Smaller Damage Area Research Articles

A comparative study on drilling characteristics of unidirectional thermosetting CF/epoxy and thermoplastic CF/PEEK composites

Thermoplastic carbon fiber reinforced polyetheretherketone (CF/PEEK) composites are increasingly utilized as substitutes for thermosetting carbon fiber reinforced epoxy (CF/epoxy) composites in high-end equipment, due to their superior mechanical performance and sustainable manufacturability. For both composite components, drilling is an indispensable operation in the manufacturing process. To distinguish the drilling characteristics of the two composites, comparative experiments on drilling unidirectional CF/epoxy and CF/PEEK under different parameters were conducted in this paper. Several aspects, including chip formation, drilling temperature, thrust force, hole damage, and dimensional accuracy, were examined. Particularly, the impact of fiber cutting angle on exit and hole wall damage was considered. Results demonstrate that due to the higher ductility and toughness of PEEK, CF/PEEK produces continuous chips, higher drilling temperatures, higher thrust forces, and smaller damage areas than that of CF/epoxy. However, CF/PEEK has more serious hole wall subsurface damage and poorer dimensional accuracy since PEEK is sensitive to temperature. Consequently, unlike CF/epoxy, increasing spindle speeds at the low feed cannot improve the hole quality of CF/PEEK. Moreover, the hole damage distribution of both composites is strongly associated with the fiber cutting angle. This study provides guidance for high-performance machining of CF/PEEK.

Weathering tests to investigate the durability of anti-corrosion coatings and on-site repair materials

Steel structures are exposed to multiple environmental impacts that lead to reduced durability. Organic paint systems are a resilient mechanism to protect hydraulic steel structures from corrosion. Coatings lead to a decreased corrosion progress at damaged areas. In this work, we investigated the time dependency of undercoating corrosion in the neutral salt spray test in detail by conducting a long-term experiment. Thereby, the fundamental model of corrosion progress was investigated, leading to an increased reliability in approval procedures of coatings and in the choice of test parameters.Additionally, repair materials for on-site repair of damaged coatings were investigated in weathering tests to compare their performance with conventional coatings. These materials are used for short-term repairs of small damaged areas in order to postpone replacement of ailing structures, thus enhancing the durability of steel structures.

MXene-based Q-switched fiber laser and application in laser thrombolysis

Near-infrared band fiber lasers exhibit strong water absorption capabilities, and their photothermal effects are often harnessed in the field of laser medical surgery. In this work, a 1.5-μm Q-switched fiber laser was realized by incorporating MXene, demonstrating its excellent performance as a saturable absorber. The output pulsed laser was amplified to achieve a maximum power of 500 mW, after which a self-made thrombus model was ablated to observe the experimental phenomenon. The obtained pulsed laser was compared with continuous wave laser thrombolysis under the same conditions. The results indicated that the 1.5-μm Q-switched fiber laser possesses thrombolytic capabilities, and the surface ablation depth and damage area of the thrombus were determined at various time and power levels. The pulsed laser thrombolysis has a smaller damage area and a greater penetration depth compared with continuous wave laser.

Self‐healing study of impact damage in carbon fiber composites based on electrostatically spun polyacrylonitrile core–shell nanofibers

AbstractCarbon fiber composites containing core–shell nanofibers (PAN@CFRP) were prepared by incorporating electrospun polyacrylonitrile core–shell nanofibers between the layers of carbon fiber reinforced polymer composites and the damage healing ability was assessed after being subjected to low‐velocity impact. Three impact energies (25.2, 33.5, and 41.9 J) were selected for the study. The incorporation of core–shell nanofibers improved the impact resistance of the composites compared with pure carbon fiber composites (CFRP); the PAN@CFRP specimens were found to have a smaller damage area and a lower damage level by visual observation and optical microscopy. The healing efficiency was 66.3%, 43.5%, and 8.83% for the residual compressive strength and was normalized to the residual compressive strength when the impact energy was less than 37.5 J. The healed materials were found to recover more than 80% of their undamaged residual compressive strength when the impact energy was less than 37.5 J. Therefore, the core–shell nanofiber healing system can, to a certain extent, solve the problems caused by the incorporation of other healing systems, and can largely recover the impact damage encountered in practical applications.

Restoration feasibility study by using alkali activated mortars based on Mt. Etna volcanic ash: The case study of Monreale Cathedral (Palermo, Italy)

This paper describes for the first time a case-study regarding the applicability of alkali activated mortars based on volcanic-ash (Mt. Etna) directly on-site on a UNESCO Heritage site known worldwide, the Monreale Cathedral (Sicily, Italy). In the perspective of “Advanced Green Materials for Cultural Heritage” project, small damaged areas of the mosaics were selected to test the application of bedding mortars for the filling of lacunae and the repositioning of detached original tesserae, as well as the replication of the mosaic decorations by engraving and painting on the finishing mortars or by the realization of new pre-casted tesserae. Both the critical aspects of preparation and the steps taken to improve operative conditions (e.g. use of Ca-additive) have been highlighted. The monitoring of results over time confirms the intervention’s success, representing in this way a pioneering on-site cultural heritage application of these materials.

An Old Photo Image Restoration Processing Based on Deep Neural Network Structure

Old photos retain precious historical image information, but today’s existing old photos often have varying degrees of damage. Although these old photos can be digitally processed and then restored, the restoration of old photos involves multiple areas of image restoration and has various types of degradation. Currently, there is no unified model for repairing multiple types of degradation of old photos. Photo restoration technology still has a lot of developments. Traditional image restoration technology mainly repairs the missing areas of the image based on mathematical formulas or thermal diffusion. This technology can only repair images with simple structures and small damaged areas and is difficult to apply in people’s daily lives. The emergence of deep learning technology has accelerated the pace of research on image restoration. This article will discuss the methods of repairing old photos based on deep neural networks. It is aimed at proposing an image restoration method based on deep neural network to enhance the effect of image restoration of old photos and provide more possibilities for restoration of old photos. This article discusses the background significance of image restoration methods, designs an image restoration model based on deep neural networks, and introduces the structure, principle, and loss function of the model. Finally, this article did a comparative experiment to compare the model in this article with other models and draw the conclusion: in the blur repair experiment, the algorithm in this paper is better than other algorithms for the peak signal-to-noise ratio and structure similarity of the repaired image; in the damage repair experiment, the value of the algorithm’ s peak signal-to-noise ratio is 32.34, and the structure similarity under different damage average levels is 0.767, which is also higher than other algorithms. Therefore, the model in this paper has the best effect on image restoration.

Experimental and numerical studies on low‐velocity impact damage of composite laminates toughened by nickel‐coated carbon fiber veil

AbstractThe low‐velocity impact response of carbon fiber composite laminates toughened by nickel‐coated carbon fiber (NiCF) veil interleaves was investigated experimentally and numerically. The experimental results indicated that the impact resistance of laminates with a layer of NiCF veil of 34 g/m2inserted in the midplane was improved, especially in terms of increased peak impact force and residual compressive strength (by 16.15%), and reduced damage area (by 30.92%). The enhancement mechanisms were attributed to the breakage, pull‐out, and crack bridging of the NiCF veil, as well as the peeling of nickel coating, which enhanced the carbon fiber/resin interfacial adhesion. A numerical model based on continuum damage mechanics and cohesive zone model was developed and its validity was verified. The simulation results confirmed that NiCF veils reduced energy absorption by enhancing the interlaminar properties of laminates, thereby reducing impact damage. Moreover, laminates with higher areal density and more layers of NiCF veils had higher impact force and smaller damage area, and thus had better impact resistance.

Quasi-static perforation response of inter-ply hybrid polypropylene composites at various temperatures

This study is motivated by the lack of knowledge in the research of mechanical characterization of thermoplastic composites (TPCs) with additional fiber hybridization. To enhance the mechanical properties of long glass fiber-reinforced polypropylene (PP) composite, hybridization via alkaline-treated aramid and carbon fabrics is performed. High performance fabrics modified with 10 wt.% sodium hydroxide (NaOH) aqueous solution are incorporated into the PP composite as reinforcements. Herewith, four arrangements (hybrid composites) for two different reinforcements and two different stacking configurations and the monolithic composite are separately investigated in terms of quasi-static perforation behavior. Failure mechanisms are also evaluated at macro level by visual observations and micro scales through a scanning electron microscopy (SEM). The experimental results provide a basis for selecting fiber-enabled hybridization and lay-up configuration with improved perforation resistance. Moreover, the influence of test temperature is reported for three different values as 20°C, 60°C, and 100°C. Based upon the results, the maximum penetration force of hybrid configuration with single-layered aramid fabric reinforcements is approximately 15.5% higher than that of single-layered carbon fabric reinforcements at 60°C test temperature. It is further observed that the absorbed energy improves as the number of fabrics is increased in both aramid and carbon reinforcements. The test temperatures significantly affect the failure mechanisms of TPCs. A smaller damaged area at the penetrated faces of the hybrid structures is obtained by comparison with the monolithic TPCs.

Effects of butein on renal ischemia/reperfusion injury: An experimental study.

Renal ischemia/reperfusion (I/R) injury is a common cause of acute kidney injury. The aim of this study was to investigate the effect of butein on renal I/R injury. Twenty-seven rats were randomly allocated to three groups (n = 9): a sham group, a renal I/Runtreated (control) group, and a renal I/R-butein group. The sham group underwent only opening and closing of the peritoneum. In the control group, an experimental I/R model was created and 1 cc isotonic saline was applied to the peritoneum. In the butein group, the experimental I/R model was created and 1 mg/kg butein was administered intraperitoneally 15 minutes before the beginning of ischemia. The left kidneys of the rats were histopathologically examined for tissue damage caused by I/R. Histopathological examination of the tissue damage revealed that all kidneys in the sham group were normal. By contrast, 2 in the control group (22.2%) had small focal damaged areas, 1 (11.1%) had < 10% cortical damage, 5 (55.6%) had 10-25% cortical damage, and 1 (11.1%) had 25-75% cortical damage. The butein group had 1 (11.1%) normal kidney, 2 (22.2%) with small focal damaged areas, 4 (44.4%) with < 10% cortical damage, and 2 (22.2%) with 10-25% cortical damage. Tissue damage was significantly lower in the sham group than in the control and butein groups (p < 0.01). No statistically significant differences were observed in the histopathology of the control and butein groups (p > 0.05). Intraperitoneal administration of butein had no significant effect on renal tissue injury.

Kinematic Changes in a Mouse Model of Penetrating Hippocampal Injury and Their Recovery After Intranasal Administration of Endometrial Mesenchymal Stem Cell-Derived Extracellular Vesicles.

Locomotion speed changes appear following hippocampal injury. We used a hippocampal penetrating brain injury mouse model to analyze other kinematic changes. We found a significant decrease in locomotion speed in both open-field and tunnel walk tests. We described a new quantitative method that allows us to analyze and compare the displacement curves between mice steps. In the tunnel walk, we marked mice with indelible ink on the knee, ankle, and metatarsus of the left and right hindlimbs to evaluate both in every step. Animals with hippocampal damage exhibit slower locomotion speed in both hindlimbs. In contrast, in the cortical injured group, we observed significant speed decrease only in the right hindlimb. We found changes in the displacement patterns after hippocampal injury. Mesenchymal stem cell-derived extracellular vesicles had been used for the treatment of several diseases in animal models. Here, we evaluated the effects of intranasal administration of endometrial mesenchymal stem cell-derived extracellular vesicles on the outcome after the hippocampal injury. We report the presence of vascular endothelial growth factor, granulocyte–macrophage colony-stimulating factor, and interleukin 6 in these vesicles. We observed locomotion speed and displacement pattern preservation in mice after vesicle treatment. These mice had lower pyknotic cells percentage and a smaller damaged area in comparison with the nontreated group, probably due to angiogenesis, wound repair, and inflammation decrease. Our results build up on the evidence of the hippocampal role in walk control and suggest that the extracellular vesicles could confer neuroprotection to the damaged hippocampus.

Carbon nanotube protected composite laminate subjected to lightning strike: Interlaminar film distribution investigation

A kind of interlaminar film with carbon nanotubes inserted into polyether ketone with cardo was used for lightning strike protection of composite laminates. The distribution of the interlaminar film was investigated by experimental and numerical methods. Artificial lightning strike tests were conducted for 12-film carbon nanotube and traditional surface silver coating protected specimens. Then corresponding finite element models (FEMs) were established to analyze the lightning strike effect and validated by the experimental results. Based on the FEMs, the number, distribution and thickness of interlaminar film were investigated in order to obtain equivalent protection effect with the traditional surface silver coating. The results show that only the first two layers were damaged for the surface silver coating protected specimen, while 5 layers were ablated for the 12-film protected specimen. Lightning strike damage area of the laminate protected with 5-film carbon nanotube is almost the same as that of the laminate protected with 12-film carbon nanotube. Compared with traditional surface silver coating protection, one film protection with thickness of 360 μm can make the laminate to obtain equivalent damage depth, 54.8% smaller damage area and 58% less additional weight. And reparability of the laminate is better than that of the laminate protected with 5 interlaminar films.

Exploiting Slow Dynamics Effects for Damage Detection in Concrete

Nonlinear ultrasonic techniques have been developed in the last decades to detect the presence of damage in materials of interest in the field of civil engineering, such as concrete or mortar. Different approaches have been proposed, exploiting the dependence on the strain amplitude of measurable quantities, such as wave velocity, damping factor, resonance frequency, etc. They have the advantage with respect to linear ultrasonic testing procedures of being much more sensitive to the presence of small variations in the sample microstructure, hence more adapt to detect the presence of small cracks or damaged areas. On the contrary, they usually require a calibrated experimental set-up working in the linear regime when using high amplitude excitations. The slow dynamics features typical of the hysteresis generated by damage have been given much less attention as a tool for damage detection even though their quantification is often less demanding in terms of experimental set-up. Here, we give a first evidence of how recovery, which is part of the slow dynamics process, is sensitive to the presence of damage in concrete samples and thus could be considered as an easy-to-measure nonlinear indicator for Structural Health Monitoring purposes.

Numerical simulation of lateral and transforaminal lumbar interbody fusion, two minimally invasive surgical approaches

The present study aims to compare spinal stability after two different minimally invasive techniques, the lateral lumbar interbody fusion (LLIF) and the transforaminal lumbar interbody fusion (TLIF) approaches. Two nonlinear three-dimensional finite element (FE) models of the L4–L5 functional spinal unit (FSU) were subjected to the loads that usually act on the lumbar spine. Findings show that the LLIF approach yields better results for torsion load case, due to the larger surface area of the implant. For extension, flexion and lateral bending loads, the TLIF approach presents smaller displacements probably due to the anterior placement of the cage and to the smaller damaged area of the annulus fibrosus.

Mechanical and Impact Properties of Packaging-Waste/E-Glass/Epoxy Sandwich Composites for Construction Applications

Using textile structural composites improves day by day in various industries due to their high specific strength and modulus, good fatigue and corrosion resistance. The most important reasons for the increased use of textile structural composites are the increased expectations for product performance and demand for lightweight materials in global markets. Rapid economic growth, urbanization, rising in population and welfare level lead to an increased amount of waste production. In Turkey, the annual average of solid waste is 25 million tons and 20% of this waste consists of packaging waste. In this study, a new sandwich material was developed for construction applications with low cost and high performance by using box wastes as core and E-Glass woven fabric as sheet materials. The mechanical properties were investigated by 3-point bending test and their impact behavior was compared after low-velocity impact tests in different energy levels. The core material had a negligible bending strength. The bending load of sandwich composites was dramatically higher than those of face material. Low-velocity impact results showed that absorbed energy and damaged area increased with increasing impact energy level. It could be concluded that the developed sandwich composites absorb more energy with small damaged areas and therefore can be considered as damage resistant materials for constructional applications as door and siding. The thermal insulation properties of these new sandwich composites will be also investigated in future researches.

Impact properties of a new hybrid composite material made from woven carbon fibres plus flax fibres in an epoxy matrix

This study is the first to characterize the impact properties of a new hybrid composite made with woven carbon fibres plus unidirectional (i.e. Type A) or cross-ply (i.e. Type B) flax fibres in an epoxy matrix. A pendulum impact tester applied a range of impact energies (5–40 J) to a series composite plates, which were assessed using photographic, thermographic, and geometric techniques. The Type B composite had better impact performance vs the Type A as indicated by lower absorbed energies, higher penetration energy, smaller crack lengths, smaller indentation depths, smaller damage areas, lower temperature rises in the impact zone vs applied impact energy, and higher impact strength. Both the Type A and B hybrid composites had superior impact properties compared to pure flax fibre-reinforced epoxy composites reported in prior literature, suggesting that hybridization using synthetic and natural fibres can be done successfully.

Impact Resistance of Plain and Twill Fabric in GFRP Measured by Active Thermography

This paper discusses the impact resistance of glass-fibre reinforced polymer (GFRP) composites depending on the type of reinforcement – plain or twill weave. The values of impact energy were: 3J, 10J and 15J. Specimens featuring twill weave transferred higher force during the impact as compared with plain weave specimens. It was observed that an increase of impact energy was accompanied by an increase of the disproportion in transferred forces, in favour of twill weave specimens. Impact damage (in both types of weave) occurring as a result of 3J impact was undetectable with active thermography method. The damage area measured by means of active thermography for impact energy values equal to 10J and 15J proved that the type of reinforcement significantly influences the impact resistance of a composite. This has been justified by smaller damage areas with high spot intensity of damage in plain weave specimens and highly dispersed damage with lower intensity in twill weave specimens.

Impact and post impact behavior of fabric reinforced geopolymer composite

Impact and post impact behavior of fabric reinforced geopolymer composites is investigated in this study. Carbon, E-glass and basalt fabrics are incorporated in the geopolymer matrix. The geopolymer composites are tested for impact resistance to an out-of-plane low velocity impact test, followed by post impact performance testing using residual strength measurement on the sample. Impact properties such as impact energy, energy absorption capacity, and damaged area of the composites were examined for fabric reinforced geopolymer composite samples. The drop weight impact tests were performed on composite samples of 15×15cm. The quality of the samples was examined using C-scan in ultrasonic vibration mode and μCT before and after impact test. The post impact behavior of the composite samples was characterized using four point bending tests. Fiber orientation and alignment was observed using SEM. The results obtained showed that E-glass fabric reinforced composites show slightly better performance than carbon reinforced composites. Especially the damaged area is smaller for E glass composites. Basalt fabric reinforced composites have low bending strength and very low impact resistance. The energy absorption in E-glass is due to post-debond fiber sliding phenomena and in carbon fiber to fiber pull out from the composite. The smaller damaged area is attributed to the higher elastic energy absorption of E-glass fibers. The residual strength of carbon and E-glass composites decreased in relation to the size of the visually damaged area, meaning that no invisible damage took place.

An experimental study on low-velocity impact response of nanocomposite beams reinforced with nanoclay

The low-velocity impact (LVI) response of the unidirectional glass/epoxy laminated composites, which were reinforced with various contents of nanoclay (i.e., 0, 3, 5 and 7 wt %) was performed using a drop-weight impact machine. The nanocomposite beams were fabricated using two different methods, including hand lay-up (HLU) and vacuum assisted resin transfer molding (VARTM) methods, to evaluate the effect of the manufacturing method on the impact response. In addition, the influence of the nanoclay type on the impact response was assessed by using Cloisite 30B and Cloisite 15A. The quasi-static and LVI responses of the nanocomposite beams were compared, and the effect of nanoclay on the delaminated area after impact was also discussed. The comparative results of the experiments indicate that the samples fabricated via VARTM method, have a smaller damage area and more energy absorption than the HLU types. However, the beams with 5 wt % nanoclay have the highest energy absorption in both manufacturing methods. Moreover, the mechanism of smaller delaminated area with increasing nanoclay contents is explained according to the impermeable nature of nanoclays.

Video restoration based on PatchMatch and reweighted low-rank matrix recovery

In this paper, a new video restoration approach is proposed. By using a modified version of random PatchMatch algorithm, nearest-neighbor patches among the video frames can be grouped quickly and accurately. Then the video restoration problem can be boiled down to a low-rank matrix recovery problem, which is able to separate sparse errors from matrices that possess potential low-rank structures. Furthermore, the reweighted low-rank matrix model is used to improve the performance of video restoration by enhancing the sparsity of the sparse matrix and the low-rank property of the low-rank matrix. Experimental results show that our system achieves good performance in denosing of joint multi-frames and inpainting in the presence of small damaged areas.

Investigation on the surface characterization of Ga-faced GaN after chemical-mechanical polishing

The relationship between the surface characterization after chemical mechanical polishing (CMP) and the size of the silica (SiO2) abrasive used for CMP of gallium nitride (GaN) substrates was investigated in detail. Atomic force microscope was used for measuring the surface morphology, pit feature, pit depth distribution, and atomic step-terrace structure. With the decrease of SiO2 abrasive size, the pit depth reduced and the atomic step-terrace structure became more whole with smaller damage area, resulting in smaller roughness. For tiny-sized SiO2 abrasive, an almost complete atomic step-terrace structure with 0.0523nm roughness was achieved. On the other hand, in order to acquire higher removal, Pt/C nanoparticle was employed as a catalyst in CMP slurry. The result indicates that when Pt/C catalyst content was reached to 1.0ppm, material removal rate was increased by 47.69% compared to that by none of the catalyst, and besides, the pit depth reduced and the surface atomic step-terrace structure was not destroyed. The Pt/C nanoparticle is proved to be the promising catalyst to the surface preparation of super-hard and inert materials with high efficiency and good surface.