The nickel-based superalloy UNS N07001 (also known as Waspaloy (R)), commonly used in gas turbine components, is conventionally manufactured through forging, but electron beam powder bed fusion (EB-PBF) is an emerging additive manufacturing method offering faster production. The effects of post-heat treatments on the microstructure and creep behavior of UNS N07001 built by EB-PBF were investigated in this study. Specimens were evaluated in three conditions: as-built, after hot isostatic pressing (HIP) alone, and combined with solution treatment and aging (STA) after HIP. In the microstructural analysis, all specimens consistently exhibited a columnar grain structure aligned with the building direction, and HIP treatment effectively eliminated the internal defects observed in the as-built specimen. STA after HIP treatment promoted the precipitation of fine secondary gamma' phase and discretely formed M23C6 carbides at the grain boundaries, thereby reducing the area fraction of the coarser primary gamma' phase. Stress-rupture tests were performed at 732 and 816 degrees C with the load axis aligned parallel to the building direction, showing that the HIP + STA specimens outperformed both the AMS5704L and the wrought material. This superior creep resistance is attributed to the synergistic effect of the macro-scale columnar grain structure, which minimizes grain boundaries perpendicular to the load, and the optimized intragranular microstructure, which provides high resistance against dislocation movement. Ultimately, EB-PBF with optimized post-heat treatment is a highly promising manufacturing route for UNS N07001 components.

The gamma' precipitate-strengthened nickel-based superalloy UNS N07001 is widely used in gas turbines because of its high-temperature strength and corrosion resistance. In this paper, optimal process parameters of electron beam melting were determined to shorten the lead time of UNS N07001. In addition, the effects of post-heat treatment on the microstructure and mechanical properties of UNS N07001 were evaluated. The optimal process parameters were determined by evaluating the appearance, surface roughness, relative density, and Brinell hardness of UNS N07001 blocks built with 32 different parameter combinations. The UNS N07001 sample produced using the optimal parameters was subjected to hot isotropic pressing (HIP) and solution treatment and aging (STA). Microstructural observation, precipitate analysis, and tensile tests of the resulting specimens were conducted. Microstructural observations and precipitate analysis revealed that the as-built specimen contained cracks and pores. These defects disappeared after HIP treatment. Additionally, STA after HIP treatment resulted in a high content of fine gamma'-phase precipitate. Tensile tests revealed that the mechanical properties of the specimen were barely changed by HIP treatment, whereas STA after HIP markedly improved the mechanical properties of the specimen to a level comparable to the requirements for the wrought material. The beneficial mechanical properties of the specimen treated by HIP and STA may be attributed to the high content of fine gamma' precipitates.

Evaluating the fatigue limit by measuring temperature changes via infrared thermography has attracted significant interest because of its potential for rapid assessments. However, the physical background and validity of this technique are not yet fully understood. In this study, notched specimens of a single crystal Ni‐base superalloy with different crystallographic orientations are subjected to cyclic loading to investigate crack initiation and temperature change. Local slip deformation is quantified using crystal plasticity finite element analyses. It is found from the experimental and analytical results that the distribution of the temperature change and the local slip deformation (a plastic shear strain on the most active slip system) are affected by the crystallographic orientation. However, the correlation between the plastic shear strain and the second harmonic amplitude, as well as the threshold values of these parameters for crack initiation, is independent of the crystallographic orientation.

The main objective of this study is to predict the temperature variation of a rubber ball under cyclic compression. The prediction scheme is composed of three parts: mechanical analysis, heat source identification and heat transfer analysis. In the mechanical analysis, a compressible hyper-viscoelastic model was employed to describe the mechanical behavior of rubber under cyclic compression, in which material constants were identified using experimental data. In the heat source identification, the heat sources caused by three effects, namely thermo-elastic, entropic and viscous dissipation effects were evaluated based on a theoretical consideration. In the heat transfer analysis, the above-mentioned heat sources were used as input to calculate the time variation of the temperature field. The temperature variation inside and on the surface of the ball under both adiabatic and non-adiabatic conditions were discussed. In addition to that, the temperature amplitude and phase difference be-tween temperature and displacement in the steady state were considered.

Debonding of solidified splats is a crucial issue for thermal sprayed coatings, which greatly influences the performance and lifetime of industrial components. The purpose of this study is to provide an in-depth understanding of the effects of impact parameters as well as residual stress on the debonding behaviors, and the related adhesion strength and driving forces of single splats. In this study, debonding behaviors of molten paraffin droplets which were impacted and solidified on stainless steel substrates, were observed considering the effects of substrate pre-set temperature, drop height (impact velocity), and droplet temperature. It was found that the debonding is prone to take place at lower substrate pre-set temperatures, lower drop heights, and lower droplet temperatures. A scraping method was then employed to measure the adhesion strength of splats formed under various conditions. The results showed good accordance with debonding behaviors in the drop impact test. The scraping tests also indicated that the residual tensile stress in splats reduces the scraping forces and prevents the complete removal of splats during the scraping processes. Peeling stress and shear stress along the splat-substrate interface, which are driving forces for debonding, were calculated using coupled thermomechanical finite element analyses. The calculated driving forces were larger for lower drop heights and lower droplet temperatures under which the debonding was more easily to occur. The results of numerical simulations coupled with scraping tests provide reasonable explanations for observed debonding behaviors of single splats. This study provides a comprehensive understanding of the effects of several droplet impact variables and residual stress on the debonding behaviors, and the related adhesion strength as well as driving forces of single splats.

Thermoelastic stress analysis is a non-contact measurement method that can evaluate the stress distribution on the surface of objects. However, it does not work well for rubbers because not only the thermoelastic effect but also the entropic effect and the viscous dissipation effect influence the temperature variation. This study focuses on determining the quantitative relationship between the temperature variation and these three effects of rubber dumbbell specimen subjected to cyclic tension. A thermo-mechanical model was utilized to simulate the temperature variation under different loading conditions, and the simulation result was compared to the experimental result obtained from the thermographic measurement.

This study measured the variation over time of the creep strain fields around a fatigue crack tip in a single crystal Ni-based superalloy in an open environment at temperatures up to 900 degrees C using digital image correlation (DIC). A high-temperature DIC measurement system was developed to overcome three difficulties: the degradation of random patterns, thermal radiation, and heat haze. Tension hold was applied to the specimens, and the time evolution of the creep strain fields around the crack tip was measured at different temperatures and under different loading conditions. The proposed DIC system measured the short-term creep strain fields with high reproducibility and reliability, and the strain and strain rate increased as the temperature and hold load increased. To confirm the utility of the measurement results, the stress distribution around the crack tip was calculated using the finite element method (FEM), and the calculation results were validated by comparing the calculated strain to the measurement results. The effect of creep deformation on the fatigue crack propagation (FCP) is discussed.

Rapid evaluation of fatigue limit using infrared camera is beneficial because it also makes possible to detect the location of fatigue damage in actual structures. However, the physical background and validity of this method have not been fully investigated. It is required to clarify the relationship between fatigue damage and temperature variation. In this study, observation of slip deformation and measurement of temperature by infrared camera are conducted to notched specimens of single crystal metallic material associated with cyclic loading. First, cyclic loadings, which are below and beyond the fatigue limit, are applied to the specimen in order to investigate the factors that generate dissipated energy at below and beyond the fatigue limit. Experimental results show that dissipated energy is generated by internal friction below the fatigue limit and by fatigue damage beyond the fatigue limit. Finally, a similar experiment is conducted to the specimens with different crystal orientation. The result shows that the slip location is affected by the crystal orientation due to the orientation-dependent stress distribution and the dissipated energy distribution.

Temperature dependency of fatigue crack growth behavior in 1 containing forged TiAl alloys is investigated. Two kinds of material with nearly-lamellar and triplex microstructures are employed in fatigue crack growth tests at room temperature, 400 degrees C and 760 degrees C. A series of AK increasing and decreasing tests exhibits that at room temperature the fatigue crack growth resistance of triplex microstructure is lower than that of nearly-lamellar microstructure, whereas the resistance of triplex becomes higher at 760 degrees C. This higher resistance of triplex microstructure at high temperature is mainly attributed to the higher volume fraction of ductile p phase. The values of fatigue crack growth threshold in two microstructures show almost comparable at three temperatures, and they reveal the same temperature dependency. The threshold is found to be the highest at 760 degrees C, while the lowest at 400 degrees C. This temperature-dependency of fatigue threshold should be related to the roughness-induced and oxidation-induced crack closure mechanisms.

Reconstruction or deconvolution has widely been known as a useful indirect method to determine impact force which is often difficult to be directly measured in reality. This paper deals with the deconvolution technique using wavelet approach for impact force reconstruction. Based on the ability of wavelet transform in representing arbitrary signal using different scaled and shifted versions of a certain wavelet, impact force reconstruction is formulated and deployed through its wavelet expansion coefficients with controlling scale and shift components. Controlling both scale and shift components can be regarded as a kind of regularization in order to mitigate the ill-posed nature which often undermines or destabilizes reconstructed result. In the author's previous publication, the theoretical analysis of wavelet deconvolution technique for impact force reconstruction was proposed and numerically verified with controlling only shift components at a particular scale after removing some small scales. Although this technique has been verified to be successful and effective, the elimination of some smaller scales (i.e., ignoring all shift components at these scales) can also cause loss of high frequency information. Therefore, in the current work, controlling shifts is further operated not only at a particular scale but at all scales with the aim of limiting the loss of important high frequency information. This task can be considered as a further development of the previous work so as to improve the accuracy of reconstructed result, especially the peak force which often contains important high frequency information. This paper also experimentally verifies the applicability of the proposed technique by reconstructing various actual forces acting on a polycarbonate plate produced by different impactors. Results first show that the impact force reconstruction is affected by the ill-posedness if the scales or shifts of wavelets are not controlled. After applying the control of shift components at all scales, results revealed that the proposed technique is actually more efficient in improving reconstruction in comparison with the technique presented in the previous paper. (C) 2020 Elsevier Ltd. All rights reserved.

Rubber materials subjected to cyclic deformation exhibit temperature variation due to the three effects of energetic elasticity, entropic elasticity, and viscous dissipation. There are many studies considering the temperature rise (heat build-up) due to the viscous dissipation effect. On the other hand, few studies consider the temperature variation due to the three effects simultaneously. In this study, the temperature variation of a rubber ball subjected to cyclic compression has been predicted by numerical analysis with considering the three effects simultaneously. The heat generation associated with each of the three effects is evaluated on the basis of the stress-strain analysis. Then the heat transfer analysis is conducted to obtain the temperature variation. The contribution of each of the three effects and the influences of heat conduction within the ball and heat convection to the surrounding air on the temperature variation are discussed.

The objective of this study was to detect water absorption of CFRP bonded joints, which is one of the causes of week bond. For this purpose, non-destructive evaluation method using the ultrasonic pulse technique was suggested. The amplitudes of the reflected waves when ultrasonic waves are incident on the adhesive joint are modeled, and it is shown that the intensity ratio of the surface reflected wave to the reflected wave from the adhesive layer is a function of the non-dimensional thickness, acoustic impedance, and attenuation ratio of the adhesive layer, and a method to identify these values is proposed. As a result of the experiment, it was shown that the amount of water absorption could be evaluated from the non-dimensional thickness of the adhesive layer, regardless of the base material CFRP laminated structure. On the other hand, from this experiment, clear relationship was not observed between the acoustic impedance and attenuation of the adhesive layer and the water absorption.

This present study has been re-established to investigate failure mode and resistance characteristics of the PC/ABS blends and their ABS constituents under impact for a range of rubber contents. This present study has still been experimentally performed under an instrumented-drop weight impact test (DWIT) at a room temperature. It has been finally revealed that with a particular size of rubber particle, content of rubber significantly influenced impact failure modes and impact resistances of the PC/ABS blends and their ABS constituents as well. The test results showed that impact strength of the blends was improved about 23.22% and 155.33% due to increase in content of rubber up to 15 wt% and 20 wt%, respectively. There was also found that an increase in impact toughness of the blends for 57.48% and 239.23% was due to increase in content of rubber up to 15 wt% and 20 wt%, respectively. Whilst, impact strength of the ABS was improved about 392.98% and 190.12% due to increase in content of rubber up to 15 wt% and 20 wt%, respectively. An increase in impact toughness of the ABS for 308.20% and 172.56% was due to increase in content of rubber up to 15 wt% and 20 wt%, respectively.

Rubber materials under cyclic mechanical loading show special properties compared to other materials. This research aims to quantitatively clarify the relationship between cyclic deformation and temperature variation of carbon black filled styrene-butadiene rubber (SBR) under steady state condition after the rubber is accommodated enough both mechanically and thermally. A dumbbell specimen was subjected to uniaxial cyclic tension at various loading conditions. Temperature variation on the gauge zone surface of the specimen was measured by infrared thermography. In addition to the experiment, the temperature variation of the specimen was also predicted theoretically. The prediction is composed of three parts. The first part shows a three-elements model to reproduce the mechanical behavior with considering residual strain and stress softening. The material parameters are determined to match the experimental data at each loading condition. The second part predicts the temperature variation under adiabatic condition by considering three factors: isentropic elastic, entropic elastic and viscous dissipation effects. Third, a correction scheme is proposed to consider the heat transfer between the specimen and the surrounding air or others. As a result, the temperature amplitude and phase difference between temperature and strain are predicted. The predicted results were compared with the experimental data. It is confirmed that the predicted results are in good agreement with ones obtained by the infrared thermography. Furthermore, the phase difference between temperature and strain is about 180 degrees at the small deformation area (isentropic elastic effect dominated) while it is almost about 0 degrees at large deformation area (entropic elastic effect dominated). In addition to this, there exists a phase transition area between these two areas. It is concluded that the proposed method is a good way to provide quantitative information of the temperature variation of rubber materials subjected to uniaxial cyclic loading under steady state.

Residual stress is inevitably generated during thermal spraying and plays a significant role in the fracture mechanisms of thermal barrier coatings. In this study, a drop experiment was conducted using a molten paraffin to simulate and simplify the actual thermal spraying process. The variation of stress and strain during the solidification and the adhesion of the paraffin droplet impacted on a stainless-steel substrate were investigated. The temperature-dependent creep properties and several thermophysical properties of paraffin materials were experimentally measured. An appropriate creep model for paraffin materials was established based on stress-relaxation tests and elastic-creep analysis. This creep model was then used to perform coupled thermo-mechanical analyses to calculate the temperature and strain variation during the solidification and cooling processes of a paraffin droplet, revealing that creep deformation is a critical factor affecting the stress–strain variation. Using the calculation results, the effect of interfacial adhesion on quenching strains was also investigated. Poor adhesion at the splat/substrate interface was shown to induce a high degree of stress–strain relaxation.

Temperature-dependent fatigue crack propagation in a Ni-based single crystal superalloy was experimentally and numerically investigated in a single crystal Ni-based superalloy. Fatigue crack propagation tests at room temperature 300, 450, and 700 °C were conducted using four types of compact specimens with different combinations of crystal orientations in loading and crack propagation directions. It was revealed in the experiments that the crack propagated along slip planes in crystallographic cracking manner at room temperature, while the cracking mode transitioned from the Mode I to crystallographic cracking at 300, 450, and 700°C. Mode I stress intensity factor range ΔKI values at the transitions depended on the testing temperature as well as crystal orientation. To interpret these temperature-dependent crack propagation, a crystal plasticity finite element analysis was conducted by taking into account the 3D inclined crack plane and the activity of slip planes in front of the crack. Slip plane activity, proposed as a damage parameter, could rationalize the fatigue crack propagation rates both during the crystallographic and Mode I cracking. It has been found that crack propagation resistance for crystallographic cracking is more or less the same at low temperature, while that for Mode I cracking decreases with the increase of the temperature. This damage parameter also provided an explanation of the critical condition that induces the transition from Mode I to crystallographic cracking.

This study presents an experimental study on failure modes and resistances of polycarbonate (PC)/Acrylonitrile Butadiene Styrene (ABS) blends and their ABS constituents under a drop weight impact test (DWIT). Failure modes and impact resistances such as impact strength and impact toughness of such blends are generally influenced by molecular weight of the PC, rubber content and size of rubber particle in ABS system. A preliminary study on ABS materials using a DWIT showed that size of rubber particle not only determined their failure modes but also influencing their resistance characteristics. However, in a previous study performed using the similar DWIT on PC/ABS blends with a 10 wt% rubber content, it was revealed that size of rubber particle did not significantly influence their resistances. Their failure modes were even macroscopically very difficult to be distinguished. This study, hence, is aimed to further explore role of the size of rubber particle on failure mode and impact resistance characteristics of the PC/ABS blends and their ABS constituents with a higher rubber content. The impact test results have revealed that with a 20 wt% rubber content, size of rubber particle only influenced the resistances of the PC/ABS blends. It did not significantly contribute to affect failure mode of the PC/ABS blends. Whilst, it significantly influenced failure modes and resistances of the ABS. The DWIT results also re-confirmed that blending a brittle ABS into PC led to produce a tougher PC/ABS blend.

Degradation detection of the electric wire connection (compression straight sleeves, compression type anchor clamps, etc.) of the electric power transmission line is usually conducted by directly measuring the resistance of the connection and judging by comparison with the wire resistance ratio.For the measurement, electric power supply to the transmission line is stopped; the worker climbs the power transmission tower and measures the resistance value.It is a time-consuming and dangerous work because of high place and accidental high voltage.If the degradation is accurately detected from the ground by using infrared thermography, it can contribute to work safety/efficiency, cost reduction, and stable electric power supply without planned power outage.In this study, we examined conditions, application range, accuracy and judgment method for detecting the degradation of wire connection quantitatively by using infrared thermography.We report the results of heat radiation test of the power line and investigation of the relationship between the measured data and the degradation.

Stage I fatigue crack propagation along crystallographic slip planes was experimentally and analytically investigated in a single crystal Ni-base superalloy, NKH-304. Fatigue crack propagation tests at room temperature were conducted using four types compact specimens with different combinations of primary and secondary orientations. It was revealed in the experiment that the fatigue crack propagated along crystallographic slip planes in a mixed mode with Mode I, II and III components. The mixture ratio and fatigue crack propagation rate were strongly influenced by the primary and secondary crystal orientations. To interpret the effect of crystal orientations on the Stage I cracking behavior, a crystal plasticity finite element analysis was conducted considering the actual geometry of the crystallographic crack planes. The slip activities of the individual octahedral slip systems were evaluated, and then a damage parameter was proposed based on the critical plane approach. As a result, a reasonable explanation was obtained for the effect of crystal orientations on the cracking path and propagation rate of the crystallographic Stage I cracking.