Key Engineering Materials Vols. 353-358

Abstract: There is an increasing interest in developing fully biodegradable materials for industrial applications. Composite combining biodegradable polymer and natural fiber could be a fully biodegradable material. This work focus on the investigation on China jute fiber reinforced PLA composites. Composites with three different fiber volume fractions were fabricated by film stacking hot press method. Mechanical properties have been investigated and the microstructure of the composites was observed. Fiber surface treatment by silane was applied in order to investigate the effects on the properties of the composites. The moisture absorption rates in a hygrothermal environment were also measured.

Abstract: Based on Brinson’s one-dimensional thermo-constitutive law of SMA and classical plate theory, linear non-axisymmetric vibration of uniform heated composite annular plate embedded with circumferential SMA fibers is investigated. Natural frequencies of the annular plates with immovably clamped boundary condition, depending on the temperature rise are obtained by using shooting method. The characteristic curves of first four natural frequencies of non-axisymmetric vibration versus temperature rise are plotted. Influences of the volume fraction and the initial strain of SMA on the natural frequencies of plate are analyzed. The numerical results show that, the activation of SMA can enhance the natural frequency both in the inverse martensite transformation temperature range and the thermal buckling temperature.

Abstract: Adopting two-step deposition processes, SiC concentration gradient layer on the surface of Cf/C composites were prepared via Self-heating Chemical Liquid Deposition (SHRCLD) technique. In second deposition process, carbon and SiC were codepositted from pure kerosene and TEOS. The temperature of deposition was 1000°C~1200°C and the system pressure was 0.1MPa. Different thickness of gradient layers would be attained via adjusting the proportion of TEOS in procurer and controlling deposition time. Oxidation resistance, and mechanical tests were investigated, and the microstructure was observed under SEM. Results showed that the flexural strength of the composites was 123.7 MPa. The antioxidation temperature of Cf/C composites with the gradient layer is up to 800°C in air. The process of SHCLD technique is simple and easy to be controlled, and the deposition rate is faster than other conventional technique.

Abstract: The Al2O3/LiTaO3 (ALT) composite ceramics were fabricated by hot pressing method and polarization treated at different temperatures along height and width directions. Effects of polarization treatment on mechanical properties of the ALT composite ceramic were investigated. Flexural strength decreased with the increase of polarization temperature. Meanwhile, the flexural strength of samples polarized in height direction is higher than that polarized in width direction. The composite ceramic fractures intragranularly, and many rupture steps in polarization direction were observed on fractographs of the composite ceramics. Domain switching in LiTaO3 particles increased the resistance of crack propagation and improved the mechanical properties of the polarized ALT composite ceramics.

Abstract: In the present work, a SiCp/Al composite was fabricated by pressureless infiltration of aluminum alloy into loose-packed SiC particles preform, and its microstructure and hardness performance were investigated. The results showed that the composite was fully infiltrated and the particles were distributed uniformly in the composite. Interfacial reactions were found in the as-cast composite and the reaction product was identified as MgAl2O4 by TEM observation and XRD analysis. The interfacial reactions enhanced the wettability and promote the spontaneous infiltration process. The thermal exposure process increased the Brinell hardness of the composite. After the thermal exposure process, the block-like interfacial reaction products were distributed discretely, but the amount of the reaction products was increased.

Abstract: 55vol% TiB2P/2024Al composite was fabricated by squeeze casting technology, and the effect of heat treatment on mechanical properties of the composites was studied by means of hardness measurement, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and tensile testing etc. Results show that heat treatment has remarkable influence on the hardness and the tensile strength of the composites. For TiB2P/2024Al composites, the composites aged at 130°C for 5h can obtain the highest hardness, and the composites peak-aged at 160°C and aged at 190°C for 24h can obtain the higher tensile strength, which is due to the type of precipitates in the composites. Considering the experimental error, heat treatments has no obvious effect on elastic modulus of the experimental composite.

Abstract: MoSi2-SiC precursor powder has been synthesized via the mechanical alloy method with the elements Mo, Si and C powder. The SiC/MoSi2 composites with different SiC volume fraction have been prepared by reactive hot-pressing the precursor powder at 1350 °C. There is a significant increase in the fracture toughness due to addition of SiC reinforcement. However, the intermediary ternary phase exists in this system—namely, Mo5Si3C, Nowotny phase, which has negative effect on the fracture toughness, and can be eliminated through high temperature treatment at 1600 °C for 2 hrs.

Abstract: Statistical diagnosis using electrical resistance changes is performed to detect a delamination crack in a CFRP beam. This method enables to reduce data required for damage identification. First, a new measuring method of multiple electrical resistance changes is proposed to perform statistical diagnosis. The proposed method measures electrical resistance changes of multiple segments in a CFRP beam although electrical interference must be considered when multiple voltages are charged at once. Next, statistical diagnosis is performed on loading to the CFRP beam. A delamination crack is detected by the change of relative relationship between multiple electrical resistance changes due to damage occurring. As a result, the monitored states of the CFRP beam are diagnosed exactly by the proposed damage detection system.

Abstract: Magnesium borate whisker reinforced aluminum alloy 2024 (AA2024) composite was fabricated by squeeze casting method, after was CuO coating of the whisker. The interfacial reaction in the composite was investigated. To change the interfacial reaction degree, the solution treatment for different time was carried out. The results show that the interfacial reaction degree increases with solution time increasing. The maximum ultimate tensile strength can be obtained when the solution time is suitable.

Abstract: Carbides reinforced intermetallic matrix composite coatings for elevated temperature environmental resistance were prepared on Ni-based suaperalloy substrate using CO2 laser cladding process. The phases of clad layer were investigated by scanning electron microscopy (SEM), X-ray diffractometer (XRD) and energy-dispersive spectrometer (EDS). The laser cladding of the Ni78Si13Ti9/WC powder shows that the products mainly consist of TiC, WC and Ni3(Si,Ti) phases. A chemical reaction between WC particle and Ti powder occurs during the laser process, therefore TiC is formed. The microhardness of the samples increases with the increase of the content of WC.