Search Results (19)

The FLASH-COMP project aims to introduce novel inspection and monitoring technologies to develop a digital solution to predict defects during manufacturing, aiming to reach a zero-waste approach in composites manufacturing. Particularly, it’s studied the integration of two different Fiber Optic Sensor (FOS) technologies: Fiber Bragg Grating (FBG) and distributed All Grating Fiber (AGF^®), to retrieve relevant data during the preforming stage and later resin infusion process for aero-space materials. During the study, both FOS technologies were introduced into the materials, varying process conditions and the introduction of some artificial defects to evaluate the sensors response to correlate them after with their signals. Both systems can retrieve relevant information during the process such as vacuum, leaks and temperature changes, presence of voids and air bubbles, detection of dry zones, and resin flow monitoring. Further developments have to be focused on the scalability in the implementation, since FOS are fragile to handle and need specific training to use it in a more industrial field. Full article

The combined insulation interface of a high-voltage cable and accessories is the weakest part of a cable system. In this paper, the parameters of the dielectric constant, thermal conductivity, and elastic modulus of cross-linked polyethylene (XLPE) and silicone rubber (SIR) are obtained experimentally. On this basis, the model of a specific type of 110 kV cable and prefabricated insulation joint is established. A simulation of the electric–thermal–stress coupling field in the presence of typical defects in the main insulation–inner semi-conductive (SEMI) shielding layer (XLPE/SEMI interface) and the main insulation–silicone rubber insulation layer (XLPE/SIR interface) is studied. The simulation results show that at the XLPE/SIR interface, the electric field distortion caused by bubble defects reached 20.17 kV/mm, and the temperature rose to 56.15 °C. The effect of air-gap defects on the interface is similar to that of bubble defects. In addition, the semi-conductive impurity defects induced an increase in temperature to 56.82 °C and an increase in stress to 0.32 MPa. At the XLPE/SEMI interface, the electric field distortion induced by bubble defects was 19.98 kV/mm, and the temperature rose to 61.72 °C. The electric field distortion caused by metallic and semi-conductive defects was 8.44 kV/mm and 8.64 kV/mm, respectively. This study serves as a reference for the fault analysis and the operation and maintenance of cable accessories. Full article

In practical applications, polyurethane (PU) foam must be rigid to meet the demands of various industries and provide comfort and protection in everyday life. PU foam components are extensively used in structural foam, thermal insulation, decorative panels, packaging, imitation wood, and floral foam, as well as in models and prototypes. Conventional technology for producing PU foam parts often leads to defects such as deformation, short shots, entrapped air, warpage, flash, micro-bubbles, weld lines, and voids. Therefore, the development of rigid PU foam parts has become a crucial research focus in the industry. This study proposes an innovative manufacturing process for producing rigid PU foam parts using silicone rubber molds (SRMs). The deformation of the silicone rubber mold can be predicted based on its wall thickness, following a trend equation with a correlation coefficient of 0.9951. The volume of the PU foam part can also be predicted by the weight of the PU foaming agent, as indicated by a trend equation with a correlation coefficient of 0.9824. The optimal weight ratio of the foaming agent to water, yielding the highest surface hardness, was found to be 5:1. The surface hardness of the PU foam part can also be predicted based on the weight of the water used, according to a proposed prediction equation with a correlation coefficient of 0.7517. The average surface hardness of the fabricated PU foam part has a Shore O hardness value of approximately 75. Foam parts made with 1.5 g of water added to 15 g of a foaming agent have the fewest internal pores, resulting in the densest interior. PU foam parts exhibit excellent mechanical properties when 3 g of water is added to the PU foaming agent, as evidenced by their surface hardness and compressive strength. Using rigid PU foam parts as a backing material in the proposed method can reduce rapid tool production costs by about 62%. Finally, an innovative manufacturing process for creating large SRMs using rigid PU foam parts as backing material is demonstrated. Full article

Background and Objectives: Spontaneous colonic perforations (SCPs) in teenagers and young adults are extremely rare. Common underlying conditions, such as colonic tumors and diverticulitis, are absent at that age. The vascular type of Ehlers–Danlos Syndrome (vEDS) is one cause of SCP. Methods: A 23-year-old male presented with an acute abdomen. The abdominal CT showed pneumoperitoneum with a large amount of fluid in the pelvis and abdomen, indicating hollow viscus rupture. At the level of the sigmoid colon, a defect in the intestinal wall and gas bubbles were seen. Results: Exploratory laparotomy confirmed sigmoid colon perforation without underlying pathology. Loop sigmoid colostomy was performed. Revisional surgery was undertaken due to clinical deterioration and intra-abdominal free fluid with small-bowel distension and air-liquid levels on abdominal CT 6 days later. Ileal subserosal hematomas were found, and many had ruptured, leaving a “zebra” pattern with lines of residual hematomas on the borders of subserosal hematomas. Genetic analysis confirmed vEDS. Conclusions: SCP in young adults or teenagers, in the absence of colonic disease, with clinical manifestations of connective tissue disorders should trigger genetic investigations for vEDS. SCP with a known vEDS could be treated with total colectomy to prevent further SCPs in the remaining colon. If segmental resections are performed, further SCP should be immediately excluded with any significant abdominal pain. Full article

A proportion of patients who undergo intraoperative cholangiogram (IOC) do not have bile duct stones at the time of endoscopic retrograde cholangiopancreatography (ERCP), either due to the spontaneous passage of stones or a false-positive IOC. Glucagon has been utilized as an inexpensive tool to allow the passage of micro-choledocholithiasis to the duodenum and resolve filling defects caused by stones or air bubbles. The purpose of our study is to understand the change in diagnostic accuracy of IOC to detect choledocholithiasis with intraoperative glucagon. We conducted a retrospective study at a tertiary care center on adult patients who underwent laparoscopic cholecystectomy with IOC. The diagnostic accuracy of IOC was assessed before and after the administration of intravenous glucagon. Of 1455 patients, 374 (25.7%) received intraoperative glucagon, and 103 of these 374 patients (27.5%) showed resolution of the filling defect with the passage of contrast to the duodenum. Pre- and post-glucagon administration comparison showed enhancement in specificity from 78% to 83%, an increase in positive predictive value from 67.3% to 72.4%, and an improvement in the diagnostic accuracy of IOC from 81.5% to 84.3%. Our findings suggest that intraoperative glucagon administration carries the potential to reduce the rate of false-positive IOCs, thereby reducing the performance of unnecessary ERCPs. Full article

In this paper, we investigated the behaviors of bubbles entrained in a film coating during spray coating. Air bubbles that remain in a film coating after diluent evaporation cause coating defects called bubbling defects, including fish-eye and crater defects. In this study, the visualization of a film coating revealed that smaller bubbles in the film shrank slowly and disappeared, while larger bubbles remained. These remaining bubbles grew during the heating process for the drying of the film coating. The shrinking phenomenon was explained using bubble dynamics based on the Young–Laplace equation of a bubble’s inner pressure and Henry’s law for bubble gas dissolution into the film coating. This shrinking model is often used in studies on microbubble dynamics. The results suggested the importance of avoiding the entrainment of large bubbles during the spraying process and enhancing the release of air bubbles from the film coating’s surface through the appropriate usage of defoaming agents. Full article

NDBs were fabricated from gum Arabic (GA) and polyvinyl alcohol (PVA) in different ratios using novel techniques (casting, dehydration, and peeling). The GA/PVA blends were cast with a novel vibration-free horizontal flow (VFHF) technique, producing membranes free of air bubble defects with a homogenous texture, smooth surface, and constant thickness. The casting process was achieved on a self-electrostatic template (SET) made of poly-(methyl methacrylate), which made peeling the final product membranes easy due to its non-stick behavior. After settling the casting of the membranous, while blind, the sheets were dried using nanometric dehydration under a mild vacuum stream using a novel stratified nano-dehydrator (SND) loaded with P₂O₅. After drying the NDB, the dry, smooth membranes were peeled easily without scratching defects. The physicochemical properties of the NDBs were investigated using FTIR, XRD, TGA, DTA, and AFM to ensure that the novel techniques did not distort the product quality. The NDBs retained their virgin characteristics, namely, their chemical functional groups (FTIR results), crystallinity index (XRD data), thermal stability (TGA and DTA), and ultrastructural features (surface roughness and permeability), as well as their microbial biodegradation ability. Adding PVA enhanced the membrane’s properties except for mass loss, whereby increasing the GA allocation in the NDB blend reduces its mass loss at elevated temperatures. The produced bioplastic membranes showed suitable mechanical properties for food packaging applications and in the pharmaceutical industry for the controlled release of drugs. In comparison to control samples, the separated bacteria and fungi destroyed the bioplastic membranes. Pseudomonas spp. and Bacillus spp. were the two main strains of isolated bacteria, and Rhizobus spp. was the main fungus. The nano-dehydration method gave the best solution for the prompt drying of water-based biopolymers free of manufacturing defects, with simple and easily acquired machinery required for the casting and peeling tasks, in addition to its wonderful biodegradation behavior when buried in wet soil. Full article

Polymer gels are usually used for crystal growth as the recovered crystals have better properties. Fast crystallization under nanoscale confinement holds great benefits, especially in polymer microgels as its tunable microstructures. This study demonstrated that ethyl vanillin can be quickly crystallized from carboxymethyl chitosan/ethyl vanillin co-mixture gels via classical swift cooling method and supersaturation. It found that EVA appeared with bulk filament crystals accelerated by a large quantity of nanoconfinement microregions resulted from space-formatted hydrogen network between EVA and CMCS when their concentration exceeds 1:1.4 and may occasionally arise when the concentration less than 1:0.8. It was observed that EVA crystal growth has two models involving hang-wall growth at the air-liquid interface at the contact line, as well as extrude-bubble growth at any sites on the liquid surface. Further investigations found that EVA crystals can be recovered from as-prepared ion-switchable CMCS gels by 0.1 M hydrochloric acid or acetic acid without defects. Consequently, the proposed method may offer an available scheme for a large-scale preparation of API analogs. Full article

A composite thin shell with a high fiber volume fraction prepared by resin transfer molding (RTM) may have void defects, which create deformations in the final curing and lead to the final product being unable to meet the actual assembly requirements. Taking a helmet shell as an example, a multi-directional compression RTM (M-CRTM) method with an adjustable injection gap is proposed according to the shape of the thin shell. This method can increase the injection gap to reduce the fiber volume fraction during the injection process, making it easier for the resin to penetrate the reinforcement and for air bubbles to exit the mold. X-ray CT detection shows that the porosity of the helmet shell prepared by the newly developed technology is 36.6% lower than that of the RTM-molded sample. The void’s distribution is more uniform, and its size is decreased, as is the number of voids, especially large voids. The results show that the maximum curing deformation of the M-CRTM-molded helmet shell is reduced by 13.7% compared to the RTM molded sample. This paper then further studies the deformation types of the shell and analyzes the causes of such results, which plays an important role in promoting the application of composite thin shells. Full article

In this work, void formation was systematically observed for the glass frit bonding technique as a function of the annealing temperature, annealing time, and annealing ambient. High annealing temperature and long annealing time were adopted to reach the maximum heat flux to avoid voids/bubbles. As demonstrated in the experiments, the voids appearing during glass frit bonding are related to the quantity of byproducts from the combustion of organic matter. The experimental results indicate that solely in air, under vacuum, or annealed for short time, the combustion products cannot be fully degassed, and voids occur. It was shown that the alternating three-step conditioning process including glass liquid forming in air, bubble removal under vacuum, and void filling-up in air can lead to void-free and uniform wafer bonding. The glass frit bonding samples with lots of voids/bubbles were compared to the ones without any defects. Full article

Digital shearography is a technique that has recently been applied to material inspections that cannot be performed by the naked eyes, including the detection of air bubble defects in tires. Although digital shearography detects bubbles that are not visible to the naked eyes, the process of determining tire defects still relies on field operators, with inconsistent results depending on the experiences of the field operator personnel. New or different types of bubble defects that AI models have not previously recognized are often missed, resulting in an inadequate quality detection model. In this paper, we propose a bubble defect detection method based on an incremental YOLO architecture. The data for this research was provided by the largest tire manufacturer in Taiwan. In our research, we classify the defects into six distinct categories, pre-process the images to allow better detections of less-noticeable defects, increase the amount of training data used, and generate an initial training model with the YOLO framework. We also propose an incremental YOLO method using small-model training for previously unobserved defects to improve the model detection rate. We have observed detection accuracy and sensitivity of 98% and 90% in the experimental results, respectively. The methods proposed in this paper can assist tire manufacturers in achieving semi-automatic quality inspections and labor cost reductions. Full article

To improve the properties of additively manufactured parts to be used in high-end applications, intrinsic defects occurring during the printing process need to be minimized. Defects such as void can significantly degrade the mechanical properties of the resulted parts. The presence of void is more evident in composite printed parts due to the inhomogeneity of the specimen. In this study, composite rectangular coupons printed with a Markforged Mark Two printer were manufactured with different fiber orientations and stacking sequences. A void content reduction/consolidation process, consisting of applying pressure at different temperature levels, was developed and implemented to remove the voids in form of air bubbles trapped in the specimen. A two-part mold with female and male components with the same dimensions as the rectangular specimen was designed and machined to be used in a hot press process. The success of the approach was evaluated by calculating the density of the specimen pre- and post-consolidation. The void content reduction results were highly dependent on fiber orientation; however, the density increased for all tested specimens, confirming the reduction in porosity. Full article

Plastic materials can absorb moisture from the atmosphere even after drying. This absorbed moisture can cause many defects in the molding process. Conventionally, a dryer is used to reduce the moisture content. However, the use of a drying unit involves huge daily power consumption and is also time-consuming. Therefore, this study proposed a new method to reduce the impact of moisture on molded product part quality through the optimization of plasticization parameters while reducing drying time. Two plastic materials, polyurethane (TPU) and polycarbonate (PC), were used for the experimental verification. Key plasticization parameters, including back pressure, screw rotation speed, and barrel temperature were chosen; their influence was investigated by the design of experiments (DOE). Moisture-induced defects, such as air bubble area, part surface gloss, and appearance were measured and correlated with the plasticization parameters. It was found, after optimization via a three-level DOE and factorial design multivariate statistical analysis using TPU, that the gloss (GU) of the PC part without drying was very close to that (98.4 GU) of the fully dried PC. The proposed methodology may help molders to improve production efficiency and achieve cost savings. Full article

A polyethylene (PE) liner is the basic element in high-pressure type 4 composite vessels designed for hydrogen or compressed natural gas (CNG) storage systems. Liner defects may result in the elimination of the whole vessel from use, which is very expensive, both at the manufacturing and exploitation stage. The goal is, therefore, the development of efficient non-destructive testing (NDT) methods to test a liner immediately after its manufacturing, before applying a composite reinforcement. It should be noted that the current regulations, codes and standards (RC&S) do not specify liner testing methods after manufacturing. It was considered especially important to find a way of locating and assessing the size of air bubbles and inclusions, and the field of deformations in liner walls. It was also expected that these methods would be easily applicable to mass-produced liners. The paper proposes the use of three optical methods, namely, visual inspection, digital image correlation (DIC), and optical fiber sensing based on Bragg gratings (FBG). Deformation measurements are validated with finite element analysis (FEA). The tested object was a prototype of a hydrogen liner for high-pressure storage (700 bar). The mentioned optical methods were used to identify defects and measure deformations. Full article

Digital impression devices are used alternatively to conventional impression techniques and materials. The aim of this study was to evaluate the precision of extraoral digitalization of three types of photosensitive resin polymers used for 3D printing with the aid of a digital extraoral optical scanner. The alignment of the scans was performed by a standard best-fit alignment. Trueness and precision were used to evaluate the models. The trueness was evaluated by using bias as a measure and the standard deviation was used to evaluate the precision. After assessing the normality of the distributions, an independent Kruskal–Wallis test was used to compare the trueness and precision across the material groups. The Mann–Whitney test was used as a post-hoc test for significant differences. The result of the analysis showed significant differences (U = 66, z = −2.337, p = 0.019) in trueness of mesiodistal distances. Upon visual inspection of the models, defects were noticed on two out of nine of the models printed with a photosensitive polymer. The defects were presented as cavities caused by air bubbles and were also reflected in the scans. Mean precision did not vary too much between these three photosensitive polymer resins, therefore, the selection of 3D printing materials should be based on the trueness and the required precision of the clinical purpose of the model. Full article