Experimental investigation of vibration pretreatment-microwave curing process for carbon fiber reinforced resin matrix composites

The vibration pretreatment-microwave curing process is an efficient,low energy consumption,and high-quality out-of-autoclave curing process for carbon fiber resin matrix composites.This study aims to investigate the impact of vibration pretreatment temperature on the fiber weight content,microscopic morphology and mechanical properties of the composite laminates by using optical digital microscopy,universal tensile testing machine and thermo-gravimetric analyzer.Additionally,the combined mode of Bragg fiber grating sensor and temperature measurement fiber was employed to explore the effect of vibration pretreatment on the strain process during microwave curing.The study results revealed that the change in vibration pretreatment temperature had a slight impact on the fiber weight content when the vibration acceleration remained constant.The metallographic and interlaminar strength of the specimen formed at a vibration pretreatment temperature of 80℃ demonstrated a porosity of 0.414% and a 10.69% decrease in interlaminar shear strength compared to autoclave curing.Moreover,the introduction of the vibration energy field during the microwave curing process led to a significant reduction in residual strain in both the 0°and 90°fiber directions,when the laminate was cooled to 60℃.

图书馆书架用改性胶粘剂的制备与性能研究

为了提升图书馆书架用胶粘剂的胶接强度,研究了反应温度、反应时间、—OH与—NCO摩尔比、催化剂用量、热压温度和热压时间对聚氨酯胶粘剂中—NCO含量和胶粘剂试样剪切强度的影响。结果表明,胶粘剂体系中适宜的反应温度为70℃、反应时间为5 h、催化剂用量为0.1%、—OH与—NCO摩尔比为0.4。随热压时间的增加,试样的干状剪切强度(τ_(d))和湿状剪切强度(τ_(m))都先增大后保持稳定。随着热压温度(T r)从130℃增至150℃,试样的τ_(d)和τ_(m)先增大后减小,当热压温度为140℃时取得最大值。在热压温度为140℃、热压时间为75 min时,胶粘剂试样具有最大的τ_(d)和τ_(m),且为适宜的热压工艺参数。

鼠尾缺陷的成因及防止

通过理论分析和试验结果表明，鼠尾的形成是由于过热的湿型砂局部型腔表面干燥砂层因膨胀受阻，内部产生热压应力，当热压应力发展到大于相邻的部分铸型的阻力时，干燥砂层会产生剪切滑移凸起，使铸件产生鼠尾缺陷。滑移阻力主要来自于相邻的干燥砂层。

TLP bonding of Ti-6Al-4V to Al 2024 using thermal spray Babbitt alloy interlayer

Thermal spray assisted transient liquid phase(TLP) bonding of Ti-6 Al-4 V to Al2024 alloys was investigated, where the interlayer was 80 μ m Babbitt thermal spray coat on Al substrate. Thermal spray creates a rough and clean surface which leads to establishing a joint with higher strength. The optimized parameters were bonding temperature of 580 ℃ and bonding time of 30 and 60 min. Microstructural observation together with XRD patterns confirmed the existence of Al2 Cu, Al2 Cu Mg, Cu3 Ti, Ti Al3, Ti Al and Mg2 Sn intermetallic compounds formed in Al weld side. On the other hand, Ti3 Al, Sn3 Ti5 and Ti3 Sn intermetallic compounds formed in Ti side. With increasing bonding time from 30 to 60 min, although the interlayer was not completely consumed, the thickness of remained Babbitt interlayer decreased to approximately 15 μ m. The study showed that shear strength of the joint reaches the high value of 57 MPa obtained at larger bonding time of 60 min.

Influences of gap size and cyclic-thermal-shock treatment on mechanical properties of TLP bonded IN-738LC superalloy

Influences of gap size and cyclic-thermal-shock treatment on the mechanical properties of transient liquid phase（TLP） bonded IN-738 LC superalloy were investigated. For this purpose, TLP bonding of IN-738 LC superalloy was carried out in a vacuum furnace using powdered AMS 4777 as the filler metal. The results showed that isothermal solidified zone（ISZ） consisted of Ni solid-solution and the distribution of alloying elements was homogeneous. High hardness of HV 409 and high shear strength of 506 MPa were observed in 40 μm gap sample. Alloying elements formed γ′ precipitates and the solid-solution in the ISZ. Hardness and shear strength of bonds were reduced with increasing the gap size（in range of 40-120 μm）. The fractured surfaces of complete isothermal solidified bonds showed dimpled rupture, but athermal solidified bonds showed cleavage fracture surface. 10, 20, 30 and 40 thermal-shock cycles were applied to 80 μm gap samples, respectively. The shear strength of the bond was measured to be 268 MPa after the 40 th thermal-shock cycle. The sample with gap size of 80 μm was failed due to crack nucleation on faying surface at 45 th thermal-shock cycle. The amount of the produced brittleness due to quenching the samples in water bath was attributed to the number of thermal-shock cycles.

Brazing behavior of ultrafine cemented carbide with stainless steel

In order to investigate the effects of brazing temperature, heating rate and cooling methods on shear strength, hardness, magnetic saturation and coercivity of the ultrafine cemented carbide, the ultrafine cemented carbide was fabricated according to conventional powder metallurgical procedures, and then brazed to the stainless steel with silver-based filler alloy by supersonic frequency induction brazing. The microstructure was observed using scanning electron microscope （SEM）, energy dispersive spectroscopy （EDS） and the magnetic properties were tested utilizing coercimeter and cobalt magnetism instrument. The results show that no micro-crack is found in the cemented carbide after brazing because of silver-based sandwich compound used as filler alloy. In the melted silver layer, there is more carbon in the region adjacent to the cemented carbide. Varied shear strengths, hardnesses, magnetic saturations and coercivities are present under different brazing temperatures, heating rates and coolings. This phenomenon is correlated with some factors such as wettability and fluidity of filler alloy, brazing stress, oxidation of cemented carbide, and allotrope transition of cobalt. Shear strength reaches the maximum of 340 MPa and hardness of ultrafine cemented carbide remains 1879 HV at the brazing temperature of 730℃. The carbon increases with the of increase of the heating rate. What＇s more, and there is no r/phase found under this condition. content decreases with the increase of brazing temperature, and it the lowest magnetic saturation reaches 81.8% of the theoretic value,