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Historic quay walls in many Dutch cities are supported by an array of vertical timber piles which run through soft soil deposits and rest on a sand layer, providing end-bearing support. As these structures experience horizontal loads, the foundation piles are loaded in bending. This is the dominant loading case of pile foundations of dams, lock heads, and sometimes bridge abutments as well. To accurately model and evaluate the timber pile foundations, a proper estimate of their bending properties is essential. Therefore the mechanical properties of existing spruce foundation piles, retrieved from a historic quay wall (1905) at Overamstel in Amsterdam, Netherlands, were studied. Six piles were subjected to a four-point bending experiment. The outer fiber stress was kept constant between the point loads, leading to a failure at the weakest cross section. Measurements of the curvature and force distribution were taken along the pile length during loading. In addition, biological decay in the outer layer of the timber piles, also referred to as the soft shell, was identified with microdrillings. Internal strains were measured successfully by gluing fiber-optic wires inside the soft shell of the timber piles. The experiments indicated significant variations in modulus of elasticity and modulus of rupture across the tested population, but indicated a strong correlation. Modulus of elasticity averaged 16.5 GPa with a variation coefficient of 0.30, whereas the modulus of rupture averaged 23.2 N/mm2 with a variation coefficient of 0.26. Bacterial deterioration was found to be independent of both the outer pile diameter and the location along the timber pile. The soft shell had an average thickness of 21 mm, but it did not contribute significantly to the structural strength of the piles. This study could present a template for assessing the remaining service life not only of historic quay walls but also of other timber pile foundations under bending loads. [ABSTRACT FROM AUTHOR]

The acoustic signals used by tool wear monitoring systems adopted in microdrilling are degraded by the noise present in manufacturing environments. To overcome this problem, the present study designed a system containing a 4 × 4 microelectromechanical system microphone array and a three-axis accelerometer to achieve accurate tool wear monitoring in noisy manufacturing environments. Features that were moderately to strongly correlated with tool wear were selected as inputs for this system's one-dimensional (1D) convolutional neural network (CNN) model for predicting tool wear. Pearson correlation analysis revealed that the frequency-domain signal features captured by a 4 × 4 microphone array with minimum variance distortion-less response (MVDR) beamforming had stronger correlations with tool wear than did those captured by a 4 × 4 or 1 × 2 microphone array with delay-and-sum beamforming or by a single microphone; this was because the signals captured by the 4 × 4 array with MVDR beamforming were less noisy. For the aforementioned microphone configurations, under the presence of noise, the 1D CNN model predicted severe wear with higher accuracy when it was trained using fused high-correlation features obtained from the signals captured by the 4 × 4 microphone array with MVDR beamforming and an accelerometer (97.6%) than when it was trained using unfused signal features captured by the accelerometer (86.7%) or the 4 × 4 microphone array with MVDR beamforming (90.3%) alone. The tool wear prediction accuracy obtained using the aforementioned fused features was close to that obtained using fused features acquired from the signals of one microphone and an accelerometer in a quiet environment (97.0%). [ABSTRACT FROM AUTHOR]

Purpose: To investigate the surgical outcomes of arthroscopic pull-out repair for medial meniscus root tear (MMRT) combined with the marrow stimulation procedures (MSP) for accompanying high-grade cartilage lesions. Methods: Patients who underwent arthroscopic pull-out repair for MMRT between 2010 and 2019 were retrospectively reviewed. Patients who had at least 3 years of follow-up were included and classified into two groups according to whether MSP (microfracture or microdrilling) were performed on cartilage lesions in the medial tibiofemoral joint (group 1, patients with International Cartilage Repair Society [ICRS] grade 0–3a lesions and did not undergo MSP; group 2, patients with ICRS grade 3b–3d lesions and underwent MSP). Comparative analyses, including non-inferiority trials, were conducted between groups for subjective and objective outcomes. In addition, group 2 was further divided into two subgroups according to cartilage lesion size and compared with group 1 (group S, ≤ 2.0 cm2; group L, > 2.0 cm2). Results: A total of 94 patients were included (group 1, 68 patients; group 2, 26 patients). There were no significant differences in clinical scores at postoperative 3 years and final follow-up between groups 1 and 2, but group 2 failed to satisfy the non-inferiority criteria compared to group 1 overall. In objective outcomes, group 2 did not meet the non-inferiority criteria for the rate of osteoarthritis progression compared to group 1, and it also showed a significantly higher proportion of high-grade osteoarthritis at final follow-up (P = 0.044) and a higher degree of osteoarthritis progression than group 1 (P = 0.03 for pre- to postoperative 3 years, and P = 0.006 for pre- to final follow-up). In additional evaluations comparing the subgroups of group 2 and group 1, group S showed relatively favourable results compared to group L in objective outcomes at final follow-up. Conclusion: Patients who underwent arthroscopic pull-out repair for MMRT combined with MSP for accompanying high-grade cartilage lesions showed suboptimal outcomes compared to those with no or low-grade lesions at mid-term follow-up. High-grade cartilage lesions ≤ 2.0 cm2 may be candidates for the surgical repair of MMRT if MSP are performed, but those with larger lesions may require alternative treatment strategies. Level of evidence: III. [ABSTRACT FROM AUTHOR]

Micro-EDM is an unconventional technology used to machine every type of electrically conductive material regardless of its mechanical properties. Material removal occurs through electrical discharges between the workpiece and the electrode immersed in a dielectric fluid. In drilling operations, the technology is able to realise microholes with excellent quality in terms of precision, quality surface, roundness, and taper to the detriment of the machining time, which is less than other technologies. Several efforts are being made to improve different features related to the process performance that are severely affected by both the operative conditions, such as the electrode material or the type of dielectric, and process parameters. The typical indexes used to characterise the performance are the machining time, the material removal rate, and the geometric indexes. These indexes are very effective and are easily measurable, but they do not give information about the evolution of the drilling process, which could be irregular due to the different phenomena occurring during machining. The aim of this paper is the development of a method able to elaborate the motion law of the electrode during the micro-EDM drilling operation. In order to do this, a single hole was manufactured in several steps, recording both the machining time and electrode wear for each step. In this way, the actual position of the electrode during the drilling can be measured without the use of a predictive model for electrode wear. It was tested to confirm that the multistep procedure did not introduce new phenomena, in contrast to the traditional drilling operation. This method was used to study the effects of the electrode diameter, the type of electrode, the length of the electrode out of the spindle, and the entity of the run-out on the process performance. The tests were executed on titanium alloy sheets using a tungsten carbide electrode and hydrocarbon oil as the dielectric. It was found that the descent of the electrode into the workpiece was not regular, but it depended on the level of debris concentration in the machining zone. The debris concentration was influenced by the type and diameter of the electrode, its length out of the spindle, and, to a lesser extent, the run-out. This method was found to be a useful method for an in-depth analysis of the micro-EDM drilling process, contributing to a better understanding of the physical aspects of the process. [ABSTRACT FROM AUTHOR]

Recently, there has been a growing awareness of environmental issues, and the concept of sustainability has been introduced. This concept applies to different fields, including the manufacturing industry. This study focuses on the sustainability of the micro-electrical discharge machining (EDM) drilling process. In EDM technology, the critical aspects of sustainability are consumed energy, electrode wear, gas emissions, and generated waste. The operational conditions impact consumption and emissions. The aim of this study is to develop a CO2 efficiency index for evaluating the environmental–economic efficiency of the micro-EDM drilling process. The index was calculated as the emissions that occurred during machining and logistic activities divided by the added value, and it was expressed as the kg equivalent CO2 per unit money. For the emissions, all process activities that have an environmental impact were considered, such as transportation, absorbed energy generation, production of fumes by the dielectric during machining, and emissions attributed to the production of nonconforming pieces. The proposed index was applied to a medical case study in which titanium bone plates were produced for fractures of small body parts. It was found that the process performance significantly depended on the operation conditions of the dielectric fluid and electrode. The material removal rate (MRR) significantly influenced the index. Quality problems and scraping influenced the overall performance significantly, whereas dielectric management had a moderate effect. The optimum conditions were determined by varying the dielectric fluid, electrode material, and process parameters. Demineralized water was the best dielectric because it facilitated a high MRR, whereas hydrocarbon oil resulted in a high quality and a low scrap rate. Vegetable oil caused problems, resulting in a low MRR and poor quality. Further investigations should be conducted to improve its performance in microdrilling applications. [ABSTRACT FROM AUTHOR]

The mechanisms of deep-hole microdrilling of pure Mg material were experimentally studied in order to find a suitable setup for a novel intraocular drug delivery device prototyping. Microdrilling tests were performed with 0.20 mm and 0.35 mm microdrills, using a full factorial design in which cutting speed v c and feed f z were varied over two levels. In a preliminary phase, the chip shape was evaluated for low feeds per tooth down to 1 μm, to verify that the chosen parameters were appropriate for machining. Subsequently, microdrilling experiments were carried out, in which diameter, burr height and surface roughness of the drilled holes were examined. The results showed that the burr height is not uniform along the circumference of the holes. In particular, the maximum burr height increases with higher cutting speed, due to the thermal effect that plasticizes Mg. Hole entrance diameters are larger than the nominal tool diameters due to tool runout, and their values are higher for high v c and f z . In addition, the roughness of the inner surface of the holes increases as f z increases. [ABSTRACT FROM AUTHOR]

Micro-EDM is an unconventional technology used to machine every type of electrically conductive material regardless of its mechanical properties. Material removal occurs through electrical discharges between the workpiece and the electrode immersed in a dielectric fluid. In drilling operations, the technology is able to realise microholes with excellent quality in terms of precision, quality surface, roundness, and taper to the detriment of the machining time, which is less than other technologies. Several efforts are being made to improve different features related to the process performance that are severely affected by both the operative conditions, such as the electrode material or the type of dielectric, and process parameters. The typical indexes used to characterise the performance are the machining time, the material removal rate, and the geometric indexes. These indexes are very effective and are easily measurable, but they do not give information about the evolution of the drilling process, which could be irregular due to the different phenomena occurring during machining. The aim of this paper is the development of a method able to elaborate the motion law of the electrode during the micro-EDM drilling operation. In order to do this, a single hole was manufactured in several steps, recording both the machining time and electrode wear for each step. In this way, the actual position of the electrode during the drilling can be measured without the use of a predictive model for electrode wear. It was tested to confirm that the multistep procedure did not introduce new phenomena, in contrast to the traditional drilling operation. This method was used to study the effects of the electrode diameter, the type of electrode, the length of the electrode out of the spindle, and the entity of the run-out on the process performance. The tests were executed on titanium alloy sheets using a tungsten carbide electrode and hydrocarbon oil as the dielectric. It was found that the descent of the electrode into the workpiece was not regular, but it depended on the level of debris concentration in the machining zone. The debris concentration was influenced by the type and diameter of the electrode, its length out of the spindle, and, to a lesser extent, the run-out. This method was found to be a useful method for an in-depth analysis of the micro-EDM drilling process, contributing to a better understanding of the physical aspects of the process.

The global demand for air travel and air transport is expected to further increase in the next couple of years, and so the environmental protection will also increasingly come into focus again. In the aviation sector, this means not only saving fuel and reducing emissions but also reducing the noise pollution caused by aircrafts. For this purpose, sound-absorbing acoustic liners are used, which consist of a sandwich structure with one perforated skin layer. To reduce weight, these outer layers are often made of carbon fiber-reinforced plastic (CFRP). For manufacturing these CFRP skin layers, laser drilling offers specific benefits, but when it comes to industrial applications, further process improvements are necessary. Although laser microdrilling is a well-known process in laser materials' processing, it has not yet been sufficiently investigated for the processing of carbon fiber-reinforced plastics. This study investigates the quality and efficiency of laser microdrilling with a 1.5 kW nanosecond-pulsed high-power laser for percussion drilling and helical drilling of thin CFRP laminates. The efficiency was evaluated in terms of drilling depth, the amount of energy required to remove a specific volume of material, and the time required to remove a specific volume of the material. The quality evaluation focused on the heat-affected zone and the hole taper. The efficiency and quality results were set in relation to higher-level parameters such as energy fluence in the laser spot, pulse overlap, or total energy applied. This facilitates future transferability to similar laser processes that may use laser machines and system technology with deviating specifications. [ABSTRACT FROM AUTHOR]

In microbiochips and microfluidic devices, microholes are a basic and important feature. The microdrilling of glass materials without cracks is still challenging in the fabrication of glass-based microdevices. This paper investigates the characteristics of microdrilling fused silica using polycrystalline diamond (PCD) tools fabricated by electrical discharge machining (EDM). In particular, peak forces, which are observed at the beginning of drilling, are discussed because crack formations are related to peak forces. To reduce peak forces and to minimize cracks, the effects of drilling conditions, such as tool shape, the surface roughness of a tool, and axial feedrate, were therefore investigated. It was observed that D-shape tools with high surface roughness was useful to reduce the peak force. In through-hole drilling, a sacrificial layer was used to prevent exit cracks, and a variable feedrate was applied to increase drilling speeds. Finally, a dressing process using EDM was conducted to recondition the worn tool's surface. [ABSTRACT FROM AUTHOR]

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This study analyses the possibility of assessing standing-tree wood density by microdrilling during tending forestry work carried out on Norway spruce stands. The research material comes from 4 experimental plots and consists of 270 trees (78 trees = control variant, 85 trees = moderate variant, and 107 trees = strong variant). The research objectives were to: (1) highlight wood density particularities, (2) identify wood resistance to microdrilling particularities, and (3) assess standing-tree wood density by microdrilling. For the control variant, average density recorded values of 0.357 ± 0.021 and 0.386 ± 0.027 g·cm−3; in the moderate variant, values were between 0.359 ± 0.029 and 0.393 ± 0.027 g·cm−3; and the strong variant was characterized by the limits of 0.364 ± 0.020 and 0.397 ± 0.027 g·cm−3. Average microdrilling resistance values were between 16.6 ± 2.6 and 22.5 ± 3.0% for the control variant; the moderate variant was characterized by the limits of 18.3 ± 3.1 and 23.4 ± 3.3%; and the strong variant recorded value of 19.7 ± 2.6 and 20.5 ± 2.6 (1.5)%. The linear regression results showed that microdrilling resistance increased as wood density increased. Additionally, generalized linear models showed that, when using covariates of microdrill resistance and tree diameter at breast height, there was a significant influence on the dependent variable, wood density, for all considered work variants. These results suggest that it is possible to consistently estimate both quality and resistance in Norway spruce standing trees using microdrilling. Our findings suggest that wood density and microdrilling resistance are dependent on biometric and qualitative characteristics, as well as the amount of tending forestry work conducted on Norway spruce stands. [ABSTRACT FROM AUTHOR]

This study analyses the influence of a planting scheme on physical properties of Norway spruce wood. The research material consisted of 326 Norway spruce trees (Picea abies (L.) H. Karst) selected from an experimental plot with four planting variants (2500, 3330, 5000, and 7510 trees·ha−1). The research aspects were: (1) wood density (measured by volumetric method and using microdrilling resistance as proxy), (2) microdrilling resistance, and (3) sound speed. There was a decrease in wood density values (from 0.3376 to 0.3367 g·cm−3) and in microdrilling resistance values (from 15.136% to 14.292%) as the number of trees·ha−1 used for plantation increased from 2500 to 5000. The planting variant with 7510 trees·ha−1 had the largest value (0.3445 g·cm−3 for wood density and 15.531% for microdrilling resistance). Sound speed decreased from 1032.8 to 989.8 m·s−1 as the number of trees·ha−1 increased from 2500 to 7510. These results show a relationship between DBH values and studied physical properties. This relationship is more evident for variants with low planting density (e.g., 2500, 3330 trees·ha−1) than that of dense planting variants (e.g., 7510 trees·ha−1). The explanation may be that the growth of trees in dense plantings is slower; in less dense planting variants, the increase in wood is greater, and as a result, wood volumetric density dependence on the DBH value is greater. [ABSTRACT FROM AUTHOR]

The mechanisms of deep-hole microdrilling of pure Mg material were experimentally studied in order to find a suitable setup for a novel intraocular drug delivery device prototyping. Microdrilling tests were performed with 0.20 mm and 0.35 mm microdrills, using a full factorial design in which cutting speed vc and feed fz were varied over two levels. In a preliminary phase, the chip shape was evaluated for low feeds per tooth down to 1 μm, to verify that the chosen parameters were appropriate for machining. Subsequently, microdrilling experiments were carried out, in which diameter, burr height and surface roughness of the drilled holes were examined. The results showed that the burr height is not uniform along the circumference of the holes. In particular, the maximum burr height increases with higher cutting speed, due to the thermal effect that plasticizes Mg. Hole entrance diameters are larger than the nominal tool diameters due to tool runout, and their values are higher for high vc and fz. In addition, the roughness of the inner surface of the holes increases as fz increases.

In microbiochips and microfluidic devices, microholes are a basic and important feature. The microdrilling of glass materials without cracks is still challenging in the fabrication of glass-based microdevices. This paper investigates the characteristics of microdrilling fused silica using polycrystalline diamond (PCD) tools fabricated by electrical discharge machining (EDM). In particular, peak forces, which are observed at the beginning of drilling, are discussed because crack formations are related to peak forces. To reduce peak forces and to minimize cracks, the effects of drilling conditions, such as tool shape, the surface roughness of a tool, and axial feedrate, were therefore investigated. It was observed that D-shape tools with high surface roughness was useful to reduce the peak force. In through-hole drilling, a sacrificial layer was used to prevent exit cracks, and a variable feedrate was applied to increase drilling speeds. Finally, a dressing process using EDM was conducted to recondition the worn tool’s surface.

[Display omitted] • The parallel transient and selective laser processing using the spatial light modulators is developed. • The methods to combine the two lasers with a different wavelength controlled with each spatial modulator is reported. • Two 100-µm depth 10-µm diameter holes are drilled in 50 µs with the parallel transient and selective laser processing. • The processing condition in the parallel transient and selective laser processing is studied. To use glass as the substrate material in next-generation large-scale integrations and biochips, the high-speed fabrication of high-aspect-ratio microholes is necessary. Transient and selective laser (TSL) processing significantly reduces the processing time per hole. To further improve the processing efficiency, parallel TSL processing using a spatial light modulator is proposed in this study. Two 100-µm depth holes are successfully machined in parallel, in 50 µs. Furthermore, the process control parameters are investigated through high-speed observation and the laser irradiation conditions required for processing are clarified. Parallel processing of three or more holes and depth control of each hole is expected to be realized in future. [ABSTRACT FROM AUTHOR]