Papers by Keyword: Thermomechanical

Abstract: Geopolymeric mortars made from a mixture of waste from the Peruvian informal mining industry, sodium hydroxide activating solution, and fine sand were studied, comparing them physically and mechanically with conventional Portland cement mortars. Both conventional and geopolymeric mortars were prepared in parallel and then subjected to uniaxial compression tests at various temperatures (ambient, 200 °C and 500 °C). The mechanical results found revealed maximum average resistance values of 63, 84 and 79 MPa for conventional mortars, and 12, 32 and 36 MPa for geopolymeric mortars, when they were tested at room temperature, 200 °C and 500 °C, respectively. The best mechanical results in geopolymeric mortars were found when considering a binder: fine sand ratio of 1:2, molarity of the hardening solution of 12 M and a hardening solution: binder ratio of 0.6. It was possible to demonstrate a good agreement between the distribution of particle sizes observed microstructurally and those found by granulometry studies by laser light diffraction.

Abstract: Cartridge case ammunition is made from brass alloy by deep drawing process with high degree of deformation. For this reason, the material with a good formability, strength, and hardness is required. The improvement of mechanical propeties of the brass alloy can be conducted by severe process such as addition of alloying element and also termomechanical process. The purpose of this study is to determine the effect thermomechanical processing by cold rolling process with 70% thickness reduction followed by annealing process with variation temperature of 400°C, 500°C and 600°C for 30 minutes to the microstructure and mechanical properties of Cu-28Zn-4Mn alloy. The samples of Cu-28Zn-4Mn alloy were produced by gravity die casting process by using the ingot of Cu, Zn as well as the Mn powder as the feeding materials. The investigation results show that thermomechanical prosess change the microstructures of Cu-28Zn-4Mn alloy. The cold rolling process with 70% thickness reduction will convert the equiaxial grain into an elongated structure (shear band). Furthermore, the heat treatment by annealing process will return the microstructure from elongated to equiaxial grain. Thermomechanical process also tends to change mechanical properties. The 70 % cold rolling process increases the hardness of the Cu-28Zn-4Mn alloy. The hardness of as homogenized and 70% cold rolled samples are 62.34 VHN and 103.96 VHN, respectively. Further, the annealing process tend to decrease the tensile strength and hardness of Cu-28Zn-4Mn alloy. Tensile strength of Cu-28Zn-4Mn after annealing process with variation of 400°C, 500°C, and 600°C are 355.13 MPa, 299.16 MPa, and 294.79 MPa, respectively. On the other hand, the hardness of Cu-28Zn-4Mn with the same treatment are 91.84 VHN, 71.76 VHN and 67.46 VHN, respectively. In contast, the annealing process tend to increase the elongation value. The samples elongation after the annealing process with variation of 400°C, 500°C, and 600°C are 25%, 28%, and 30%, respectively.

Abstract: This research was conducted to investigate the effect of thermomechanical process on microstructures and mechanical properties of Cu-28Zn-2Al alloys. Thermomechanical process was carried out by cold rolling process with 70% thickness reduction and followed by annealing process with variation temperature of 400°C, 500°C and 600°C. The result show that the β phase and shear bands are found in the samples. Further, cold rolling process can increase hardness of Cu-28Zn-2Al alloys from 100 to 172 VHN. The heat treatment with annealing process at 400°C tend to decrease the tensile strength of cold rolled samples from 695 to 472 MPa and more decreased until 422 MPa at 600°C. In contrast, annealing process at 400°C tend to increase the elongation from 10 to 28% and more increased up to 56% at 600°C. This phenomenon prove that the annealing process will increase ductility of cold rolled samples of Cu-28Zn-2Al alloys.

Abstract: The incorporation of filler and plasticizer provides effective nucleation and mechanical reinforcement in polymer composites to impart flexibility, toughness, thermal stability and tensile strength of PLA composites that can be used in the development of packaging applications. In this paper, the inclusion of plasticizer and reinforcement of nanofiller in PLA matrix prepared using solvent casting method aims to improve the thermomechanical properties that consequently alter the crystallization and melting behavior of PLA composites. Plasticized PLA with different percentages of TiO₂ at 2.0, 3.5, 5.0 and 7.0 % w/w were dispersed in PLA solution using mechanical mixer and ultrasonication technique to introduce a matrix reinforcing nanophase within the composite. The thermomechanical properties and thermal behavior of PLA nanocomposites were characterized using dynamic mechanical analysis (DMA) and differential scanning calorimeter (DSC). DSC cooling curves at low scanning rate of 2.0 K·min^-1 proved that the presence of TBC in PLA matrix increased the crystallinity of plasticized PLA nanocomposites that initiated the formation of perfect spherulites. TBC increased the crystallization activity during cooling, which in turn reduced the recrystallization effect on heating, in parallel with DMA results that revealed small peak of cold-crystallization activity on PLA nanocomposites with the addition of plasticizer observed at temperature range of 80 °C to 100 °C. Nanofiller induced nucleation for crystallization of PLA matrix and plasticizer accelerated the overall crystallization process. Considerable adjustments of plasticizer and nanofiller in PLA matrix in having a good balance of stiffness and flexibility are a practical strategy that has a potential in biopolymer medical engineering and in the development of packaging applications.

Abstract: Poly (lactic acid) (PLA) is a useful alternative to petrochemical commodity material used in such as in food packaging industries. Due to its inherent brittleness, low thermal stability, and poor crystallization, it needs to improve its properties, namely in terms of thermal and mechanical performance. The plasticized PLA composites reinforced with nanofiller were prepared by solvent casting and hot press methods. Thermal and mechanical properties, as well as the crystallinity study of these nanocomposites, were investigated to study the effect of tributyl citrate (TBC) and TiO₂ on the PLA composites. The addition of TBC improved the flexibility and crystallinity of the composites. Reinforcement of TiO₂ was found as a practical approach to improve the mechanical properties, thermal stability, and enhanced crystalline ability for plasticized PLA nanocomposites. Based on the results achieved in this study, the composite with 3.5% nanofiller (pPLATi3.5) presented the optimum set of mechanical properties and improved thermal stability.

Abstract: The combustion of biomass for energy generation is practiced in an increasing scale in Indonesia as the country heads towards the long-term national energy mix targeted by 2025. However, biomass combustion is prone to operational problems caused by the generally low-melting nature of biomass ashes. This work discusses the effects of co-combusting coal with POEFB (palm oil empty fruit bunch) and bamboo with respect to the thermomechanical behavior of the produced ashes. Coal is observed to increase the ash fusion temperatures (AFT) of neat and combined POEFB and bamboo ashes by as much as 300 °C. Aluminosilicate minerals in the coal combine with potassium in the biomass during co-combustion, producing high-melting K-aluminosilicates. A linear correlation is identified between measured AFT and ash liquidus temperatures estimated by FactSage thermochemistry calculation software, enabling the prediction of AFT of coal-biomass co-combustion systems.

Abstract: The ability of a draping simulation to accurately predict the outcome of a forming process mainly depends on the accuracy of the input parameters. For pre-impregnated composites, material must be characterised in the same conditions as forming occurs, i.e. in temperature regulated environment. Given the issues encountered while testing specimens enclosed in a thermal chamber and mounted on a tensile testing machine, new test methods have to be developed. A new approach using a Dynamic Mechanical Analysis system is presented for the investigation of tensile properties perpendicular to fibre direction of unidirectional pre-impregnated composites. Analyses are focused on a unidirectional carbon fibre thermoplastic tape reinforced polyamide 6 in its molten state. Quasi-static tests are performed at forming temperature for different loading rates with specimens of different geometries in order to assess the reproducibility of the test method.

Abstract: Doped lanthanum chromite has been the most common material used as interconnectors in solid oxide (SOFC) fuel cell, allowing for the stacking of the SOFC. Reducing the operating temperature, to around 800°C, the cells of solid oxide fuel have made the use of metal interconnectors possible as an alternative to ceramic LaCrO₃. From the practical point of view for the material to be a strong candidate as an interconnector, it must have good physical and mechanical properties, such as resistance to oxidizing environments and reducers, facility to manufacture, and adequate thermomechanical properties. In this work, a study was conducted on the thermomechanical properties of metallic interconnectors (AISI 444) covered with La_0,8Ca_0,2CrO₃ by way of deposition technique for pyrolysis spray for the intermediate temperature (IT-SOFC) fuel cell. The material was characterized by X-ray diffraction (XRD), oxidative test, flexural strength at room temperature and at 900°C, and scanning electron microscopy (SEM). The evaluation of the phases formed on metallic interconnectors coated with La_0,8Ca_0,2CrO₃ on both the deposition and after oxidative assay was performed by XRD. The oxidative behavior showed increased resistance to oxidation of the metal substrate covered by La_0,8Ca_0,2CrO₃. In the flexural strength of the coated metal substrate, it was noted only in the increasing temperature. With the aid of SEM, the formation of layers of Cr₂O₃ and (Cr, Mn)₃O₄ on the metallic substrate was seen, and confirmed stability of La_0,8Ca_0,2CrO₃ ceramic film after oxidative test.

Abstract: This paper deals with an identification methodology of the interfacial fracture parameters to predict the lifetime of a metallic brazed joint. The methodology is based on an experimental-numerical study whereby the optimal parameters are obtained. The experimental data, using the scanning electron microscope analysis, allowed approving that failure of the assembly based AuGe solder seems first to appear near the interfaces. These results were confirmed by micrographs analysis of the solder/insert and solder/substrate interfaces. Then, using shear test results and parametric identification coupled with a finite elements model (FEM) simulation, the damage constitutive law of the interfacial fracture based on a bilinear cohesive zone model are identified. The agreement between the numerical results and the experimental data shows the applicability of the cohesive zone model to fatigue crack growth analysis and life estimation of brazed joints.

Abstract: In order to research the thermomechanical behavior of multidisc friction pairs system, three dimensional model is established for numerical simulation under simulated braking process. Based on some accurate boundary conditions, the temperature fields and thermal stress fields of friction discs and separator discs are simulated using finite element method. The temperature fields and contact stress fields of friction disc and separator discs are obtained, and their regularities of distribution are studied spatially and historically. To verify the simulation results, an experimental investigation is carried out. The results offered references for analyzing failure forms and causes of the wet multidisc friction pairs system.