Delamination In Materials Research Articles

Inlay‐fixed partial dentures adhesively retained and reinforced by glass fibers: clinical and scanning electron microscopy analysis after five years

Fifty-three posterior glass fibre-reinforced composite inlay-fixed partial dentures (IFPDs) in 36 patients were followed for 5 yr. For statistical analysis, one IFPD per patient was randomly selected. The survival rate and influence of discrete predictors (gender, location) and continuous variables (age, abutment surfaces) were determined. Clinical observations were recorded by using modified United States Public Health System (USPHS) criteria. Replicas of 17 randomly selected abutments were analysed by scanning electron microscopy (SEM) for marginal adaptation and the results were compared by using a repeated-measures analysis of variance (anova). The main reason for failure was veneering material delamination from the framework. The cumulative survival rate after 5 yr was 73% (95% confidence interval: 57-89%) for not delaminating and 96% (95% confidence interval: 88-100%) for not debonding. No significant influence of the tested predictors was found. Significant changes between baseline USPHS criteria and counterparts recorded at recall were fractures of the veneering material (chipping), wear, surface texture, and staining. Significant margin changes were only found between baseline and 1 yr. Thereafter, marginal adaptation remained stable. After 5 yr, 90% of the margins were termed as perfect. It was concluded that hard-tissue saving IFPDs with the current design maintained acceptable retention and marginal integrity. Future studies should aim at reducing delaminations by searching for improved framework designs and materials.

Nonlinear acoustic scattering by a partially closed surface-breaking crack

A theoretical model describing the nonlinear scattering of acoustic waves by surface-breaking cracks with faces in partial contact is presented. The nonlinear properties of the crack are accounted for by suitable boundary conditions that are derived from micromechanical models of the dynamics of elastic rough surfaces in contact. Both linear and nonlinear responses of the crack are shown to be largest for a shear vertical wave incident on the surface containing the crack at an angle just above the critical angle for longitudinal waves. These findings question the fitness for the purpose of a conventional inspection method, which utilizes shear vertical waves at 45 degrees of incidence to search for surface-breaking cracks in many engineering components. For angles of incidence proximal to the critical angle of longitudinal waves, the efficiency of the second harmonic's generation appears to be the highest. Thanks to the increased sensitivity to surface-breaking cracks, this configuration seems to offer a solution to the localization problem, a task that has eluded nonlinear techniques operating under other circumstances. Finally, this model suggests a simple interpretation of the highly localized nonlinear response of delaminations in composite materials.

New development of inorganic ion exchanger: Preparation, Hydrothermal Treatment and Photocatalytic Activity of Zr(HPO4)2/TiO2 Nanocomposites

α-type zirconium hydrogenphosphate (α-ZrP) /TiO2nanocomposite was fabricated by the intercalation of titanium tetraisopropoxide into butylamine-intercalated α-ZrP in ethanol medium and followed by photocatalytic decomposition of organic compounds with UV irradiation. Prior to the photocatalytic decomposition, hydrothermal treatment was conducted in the temperaure range of 100-250°C. All materials were characterized by X-ray diffractometry, SEM, TG-DTA, chemical analyses, FTIR, 31P MAS NMR, UV-VIS absorption spectroscopy, and photocatalytic hydrogen evolution from an aqueous methanol solution. On the basis of the SEM observation, no significant deformation of the bulk samples occurred after hydrothermal treatment and UV-irradiation whereas delamination of host materials was caused by the intercalation of butylamine. 31P MAS NMR and FTIR revealed that no chemical bonding between TiO2and phosphate groups of the host material. TiO2in zirconium hydrogenphosphate could be crystallized to anatase by the hydrothermal treatment. The hydrothermal treatment was effective for the photocatalytic decomposition of organic compounds. Complete decomposition was obtained in shorter UV irradiation time by the hydrothermal treatment due to the existence of anatase phase. Hydrothermally untreated α-ZrP/TiO2exhibited negligible photocatalytic activity due to amorphous TiO2. The photocatalytic activity of α-ZrP/TiO2was enhanced by the hydrothermal treatment whereas the activity was decreased with an increase in the hydrothermal temperature. α-ZrP/TiO2hydrothermally treated at 100°C exhibited the highest photocatalytic activity and showed large blue-shift in UV absorption spectra due to the quantum-size effect.

Helicopter rotor blade frequency evolution with damage growth and signal processing

Structural damage in materials evolves over time due to growth of fatigue cracks in homogenous materials and a complicated process of matrix cracking, delamination, fiber breakage and fiber matrix debonding in composite materials. In this study, a finite element model of the helicopter rotor blade is used to analyze the effect of damage growth on the modal frequencies in a qualitative manner. Phenomenological models of material degradation for homogenous and composite materials are used. Results show that damage can be detected by monitoring changes in lower as well as higher mode flap (out-of-plane bending), lag (in-plane bending) and torsion rotating frequencies, especially for composite materials where the onset of the last stage of damage of fiber breakage is most critical. Curve fits are also proposed for mathematical modeling of the relationship between rotating frequencies and cycles. Finally, since operational data are noisy and also contaminated with outliers, denoising algorithms based on recursive median filters and radial basis function neural networks and wavelets are studied and compared with a moving average filter using simulated data for improved health-monitoring application. A novel recursive median filter is designed using integer programming through genetic algorithm and is found to have comparable performance to neural networks with much less complexity and is better than wavelet denoising for outlier removal. This filter is proposed as a tool for denoising time series of damage indicators.

Abrasive wear mechanisms of VPS‐ and HVOF‐sprayed TiC‐Ni based nanocrystalline coatings

AbstractNanocrystalline coatings have a high potential for various engineering applications, e.g. against wear of rolls in the paper fabrication and as corrosion protection. Using vacuum plasma spray (VPS) and high velocity oxy‐fuel (HVOF) spray techniques, coating materials are exposed to high flame temperatures only for less than a millisecond. Therefore, high‐energy milled powders can be used as feedstock material without losing its nanocrystalline microstructure during the thermal spray process. In this way, homogeneous, dense nanocrystalline coatings can be produced, which show enhanced hardness, thus obtaining promising superior wear resistance. In the present study, (Ti,Mo)(C,N)‐45vol.%NiCo nanocrystalline coatings were prepared by VPS‐ and HVOF‐spraying of high‐energy milled powders. Abrasive wear tests JIS H 8615 with varying number of strokes and scratch tests with a Vickers indenter were applied to produce wear traces on the polished surfaces of the nanocrystalline coatings. Abrasive wear behaviour was analyzed by investigating the surface morphologies with optical microscopy (OM), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Experimental results indicate that the VPS‐coating has higher abrasive wear resistance than the HVOF‐coating according to the JIS H8615 test. The abrasive wear mechanism of VPS‐sprayed nanocrystalline coatings can be delineated as cutting plus ploughing. For HVOF‐sprayed nanocrystalline coatings the abrasive wear mechanism can be described as cutting plus material delamination.

Crustal structure of seismic velocity in southern tibet and east-westward escape of the crustal material

The reflecting events from Moho and other interfaces within the crust are recognized from the wavefield characteristics of P- and S-wave for the 480km long wide-angle seismic profile between Peigu Tso and Pumoyong Tso. Then, seismic crustal structures of P- and S-wave velocities and Poisson ratio under the nearly east-west profile in southern Tibet are interpreted by fitting the observed traveltimes with the calculated ones by forward modelling. Our interpreting results demonstrate that the crustal thickness varies remarkably in the east-west direction, showing a pattern that the crust could be divided into three parts bounded by the west of Dingri and the east of Dinggye, respectively, where the depth of Moho is about 71km for the western part, about 76km for the middle and about 74km for the eastern. There is one lower velocity layer (LVL) at the bottom of the upper crust with depth of 20—30 km. One of the distinct features is that the thickness of LVL abruptly thins from 24 km on the west to 6km on the east. The other is that the velocity variation in the crust along east-west direction for both P- and S-wave displays a feature as quasi-periodic variation. The lower velocity (compared to the average value for the continent of the globe) in the lower crust and three sets of north-southward active normal faults are probably attributed to the coupling process of material delamination in the lower crust, crustal thicking and east-westward escape of the crustal material accompanied with the continental collision between India and Eurasia Plate.

複合材中のはく離欠陥に対する受動型電気ポテンシャルCT法の適用性に関する実験的検討(OS1-3 はく離モニタリング,OS1 構造ヘルスモニタリング)

複合材中のはく離欠陥に対する受動型電気ポテンシャルCT法の適用性に関する実験的検討(OS1-3 はく離モニタリング,OS1 構造ヘルスモニタリング)

Theoretical description of a delamination mechanism in fibrous micro- and nanocomposites

Theoretical analysis and numerical modeling of unidirectional fibrous micro- and nanocomposites carried out based on the theory of two-component mixture testify that the second mode of a transverse wave propagating along and polarized across the fibers may produce, at high frequencies, a kinematical pattern critical for the strength of the composite material. While the wave propagates, the components (matrix and fibers) of the mixture oscillate in antiphase. This fact may be critical because such oscillations generate forces separating the matrix and fibers, which is typical for the delamination of composite materials.

Mixed‐Mode Delamination – Experimental and Numerical Studies

Abstract: A fracture energy approach for modelling mixed‐mode delamination of composite materials and other bonded structures is introduced. The model is incorporated within an explicit finite element (FE) code and ties layered shell elements together via a stiffness condition, a failure criterion and post‐failure damage law. The procedure for predictive modelling of delamination using the approach is described and the set of required input parameters is presented. A benchmark test comparing experimental results for a continuous filament random E‐glass/polyester composite and explicit FE simulations for standard fracture toughness tests for a range of mode mixities is included.

Numerical Simulation of Mixed-Mode Progressive Delamination in Composite Materials

A new decohesion element with the capability of dealing with crack propagation under mixed-mode loading is proposed and demonstrated. The element is used at the interface between solid finite elements to model the initiation and non-self-similar growth of delaminations in composite materials. A single relative displacement-based damage parameter is applied in a softening law to track the damage state of the interface and to prevent the restoration of the cohesive state during unloading. The softening law is applied in the three-parameter Benzeggagh-Kenane mode interaction criterion to predict mixed-mode delamination propagation. To demonstrate the accuracy of the predictions, steady-state delamination growth is simulated for quasi-static loading of various single mode and mixed-mode delamination test specimens and the results are compared with experimental data.

The effects of shear on delamination in layered materials

The effect of transverse shear on delamination in layered, isotropic, linear-elastic materials has been determined. In contrast to the effects of an axial load or a bending moment on the energy-release rate for delamination, the effects of shear depend on the details of the deformation in the crack-tip region. It therefore does not appear to be possible to deduce rigorous expressions for the shear component of the energy-release rate based on steady-state energy arguments or on any type of modified beam theory. The expressions for the shear component of the energy-release rate presented in this work have been obtained using finite-element approaches. By combining these results with earlier expressions for the bending-moment and axial-force components of the energy-release rates, the framework for analyzing delamination in this type of geometry has been extended to the completely general case of any arbitrary loading. The relationship between the effects of shear and other fracture phenomena such as crack-tip rotations, elastic foundations and cohesive zones are discussed in the final sections of this paper.

425 複合材料におけるはく離欠陥導出に対する受動型電気ポテンシャル CT 法の適用性に関する検討

425 複合材料におけるはく離欠陥導出に対する受動型電気ポテンシャル CT 法の適用性に関する検討

Dual particle size (DPS) composites: effect on wear and mechanical properties of particulate metal matrix composites

Al–Si–Mg alloy composites reinforced with up to 15 vol.% of SiC particles were prepared by the melt-stirring process. The wear behavior, under low loads, of the unreinforced Al–Si–Mg alloy and the metal matrix composites (MMCs) was investigated using a ball-on-disc test at room temperature under dry conditions. It was found that the maximum effective increase in wear resistance (ratio of percentage reduction in weight loss and volume percent of SiC added to achieve the reduction) occurred for the composite with about 7 vol.% SiC. Metallographic investigations have revealed that the wear zone of the unreinforced alloy consisted of a hardened layer, in which fragmented Si phase was observed to be redistributed and aligned parallel to the wear direction. The delamination of material from the hardened layer was responsible for higher wear loss observed in the unreinforced alloy. The thickness of the hardened layer formed on the MMC specimens (10–30 μm as against 30–60 μm in the unreinforced specimens) was reduced by the fragmentation of the incorporated SiC particles. The fragmentation of Si phase was also found to be of much lesser magnitude in the MMC specimens. This led to lesser wear in the case of the MMC specimens. It is proposed that an effective method of optimizing the wear resistance and mechanical properties of low volume fraction composites is to incorporate small and large SiC particle sizes (DPS) within the same composite. The improvement in wear resistance of the DPS composites could be attributed to the ability of the larger SiC particles to carry a greater portion of the applied load, as well as to the function of the larger SiC particles in protecting the smaller SiC particles from being gouged out during the wear process. Furthermore, the incorporation of larger particles increased the charpy impact energy of the DPS composites with respect to the composite with fully small sized particles.

Modelling and simulation of the delamination in composite materials

Delamination is a phenomenon characterized by the loss of adhesion between two adjacent laminae. This is a damage process frequently observed in composite materials and it may cause either loss of structural stiffness or total failure of the laminate. This contribution presents a model to describe composite delamination. The proposed model considers a laminate with a finite thickness interlayer. Interlaminar stresses are evaluated from a modified lamination theory. This result is used as input in the constitutive adhesion model which describes the damage evolution of the interlayer. An iterative numerical procedure is developed, solving the model equations separately. This work considers numerical simulations of a laminated tube and a laminated bar as applications of the proposed general formulation. Numerical results are capable of capturing the general behaviour of experimental data.

Non-destructive characterization of delaminated areas at interfaces between plies in carbon fiber/epoxy laminates with Foucault currents

Carbon fiber epoxy laminates are extensively used in the aerospace industry as they offer a combination of high performance with relatively low weight. However, damage may occur in these materials, either at the manufacturing level or during use, which may affect their structural integrity. Among the type of damage which may occur, delamination is a common defect which causes a reduction in compressive strength and thus limits the life of laminated composites. If undetected, delamination may propagate during use due to mechanical loads and in the worst case may cause fracture of the material. Therefore, delamination in composite materials needs to be efficiently detected and accurately quantified for safety and economic reasons. Because of their heterogeneity, multi-layered structure and anisotropy, the inspection of composite materials remains difficult with conventional NDT methods. A method making use of Foucault currents, and relying on the principle of electromagnetic induction, can be adapted for the detection and characterization of damage in composite materials. The use of Foucault currents in characterizing delaminated areas at interfaces between plies in carbon fiber/epoxy laminates is addressed in this paper. It is demonstrated that Foucault currents can accurately detect and quantify delamination in CFRP materials. Furthermore, the potential of this technique for monitoring defect propagation in composite materials is discussed.

Ultrasonic evaluation of matrix damage in impacted composite laminates

Conventional ultrasonic inspection methods are largely used for detection of delaminations in composite materials while only recently new techniques have been proposed to identify matrix cracks in simple tension loaded coupon specimens. In this study delaminations and matrix cracking caused by low-energy impacts on quasi-isotropic carbon/PEEK laminated plates are examined by means of different pulse-echo techniques: conventional time-of-flight and amplitude C-scans at normal incidence are used to check for the presence of delaminations, while backscattering C-scans (in which the transducer is set at an angle to the laminate plane) allow the detection of matrix cracks through the laminate thickness. Selected results from full waveform ultrasonic analysis of impacted carbon/PEEK laminates are discussed and compared with X-ray data in order to demonstrate the efficiency of the proposed inspection technique.

Predicting Progressive Delamination of Composite Material Specimens via Interface Elements

This article describes the application of interface elements to the prediction of progressive delamination in composite materials. The work has been implemented in two separate commercial finite-element computer packages, ABAQUS [1] and LUSAS [2]. In the former case, this has been achieved via a "user subroutine", while in the latter case the elements are embedded directly within the system, either in the standard "release version" of the code or in a research version, to which the authors have access and in which they have implemented various algorithms directly. Comparisons are made with a range of experimental results for composite material specimens. In addition to the finite-element solutions, closed-form results are also presented that are based on a corrected beam theory.

On the Method of Determination of Strain Energy Release Rate During Fatigue Delamination in Composite Materials

In this paper, the problem of calculation of the energy release rate for a fatigue test on composite material has been investigated. The application of the Linear Elastic Failure Mechanics (LEFM) leads to the use of varation of the energy release rate (Δ G). As the energy release rate is a function of the load squared, the variation of G becomes either a function of variation of the load squared (Δ G = f(Δ(P2))) or a function of the square of the load variation (Δ G = f((Δ P)2)). In this paper, we determine, by different fatigue tests, which of the two theoretical results is the best to describe the experiments. These fatigue tests have been made on DCB test-specimen in mode I with different R ratios (R = Pmax / Pmin) and different maximum loads. The material was a unidirectionnal glass-epoxy. The results show that considering Δ G as a function of (Δ P)2 $$(\Delta G = \frac{1}{2}(P_{\max } - P_{\min } )^2 \frac{{\partial C}}{{\partial A}} = \frac{1}{2}(P_{\max }^2 (1 - R)^2 \frac{{\partial C}}{{\partial A}}$$ seems more appropriated to describe a cracking test in fatigue.

Finite element analysis of fracture behaviour of piezoelectric smart materials

Smart materials with embedded distributed piezoelectric layers as sensors and actuators have been used frequently in engineering over the past few years. Unfortunately, cracks and delaminations, which are typical early damage phenomena in such materials, may result in significant changes of the static and dynamic response of the structure. The main focus of the paper is to investigate and to develop an efficient finite element procedure to model and analyse the fracture behaviour of piezoelectric smart materials. Possible fracture criteria are discussed. A catalogue of multifunctional finite elements with coupled electromechanical fields has been developed, to analyse smart structures. Together with the fracture criterion these finite elements are used to simulate crack and delamination in piezoelectric materials and laminated smart structures. The results indicate that an electric field can either aid or retard crack propagation depending on the direction of the electric load.

Abrasive wear behaviour of SiC whisker-reinforced silicate matrix composites

The abrasive wear behaviour of SiC whisker-reinforced borosilicate and magnesium aluminosilicate (MAS) composites is investigated under different conditions. Generally, MAS composites exhibited superior wear resistance compared to borosilicate composites. The superior wear resistance of MAS composites is attributed to its higher mechanical properties. The wear resistance increased by increasing volume fraction of whiskers. Sliding distance, sliding velocity and load exhibit significant influence on the material loss. During abrasive wear, silicate matrices undergo extensive contact damage due to repeated indentation of SiC particulates/whiskers. Under repeated contact events, cracks generated at various locations of the matrix simultaneously grow and join resulting in delamination of composite material. In the composites, material removal is delayed by various toughening mechanisms like crack deflection, bridging and whisker pull-out.