Abstract:

Longitudinal torsional ultrasonic vibration-assisted milling （LTUVAM） is an auxiliary milling technology that applies high-frequency micro amplitude vibration in the axial and torsional directions of the tool. It has many advantages，such as reducing cutting force and cutting heat， improving the surface quality of the workpiece， increasing residual compressive stress on the surface，and reducing tool wear. This paper presents a systematic review on the milling of difficult to machine materials. In terms of equipment manufacturing，the structural design method and working principle of longitudinal torsional ultrasonic vibration system were described；In terms of process development，the cutting performance of various materials was analyzed from the cutting edge motion track and the cutting characteristics of LTUVAM. The advantages and applications of LTUVAM are summarized. Finally，this paper provides an outlook on the future development trends of LTUVAM.

Abstract:

Aerodynamic heating caused by high Mach number flight has always been the major factor that restricts the development of aircrafts to higher speed ranges and airspaces. In particular， parts with large dynamic clearance between the engine nozzle and fuselage， and the control rudder of the tail wing， pose a technical challenge for dynamic thermal sealing more difficult than fuselage surface heat protection. Hence， dynamic thermal sealing technology is a critical bottleneck for developing new hypersonic space vehicles. This paper surveys the foreign dynamic thermal sealing technology with examples of X-38 and other aircrafts，reviews its main technical categories and key performance test methods，and finally offers a summary and future outlook on the development of dynamic thermal sealing technology.

Abstract:

For the composite component assembly interference problem caused by molding errors， this paper proposed a method of dimensional reduction of composite component assembly interference and clearance based on point cloud data obtained from laser equipment， it converts the interference and clearance calculation of the three-dimensional assembly into the calculation of the two-dimensional boundary distance. Taking a certain type of aircraft random assembly as an example，the feasibility of the proposed method and algorithm is verified through experiments， and the assembly accuracy and efficiency are improved compared with the original assembly process.

Abstract:

To elucidate the removal mechanism and surface damage characteristics of 2.5D C/SiC ceramic matrix composites during the milling process， experiments were conducted on both traditional milling and ultrasonic vibration-assisted milling. A three-dimensional numerical model was established for both milling conditions. The results indicate that， compared to traditional milling， ultrasonic vibration-assisted milling， under its high-frequency alternating load， reduces the micro-cutting thickness of the material and decreases the material''s deformation deflection， leading to a reduction in radial and tangential cutting forces by 68% and 72% respectively. It can effectively improve the surface damage of 2.5D C/SiC composites， such as inclined and rough fracture surfaces. The residual compressive stress on the processed surface is significantly greater than that of traditional milling. The established numerical model has been experimentally verified to effectively simulate the material removal process and the fracture morphology of 0° and 90° fibers. This work provides theoretical basis and guidance for the efficient and low-damage processing of 2.5D C/SiC composites.

Abstract:

T700/TDE-86 carbon fiber reinforced composites were subjected to artificial accelerated hygrothermal aging experiments.By comparing and analyzing the cross-sectional morphology and physical and chemical properties of the composite before and after aging，the moisture absorption and diffusion behavior of the composites were discussed， and the evolution law of the mechanical properties of composites was studied. The residual strength calculation model was constructed， and aging life of the composite in the hygrothermal environment was predicted by combining with the environmental coefficient. The results showed that the moisture absorption rate of the composite gradually increased until it turned flat with prolongation of aging time， which conformed to Fick''s diffusion law. Compared with composite without the hygrothermal aging， the mechanical properties of aged composite decreased under 60℃ and 95%RH， among which the shear strength was the most serious， up to 25% after 64 days of aging.The life of T700/TDE-86 carbon fiber reinforced composites estimated based on residual strength and environmental coefficients was about 30 years， laying a foundation for determining the future service reliability of resin-based composites.

Abstract:

In this paper，the in-plane anisotropy of super high-strength 2A55 Al-Li alloy sheets with thicknesses of 10 mm and 2 mm were compared and analyzed by means of tensile test at room temperature， X-ray and EBSD texture detection，etc.The effects of different heat treatments and grain structures were studied. The results show that the hard orientations were parallel to the rolling direction （0°） and the transverse direction （90°） after heat treatments. The anisotropic behavior of the sheets can be mainly attributed to the crystallographic texture， because the calculated Taylor factors were consistent with the yield strength anisotropy of the solutionized sheets and the sheets in condition T6. The severer anisotropy of 10 mm-thickness sheets was attributed to higher volume fraction of textures and aspect ratio of grains.Moreover， the aging treatments weakened the anisotropy of 10 mm-thickness sheets， but it had an opposite effect on 2 mm-thickness sheets. Sheets in condition T3 and T8 displayed severer in-plane anisotropy than those in condition T4 and T6. The pre-deformation before aging treatments increased the anisotropic behavior of the sheets.

Abstract:

This paper demonstrated that the strength and toughness of Al alloy could be improved when ultrasonic melt treatment， Sr/Ce complex modification and heat treatment worked together. The effect of solid solution treatment on the microstructure and properties of A356 alloy was also studied by metallographic microscope （OM），scanning electron microscope （SEM）， tensile machine and hardness instrument. The research results showed that melt treatment contributed to the improvement of the α-Al dendrites， and eutectic silicon phases， and the tensile strength of as-cast alloy reached 215MPa with elongation of 9.5%. After T6 heat treatment， the morphology of eutectic silicon changed from fibrous to spherical particles distributed independently， and mechanical properties were significantly also improved， except for elongation. As the solution time increased， the equivalent diameter of eutectic silicon decreased first and then increased， while the aspect ratio gradually decreased. Meanwhile， the tensile properties and microhardness of the alloys showed a trend of first increasing and then decreasing.When solution time was 4h， the optimized comprehensive mechanical properties of the alloy were obtained and its tensile strength，yield strength，elongation and microhardness reached 300MPa， 240MPa，8.0% and 110HV，respectively.

Abstract:

This article uses selective laser melting （SLM） to print and form AlMgScZr alloy， and analyzes the influence of different laser powers on the density， surface morphology， microstructure， and mechanical properties of printed samples. In the range of laser power from 80W to 240W， the packed density of AlMgScZr alloy first increases and then decreases， reaching its maximum value at a laser power of 200W，with a maximum packed density of 99.6%.The tensile strength and packed density of AlMgScZr alloy are closely related.In a nearly fully compact state，the mechanical properties of the alloy reach their optimal level， with tensile strength and elongation of 492 MPa and 18.4%，respectively. Due to the addition of Sc and Zr elements，a Al₃（Sc，Zr） phase is formed inside the alloy coherent with the matrix.Al₃（Sc，Zr） phase can serve as an effective nucleation particle to promote grain refinement， and its strengthening mechanism mainly includes fine grain strengthening and precipitation strengthening.

Abstract:

In order to meet the higher temperature resistance requirements of spacecraft solar wing substrate for future deep space exploration， this paper introduced a new forming process of solar wing substrate： co-curing of polyimide film and carbon grid panel. The study focused on the stripping performance of the polyimide film and the grid panel， the tensile performance of the grid panel， the bending performance of the honeycomb sandwich structure， and the temperature resistance of the co-cured substrate was made comparison of performance of samples by traditional process of using J-133 adhesive to bond polyimide film. The results showed that the peel strength of the co-curing polyimide film was about twice that of the traditional process， and the mechanical properties of the film were more than 87% at 140℃， showing good temperature resistance.After the thermal vacuum test from -100℃ to 140℃， the appearance quality and various properties of the co-cured substrate passed qualification， which met the needs of the solar wing substrate to withstand the space environment of 140℃ and below.

Abstract:

To detect the debond defects in the foam sandwich structure material with aluminum panel， ultrasonic multiple echo-pulse method was performed. The method principle was analyzed， the artificial defect samples were made， and the automatic C-scan imaging detection was performed. The defect recognition results were analyzed by statistic calculation of the scan image gray pixel numbers. The result shows that the ultrasonic multiple echo-pulse method is effective on debond defect detection of the foam sandwich structure material with aluminum panel and provides basis for material research and evaluation.

Abstract:

Water jacket plays an important role in ultrasonic water spray penetration detection.In order to design a water jacket with good coupling effect and to reduce the influence of water flow turbulence on acoustic coupling，this paper constructs a finite element simulation of geometric model，physical model，and numerical solution for the probe jacket to conduct fluid dynamics simulation.The simulation results show that without a rectification device，the water injected from the inlet collides with the inner wall of the probe sleeve，causing severe turbulence.After entering the outlet pipe，the turbulent state is still maintained，and the direction of the water flow line is chaotic.After adding a rectification device，the turbulence inside the probe sleeve is well suppressed，making the direction of the water flow into the outlet pipe conforming to consistency.This phenomenon becomes more pronounced as the number rectifying element increase.This article aims to simulate the state of the water column after the water flow passes through the outlet， especially after increase of initial water flow velocity. The use of FEM’s muti_physical field simulation function with addition of sound fields has laid the foundation for simulating changes in sound fields under turbulent conditions.

Abstract:

In the process of rotary ultrasonic machining，the change of load will cause amplitude attenuation， which will lead to the decrease of machining accuracy and efficiency. In this paper， in order to solve the problem of amplitude attenuation in the machining process of the rotary ultrasonic machining system with non-contact power supply， the influence of load on the electrical parameters of ultrasonic oscillator is obtained through static loading experiment. On the basis of the static loading experiment， the loading experiment of the non-contact energy transmission system of ultrasonic oscillator is carried out， and the effect of load on energy transmission characteristics is obtained. The results show that the electrical parameters of the ultrasonic oscillator are changed by the combined influence of the load force， the direction of the load force and the characteristics of the machined materials.Change of the electrical parameters of the ultrasonic oscillator leads to the change of the output power of the ultrasonic system with non-contact power supply， which leads to the problem of amplitude attenuation.In this paper， the circuit compensation method of main side series capacitor and secondary side parallel capacitor is adopted to reduce the amplitude attenuation. The research results of this paper provide an experimental basis for solving the problem of amplitude attenuation.

Abstract:

This research focuses on the structure of a certain type of crane ship. It adopts post-weld heat treatment as a measure to eliminate welding residual stress and studies the residual stress status of the structure as well as the effectiveness of the elimination measures. Firstly， two groups of test plates in welding state and after post-weld heat treatment were used to detect and compare the welding residual stress. The results showed that the maximum longitudinal residual stress of the test plate in welding state reached 552.5 MPa， close to the yield strength of the material. The maximum longitudinal residual stress of the test plate after post-weld heat treatment was 385.3 MPa， reduced by 167.2 MPa compared with the welding state， a decrease of about 30%. At the same time， the distribution of residual stress was obtained. Furthermore， post-weld heat treatment was applied to the weld seams of the crane ship''s guide base structure， and stress detection was conducted. The maximum longitudinal welding residual stress was 310.8 MPa， far below the yield strength of the base material.The research indicates that the welding residual stress of the heavy-gauge steel plates in the crane ship is relatively high in the welding state， and measures need to be taken to eliminate the residual stress. Post-weld heat treatment can significantly reduce the level of welding residual stress in heavy-gauge steel plates， which is both economical and easy to operate. Therefore， post-weld heat treatment isrecommended for weld seams of heavy-gauge steel plates during the construction of crane ships to eliminate welding residual stress.