Ground Speed Research Articles

Research on Flight Safety Indicators Based on Confidence and Principal Component Analysis

Modern technology protects flight safety, especially in the specific research and application of flight quality monitoring, and similar studies are currently focusing on large-scale reading of flight data, and storing and analysing it. In this paper, the data from switching on the autopilot is extracted and the reliability is firstly investigated using the Cronbach's alpha reliability coefficient method. Considering the various types of data as the questions of the questionnaire, and the result of Min-Max normalisation of the data as the score of the questionnaire, the size of the reliability coefficients of the data for the eight flight segments was finally derived, and the reliability of the data was quantitatively described based on this. In order to filter the importance of factors reflecting flight safety, seven indicators related to flight safety were then extracted. Then, through principal component analysis, the importance of the indicators was analysed by the size of the coefficients, and the degrees of importance, from the largest to the smallest, were as follows: airspeed, ground speed, descent rate, altitude, and attitude.

Scouts vs. usurpers: alternative foraging strategies facilitate coexistence between neotropical Cathartid vultures

Understanding how diverse assemblages of scavengers can coexist on shared ecological resources is a fundamental challenge in community ecology. However, current approaches typically focus on behaviour at carcass provisioning sites, missing how important differences in movement behaviour and foraging strategies can facilitate sympatric species coexistence. Such information is particularly important for vultures – obligate scavengers representing the most endangered avian foraging guild. Their loss from ecosystems can trigger trophic cascades, mesopredator release and disease outbreaks. We provide the first‐ever analyses of GPS location data from wild King Vultures Sarcoramphus papa and Greater Yellow‐headed Vultures Cathartes melambrotus, coupled with trait data (from both wild‐living and museum specimens) and visitation data from camera traps deployed at provisioned carcasses, to characterize vulture flight behaviour and strategies in the Peruvian Amazon. We found marked species differences in several key movement characteristics, including: King Vultures having home‐ranges five times larger, average flight heights four times greater and ground speeds 40% faster than those of Greater Yellow‐headed Vultures. Despite these differences, both species flew similar distances each day (on average), probably due to King Vultures taking 50% fewer flights and spending 40% less time in the air per day. Consistent with these patterns, King Vulture body mass was more than double that of the Greater Yellow‐headed Vulture, with a substantially larger hang wing index (a measure of long‐distance flight efficiency). At carcasses, Greater Yellow‐headed Vultures typically arrived first but were rapidly outnumbered by both King and Black Vultures Coragyps atratus. We find that the movement behaviour of obligate apex scavengers in the western Amazon is linked to their ability to coexist – Greater Yellow‐headed Vultures, a smaller stature ‘scouting’ species adapted to fly low, forage early and arrive first at carcasses, are ultimately displaced by larger‐bodied, wider ranging King Vultures at large ephemeral carrion resources. Expansion of future GPS tracking initiatives could facilitate the exploration of direct facultative interactions from animal movement data and give further insight into how diverse communities assemble and interact.

Four-Dimensional Aircraft Trajectory Prediction Based on Generative Deep Learning

Aircraft four-dimensional (4D) trajectory prediction (TP) is among the critical techniques of current existing automation systems in air traffic management (ATM), which is also the basis of future airspace operation models. This paper proposes a 4D TP method based on a conditional tabular generative adversarial network (CTGAN). The model is trained and tested using historical 4D trajectory data from the Hong Kong region. It is then compared with the most extensively researched conditional generative adversarial network (CGAN) and LSTM methods in the field of TP. The results show that Jensen–Shannon (JS) divergence, maximum mean discrepancy (MMD), and mean Euclidean distance (MED) of the model evaluation metrics for the selected route are 0.0539, 0.0150, and 0.0085, respectively. This confirms that the model for predicting 4D trajectory can accurately learn complex airspace’s trajectory distribution characteristics. Compared with the CTGAN algorithms shown in previous studies, the enhanced CTGAN approach developed in our research can reduce around 10% running time and 20% MED. Compared to CGAN, it results in an 81.55% reduction in MED. Compared to LSTM, when predicting with a 10-minute time span, the average mean absolute error for parameters latitude (Lat), longitude (Lon), geometric height (GH), and ground speed (GS) decreases by 7.76, 84.48, 81.98, and 36.51%, respectively.

Characterization and Analysis of Inconel 718 Alloy Ground at Different Speeds

Inconel 718 (IN718) alloy is widely applied to fabricate high temperature resistant or corrosion resistant parts due to its excellent mechanical performance. However, the machining of IN718 alloy is difficult as it may cause serious tool wear and poor surface quality (SQ) of the workpiece. In this work, grinding experiments on IN718 alloy at different speeds were conducted by using a CBN grinding wheel. The relationship between grinding speed, SQ and subsurface damage (SSD) was well studied. With increasing grinding speed, surface roughness decreased, and SQ was greatly improved. Meanwhile, the microhardness of the grinding surface declined as the grinding speed increased. The SSD depth was almost unchanged when the grinding speed was lower than 15 m/s, then it decreased with higher grinding speeds. It was attributed to the mechanical-thermal synergistic effect in the grinding process. The results indicated that increasing grinding speed can effectively improve the SQ and reduce the SSD of IN718 alloy. The conclusion in the work may also provide insight into processing other hard-to-machining materials.

Atomic-scale simulation of ultrasonic vibration-assisted polishing process for graphene/GaN-layered composites

In the realm of semiconductor materials, the integration of graphene (Gr) and gallium nitride (GaN) has emerged as a promising avenue for enhancing device performance. In this study, a Gr/GaN layered nanocomposite was constructed using molecular dynamics simulation and the LAMMPS code. Diamond abrasive was pressed into the composite at a speed of 50 m/s at 300 K, followed by ultrasonic vibration-assisted polishing on the (0001) plane along the [01‾10] direction. By rigorously exploring various factors such as number of Gr layers, vibration amplitudes, vibration frequencies and grinding speeds, the study elucidates the intricate mechanisms governing material removal and subsurface damage. Key findings reveal optimal processing conditions, including three layers of Gr, an amplitude of 5 Å, a vibration frequency of 80 GHz and a grinding speed of 100 m/s, which result in enhanced material removal rates and improved surface quality. Additionally, the insertion of Gr layers within the GaN matrix demonstrates a remarkable reduction in friction and wear rates, highlighting the potential for enhancing device reliability and performance. This comprehensive investigation not only advances our understanding of ultrasonic vibration-assisted grinding processes but also underscores the transformative impact of Gr/GaN composites in semiconductor device fabrication.

Cotton (Gossypium hirsutum) Response to Plant Protection Products using Different Spray Nozzles

Application of dicamba to dicamba-tolerant cotton (Gossypium hirsutism L.) cultivars (Xtend Cotton, Bayer Crop Science, Research Triangle Park, NC) requires use of nozzles that deliver large spray droplets to avoid off-site movement through particle drift onto susceptible crops and other plants including endangered species. Twenty trials over a three-year period were conducted to determine if nozzles required to deliver dicamba plus glyphosate would be equally effective in delivering other pesticides including the herbicide glufosinate, the plant growth regulator mepiquat chloride, the insecticide bifenthrin plus dichrotophos and co-application of ethephon plus thidiazuron plus tribufos for removal of cotton foliage to improve harvest efficiency. Agrichemicals were applied using: a) Air Induction (AI) nozzles for agrichemicals except dicamba plus glyphosate b) Turbo Teejet Induction (TTI) nozzles for all agrichemicals c) TTI nozzles for glufosinate and dicamba plus glyphosate and AI nozzles for other agrichemicals. Applications were made in 145 L/ha at 152 kPa at a ground speed of 5 km/h. Cotton height at the end of the season, node above first fruiting branch, nodes above cracked boll, node of uppermost boll, total nodes, lint yield, and cotton fiber quality were similar regardless of nozzles used to deliver agrichemcials. Control of a complex of broadleaf signal grass (Urochloa platyphylla L.), goosegrass [Eleusine indica (L.) Gaert.], and large crabgrass (Digitaria sanguinalis L.) and Palmer amaranth (Amaranthus palmeri Watts.) was slightly lower when glufosinate was applied with TTI nozzles rather than AI nozzles. However, control of these weeds was similar regardless of nozzle selection when dicamba plus glyphosate was applied after glufosinate. These results suggest that growers can use nozzles that limit off-site movement through particle drift of agrichemicals throughout the cropping cycle with no major adverse effect on weed control and cotton growth and yield.

Performance Test of Coconut Shell Grinding Machine For Pyrolysis Process

Coconut shell is a solid waste of biomass from processed coconuts separated from the flesh. Coconut shells can be reprocessed into products of high economic value. Coconut shells can be processed for bio-oil production via high-temperature pyrolysis. In the pyrolysis process, the coconut shell raw materials are reduced in size to facilitate combustion. The aim of this research was to test the performance of the modified coconut shell grinding machine, determine the effect of water content on the milling process, achieve coconut shell sizes of 3, 5, and 10 mm to enhance the pyrolysis process, and analyze the economics of grinding machine engineering. The size reduction process was carried out using a custom-designed coconut shell grinder that was altered in its sieve section. The sieve sections had diameters of 10, 5, and 3 mm. The coconut shell to be ground had a moisture content of 8–10%. The grinding machine capacity varies with each size, namely 10 mm, 5 mm, and 3 mm, achieving throughput rates of 14.892 kg/h, 7.214 kg/h, and 2.94 kg/hour, respectively. The resulting yield was notably high, ranging from 95 to 96.780%, and the associated yield loss remained low, between 3.2% and 4.8%. During the material size tests, the working RPM was observed at 630.6 for 10 mm, 711.2 for 5 mm, and 1017.18 for 3 mm, and these RPM variations influence the grinding speed.

Field Sprayer with Application Rate Control Using Fast Response Proportional Valves under Variable Speed Conditions

In modern agriculture, which is characterised by dynamic field environments, challenges are faced in maintaining consistent application rates due to varying tractor speeds, field conditions, and certain calibration errors. Conventional control systems, which rely on slower valves, have difficulty adapting to these dynamic field conditions. By contrast, the integration of fast-acting proportional valves improves the precision and flexibility of flow rate adjustment during spraying applications. This research focused on evaluating the accuracy of spraying applications under different tractor speed conditions through field experiments and data analysis. This study involves a field sprayer with boom wings divided into right and left sections, where the flow rate of the liquid to each section is controlled by proportional valves with a 3 s full opening and closing time, dependent on speed information. Using a closed-loop control system consisting of a flow meter, proportional valve, and PLC, the valves are controlled by the PLC’s internal PID blocks. Observations reveal that as the tractor speed increases to a certain level, the system effectively adjusts the application rate close to the target value and maintains control against the changing ground speed during all field tests. The study included five different application tests, with target application rates of 100, 150, 200, 250, and 300 L ha−1, with each repeated three times, resulting in a total of 15 field tests at different ground speeds. During these tests, the data were meticulously recorded every second, covering the tractor speed, flow rate, and pressure values for both right and left boom sections, along with regulator pressure, proportional valve opening rates, and application rates. The durations for each application rate were documented alongside instances within specified periods where error boundaries of ±10% were exceeded. During the total test duration of 9734 s, the actual application rate value exceeded error boundaries during only 209 s. Within the application durations, the speed variation intervals ranged from 5.10 to 10.23 km h−1, 4.64 to 9.91 km h−1, 3.68 to 7.89 km h−1, 4.80 to 8.21 km h−1, and from 4.90 to 8.69 km h−1. The absolute percentage mean application errors were recorded as 2.81%, 2.68%, 2.28%, 2.14%, and 2.51% for respective application rates. Furthermore, statistically significant correlations (p < 0.01) were identified among the variables (speed, valve opening rate, flow rate, pressure) in both the right and left boom sections across all application rates.

Suitability of Using LA Abrasion Machine for the Nano Manufacturing of Palm Oil Fuel Ash and Incorporating in Mortar Mixture

Background In order to enhance the properties of palm oil fuel ash-based mortar, researchers have explored the concept of reducing palm oil fuel ash (POFA) to a nanoscale. While previous studies have utilized ball milling machines with high grinding speed to achieve nano-scale POFA, the Los Angeles abrasion machine, which is more readily available and has a slower grinding speed, has been rarely employed. Objective The study aimed to investigate the suitability of using a Los Angeles abrasion machine with a low grinding speed to produce nano palm oil fuel ash. This paper also provides a comparison of the effect of using the nano POFA with different particle sizes within the range of 982 to 150 nm on the mortar’s flowability and compressive strength. Methods To produce nano-size palm oil fuel ash using the Los Angeles abrasion machine, the received palm oil fuel ash was thermally treated and ground using a Los Angeles abrasion machine with varying grinding periods. The grinding process parameters were kept constant, but second grinding periods of 50,000, 80,000, and 110,000 cycles were introduced. All three types of nano palm oil fuel ash were analyzed for their physical properties, chemical properties, morphology, and mineralogy. Furthermore, these nano palm oil fuel ashes were incorporated into a designed mortar mix along with micro palm oil fuel ash. The mortar’s fresh properties and compressive strength at different curing ages were observed and analyzed. The relationship between various factors, such as the replacement rate of micro, nano palm oil fuel ash, the grinding cycles of nano POFA, and the corresponding responses, specifically the compressive strength at different curing ages, was analyzed and explained using the response surface methodology. Results The 110k cycle nano palm oil fuel ash had a smaller particle size of 103.1 nm, while a particle size of 529 nm and 325 nm was found in the 50k and 80k cycle nano palm oil fuel ash. In terms of the combination of micro and nano palm oil fuel ash in the mortar, increasing the dosage of nano palm oil fuel ash contributed to improvements in flow diameter and compressive strength. However, the opposite trend was observed with micro palm oil fuel ash. The optimal mix design for the combination involved using 10% micro and 2 to 3% nano palm oil fuel ash. This composition led to an improvement rate of 7.9%, 1.48%, and 4.6% in compressive strength at 7, 28, and 90 days, respectively. While, the response surface methodology’s numerical optimization also supported the use of a similar combination. However, it additionally recommended employing the 50,000-cycle nano palm oil fuel ash in the mortar for earlier curing stages, while the 110,000-cycle nano palm oil fuel ash was suggested for later curing stages. Conclusion Los Angeles abrasion machine could be utilized to produce nano palm oil fuel ash with a particle size up to 103 nm with the aid of designed parameters. In this mortar mix design, the impact of a small variance in nano palm oil fuel ash’s particle size was trivial compared to the replacement rate of micro palm oil fuel ash on the mortar’s compressive strength.

Comparative study on grinding kinetics behavior of vanadium-titanium magnetite ore before and after microwave pretreatment

Vanadium-titanium magnetite underwent closed circuit crushing before and after microwave pretreatment. Subsequently, batch grinding tests were conducted on the crushed products, with varying grinding times. Ultimately, the m-order grinding kinetics model of the ore was established both before and after microwave pretreatment. The results show that microwave pretreatment causes a significant increase in the number of micro-cracks on the ore's surface. Moreover, the specific surface area and pore volume of the ore increase by 17.29% and 40.98% respectively. These changes result in a reduction in the mechanical properties of the ore. During the grinding tests, the number of micro-cracks is found to be the primary factor influencing the grinding speed in the initial stage. However, as the grinding progresses, the grinding probability becomes the main factor affecting the grinding speed. The coarse particle size of the microwave-treated ore exhibits a significantly higher grinding speed than the untreated ore. Conversely, the grinding speed of fine particle size ore change slightly. The application of microwave-assisted grinding for vanadium-titanium magnetite proves advantageous in improving the particle size composition of the grinding product. Consequently, this can lead to enhanced separation efficiency and concentrate quality.

Optimization of the parameters of a ground speed meter of low-flying aircraft based on the application of the theory of optimal filtration

The basic principle of parametric optimization according to the criterion of minimax of variance of the resulting error of estimation of the measured parameter is considered using the example of one of the main elements of an integrated measuring system – a ground speed meter. The meter consists of a Doppler ground speed sensor (location) and an accelerometer with a longitudinal axis of sensitivity (inertial). Based on the data on their measurement errors, the coefficients of the transfer functions of each channel of the meter containing these sensors were optimized. The result of the research is a comparative analysis of the resulting accuracy of the optimized meter for the invariant and non-invariant cases, based on the obtained graphs of the frequency distribution of variances. A reasonable conclusion is made about the advantage of an invariant or non-invariant meter depending on the frequency of the signal. The Matlab R2015a software was used for calculations.

Investigation of seeding performance of a novel high-speed precision seed metering device based on numerical simulation and high-speed camera

Numerical simulation and high-speed photography technology are used in this work to obtain the key factors affecting the seeding performance of a novel high-speed centrifugal filling-cleaning precision seeding metering device under different conditions. The effects of key parameters, including seed-metering diversion turbine structure, dynamic wind pressure, seed quantity, and ground speed, on the seeding performance of the high-speed seed metering device are investigated. The results show that a diversion turbine structure with diversion and controlled disturbance flow increases seed pressure and enhances the filling process. Meanwhile, a correlation between dynamic wind pressure and seed movement velocity is established using a high-speed camera-based experimental approach. Maintaining 24 internal seeds is crucial to guaranteeing the quality of feed index. Specifically, under the simulation conditions, when the ground speed is 14 km/h (corresponding to a rotation speed of 194.5 rpm), the corresponding dynamic wind pressure is identified as 1.5 kPa, the corresponding seed plate speed is 2 m/s, the corresponding optimal feeding rate should be maintained at about 14 seeds/s, and the seed inlet velocity is 3 m/s. Additionally, the results of comprehensive bench and field seeding performance experiments demonstrate that, as the seeding speed increases, there is no apparent seeding performance decline, and even under high-speed operational conditions, the quality of feed index under different ground speeds exceeds 90%.

Precision of grain yield monitors for use in on-farm research strip trials

On-farm research (OFR) has become popular as a result of precision agriculture technology simplifying the process and farm software capabilities to summarize results collected through the technology. Different OFR designs exists with strip-trials being a simple approach to evaluate different treatments. Common in OFR is the use of yield monitors to collect crop performance data since yield represents a primary response variable in these type studies. The objective was to investigate the ability of grain yield monitoring technologies to accurately inform strip trials when frequent yield variability exists within an experimental unit. A combination of six sub-plot treatment resolutions (TR) that differed in length of imposed yield variation (7.6, 15.2, 30.5, 61.0, 121.9, and 243.8 m) were harvested at combine ground speeds of 3.2, 6.4, 7.2, and 8.1 kph, depending on study site (three study sites total). Intentional yield differences in maize (Zea mays L.) were created for each sub-plot by alternating the amount nitrogen (N) applied: 0 or 202 kg N/ha. Yield was measured by four commercially available yield monitoring (YM) technologies and a weigh wagon. Comparisons were made between the accumulated mass of the YM technology and weigh wagon through percent differences along with testing the significance of the plotted relationship between YM and weigh wagon. Results indicated that yield monitoring technology can be used to evaluate strip trial performance regardless of yield frequency and variability (error < 3%) within an experimental unit when operating within the calibrated range of the mass flow sensor. Operating outside of the calibrated range of the mass flow sensor resulted in > 15% error in estimating accumulated weight and overestimation of yield by 23%. Finally, no significant differences existed in estimating accumulated weight values between grain yield monitor technologies (all p-values ≥ 0.54).

Comparison of data-based and modeled-based analysis of aircraft departure noise using noise monitor network recordings

A comparison of data-based regression analysis and modeled-based analysis of aircraft departure noise variations using airport noise monitor network recordings is presented. Accurate modeling of aircraft noise is useful for the assessment of departure procedures and provides insight into the noise reduction potential of noise abatement flight procedures. In addition, many airports employ monitor networks that continuously record noise data produced by aircraft on departure, which can be used for assessing potential factors leading to variation in departure noise and for comparison to results from modeling methods. In this paper, departure noise variations of Boeing 737-800 aircraft are correlated to departure climb procedure factors using both data-based approaches incorporating recorded noise collected at the Seattle International Airport monitor network, and a method to model departure noise from on altitude, ground track, and ground speed from recorded operational surveillance data. Examples using both approaches indicate altitude and velocity result in the highest correlating factors for noise at the three noise monitor locations studied. Limitations and areas of needed improvement for the different noise modeling methods are highlighted.

Longitudinal-torsional compound ultrasonic vibration end grinding sapphire: A study on surface topography and roughness

Owing to excellent physical and optical characteristics, Sapphire has wide applications in detection, military, photoelectric and other industries. Nevertheless, it's difficult to use the conventional processing methods to process sapphire with high precision and efficiency due to its hardness and brittleness. This study adopted longitudinal-torsional compound ultrasonic vibration end grinding (LTUEG) method to grind sapphire. Firstly, the grinding trajectory equation of single grain under LTUEG was established. Then, combining with the motion state of single grain, the removal mechanism of sapphire under LTUEG was clarified. Finally, a comparative experiment between LTUEG and conventional end grinding (CEG) of sapphire was conducted, and the effects of processing parameters on surface topography and surface roughness were investigated. Results showed that surface roughness declined with grinding speed, enhanced with feed rate and grinding depth, declined first and then went up with amplitude, and the minimum value was 0.522 μm. Compared with CEG, LTUEG could significantly reduce the surface roughness, with a maximum reduction of 20.98 %. LTUEG could reduce the pits size. Meanwhile, when the longitudinal amplitude AL was 0.8 μm, the average pits length and pits depth reached the minimum, which were 33.13 μm and 5.296 μm, respectively. The research found that LTUEG could reduce block spalling, increase the ratio of plastic domain removal as well as improve the surface flatness of workpiece.

Investigating image-based fallow weed detection performance on Raphanus sativus and Avena sativa at speeds up to 30 km h−1

Site-specific weed control (SSWC) can provide considerable reductions in weed control costs and herbicide usage. Despite the promise of machine vision for SSWC systems and the importance of ground speed in weed control efficacy, there has been little investigation of the role of ground speed and camera characteristics on weed detection performance. Here, we compare the performance of four camera/software combinations using the open-source OpenWeedLocator platform – (1) default settings on a Raspberry Pi HQ camera (HQ1); (2) optimised software settings on a HQ camera (HQ2), (3) optimised software settings on the Raspberry Pi v2 camera (V2); and (4) a global shutter Arducam AR0234 camera (ARD) – at speeds ranging from 5 km h−1 to 30 km h−1. A combined excess green (ExG) and hue, saturation, value (HSV) thresholding algorithm was used for testing under fallow conditions using tillage radish (Raphanus sativus) and forage oats (Avena sativa) as representative broadleaf and grass weeds, respectively. ARD demonstrated the highest recall among camera systems, with up to 100 % recall for tillage radish and 91.6 % for forage oats at 5 km h−1. At 30 km h−1 ARD recall for forage oats declined (P < 0.05) by 12.4 %. There was no significant change for tillage radish. All cameras experienced a decrease in recall as speed increased. The highest rate of decrease was observed for HQ1 with 1.12 % and 0.90 % reductions in recall for every km/h increase in speed for tillage radish and forage oats, respectively. Detection of the ‘grassy’ forage oats was worse (P < 0.05) than the broadleaved tillage radish for all cameras. Despite the variations in recall, HQ1, HQ2, and V2 maintained near-perfect precision at all tested speeds. The variable effect of ground speed and camera system on detection performance of grass and broadleaf weeds, indicates that careful hardware and software considerations must be made when developing SSWC systems.

Towards understanding the crack suppression mechanism in brittle materials with high grinding speed at different temperatures

Ductile-regime grinding has been used to eliminate the formation of subsurface cracks by setting an extremely small depth of cut (DOC). The critical DOC is affected by multiple factors, including the grinding speed and material temperature. The underlying mechanism of DOC affected by the grinding speed is still unclear. To reveal the role of grinding speed and material temperature during the formation of cracks, we conducted a series of single-point grinding experiments with the different grinding speeds (26.7–192.3 m/s) and the initial material temperatures (25–200 °C). The experimental results showed that cracks were suppressed with an increase in the grinding speed and initial material temperature even when the DOC was much deeper than the critical DOC determined by the ductile-regime grinding. To understand the mechanisms underlying crack nucleation and suppression, we conducted systematic molecular dynamics simulations. Both simulation and experimental results showed that a crack can be formed by a single slip band. The crack nucleates from a microvoid within the slip band. With the aid of the local tensile stress on one side of the slip band tip, the crack nucleation forms an opening crack. The crack suppression is primarily caused by the high‐pressure field during high‐speed grinding, where the high‐pressure field superposes the local tensile stress to forming a compressive stress state that prevents crack nucleation. In addition, the brittle‐ductile transition is induced by the high temperature on the surface during high‐speed grinding. This study provides insights into building the DOC criterion for different grinding speeds and temperatures based on a ‘bottom-up’ approach.

Surface damage characteristics and identification based on acoustic emission in diamond point grinding carbon/carbon ceramic matrix composites

This study mainly investigated the effect of machining parameters on acoustic emission (AE) characteristics in grinding three-dimensional carbon/carbon ceramic matrix composites with superabrasive diamond grinding points. Signal processing techniques including fast Fourier transform (FFT) and short-time Fourier transform (SWFT) were applied to evaluate frequency features of AE signals. The RMS values were used as an indicator to detect grinding energy releasing characteristics. Results indicated that grinding speed and grinding depth were the main influencing factors on RMS values, while feed speed presented limited effects. The maximum undeformed chip thickness hmax and active grits number were two key factors affecting RMS variation of the AE signals, which corresponded to the intensity of single AE source and the number of total AE ones, respectively. The material removal mechanisms were studied via detailed SEM micrographs of machined surfaces, revealing that fiber fracture and debonding were the main material removal modes in point grinding carbon/carbon composites. The material removal mode can be possibly identified from the frequency of AE signal, as the band of 12–35 kHz mainly corresponded to fiber fracture, 35–70 kHz referred to debonding between the fiber and matrix, 70–90 kHz indicated the frictions, and the fourth band (90–120 kHz) was related to the matrix cracks.

Investigation on tearing damage of CFRP circular cell honeycomb in end-face grinding

CFRP circular cell honeycomb has promising applications in the aerospace field due to its excellent mechanical properties. However, a large number of periodically distributed tearing damages severely restrict the high-quality machining of CFRP circular cell honeycomb. This paper investigates the formation mechanism of tearing damages during end-face grinding of CFRP circular cell honeycomb and proposes suppression strategies. In this paper, a maximum undeformed chip thickness model considering tearing damage distribution is developed, and the evolution behavior of tearing damage is studied by combining the material removal process and grinding force. The grinding force and maximum tearing damage depth in different grinding conditions are analyzed. The results show that the formation of tearing damage in the cut-in stage is related to the weak stiffness of thin walls and the radial grinding force. The radial grinding force and maximum tearing depth can be altered by changing the maximum undeformed chip thickness which can be adjusted for different grinding speeds, feed rates, and offset ratios. The low-damage machining of CFRP circular cell honeycomb can be achieved by using a large offset ratio and variable feed rate.

Comprehensive investigation into grinding characteristics and damage behavior of Cf/SiC composite modified by picosecond-laser ablating

Cf/SiC composite is known as difficult-to-machine materials. This study introduced laser-ablating assisted grinding (LAAG) method, and explored the relationship between processing parameters and surface/subsurface damage behavior of Cf/SiC composite. It was revealed that SiO2 ablation products with a loose structure were formed during picosecond-laser ablating, and the ablated layers showed excellent machinability during grinding. Cf/SiC composite underwent brittle removal during conventional grinding (CG); however, significant ductile fracture and smeared removal appearance were clearly observed on the ground surfaces during LAAG. As the grinding speed increased, the grinding forces during LAAG were further decreased, and the brittle-ductile transformation of the normal fiber became more significant. The increase of feed speed would increase the grinding forces and enhance the brittle removal behavior of Cf/SiC composite. The laser power affected the machined quality through the ablation depth and the ablative transformation, and a smaller laser scanning distance would result in a flatter ground surface. Furthermore, subsurface damage of Cf/SiC composite after LAAG was slight, which primarily displayed as interface debonding and SiC matrix cracking. The grinding chips generated during LAAG were primarily composed of cut fiber-bundle and curled SiC matrix, rather than macro-fractured fiber and matrix with unordered size and shape.