Investigation of material removal mechanisms and ductile-brittle transition zone of zirconia ceramics sintered at various temperatures.

Sintering is a comprehensive process that involves the complex evolution of material microstructures and properties, being recognized as a critical factor to improve the machinability of ceramics. The present work aims to address the evolution of the material removal mechanisms of the 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) during the sintering process based on the micro scratching tests. The impacts of sintering temperatures on the material removal behaviors, including scratching forces, scratch morphologies, specific scratching energies, and critical transition depths, were rigorously studied. The acquired results indicate that the intergranular bonding strength is a critical factor that determinines the material removal mechanisms of 3Y-TZP, and 1100 °C signifies the transition threshold for the material removal mode. After 1100 °C, the material removal mechanism has gradually converted into the typical ductile-brittle removal regime. Moreover, the critical depth in ductile regime at 1200 °C is about 1.89 times that at 1500 °C, and the critical depth of ductile-brittle transition at 1200 °C is approximately 2.08 times that at 1500 °C.

Implementation and Characterization of a Laminate Hybrid Composite Based on Palm Tree and Glass Fibers.

In this work, laminated polyester thermoset composites based on palm tree fibers extracted from palms leaflets and glass mats fibers were manufactured to develop hybrid compositions with good mechanical properties; the mixture of fibers was elaborated to not exceed 25 vol.%. Samples were prepared with a resin transfer molding (RTM) method and mechanically characterized using tensile and flexural, hardness, and impact tests, and ultrasonic waves as a non-destructive technique. The water sorption of these composite materials was carried out in addition to solar irradiation aging for approximately 300 days to predict the applicability and the long-term performance of the manufactured composites. Results have shown that the use of glass fibers significantly increased all properties; however, an optimum combination of the mixture could be interesting and could be developed with less glass sheet and more natural fibers, which is the goal of this study. On the other hand, exposure to natural sunlight deteriorated the mechanical resistance of the neat resin after only 60 days, while the composites kept high mechanical resistance for 365 days of exposure.

A Study on Drilling High-Strength CFRP Laminates: Frictional Heat and Cutting Temperature.

High-strength carbon fiber reinforced polymer (CFRP) composites have become popular materials to be utilized in the aerospace and automotive industries, due to their unique and superior mechanical properties. An understanding of cutting temperatures is rather important when dealing with high-strength CFRPs, since machining defects are likely to occur because of high temperatures (especially in the semi-closed drilling process). The friction behavior at the flank tool-workpiece interface when drilling CFRPs plays a vital role in the heat generation, which still remains poorly understood. The aim of this paper is to address the friction-induced heat based on two specially-designed tribometers to simulate different sliding velocities, similar to those occurring along the flank tool-work interface in drilling. The elastic recovery effect during the drilling process was considered during the tribo-drilling experiments. The drilling temperatures were calculated by the analytical model and verified by the in-situ experimental results gained using the embedded thermocouples into the drills. The results indicate that the magnitudes of the interfacial friction coefficients between the cemented carbide tool and the CFRP specimen are within the range between 0.135⁻0.168 under the examined conditions. Additionally, the friction caused by the plastic deformation and elastic recovery effects plays a dominant role when the sliding velocity increases. The findings in this paper point out the impact of the friction-induced heat and cutting parameters on the overall drilling temperature.

Cutting Modeling of Hybrid CFRP/Ti Composite with Induced Damage Analysis.

In hybrid carbon fiber reinforced polymer (CFRP)/Ti machining, the bi-material interface is the weakest region vulnerable to severe damage formation when the tool cutting from one phase to another phase and vice versa. The interface delamination as well as the composite-phase damage is the most serious failure dominating the bi-material machining. In this paper, an original finite element (FE) model was developed to inspect the key mechanisms governing the induced damage formation when cutting this multi-phase material. The hybrid composite model was constructed by establishing three disparate physical constituents, i.e., the Ti phase, the interface, and the CFRP phase. Different constitutive laws and damage criteria were implemented to build up the entire cutting behavior of the bi-material system. The developed orthogonal cutting (OC) model aims to characterize the dynamic mechanisms of interface delamination formation and the affected interface zone (AIZ). Special focus was made on the quantitative analyses of the parametric effects on the interface delamination and composite-phase damage. The numerical results highlighted the pivotal role of AIZ in affecting the formation of interface delamination, and the significant impacts of feed rate and cutting speed on delamination extent and fiber/matrix failure.