Spatial distribution characteristics of spectra measured at several points on a vibrating membrane surface are investigated. Three membrane models, which are square polyimide films with a flat surface, a wrinkled surface and a creased surface, are treated. An impact load is applied to the corner of the membranes, and a flexural wave propagation as well as a stationary vibration appearing on the membrane surfaces is measured by photogrammetry using a grating projection method. The results show that the vibration characteristics of the membrane surfaces, which are a flexural wave propagation, a natural frequency and a maximum amplitude of the response, are strongly affected by the surface features of the membranes, while the spatial distribution of the logarithmic magnitude of the spectra on the membrane surface has a similar distribution property regardless of the existence of wrinkles and creases.
Deformation band formed on the surface during the plastic deformation in Al-Mg alloy was observed by digital image correlation method. As a result, the observed characteristic deformation processes are divided into three types, which correspond to the serrated flow of the A type, the B type and the A+B type, respectively. The deformation process type was shifted to the B type from the A type through the A+B type as the plastic deformation progresses. This phenomenon is considered due to the relationship between the diffusion velocity of solute elements and the moving velocity of dislocations.
A cyclic stress measurement method that focuses on the density and the preferred orientation of grown grains was investigated using an electrodeposited nickel foil. The nickel foil was adhered to the titanium alloy specimen and the cyclic loading test under various biaxial stress conditions was carried out. The ambient temperature during the test was set to 175 － 250℃. Then the grown grain density was measured and the crystallographic orientations were also analyzed by electron backscatter diffraction. Since surface state of the substrate on which mirror finishing had been performed was transferred to the initial electrodeposited surface, grown grains can be observed by the microscope without electrochemical polishing and etching. The relationship among grain growth density, maximum shearing stress, number of cycles and ambient temperature was formulated on the basis of the experimental results. In addition, due to the difference in the original orientation between nickel and copper foils, preferred orientation of grown grains was also different in both foils. However, the slip direction of grains agreed well with the maximum shearing stress direction in both foils. On the basis of this feature, principal stresses can also be determined using the pole figure of grown grains.
In this study, the effect of binder type on the elastic moduli of inorganic adhesives is investigated at elevated temperatures using an impact exciting method for measuring natural frequencies of adhesive bulk specimens with rectangular cross section. The specimens are treated as the Bernoulli-Euler beam and the elastic moduli of the adhesive bulk specimens are obtained by the impact exciting method at temperatures from room temperature to 900 degrees Celsius. To compare with the results for the natural frequencies, the elastic moduli are also measured by the static bend tests at room temperature. The experimental results obtained by the impact exciting method show good agreement with those by the static bending method. An adhesive composed of an aluminum di-hydrogen phosphate binder shows the highest value of longitudinal elastic modulus in the inorganic adhesives of three different binders. The elastic modulus of an adhesive composed of water glass binder remains constant up to 600 degrees Celsius.
A two-dimensional (2D) scanning moiré method was proposed to measure the micron/nano-scale deformation distributions in two dimensions using a single moiré pattern under a laser scanning microscope. The 2D scanning moiré pattern in a large view field (width is 500~2000 times the grating pitch) comes from the interference between a cross specimen grating and the 2D laser scanning dots which serve as the reference grating. The 2D scanning moiré fringes can be separated to two groups of parallel one-dimensional moiré fringes in two directions using complex Fourier transform. The full-field micron/nano-scale deformation distributions in the x and the y directions are measureable from the corresponding parallel moiré fringes, respectively. Consequently, the 2D displacement and strain distributions can be determined using a single 2D moiré pattern, instead of two moiré patterns in two directions. The proposed method possesses the advantages of time saving, large view field, non-destruction, and high accuracy for two-dimensional deformation measurement of various materials evaluation.
Displacement distribution gives useful information to understand the deformation behavior in materials science. Full-field optical methods, including the digital image correlation method and the sampling moiré method, are useful and effective to measure the displacement and strain distribution of materials by using a random pattern or a regular repeated pattern. In this study, we performed a comparative study to evaluate the measurement accuracy for digital image correlation and sampling moiré method using a same camera and an aluminum specimen subjected to same lighting condition. We discuss the advantage and disadvantage of both methods from the viewpoint of the accuracy under different signal-to-noise ratio (SNR) measurement conditions, and the analysis speed in case of single-core and multi-core CPU computing. Experimental results indicated that digital image correlation method is useful to measure the deformation under a high SNR condition in an easy way, and the sampling moiré method is robust to the measurement condition. Compared with the analysis speed, sampling moiré method is much faster than digital image correlation method. Furthermore, both methods are useful as a full-field measurement tool in experimental mechanics if a random pattern or arbitrary repeated pattern can be observed on the surface of materials.
When external force or stress is applied to the object, displacement could be occurred. Therefore, accurate displacement distribution measurement is important to maintain of their structures. Sampling moiré (SM) method is one of the optical full-field displacement measurement method used in field experiments. In the SM method, the in-plane displacement distribution can be accurately determined using a digital camera and repeated patterns. In this study, we developed a dynamic out-of-plane displacement distribution measurement method based on the SM method using a single camera. In the proposed method, the out-of-plane displacement was measured by considering the relationship between the change of grating pitch in captured image and the magnification of used camera lens. Some researchers proposed the out-of-plane displacement distribution measurement methods by using two or multiple cameras. Compared with their methods, our method has advantages including fast, ease-of-use, and inexpensive equipment. The basic principle and an experimental validation of measurement accuracy were presented. As an application, this technique can be potentially extended to measure the out-of-plane direction vibration frequency in full-field.
A sampling moiré method is applied to a dynamic deflection angle distribution measurement. The accuracy of phase difference analysis using the sampling moiré method is from 1/100 to 1/1000 of the grating pitches. 2D phase distributions of the 2D grating are also obtained with the sampling moiré method. 2D phase difference before and after the deformation gives the displacement at the point and the 2D phase gives the coordinates at the point when the grating pitch is known. Authors proposed an analysis method of a rotation angle from the 2D phase difference distribution and the 2D phase distribution. In this paper, the analysis method of a rotation angle is applied to the dynamic deflection angle distribution measurement of a cantilever. The results are compared with the results obtained using laser displacement meters.
This paper describes development and improvement of mechanical properties of environment-friendly composites that was fabricated by reinforcing a polylactic acid (PLA) resin with natural fibers extracted from rice straw. Alkali treatment was performed on rice straw fibers to improve their mechanical properties. Rice straw fibers were dipped into 5 mol/L concentrated sodium hydroxide solutions for 2 h at 30, 60 and 90 degree C. Tensile tests of untreated and alkali treated rice straw fibers were carried out in order to evaluate the effects of treatment temperature conditions of rice straw fibers. The result showed that the tensile strength of the treated fibers decreased in comparison with untreated fibers. In addition, green composites reinforced by untreated and alkali-treated rice straw fibers were fabricated by a vacuum assisted hot press molding method. Three-point flexural tests were carried out for both green composites. The results showed that both flexural strength and maximum displacement of green composites reinforced by alkali-treated rice straw fibers increased in comparison with green composites reinforced by untreated fibers.