Temperature Dependence of Fracture Characteristics of Variously Heat-Treated Grades of Ultra-High-Strength Steel: Experimental and Modelling

The temperature dependence of tensile characteristics and fracture toughness of the standardly heat-treated low-alloyed steel OCHN3MFA along with three additionally heat-treated grades was experimentally studied. In the temperature range of ⟨−196; 22⟩ °C, all the additional heat treatments transferred the standard steel from a high- to ultra-high strength levels even with improved tensile ductility characteristics. This could be explained by a reduction of the inclusion content, refinement of the martensitic blocks, ductile retained austenite content, and homogenization of the shape ratio of martensitic laths as revealed by metallographic, X-ray, and EBSD techniques. On the other hand, the values of the fracture toughness of all grades were found to be comparable in the whole temperature range as the cause of a high stress triaxiality in the pre-cracked Charpy V-notch samples. The values of the fracture toughness of the standard steel grade could be predicted well using the fracture model proposed by Pokluda et al. based on the tensile characteristics. Such a prediction failed in the case of additionally heat-treated grades due to the different temperature dependence of the fracture mechanisms occurring in the tensile and fracture-toughness tests. While the tensile samples fractured in a ductile-dimple mode at all temperatures, the fracture-toughness specimens exhibited a transition from the ductile to quasi-brittle fracture mode with decreasing temperature. This transition could be interpreted in terms of a transfer from the model proposed by Rice and Johnson to the model of Tvergaard and Hutchinson.

Improving the Gridshells’ Regularity by Using Evolutionary Techniques

Designing and optimizing gridshell structures have been very attractive problems in the last decades. In this work, two indexes are introduced as “length ratio” and “shape ratio” to measure the regularity of a gridshell and are compared to the existing indexes in the literature. Two evolutionary techniques, genetic algorithm (GA) and particle swarm optimization (PSO) method, are utilized to improve the gridshells’ regularity by using the indexes. An approach is presented to generate the initial gridshells for a given surface in MATLAB. The two methods are implemented in MATLAB and compared on three benchmarks with different Gaussian curvatures. For each grid, both triangular and quadrangular meshes are generated. Experimental results show that the regularity of some gridshell is improved more than 50%, the regularity of quadrangular gridshells can be improved more than the regularity of triangular gridshells on the same surfaces, and there may be some relationship between Gaussian curvature of a surface and the improvement percentage of generated gridshells on it. Moreover, it is seen that PSO technique outperforms GA technique slightly in almost all the considered test problems. Finally, the Dolan–Moré performance profile is produced to compare the two methods according to running times.

Numerical Investigation on Hydrodynamic Characteristics of Immersed Buoyant Platform

The Next Generation Subsea Production System (NextGen SPS) is considered as a competitive alternative system used for offshore petroleum production in ultra-deep sea based on the artificial seabed technology. The Immersed Buoyant Platform (IBP), which is located at a constant depth below the free surface of the water to minimize wave loading, provides a buoyant stable platform for supporting the well completion equipment. Therefore, the hydrodynamic characteristics of IBP in the currents play an essential role in determining the global responses of NextGen SPS. In this paper, aiming at acquiring an optimum structural form of IBP, the hydrodynamic characteristics of the flow past the cylindrical IBP with different height-to-diameter ratios are systematically investigated by use of the large eddy simulation (LES) approach. The simulations with fifteen different height-to-diameter ratios (H/D) are investigated. The Reynolds numbers are ranged from 0.94×106 to 3.45×106. It can be verified that the separated fluid reattaches on the surface of the cylinder when the aspect ratio is between 0.1 and 0.4. Due to the specific shape ratio and obvious 3D effect of the cylindrical IBP, no significant vortex shedding has been clearly observed when the aspect ratio is between 0.1 and 0.4. In the case of 0.4≤H/D≤5.0, a series of regular and alternating vortex street shedding appear behind the circular cylinder. The simulation results also show that the recirculation region length behind the cylindrical IBP can be significantly reduced with the decreasing aspect ratio. It can be concluded that the cylindrical IBP performs the best hydrodynamic characteristics when the aspect ratio is between 0.3 and 0.4. The research findings will be of great significance to providing valuable reference and foundation to determine the optimum form of underwater structures, such as the buoyancy cans of the hybrid riser system.

Are Early or Late Maturers Likely to Be Fitter in the General Population?

The present study aims to identify the optimal body-size/shape and maturity characteristics associated with superior fitness test performances having controlled for body-size, sex, and chronological-age differences. The sample consisted of 597 Tunisian children (396 boys and 201 girls) aged 8 to 15 years. Three sprint speeds recorded at 10, 20 and 30 m; two vertical and two horizontal jump tests; a change-of-direction and a handgrip-strength tests, were assessed during physical-education classes. Allometric modelling was used to identify the benefit of being an early or late maturer. Findings showed that being tall and light is the ideal shape to be successful at most physical fitness tests, but the height-to-weight “shape” ratio seems to be test-dependent. Having controlled for body-size/shape, sex, and chronological age, the model identified maturity-offset as an additional predictor. Boys who go earlier/younger through peak-height-velocity (PHV) outperform those who go at a later/older age. However, most of the girls’ physical-fitness tests peaked at the age at PHV and decline thereafter. Girls whose age at PHV was near the middle of the age range would appear to have an advantage compared to early or late maturers. These findings have important implications for talent scouts and coaches wishing to recruit children into their sports/athletic clubs.

Research on an Improved Neural Network Model for Film Text Image Segmentation in Film Internet of Things

In order to solve the problem that Film text is difficult to recognize and difficult to handle in Film Internet of Things, a method that can effectively identify the content in Film text is sought. This paper uses the Mask RCNN algorithm with ResNet101 as the backbone network to establish a Film document image segmentation model.The optimal hyperparameters are: the shape ratio of the anchor frame is [0.5, 1, 3], the threshold for non-maximum suppression is 0.15, and the confidence level is 0.85. The F1 score obtained at this time is 0.8951. When these hyperparameters are substituted into the IOU of 0.8, the F1 score is 0.7417. According to the results of the Pattern Recognition Laboratory of the Chinese Academy of Sciences, this algorithm model ranked first with an IOU of 0.6. Under the premise that IOU is 0.8, it is ranked second, and the first is a non-end-to-end model with a single task. It can be seen that the adjustment of the hyperparameters and the training of the algorithm model are relatively successful.The experimental results show that the MASK RCNN can accurately identify all the formulas in the Film Text. MASK RCNN is significantly better at identifying small objects such as formulas in Film Text images than traditional fast cnn and faster cnn.

Use of mode shape ratios for pier scour monitoring in two-span integral bridges under changing environmental conditions

In this paper, a novel pier scour indicator is introduced, which uses the ratio between mode shape amplitudes identified at two points on an integral bridge structure to monitor the progression of scour erosion. The mode shape ratio (MSR) is investigated as an additional parameter to complement the use of changes in natural frequency as a scour indicator. The approach is demonstrated using numerical modelling and the MSR is extracted from acceleration signals arising in the structure due to modelled ambient and vehicle-induced vibrations. The MSR shows higher sensitivity to scour erosion than the more commonly researched natural frequency. Furthermore, the variation in MSR under temperature fluctuations is inversely related to that of frequency, in that it increases with increasing temperature whereas frequency decreases with increasing temperature. This inverse relationship potentially enables the separation of the scour effect from the temperature influence on the dynamics of the system.

Bulb Size Interacts with Lifting Term in Determining the Quality of Narcissus Poeticus L. Propagation Material

Geophytes are an increasingly widely used group of plants. Its high biodiversity, however, significantly impacts the cultivation process. Therefore, every new insight into the behavioral aspects of each single species is crucial for production. This study, for the first time, aims at contributing to a better understanding of the interplay between the bulb size potential of Narcissus poeticus and the pattern of bulb lifting time to find the optimal combination of these factors in obtaining the best quality propagation material. Twelve bulb size groups were examined. Plants were planted in the open air in two locations of Central East Europe and lifted in three terms: immediately and two and four weeks after flowering. Bulb fresh and dry weight, as well as leaf, root and total plant dry weight, increased with growing bulb size and delayed the time of lifting. The bulb weight increase indicator was twice as high for bulbs lifted in the third date compared to those lifted earlier. Its value was the highest for the smallest bulbs. Bulb shape ratio gradually decreased together with the increase of bulb weight and later lifting term. Principal components analysis allowed singling out two principal components that accounted for 86.58% of total variability.

Quantification of role of impedance contrast in site-city-interaction effects on the responses of buildings and basin

This paper presents the role of impedance contrast (IC) at the base of 2D deep elliptical basin (shape-ratio > 0.25) in the site-city-interaction (SCI) effects on both the SH- and SV-wave responses of buildings and basin. The obtained SCI effects in the form of reduction of fundamental frequencies of building (F02DSB) and basin (F02DB), corresponding amplification and splitting of the bandwidth of fundamental mode of vibrations of both the building and basin corroborates with the findings in the past SCI studies. The F02DB of basin and F02DSB of building are unaffected by an increase of IC during site-city-interaction, even though, there is an increase of F02DB of basin with an increase of IC in the absence of city. A drastic increase of SCI effects on the basin response but only minor increase of SCI effects on the building response with an increase of IC is observed for both the polarizations of the S-wave. However, the rate of increase of SCI effects with IC is more in the case of SV-wave responses of buildings and basin. The obtained larger % reduction of F02DB and corresponding amplification in the case of SH-wave responses as compared to those in the case of SV-wave responses may be due to the larger height of B16-buildings compared to B12-buildings used in the SV-wave simulations or due to the buildings behaving as a shear beam for the SH-wave or may be due to both.

Full paleostress tensor determination: case of the Panasqueira Mine, Portugal.

<p>The quantification of tectonic forces or, alternatively, stresses represents a significant step towards the understanding of the natural processes governing plate tectonics and deformation at all scales. However, paleostress reconstructions based on the observation and measurement of natural fractures are traditionally limited to the determination of four out of the six parameters of the stress tensor. In the present study, we attempt to reconstruct full paleostress tensors by extending the methodologies advanced by previous authors. We selected Panasqueira Mine, Central Portugal, as natural laboratory, and focused on the measurement of sub-horizontal quartz veins, which are favorably exposed in three dimensions in the underground galleries of the mine. Inversion of the vein data allowed for quantifying the respective orientations of the stress axes and the shape ratio of the stress ellipsoid. In order to reconstruct an additional stress parameter, namely pressure, we extensively sampled vein material and combined fluid inclusion analyses on quartz samples with geothermometric analyses on sulphide minerals. Finally, we adjusted the radius of the obtained Mohr circle with the help of rupture laws, and obtained the six parameters of the paleostress tensor that prevailed during vein formation. Our results suggests a NW-SE reverse stress regime with a shape ratio equal to ~0.6, lithostatic pore pressures of ~300 MPa and differential stress lower than ~20 MPa.</p>