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1.
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 moiré interferometry.
A full-node localized hybrid analysis is introduced to perform efficient reduction of moiré 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. 相似文献
2.
A method of combining moiré interferometry and the finite-element method to effect localized stress analysis is presented.
The displacement data from local regions of interest in the optical experiment are used as boundary conditions for the finite-element
stress analysis.
The stability of the method is examined with data from simple numerical models one of which corresponded to the stress analysis
of a pin-loaded plate with friction. These studies show that the method requires the sensivity of moiré interferometry for
successful implementation, i.e., displacement data accuracy within 0.1 μm or 4 μin.
This localized hybrid method of stress analysis provides a powerful and efficient method for the reduction of experimental
data. 相似文献
3.
The theory of an automated fringe-pattern analysis using temporal phase stepping method for moiré interferometry is presented.
The automated method provides a fast and accurate strain measurement for moiré interferometry. Measurements on a tapered composite
specimen with a dropped ply are shown to highlight the capability of this technique to obtain the strain distribution, particularly
around the region with a dropped ply. 相似文献
4.
The deflection of micro-structures have been previously measured using optical interferometry methods. In this study, the
classical phase-shift shadow moiré method (PSSM) was applied to measure the deflection of a silicon micro-cantilever and to
determine the Young’s modulus of the cantilever material. The modulus value was determined from the profile based on deflection
equation. A normal white light source and a grating of 40 line pairs per mm were used to generate the moiré fringes. Since
the use of white light and high-resolution grating produces low contrast moiré fringes, the fringe visibility was enhanced
by applying contrast enhancement and filtering techniques. The Young’s modulus of the silicon cantilever material was estimated
to be 165.9 GPa with an uncertainty of ±11.3 GPa (6.8%). The experimental results show that the PSSM method can be successfully
applied for characterizing micro-cantilevers. Comparison of the deflection profile from the proposed method and a commercial
3-D optical profiler showed that the measurement range and sensitivity of PSSM are not affected by the poor contrast images. 相似文献
5.
Study of three-dimensional deformation of a pallet using phase-shiff shadow moiré and finite-element analysis 总被引:3,自引:0,他引:3
We present the results of a comparative study on the static deformation of a pallet, made from oil-palm fiberreinforced composite
material, using the phase-shift shadow moiré method and finite-element analysis (FEA). The pallet was designed and analyzed
using a commerical software package. The effect of various joint types on the deformation profile was studied to obtain a
simplified model to represent the actual design. A one-fifth scale model of the pallet was fabricated and the deformation
due to static loading was measured using the phase-shift shadow moiré method. The comparison between the measurement and FEA
results on the deformed profile showed a maximum difference of 13.7% at the center of the some of the deck boards, but a smaller
difference at other deck boards. The FEA results also produced a larger deformation gradient compared to the measurements. 相似文献
6.
Moiré techniques were developed, adapted and applied to the determination of strain fields in filamentary composite laminates. Conventional techniques, using 1000 line-per-inch (Ipi) arrays bonded or photoprinted onto the specimen, were applied to glass-epoxy and boron-epoxy specimens with holes and cracks. Techniques for tenfold fringe multiplication were also applied to glass-epoxy and boron-epoxy laminates with holes. A reflective surface of glass-like smoothness was produced on the specimen and a 500 dot-per-inch grid photoprinted on it. A rigid distortion-free camera was used for recording replicas of the specimen grid by projection photography. These replicas were analyzed with a 200 line-per-millimeter (5080 Ipi) grating for reconstruction of moiré-fringe patterns. These patterns were analyzed by graphical and mechanical differentiation using second-order moiré. Strain distributions and strain-concentration factors were in very good agreement with theoretical and other experimental results. 相似文献
7.
Methods of employing scanning moiré at high magnification are developed and demonstrated. Modern lithographic techniques for
producing custom moiré gratings with a frequency up to 250l/mm are described. On a probing station equipped with a video system, pseudo-color moiré fringes are produced using the scannning
lines of the color charge-coupled-device (CCD) camera. Fringe multiplication from 1 to 5 is possible with correct combinations
of magnification and grating pitch. An analysis is given to show that strain sensitivity depends only on the number of scanning
lines used to record the image. The grating pitch and the magnification are important because they reduce the gage length
of the strain measurement. The high-magnification scanning moiré was used to study plastic- strain fields in an aluminum tensile
specimen. Local disturbances in the strain field were observed at 2 to 2.5 percent applied strain. These discontinuities became
more significant at higher levels of applied strain. 相似文献
8.
In this paper, we introduce the two-dimensional continuous wavelet transform for the automated strain analysis of the moiré
interference fringe pattern. The Fourier transform method has been widely used for automated analysis of an optical interference
fringe pattern. However, this method is hardly applicable to the analysis of the fringe pattern, which includes large displacement
range or discontinuities. We show the advantages of the wavelet transform method by applying it to experimental results on
composite laminates. 相似文献
9.
Short duration stress pulses are of particular interest in determining the interfacial crack tip instability criteria for
the dynamic fracture behavior of laminated carbon-fiber/epoxy composites. However, the heterogeneous architectures of laminated
composites can alter the characteristics of a stress pulse as it propagates toward a crack tip. This makes it difficult to
use standard dynamic testing techniques for characterizing these materials, since these techniques assume the characteristics
of the stress pulse do not change as a result of propagation and can therefore be unambiguously determined from impact conditions.
This paper presents a novel experimental technique that has been developed for characterizing short duration stress pulse
propagation in laminated composite materials. In this technique, a dynamic moiré interferometer is used to capture fringe
patterns corresponding to displacement fields associated with short duration stress pulses that were generated by impacting
0° and 90°/0°/90° carbon-fiber/epoxy composites with a magnetic flyer plate. Appropriate dynamic testing conditions for capturing
high fidelity fringe patterns were determined using the recently developed dynamic moiré fringe contrast factor. The effects
of the composite architecture on the propagation of short duration stress pulses observed with the dynamic moiré interferometer
were confirmed by transient dynamic finite element analysis. From comparisons of experimental and numerical data, it was determined
that the impact conditions for the magnetic flyer plate and laminated composite will not necessarily be planar, which has
a significant effect on the intensity and duration of the propagating stress pulse. 相似文献
10.
Finite element procedures are applied to the modeling, analysis and visualization of experimental moiré data. Smoothing elements
are introduced and evaluated with respect to data sparseness and error. A one-dimensional smoothing element is uniquely coupled
with the method of principal curves to extract moiré fringe centers. A two-dimensional smoothing element is then used to produce
a full-field representation given the fringe locations. The moiré technique is applied to the four-point bend experiment,
and the surface-modeling technique is used to obtain displacement and gradient (strain) information. 相似文献
11.
The strain distribution produced by heating in a plate cut from a welded austenitic-ferritic steel transition joint has been measured using high resolution moiré photography Two methods of doing this are discussed one using a random pattern on the specimen surface and the other using a regular, orthogonal grating stencilled on to the surface. The strains parallel and perpendicular to the interface are presented and show strain peaks near the interface. The effect on strain of introducing a simulated crack along the interface was also examinec. The measurements are compared with the strains computed from a finite-element analysis. 相似文献
12.
As a method for measuring full-field out-of-plane displacement, projection moiré provides high measuring quality with simple experimental setup. Based on an image processing program developed by Heredia and Patterson, this article presents the implementation of projection moiré in low-velocity impact testing. Results from projection moiré agree reasonably well with those obtained from the commonly used load cell method. In an attempt to better document composite response to impact loading, the possibility of correlating the external out-of-plane displacement measurement with the internal delamination is discussed. The technique is further applied to composites with various microstructures, including laminated, two-dimensional woven and quasi-three-dimensional (Q3D) woven composites. Projection moiré is able to provide some insights of the delamination propagation of the composites under impact loading. 相似文献
13.
The micro-connection method for determining the centre lines of second-order moiré fringes presented in this paper can enhance
the accuracy in measuring strain fields, and generally can determine the absolute order of the second-order moiré fringes.
The strain data obtained from curved beam experiment are in good accordance with theory. The relationship between the second-order
moiré fringe and the strains at the specific points of the specimen is derived. Hence a reciprocate shift method is presented
for determining strain distributions in the non-overlapping region of the shifted moiré patterns, (usually in the region of
specimen where no second-order moiré fringes occur is the boundary region). 相似文献
14.
A set of similarity relationships is developed and discussed for use in the study of transient and steadystate thermal displacements, strain and stresses between model and prototype. The similarity relationships are shown to be dependent upon the existing state of stress in the thermally loaded member. Their utilization in the design or analysis of data for such experimental techniques as photoelasticity and the moiré method is cited. 相似文献
15.
Experimental and finite-element analyses are presented for the anisotropic states of stress, strain and fracture of a glass-epoxy plate containing a circular hole and subjected to uniaxial tension. Strains were experimentally measured using foil gages, moiré and birefringent coating. Stresses are computed in the linear range from the measured strains. While the hole reduces the plate strength by a factor of two, the maximum tensile strain at fracture is greater than the ultimate strain in a plate without a hole. Fracture consists of crack initiation at the hole boundary but off the horizontal axis. Away from the hole, failure is accompanied by considerable delamination. Discontinuous crack propagation is present. 相似文献
16.
17.
Moiré interferometry has been a valuable experimental technique for the understanding of the mechanical behavior of materials and structures. Over the last decade less emphasis has been placed on the development of the technique and more towards applications. This paper is a review article on recent applications using moiré interferometry in the fields of microelectronics devices, material characterization, micromechanics, residual stress, composite materials, fracture mechanics, and biomechanics. The general principles of moiré interferometry and advancement of techniques will not be discussed in this text, but references will be provided. 相似文献
18.
19.
In the electron moiré method, a high-frequency grating is used to measure microscopic deformation, which promises significant potential applications for the method in the microscopic analysis of materials. However, a special beam scanning control device is required to produce a grating and generate a moiré fringe pattern for the scanning electron microscope (SEM). Because only a few SEMs used in the material science studies are equipped with this device, the use of the electron moiré method is limited. In this study, an electron moiré method for a common SEM without the beam control device is presented. A grating based on a multi-scanning concept is fabricated in any observing mode. A real-time moiré pattern can also be generated in the SEM or an optical filtering system. Without the beam control device being a prerequisite, the electron moiré method can be more widely used. The experimental results from three different types of SEMs show that high quality gratings with uniform lines and less pitch error can be fabricated by this method, and moiré patterns can also be correctly generated.The project supported by the National Natural Science Foundation of China (10662005) and JSPS fellowship in Japan. The English text was polished by Keren Wang. 相似文献
20.
Daniel Post 《Experimental Mechanics》1965,5(11):368-377
The complete state of strain throughout an extended field can be determined from a single photograph by the moiré grid-analyzer method. Grids are used for the active, or specimen screen, and for the rigid analyzer screen. Hence, two families of moiré fringes appear simultaneously, providing displacements inx andy directions throughout the field. Interweaving of moiré fringes so as to disguise the identity of each family is prevented by use of an initial pattern. The initial pattern also eliminates uncertainties in assignment of moiré fringe orders throughout the field, and it provides numerous data points in any local region for reliable evaluation of fringe gradients. A rigorous derivation is presented for interpretation of such patterns in terms of strains. Errors in computed shear strains caused by analyzer misalignment are automatically canceled. The effects of rigid-body rotation of elements within the specimen are routinely eliminated in strain computations. Since calculated strains are independent of analyzer orientation, no fine control of analyzer alignment is required, and small shifts of analyzer position during the experiment are permissible. Accordingly, the moiré grid-analyzer method not only makes possible analysis of problems that previously could not be approached, but also offers vast simplifications for all extended-field moiré analyses. 相似文献