Significant Reduction in Energy Consumption and Carbon Emission While Improving Productivity in Laser Drilling of CFRP Sheets with a Novel Stepped Process Parameter Parallel Ring Method

Although laser drilling of carbon fibre-reinforced polymer (CFRP) composites offers the advantages of zero tool-wear and avoidance of fibre delamination compared with mechanical drilling, it consumes considerably more energy during the drilling process. This research shows that by using a new, stepped parameter parallel ring laser hole drilling method, an energy saving of 78.10% and an 18.37 gCO2 reduction for each hole, while improving productivity by more than 300%, can be achieved in laser drilling of 6 mm diameter holes in CFRP sheets of 2 mm in thickness, compared with previous laser drilling methods under the same drilling quality. The key reason for this is an increase in energy input to the inner rings enabling more rapid removal of the material, while the lower energy input for the outer ring provides a shielding trench to reduce the heat loss into the parent material. The results are compared with single-ring laser drilling and multiple-ring laser drilling with constant processing parameters, and a discussion is given on comparing with mechanical drilling and future prospects, including a combined mechanical drilling and laser pre-scribing process.

Evaluation of permissible amplitudes of external impact on free-of-platform inertial navigation systems

In modern aerospace technology, strapdown inertial navigation systems (SINS) are widely used, using fiber-optic (FOG) or ring laser (CLG) gyroscopes. During the operation of such systems, the sensitivity axes are rotated relative to the basic coordinate system. The resulting angles between the axes of the base coordinate system and the axes of sensitivity of the navigation system (non-orthogonality) are one of the factors leading to an increase in the measurement errors of the device, which affects the measurement accuracy. During operation, the system is affected by vibrations of various nature, the impact of which can contribute to the appearance of non-orthogonality. The purpose of this work is to determine the maximum permissible vibration amplitudes affecting the SINS body according to the permissible values ​​of the deviation of the FOG sensitivity axes for two variants of the SINS layout. An approach to determining the permissible amplitudes of an external harmonic impact on the unit of a strapdown inertial navigation system based on fiber-optic or ring laser gyroscopes is considered. A design scheme, mathematical and finite element models for calculating natural frequencies and forced oscillations of a strapdown inertial navigation system unit have been developed. In various frequency ranges, numerical calculations have determined the boundary values ​​of the amplitudes of the external harmonic impact on the base of specific configurations of the SINS assembly. It has been established that dangerous states take place in the region of the 1st natural frequency of the system, as well as near higher frequencies. Comparison of the results for design options 1 and 2 allows us to conclude that in order to weaken the effect of vibrations on the accuracy of the SINS unit, it is advisable that the lowest natural vibration frequencies for the SINS assembly be as high as possible (more than 1000 Hz). Key words: vibration; fiber optic gyroscope; strapdown inertial navigation system; finite element method; natural frequencies and modes of vibration.

Saturable absorption and its consequent effects in bistable erbium‐doped fiber ring laser

The linear absorption in erbium-doped fiber contributes to its excellent role in erbium-doped fiber amplifiers and lasers. A nonlinear optical contribution in the absorption of erbium-doped fiber is responsible for optical bistable action when it is present in a laser cavity. To quantify this effect, the variation of absorption coefficient is measured at different signal powers at multiple wavelengths in the C-band for different EDF lengths, and saturable absorption parameters such as the saturation power are extracted. Then the modification in the output characteristics of erbium-doped fiber ring laser with change in fiber length and in the presence of self-induced saturable absorption effect within the gain medium which leads to optical bistability is measured. By comparing the measured parameters obtained from saturable absorption in erbium-doped fiber and optical bistability in erbium-doped fiber ring laser, we estimated the length of the gain medium which acts as the saturable absorber inside the cavity of the laser. This is useful in constructing bistable lasers with optimized conditions. The temporal evolution of cavity loss and gain with the intra-cavity power and up- and down-thresholds helps in understanding why the down-threshold will be lesser than the up-threshold in bistable laser systems.