Calibration of Drucker-Prager Cap Constitutive Model for Ceramic Powder Compaction through Inverse Analysis

Method for Determining the Coefficient of Friction Variation Pattern as a Function of Density at Low Temperatures Using the Example of Dry Ice-Steel Contact

The developments in manufacturing technologies are expected to reduce energy input without compromising product quality. Regarding the material densification process, numerical simulation methods are applied to achieve this goal. In this case, relevant material models are built using functions that describe the variation in mechanical parameters of the material in question due to its deformation. The literature review conducted for this research has revealed a shortage of experimental research methods allowing a determination of the coefficient of friction at low temperatures, approximately 200 K. This article proposes a method for determining the friction coefficient of dry ice sliding against steel. The experimental results were analysed to obtain several functions describing the variation in the coefficient of friction. These functions were then compared using goodness-of-fit indexes. Finally, two functions with similar goodness-of-fit values were chosen. The findings of this research project will complement the already available information and may be used in various research and implementation projects related to the development or improvement of currently used crystallised carbon dioxide conversion processes.

Computer-Aided Structural Diagnosis of Bridges Using Combinations of Static and Dynamic Tests: A Preliminary Investigation

Reinforced concrete bridges deteriorate over time, therefore displaying a regular need for structural assessment and diagnosis. The reasons for their deterioration are often the following: (a) intensive use, (b) very dynamic loads acting for long periods of time, (c) and sometimes chemical processes that damage the concrete or lead to corrosion of the reinforcement. Assuming the hypothesis that both the stiffness of the material and its density change over time, these parameters shall be identified, preferably in a non-destructive way, in different locations of the investigated structure. Such task is expected to be possibly exerted by means of one or more tests, which must not be laborious or cause the bridge to be out of service for a long time. In this paper, an attempt is made to prepare a procedure based on dynamic tests supplemented with several static measurements, in order to identify the largest number of parameters in the shortest possible time, within an inverse analysis methodology. The proposed procedure employs a popular algorithm for minimizing the objective function, i.e., trust region in the least square framework, as part of the inverse analysis, where the difference between measurements made in situ and those calculated numerically is minimized. As a result of the work performed, optimal sets of measurements and test configurations are proposed, allowing the searched parameters to be found in a reliable manner, with the greatest possible precision.

Numerical Simulation of Physical Fields during Spark Plasma Sintering of Boron Carbide

Spark plasma sintering is a new technology for preparing ceramic materials. In this article, a thermal-electric-mechanical coupled model is used to simulate the spark plasma sintering process of boron carbide. The solution of the thermal-electric part was based on the charge conservation equation and the energy conservation equation. A phenomenological constitutive model (Drucker-Prager Cap model) was used to simulate the densification process of boron carbide powder. To reflect the influence of temperature on sintering performance, the model parameters were set as functions of temperature. Spark plasma sintering experiments were conducted at four temperatures: 1500 °C, 1600 °C, 1700 °C, and 1800 °C, and the sintering curves were obtained. The parameter optimization software was integrated with the finite element analysis software, and the model parameters at different temperatures were obtained through the parameter inverse identification method by minimizing the difference between the experimental displacement curve and the simulated displacement curve. The Drucker-Prager Cap model was then incorporated into the coupled finite element framework to analyze the changes of various physical fields of the system over time during the sintering process.

Experiment and Simulation Research on Rock Damage Mechanism in Tooth Indentation

In the oil and gas drilling industry, cemented carbide teeth are one of the most widely used rock-breaking elements. In order to reveal the rock damage mechanism of tooth indentation, a series of tooth indentation experiments were conducted in this study, and an indentation simulation was also conducted as a supplement to the experiment. In the experiment, a new method to observe the inner damage status of the rock was put forward, i.e., utilizing the splitting action of the teeth to avoid unexpected rock damage that may affect the actual experiment results. The load-displacement curves and the damage status of the rock revealed that the wedge tooth was more efficient in fracturing and damaging the rock because the load requirement of the wedge tooth was lower, the narrow tooth crown generated larger specific stress in the rock; that rock-breaking advantage of the wedge tooth resulted from the occurrence of the compacted core and the tension stress generated by the core. According to the simulation results, the plastic strain in the intermediate area between the wedge teeth appeared more concentrated and increased faster, and the rock material beneath the wedge teeth was removed earlier than beneath the conical teeth, indicating that wedge teeth, disposed with proper spacing, can break rock more effectively than the conical teeth. The experiment and simulation results in this paper have proved the advantages of the wedge tooth in rock fracturing and damaging, which will provide technical support for the design and development for the drill bits applied in oil and gas drilling.

Experimental Investigation on the Effect of Dry Ice Compression on the Poisson Ratio

In the processing of waste materials, attention must be given to the efficient use of energy. The pelletization of dry ice is a good example of such processes. A literature review shows that in the pelletizers available on the market, the force applied in the process is excessive. As a result, the efficiency of the utilization of inputs, including electricity and carbon dioxide, is at a very low level. This article presents the results of experimental research on the effect of the degree of dry ice compression on the value of the Poisson ratio. The first part of this article presents the research methodology and a description of the test stand, developed specifically for this research, bearing in mind the unique properties of carbon dioxide in the solid state. The results presented show the behavior of dry ice during compression in a rectangular chamber for different final densities of the finished product. As a result, it is possible to determine the values of the Poisson ratio as a function of density, using for this purpose four mathematical models. The findings of this research may be useful for research work focused on the further development of this process, such as by using the Drucker–Prager/Cap numerical model to optimize the geometric parameters of the parts and components of the main unit of the machine used in the extrusion process of dry ice.

The Influence of Density on the Value of Young's Modulus for Dry Ice

The efficiency of material consumption is an important consideration for production processes; this is particularly true for processes that use waste materials. Dry ice extrusion serves as a good example. An examination of the literature on this subject leads to an observation that the commercially available machines for dry ice compression are characterized by a high value of working force. Consequently, the effectiveness of the source consumption, electric energy and carbon dioxide, is very low. The subject of the experimental research presented in the article is the influence of the density of dry ice on the value of Young’s modulus. The first part of the article presents the test methodology and the special test stand that was developed to accommodate the unique characteristics of solid-state carbon dioxide. The test results present the characteristics of compaction and relaxation used as the basis for determining the value of Young’s modulus. Based on the test results obtained for various material density values, the characteristics of Young’s modulus are developed and graphed as a function of the density. The presented results are important for furthering the research on the development of extrusion and compaction processes; for example, using the Drucker–Prager/Cap model for the purpose of optimizing the geometrical characteristics of the work assembly components.