screening the properties of a resin sample is described for the evaluation of the mechanical properties of resins relevant to the requirements of aerospace matrix materials. For this purpose approxi- mately 50 g of resin are required to obtain objective measurements of fracture toughness, fracture strength, yield strength and tensile modulus. These tests are then complemented by the characterization of the mechanical properties of the composite material. The screening procedure for the composites measures unidirectional compressive strength, transverse strength in flexure (with and without hot/wet conditioning), short beam shear strength and interlaminar fracture toughness. Results reported from these tests by the authors suggest that data for the resins and composites may be linked and also reflect performance in the aerospace industry tests such as compression after impact.

Radiation-curable prepreg composites Saunders, C.B., Carmichael, A.A., Kremers, W., Lopata, V.J. and Singh, A. Pol.vmer Composites Vol 12 No 2 (1991) pp 91-95

Radiation curable prepreg by electron beam (EB) offer advantages over thermal cure prepregs of ambient temperature cure, reduced curing times and fewer volatiles. In this work

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an EB curable acrylated epoxy resin was developed and its properties studied for various processing conditions. Tensile prop- erties of carbon fibre composites were compared favourably with those of a thermally cured composite.

Solidification in anisotropic thermoplastic com- posites Gilmore, SD. and Guceri, S.I. Polymer Composites Vol II No 6 (1990) pp 406-417

The presence of fibres causes anisotropic heat transfer in composites and a complex melting/ solidification interface. The effects of this anisotropy on the processing of thermoplastic matrix composites is studied using a numerical grid technique with the anisotropic effects of thermal conductivity considered as a second order tensor. The applicability ofthe technique is demonstrated on sample composite parts.

Stamping rheology of glass mat reinforced thermoplastic composites Davis, S.M. and Mcalea, K.P. Polymer Composites Vol II No 6 (1990) pp 368-378

The matrix material in a glass mat reinforced thermoplastic (GMT) should possess a balance of rheological properties, ideally highly viscous for extrusion but with a low shear viscosity in order to wet the fibres. These criteria limit the choice of matrix materials. This paper outlines the problems in GMT processing and uses an isothermal squeezing flow technique to determine the biaxial extensional viscosities of three GMT materials (polycarbonate, polybutylene terephthalate and polypropylene). The main conclusions are that the composites strain harden during deformation and that the biaxial extensional viscosities correlates with the deformation rheology of the matrix.

Thermal joining of carbon fibre-reinforced PEEK laminates Cantwell, W.J., Davies, P., Bourban, P.E., Jar, P-J., Richard, H. and Kausch, H.H. Composite Struclures Vol 16 No 4 ( 1990) pp 3OS-32I

Carbon fibre-reinforced PEEK was joined using the heated press technique and the resulting lap-shear specimens tested to determine the effect of sample geometry and processing parameters. Elevated temperature tests showed that the joints performed well, even above the glass transition point of the PEEK matrix. A strong correlation between the orientation of the outermost fibres in the adherent ply and

joint strength was determined. The effectiveness of ‘low’ temperature joining was also investigated yielding very high joint strengths just above the melting temperature of PEEK.

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