This paper provides a review of the strain rate effect on the through-thickness mechanical properties of fibre-reinforced polymer composites. The challenges and limitations associated with existing methods for through-thickness testing are discussed. Specific attention is given to the split Hopkinson pressure bar, and implications of the intrinsic limitations for measuring mechanical properties. The influence of strain rate on elastic modulus, ultimate strength and ultimate strain is provided for compressive, tensile and shear loading conditions. The review is concluded with a discussion on the direction of future research focussed around full-field imaging techniques.
The present study examined the structural change in micelles induced by surfactant flow in a channel with complex geometry. The channel used in experiments was a slit channel repeating a periodical expansion-contraction in a flow direction. Test fluid is a mixture of CTAB (cetyltrimethylammonium bromide) and NaSal (sodium salicylate) in distilled water and their concentrations are CTAB 0.03mol/l and NaSal 0.12mol/l. In the present experiments, the measurement of pressure loss through the expansion-contraction channel and the flow visualization using a crossed polarizing system were carried out. In the measurement of pressure loss, we found that the abrupt increment of flow resistance appeared in the flow curves. This abrupt increment of flow resistance was related to the structural change in micelles because the increment tendency was similar to the shear thickening property appearing in steady shear viscosity of fluid. However, with respect to the behavior after the occurrence of shear thickening property, the results for the periodic channel were different from the property of shear viscosity. In the flow image at the condition after the increment of flow resistance, we observed the white turbidity of fluid. Because the white turbidity represents flow birefringence caused by the structural change in micelles, we examined the change in retardation in a proportional relationship with birefringence. We found that the change in retardation around the contraction part became remarkable.
The dynamic response of a magnetic fluid bridge between two cylindrical permanent magnets subject to an alternating magnetic field was investigated with a high-speed video camera analysis system. When the magnetic fluid bridge system was subjected to an alternating magnetic field, the bridge showed shape oscillation. The relationship between the shape of magnetic fluid bridge and the magnetic field around the bridge was revealed experimentally. The magnetic field distribution around the bridge system was measured, and the relation between the magnetic field distribution and the magnetic fluid surface motion was discussed. The complicated capillary phenomena of a magnetic fluid bridge under the influence of a dynamic magnetic field were revealed experimentally.
Experimental investigations have been carried out on the fluid flow and heat transfer of opposing flows induced over a vertical heated plate placed in a uniform downward flow of water. The vertical plates of lengths L = 50 and 100 mm, heated with uniform heat flux were utilized in the experiments. The Reynolds and modified Rayleigh numbers based on the plate length were ranged as; ReL = 4×102 - 4×103 and RaL* = 4×106 - 3×1010, respectively. The flow fields around the heated plates were first visualized with dye. The result showed that the separation of the laminar boundary layer of forced convection appears first at the bottom edge of the plate and the separation point shifts from the bottom to the leading edge of the plate with the surface heat flux. We also found that the separations of flow at the bottom and upper edge can be predicted with the non-dimensional parameter as; (GrL*/ReL2.5) = 0.4 and 3, respectively, where the parameter (GrL*/ReL2.5) stands for the ratio of the buoyancy to the inertia force. The local heat transfer coefficients from the plates were subsequently measured with thermocouples. The result showed that the coefficients deviate from those of the pure-forced convection with the onset of flow separation at the bottom edge. We have also found that the overall Nusselt numbers from the plate show minima at around (GrL*/ReL2.5) = 1.0. Moreover, by comparing the overall Nusselt numbers to those of the forced and natural convections, the combined convection region was determined as; 0.35< (GrL*/ReL2.5) <4.0.
This paper attempts to give an approach on the already researched areas of unsteady flow field including shockwaves which were measured integrating density gradients by using the BOS (background oriented schlieren) method. Our BOS measurement systems consists of a digital camera, a background of the stripe patterns and a LED flash lamp. Projection data have been obtained by using BOS results which are the pixel displacement distribution data in the background. In regards to our previous study, we have constructed a three-dimensional distribution data from the obtained projection data using the ART (algebraic reconstruction technique) or the PSACT (parallel computing simulated annealing computed tomography) reconstruction technique. However, upon the existing obstacles, the BOS measurement presented some partial defects of measurement data. Related to this fact in the CT artifacts occurred defects of the projection data. Therefore, we need to evaluate the projection data which is used in the CT reconstruction. In this paper, we have discussed about and evaluated the projection data which was obtained from the projection angle with a range of 0 to 180 degrees.
We have been studying a validation scheme for the effects of wind-tunnel blockage on grid-generated turbulence. The focus is the effects of the streamwise variation of the acceleration parameter characterizing the fluid acceleration. First, a method is used for calculating the value of the acceleration parameter from the profile of the streamwise mean velocity. Then, a validation scheme based on the spatially varying acceleration parameter is derived. This derived validation scheme builds on the standard k-ε model. The effects of the streamwise variation of the acceleration parameter are found to be somewhat large. Also, the decay exponent of grid-generated turbulence is sensitive to the streamwise variation of the acceleration parameter.
To investigate the dynamics of the object plunging into water, the sequential images of water entry of rotating hydrophilic and hydrophobic cylinders were captured with high speed cameras, and the underwater trajectories of the cylinders were measured at various impact angles, velocities, and rotational rates. The captured images reveal that the hydrophobic cylinder splashes sheet-shaped water and turns to the left opposite to pre-impact moving direction while the hydrophilic cylinder continues moving in the right direction without the splash. The hydrophobic cylinder commonly produces a fully developed air cavity behind, although the hydrophilic one generates it only at the impact velocity higher than a critical value. The hydrophilic cylinder with the high impact velocity turns more rightward, and the fast rotation of the cylinder changes the trajectory leftward regardless of wettability. From the captured images and the estimated force by trajectory analysis, it can be deduced that the changes of the trajectory are due to the reaction force of the splash, additional hydrostatic force induced by the cavity, and lift force by Magnus effect.
Secondary currents strongly influence shapes of meandering rivers and cause sediment deposition on the inner banks and erosion on the outer banks. We report the curved channel measurements on secondary flow effects on flow pattern and on bed formation. The laboratory experiments were performed with a steady discharge until an equilibrium conditions was reached. A physical hydraulic model of the Sai Gon river portion around Thanh Da peninsula in Ho Chi Minh City was built respectively at scales of 1:500 and 1:100 in the horizontal and vertical directions. Both streamwise velocity and transverse velocity were obtained using three-dimensional Acoustic Doppler Velocimeter while sediment transport rates were evaluated by a sand trap. Our laboratory investigation provided evidence of secondary flow development in terms of position and magnitude and the relation to the bed morphology of the studied river. These results emphasize the crucial role of secondary flow in river dynamics and can be attributed to the numerical simulation process.
Electronic packages are composed of various components that have different coefficients of thermal expansion (CTE) values. Thermal strain occurs due to CTE mismatch of the components. However, when the thermal strain distributions are measured by digital image correlation (DIC), a periodical measurement error is observed. In this study, a displacement measurement method with periodical error elimination is applied to the measurement of thermal strain in an electronic package structure. In this method, rotated and multiple translated images in the horizontal and vertical directions are used to determine actual translation amounts. The periodical errors are eliminated using the relation between measured and actual translation amounts. As a result, the periodical errors in the measured thermal strain distributions on a test specimen can be eliminated, and measurement spatial resolution and accuracy are improved. In addition, precise thermal strain distributions can be observed. This method is effective for in-plane thermal strain measurement of electronic packages.
In order to predict the nonuniform deformation behavior of engineering materials, both the evaluation and modeling of the strain field are very important. Recently, accurate and contactless measurement of the strain field was performed using digital image correlation (DIC). Evaluation of the stress field is also required to model the nonuniform deformation behavior of the material. In this study, the stress and strain fields are evaluated by coupling the DIC and the finite element methods (FEM). The local strain can be decomposed into elastic and inelastic parts, based on the stress equilibrium around the displacement-measurement points. The local stress tensor can then be obtained by introducing the elastic strain components into a generalized Hooke’s law. The large deformation theory, based on the updated Lagrange method, is also introduced to evaluate the local true stress and true strain tensors for large strain range. The stress and strain fields for pure copper specimens that had two different shapes, namely, specimens NU and U, were evaluated during tensile tests. The cross-section of specimen NU continually changes whereas it is constant for specimen U. Furthermore, two specimens with different crystal grain size were used to investigate the effect of the microscopic heterogeneity. The local true stress ̶true strain relationship spanned regions in the proximity of the global response, while the relationship for specimens NU and U were almost similar. The effect of the microscopic heterogeneity on the macroscopic nonuniform deformation was investigated using the evaluated stress and strain fields. In larger-grain specimens, the evaluated stress gradient was lower than that estimated using the strain gradient since the hardening rate spatially distributed owing to the microscopic heterogeneity.
Rolling contact machine elements like bearing, gear wheel and railway rail have a problem of delamination failure such as flaking, pitting and shelling. It is known that this failure is closely related to shear-mode (mode II and mode III) as well as opening-mode (mode I) fatigue crack growth. In general, the shear-mode fatigue crack growth and its threshold behavior can be significantly influenced by the interaction of opposing crack faces. Therefore, understanding of the mechanism of friction and surface damage of crack faces is essential and a novel testing method that can estimate appropriately these properties is required. In this study, the influences of the cyclic reciprocating sliding contact with microscale relative motion on the frictional behavior and the surface damage of a bearing steel were studied under dry condition. The material investigated was a heat-treated high carbon-chromium bearing steel (JIS SUJ2). As a new friction and wear testing method, a cyclic ring-on-ring test was performed by making use of a hydraulic-controlled combined axial and torsional fatigue testing machine. The coefficient of kinetic friction was ranged from 0.4 to 1.0 and its average value was about 0.75.
The fatigue strength of ductile cast iron is influenced by small defects such as graphite particles and casting defects in the material. Therefore, establishment of a reasonable predictive method of fatigue limit applicable to various shapes and sizes of defects is necessary to optimally design the ductile cast iron products. In this study, high cycle fatigue tests of sharply notched and drill-holed specimens as well as smooth specimens were performed for a ductile cast iron, JIS-FCD550, with ferrite and pearlite evenly distributed in the matrix.From the microscopic observation of the near-threshold crack growth behavior, it was revealed that the fatigue limit is determined by the threshold condition for propagation of a small crack emanating from a detrimental defect. A predictive method of the fatigue limit was presented based on a fracture mechanics approach that was composed of three different methods classified according to the defect size.
In this paper, a method for evaluating J-integral for displacement fields obtained by digital image correlation (DIC) is proposed. First, the displacement gradient and strain are determined from the displacement using a least squares method on the domain of integration. Next, the stress components are determined from the strain using the Newton-Raphson method and material properties. Finally, the J-integral value is determined by the numerical integration on the domain of integration. The usefulness of this evaluation method is verified by applying this method to the displacement field obtained from the elasticplastic finite element analysis, and by applying to the experimental displacement field obtained by DIC.
Titanium alloys containing beta stabilizing elements exhibit several superior properties compared to other conventional metals. However, there are unknowns about the mechanical behavior of titanium alloys under biaxial compressive stress conditions. In this study, uniaxial compression and biaxial compressions along linear strain paths and bilinear strain path were performed on titanium-niobium alloys (Ti-Nb alloys) in order to investigate the influence of Nb contents on the compressive deformation behaviors. The results of compressions along linear strain paths revealed that the flow stress decreased while the ductility increased with the increase of the Nb content. It was found that the phenomenon was mainly due to changes of the microstructure and the primary plastic deformation mechanism. Those changes also induce anisotropic hardening. Based on those results, quantitative expression of the stress-strain relation with taking into account the Nb contents was discussed. The investigation on the effect of strain path change on the flow stress revealed the niobium dependency of the stress-strain response before and after the abrupt strain path change.
A grating projector using a linear light-emitting diode (LED) array with a grating plate can easily project wideangle, phase-shifted grating patterns. It is optimal for a linear LED array to be placed at an angle to the grating plate in order to maintain the brightness of the grating projection. In this case, the amount of phase shifting significantly varies at each location within the viewing area. Therefore, the authors propose a method to create a map of the optimal number of phaseshifting steps for each pixel and confirm the amount of phase shifting at each position in a grid-projected image. Further, a three-dimensional shape measurement system using a light-source-stepping method is developed. The experimental results obtained with this system using the proposed method confirm that the accuracy obtained using the proposed method is higher than that obtained using the conventional method.
To understand high work hardening behavior in lath martensitic steels, in situ neutron diffraction studies during tensile deformation for 22SiMn2TiB steel (contained 0.22 mass% of carbon) and carbon–free Fe–18Ni alloy were performed using a high–resolution and high–intensity time–of–flight neutron diffraction. Profile analyses were conducted using the Convolutional Multiple Whole Profile (CMWP) procedure and the Williamson–Hall (W–H) method. As results, the dislocation densities as high as 1015 m–2 in the undeformed states of both steels were observed hardly to change or slightly increase by the CMWP procedure. The reliability of the dislocation density obtained by the W–H method was low, because the whole profile was not considered for the analysis. In the former method, the values of parameter M related to dislocation arrangement were found to decrease rapidly in both steels at the beginning of plastic deformation, regardless of the solution of carbon atom. Hence, the high work hardening in the lath martensitic steel was considered by taking into account not only the increase of the dislocation density but also the change in dislocation arrangement.
In recycling a lot of low grade ferrous scraps, we cannot remove tramp elements, such as copper and tin, which are inevitably dissolved in molten iron. Accordingly, the thermodynamic data between copper and alloying elements in molten iron are necessary to know the influence of copper on the property of steel. However, the available data are not enough because of the difficulty of the measurements. One of the purposes of this study is to develop a new method to measure the thermodynamic data of tramp elements in iron. In this work, we have tried to measure the oxidation equilibria of copper in molten iron by using silver as an intermediate phase. By applying this method, the interaction between copper and boron in molten iron has been investigated at 1873 K.
Characterisation on a series of bulk Al65Cu20Fe15 quasicrystal alloy synthesised via in-situ induction casting under argon (Ar) enriched atmosphere and standard room ambient is the focal point of this research. The significance of atmospheric inertness in the course of induction casting process as well as the impacts of subsequent heat treatment at 650°C, 750°C and 850°C on the mechanical properties of Al65Cu20Fe15 quasicrystal alloy were investigated. The Al65Cu20Fe15 quasicrystal alloy samples produced by induction casting under critically controlled inert environment and standard room ambient as well as subjected to posterior annealing process were inspected in terms of their surface hardness as well as compressive strength. Vickers hardness test was performed in accordance to ISO 6507-1:1997, while compression test was conducted according to ISO 13314:2011 and ASTM E 9-89a (2000). Research findings inferred that the employment of argon (Ar) gas during on-site induction casting altered the pore size, composition, indentation hardness and the fracture mechanisms of Al65Cu20Fe15 quasicrystal alloy.
This paper describes the dependence of measuring temperature on the thin films for organic light emitting diodes (OLEDs). The final target of the present research is the improvement of flexibility of organic devices, flexible displays and flexible OLEDs. In the previous reports, the authors have demonstrated that organic thin films cause cracking as well as transparent conductive oxide (TCO) thin films in a strain of several percent at room temperature while the conductive polymer film such as PEDOT does not cause cracking. The temperature of OLED device, however, is generally heated up to less than 40ºC due to the heat generation by energy loss. Of course the temperature raise depends on the design of the device and heat sink of the panel further it influences on the life time of the device so that OLEDs cause degradation at higher temperature. Therefore, the tensile tests of Alq3, PVK, NPB, and spiro-NPB, which were prepared on PEN substrates, were conducted at a temperature of 54ºC then the critical cracking strains were compared with those measured at room temperature. As a result, it was found that the critical cracking strain of Alq3 thin films at 54ºC is higher than that at room temperature which agreed with the authors expectation, however PVK, NPB, and spiro-NPB shows lower critical cracking strain at 54ºC than at room temperature. Further study is required to understand the results from a point of the change of ductility and adhesion.
Safety assessment against penetrating injury such as skin laceration requires a soft tissue simulant that can mimic the mechanical behavior of human soft tissue. In this study, in order to investigate the mechanical characteristics of soft tissue simulant materials available in the market, several kinds of simulant material (silicones and urethanes) were characterized using uniaxial tensile, planar tensile and equibiaxial tensile tests. The mechanical behaviors of those simulant materials were also compared with the mechanical behavior of porcine skin reported in the literature. Furthermore, the simulant materials were modeled using hyperelastic Ogden model by identifying the values of model parameters according to the tensile test results.
Degeneration of collagen fibres at 60ºC is well known, and therefore mechanical testing of compact bone at the elevated temperatures higher than 60ºC could give us the similar results to that of the degenerated compact bone due to aging. In the present study, a series of fracture toughness tests on compact tension specimens of bovine compact bone under mode I loading has been performed at various temperatures between 50ºC and 70ºC according to ASTM standards. Two types of bone tissue, namely plexiform and Haversian bone were taken from the mid-diaphyseal region of bovine femurs and then tested. An initial crack was introduced in the direction parallel or perpendicular to the long axis of the femur so as to observe anisotropic behaviour. Plexiform bone showed higher fracture toughness than Haversian bone independently of the initial crack direction and temperature. Both compact bones appeared to show lower fracture toughness at higher temperatures. These results were discussed with an assistance of observation of the fracture surfaces using an optical and scanning electron microscope.
We developed a mechanical measurement system, which we then used in this PAFO gait experiment. We report that differences between hemiplegic patients and healthy subjects in the mechanical load acting on gait using a PAFO in swing phase. Moreover, there is a large difference between volunteers and patients in initial swing phase and especially in decreasing belt reaction force toward the end of terminal swing phase. We consider that this difference is relevant to control of voluntary movement. In conclusion, a large deformation can be observed between volunteers and patients by analyzing the belt reaction force and load waveform.
This paper studies the use of rice husk ash (RHA) to improve compressive strength in soft soil clay (SSC) using alkaline liquid (L) based geopolymer. The research is carried out in a laboratory to investigate the compressive strength development of soil when changing some factors including RHA/SSC ratios, L/(RHA+SSC) ratios and curing time. The results revealed that the compressive strength increased with the increase in an amount of rice husk ash and curing time, and with the decrease in alkaline liquid. The compressive strength was 1550 kPa when sample was cured in room temperature for 28 days, with the RHA/SSC ratio of 0.5 and the L/(RHA+SSC) ratio of 0.4. In addition, with the result of scanning electron microscopy (SEM) analysis showed a potential development of the compressive strength in soft soil clay reinforced by geopolymer rice husk ash.
As the results of dredging activities, a huge amount of sludge has been generated. And one of recycling methods for the sludge has been developed by using paper debris and cement. This is called “Fiber-cement-stabilized soils method” (FCSS). The modified-sludge produced by this method has several features such as high failure strength, high failure strain, and high durability. However, it is almost difficult to apply this method directly for the dredged sludge in Mekong delta, because it is hard to obtain a large amount of paper debris. By the way, a large amount of agricultural wastes are discharged, especially in the case of rice husk in Mekong delta. If the rice husk (RH) can be used instead of paper debris, it will be possible to recycle the dredged sludge in Mekong delta by FCSS. Moreover, FCSS is generally carried out by compaction method. However, compaction method cannot be used in some constructions such as backfilling. In these cases, placing method is generally used and one of recycling methods that applied placing type is Liquefied-Stabilized Soil Method (LSS). In this method, high flowability and low bleeding rate materials are made by adding the cement and water with excavated soil. LSS is possible to simplify construction sequence because LSS flows like concrete mortal and compaction is not necessary. However, LSS method showed some disadvantages such as low durability for drying and wetting conditions. In this study, several specimens were made by using rice husk with FCSS and LSS, and unconfined compression tests were carried out. It was confirmed that rice husk can be used as a substitute of paper debris in FCSS and LSS. Furthermore, empirical equations were obtained as a function of initial water content of the sludge to estimate the optimum additive amount of rice husk and cement for both compaction and placing types.
Geopolymer, an environmentally friendly alternative to ordinary Portland cement, is currently receiving increased attention in academic and industrial communities for its ability to produce fly ash based geopolymer material in several applications. Geopolymer material is known as an inorganic-polymer composite and is synthesized by the aluminosilicate compound materials with alkali hydroxide and alkali silicate. Current researches on geopolymer are mainly focused on geopolymer concrete properties such as mechanical properties, paste properties and durability properties in laboratory. However, few specific publications are available concerning the feasibility of geopolymer modified soft soil (sludge) in the actual landslide area which is mainly due to earthquake and heavy rainfall. This paper presents the details of studies carried out on strength of sludge improved with various geopolymer contents. The composition of sludge is 60% silt, 40% clay and water content is 70%. Sodium hydroxide (NaOH) 12 Molar and sodium silicate solution (Na2SiO3) were prepared. The test specimens were made of 50 x 100 mm cylindrical mold and 20oC temperature curing condition. By adding paper debris, the specimens were made immediately after mixing by compaction, in contrast without adding paper debris, after 24 hours the specimens were made with same conditions to compare. Compressive strength after 12 and 18 hours was measured. The results showed that the modified soil with paper satisfied the target (125kN/m2) with geopolymer content nearly 9% after 12 hours and all of them obtained enough strength after 18 hours. Moreover, modified soil without paper reached target after 12 and 18 hours but revealed lower strain performance.