New Inverse Method for Determining Uniaxial Flow Properties by Spherical Indentation Test

The spherical indentation test has been successfully applied to inversely derive the tensile properties of small regions in a non-destructive way. Current inverse methods mainly rely on extensive iterative calculations, which yield a considerable computational costs. In this paper, a database method is proposed to determine tensile flow properties from a single indentation force-depth curves to avoid iterative simulations. Firstly, a database that contain numerous indentation force-depth curves is established by inputting varied Ludwic material parameters into the indentation finite elements model. Secondly, for a given experimental indentation curve, a mean square error (MSE) is designated to evaluate the deviation between the experimental curve and each curve in the database. Finally, the true stresses at a series of plastic strain can be acquired by analyzing these deviations. To validate this new method, three different steels, i.e. A508, 2.25Cr1Mo and 316L are selected. Both simulated indentation curves and experimental indentation curves are used as inputs of the database to inversely acquire the flow properties. The result indicates that the proposed approach provides impressive accuracy when simulated indentation curves are used, but is less accurate when experimental curves are used. This new method can derive tensile properties in a much higher efficiency compared with traditional inverse method and are therefore more adaptive to engineering application.

Assessing sprinkler systems performance with a novel experimental benchmark

Sprinkler systems are one of the most popular methods of irrigation worldwide. One of their key parameters is the so-called level of uniformity, i.e. every portion of the soil should be irrigated with the same amount of water. Assessing the level of uniformity is crucial for optimal design of sprinkler systems. In this manuscript, a novel experimental benchmark is presented in order to test irrigation sprinklers, assess their performance, and define their acceptable working conditions. Different sprinklers have been tested, their water application depth curves have been determined, and their performance has been evaluated using a combination of metrics. Results show that the majority of sprinklers are characterized by very good performance in terms of operating pressures in the range 2.0-3.0 bar and tend to decrease their efficiency for operating pressures outside of that range.

Initial response mechanism and local contact stiffness analysis of the floating two-stage buffer collision-prevention system under ship colliding

A floating two-stage buffer collision-prevention system (FTBCPS) has been proposed to reduce the impact loads on the bridge pier in this paper. The anti-collision process can be mainly divided into two stages. First, reduce the ship velocity and change the ship initial moving direction with the stretching and fracture of the polyester ropes. Second, consume the ship kinetic energy with the huge damage and deformation of the FTBCPS and the ship. The main feature of the FTBCPS lies in the first stage and most of the ship kinetic energy can be dissipated before the ship directly impacts on the bridge pier. The contact stiffness value between the ship and the FTBCPS can be a significant factor in the first stage and the calculation method of it is the focus of this paper. The contact force, the internal force and the general equation of motion have been given in the first part. The structure model of the ship and the FTBCPS are then established in the ANSYS Workbench. After that, 38 typical load cases of the ship impacting on the FTBCPS are conducted in LS-DYNA. The reduction processes of the ship kinetic energy and the ship velocity in different load cases have been investigated. It can be summarized that the impact angle and the ship initial velocity are the main factors in the energy and velocity dissipation process. Moreover, the local impact force-depth curves have also been studied and the impact angle is found to be the only significant factor on the ship impact process. Next, the impact force-depth curves with different impact angles are fitted and the contact stiffness values are accordingly calculated. Finally, the impact depth range, the validity of the local simulation results and the consistency of the fitted stiffness value are verified respectively, demonstrating that the fitted stiffness values are applicable in the global analysis.

A New Inverse Method for Determining Uniaxial Flow Properties by Spherical Indentation Test

This study presents a new inverse method to determine tensile flow properties from a single indentation force-depth curves. A database is established to replace the iterative FE calculations in conventional inverse methods and therefore can process the indentation data more quickly and easily. An axisymmetric FE model is constructed to simulate the elastic-plastic response of indention. Assuming the materials follow Ludwic constitutive model, by systematically changing the material parameters, numerous indentation force-depth curves are extracted from simulation results to establish the database. For a given experimental indentation curves, a mean square error (MSE) is designated to evaluate the deviations between the experimental curve and each curve in the database. Then, the relation of deviations versus stresses are investigated to acquire the true stresses at a series of plastic strain. To validate the new method, three different steels, i.e. A508, 316L and 2.25Cr1Mo are selected. Both simulated indentation curves and experimental indentation curves are used as inputs of the database to inversely acquire the flow properties. The result indicates that the proposed approach provides impressive accuracy when simulated indentation curves is used, but is less accurate when an experimental curve is used. This new method can quickly derive tensile properties without iterative calculations that yield a considerable computational costs and are therefore adaptive to engineering application.

Influence of Plasticity and Friction on the Contact Mechanics of Auxetic Materials

Contact interactions play an important role in the tribological behavior of engineering materials. This paper develops a finite element model to investigate the contact mechanics and stress distribution of auxetic materials, i.e., materials with negative Poisson’s ratio. The model results are compared with numerical and mathematical models for isotropic auxetic polymers. The indentation of auxetic materials is analyzed for the effects of friction, plasticity and allowing separation after contact with a spherical indenter using a commercial software, abaqus. The results are discussed in terms of stress profiles, force-indentation depth curves, plasticity, friction, internal energy, compressibility, sink-in, and the pile-up of material. It is concluded that for purely elastic contact, the indentation resistance increases for auxetic materials and the inclusion of friction shifts subsurface stresses closer to the surface. However, the introduction of plasticity negates the improvement of increased indentation resistance. The pile-up of material around the indent reduces for auxetic materials which makes them more suitable for rolling/sliding contacts. The internal strain energy decreases for purely elastic contact and increases for an elastic/plastic contact.

A Simple Method for Measuring Plastic Properties of Power Hardening Metals via the Indentation Curve with a Large Depth

The spherical indentation technique provides an easy way to evaluate the integrity of in-service structures because it is nondestructive. In this study, a simple method was proposed to measure mechanical properties such as the yield strength, the ultimate tensile strength, and the strain hardening exponent from the indentation curve at a large indentation depth, which is 0.4 times of the indenter radius. Based on finite element analyses, a simple function was proposed to relate representative stress to indentation data. Besides, representative strains at different indentation depths were identified according to the load-depth curves from simulations. The calculated plastic properties from the developed method were compared well with experimental results.

Mechanical Properties of Duplex Treated Steels Obtained by Instrumented Indentation

Nowadays there is a growing need to reduce or control wear, corrosion and fatigue in order to extend the lifetime of mechanical parts, to make engines and devices more efficient, to develop new advanced products, to conserve material resources, to save energy and to improve the safety. The surface properties of mechanical parts may be improved through Duplex treatments. A Duplex treatment is a sequence of two treatments, combining their advantages and leading to better surface properties. A Duplex treatment consisting in nitriding and work hardening through shot peening has been chosen as a solution for improving the properties of EN 34CrNiMo6 alloyed steel. This paper reports the results obtained for hardness and bulk modulus on treated and untreated samples. The samples were examined using a Dynamic Ultra Micro Hardness (DUH) tester under a set of maximum loads ranging from 100 to 1000 mN. Each sample was subjected to load-unload cycle under the same amount of maximum load and the loads vs. penetration depth curves were plotted. Results showed a better mechanical behavior of Duplex treated.

A new approach to determine the discharge passing over ogee spillway

The main purpose of this study is investigation of flow over an ogee spillway experimentally and comparison with the analytical results. An experimental study was conducted to obtain discharges and heads over an ogee spillway. 30 different discharge and flow depths of flow in physical model were measured. Nondimensional discharge and flow depth curves are used to compare the results. Experimental results indicate that some regulations can be done in analytical formulas. In this way the analytical results can be get more accurately.

Validation of the shoal-biased pattern of bathymetric information on nautical charts

<p><strong>Abstract.</strong> The compilation of nautical charts comprises a number of tasks that are often monotonous, time consuming, and, as such, prone to human error. A long-term goal of the hydrographic community has thus been the automation of the process due to the unquestionable advantages of automation to the accuracy, reliability, and consistency of products for a reduced cost-to-productivity ratio. One of the tasks that has received the attention of automation efforts is the compilation of bathymetry on charts and more precisely the generation and generalization of depth curves and the selection and validation of charted soundings. There is, however, much room for improvement with current methods.</p><p>Charted soundings and depth curves complement each other in maintaining and emphasizing the morphological details and characteristic features of the seafloor on charts. They are derived from a more detailed dataset, either survey data or a larger scale chart, with generalization. Once the cartographer delineates the depth curves, he/she makes the selection of soundings to be charted following established cartographic practice rules (see, e.g., IHO 2017; NOAA 2018). Both tasks may be performed either fully manually, or partially manually through a computer-assisted method.</p><p>The goal is for the cartographer to retain the morphology and the characteristic features of the seabed and at the same time to honor the overarching principle that the expected depth (based on the charted bathymetric information) must not appear, at any location, deeper than the source information. According to S-4 (IHO, 2017), for well surveyed areas the “shoal-biased” pattern of charted soundings is achieved through the “triangular method of selection”, where:<ol type="a"><li>No actual sounding exists within a triangle of selected soundings which is less than the least of any of the soundings defining the edges of the triangle (hereinafter: triangle test); and</li><li>No source sounding exists between two adjacent selected soundings forming an edge of the triangle which is less than the lesser of the two selected soundings (hereinafter: edge test).</li></ol><p>Motivated by the need for automated tools that perform consistently and satisfactorily in every geographic situation, and in the context of a developing project for a fully automated solution in nautical chart production, this paper presents our research work on the development of a comprehensive solution for the validation of the shoal-biased pattern of charted bathymetric information. This includes an algorithmic implementation of the triangle test that eliminates the false positives of previous implementation efforts near and within linear features (see Figure 1), as well as the first automated implementation of the edge test in the literature. For the above implementations we incorporate the available bathymetric information on the chart, e.g., coastlines (natural and man-made), depth curves, soundings, obstructions, and wrecks (see Kastrisios and Calder 2018; Kastrisios et al. 2019).</p><p>The presented work also illustrates the importance of the edge test in the validation of the charted bathymetric information as it can identify shoals that the triangle test may not identify (see Figure 2), thereby proving that the edge test must not be disregarded by cartographers in the validation process.</p><p>However, the two tests share the intrinsic limitation of missing discrepancies between the charted and source bathymetric information, even if they are significant (see Figure 3). Thus, a fully automated solution based on a verbatim interpretation of the two tests as written in S-4 does not seem feasible. Therefore, we propose a surface-based validation test that will account - at the appropriate charting resolution - for the configuration of the seabed that would be mentally reconstructed by the mariner from the charted bathymetric information. This is expected to lead to a more realistic representation of the submarine relief and its navigationally significant features on charts from the available source information (see Kastrisios et al. 2019).</p>