Direct measurement of triaxial strain fields around ferroelectric domains using X-ray microdiffraction

Ferroelectric materials, such as BaTiO(3), have piezoelectric properties that make them attractive for microelectronic and sensing applications. It is well known that the application of mechanical stress or electric field can alter the domain structure in ferroelectrics. Indeed, the constitutive behaviour of a ferroelectric is largely governed by the formation, movement and interaction of its domains. Therefore, it is crucial that the micromechanics of domains and their effect on internal stresses in ferroelectrics be understood. Here we show that the emerging technique of scanning X-ray microdiffraction can be used to measure directly, for the first time, the local triaxial strain fields around 90 degrees domains in single-crystal BaTiO(3). Specifically, residual strain maps in a region surrounding an isolated, approximately 40 microm wide, 90 degrees domain were obtained with 3 microm resolution, revealing significant residual strains. This information is critical for accurate micromechanical modelling of domain behaviour in ferroelectrics.     

Large deformation and slippage mechanism of plain woven composite in bias extension

Stamping operation is the most efficient way to form textile composites in industry. During a stamping process, the material undergoes large shear deformation, which may lead to two major failure mechanisms: out-of-plane wrinkling and in-plane slippage. The present paper mainly focuses on the large deformation mechanism and slippage of the plain woven composite during a bias extension. Bias extension experiments were carried out under different conditions. In addition to the data processing on the experimental curve, digital image correlation analysis was conducted on the test photographs, from which three typical deformation phases are identified. A theoretical model is then proposed to interpret the large deformation and slippage phenomenon from an energy point of view.     

Analysis of laminated composite plates using a higher-order shear deformation theory

A higher-order shear deformation theory is used to analyse laminated anisotropic composite plates for deflections, stresses, natural frequencies and buckling loads. The theory accounts for parabolic distribution of the transverse shear stresses, and requires no shear correction coefficients. A displacement finite element model of the theory is developed, and applications of the element to bending, Vibration and stability of laminated plates are discussed. The present solutions are compared with those obtained using the classical plate theory and the three-dimensional elasticity theory.     

Visualization of voids in actual C/C woven composite structure

Void statistic is an important C/C composite parameter since the voids presence decreases the predicted properties. On the other hand minimum number of voids is needed for medical application. Void study supposes finding its exact 3D shape. Since the void distribution is statistic, many samples must be processed. Therefore automated methods are necessary. In the paper the set of plan-parallel structure images were scanned by optical microscopy. The void contours on 2D images were found automatically by the use of MATLAB procedures with the same accuracy as hand marking. The 3D void surface was created by small triangles from its plan-parallel cuts. The 3D void was studied by virtual reality that makes possible almost all ways of inspection.     

Shear deformation and micromechanics of woven fabrics

This paper includes an experimental study and a mathematical analysis of the shear deformation of woven fabrics by using picture-frame type shear testing. Four types of weaves were tested and compared: a loose plain weave, a tight plain weave, a twill and a satin weave. The locking shear angle was determined both in picture-frame tests and manual shear tests. The experimental data presented for each fabric include curves of shear load–shear stress as a function of either the shear angle or the shear rate, and measured locking shear angles. The shear deformation data were analysed by following elasticity principles and taking into account the effects of fibre inextensibility. A microstructural analysis was carried out in all four fabrics to investigate the shear locking on the basis of a geometrical approach and the maximum packing fibre fraction.     

Interface fracture toughness of a multi-directional woven composite

The aim of this investigation is to measure the interface fracture toughness of a woven composite. For this purpose, double cantilever beam (DCB) specimens are tested to measure the load as the delamination grows. The specimen is composed of 15 layers of a carbon–epoxy, balanced weave with alternate layers containing fibers in the $0^{\circ }\!/90^{\circ }$ 0 ° / 90 ° directions and the $+45^{\circ }\!/\!\!-\!45^{\circ }$ + 45 ° / - 45 ° directions. A thin piece of Teflon is placed between two layers of differing directions. The specimens are analyzed by means of the finite element method and an interaction energy or $M$ M -integral to determine the stress intensity factors, interface energy release rate and phase angles. The first term of the asymptotic solution for the stress and displacement fields obtained by means of the Stroh and Lekhnitskii formalisms is used to define auxiliary solutions for the $M$ M -integral. The critical interface energy release rate is found and exhibits a slowly increasing resistance curve. Comparisons are made to a simple expression from the literature.     

Vibro-acoustic analysis of a post-impacted woven composite panel

In this study, vibro-acoustic behavior of centrally damaged woven carbon composite panels is investigated experimentally. For this purpose, evaluations are considered by the followings: (i) ballistic impact measurements are completed regarding with two different shooting distance, (ii) ballistic impact measurements with three different projectiles are obtained, (iii) vibration and vibro-acoustic tests are performed to present the vibration characteristics of the post-impacted woven composite panels. Effects of shooting distance and projectile on modal and sound characteristics are examined. Results are given in tabular and graphical forms.     

A thermo-micro-mechanical modeling for smart shape memory alloy woven composite under in-plane biaxial deformation

This paper presents a theoretical study of the in-plane behavior of Smart Shape Memory Alloy Woven Composites (SSMAWC) under biaxial loading by developing an integrated micromechanical constitutive model. The model studied in this research is established on the geometric parameters of fibers, metal layers, unit cell, the material constants of composite constituents, and the orientation of fibers, in which the fibers in one direction are SMA ones. The Helmholtz free energy of a Shape Memory Alloy, in 3-Dimensional and 1-Dimensional applications is derived. Using mechanical energy of matrix and elastic yarns, the constitutive relations are developed with the use of strain energy approach and energy variation theorem. The kinetic relations of SMA depicted by Brinson is coupled with the final governing equation of the composite to predict the stress history in smart shape memory alloy woven composites. The deflection of the structure, subjected to uniform biaxial loading is studied numerically. It is found that the effect of Shape Memory Effect (SME) of the SMA wires on the behavior of plain woven flexible fabric composite is significant.     

Study on intra/inter-ply shear deformation of three dimensional woven preforms for composite materials

This study presents the in-plane shear and interlaminar shear behavior of the three dimensional (3D) angle interlock preforms with different fabric densities. Picture frame shear tests for the 3D woven preform were carried out, the non-linear curves of shear stress versus shear angle and the deformation mechanism were analyzed. A new test method was designed to characterize the inter-ply shear property. The samples after interlaminar shear tests were also investigated through the yarn pulling-out and meso-structure to discover their deformation and failure mechanism. The results have shown that the fabric density has significant influence on the in-plane shear and inter-ply shear properties of 3D angle interlock preforms and the shear performance decreases with the increasing of the fabric density. The lower fabric density, the better deformability. The inter-ply shear damage mode is the binder yarn pulling out from the fabric. It is expected that the study can provide an experimental basis for building up the theoretical model.     

Progressive failure modeling of woven fabric composite materials using multicontinuum theory

Failure of composite materials often results from damage accumulation in the individual constituents (fiber and matrix) of the composite. At times, damage may even be limited to a single constituent. The ability to accurately predict not only ultimate strength values but also intermediate constituent level failures is crucial to the success of introducing composite materials into demanding structural applications.In this paper, we develop two progressive failure models for the analysis of a plain weave composite material. The formulations are based on treating the weave as consisting of separate but linked continua representing the warp fiber bundles, fill fiber bundles, and pure matrix pockets. Retaining constituent identities allows one to access constituent (phase averaged) stress fields that are used in conjunction with both a stress based and damage based failure criterion to construct a nonlinear progressive failure algorithm for the woven fabric composite material. The MCT decomposition and the nonlinear progressive failure algorithm are incorporated within the framework of a traditional finite element analysis.The constituent based progressive failure algorithm combined with both the stress based and damage based failure criteria are compared against experimental data for a plain weave, woven fabric composite under various loading conditions. The analytical results from the damage based approach show a marked improvement over the stress based predictions and are in excellent agreement with the experimental data.     

Piezoelectric micromotor using a metal-ceramic composite structure

This paper presents a new piezoelectric micromotor design, in which a uniformly electroded piezoelectric ring bonded to a metal ring is used as the stator. Four inward arms at the inner circumference of the metal ring transfer radial displacements into tangential displacements. The rotor ends in a truncated cone shape and touches the tips of the arms. A rotation takes place by exciting coupled modes of the stator element, such as a radial mode and a second bending mode of the arms. The behavior of the free stator was analyzed using the ATILA finite element software. Torque vs. speed relationship was measured from the transient speed change with a motor load. A starting torque of 17 muNm was obtained at 20 Vrms. The main features of this motor are low cost and easy assembly because of a simple structure and small number of components.     

Fractal characteristics of the deformation surfaces of a composite material and their correlation with the structure

An investigation was made of the deformation relief formed at the surface of a solid under active deformation, and its fractal properties were determined. A correlation was established between the fractal dimension of the surface profile and the parameters of the fine crystalline structure of the material. Pis’ma Zh. Tekh. Fiz. 25, 34–38 (January 26, 1999)     

Characterization and integration of polymeric and microdiffraction specimens using a two-dimensional position-sensitive detector

An automated x-ray diffraction system configured with a two-dimensional position sensitive detector (PSD) was used to characterize both polymeric and microdiffraction specimens. Pinhole collimation and an incident beam monochromator were used for the polymer applications, while dual nickel coated x-ray mirrors were used to focus and monochromatize the x-ray beam for microdiffraction experiments. Radial and azimuthal integration techniques automatically convert the two-dimensional PSD data into a traditional powder pattern for data manipulation.

The complete or partial Debye ring(s) of a diffraction pattern can be imaged simultaneously with the Siemens two-dimensional PSD. For polymeric specimens this allows data to be collected rapidly (in seconds) and in digital form eliminating cumbersome film techniques. The integration over a large section of the Debye ring(s) also enhances the diffracted beam detectability making this system sensitive for microdiffraction experiments.     

Assessment of fatigue damage evolution in woven composite materials using infra-red techniques

Thermoelastic stress analysis (TSA) is used to study the growth of fatigue damage in single and two ply, 2 × 2 twill woven composite materials. Test specimens were subjected to a uniaxial tensile cyclic loading with maximum stresses of 10%, 15% and 20% of the ultimate failure stress. The development of fatigue damage locally within the weft yarns is monitored using high resolution TSA. The specimens were subsequently inspected using optical microscopy to evaluate the location and extent of cracks. Cracks were found in the weft fibres, running transverse to the loading direction. It is demonstrated that the lighter weight fabric is more resilient to damage progression. A signature pattern is identified in the TSA phase data that indicates the onset and presence of fatigue damage in the composite material.     

Combined X-ray microdiffraction and topography experiment for microstructural analysis of heterogeneous materials

A new experimental set-up combining X-ray topography and microbeam diffraction has been designed for the investigation of heterogeneous microstructures with features in the size range of more than 50m. Built around a four-circle goniometer of 5/1000° angular resolution, this apparatus offers similar facilities to those obtained by TEM but at a different scale. In the Berg-Barrett position, grain and subgrain boundaries can be observed over large surface areas (typically 100 mm²). Based on topography observations, areas of interest of typically 100m diameter can be precisely selected for microdiffraction measurements. A laser beam directed through the pinhole system of the X-ray microbeam collimating system permits one to directly visualize the irradiated zone. The divergence of the X-ray microbeam is typically 0.034° (full width at half maximum) and permits the measurement of lattice spacing variations (a/a) of the order of 10^–4. While TEM permits one to examine very localized areas, this new device is appropriate to detect long-distance effects and phase interactions in materials with coarse distributed heterogeneities. In order to demonstrate the versatility of this new device, the orientation distribution, variation of lattice spacing and mosaic structure of dendrites in directionally solidified nickel-base alloys are analysed.     

Computer modelling of woven composite materials

In this paper the reasons for choosing woven fabric reinforcements for composite components are given and the alternatives to woven structures are examined. The philosophy behind the development of the computer-generated model of a woven composite fabric reinforcement is discussed. The model described here is a general one, capable of producing a 3-D representation of any single layer fabric, and has been designed to facilitate manufacture of the weave and also finite element analysis of the finished composite component, as well as providing a very useful visualization of the weave. The model has the potential to be developed along a number of fronts, including improved visualization and extension to 3-D weaves.     

Characterization of a novel bioactive composite using advanced X-ray computed tomography

A novel bioactive, porous silica–calcium phosphate nanocomposite (SCPC) that can be used to treat large bone defects in load-bearing positions has been tested and has shown great potential for applications in tissue engineering. Porosity is essential to the performance of the composite material as a tissue engineering scaffold, as porous scaffolds provide a physical, 3-D template to support new tissue formation. However, porosity characterization using conventional techniques such as porosimetry or scanning electron microscopy requires extensive preparation of samples and may destroy important features during preparation and analysis stage. In this work, the new composite is characterized using an advanced high resolution X-ray computed tomography, which is a non-destructive testing technique that allows construction of the 3-D topology of the microstructure. The results clearly show the effectiveness and versatility of this technique in characterizing the porous architecture of the novel composite biomaterial. The pore distribution, morphology and interconnectivity in the composite scaffolds were found to be ideal for use in tissue engineering applications.     

X-ray microdiffraction and EBSD study of FSP induced structural/phase transitions in a Ni-based superalloy

Severe plastic deformation during Friction Stir Processing (FSP) of an IN738 Ni-based superalloy was studied by means of X-ray polychromatic microdiffraction, EBSD, scanning electron and optical microscopies. Modeling of the physical properties and phase composition was also performed. Several distinct zones are formed during FSP including a stir zone (SZ), a thermal-mechanical affected zone (TMAZ) and a heat affected zone (HAZ). Each zone has distinct microstructure after FSP. The initial dendrite structure is preserved in the HAZ, while strengthening γ′-phase particles partially dissolve and coagulate. Plastic deformation of the base material dendrites takes place in the TMAZ and a large number of geometrically necessary dislocations are formed. The extent of deformation increases toward the SZ and the dendrite structure is completely destroyed in the SZ and replaced by a fine submicrocrystallinne microstructure.     

High-intensity X-ray microbeams obtained using a cylindrical polycapillary structure

High-intensity quasi-parallel X-ray microbeams with a radiation flux density on the order of 10¹⁰ photon/(s mm²) and a divergence of several milliradians, which is close to the parameters of synchrotron radiation, were obtained using a microfocus source based on a transmission-type X-ray tube. The divergent X-ray radiation was converted into a quasi-parallel beam using a cylindrical structure of Kumakhov polycapillary optics with a micron channel diameter.