Interface Of Laminate Research Articles

ANALYSIS OF THE EFFECTS OF LAMINATE DEPTH AND MATERIAL PROPERTIES ON THE DAMPING ASSOCIATED WITH LAYERED STRUCTURES IN A PRESSURIZED ENVIRONMENT

In aerodynamic and machine structures, one of the effective ways of dissipating unwanted vibration or noise is to exploit the occurrence of slip at the interface of structural laminates where such members are held together in a pressurised environment. The analysis and experimental investigation of such laminates have established that when subjected to either static or dynamic loading, non-uniformity in interface pressure can have significant effect on both the energy dissipation and the logarithmic damping decrement associated with the mechanism of slip damping. Such behaviour can in fact be effectively exploited to increase the level of damping available in such a mechanism. What has however not been examined is to what extent is the energy dissipation affected by the relative sizes or the material properties of the upper and lower laminates? In this paper the analysis is extended to incorporate such effects. In particular, by invoking operational methods, it is shown that variation in laminate thickness may provide less efficacious means of maximizing energy dissipation than varying the choice of laminate materials but that either of these effects can in fact dwarf those associated with non-uniformity in interface pressure. To achieve this, a special configuration is required for the relative sizes and layering of the laminates. In particular, it is shown that for the case of two laminates, the upper laminate is required to be thinner and harder than the lower one. These results provide a basis for the design of such structures.

Effects of surface pre-treatment and void content on GLARE laminate process characteristics

In this paper the effects of surface morphology and voids formed in the metal sheet–prepreg interface of GLARE laminates were evaluated. The experiments were carried out with aluminum sheets on which the surface morphology was systematically varied by different roughness levels of surface textures (sanding and nylon-pad abrasion) and chemical etches. The surface morphology of the substrates was characterized with profilometry and the static contact angle technique. Void contents at the metal sheet–prepreg interfaces were determined by scanning electron microscopy. The changes in surface roughness and surface energy effectively enhance the bonding strength of GLARE laminates. Experimental results also indicate that the autoclave pressure enhances GLARE interfacial bonding, to a certain extent, with low void content.

銅電解精製におけるワックスレスパーマネントカソードプロセスのラミネーション界面

The lamination interface generated by a power outage during the electrorefining of copper using a wax-less permanent-cathode was investigated to elucidate the formation mechanism of the interface. X-ray diffraction, X-ray photoelectron spectroscopic measurements and electrochemical quartz crystal microbalance measurements revealed that the interface is composed mostly of CuCl (s) . Based on the thermodynamics of aqueous solution containing copper ions and chloride anions, it is considered that Cu+ ions are spontaneously generated through the reaction Cu + Cu2+ → 2Cu+ at the surface of the copper cathode, resulting in the deposition of insoluble CuCl (s) . Circulation of electrolyte during the power outage could suppress the accumulation of Cu+ ions in the vicinity of the cathode and minimize the formation of CuCl (s) layer, which makes the lamination interface after recovery from the power outage.

Fracture of adhesively-bonded pultruded GFRP joints under constant amplitude fatigue loading

The fracture behavior of adhesively-bonded structural joints under tensile constant amplitude fatigue has been investigated. Double-lap joints (DLJs) and stepped-lap joints (SLJs) composed of pultruded GFRP laminates and an epoxy adhesive were examined. Both joint types exhibited a fiber-tear failure with cracks that initiated at the joint edges in the adhesive–laminate interface and then propagated in the laminates’ mat layers. A linear trend of crack growth and compliance was observed for the DLJs whereas a sigmoid trend was found for SLJs. The experimental compliance method was used for the calculation of the maximum strain energy release rate, G max, and the incremental polynomial method for the calculation of the crack propagation rate, da/dN. Fatigue crack growth (FCG) curves established for both joint types showed that empirical constants are dependent on the joint configuration. Based on this fatigue life modeling, design allowables that correlate the developed damage with fatigue life were derived.

Effect of interfacial bonding strength on tensile ductility of multilayered steel composites

The effect of the bonding strength of the laminate interface on ductility in the tensile deformation of multilayered steel composites was investigated. Multilayered steel composites consisting of alternating layers of as-quenched martensitic and austenitic steels were prepared with various bonding strengths, ranging from weak bonding obtained by alpha-cyanoacrylate adhesive to strong bonding obtained by cold rolling with a subsequent heat treatment. Tensile tests and peel tests were conducted to investigate the relationship between tensile behavior and bonding strength at the interface. It was demonstrated that tensile ductility could be markedly enhanced as the bonding strength increased, and that three types of tensile fracture behavior were identified depending on the bonding strength of the interface.

Failure Analysis of Bolted Joints in Foam-core Sandwich Composites

This study represents an effort to predict the bearing strength, failure modes, and failure load of bolted joints in foam-core sandwich composites. The studied joints have been used in a light full composite airplane. By using solid laminates, a new design for the joint zone is developed. These solid laminates include a number of glass plies with total thickness equal to core thickness. The effect of solid laminate size and interface angle of foam—solid laminate in the bonding zone on the bearing strength, failure loads and type of modes are investigated. The numerical study is performed using 3D FEM in ANSYS commercial code. Tsai—Wu failure criterion is used in the failure analysis. The results indicate that the most important parameter in the proposed joint zone design is the foam—solid laminate interface angle which plays an important role on the value of failure criterion (damage) in the bonding zone. Also, the use of squared shaped solid laminate as compared with a circular laminate will decrease the criterion value significantly. Finally, the influence of solid laminate size and interface angle on the buckling strength was discussed. As obtained through eigenvalue buckling analysis, the increase of solid laminate size or interface angle could result in considerable higher buckling strength.

The distribution of magnesium and silicon across the as-cast interface of aluminum laminates produced via the Novelis Fusion™ process

Novelis Inc. recently introduced a multi-alloy, multi-layered, aluminum ingot solidification technology that allows the production of a variety of engineered clad products on a commercial scale. The technology allows selection of the appropriate combinations of clad and core alloys to produce desired mechanical properties as well as forming and surface characteristics superior to either monolithic material alone. It has been shown that the Novelis Fusion™ interface is oxide film and porosity free. This article analyzes the interplay of the aforementioned alloy combinations giving particular attention to the cast intermetallics, the diffusion of silicon and magnesium, the population of secondary phase particles (dispersoids) at the interface, and the rate of diffusion.

Effect of bar sealing parameters on OPP/MCPP heat seal strength

The effect of bar sealing parameters on the heat seal strength of oriented polypropylene (OPP)/metallic cast polypropylene (MCPP) laminate film was investigated. Based on the results obtained from the parametric study, a bar seal- ing process window was developed. All points drop within the process window are combinations of platen temperature and dwell time that produce acceptable heat seal. Optimum combinations are indicated by the lower border of the window. The plateau initiation temperature, Tpi of OPP/MCPP laminate film used in the present study occurred before the final melting temperature, Tmf of the sealant material. The highest achievable heat seal strength was at the plateau region, and the corre- sponding failure modes were delaminating, tearing or combine failure modes (delaminating and tearing). Minimum pres- sure level of 1.25 bars is necessary to bring the laminate interface into intimate contact in order to effect sealing.

Stress analyses of laminates under cylindrical bending

AbstractA semi‐analytical approach for evaluation of stresses and displacements in composite and sandwich laminates under cylindrical bending subjected to transverse load has been developed in this paper. Two dimensional (2D) partial differential equations (PDEs) of such a laminate are obtained by imposing plane‐strain conditions of elasticity. The fundamental dependent variables are so selected in this formulation that they satisfy the continuity of displacements and transverse interlaminar stresses at the laminate interface through the thickness. The set of governing PDEs are transformed into a set of coupled first‐order ordinary differential equations (ODEs) in thickness direction by assuming suitable global orthogonal trigonometric functions for the fundamental variables satisfying the boundary conditions. These ODEs are numerically integrated by a specially formulated ODE integrator algorithm involving transformation of a two‐point boundary value problem (BVP) into a set of initial value problems (IVPs). Numerical studies on both composite and sandwich laminates for various aspect ratios are performed and presented. Accuracy of the present approach is demonstrated by comparing the results with the available elasticity solution. It is seen that the present results are in excellent agreement with the elasticity solutions. Some new results for sandwich laminates and for uniform loading condition are presented for future reference. Copyright © 2006 John Wiley & Sons, Ltd.

Thermoforming-Stamping of Continuous Glass Fiber/Polypropylene Composites: Interlaminar and Tool–Laminate Shear Properties

The results of interlaminar and tool–laminate shear tests performed on a twill 2 2 PP/glass fabric are described in this paper. The influence of the laminate temperature, pullout velocity and normal pressure on the interlaminar shear stress and friction coefficient are evaluated, as well as the effect of cooling the specimen from the melt to simulate real forming conditions. Opposite trends were observed for the variation of the shear stress and friction coefficient whether the tests were performed above the melt temperature of the matrix or above the crystallization temperature (135, 140, and 155 after cooling from the melt temperature. For the interlaminar shear tests, this was caused by the shift from an interlaminar to an intralaminar shear deformation mode occurring. For the tool–laminate shear tests, this was caused by the shift from matrix shear at the interface tool–laminate to direct Coulomb friction of the fibers with the tool with an increase of the normal pressure and/or an increase of the matrix viscosity with decreasing temperatures. Above the melt temperature of the matrix, the friction coefficient and shear stress were higher at the tool–laminate interface than in the interlaminar region while at temperatures close to the crystallization temperature they became lower at the tool–laminate interface. A summary of these observations is made and a discussion of their possible impact on the forming of parts is enlightened.

Effect of Fiber Bridging on Growth Behavior of Mode I Interlaminar Fatigue Cracks in High Strength GFRP

The mode I crack growth behavior from delamination was investigated with two kinds of laminates, UD laminates (made of unidirectional laminates) and C laminates (made of unidirectional laminates and cloth laminates), of high strength glass fiber reinforced plastics (GFRP). Crack growth tests were carried out by double cantilever beam specimens under cyclic and monotonic loadings. The fracture toughness at the onset of crack propagation, CIc., was not influenced by the lot of laminates and nearly equal for UD laminates and C laminates. On the other hand, the increase of the fracture toughness with crack extension, GIR, was very much dependent on the lot, and the value for C laminates was much higher than that of UD laminates. Under cyclic loading with a stress ratio of R=0.1, the fatigue crack propagation rate expressed in terms of a power function of the maximum crack-tip value, GI tipmax, of the energy release rate was nearly identical in UD and C laminates. The increase of the bridging component of the energy release rate, GIbridgemax /GI max, with crack extension was dependent on the lot and the kind of laminates. Fractographic observation of UD laminates showed mode II crack propagation on the surface of fibers, while mode I crack propagation in resin. In C laminates, crack propagation path was on the interface of cloth laminates and fiber bridging caused by fibers of cloth laminates.

Influence of fiber direction and mixed-mode ratio on delamination fracture toughness of carbon/epoxy laminates

Surface free energy has been often treated as a scalar constant without considering its dependence on propagation direction. It is desirable, however, to investigate how surface free energy or fracture toughness of delamination in a single interface varies with both the local mismatch angle of fiber directions and the direction of crack propagation in polymeric laminate composites. As a materials constant, fracture toughness is effectively used for various mechanical analyses of fiber-reinforced composites as well as conventional materials. This study investigates quantitatively and qualitatively the dependence of delamination fracture toughness on mismatch angle and crack propagation direction in laminated structures. AS4-Carbon/Epoxy prepregs were used for fabricating test specimens, and 50 different mismatch angles of fiber direction were applied on the delaminated interface of laminates. Fracture toughness was measured using the Mixed-mode Bending (MMB) test. This test method is composed of fracture mode-I and mode-II, and the mixed-mode ratio ( G II/ G) can be controlled. The mixed-mode ratios used here were 20, 35, 50, 65, and 80%. The crack path and the delamination fracture toughness were observed and calculated for specimens, and the dependence of the toughness was shown to be related to the mismatch angle of ply fibers at the delaminated interface. The relationship between mismatch angle and delamination fracture toughness was newly revealed and discussed for various angles. These results can be usefully applied to various fracture mechanics analyses in fiber-reinforced laminated composites.

Improvement of the interlaminar fracture toughness of composite laminates by whisker reinforced interlamination

In this study, an attempt is made to improve the interlaminar fracture toughness of composite laminates by distributing whiskers along the interface of composite laminates during the lay-up process. Commercially available T800H/3631 CFRP prepreg and β-SiC whisker are employed to prepare the specimens. A simple spray method is developed to distribute whiskers on the prepreg. Unidirectional laminates of 24 plies with whisker reinforced interlamination are made. The conventional double cantilever beam (DCB) and end loaded split (ELS) tests are conducted to investigate the effects of whiskers on the Mode I and Mode II interlaminar fracture toughness, respectively. Microscopic analysis of the side-edge, cross-section and fracture surface of specimens is performed by optical microscopic, scanning electron microscope (SEM) and electron probe micro-analyzer (EPMA) to investigate the distribution of whiskers and the improvement mechanism of the distributed whiskers on the fracture toughness.

Mullite/zirconia laminate composites for high temperature application

Mullite/zirconia laminate composites were studied for a better understanding of crack formation and crack propagation behavior at the interface of laminates. The laminate composites were fabricated by tape casting method and hot-pressing. It was demonstrated that the thermal mismatch stress was closely related to the crack formation and crack deflection behavior in the mullite/zirconia laminate composites. Two kinds of cracks were observed in zirconia layers; one is channel cracks in layers subjected to tensile stress, the other is the edge cracks in layers subjected to compressive stress. Among three forms of zirconia (monoclinic, tetragonal, cubic) tetragonal zirconia was effective to deflect the crack at the interface due to the stress induced tetra-mono phase transformation.

Analysis of reinforced concrete beams strengthened in flexure with composite laminates: Discussion

Discussions 835 The authors are to be commended for attempting to pro- vide a refined, yet simple, flexural analysis tool for rein - forced concrete beams strengthened with composite laminates. Although there is much merit in the paper, there are also some aspects of the work that need careful examina- tion before anyone begins to apply it to any real structure. The purpose of this discussion is to point out the danger that is inherent in analyses that (i) assume perfect bond between the FRP laminate and the concrete and (ii) assume the shear and normal stresses at the interface of the laminate and the substrate to be governed by classical beam theory. The writer is confident that the authors know about these dan- gers, but have forgotten to mention them in the paper. Both experiments (Tumialan et al. 1999) and theory (e.g., Rabinovitch and Frostig 1999) have shown that the shear and normal stresses at the interface of the laminate-epoxy and epoxy-concrete have a complex distribution which can- not be found by using the simple beam theory. In fact, beam theory erroneously gives the normal stresses perpendicular to the interface to be zero, but more refined analyses based on theory of elasticity indicate significant tensile stresses de - veloping at the interface. The beam theory also leads one to believe that the interfacial longitudinal shear stresses can be calculated using the elementary shear stress equations given in strength of material books. In reality these stresses have a much more complex distribution. Furthermore, when a con- crete beam cracks, the stresses at the interface in the vicinity of the crack greatly deviate from the distribution predicted by simple beam theory or by any other theory that ignores the presence of cracks. The experimentally observed delamination of either the substrate concrete or the FRP laminate is caused by the combined effect of these high in- terfacial stresses. Given that premature delamination will cause a strength- ened reinforced concrete beam to fail at a load lower than predicted by the program described in the paper, the results of the program could lead to unsafe design. This is the dan- ger that users of the program must be aware of. Figure 6 of the paper illustrates this point where the predicted and the actual load differ significantly. Note that the measures taken to prevent delamination, namely, the use of the U-shaped composite anchors, cannot be modelled by the program as described. The program is unable to quantify the effect of the end anchors and thus unless it can be shown by some other method that delamination cannot occur, it may overes- timate the actual capacity of a member with or without an- chors.

Prestressed composite laminates featuring interlaminar imperfection

The third-order zigzag displacement model is improved to include inplane displacement jumps across each layer interface of composite laminates to enable interlaminar imperfection to be incorporated. The imperfection is characterized by a linear spring-layer model which includes perfect bonding as a special case. The principle of virtual work is used to derive a boundary value formulation for laminated composite plates initially in a prestress state. Bending, buckling and vibration problems are studied for the case of rectangular cross-ply laminated plates for illustrative purpose.

The effect of material properties on stress state near the ply interface of laminates

In this paper, the attention is restricted to the cases of symmetric angleply laminates. The stress distributions are studied at the ply level with an emphasis on the interface effect in the central region of symmetric composite laminates. It has been discovered that the numerical distributions of stresses in angle-ply laminates are quite different from the results by the classical laminate theory. There are in-plane stress concentrations near ply interface in the interior region of laminated composites due to the abrupt change of fiber orientation. Because interlaminar stresses and thus delamination can arise in any gradient stress field in a laminated composite, there exist interlaminar stresses near the ply interface in the interior region. The effects of the material properties on the concentration of in-plane stress are also discussed.

Depth Profiling Study of Effect of Annealing Temperature on Polymer/Polymer Interfaces in Laminates Using Confocal Raman Microspectroscopy

The effect of annealing temperature on molecular interactions at the interface of polymer laminates is reported. Depth profiling has been carried out by using confocal Raman microspectroscopy to study poly(acrylonitrile)/poly(vinyl alcohol) (PAN/PVOH) and poly(acrylonitrile)/poly(acrylic acid) (PAN/PAA) laminates. The laminates have been annealed at 65, 75, and 90 °C. It is demonstrated that the degree of hydrogen-bonding interaction between the nitrile and alcohol groups near the interfacial region changes between laminates annealed at different temperatures. Increasing the annealing temperature up to near the glass transition temperature, Tg, of both polymers facilitates hydrogen bonding. However, above Tg, as a result of molecular flexibility, weakening of such interactions begins. Due to the lower molecular weight of PAA, and thus greater mobility in comparison with PVOH, the interfacial region of a PAN/PAA laminate is broader than that of a PAN/PVOH laminate. Hydrogen-bonding interaction between PAN and PAA was not observed. This result is rationalized by the hypothesis that, as a result of intramolecular interaction between the carbonyl and hydroxyl groups of PAA, formation of intermolecular hydrogen bonding has been hindered. In addition, the variations in the full width at half-height (FWHH) of the v(C≡N) band of a PAN–PVOH blend has been mapped by using the same technique.

熱可塑性樹脂の分子配向をガラス繊維に連成させた複合積層板の温水環境試験による微視界面状態の検討

Recent thermoplastic composites have the potential to offer improved environmental tolerance, damage tolerance and decreased manufacturing cost compared with thermoset composites. However, it is difficult to impregnate the melted thermoplastic resin into reinforcement strands due to high viscosity of resin. Therefore, the laminate composite materials in which fiberous thermoplastic resin is coupled to the reinforcement strands have been developed. It is expected that the adhesive condition in micro interface of coupling laminate will be better, because there is thermoplastic resin in the orthogonal interface of reinforcement stands before the resin melt.The purpose of this study was to estimate the adhesive condition of micro interface of the coupling laminate through immersion testing of the film stacked laminate under hot water environment. After immersion tests of water absorption, the mechanical properties, flexural modulus retention and flexural strength retention were determined. The degradation behaviors of coupling laminate and film stacked one were simulated by the finite element method with consideration for the degradation of constituent materials.It was found that the material constants depended on water absorption under hot water environment by material testing and they were predicted quantitatively from classical Fick's diffusion equations. The numerical results were in good agreement with those of experiments under flexural conditions.

Elastic-plastic analysis of laminated anisotropic shells by a refined finite element laminated model

This paper presents a refined finite element shell model for the numerical analysis of thick or thin anisotropic laminated shells. A layered approach is adopted for solution with displacement variables assumed at each laminate interface. Elastic-plastic numerical analysis is performed based on flow theory and a Huber-Mises yielding surface extended by Hill for fully three-dimensional anisotropic materials. Numerical results obtained for both nonlaminated and laminated shells are presented and the effects of boundary constraints on the load-boundary deformation characteristics and on the spread of plastic zones are discussed. Comparisons are made to show the effects of anisotropy and bending-stretehing coupling on the elastic-plastic response. The effects of lamina angle sequences on the structural characteristics are also illustrated.