Synergistic effects of iron and hexagonal-Boron Nitride additions in copper-based composites for braking application

This paper explores the addition of h-BN and iron to Cu-based brake pads on the performance benefits. It also investigates the effect of graded layering by synthesizing three and four-layer brake pads by powder compaction and sintering route. The top one or two layers are made of Cu-based composite containing Fe, h-BN, and W, while the middle layer is pure Cu and, bottom steel plate. Two different compositions were explored for the composites by varying Fe content. From the two composite compositions, brake pads with single-layer composite or two-layer composite were synthesized. Characterization of brake pad specimens was carried out using density measurements, optical microscopy, scanning electron microscopy, energy dispersive spectroscopy. The brake pads were subjected to simulated braking tests at braking energy/cycle of 60, 96, and 136 K Joules. Wear rate, coefficient of friction, stopping distance, stopping time, and hardness were measured and compared among other brake pads. The brake pad containing single-layer Fe rich Cu composite showed the best performance in the simulated braking tests. EDS analysis of wear debris shows the formation of iron (boride, nitride, oxide) complex which is indicative of a surface with superior dry lubricating properties. This surface is a result of synergetic interaction between h-BN and Fe particles. The iron particles which are scattered in the Cu matrix composite act as low friction regions on the brake pad surface that interrupt the high friction regions on the Cu matrix, thus reducing the local and bulk temperature rise. The two-layer composite brake-pad showed performance intermediate to the two single-layer brake pads. No advantage due to higher thermal conductivities in Fe deficient composite was observed as the two composite layers, showed similar Fe contents in their matrix phases.

Cross-Section Configuration Coefficient in the Zhurkov’S Generalized Equation

Постановка проблемы. Исследование долговечности строительных материалов с термофлуктуационной позиции является наиболее сложным, но и в тоже время наиболее адекватным методом. Ввиду того, что данная концепция является нечувствительной к изменениям физической структуры, возникает необходимость учета не только материала, но и конфигурации конструкции. Необходимо провести сравнение механизма разрушения при различных вариантах сечения для двух структурно отличающихся элементов - поливинилхлорида (ПВХ) и древесины. Результаты. Для элементов ПВХ и дерева составного сечения в два слоя без специальных связей получен одинаковый коэффициент k = 2. Для элементов составного сечения в три слоя без специальных связей получен коэффициент с интервалом k = 3,5…5,5, что требует дальнейшего уточнения. Выводы. На основе проведенного исследования теоретически обоснованы и экспериментально выявлены закономерности деформирования и разрушения ПВХ-элементов цельного сечения и составного сечения без специального соединения в два и три слоя. Определение термофлуктуационных зависимостей позволяет приблизить теоретические представления о работоспособности строительного материала в конструкции к реальным условиям. Statement of the problem. Studying the durability of construction materials in the aspect of thermal fluctuations is the most complicated, yet the most appropriate method. Considering that this concept does not take into account the changes of the physical structure, it becomes necessary to consider not the material alone but also the configuration of the structure. Therefore it is necessary to make a comparison of two structurally different elements - PVC and wood. Results. The coefficient of the 2-layer composite cross-section (no special connection) is the same for the PVC and wood elements: k = 2. The derived coefficient of the 3-layer composite cross-section (no special connection) is within the following range: k = 3,5…5,5, which requires a more precise definition. Conclusions. Based on the above experiment, we have theoretically established and experimentally confirmed the regularities of deformation and destruction of PVC elements of the 2 and 3-layer solid and composite cross-section without a special connection. Determining the thermal fluctuation relations allows us to bring theoretical concepts of the capacity of the construction material in a structure closer to actual conditions.

Effect of Potassium Phosphate Content in Aluminosilicate Matrix on Mechanical Properties of Carbon Prepreg Composites

Six matrices based on alkali-activated aluminosilicate with different amounts of potassium phosphate were prepared for the production of six-layer composite plates. The addition of potassium phosphate in the matrix was 2 wt%, 4 wt%, 6 wt%, 8 wt% and 10 wt% of its total weight. The matrix without the potassium phosphate was also prepared. The aim of this study was to determine whether this addition has an effect on the tensile strength or Young’s modulus of composites at temperatures up to 800 °C. Changes in the thickness and weight of the samples after this temperature were also monitored. Carbon plain weave fabric was chosen for the preparation of the composites. The results show that under normal conditions, the addition of potassium phosphate has no significant effect on the mechanical properties; the highest measured tensile strengths were around 350 MPa. However, at temperatures of 600 °C and 800 °C the addition of potassium phosphate had a positive effect, with the tensile strength of the composites being up to 300% higher than the composites without the addition. The highest measured values of composites after one hour at 600 °C were higher than 100 MPa and after 1 h at 800 °C higher than 85 MPa.

Hydrophobicity and Macroscale Tribology Behavior of Stearic Acid/Hydroxypropyl Methylcellulose Dual-Layer Composite

Hydroxypropyl methylcellulose (HPMC) and stearic acid (SA) are integrated to fabricate a double-layer thin film composite material with potential applications in sustainable packaging and coating materials. The effect of SA concentration on the moisture and wear resistance at the macroscale of the composite are studied. The amount of SA on the surface (>SA5H) is beneficial in increasing anti-wear behavior and reducing the friction coefficient by 25%. The petal-shaped crystals formed by SA are distributed on the surface of the double-layer film, increasing its hydrophobicity. When subjected to wear, the SA crystals on the surface of the double-layer film are fractured into debris-like abrasive particles, forming an optimal third-body of moderate shape and particle size, and imparting anti-wear and lubricating characteristics.

Electromagnetic Wave Absorption and Mechanical Properties of CNTs@GN@Fe3O4/PU Multilayer Composite Foam

With the development of intelligent communications and stealth technology in the military field, electromagnetic wave pollution cannot be ignored, and absorbing materials have entered people’s field of vision and gradually become a research hotspot. The ideal absorbing material should have the characteristics of “strong, wide, thin, and light”, but a single absorbing material often cannot meet the above conditions. At present, absorbing metal powder combined with two-dimensional carbon nanomaterials (such as carbon nanotubes, graphene, etc.) has became a trend. This article focus on a three-layer composite of Fe3O4, Carbon nanotubes@ Fe3O4, Carbon nanotubes@Graphene nano-platelets@ Fe3O4, which was synthesized by solvothermal method. The results show that the electromagnetic wave absorption performance of the three-layer foam at a thickness of 3.0 mm is more excellent. The minimum of RL can reach −67.0 dB, and the effective bandwidth is above 5.0 GHz. All this is due to the synergy of dielectric and magnetic loss between Fe3O4, CNTs, and GN, the increase of interface polarization and the path of electromagnetic wave reflection and scattering by three-layer foam.