Showing papers on "Composite laminates published in 1997"

Mechanics of laminated composite plates : theory and analysis

Abstract: Introduction and Mathematical Preliminaries Fiber-Reinforced Composite Materials. Vectors and Tensors. Matrices. Transformation of Vector and Tensor Components. Integral Relations. Equations of Anisotropic Elasticity Classification of Equations. Kinematics. Kinetics. Constitutive Equations. Equations of Thermoelasticity and Electroelasticity. Summary. Virtual Work Principles and Variational Methods Virtual Work. The Variational Operator and Functionals. Extrema of Functionals. Virtual Work Principles. Variational Methods. Summary. Introduction to Composite Materials Basic Concepts and Terminology. Constitutive Equations of a Lamina. Transformation of Stresses and Strains. Plane Stress Constitutive Relations. Classical and First-Order Theories of Laminated Composite Plates Introduction. An Overview of ESL Laminate Theories. The Classical Laminated Plate Theory. The First-Order Laminated Plate Theory. Stiffness Characteristics for Selected Laminates. One-Dimensional Analysis of Laminated Plates Introduction. Analysis of Laminated Beams Using CLPT. Analysis of Laminated Beams Using FSDT. Cylindrical Bending Using CLPT. Cylindrical Bending Using FSDT. Closing Remarks. Analysis of Specially Orthotropic Plates Using CLPT Introduction. Bending of Simply Supported Plates. Bending of Plates with Two Opposite Edges Simply Supported. Bending of Rectangular Plates with Various Boundary Conditions. Buckling of Simply Supported Plates Under Compressive Loads. Buckling of Rectangular Plates Under Inplane Shear Load. Vibration of Simply Supported Plates. Buckling and Vibration of Plates with Two Parallel Edges Simply Supported. Closure. Analytical Solutions of Rectangular Laminates Using CLPT Governing Equations in Terms of Displacements. Admissible Boundary Conditions for the Navier Solutions. Navier Solutions of Antisymmetric Cross-Ply Laminates. The Navier Solutions of Antisymmetric Angle-Ply Laminates. The LTvy Solutions. Analysis of Midplane Symmetric Laminates. Transient Analysis. Summary. Analytical Solutions of Rectangular Laminates Using FSDT Introduction. Simply Supported Antisymmetric Cross-Ply Laminates. Simply Supported Antisymmetric Angle-Ply Laminates. Antisymmetric Cross-Ply Laminates with Two Opposite Edges Simply Supported. Antisymmetric Angle-Ply Laminates with Two Opposite Edges Simply Supported. Transient Solutions. Summary. Finite Element Analysis of Composite Laminates Introduction. Laminated Beams and Plate Strips by CLPT. Timoshenko Beam/Plate Theory. Numerical Results for Beams and Plate Strips. Finite Element Models of Laminated Plates (CLPT). Finite Element Models of Laminated Plates (FSDT). Summary. Refined Theories of Laminated Composite Plates Introduction. A Third-Order Plate Theory. Higher-Order Laminate Stiffness Characteristics. The Navier Solutions. LTvy Solutions of Cross-Ply Laminates. Displacement Finite Element Model. Layerwise Theories and Variable Kinematic Models In troduction. Development of the Theory. Finite Element Model. Variable Kinematic Formulations. Nonlinear Analysis of Composite Laminates Introduction. Nonlinear Stiffness Coefficients. Solution Methods for Nonlinear Algebraic Equations. Computational Aspects and Numerical Examples. Closure. Index Most chapters include Exercises and References for Additional Reading

Stress analysis of fiber-reinforced composite materials

Abstract: 1 Fiber-Reinforced Composite Materials2 Linear Elastic Stress-Strain Characteristics of Fiber-Reinforced Material3 Prediction of Engineering Properties Using Micromechanics4 The Plane-Stress Assumption5 Plane-Stress, Stress-Strain Relations in a Global Coordinate System6 Classical Lamination Theory: The Kirchoff Hypothesis7 Classical Lamination Theory: Lamination Stiffness Matrix8 Classical Lamination Theory: Additonal Examples9 Failure Theories for Fiber-Reinforced Materials Maximum Stress Criterion10 Failure Theories for Fiber-Reinforced Materials The TSAI-Wu Criterion11 Environmentally-Induced Stresses in Laminates12 Through-Thickness Laminate Strains13 Introduction to Fiber-Reinforced Laminated Planes14 Appendix Manufacturing Composite Laminates

Some experimental investigations in the drilling of carbon fiber-reinforced plastic (CFRP) composite laminates

Abstract: In this paper, a concept of delamination factor F d (i.e. the ratio of the maximum diameter D max in the damage zone to the hole diameter D ) is proposed to analyze and compare easily the delamination degree in the drilling of carbon fiber-reinforced plastic (CFRP) composite laminates. Experiments were performed to investigate the variations of cutting forces with or without onset of delamination during the drilling operations. The effects of tool geometry and drilling parameters on cutting force variations in CFRP composite materials drilling were also experimentally examined. The experimental results show that the delamination-free drilling processes may be obtained by the proper selections of tool geometry and drilling parameters. The effects of drilling parameters and tool wear on delamination factor are also presented and discussed. Cutting temperature has long been recognized as an important factor influencing the tool wear rate and tool life. An experimental investigation of flank surface temperatures is also presented in this paper. Experimental results indicated that the flank surface temperatures increase with increasing cutting speed but decreasing feed rate. Optimal cutting conditions are proposed to avoid damage from burning during the drilling processes.

Composites Engineering Handbook

Abstract: Introduction - definitions, classifications and applications. Part 1 Constituents: fibres, fabrics and fillers matrix resins and fibre/matrix adhesion. Part 2 Mechanics: micromechanics mechanics of laminated structures mechanics of woven fabric composites fracture and damage mechanics in laminated composites. Part 3 Processing: processing for laminated structures press moulding processes filament winding the pultrusion process for continuous automated manufacture of engineered composite profiles processing of thermoplastic matrix composites processing of particle-reinforced metal matrix composites joining and repair of aircraft composite structures machining of composite materials. Part 4 Properties and performance: laminated polymer matrix composites random fibre composites selection guidelines for metal matrix composites ceramic matrix composites cement matrix composites. Part 5 Testing: mechanical property measurements nondestructive tests. Part 6 Engineering with composite materials: design methodology and practices materials selection, preliminary design and sizing for composite laminates design guidelines for laminated composites.

Effects of hole machining defects on strength and fatigue life of composite laminates

Abstract: The effects of hole machining defects on strength and fatigue life of carbon/epoxy laminates subjected to static and fatigue loading are presented. Dry specimens were subjected to pin loading and uniaxial compressive loading at room temperature. The KTH method, a new method which gives defect-free holes, was used to machine holes in the specimens. For comparison, holes were also machined using two traditional drilling techniques causing varying extents of damage. X-ray techniques were used to detect the hole machining defects. The permanent deflection of compressively loaded specimens was monitored during cyclic loading. Hole machining defects significantly reduced the static and fatigue strengths of pin-loaded laminates; the effects on the strengths of compressively loaded laminates were less pronounced.

Design and performance of bonded patch repairs of composite structures

Abstract: The compressive behaviour of bonded patch repaired composite laminates is examined. A non-linear stress analysis is performed on a double-lap joint in order to identify critical joint parameters and design an efficient external patch repair. It is found that oversized patches not only increase the structure's weight but also increase the stress concentrations in the repaired region which can cause premature failure. Reducing the patch thickness near the edges of the overlap and increasing the local adhesive thickness decreases the stress concentration in both shear and peel stresses. A three- dimensional finite element analysis is then performed to determine the stresses in the optimum repaired configuration and is used with a stress failure criterion to predict the ultimate failure load. Experimental measurements show that carefully designed bonded patch repairs can recover almost 80 per cent of the undamaged laminate strength.

Dynamic mechanical analysis of FRP composites based on different fiber reinforcements and epoxy resin as the matrix material

Abstract: Three-ply composite laminates prepared from E-glass or N-glass chopped strand mats (CSMs) and jute (J) fabrics as reinforcing agents and amine-cured epoxy resin as the matrix material were subjected to dynamic mechanical thermal analysis at a fixed frequency of 1 Hz over a temperature range of 30–180°C. The volume fraction of fibers ranged between 0.21 and 0.25. The reinforcing effect for the three fibers is in the order E-glass > N-glass ≫ jute. Glass-reinforced composites show a higher storage modulus (E′) than that of jute-reinforced composites. The E′ values of glass-jute hybrid composites lie between those of glass-reinforced and jute-reinforced composites. Odd trends in temperature variability of the loss modulus (E′) and the damping parameter, tan δ, and in the glass transition temperature (Tg) for the three different unitary and four different hybrid composites are interpreted and understood on the basis of odd differences in (1) the chemical nature and physical properties of the three different fibers (E-glass, N-glass, and jute), (2) the void content and distribution, (3) the thermal expansion coefficients of the main phases in the composites, (4) the degree of matrix stiffening at or near the fiber-matrix interface, and (5) the extents of matrix softening in the zone next to the interface. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2467–2472, 1997

Viscoelastic analysis of processing-induced residual stresses in thick composite laminates

Abstract: Residual stresses induced during the processing of thick composite laminates are analyzed. A two-dimensional thermochemical analysis is used to obtain temperature and degree of cure distributions during cure. A two-dimensional finite-element model is developed to predict the residual stress history in rectangular laminated plates. A cure-dependent visco-elastic material model is used in the analysis. Both unidirectional and cross-ply laminates are investigated. Unidirectional laminates are studied because residual stresses in this class of laminates is driven purely by thickness effects. Regardless of the layup,for moderately thick (2.54-cm) laminates the nonuniformities in temperature and degree of cure are mild. As a result, the development of residual stress is very similar to the analysis of thin laminates. For laminates of large thickness (7.5 cm), stronger variations in temperature and degree of cure develop during the cure cycle. The development of residual stress in this case is more complex. The ...

A higher order theory for modeling composite laminates with induced strain actuators

Abstract: A refined higher order laminate theory is developed to analyze smart materials, surface bonded or embedded, in composite laminates. The analysis uses a refined displacement field which accounts for transverse shear stresses through the thickness. All boundary conditions are satisfied at the free surfaces. Non-linearities are introduced through the strain dependent piezoelectric coupling coefficients and the assumed strain distribution through the thickness. The analysis is implemented using the finite element method. The procedure is computationally efficient and allows for a detailed investigation of both the local and global effects due to the presence of actuators. The finite element model is shown to agree well with published experimental results. Numerical examples are presented for composite laminates of various thicknesses and the results are compared with those obtained using classical laminate theory. The refined theory captures important higher order effects which are not modeled by the classical laminate theory, resulting in significant deviations.

Development of an Autoclave Cure Cycle with Cooling and Reheating Steps for Thick Thermoset Composite Laminates

Abstract: In this study, an autoclave cure cycle for thick thermosetting resin matrix composite materials was developed to reduce the temperature overshoot. To predict the temperature distribution of thick thermosetting composite laminates during cure, the heat transfer equation, including the heat generation term, was simulated by the finite difference method (FDM). Using the simulated results, the cure cycle was obtained by modifying the conventional cure cycle. The steps of cooling and reheating, which were determined by the cure rate and temperature at the midpoint of the laminate, were introduced into the conventional cure cycle. The developed cure cycle was used to cure 15 and 30 mm (100 and 200 ply) thick laminates and was found to be effective for the reduction of temperature over-shoot

Method for manufacture of a fiber reinforced composite spar for rotary wing aircraft

Abstract: A method for manufacture of a fiber reinforced composite spar for a helicopter rotor blade including upper and lower sidewall regions and forward and aft conic regions. Constant width crossplies and unidirectional plies are stacked and arranged to form crossply and unidirectional laminates. The composite spar is manufactured via a vacuum forming technique which includes forming the composite laminates directly over an inflatable mandrel assembly. Regarding the latter method, a spar forming apparatus is used to position and manipulate the mandrel assembly as composite laminates are laid. The spar forming apparatus includes first and second pedestal supports being suitably configured so as to facilitate formation of the butt joints in the conic regions of the composite spar. The pedestal supports are movable from a first orientation to facilitate lay-up of composite laminates over the mandrel assembly, to a second orientation to facilitate transfer of the mandrel assembly from one to the other of the pedestal supports. The spar forming apparatus further includes an electromagnetic coil system comprising at least one electrically activated coil and a controllable power source. The electrically activated coils are disposed in combination with each of the pedestal supports and the controllable power source selectively energizes the electrically activated coils to effect a magnetic clamping force between the mandrel assembly and one of the pedestal supports. Such electromagnetic coil system accurately positions the inflatable mandrel assembly during lay-up of the composite laminates and effects transfer of the mandrel assembly.

Fracture Criterion for Notched Thin Composite Laminates

Abstract: Fracture behavior of fiber-dominated center-notched AS4/3501-6 graphite-epoxy laminates is investigated in this study. Nine laminate configurations are studied to examine flaw size effects, crack tip damage mechanisms, and failure modes under uniaxial tensile loading. Results indicate that a constant value of fracture toughness K Q is a laminate material property. A layup independent failure criterion is proposed, which relates laminate fracture toughness to the fracture toughness K Q 0 of the principal load bearing ply. K Q 0 characterizes the in situ fracture toughness of a notched 0-deg layer in the event of fiber breakage along the plane of the notch. Once its value is estimated from preliminary tests, this parameter can be used to predict fracture toughness, and hence residual strength, of other fiber-dominated laminates of the same material system. The model predictions agree well with current experimental results, as well as with data published by other researchers. The model is further extended to predict residual strength of laminates with inclined cracks (mixed-mode loading). It is demonstrated that the normal projection of the crack to the applied load can be considered as the equivalent crack and governs laminate residual strength.