A fringe career

Evaluation of the residual stresses in metallic materials produced by additive manufacturing technology: effect of microstructure

Determination of residual stresses in metals, subjected to secondary processing, is necessary from the point of view of their applications and is widely studied in literature. However, residual stresses induced during service is generally ignored when evaluating the performance of the component. The residual stress in a component could be tensile or compressive in nature and eventually affects its service life under external loading. In this regard, industries demand rapid, efficient, and easier methods of non-destructive testing to identify and control the residual stress in such components. The present work aims at evaluation of residual stress in an LM-25 aluminium alloy/fly Ash Metal Matrix Composites (AMC) after subjecting the specimen to dry sliding wear tests. X-ray diffraction technique was used to measure the residual stress in the “pin” specimen of the pin-on-disc set-up. The residual stress was ~ 24 % higher in the composite compared to the un-reinforced alloy after the wear test while the wear rate, measured in terms of weight loss of the pin, was lower by about 50%, under similar test conditions.

The ultrasonic regulation of internal residual stress in metal and nonmetal elastic solid component has been investigated. High-energy ultrasonic wave is applied to carbon steel and ordinary flat glass for residual stress control. An ultrasonic residual stress measurement device developed with the acoustoelastic theory is used to measure macro residual stress in time, to evaluate the residual stress regulation effectiveness. Based on the essence of residual stress, the interaction between acoustic wave and residual stress is analyzed, and dislocations theory is considered. When the ultrasonic energy supplied to the elastic solid is greater than the energy of dislocation, the internal residual stress will be released. Experiments result shows that as high energy acoustic field is applied, the local residual tensile stress in elastic solid specimen will shift gradually to beneficial compressive stress, thus the component’s fatigue strength, corrosion resistance and service life will be greatly improved.

Organic contaminants adsorbed on the surface of a silicon stencil mask in a high-vacuum chamber in an electron-beam exposure lithography system have been analyzed and identified using thermal-desorption gas chromatography/mass spectrometry (TD-GC/MS), X-ray photoelectron spectrometry (XPS), and electron energy loss spectroscopy (EELS). The major organic compound adsorbed onto the surface of the silicon stencil mask in the high vacuum chamber has been found to be di-2-ethylhexyl phthalate (DOP). The amount of DOP adsorbed onto the silicon surface in high vacuum is much larger than that adsorbed in ambient air. A relatively high molar ratio and long mean free path of organic molecules with a low vapor pressure, such as DOP, in high vacuum is considered to enable them to be easily adsorbed onto the silicon surface in high vacuum. On the other hand, organic volatiles with higher vapor pressure are not adsorbed on the silicon surface in high vacuum. It has been found by XPS and EELS that the organic contaminants adsorbed on the surface of the silicon stencil mask are transformed into graphite-like carbon by electron beam irradiation during the exposure process.

Viscoelastic stress analysis of thermally compatible and incompatible metal–ceramic systems

Authentication of coins is frequently presenting complicated problem in numismatics practice. Metal composition only may not be enough to identify forgeries, notably when one deals with noble metals – silver, gold or electron. Isotopic ratios, providing in certain cases information regarding metallic ore source (geographical provenance), require a sample to be extracted for MS-analysis while sampling is not permissible for numismatic material in principle. To solve the problem it becomes crucial, in addition to metal’s composition, to establish the method used for a coin’s manufacturing, as forgers are rarely realizing or following the method that was used in the original historical production. Conventional visual studying under microscope is not always being enough to understand how the coin was produced while metallographic examination of polished and etched metal samples, which might provide necessary information, is not applicable here for its destructive character. Necessary information regarding manufacturing could have been extracted from residual stress analysis, but, in general, there were very few published works regarding this kind of analysis for coins, and those few did not consider any connection between manufacturing process and residual stress in metal. The expected types of residual elastic stress arisen under historically known methods of coins production (casting in hot or cold mold, striking hot or cold metal) are considered in this work. On this base, non-destructive X-rays diffraction method (Sin²Ψ-method) is offered to distinguish between various methods of manufacturing. The results may be applied in museum’s laboratory as useful criterion for authentication of coins and medals.

Experimental and computational studies were performed to determine the effects of different blade designs on a flow pattern inside a double-spindle counter rotating mower deck. In the experimental study, two different blade models were tested by measuring air velocities using a forward-scatter LDV system. The velocity measurements were taken at several different azimuth and axial sections inside the deck. The measured velocity distributions clarified the air flow pattern caused by the rotating blades and demonstrated the effects of deck and blade designs. A high-speed video camera and a sound level meter were used for flow visualization and noise level measurement. In the computational works, two-dimensional blade shapes at several arbitrary radial sections have been selected for flow computations around the blade model. For three-dimensional computation applied a non-inertia coordinate system, a flow field around the entire three-dimensional blade shape is used to evaluate flow patterns in order to take radial flow interactions into account. The computational results were compared with the experimental results.

For examining the characteristics of residual stress generated by fillet welding of a stiffener to a steel plate under tensile or compressive loading, a series of numerical simulation was carried out. In both cases of welding under constant tensile and compressive loading in the welding direction, the residual stress around the weld metal was almost the same as that by welding without external loading. On the other hand, the residual stress in the base metal was variously changed by the difference of the tensile and compressive loading and those magnitudes. It was proposed that the average residual stress in the base metal under the external loading could be predicted by superposing the welding residual stress without loading and the nominal stress due to the external loading.

The inner surface of reactor pressure vessels is protected against corrosion by an austenitic cladding. Generally, the cladding is welded on the ferritic base metal with two layers to avoid cracks under the cladding and to improve the microstructure of the cladding material. On the other hand, due to the cladding process and the difference of the thermal expansion coefficient of the austenitic cladding and the ferritic base material, residual stresses are acting over the wall thickness. This residual stress field is important for the integrity assessment of the component. For the determination of the residual stress field, plates of a reactor pressure vessel steel were cladded by submerged arc welding and heat treated, representative of the real component. The numerical simulation was performed with the finite element code SYSWELD. The heat source of the model representing the welding process was calibrated against the temperature profiles measured during welding. In the analysis, the temperature-dependent material properties, as well as the transformation behaviour of the ferritic base metal, were taken into account. The calculated residual stresses show tensile stresses in the cladding followed by compressive stresses in the base metal that are in agreement with measurements with X-ray diffraction technique. After post-weld heat treatment the residual stresses in the ferritic base metal are reduced significantly.

Tensile residual stress is a major issue in integrity of the welded structures. Undesirable tensile residual stress in welding may reduce fracture toughness and fatigue life of welded structures. The low transformation-temperature (LTT) fillers, due to introducing compressive residual stresses caused by prior martensitic transformation, can reduce tensile residual stresses in the weld zone. The effects of using LTT fillers on welding residual stresses of high strength steel sheets are studied and compared with conventional fillers. 3D finite element simulations including coupled thermal-metallurgical-mechanical analyses are developed using SYSWELD software to predict the welding residual stresses. For validation of the finite element model, the residual stresses are measured through hole drilling strain gage method. The results indicate that using the LTT fillers cause a decrease of the longitudinal tensile residual stresses of the weld metal from 554 MPa to 216 MPa in comparison with conventional fillers. The transverse residual stresses of the weld line are changed from tensile 156 MPa to compressive 289 MPa with using LTT fillers instead of conventional fillers.

For Lift-type Vertical Axis Wind Turbine (VAWT), it is difficult to evaluate the performance through the scale-model wind tunnel tests, because of the scale effect relating to Reynolds number. However, it is beneficial to figure out the critical value of Reynolds number or minimum size of the Lift-type VAWT, when designing this type of micro wind turbine. Therefore, in this study, the performance of several scale-models of Lift-type VAWT (Reynolds number : 1.5x10 4 to 4.6x10 4 ) was investigated. As a result, the Reynolds number effect depends on the blade chord rather than the inlet velocity. In addition, there was a transition point of the Reynolds number to change the dominant driving force from Drag to Lift. Keywords : Vertical Axis Wind Turbine, Wind tunnel, Reynolds number, Performance, Scale effect. 1. Introduction and background Lift-type Vertical Axis Wind Turbine (VAWT) has difficulty of performance evaluation with scale-model wind tunnel tests, because of the scale effect depending on Reynolds number, and there is cost problem in field test with actual size Lift-type VAWT to evaluate several blade shapes or the size and setting angle of blade for performance improvement. If possible, it is useful to evaluate the performance of Lift-type VAWT with scale-model wind tunnel tests and these results can help us to investigate the possibility of Lift-type VAWT as micro wind turbine. However there were few reports [1][2][3] for the performance evaluation of Lift-type VAWT with scale-model wind tunnel tests and almost only the data of field test for actual size Lift-type VAWT [4] that is same type we are investigating in field test [5] were reported. For the reasons mentioned in the above, in this study, several scale-models of Lift-type VAWT were investigated for the performance with changing the pitch angle, blade chord length and blade shape as the experimental parameter of Lift-type VAWT. In performance test, low speed wind tunnel of blow down type was used and the diameter of scale-model of Lift-type VAWT was 1/7 to 1/10 compared with the one for field test [5] mentioned before. The data acquired from the performance tests were evaluated with Reynolds number (

This work reports a novel method of microfabrication for silicon nitride based piezoresistive microcantilever device, to minimize the residual stress induced bending. The microcantilever of dimension L × W ~ 250 × 100 µm2 with stack (Si3N4/Poly-Si/Si3N4/SiO2) thickness ~ 1 µm was realized, by using standard six masks and bulk silicon micromachining fabrication process. In order to compensate the residual inbuilt stress, asymmetric structure layers for microcantilever was proposed and the presence of thin oxide layer underneath the released microcantilever stack was used to control the bending. The surface profiler measurement results showed the curvature bending in the range of ~ 4 ± 3 µm. The microcantilever was characterized further to evaluate its physical parameters such as mechanical deflection sensitivity and spring constant. The deflection sensitivity and spring constant values were ~ 0.161 ppm/nm and ~ 0.2 N/m, respectively. Finally, the practical application of fabricated piezoresistive microcantilevers was demonstrated by using it for explosive vapors sensing.

A polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method for salmon species identification was optimized for use with U.S. commercial products. Reference specimens of six salmonid species were collected and morphologically verified. A 463- to 464-bp fragment of the mitochondrial tRNAGlu/cytochrome b gene was PCR-amplified, digested with two restriction enzymes (Sau3AI and NlaIII), and analyzed with agarose gel electrophoresis. All six species were successfully differentiated with this method and the restriction digest was shortened to 1 h rather than overnight. A decision-making flowchart was developed based on these results that allows for species diagnosis within two–three steps. After the method was optimized, it was tested with a variety of commercial salmon products (n = 29), including canned, smoked, jerky, and fresh fillet samples. Salmon species identification was successful for all 14 smoked and fresh/frozen fillet products, with the possibility of same-day species diagnosis. Species identification was also achieved for two out of three jerky products, but required overnight lysis. The remainder of the samples could not be diagnosed—including canned salmon, pouch-sterilized salmon, and canned paté. Overall, this method showed high potential for use in same-day species authentication with lightly processed seafood, but heavily processed products will require alternate methods.

This study was performed to investigate the effect of ultrasonic nano crystal surface modification (UNSM) on residual stress mitigation after Weld Inlay repair for butt dissimilar metal weld with Alloy 82/182 in reactor vessel In/Outlet nozzle. As-welded and Weld Inlay specimens were made in accordance with design standard of ASME Code Case N-766, and two planes of their weld specimens were peened by the optimum UNSM process condition. Peening characteristics for weld specimens after UNSM treatment were evaluated by surface roughness and Vickers hardness test. And, residual stress for weld specimens developed from before and after UNSM treatment was measured and evaluated by instrumented indentation technique. Consequently, it was revealed that the mitigation of residual stress in weld metal after Weld Inlay repair of reactor vessel In/Outlet nozzle could be possible through UNSM treatment.

The onset of disintegration and corona in water drops falling at their terminal velocity in a vertical wind tunnel and exposed to horizontal electric fields has been investigated. Contrary to previous observations, the drops elongate in horizontal direction and distort into the shape of a concavo‐convex lens with a convex bottom and a sharp‐edged rim facing upward. Drops of diameter < 6.6 mm which do not break up in absence of electric field in this wind tunnel, break up in presence of the horizontal electric field. The values of horizontal electric field required for instability of the drops are much lower than those either predicted by Taylor's criterion of instability or observed in previous experimental studies. The criterion for instability of water drops freely suspended in presence of horizontal electric fields can be expressed as FH (ro/σ)½ = 0.98 ± 0.03 where FH is the horizontal electric field in esu, ro is the drop radius in centimeters and σ is the surface tension in dynes per centimeter. Most of the drops produce corona just before their breakup. Among various drops that are freely suspended in the wind tunnel, one by one, the number of drops that produce corona and/or breakup increases with increase in the electric field and/or drop size. While all drops of diameter ≥ 7.1 mm produce corona in a horizontal electric field of 500 kV/m, only a small fraction of very large drops of 8.0 mm diameter produce corona when the electric field is equal to 200 kV/m. Comparatively, very low values of instability field observed in our experiment are qualitatively explained because of long exposure of the freely suspended drops to the horizontal electric fields. The drops become unstable and produce corona when the drop's oscillation amplitude overshoots its equilibrium value and the plane of the drop oscillation coincides with the direction of electric field. From the results, it seems likely that horizontal electric fields in the bases of thunderclouds may cause disintegration of large raindrops and the occurrence of corona from their surfaces may trigger a lightning discharge.