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Experimental collapse determination of cylindrical composite panels with large cutouts under axial load
Pitch based processing of carbon-carbon composites White, J.L. and Sheaffer, P.M. Carbon Vol 27No5 In this paper a microstructural approach is used to study the efficiency of pitch based composites fabrication. The microstructure formed in the liquid phase pyrolysis of pitch is established by the mesophase interactions. It is shown that common patterns of wetting, mesophase alignment on fibre substrates and disinclination structure, exist for mesophase formed in fibre bundles and 3D preforms, for various pitches and fibres, and as affected by pressure. In a process likened to the stabilization of mesophase fibre air oxidation is used to control the bloating of the mesophase and so prevent the expulsion of matrix from the fibre preform. The use of oxidation thus removes the need for high pressure pyrolysis.
GENERAL Adhesion through molecular entanglements in polymer interfaces Raghava, R.S. and Smith, R.W. Journal o f Polymer Science Part B Vo127 No 12 (1989) pp 2525-2551 Sandwich laminates of poly methyl methacrylate (PMMA) and poly (vinylidene fuoride) (PVF2) are prepared in order to examine the role of polymer interdiffusion or interpenetration along a boundary between two compatible but dissimilar polymers in interfaciai adhesion. The interphase developed is characterized using electron and optical microscopy, dynamic mechanical spectroscopy, and X-ray microanalysis. Fracture behaviour is observed during tensile testing. Multiple crazing/fracture is seen to occur in the brittle PMMAphase, and shear yielding is observed in the ductile phase. Analysis of hybrid effect in unidirectional composites under longitudinal compression Yao, Li Ning, and Chou, Tsu-Wei. Composite Structures Vo112 No I (1989) pp 27-37 This paper describes a theoretical analysis of the hybrid effect in composites under longitudinal compression. The analysis is based on the instability of different types of fibre on a common elastic foundation of the matrix material. It depends on the elasticity of the matrix and the flexural stiffness of the fibres. The model assumes that instability in the low flexural stiffness fibre occurs first. As the load is further increased, instability in the high flexural stiffness fibre follows, and it results in the failure of the composite. The transverse deformation of the matrix induced by the low flexural stiffness fibres enhances the stability of the high flexural stiffness fibres in compression. Evaluation of the critical compressive load has been made. The paper shows that a synergistic effect in compressive strength can be realized through fibre hybridization. Analysis of viscoelastic laminated composite plies Aboudi, J., and Cederbaum, G. Composite Structures Vo112 No 4 (1989) pp 243-256 This paper describes a micromechanical analysis for the determination of five independent elastic moduli of unidirectional fibre composites. The five time dependent func-
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tions which characterize the effective behaviour of viscoelastic composites are established by using the correspondence principle, the inversion of the Laplace transform and by considering viscoelastic phases. The predicted time dependent behaviour is applied for the analysis of viscoelastic plates. The resulting viscoelastic effects are shown, and comparison between the results obtained within the classical laminated plate theory and the first order shear deformation theory is discussed. Burst pressure indication of metallic/fibre reinforced rocket motor cases using an elastoplastic instability analysis Groves, A. and Margetson, J. International Journal o f Mechanical Sciences Vo131 No 10 (1989) pp 737-750 This paper develops a numerical elastoplastic instability analysis which aims to predict the axial burst of fibre reinforced metallic rocket motor cases. Numerical and experimental results were found to be in good agreement. The analysis was extended to predict the hoop burst of an unwound motor and when combined with a simple reinforcement failure criterion the failure of motors due to overwinding of the reinforcing fibres. Delamination shape effects in Aramid-EpoxyAluminium (ARALL) laminates with fatigue cracks Macheret, J., Teply, J.L. and Winter, E.F.M. Polymer Composites Vol 10 No 5 (1989) pp 322-327 This paper examines the fatigue crack growth mechanisms in A R A L L laminates and relates them to the loading situation, delamination zone shapes and the number of intact fibres in the wake of a crack. An analytical model was developed using a residual strength criterion based on the maximum tensile stress in the aramid/epoxy layer. Analytical results for residual strength were compared with available experimental data. Effects of morphology on properties of graphite composites Herakovich, C.T. Carbon Vol 27 No 5 pp 663--678 The relationship between the morphology of graphite fibre composites and their effective mechanical properties, thermal properties, and failure characteristics is demonstrated. Typical results are presented for studies at the fibre matrix, lamina and laminate levels of analysis. It can be shown that the range of property variations in nonhomogeneous, laminated graphite materials can be very large, in particular when compared to monolithic materials. Further this dependence of material response on morphology can generally be predicted using the fundamental principles of mechanics. An electrical and microstructural study of composite films of a carbon black in a polyimide Norian, K.H. and Rieck, U. Composites Science and Technology Vol 36 No 1 (1989) pp 95-98 Composite films of Printex 200 (a carbon black) in polyimide are of interest as thickfilm resistors in hybrid circuits, and as coatings for electromagnetic shielding of microcircuits. Microstructural studies using transmission electron microscopy show that the carbon black particles are roughly spheri-
cal, and cross-sectional area within a unit cube is calculated. Volume fraction of carbon black (Vc) is varied and resistances of composite films are measured for various Vc values. The theory of Scarisbrick, which predicts the conductivity of spherical particles in an insulator, is applied, giving a value of 1 × 10-5 tim as the specific resistivity of carbon black within the composite films. Experimental collapse determination of cylindrical composite panels with large cutouts under axial load Palazotto, A.N. and Tisler, T.W. Composite Structures Vo112 No 1 (1989) pp 61-78 The paper describes an experimental program for the evaluation of the effect of large rectangular cutouts on the collapse of cylindrical panels. The effects of boundary conditions and residual stress are considered. The experimental results are compared to those obtained by a finite element analysis. Failure of a composite laminate under biaxial loading Neale, K.W. and Labossiere, P. Polymer Composites Vo110 No 5 (1989) pp 285-292 A general failure criterion for thin fibre reinforced composites under plane stress loading was presented. A parametric failure criterion was adapted from Budiansky's work on predicting plastic yielding in sheet materials. The proposed failure criterion encompasses all the previous failure theories including tensor polynomial theory and can be used to describe irregular failure surfaces. Advantages and disadvantages of the criterion were discussed. Examples of application of the failure criterion were provided for conditions of static loading and fatigue loading. Free edge delamination: laminate width and loading condition effects Pappu, L., Murthy, N., and Chamis, C.C. Journal o f Composite Technology and Research Vo111 No I (1989) pp 15-22 This paper describes the width and loading conditions effects on free edge stress fields are investigated using three dimensional finite element analysis. The loading conditions studied include in plane and out of plane bending, combined axial tension and inplane shear, twisting, uniform temperature and uniform moisture. The paper indicates that the lowest magnitude of free edge stress is obtained under conditions of axial tension. The magnitude of these stresses is found to be insignificant for laminates of practical dimensions and thus delamination may not occur because of free edge stresses alone. Geometrical effects in the low velocity impact response of CFt~ Cantwell, W.J., Morton, J. Composite Structures Vo112 No I (1989) pp 39-59 The influence of specimen geometry on the low velocity impact response of a series of CFRP laminates is described. Damage initiation and development in a range of beams were assessed using optical microscopy and c-scanning. Two forms of damage initiation are highlighted, top surface contact failure in short thick targets and a lower surface flexural failure in long thin laminates. The authors show that the subsequent development of damage depends strongly upon the energy absorbing capability of the structure. This is further shown by a study of the effect of geometry on the perforation threshold.
GENERAL Adhesion through molecular entanglements in polymer interfaces Raghava, R.S. and Smith, R.W. Journal o f Polymer Science Part B Vo127 No 12 (1989) pp 2525-2551 Sandwich laminates of poly methyl methacrylate (PMMA) and poly (vinylidene fuoride) (PVF2) are prepared in order to examine the role of polymer interdiffusion or interpenetration along a boundary between two compatible but dissimilar polymers in interfaciai adhesion. The interphase developed is characterized using electron and optical microscopy, dynamic mechanical spectroscopy, and X-ray microanalysis. Fracture behaviour is observed during tensile testing. Multiple crazing/fracture is seen to occur in the brittle PMMAphase, and shear yielding is observed in the ductile phase. Analysis of hybrid effect in unidirectional composites under longitudinal compression Yao, Li Ning, and Chou, Tsu-Wei. Composite Structures Vo112 No I (1989) pp 27-37 This paper describes a theoretical analysis of the hybrid effect in composites under longitudinal compression. The analysis is based on the instability of different types of fibre on a common elastic foundation of the matrix material. It depends on the elasticity of the matrix and the flexural stiffness of the fibres. The model assumes that instability in the low flexural stiffness fibre occurs first. As the load is further increased, instability in the high flexural stiffness fibre follows, and it results in the failure of the composite. The transverse deformation of the matrix induced by the low flexural stiffness fibres enhances the stability of the high flexural stiffness fibres in compression. Evaluation of the critical compressive load has been made. The paper shows that a synergistic effect in compressive strength can be realized through fibre hybridization. Analysis of viscoelastic laminated composite plies Aboudi, J., and Cederbaum, G. Composite Structures Vo112 No 4 (1989) pp 243-256 This paper describes a micromechanical analysis for the determination of five independent elastic moduli of unidirectional fibre composites. The five time dependent func-
268
C O M P O S I T E S . M A Y 1990
tions which characterize the effective behaviour of viscoelastic composites are established by using the correspondence principle, the inversion of the Laplace transform and by considering viscoelastic phases. The predicted time dependent behaviour is applied for the analysis of viscoelastic plates. The resulting viscoelastic effects are shown, and comparison between the results obtained within the classical laminated plate theory and the first order shear deformation theory is discussed. Burst pressure indication of metallic/fibre reinforced rocket motor cases using an elastoplastic instability analysis Groves, A. and Margetson, J. International Journal o f Mechanical Sciences Vo131 No 10 (1989) pp 737-750 This paper develops a numerical elastoplastic instability analysis which aims to predict the axial burst of fibre reinforced metallic rocket motor cases. Numerical and experimental results were found to be in good agreement. The analysis was extended to predict the hoop burst of an unwound motor and when combined with a simple reinforcement failure criterion the failure of motors due to overwinding of the reinforcing fibres. Delamination shape effects in Aramid-EpoxyAluminium (ARALL) laminates with fatigue cracks Macheret, J., Teply, J.L. and Winter, E.F.M. Polymer Composites Vol 10 No 5 (1989) pp 322-327 This paper examines the fatigue crack growth mechanisms in A R A L L laminates and relates them to the loading situation, delamination zone shapes and the number of intact fibres in the wake of a crack. An analytical model was developed using a residual strength criterion based on the maximum tensile stress in the aramid/epoxy layer. Analytical results for residual strength were compared with available experimental data. Effects of morphology on properties of graphite composites Herakovich, C.T. Carbon Vol 27 No 5 pp 663--678 The relationship between the morphology of graphite fibre composites and their effective mechanical properties, thermal properties, and failure characteristics is demonstrated. Typical results are presented for studies at the fibre matrix, lamina and laminate levels of analysis. It can be shown that the range of property variations in nonhomogeneous, laminated graphite materials can be very large, in particular when compared to monolithic materials. Further this dependence of material response on morphology can generally be predicted using the fundamental principles of mechanics. An electrical and microstructural study of composite films of a carbon black in a polyimide Norian, K.H. and Rieck, U. Composites Science and Technology Vol 36 No 1 (1989) pp 95-98 Composite films of Printex 200 (a carbon black) in polyimide are of interest as thickfilm resistors in hybrid circuits, and as coatings for electromagnetic shielding of microcircuits. Microstructural studies using transmission electron microscopy show that the carbon black particles are roughly spheri-
cal, and cross-sectional area within a unit cube is calculated. Volume fraction of carbon black (Vc) is varied and resistances of composite films are measured for various Vc values. The theory of Scarisbrick, which predicts the conductivity of spherical particles in an insulator, is applied, giving a value of 1 × 10-5 tim as the specific resistivity of carbon black within the composite films. Experimental collapse determination of cylindrical composite panels with large cutouts under axial load Palazotto, A.N. and Tisler, T.W. Composite Structures Vo112 No 1 (1989) pp 61-78 The paper describes an experimental program for the evaluation of the effect of large rectangular cutouts on the collapse of cylindrical panels. The effects of boundary conditions and residual stress are considered. The experimental results are compared to those obtained by a finite element analysis. Failure of a composite laminate under biaxial loading Neale, K.W. and Labossiere, P. Polymer Composites Vo110 No 5 (1989) pp 285-292 A general failure criterion for thin fibre reinforced composites under plane stress loading was presented. A parametric failure criterion was adapted from Budiansky's work on predicting plastic yielding in sheet materials. The proposed failure criterion encompasses all the previous failure theories including tensor polynomial theory and can be used to describe irregular failure surfaces. Advantages and disadvantages of the criterion were discussed. Examples of application of the failure criterion were provided for conditions of static loading and fatigue loading. Free edge delamination: laminate width and loading condition effects Pappu, L., Murthy, N., and Chamis, C.C. Journal o f Composite Technology and Research Vo111 No I (1989) pp 15-22 This paper describes the width and loading conditions effects on free edge stress fields are investigated using three dimensional finite element analysis. The loading conditions studied include in plane and out of plane bending, combined axial tension and inplane shear, twisting, uniform temperature and uniform moisture. The paper indicates that the lowest magnitude of free edge stress is obtained under conditions of axial tension. The magnitude of these stresses is found to be insignificant for laminates of practical dimensions and thus delamination may not occur because of free edge stresses alone. Geometrical effects in the low velocity impact response of CFt~ Cantwell, W.J., Morton, J. Composite Structures Vo112 No I (1989) pp 39-59 The influence of specimen geometry on the low velocity impact response of a series of CFRP laminates is described. Damage initiation and development in a range of beams were assessed using optical microscopy and c-scanning. Two forms of damage initiation are highlighted, top surface contact failure in short thick targets and a lower surface flexural failure in long thin laminates. The authors show that the subsequent development of damage depends strongly upon the energy absorbing capability of the structure. This is further shown by a study of the effect of geometry on the perforation threshold.