Stress Relaxation in Prestressed Composite Laminates

2002 ◽  
Vol 69 (4) ◽  
pp. 459-469 ◽  
Author(s):  
A. P. Suvorov ◽  
G. J. Dvorak
Keyword(s):  
Stress Relaxation ◽  
Composite Laminates ◽  
Constitutive Relations ◽  
Tensile Load ◽  
Free Edge ◽  
Laminated Plates ◽  
Curing Temperature ◽  
Field Analysis ◽  
Viscoelastic Deformation ◽  
Transformation Field Analysis

Viscoelastic deformation caused in symmetric laminated plates by release of fiber prestress and by uniform thermomechanical loads is analyzed on the constituent, ply and overall laminate scales with the Transformation Field Analysis (TFA) method (G. J. Dvorak, Proc. R. Soc. Lond., 1992, A437, pp. 311–327). Fiber prestress is applied in individual plies prior to matrix cure and released after matrix consolidation. Linear or nonlinear viscoelastic constitutive relations are used to evaluate the inelastic deformation rates in terms of current constituent stress averages. The TFA method regards both thermal and inelastic strains as piecewise uniform eigenstrains acting in superposition with mechanical loads and fiber prestress release on an elastic laminate. Interactions between the eigenstrains at the three different size scales are described by certain influence functions derived from micromechanical analysis of the plies and laminates. Applications describe stress relaxation in two carbon/epoxy laminates after cooling from the curing temperature and release of optimized fiber prestress, that allows maximum tensile load application while keeping both interior and free-edge stresses within prescribed strength limits. Subsequent viscoelastic deformation under constant rate loading, and stress relaxation caused by a sustained application of an elevated temperature to a laminate without prestress are also analyzed. Results are presented in the form of initial failure maps that identify overall stress states which may or may not initiate a specific damage mode in the laminate.

Simple Solutions of the Free-Edge Stresses in Composite Laminates under Thermal and Mechanical Loads

1994 ◽  
Vol 28 (6) ◽  
pp. 573-586 ◽  
Author(s):  
Wan-Lee Yin
Keyword(s):  
Composite Laminates ◽  
Constitutive Relations ◽  
Free Edge ◽  
Normal Derivative ◽  
Boundary Region ◽  
Material Behavior ◽  
Interlaminar Stresses ◽  
Inelastic Material ◽  
Stress Functions ◽  
Temperature Loads

Intense and localized interlaminar stresses generally occur in a narrow boundary region near the free edge of a multilayered anisotropic laminate under mechanical and temperature loads. Quantitative measures of interlaminar action across interfaces may be readily obtained through purely algebraic operations, even if nonlinear and inelastic material behavior becomes significant in the boundary region due to severe strain concentration. These measures are the limiting values of the Lekhnitskii stress functions F and $$ (and of the normal derivative of F) along interfaces and toward the interior region of the laminate. In the present work, they are used as the basis of an exceedingly simple and efficient method of interlaminar stress analysis that is potentially applicable to free-edge problems involving nonlinear thermoelastic constitutive relations. Example solutions are obtained for symmetric, four-layer, cross-ply and angle-ply laminates under a temperature load and two different types of strain loads, and the results are found to be in reasonable agreement with the existing numerical and analytical solutions based on elaborate analysis methods.

Free Edge Stresses in Elastic and Viscoelastic Composites Under Uniaxial Extension, Bending, and Twisting Loadings

1997 ◽  
Vol 119 (3) ◽  
pp. 266-272 ◽  
Author(s):  
Sung Yi ◽  
H. H. Hilton
Keyword(s):  
Stress Relaxation ◽  
Constitutive Relations ◽  
Plane Deformation ◽  
Uniaxial Extension ◽  
Free Edge ◽  
Time Dependent ◽  
Interlaminar Stresses ◽  
Shear Moduli ◽  
Deformation State ◽  
Interlaminar Shear

Time-dependent interlaminar stresses in elastic and viscoelastic laminated composites subjected to arbitrary combinations of axial extension, bending and/or twisting loads are obtained based on integral constitutive relations and Pipes and Pagano’s displacement field for laminates under a generalized plane deformation state. Numerical results obtained from the present formulation are compared against experimental data and excellent agreement within two percent was obtained between these results. Time-dependent interlaminar stresses for cross-ply and angle-ply laminates subjected to uniaxial extension, bending and twisting are also presented. Appreciable stress relaxation occurred during the loading period resulting in decreased magnitudes of residual stresses. It is seen that the rate of interlaminar shear stress relaxation is greater than the normal one, since the relaxation of shear moduli is larger than that of the normal moduli.

Approximate Design Analysis of Failure Within Composite Laminated Plates

1982 ◽  
Vol 104 (3) ◽  
pp. 604-611 ◽  
Author(s):  
R. L. Gallo ◽  
A. N. Palazotto
Keyword(s):  
Computer Simulation ◽  
Analytical Study ◽  
Three Dimensional ◽  
Free Edge ◽  
Laminated Plates ◽  
Curing Temperature ◽  
Laminated Plate ◽  
Approximate Design ◽  
Composite Laminated Plates ◽  
Good Agreement

This paper is an analytical study of the effects of interlamina stresses near the free edge of a laminated plate due to axial and moment loading variations. A three-dimensional extension of the Tsai-Hill failure criterion is introduced to predict delamination. Results achieved by computer simulation show good agreement with experimental observations made by other sources. The distance from the free edge is decidedly important as is the effect of curing temperature because of the consequences these parameters have on the magnitude of the stress field. The failure estimations provide an approximate bound and are worthy of due consideration by the design engineer in the stress analysis of test specimens.

Physical Ultrasonics of Composites

2011 ◽  
Author(s):  
Dale Chimenti ◽  
Stanislav Rokhlin ◽  
Peter Nagy
Keyword(s):  
Composite Laminates ◽  
Stiffness Matrix ◽  
Composite Plates ◽  
Anisotropic Media ◽  
Anisotropic Materials ◽  
Ultrasonic Waves ◽  
Laminated Plates ◽  
Structure Characteristic ◽  
Major Advance

Physical Ultrasonics of Composites is a rigorous introduction to the characterization of composite materials by means of ultrasonic waves. Composites are treated here not simply as uniform media, but as inhomogeneous layered anisotropic media with internal structure characteristic of composite laminates. The objective here is to concentrate on exposing the singular behavior of ultrasonic waves as they interact with layered, anisotropic materials, materials which incorporate those structural elements typical of composite laminates. This book provides a synergistic description of both modeling and experimental methods in addressing wave propagation phenomena and composite property measurements. After a brief review of basic composite mechanics, a thorough treatment of ultrasonics in anisotropic media is presented, along with composite characterization methods. The interaction of ultrasonic waves at interfaces of anisotropic materials is discussed, as are guided waves in composite plates and rods. Waves in layered media are developed from the standpoint of the "Stiffness Matrix", a major advance over the conventional, potentially unstable Transfer Matrix approach. Laminated plates are treated both with the stiffness matrix and using Floquet analysis. The important influence on the received electronic signals in ultrasonic materials characterization from transducer geometry and placement are carefully exposed in a dedicated chapter. Ultrasonic wave interactions are especially susceptible to such influences because ultrasonic transducers are seldom more than a dozen or so wavelengths in diameter. The book ends with a chapter devoted to the emerging field of air-coupled ultrasonics. This new technology has come of age with the development of purpose-built transducers and electronics and is finding ever wider applications, particularly in the characterization of composite laminates.

scholarly journals Theory of the deformation of aligned polyethylene

2015 ◽  
Vol 471 (2180) ◽  
pp. 20150171 ◽  
Author(s):  
A. Hammad ◽  
T. D. Swinburne ◽  
H. Hasan ◽  
S. Del Rosso ◽  
L. Iannucci ◽  
...  
Keyword(s):  
Load Transfer ◽  
Tensile Load ◽  
Equation Of Motion ◽  
Dislocation Dynamics ◽  
Viscoelastic Deformation ◽  
Transfer Length ◽  
Soliton Dynamics ◽  
Fluctuation Dissipation ◽  
Pull Out ◽  
Definition Of

Solitons are proposed as the agents of plastic and viscoelastic deformation in aligned polyethylene. Interactions between straight, parallel molecules are mapped rigorously onto the Frenkel–Kontorova model. It is shown that these molecular interactions distribute an applied load between molecules, with a characteristic transfer length equal to the soliton width. Load transfer leads to the introduction of tensile and compressive solitons at the chain ends to mark the onset of plasticity at a well-defined yield stress, which is much less than the theoretical pull-out stress. Interaction energies between solitons and an equation of motion for solitons are derived. The equation of motion is based on Langevin dynamics and the fluctuation–dissipation theorem and it leads to the rigorous definition of an effective mass for solitons. It forms the basis of a soliton dynamics in direct analogy to dislocation dynamics. Close parallels are drawn between solitons in aligned polymers and dislocations in crystals, including the configurational force on a soliton. The origins of the strain rate and temperature dependencies of the viscoelastic behaviour are discussed in terms of the formation energy of solitons. A failure mechanism is proposed involving soliton condensation under a tensile load.

scholarly journals Progressive Failure Analysis in Open-Hole Tensile Composite Laminates of Airplane Stringers Based on Tests and Simulations

2020 ◽  
Vol 11 (1) ◽  
pp. 185
Author(s):  
Jian Shi ◽  
Mingbo Tong ◽  
Chuwei Zhou ◽  
Congjie Ye ◽  
Xindong Wang
Keyword(s):  
Failure Analysis ◽  
Composite Laminates ◽  
Progressive Failure ◽  
Tensile Load ◽  
Fiber Failure ◽  
Stress Criterion ◽  
Progressive Failure Analysis ◽  
Analysis Technique ◽  
Open Hole ◽  
Failure Types

The failure types and ultimate loads for eight carbon-epoxy laminate specimens with a central circular hole subjected to tensile load were tested experimentally and simulated using two different progressive failure analysis (PFA) methodologies. The first model used a lamina level modeling based on the Hashin criterion and the Camanho stiffness degradation theory to predict the damage of the fiber and matrix. The second model implemented a micromechanical analysis technique coined the generalized method of cells (GMC), where the 3D Tsai–Hill failure criterion was used to govern matrix failure, and the fiber failure was dictated by the maximum stress criterion. The progressive failure methodology was implemented using the UMAT subroutine within the ABAQUS/implicit solver. Results of load versus displacement and failure types from the two different models were compared against experimental data for the open hole laminates subjected to tensile displacement load. The results obtained from the numerical simulation and experiments showed good agreement. Failure paths and accurate damage contours for the tested specimens were also predicted.

Experimental Investigation of Impacted and Non-Impacted Composite Laminates under Compressive Loading

2011 ◽  
Vol 284-286 ◽  
pp. 607-610
Author(s):  
Jiang Tao Ruan ◽  
Min Shen ◽  
Jing Wei Tong ◽  
Shi Bin Wang ◽  
Francesco Aymerich ◽  
...  
Keyword(s):  
Composite Laminates ◽  
Optical Measurement ◽  
Speckle Pattern ◽  
Compressive Loading ◽  
Laminated Plates ◽  
Low Velocity Impact ◽  
Compressive Deformation ◽  
Electronic Speckle Pattern Interferometry ◽  
Low Velocity ◽  
The Impact

In this paper, the deformation measurements of impacted and non-impacted composite laminates under compressive loading are taken. [03/903]S orientated cross-ply laminated plates with impact delamination and without delamination are tested using an anti-buckling testing device in compression experiment. The delamination is induced by low-velocity impact test at the impact energy level of 3.105J. For both impacted and non-impacted specimens, the compressive deformation is measured by a carrier electronic speckle pattern interferometry (CESPI) optical measurement technique. It is found that the deformation behavior of the two specimens presents a mixed deformation mode. However, the delamination has significant effect on the compressive deformation of composite laminates.

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