Moire Interferometry Research Articles

Shear Testing of Textile Composite Materials

A new in-plane shear-test methodology, developed for laminated composite materials, was extended to textile composites. The methodology incorporates two recently developed advances: a new specimen and a special strain gage. When used together, they produce accurate and consistent shear characterization of laminated and textile composite materials. The “compact shear specimen” incorporates many of the advantages of the similar Iosipescu shear specimen but has a larger test section. A special strain gage called the “shear gage” integrates the shear strain across the entire test section of the specimen to obtain the average shear strain, regardless of the shear-strain distribution in the test section. The methodology was used to test both 2-D braided and 3-D woven textile composites. The entire shear stress-strain response, including the shear modulus and shear strength, was measured for nine textile composite architectures. The variation in shear modulus and shear strength were low and were comparable to the variation of tensile and compressive modulus for the respective materials. Moire interferometry, a full-field optical method, was used to validate the test methodology. Enhanced X-rays were used to document the damage accumulated during failure of the specimens.

Mixed Modes I and II Concrete Fracture: An Experimental Analysis

The development of the fracture process zone associated with subcritical crack growth in a three-point bend concrete specimen with an off-centered, single-edged precrack was monitored with moire interferometry. The applied load and the crack opening and sliding displacements together with a finite element model of the concrete specimen were used to determine the crack closing stress due to aggregate bridging. Under this mixed-mode fracture, aggregate interlocking increased the crack closing stresses in the fracture process zone and hence the load carrying capacity of the concrete specimen. The dissipated energy rate in the fracture process zone also increased with aggregate interlocking.

Moiré analysis of thick composites with embedded optical fibers

Moire interferometry is used with Fourier transform fringe analysis to investigate the strain fields in a region local to 125-μm uncoated silica optical fibers embedded in a quasi-isotropic graphite/PEEK thick composite compression specimens. Analysis of several regions in several specimens showed no measurable strain concentrations resulting from the embedded optical fibers, even though the optical fibers clearly alter the local microarchitecture of the host material system.

A historical review of moiré interferometry

High sensitivity moire interferometry is now a technique in fairly general use. Its development arose from the efforts of a number of workers over a period of nearly 40 years. This progress is reviewed in the ligh of the individual contributions that have led to the presentday accurate and user-friendly systems. In the first instance, the story is related in approximate chronological order; the contributions of individuals and groups are outlined in more detail in a series of appendices. It will become apparent that moire has not developed in a smooth, linear fashion—rather, a number of people reacted to the problems they were asked to solve, in a particular manner, and using methods and equipment available at the time. This view of the progress of science and technology as the creation of a climate of opinion and opportunity is very much in line with modern analyses of the history of science.

Application of refractive medium in optical micromechanics

The refractive medium is used in moire interferometry and holographic grating fabrication technique. The sensitivity of traditional interferometry and the frequency of grating are enhanced effectively. These two novel techniques extend the application scope of the moire interferometry and facilitate the realization of superlattice method in micromechanics study.

Fracture process zone associated with mixed mode fracture of SiCw/Al2O3

Abstract An experimental-numerical analysis based on moire interferometry and static finite-element analysis was used to study the trailing fracture process zone of a SiCw/Al2O3 precracked, three-point bend specimen subjected to mixed-modes I and II loading. Through an inverse analysis, the crack closing stress distribution, which provided the best fit between the measured and computed crack opening displacements, along the fracture process zone was determined. The energy dissipation rate in the fracture process zone accounted for about 44% of the released energy rate with the remainder being dissipated through whisker breakage and matrix fracture. The computed static stress intensity factors were used to predict the crack kinking angle, which agreed with the measured crack kinking angle of 5°, by the maximum circumferential stress criterion. Dynamic analysis showed that the crack propagated with a reduced energy dissipation rate.

Carrier pattern analysis of moire interferometry using the Fourier transform moire method

The Fourier transform moire and grid method, which we previously presented, is extended to analyze strain distributions from the image of a fringe pattern with carrier fringes obtained by moire interferometry. The characteristics of the carrier fringes and the procedure of obtaining strain distributions are explained in the spatial frequency domain. The fringe pattern without carrier fringes is obtained from the fringe pattern with carrier fringes by extracting the first harmonic of the spectrum of the fringe pattern with carrier fringes and shifting it. The strain distribution is obtained by analyzing the phase of the image obtained from the inverse Fourier transform of the shifted first harmonic. Strain distributions of a composite material with a wavy ply under compressive loading are analyzed.

New moire interferometry for measuring three-dimensional displacements

A new modified moiré interferometry for measuring <i>u</i>, <i>v</i>, and <i>w</i> displacement fields is proposed. The method is actually integrated with in-plane moiré interferometry and a new interferometry that can attain out-of-plane displacements. The sensitivity of the measurement of the out-of-plane displacement is as high as a half-wavelength of the illuminating light. The measured in-plane and out-of-plane displacement fields are mutually independent and definitely defined.

Hybrid experimental-numerical approach for determining strain energy release rates

A new approach is presented for determining strain energy release rates using a hybrid experimental-numerical method. The deformation around a crack in a body under load is measured by moire interferometry and a finite element procedure is used to convert the displacement into crack closure parameters to calculate strain energy release rates. A titanium specimen with a single edged crack under Mode I fracture has been used to demonstrate the approach. The stress intensity factor K I was first calculated using the commonly used crack tip opening displacement method. The strain energy release rate G I was then calculated using the hybrid experimental-numerical approach. The experimental values of K I and G I were compared with the published results to assess the accuracy of the experimental method. The experimental technique reveals the importance of residual stresses.

Experimental Study of Stress‐Induced Localized Transformation Plastic Zones in Tetragonal Zirconia Polycrystalline Ceramics

Stress‐induced martensitic transformation plastic zones in ceria‐stabilized tetragonal zirconia polycrystalline ceramics (Ce‐TZP), under loading conditions of uniaxial tension, compression, and three‐point bending, are studied by experiments. The transformed monoclinic phase volume fraction distribution and the corresponding plastic strain distribution and the surface morphology (surface uplift) are measured by means of moire interferometry, Raman microprobe spectroscopy, and the surface measurement system. The experimental results from the above three kinds of specimens and methods consistently show that the stress‐induced transformation at room temperature of the above specimen is not uniform within the transformation zone and that the plastic deformation is concentrated in some narrow band; i.e., macroscopic plastic flow localization proceeds during the initial stage of plastic deformation. Flow localization phenomena are all observed in uniaxial tension, compression, and three‐point bending specimens. Some implications of the flow localization to the constitutive modeling and toughening of transforming thermoelastic polycrystalline ceramics are explored.

Study of mode I interlaminar fracture in CFRP laminates by moir� interferometry

Moire interferometry was utilized to study mode I interlaminar fracture in double cantilever beam specimens of unidirectional carbon fiber/epoxy composites. The crack opening displacement was experimentally determined in the vicinity of the crack tip to evaluate the distortion at the beam root of the specimen. The beam root distortion was found to make an important contribution to increasing the value of crack opening displacement. The effect of the beam root distortion on the evaluation of fracture toughness value was also examined.

Low-spatial-frequency steep grating for use in moire interferometry

The theoretical background and the procedure for executing a new moiré interferometry method, which combines the advantages of geometric and traditional moiré interferometry, are reported. The method uses a low-spatial-frequency steep grating of about 40 lines/mm on a mirror-finished specimen surface to achieve high-contrast moiré fringes. A special four-beam moiré interferometry bench is designed for the low-grating frequency used. An application to experimental fracture mechanics analysis is briefly discussed.

Thermal Stresses in a Bimaterial Joint: An Experimental Analysis

An experimental analysis was conducted on a bimaterial plate subjected to a uniform change of temperature. Whole-field displacement measurements U and V were made on the free surface by means of high-sensitivity moire interferometry, and stresses were calculated from these data. Stresses resembled those of stress singularities, but they reached finite tensile and compressive peaks on opposite sides of the interface. The peaks and a severe stress gradient between them occurred in a narrow zone of about ±25 μm from the interface. The results pertain to an elastic three-dimensional body.

In-plane shear testing of graphite-woven fabric composites

The losipescu shear test method was used to determine the in-plane shear response of AS4 and Celion carbon fiber/epoxy fabric composite materials. Several weave architectures were studied: AS4 uniweave, AS4 and Celion plain weaves, Celion 5-harness and 8-harness satin weaves. Specimens were tested using traditional strain gage techniques and full-field moire interferometry. A full-node localized hybrid analysis is introduced to perform efficient reduction of moire data, producing whole-field strain distributions in the specimen test section. It was found that the fabric yarn size greatly influenced the uniformity of the shear field in the specimen test section. However, consistent shear moduli still can be obtained using the modified losipescu specimen and Wyoming fixture except for fabrics with large fiber yarns.

Residual surface stresses in laminated cross-ply fiber-epoxy composite materials

Residual (curing) stresses in a cross-ply laminated plate are related to the strains released when individual plies are separated. Released displacements are determined using high-sensitivity moire interferometry and linearized strain-displacement equations are used to determine residual strains. Elastic orthotropic stress-strain relations are used to calculate residual stresses remote from free-edges of a [9020/020/9020] graphite-epoxy cross-ply panel. The measured strains compare favorably with those predicted by laminated plate theory. In a second example, the circumferential and radial residual strains and stresses at the end-section of a thick-walled cross-ply graphite-epoxy cylinder are determined.

A study ofJ-integral of the orthotropic composite material

The relation between J-integral near model I crack tip in the orthotropic plate and displacement derivative is derived in this paper. Meanwhile, the relation between stress intensity factor KI and displacement is also given in this paper. With sticking film moire interferometry method, the three-point bending beam is tested, thus the values of J-integral and KI can be obtained from the displacement field, and then the truth of relation formula between J-integral and KI in the orthotropic composite materials is experimentally verified.

Analysis of Mode I Interlaminar Fracture Behavior in Unidirectional CFRP Laminates. (2nd Report, Examination of Interlaminar Deformation).

Double cantilever beam (DCB) specimens were used to study mode I interlaminar fracture of unidirectional carbon fiber/epoxy composites. An improved analytical model was introduced to analyze the crack opening displacement (COD) of the DCB specimen. Theoretical values of COD were compared with those measured by moire interferometry to evaluate an effective interlaminar tensile modulus and strain in the vicinity of a crack tip. The results showed that the modulus plays an important role in increasing the values of COD, and that there is a correlation between the modulus and the strain.

Further studies on fracture process zone for mode I concrete fracture

The development of a fracture process zone associated with stable crack growth in single edge-notched (SEN), three-point bend concrete specimens of different tensile strengths was monitored with moire interferometry. The experimental data was then used to drive a finite element model of the fracture specimen in its generation/propagation mode and to determine the crack closure stress due to aggregate bridging, the energy release and dissipation rates and the resistance curve.

Matrix cracking and interface debonding in fiber-reinforced cement-matrix composites

The processes of matrix cracking and interface debonding were studied using the high sensitivity Moire interferometry technique. The experiments were conducted with continuous steel fiber reinforced cementitious composites subjected to uniaxial tension. The initiation and propagation of cracking and debonding were observed during the tests with the specimens of different fiber-volume ratios. Based on the experiments, the fiber stress, the interface slip, the interface shear stress, and the matrix strain distribution were calculated. It was shown that interfacial frictional shear stresses were not constant either along the whole interface or at different loading levels. The strain localization was observed in the matrix where it was bonded to the fiber. The average contribution of the matrix was greater for the composites with the higher fiber-volume ratio.

Study of transformation plasticity in tetragonal zirconia polycrystals by moiré interferometry

Transformation plasticity in ceria-stabilized tetragonal zirconia polycrystals due to the stress-induced tetragonal-to-monoclinic martensitic transformation under tension and bending is studied by moire interferometry. The whole fringe patterns includingu fields andv fields are acquired. According to these patterns, the distributions of transformation plasticity in transformation zones are obtained, and the phenomenon of plastic flow localization for transformation is revealed. The above work provides a significant experimental foundation for establishing transformation constitutive relations