Microcrack Detection Using Spectral Response Data Alone

Microcracks of depth less than 200 μm in mechanical components are difficult to detect because conventional methods such as X-ray or eddy current measurements are less sensitive to such depths. Nonetheless, an efficient microcrack detection method is required urgently in the mechanical industry because microcracks are produced frequently during cold-forming. The frequency response function (FRF) is known to be highly sensitive even to microcracks, and it can be obtained using both the input data of an impact hammer and the response data of an accelerometer. Under the assumption of an impulse force with a similar spectral impulse pattern, spectral response data alone could be used as a crack indicator because the dynamic characteristics of a microcrack may be dependent solely on these measured data. This study investigates the feasibility of microcrack detection using the response data alone through impact tests with a simple rectangular specimen. A simple rectangular specimen with a 200 μm microcrack at one face was prepared. The experimental modal analysis was conducted for the normal (uncracked) specimen and found-first bending mode about 1090 Hz at the X-Y plane (in-plane). Response accelerations were obtained in both at in-plane locations as well as X-Z plane (out-of-plane), and the crack was detected using the coherence function between a normal and a cracked specimen. A comparison of the crack inspection results obtained using the response data and the FRF data indicated the validity of the proposed method.

Определение трещиностойкости образцов с шевронным надрезом с использованием трехточечного изгиба

A method is proposed for the experimental determination of the specific fracture energy of a material under loading by a 3-point bending of a rectangular specimen with a chevron notch. It is shown that at the initial stages of crack propagation in the chevron notch zone, a linear dependence of the specimen compliance on the crack length is observed. This makes it possible to calculate the specific fracture energy of the material without using the phenomenological equations used under standard test conditions. The calculations were carried out for technical titanium VT1-0.

Characterization of the Mechanical and Fatigue Behavior of Braided Composites Made of Twisted Yarns

In this study an experimental investigation was undertaken to characterize the influence of twisted yarns on the mechanical and fatigue behavior of 2D braided composites with a braiding angle of ±45°. Rectangular specimen made of untwisted and twisted carbon yarns are tested in the braiding (±45° fiber orientation) and in the yarn direction (0/90° fiber orientation). Experimental results will include modulus and strength values based on tensile and compression tests for both test directions. In addition, the effect of fiber twisting on S/N-curves are discussed.

Influence of the Disturbance in the Orthogonal Direction on the Kaiser Effect Using Discrete Element Method

When a rock sample is subjected to cyclic loadings, acoustic emission (AE) events increase sharply when the peak stress value applied previously is attained. This phenomenon is called Kaiser effect (KE). One important application of the KE is to determine the in situ stress, the knowledge of which is critical for the design work for underground engineering. Compared to the traditional methods, the acoustic emission (AE) method based on KE is done in the laboratory with special loadings on the rock cores and thus very economical. However, one fundamental question needs to be answered is the influence of the damage introduced by many factors during the period of the coring and samples preparation and so on. In this paper, we explore the influence by a series of loadings on samples in the direction perpendicular to the direction of the previous peak stress. Cyclic uniaxial compressions on the rectangular specimen and cyclic Brazilian tests were carried out based on the contact model in the particle flow code. The results demonstrate that, the disturbance in the orthogonal direction cannot influence Kaiser effect of the rock sample.

Parameter identification for anisotropic plasticity model using digital image correlation

The basic principle of the described procedure for plastic material identification is the generation of a complex and heterogeneous deformation field, which is measured by digital image correlation (DIC) and compared to Finite Element (FE) simulations. In this paper two tests for the identification of the hardening behaviour and the yield locus of DC06 steel are compared: a uni-axial test on a perforated rectangular specimen and a bi-axial tensile test on a cruciform specimen. The work hardening of the material is assumed to be isotropic and the yield locus is modelled by the anisotropic Hill48 criterion. The identification results for the different material parameters, based on both the uni- and the bi-axial test, are discussed and show a significant agreement.

MEASUREMENTS OF SOLID–LIQUID INTERFACIAL ENERGIES IN THE ORGANIC MONOTECTIC ALLOYS

The commercial purity dibromobenzene (DBB) and succinonitrile (SCN) were purified using a columnar distillation system. Thin walled rectangular specimen cells (60–80 μm thick) were fabricated and filled with the purified materials under the vacuum. The specimen cell was placed in a horizontal temperature gradient stage. A thin liquid layer was melted and the specimen was annealed in a constant temperature gradient for an enough time to observe the equilibrated grain boundary groove shapes. The thermal conductivities of solid and liquid phases for the purified DBB and DBB–5.7 mol% SCN alloy were determined with the radial heat flow and the Bridgman-type growth apparatuses. From the observed grain boundary groove shapes, the Gibbs–Thomson coefficients, solid–liquid interfacial energies, and the grain boundary energies for solid DBB in equilibrium with its melts and solid DBB in equilibrium with DBB–SCN monotectic liquid have been determined. The temperature coefficients of the purified DBB and DBB–5.7 mol% SCN alloy were also determined from thermal conductivity curve vs temperature.

Novel experimental approach for longitudinal-radial stiffness characterisation of clear wood by a single test

Experimental results obtained from maritime pine (Pinus pinaster Ait.) wood are presented for the characterisation of all LR=(1,2) orthotropic stiffness parameters of clear wood specimens by a single test. The approach relies on application of the virtual field method (VFM) to a rectangular specimen loaded in the Iosipescu fixture. The displacement field over the gauge surface of the specimen is measured by the grid method. Two configurations are investigated: (1) with grain aligned along the specimen length (0° configuration) and (2) with grain at 45°. For the 0° configuration, only the parameters Q 11 and Q 66 are correctly identified, with coefficients of variation of the same order of magnitude as those obtained from reference tensile and shear tests. Better identification is obtained for the 45° configuration, for which only the parameter Q 12 exhibits large scatter. This improvement results from a more balanced influence of all stiffness parameters on the response of the 45° specimen. However, all stiffness parameters identified were systematically underestimated by approximately 30% in comparison to reference values. This deviation is due to the vertical spatial variation of the mechanical properties of wood within the stem. Literature data confirm this interpretation.

UHV-TEM/REM Study of Palladium Silicide Islands Grown on Silicon (111) 7×7 Surface

The growth of self-organized nanoislands and nanowires on a substrate has been extensively studied with a view to fabricating the new functional materials and advanced electric devices. in the present work, Pd silicide islands and wires grown on Si (111) 7x77×7surface were observed in situ by ultrahigh vacuum transmission and reflection electron microscopy (UHV-TEM/REM). Pd was deposited on Si (111) 7×7 surface at about 700 K using an electron beam evaporator attached to the column of a UHV microscope. Two kinds of specimens were prepared: a <111> oriented rectangular specimen with a thin area, whose (111) top surface was observed by plan viewed TEM, and a <110> oriented bulk rectangular specimen, whose (111) side surface was observed by REMFigure la shows a REM image of Si (111) 7×7 surface. An incident electron beam is directed from the top to the bottom of the figure, which is foreshortened in the beam direction.