Experimental Techniques最新文献

Residual stresses are usually not considered in engineering calculations of components and structures, however, they are present more or less in most of components, such as castings, welded components, components produced by rolling, bending, etc. The main objective of presented research is to determine the residual stresses in seamless thin-walled pipes, i.e. in ring specimens cut out from hot-rolled pipes. Pipe Ring Notched Bend specimens cut out from a pipe are considered as an alternative to the standardized Single Edge Notched Bend specimen used for determination of pipe material fracture toughness. In this research, residual stresses in ten ring specimens are measured by two methods: Incremental Hole Drilling Method (IHDM) and X-Ray Diffraction (XRD). Hoop residual stress is considered as the most important one in pipes. Principal stresses, as well as orientation of principal coordinate system, are determined by IHDM, and subsequently, hoop residual stress is calculated. Direct residual stress in hoop direction is measured by XRD. All results are shown on diagrams up to the depth of 1 mm from outer surface of each ring. Direct comparison of results referring to residual stresses obtained by both methods of measurement is presented to conclude that measurement with XRD shows uncertainty at some depths of measurement, since that method of measurement gives results with some large local oscillations.

This research aims to measure the material parameters and porosity of the resin matrix composite material produced by hot moulding process under various pressures. The laser ultrasonic technique has been used as the measurement technique and the guided wave dispersion relationship was obtained in the resin matrix. In the resin substrate, the single-layer flat plate Lamb wave model was applied to inversely calculate the material parameters and compared with tensile test and traditional ultrasonic measurements. In the woven composite laminate, the specimens were produced with different porosity using the hot pressing moulding process, scanned with computed tomography to confirm the porosity under different pressure and the dispersion curve changes were observed using the laser ultrasonic technique. Result showed that the inversely calculated thickness of pure resin test pieces were consistent with the laser ultrasonic measurement within an error of 5%. The elastic modulus of inverse calculation and the actual tensile test values showed within 12% of error. In the woven fibre composite, the dispersion curve obtained by the laser ultrasonic measurement showed that, as the porosity increases, the dispersion curve tends to shift to a lower wave velocity. In addition to that, the porosity of the woven composite is not changed under different hot pressing pressures. The computed tomography scanning indicated that the pores are mostly concentrated in the overlap of the carbon fibre weaving and extended along the fibre warp and weft directions, showing cross-shaped pores.

A new methodology was used to determine the speed of sound in water by using low frequency ultrasound over the temperature range 20 to 95° C. The initial procedure was developed based on finding the resonant locations over variable pathlengths in an acoustic tube and calculating their separation distances through the water, yielding the wavelength (λ) measurement. An in-house gain detector was employed to detect the resonant points, through detection of the amplitude voltage peaks in response to the displacement of the moving transmitter. The λ was calculated as 53 mm for water at 20° C with the fixed frequency of 28 kHz. As a result, using the universal wave equation, the speed of sound was estimated to be 1484 m/s with an accuracy of 99.89% compared to the references. The methodology was then followed through the second procedure to measure the sound speeds at temperatures higher than 20 °C, using coincidence frequency determination over different temperatures. In a fixed acoustic pathlength equal to the calculated λ at 20° C, the initial frequency, 28 kHz, was linearly swept to track the coincidence frequency corresponding to certain temperatures. The gain detector was used to obtain the coincidence frequencies, wherein the amplitude voltage peaks were recorded during the frequency adjustment. The simultaneous monitoring with an oscilloscope consolidated data when the phase differences between radiated and received waves were eliminated at the coincidence frequencies. The measured coincidence frequencies were then directly used to determine the speed of sound in water as function of temperature. The third order curve fitted to the results yielded an R² equal to 0.9856, representing excellent agreement with the reference data.

Abstract

In this work, an off-axis 2D Particle Image Velocimetry system is used to obtain the 3D flow field at the outlet of a tubular reactor equipped with Kenics static mixers. The 3D flow fields are obtained exploiting the out-of-plane velocity component and considering the symmetrical features of the flow generated by the static mixers. The raw results show that the velocity vectors, measured on a cross section perpendicular to the tube axis by 2D-PIV with the camera located at 24° from the measurement plane, are affected by the axial component of the flow. However, taking into account the symmetry of the flow field with respect to the tubular reactor axis and evaluating the effect of the out of plane velocity component, the correct 2D velocity vectors on the plane and also the velocity component in the axial direction can be calculated from the raw 2D PIV data. The consistency of the methodology is demonstrated by comparison of the results with the flow field measured in a smaller tubular reactor of similar geometry and Reynolds number with a symmetrical 2D-PIV system, with the camera located perpendicularly to the laser plane. Then, the 3D features of the flow are analyzed to characterize the effects of the different combinations of static mixer configurations on the fluid dynamics of the system in turbulent conditions. The results show that, as the pressure drop increases, a more uniform velocity distribution is achieved.

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So far, many studies have been completed on the traditional soil stabilisation using cement or lime, however, very limited literatures pay attention to the mechanical behavior of stabilised soil with new materials. The main objective of the current study was to investigate the mechanical behavior of stabilised soil with polyurethane (PU) foam. For this purpose, a series of direct shear tests were performed on soil specimens which were stabilised by PU foam. The study revealed that adding PU foam to sand resulted in a remarkable increase in the shear strength parameters (c and ϕ), which the increase of cohesion was more pronounced than the increase of angle of internal friction. The strength of PU foam-stabilised specimens increased gradually as the PU foam content increased from 0 to 10% and then decreased for additional PU foam content. The interaction between the sand particles and PU foam was investigated by optical micrograph analysis. Finally, a new model was developed to predict the shear strength of PU foam-stabilised specimens. Results indicated a satisfactory performance of the proposed model where the Pearson correlation coefficient was 0.94.

Existing guidance from ASTM standards on extracting mechanical properties from uniaxial tension test data is not suitable for high-volume applications because it lacks automation. The Pacific Gas and Electric Company (PG&E) has performed over 450 uniaxial tension tests on samples extracted from dozens of distinct natural gas pipeline features in support of materials verification efforts; 144 of these tests recorded the entire deformation response up to fracture and were subsequently analyzed herein. Algorithms were developed to enable automatic, batch post-processing of the tensile data. Among the mechanical properties that this software extracts from the tensile data are the power-law hardening exponent and strength coefficient. A novel algorithm was developed to calculate these power-law parameters while accommodating the range of yielding and hardening behaviors present among the low carbon pipeline steels tested in this effort. The algorithm, presented in this brief technical note, first identifies the lower limit of the hardening region by calculating the tangent modulus of the stress–strain curve, which reaches its maximum value at the onset of strain hardening. The end of uniaxial hardening coincides with the ultimate tensile stress and the end of uniform deformation. From there the algorithm computes the power-law hardening parameters using conventional linear regression. Analysis of the data shows that this approach is more accurate than two other approaches: (1) regressing from 0.2% plastic strain to the limit load, and (2) iteratively regressing to identify the region that minimizes the regression error. The advantage of this approach, over existing methods, is observed for materials that exhibit a yield plateau. To further demonstrate the utility of the strain hardening information collected during this effort, the relationship between strain hardening exponent and ratio of yield strength to ultimate tensile strength from this data was compared to those reported in previous literature pertaining to remaining life assessments of steel line pipe. Overall, the strain hardening data obtained in this algorithm indicates greater hardening in pipeline steels than some previously published results. This algorithm has been made available as part of this paper’s supplementary materials.

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