A Numerical Study on 3D Printed Cementitious Composites Mixes Subjected to Axial Compression

Aptly enabled by recent developments in additive manufacturing technology, the concept of functionally grading some cementitious composites to improve structural compression forms is warranted. In this work, existing concrete models available in Abaqus Finite Element (FE) packages are utilized to simulate the performance of some cementitious composites numerically and apply them to functional grading using the multi-layer approach. If yielding good agreement with the experimental results, two-layer and three-layer models case combinations are developed to study the role of layer position and volume. The optimal and sub-optimal performance of the multi-layer concrete configurations based on compressive strength and sustained strains are assessed. The results of the models suggest that layer volume and position influence the performance of multi-layer concrete. It is observed that when there exists a substantial difference in material strengths between the concrete mixes that make up the various layers of a functionally graded structure, the influence of position and of material volume are significant in a two-layer configuration. In contrast, in a three-layer configuration, layer position is of minimal effect, and volume has a significant effect only if two of the three layers are made from the same material. Thus, a multilayered design approach to compression structures can significantly improve strength and strain performance. Finally, application scenarios on some structural compression forms are shown, and their future trajectory is discussed.

Research on the Influence of the Key Stratum Position on the Support Working Resistance during Large Mining Height Top-Coal Caving Mining

In recent years, in order to increase the coal recovery rate, the large mining height fully mechanized top-coal caving mining has been widely used because it has the advantages of both fully mechanized mining method and large mining height mining method. When this mining technology is used to exploit thick coal seam under upper goaf, the movement characteristics of the overlying strata and the bearing structure formed by the broken rock are complicated, which results in the abnormal pressure during mining, such as severe coal slabs and hydraulic supports being crushed. The key to solve these problems is to study the movement law and the structural evolution characteristics of the overlying strata during large mining height fully mechanized top-coal caving mining, and the movement characteristics of the overlying strata are all determined by the layer-position of the key stratum. UDEC models with different layer-position of the key stratum are established to investigate the influence of the key stratum position on the support working resistance during large mining height top-coal caving mining. Through comprehensive research, the source of support resistance comes from under different geological conditions was analyzed, and the formula for estimating the maximum support working resistance was deduced. In addition, in order to release the severe pressure during large mining height fully mechanized top-coal caving mining, it is recommended to use hydraulic fracturing method to weaken the key stratum in situ.

Finite Element Modeling for the Antivibration Pavement Used to Improve the Slope Stability of the Open-Pit Mine

Vibrations induced by traffic are of concern for the slope stability of the open-pit mine. Different solutions to mitigate this phenomenon are under investigation. In the field of pavement engineering, the so-called antivibration paving technologies are under investigation in order to avoid the generation of excessive vibration and contains propagation. To more fully examine the effectiveness and potential of the antivibration pavement in the application of vibration absorbing for the open-pit mines, numerical simulations based on a two-dimensional (2D) finite element (FE) model were conducted. Sensitivity analysis of varying monitored points and varying loads are performed. Several important parameters such as the damping layer position and thickness and damping ratio are evaluated as well. By using this FE simulation to model the vibration response induced by traffic, the costly construction mistakes and field experimentation can be avoided.

Dynamic behavior of resilient wheels at a rail weld joint

The aim of this paper is to investigate the dynamic response of the resilient wheel equipped on the intercity train at the rail weld. A vehicle-track coupling dynamics model with resilient wheels is developed. A rigid multi-body system with 55 degrees of freedom is utilized to model the vehicle system. The rubber layer of the resilient wheel is modeled as a three-directional spring-damper unit between the wheel rim and the wheel core. For the track sub-model, the rails were modelled as Euler Beam and supported by concrete sleepers modelled as mass block. The vehicle and track motion equations are represented as mass-stiffness-damping matrixes. The accuracy of this modeling method at low frequencies is verified via the comparison between the field measured data and numerical results. The dynamic results of the rigid wheel are compared with those of the resilient wheel. Results show that the dynamic wheel-rail force of the rigid wheel is slightly higher than that of the resilient wheel. Furthermore, the mass factor is introduced to investigate the effect of the rubber layer position on the tire acceleration and the wheel-rail impact force. The numerical simulation results are expected to provide references for resilient wheel application into the intercity train.

A Multifunctional Mineral Binder for Plywood Production: The Effect of Manufacturing Parameters on Bonding Quality

Geopolymers show great potential for use as binders in developing and manufacturing multifunctional wood products. The objective of this study was to improve the bonding quality of a geopolymer binder, with wood veneers, using different manufacturing parameters. To this end, we produced five layered plywood panels treated with various lay-up times (1, 5, 10, 15 min), panel compressibility values during hot pressing (5%, 10%, 15%, and 30% compression), veneer roughness values (low, medium, and high roughness), press temperatures (120, 140, and 160 °C), and veneer layouts via changing the middle layer position of plywood relative to the surface layers. The results show that the shear strength and thickness swelling were negatively influenced by increasing the lay-up time of resinated veneers and panel compressibility. Increasing the veneer roughness significantly increased the panels’ properties. Furthermore, the panels produced with a pressing temperature of 140 °C showed the best performances. The veneer layouts also significantly changed the physical and mechanical properties of the plywood panels. Generally speaking, the results obtained in this study show that improving the bonding quality of geopolymer binders with wood can be done through the manipulation of plywood manufacturing parameters.

Adaptive Structure Design of Raingarden in Shanghai Coastal Saline Alkali Area for Improving Urban Resilience

<p>Shanghai is one of the demonstration sites of Sponge City which is a typical coastal saline-alkali area. To improve the urban resilience and mitigate storm water, green infrastructure as raingarden, bioswale and green roof, etc. are used to regulate runoff. However, the design of raingarden have the disadvantage of solutions for high groundwater levels and soil salinization in Shanghai. In order to improve the regional adaptability and optimize the design of the raingarden, the indoor rainfall simulation experiments and orthogonal experiments were used to analyze the effect of salt isolation and rain infiltration impacted by different structures (salt-insulated layer material, salt-insulated layer position, filler layer thickness). The results show that the order of influence on salt isolation is: salt-insulated material>filler layer thickness>salt-insulated layer position. The order of impact on rain infiltration is: salt-insulated material>salt-insulated layer location>filler layer thickness. Three types of rain garden structures are proposed. The first is strong salt-insulated rain garden suitable for severe saline-alkali areas. The second is suitable for the comprehensive rain garden in the moderate saline-alkali area. The third is suitable for the permeable rain garden in the light saline-alkali area.</p>

Research on theoretical modeling and numerical simulation of viscoelastic-plastic bending neutral layer in T-welding stiffened panels-based aged stress relaxation forming

A new mathematical model-based on aging-stress relaxation forming for heterogeneous stiffened panel that is T-welded together is developed. The corresponding theoretical method for calculating its neutral layer positions and forming die shapes in viscous-elastic-plastic bending is obtained by gradually deriving the modeling process of age forming of T-section beam, and comparisons of the theoretical data and simulated solutions are presented. It is found that the hot form solutions can be obtained for cylindrical die shapes, and the actual neutral layer position of stiffened panel can be accurately determined by the established theoretical model. Meanwhile, for the elastic bending and plastic bending stages, the neutral layer positions of stiffened panel are greatly different. The neutral axis of the former passes through its section centroid, while the latter does not, but it gradually, but significantly shifts to the outer layer of thin plate as the bending radius of die decreases.