Abstract: Interference-fit fasteners are used in large numbers throughout aircraft structures.
Conventional installation methods are driving fasteners into aperture using pneumatic or hydraulic
tooling, installation damage always occurs using these methods. This paper introduces a new
method of driving interference-fit fastener using stress wave, reports on a comparison of driving
quality between stress wave driving and hydraulic force driving. The experiments completed by
authors indicate that stress-wave method can drive the fasteners with larger interference which
conventional installation method can not implement; stress wave driving method provides high
installation quality and repeatable results compared with the conventional driving method; and
stress wave driving method is convenient to be used. The experiments prove that the protuberant
material produced by stress wave method is less than that of conventional installation methods, this
is advantaged to improve the fatigue strength of joint.
Abstract: The introduction of ceramic particulate into metallic powder will unavoidably lower the
compressibility and formability of the mixed powder. In order to overcome these problems, in this
study, warm compaction was introduced in the forming of an NbC particulate reinforced iron-base
valve-guide cup, which is used in a combustion engine. Warm compaction was used not only
because it can provide compacts with high green density but also it can increase the formability of
the mixed powder. The part composed of an iron-base material which possesses 10wt%NbC with a
relative density of 97.7%, a tensile strength of 815MPa, an elongation of 1.5%, a hardness of
HRC33 and an impact toughness of 11J/cm2. Its working surface composed of an iron-base material
which possesses 15wt% NbC with a high relative density of 98.2%, a tensile strength of 515MPa, a
hardness of HRC 58 and a remarkable tribological behavior. The sintered part successfully passed a
500 hours bench test. No serious wear on the working surface can be observed after the test. Results
indicated that the sintered part has excellent wear resistivity and the NbC particulate reinforced
iron-base composite is a suitable material for parts that work under severe wear condition.
Abstract: Based on the two-stage forming technology, the casting AZ31 Magnesium alloy bar was
forged into cylindrical straight inner gear between the temperature 250°C-400°C. At 250°C, the teeth
of the inner gear are almost formed. But there are some cyclic cracks on the surface of the sample.
When improving the temperature above 300°C, the surface quality of the sample has greatly
improved. According to the result of this experiment, the best temperature range for forging AZ31
magnesium gear is 280°C to 380°C.The forming load gradually reduced with the temperature
improved. At 250°C, the forming load is 93t. At the 400°C, the forming load reduces to 80t.The initial
grain size of AZ31 magnesium alloy bar is 22μm. The microstructure evolution during the warm
deformation was observed by optical microscopy (OM). It is demonstrated that the grain refinement
happened during the deformation process.
Abstract: 3A21 metal sheet was shocked by Nd-glass laser in oblique angle under the function of
pulse energy 42 J, pulse width 23 ns, pulse power 1.2×109 W, the angle between input beam and
normal of sample is 30°. The center of the deformation of the sheet is 3 mm away from the
geometric center. Residual stresses of crossing center side in length direction and the distribution of
space in the positive and negative sides are measured by XRD, which are compressive stress 100
MPa. The diagonal length of the sheet is longer than the one of the crossing center side in length
direction, the force that needs to form in the diagonal direction is bigger, so compressive stress is
much bigger. The capstone of the square sheet is squeezed, the procession seriously increase, so
compressive stress is the biggest one.
Abstract: It is necessary to drill micro holes in some hard brittle materials. Comparing with electro
discharge machining, electrochemical machining and laser machining, the ultrasonic machining
(USM) has unique advantages in hard brittle materials machining. The aim of this paper is to
present experimental work that has been done in micro holes machining by micro USM. The main
machining mechanisms of USM are discussed. It is pointed out that the contributions of each
mechanism to material removal rate are different in different cases. By using micro USM with
workpiece vibration and tool feeding in constant rate, the experiments of micro holes machining are
carried out and the process laws of tool wear are studied. Some phenomena are found and the
causation of causing these phenomena is analyzed. A Ø13μm micro hole is obtained.
Abstract: Si3N4- Si2N2O composites were fabricated with amorphous nano-sized silicon nitride
powders by the hot press sintering(HPS). The Si2N2O phase was generated by an in-situ reaction
2Si3N4(s)+1.5O2(g)=3Si2N2O(s)+N2(g). The content of Si2N2O phase up to 60% was accepted when
the sintering temperature was 1650°C and decreased whether the sintering temperature was increased
or not, which indicated that the reaction was reversible. The mass loss, relative density and average
grain size increased with raising of sintering temperature. The average grain size was less than 500nm
if the sintering temperature was below 1700°C. The sintered body crystaled completely at 1600°C .
The microstructure crystaled in 1600°C indicated that most of the grain size was in 150-250nm. The
aspect ratio of some grains reached 1.5. The superplastic deep-drawing forming could be undertaken
at 1550°C with a forming velocity of 0.2mm/min. The complex-shape gears could be formed by a
sinter-forging technology when the sintering temperature was 1600°C and the superplastic forging
temperature was 1550°C.
Abstract: Micro-flowing technique gained popular applications in microdevices of microelectromechanical
systems (MEMS), and the performance of micro-devices is greatly determined by the
properties of micro-flow. This paper studied the characteristics of different viscosity fluid flowing
over microchannels with different diameters and lengths under low pressure driving, and the
influence of scale effects on the flowing characteristics of low viscosity fluids was also examined.
The experiments studied the flow rate–pressure characteristics of distilled water flowing over
microchannels with diameter of 13 μm, 20 μm, and silicon oil flowing over microchannels with
diameters of 50 μm, 100 μm. The results indicate that, when the diameter of micro-channel is more
than 20 μm, the flowing characteristics of distilled water and silicon oil agrees well with conventional
flow theory, and when the diameter of microchannels is 13μm, the flowing characteristics are related
to the length of micro-channel. When the length is relatively shorter, the flowing characteristics are
almost in agreement with the conventional flow theory. When the length reaches 100 mm, the flow
rate is much higher than the values predicted by theoretical calculation when the length reaches 100
mm. It is obvious that scale effect arises when the length arrives to 100 mm and the velocity slippage
results in the great increase of flow rate.