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Cement-based composite is a kind of heterogeneous and discontinuous material. It is not appropriate to conduct stress analysis on a model constructed by continuous mean theory when subjected to external loads. A granular flow model based on discrete element theory is constructed to simulate the dynamic process of cementstabilized macadam during uniaxial compression test in this article. The appropriate contact bonding model is selected, and the contact parameters are calibrated. After the uniaxial compression test in the laboratory, the relative displacement, stress transfer process and crack propagation between aggregate particles in the structure are verified by the results calculated by the model. It can be seen from the research results that the parallel bond model can well reflect the mechanical characteristics of cementstabilized macadam. In the process of the specimen being loaded, the vertical displacement between particles leads to the specimen being compacted, and the horizontal displacement between particles leads to the crack. The displacement angle of cementitious particles in the upper model is larger than that of coarse aggregate. The displacement angle of cementitious particles in the lower model is less than that of coarse aggregate. The particle displacement angle generally shows a decreasing trend. [ABSTRACT FROM AUTHOR]

Trabecular bone plays an important role in the load-bearing capacity of the femur. Understanding the structural characteristics, biomechanics, and mechanical conduction of the trabecular bone is of great value in studying the mechanism of fractures and formulating surgical plans. The past decade has witnessed unprecedented progress in imaging, biomechanics and finite element analysis techniques, translating into a better understanding of trabecular bone. This article reviews the research progress achieved over the years regarding femoral trabecular bone, especially on factors influencing the strength of the proximal femoral cancellous bone and cancellous bone microfractures and provides a comprehensive overview of the latest findings on proximal femoral trabecular bone and their clinical significance. [ABSTRACT FROM AUTHOR]

The root cause of premature failures in relatively thin (

Flexible strain sensing system has a broad application prospect in the field of personalized monitoring. Here, a flexible intelligent sensing system based on the synergistic effect of sensor technology, communication technology, and computer technology has been designed to monitor the strain distribution of the measured objects directly. The system consists of several sensing modules that can be customized according to actual needs, each of which is composed of flexible sensing arrays that can be closely attached to the surface of the object in different directions to obtain tiny strain signals. The single sensor using PDMS as the flexible substrate and Ni‐Au metal thin film as the sensing layer is easy to prepare and adjust the performance. By artificially fabricating bioinspired parallel cut‐through channel cracks on the metal thin film, high sensitivity in a small sensing range (gauge factor value up to 4500 for 1.4% strain), fast response time (25 ms), and excellent mechanical stability of nearly 2000 cycles of strain sensors are achieved. Meanwhile, combined with a PI‐based ultra‐thin flexible signal processing circuit, the system exhibits promoted flexibility, higher sensitivity, better adaptability to complex environments, and finally displays the 2D mapping of strain distribution precisely in each part of the measured object in real‐time on a computer. This flexible intelligent strain sensing system can work for deformation detection, damage monitoring, motion tracking, and other strain sensing fields. [ABSTRACT FROM AUTHOR]

Heritage buildings always pose challenges due to experiencing high temperatures and pressure over time. Sandstone is one of the common sedimentary rock types used for these buildings. Therefore, it is very important to understand the microstructural variations of rocks associated with these constructions along with the mechanical variations. In this study, the microstructural and mechanical alteration of selected types of sandstones is investigated after it is heated from room temperature to 800 °C. Micro X-ray computed tomography (µXCT), X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry (TG) and derivative thermogravimetry (DTG) techniques were used to identify the physical, chemical, mineralogical and microstructural changes of sandstone after different heat treatments. The mechanical alteration of the heated rock specimens was also studied using the point load index (PLI). The main changes in microstructure were observed when the sandstone's temperature was greater than 400 °C. The total porosity measured by µXCT of sandstone increased by more than 70% at 800 °C compared to its porosity at room temperature. When the temperature increases, the open porosity increases while the closed porosity decreases. Noticeable changes in rock mineralogy were identified at temperatures exceeding 400 °C, which can be attributed to the phase transition of quartz, decomposition of feldspar and dehydroxylation of kaolinite. The TG and DTG analyses and point load index were in good agreement concerning these changes in rock mineralogy. Microstructural variation is one of the main reasons for the discrepancy in threshold values between different sandstones. [ABSTRACT FROM AUTHOR]

One of the important parameters in electrical discharge machining is the presence of micro cracks on the workpiece surface (recast layer). Therefore, the aim of this study was to investigate the possibility of increasing the mechanical properties of aluminum surface by alloying elements (copper and nickel) diffusion to the recast layer and thus removing surface micro cracks. For this purpose, pulse on time and pulse current in with and without ultrasonic vibration have been considered as input parameters and the presence of surface micro cracks has been investigated using microscopic images. Also, the yield stress of the surface layer was calculated using the surface micro hardness. Based on the obtain results, surface without micro cracks has been created on the aluminum surface due to the diffusion of copper and nickel into the workpiece surface which increased aluminum surface yield strength from 90MPa to 280MPa without ultrasonic vibrations and to 310MPa while applying ultrasonic vibrations. In other words, ultrasonic vibrations cause an average of 20% increase in surface layer yield strength. In addition, according to the wear test, in the case of using ultrasonic vibration, improving the mechanical properties of the surface has caused thinner grooves on the aluminum surface.

The root cause of premature failures in relatively thin (<50 mm) asphalt surfaced roads is often a challenge to solve during forensic investigations in South Africa (SA). This description is based on peer review type discussions with forensic investigations experts as well as published research papers. The areas of ignorance or areas where research effort is needed are identified. These observations serve to identify areas of new knowledge needed in terms of actual verification with measurements, measurement technology, and modeling of the observed phenomena. The main objectives of this discussion paper are to highlight the evolution of distress development in asphalt layers starting from the identification and description of the kind of microcracks, effects of microcracks in the debonding of the asphalt layer from lower layer, and vehicle–pavement interactions (VPI) of moving truck wheels focusing on the thin asphalt layer. Specific reference is made to the need to measure and model the effects of bow waves in front of and next to the loaded rolling wheel. [ABSTRACT FROM AUTHOR]

In order to understand the nonlinear characteristics of granite after exposure to high temperature, fracture tests were carried out. The fracture process of granite was monitored by combining digital image correlation (DIC) method and acoustic emission (AE) technology, and the changes of microcracks in granite after high-temperature treatment were observed. The apparent fracture toughness of granite decreased significantly after high-temperature treatment and showed obvious size effect, which is consistent with the size effect law of Bažant. The combined observations by DIC and AE showed that the crack of granite at room temperature started to grow significantly only when it approached the failure load, and the fracture process was rapid. However, the crack growth was observed clearly in the early stage of loading for the granite subjected to high temperature, and the process was slow and persistent. After granite was heated at high temperature, the critical crack tip opening displacement (CTODc), AE b value, effective fracture process zone length, and many other indicators all increased significantly. This indicates that the fracture types of granite changed from brittle to ductile. The microscopic results showed that the granite microcracks developed after high-temperature treatment, the number of microcracks increased significantly, and the porosity and fractal dimension increased. Finally, the relationship between work of cohesion and cumulative AE counts was estimated based on the fictitious crack model. The results showed that there was a significant linear correlation between the two variables, regardless of room temperature granite or heat-treated granite. The work of cohesion can characterize the activity of microcracks in the fracture process zone and it can be quantified by AE technology. This provides a new way to study crack propagation by AE technology. [ABSTRACT FROM AUTHOR]

The characterization of micro cracks on metal surface plays an important role in the process of manufacturing and using, which has attracted a lot of attention. This is mainly due to the fact that the size of defects is smaller and the depth of defects is difficult to predict compared with metal materials with larger plane, which is still challenging. In order to solve this problem, this paper proposes a characterization method of surface defects based on reflective laser thermography, and designs a laser heating nondestructive testing system based on reflection. The system includes a semiconductor laser to heat the surface of metal cracks, and an infrared imager to record changes in the temperature field of the metal surface. In the process of data analysis, an Otsu adaptive threshold segmentation method is selected to quantify the defect size, which can control the quantification accuracy of defect size within 25%. A derivative analysis method is proposed to quantify the depth of defects, which can control the depth quantification accuracy of tiny defects within 7%.

AISI D3 die steel is extensively used in longrun dies for blanking, forming, deep drawing, and thread rolling. Among all the non-traditional machining processes, the Electric Die Sinking Process (EDSP) is mostly employed to manufacture these long-run dies. The EDSP method produces a surface of high quality, which impacts product performance significantly. The surface roughness of AISI D3 die steel is examined in relation to a number of parameters, including peak current, pulse-on duration, gap voltage, and powder concentration. Copper is selected as the tool. Orthogonal array concept coined by Taguchi has been deployed to execute the experiments. It is clearly understood from the results that powder concentration has a key impact on machined surface quality by lessening the generated cracks and enhancing the surface finish by 20%. Further, peak current has more impact on the performance characteristics than pulse-on time and the gap voltage. [ABSTRACT FROM AUTHOR]

In the latest period hundreds of concrete viaducts were built in Poland within a short time range. The cases of destruction of concrete road viaducts described by the author in the article concern in the construction of such structures in various parts of our country, such as central regions of Poland, Warmia-Masuria, south – east - a total of about 30 objects. The occurring phenomenon is related to the micro cracks of the cement matrix which are not visible on the surface of the elements and become visible only after the cyclic freezing process as a result of the standard F150 frost resistance test, the so-called the standard method according to Annex N to the PN-B-06265: 2018 standard. The destruction took an unprecedented course and aroused much discussion in the scientific community. This article summarizes this discussion and indicates the root cause of the destruction.

Copyright of BHM Berg- und Hüttenmännische Monatshefte is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The microstructure of rock is one of the most important factors that affect its mechanical behaviors. In order to study the effects of grain size on the strength and failure behaviors of granites, a breakable polygonal grain–based discrete-element model is developed to simulate the microstructure of rocks. In the model, mineral grain types, grain size distributions, and mineralogical composition are incorporated, and the intergranular and intragranular cracks are captured in the failure process. Using this method, six kinds of specimen with varying grain size are established, and the effects of grain size on peak strength, deformation properties, microcrack distributions, and macroscopic failure pattern are studied through conducting a series of compressive loading tests. The results indicate that rock strength is inversely proportional to the grain size, while a decreasing tendency in peak strain, an increasing tendency in Young's modulus, and Poisson's ratio with the grain size are observed. Meanwhile, an increase of grain size also results in a dramatic rise in crack initiation stress, ratios of shear cracks/intragranular cracks to generated total cracks. Under uniaxial compression tests, rocks consisted of small grains are trend to fracture with a single shear band, while rocks consisted of large grains are trend to fracture with an axial splitting. The failure pattern of rocks under high confining pressure is mainly double shear in a "X" fashion, and the width of fractures increases as the grain size increases. The proposed model provides a reliable method for investigating the influences of grain size on the rock mechanical behaviors in microscopic scale, and the results can be used to predict the macroscopic behaviors of brittle rocks. [ABSTRACT FROM AUTHOR]

One of the important parameters in electrical discharge machining is the presence of micro cracks on the workpiece surface (recast layer). Therefore, the aim of this study was to investigate the possibility of increasing the mechanical properties of aluminum surface by alloying elements (copper and nickel) diffusion to the recast layer and thus removing surface micro cracks. For this purpose, pulse on time and pulse current in with and without ultrasonic vibration have been considered as input parameters and the presence of surface micro cracks has been investigated using microscopic images. Also, the yield stress of the surface layer was calculated using the surface micro hardness. Based on the obtain results, surface without micro cracks has been created on the aluminum surface due to the diffusion of copper and nickel into the workpiece surface which increased aluminum surface yield strength from 90MPa to 280MPa without ultrasonic vibrations and to 310MPa while applying ultrasonic vibrations. In other words, ultrasonic vibrations cause an average of 20% increase in surface layer yield strength. In addition, according to the wear test, in the case of using ultrasonic vibration, improving the mechanical properties of the surface has caused thinner grooves on the aluminum surface. [ABSTRACT FROM AUTHOR]

Computed tomography (CT) of aluminum welded joint specimen has been performed. On the tomographic cross sections some defects have been found. To verify them the metallography cross sections of welded has been done. It was found that selected defects are micro cracks.

Ultrafine β grain structures with recrystallized morphologies were fabricated by severe plastic deformation and subsequent annealing in Ti-10Mo-8 V-1Fe-3.5Al alloy. The minimum mean β grain size of 480 nm was obtained for the first time as a recrystallized structure in Ti alloys. Precipitation behavior of α in subsequent aging significantly changed with decreasing the recrystallized β grain size. Both tensile strength and total ductility of the aged Ti-alloy were increased by the β grain refinement. Tensile strength of 1.6 GPa and total elongation of 9.1% were achieved in the aged specimen having the prior β grain size of 480 nm, which was attributed to its finer and more homogeneous precipitated microstructure having a mixture of nanoscale thin-plate α and globular α without side α plates along β grain boundaries.

The obstruction offered by the surrounding concrete to the pulling out of embedded steel bar is known as bond strength. Steel fibers addition to concrete improves its bond strength by arresting the cracks due to their bridging effect. Bond failure occurs when cracks in the surrounding concrete initiates, providing enough space for bar to be pulled-out. Micro steel fibers efficiently control the formation of micro cracks and may improve bond strength to a greater extent compared to the longer steel fibers. However, it reduces the workability of concrete which is of greater importance in case of self-compacting concrete (SCC). Reduction of workability is less pronounced when straight micro steel fibers are used due to their shorter lengths and straight geometry. Thus, different amount of straight micro steel fibers (0.25%, 0.5%, 0.75%) were incorporated in to SCC to investigate their fresh and mechanical properties with major emphasis on the bond strength. Results indicate that steel fibers addition to SCC improve the splitting tensile strength and bond strength significantly with a maximum increase of 33.5% and 54.9% respectively with 0.75% fibers addition. An equation is proposed for the calculation of bond strength with micro steel fibers addition to SCC with a maximum variation of 4% to those of experimental values. [ABSTRACT FROM AUTHOR]

The present study investigates the influence of adding multi-wall carbon nanotube (MWCNT) into the dielectric fluid of electric discharge machining (EDM) in terms of material removal rate (MRR), surface roughness (SR) and surface topology of EN-31 die steel using Cu electrode. A customized rotary electrode set-up has been developed to compare the performance improvement of powder mixed rotary electrical discharge machining (PMREDM) as compared to powder mixed electrical discharge machining (PMEDM) and conventional EDM. The present study attempts to investigate the optimization of process parameters of MWCNT mixed rotary EDM of EN-31 die steel using response surface methodology (RSM) and genetic algorithm (GA) in terms of MRR and SR. The optimization results show that MWCNT mixed rotary EDM shows highest value of MRR (9.72 mm3/min) and lowest value of SR (Ra = 2.03 µm), which are approximately 46.17% higher and 45.43% lower than conventional EDM values respectively. Further, various combinations of optimal values of MRR and SR and their corresponding input parameters setting have been shown in pareto table created by multiobjective optimization GA technique available in MATLAB. Finally, field emission scanning electron microscope (FESEM) analysis of MWCNT mixed rotary EDM and EDM surfaces is carried out which revealsthat MWCNT mixed rotary EDM shows better surface topography as compared to EDM process. [ABSTRACT FROM AUTHOR]

Chemically strengthened glass (also known as ion exchanged glass) is widely used for hand-held devices due to excellent mechanical strength. However, only top and bottom planar surfaces are sufficiently protected following a series of machining processes such as drilling, cutting and milling for manufacturing and assembly. Micro cracks that remain on the machined surface of the glass edges become very vulnerable to shock impact loading. In this study we suggest a novel PEALD technique to encapsulate surface defects with a 100 nm thickness layer of high-strength ceramics such as Al 2 O 3. In order to optimize PEALD parameters, we have examined best practices for testing chemically strengthened cover glasses. By conducting both Charpy impact test and 3-point bending test, it was found that impact resistance and flexural toughness of the PEALD-coated cover glass were 35%–40% and 21% higher compared to non-coated samples. Through the analysis of the state and elements of the machined surface with Al 2 O 3 (500 nm) coating it was verified that the coated layer uniformly covers the entire surface of the glass and fully infiltrates into the micro cracks. This study confirms that Al 2 O 3 ceramic coated with PEALD improves not only overall glass strength, but also overcomes the shortcomings of chemically strengthened glass machining. [ABSTRACT FROM AUTHOR]

EDM machining of Al 6061 was performed under varying condition of pulse current and pulse duration. Graphite was used as an electrode material with distilled water and paraffin oil as two different dielectric mediums. The aim is to characterize the surface integrity produced as a result of EDM machining under varying both electrical and non-electrical parameters as it is important in determining the service life of EDM machined components. The vertical, horizontal and corner surfaces are independently studied for each single set of conditions. The average white layer thickness (AWLT) and surface roughness was found to be dependent on pulse current values and pulse duration. Dielectric medium has also influence on the thickness and nature of white layer. It was found that the thickness and nature of white layer formed for distilled water is different from that of paraffin oil. New methods of AWLT and surface roughness measurement through optical microscope are described. The surface roughness method developed was also calibrated against an identical surface roughness tester. Finally material removal rate, tool wear rate, the presence of micro cracks, voids and globules were compared for different conditions and conclusions were drawn according to the actual physical conditions during machining.

The shock wave damage during explosive welding has not been reported in a flyer Mo plate of the Mo/Cu clads. However, it would be an inevitable problem in group VI elements. This study was aimed to characterize the shock wave damage in the Mo plate, that is less brittle than a W plate, of explosive welded Mo/Cu clads. Cladding at low horizontal collision velocities leading to high collision angles was expected to enhance the shock wave damage, and the clads resulted in less elongation in bending tests. On the other hand, in the clads obtained at high horizontal collision velocities (HCVs) with low collision angles, their bending elongation increased significantly. The shock wave damage penetrated from the surface of a Mo plate to the Mo/Cu interface, and thus reducing thickness of a Mo plate of bending specimens increased bending plastic strain. The shock wave damage is associated with kinetic energy imparted to the flyer Mo plate, and thus loss of kinetic energy due to formation of an intermediate layer at the interface and reducing thickness of a flyer Mo plate would be very helpful for decrease of shock wave damage.

This paper presents the development of a solar cell inspection manufacturing execution system (MES). The main objective of the MES is to detect micro cracks in the manufacturing process of solar cells. Hence, to accept or reject a solar cell during the assembling unit. The proposed MES consists of three stages, at first stage, the inspection system will be placed on the manufacturing process of the solar cell. After the solar cell has been manufactured, it will pass under an in-line electroluminescent (EL) system. At this stage, an OR operation between a healthy/no-crack and the inspected solar cell image will be obtained. This OR operation will generate a better calibration for the cracks in the photovoltaic solar cell image. The final calibrated image presents a high quality, and low noise structure, thus easier to identify the micro cracks size, location, and orientation. The last stage evaluates the calibrated image using the plot profile which is well known as the distance in pixels versus the gray level of the image. The plot profile will indicate whether to accept or reject the solar cell, 10% confidence interval for the gray level was used to identify the upper and lower detection limits. [ABSTRACT FROM AUTHOR]

This paper presents a novel detection technique for inspecting solar cells’ micro cracks. Initially, the solar cell is captured using the electroluminescence (EL) method, then processed by the proposed technique. The technique consists of three stages: the first stage combines two images, the first image is the crack-free (healthy) solar cell, whereas the second is the cracked solar-cell image. Both output images are processed into a bit-by-bit gridding technique, which enables the detection of all bits in the considered area of the cracked solar cell. The second stage uses an OR gate between each examined bit for both healthy and cracked solar cells. The final calibrated image presents a high-quality and low-noise structure, thus making it easier to identify the micro crack size, location, and its orientation. In order to examine the effectiveness of the proposed technique, three different cracked photovoltaic (PV) solar cells have been examined. The results show that the micro cracks’ size, orientation, and location are more visible using the proposed technique. In addition, the developed technique has been validated using a full-scale PV module, and compared with up-to-date available PV micro crack detection methods. [ABSTRACT FROM AUTHOR]

The critical effect of micro level defects should be examined at macro level to better understand the fracture behaviors of engineering materials. This study investigates the branching and deflecting behavior of a macro (main) crack in presence of multiple number of micro-cracks at the vicinity of the crack tip. For this purpose, a non-local continuum theory, known as Peridynamics (PD), is utilized based on the original set of bond-based PD equations. The main advantage of using PD is its characteristic superiorities on the modelling of dynamical fracture. Various example problems with inclined-linear and/or curvilinear micro-crack clusters are solved through the implementation of different numerical models to better understand the micro-crack toughening mechanisms. After validating the PD implementation with a benchmark case, several combinations of multiple micro-cracks with various locations are considered. To capture complex forms of crack branches, the positions of micro-cracks are designated to follow an encircling and spreading patterns at the vicinity of the main-crack tip. Hence, more internal energy is dissipated through the generation of new crack surfaces such that the main-crack deflects along a more twisting path. It has been observed that depending on the amount of dissipated energy, the propagation speed of main-crack alters. Also, it has been demonstrated that encircling potential crack propagation regions with micro-cracks provides an augmented toughness to the brittle materials. Overall, the efficiency and robustness of the PD theory are revealed for simulating crack propagation in brittle materials. [ABSTRACT FROM AUTHOR]

Copyright of China Sciencepaper is the property of China Sciencepaper and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The digitization of materials is the prerequisite for accelerating product development. However, technologically, this is only beneficial when reliability is maintained. This requires comprehension of the microstructure-driven fatigue damage mechanisms across scales. A substantial fraction of the lifetime for high performance materials is attributed to surface damage accumulation at the microstructural scale (e.g., extrusions and micro crack formation). Although, its modeling is impeded by a lack of comprehensive understanding of the related mechanisms. This makes statistical validation at the same scale by micromechanical experimentation a fundamental requirement. Hence, a large quantity of processed experimental data, which can only be acquired by automated experiments and data analyses, is crucial. Surface damage evolution is often accessed by imaging and subsequent image post-processing. In this work, we evaluated deep learning (DL) methodologies for semantic segmentation and different image processing approaches for quantitative slip trace characterization. Due to limited annotated data, a U-Net architecture was utilized. Three data sets of damage locations observed in scanning electron microscope (SEM) images of ferritic steel, martensitic steel, and copper specimens were prepared. In order to allow the developed models to cope with material-specific damage morphology and imaging-induced variance, a customized augmentation pipeline for the input images was developed. Material domain generalizability of ferritic steel and conjunct material trained models were tested successfully. Multiple image processing routines to detect slip trace orientation (STO) from the DL segmented extrusion areas were implemented and assessed. In conclusion, generalization to multiple materials has been achieved for the DL methodology, suggesting that extending it well beyond fatigue damage is feasible.

This article brings selected knowledge from the long-term cooperation between the Brno University of Technology, the Faculty of Civil Engineering, the Institute of Technology of Building Materials and Components, and the Academy of Sciences of the Czech Republic, v.v.i., Institute of Geonics, Ostrava - Poruba in the field of the interaction of water jets and concrete, especially with regard to the use of water jet technology for the removal of surface layers of concrete during repair of concrete. Attention is paid to monitoring the quality of the concrete surface treated by water jet technology and creating a relief in concrete to achieve good cohesion of concrete with repair mortar. The absence of cracks in the concrete structure after water jet blasting has been proven. [ABSTRACT FROM AUTHOR]

Curing conditions influence the properties of wood modified with melamine resin. Beech wood (Fagus sylvatica L.) was impregnated with melamine resin and cured in a dry and a hot steam process to investigate the influence of the relative humidity while curing. The topochemistry of the modified wood was assessed by light microscopy (LM) and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX) to visualise structural and chemical changes on cell wall level. LM in combination with staining did not show differences between the curing processes but allowed to distinguish untreated and treated wood. SEM micrographs revealed a more severe impact of dry curing conditions on the structural integrity of the material than steam curing by the formation of micro cracks. Dry-cured specimens showed a higher resin concentration in the cell wall than steam-cured specimens with the same overall distribution pattern as shown by EDX line scans. [ABSTRACT FROM AUTHOR]

A study of mechanical properties of mesoporous silicon (PS) is presented in this article. PS was prepared by electrochemical etching of a heavily doped P ++ silicon wafer in a hydrofluoric acid electrolyte. The mechanical properties of PS and oxidized PS obtained by thermal treatment, were characterized by the nanoindentation technique associated to the continuous stiffness measurement option. The morphology of PS and oxidized PS were both characterized by scanning electron microscope. It is shown that the Young's modulus and hardness are related to the PS preparing conditions and decrease with increasing porosity. In particular, oxidation improves the mechanical properties of the mesoporous silicon. Surprisingly, modulus and hardness decrease with penetration depth, whereas a compaction could be expected resulting in a rising modulus and hardness. These results are mainly attributed to micro cracks formation, highlighted by focused ion beam cross section. [ABSTRACT FROM AUTHOR]

This paper concentrates on the effects of misalignment on meshing behaviour of acetal gears as hardly any misalignment investigations on polymer gears in the existing literature. The experimental results show that the wear of acetal gears is insensitive to radial and axial misalignments but sensitive to yaw and pitch misalignments which degrade the conjugate contact action. Yaw misalignment leads to ‘scoop’ wear marks near tooth pitch points. Pitch misalignment causes ‘superimposed palisade’ wear marks and micro cracks near tooth roots. Compared with metal gears, the effects of small pitch angle on acetal gears are insignificant which may be linked closely to polymer's low elastic modulus. Strikingly different wear striations and various debris morphologies are observed by using scanning electronic and optical microscope (SEM, OM) and misalignment effects can be noted. [ABSTRACT FROM AUTHOR]

New materials require the use of advanced technology in manufacturing complex shape parts. One of themodernmaterialswidely used in the tool industry for injectionmolds or hot stamping dies is high conductivity tool steel (HTCS) 150. Due to its hardness (55 HRC) and thermal conductivity at 66 W/mK, this material is difficult to machine by conventional treatment and is being increasingly manufactured by nonconventional technology such as electrical discharge machining (EDM). In the EDM process, material is removed from the workpiece by a series of electrical discharges that cause changes to the surface layers properties. The final state of the surface layer directly influences the durability of the produced elements. This paper presents the influence of EDM process parameters: discharge current Ic and the pulse time ton on surface layer properties. The experimental investigation was carried out with an experimental methodology design. Surface layers properties including roughness 3D parameters, the thickness of the white layer, heat affected zone, tempered layer and occurring micro cracks were investigated and described. The influence of the response surface methodology (RSM) of discharge current Ic and the pulse time ton on the thickness of the white layer and roughness parameters Sa, Sds and Ssc were described and established. [ABSTRACT FROM AUTHOR]

When physical forces are applied to bone, its mechanical adaptive behaviors change according to the microarchitecture configuration. This leads to changes in biological and physical thresholds in the remodeling cell population, involving sensor cells (osteocytes) interacting with each other and changes in osteocyte shape due to variation in lacunar shape. The resulting alterations in fluid flow leads to changes in the membrane electrical potential and shear stress. Eventual creation of microcracks, may lead in turn to modify cell activity. In contrast, the redundancy in the lacuno canalicular network (LCN) interconnectivity maintains partial flow. Our goal was to investigate the role of fluid flow in LCN by proposing a model of electro-mechanical energy spread through inhomogeneous microarchitectures. We focused on mechano-sensitivity to changes in load-induced flow impacted by neighboring micro cracks and quantifying its critical role in changing, velocity, shear stress and orientation of liquid mass transportation from one cell to another. To enhance the concept of intricacy LCN micro-structure to fluid flow, we provide a new combined effects factor considered as osteocytes sensor efficiency. We customized an influence function for each osteocyte, coupling: in one hand, the spatial distribution within remodeling influence areas, conducting a significant fluid spread, leading hydro-dynamic behavior and impacted further by presence of micro cracks and; in other hand, the fluid electro kinetic behavior. As an attempt to fill the limitations stated by many of the recent studies, we reveal in numerical simulation, some results which cannot be measured in vitro/in vivo studies. Numerical calculations were performed in order to evaluate, among many others, how liquid flow conditions changes between lacunas, how the orientation and the magnitude of the governing flow in LCN can regulate osteocytes efficiency. In addition to be regulated by osteocytes, a direct effects of fluid flow are also acting on osteoblast activity. In summary, this new approach considers mechano-sensitivity in relation to liquid flow dynamic and suggests additional pathway for Osseo integration via osteoblast regulation. However, this novel modeling approach may help improve the mapping and design bone scaffolds and/or selection of scaffold implantation regions. [ABSTRACT FROM AUTHOR]

Yüksek gerilim güç kablolarının güvenliği ile ilgili en önemli konulardan biri, güç kablolarına ait parça ve malzemelerin bozulmasıdır. Güç kablolarının performansı yalıtkan malzemenin mekaniksel ve elektriksel bütünlüğüne bağlıdır. Yüksek gerilim güç kablolarındaki mikro çatlaklar, güç kablolarının yalıtım özelliklerini tehdit edebilir. Bu nedenle yüksek gerilim güç kablolarında mikro çatlakların oluşması istenmez. 2XS(FL)2Y 87/150(170) kV yüksek gerilim güç kabloları çapraz bağlı polietilen (XLPE) ve etilen propilen kauçuk (EPR) gibi çeşitli katı yalıtım malzemelerini kullanır. Elektriksel ölçümler ve kimyasal analizler yüksek gerilim güç kablolarında en iyi örnek karışımı bulmak için kullanılır. Bu çalışmada, 2XS(FL)2Y 87/150(170) kV yüksek gerilim güç kablosunun yalıtım arızası incelenmiş ve arıza tespiti için uygulanan elektriksel ölçüm testleri anlatılmıştır. Arızanın tespit edilmesi ve yok edilmesi yönünde karşılaşılan sorunlar, çözüm önerileri ve önleyici tedbirler açıklanmıştır.