Study on the Distribution of Frictional Forces on Z-Yarn Continuous Implanted Preforms and Its Application

In order to improve the quality and efficiency of the Z-directional 3D preform forming, the Z-yarn friction force distribution model of the preform and its wear mechanism were investigated. Designed the tensile force measuring device of the replacement guide sleeves,the measured tensile force is equivalent to the Z-yarn friction force. Found that the frictional force was proportional to the number of preform layers, the frictional force applied to the one preform decreased from the corner, edge, sub-edge and middle in order. Established BP neural network model to predict the friction at different positions of preform with different layers, the error is within1.9%. The wear of Z-yarn was studied at different frictional positions and after different times of successive implantation into the preform, showed that with the increase of the number of Z-yarn implantation and the friction force, the amount of carbon fiber bundle hairiness gradually increase, and the tensile fracture strength damage of the fiber is increasingly affected by the friction force,and in the corner position of the preform, when the number of implantation is 25 times, the fiber fracture strength will occur non-linearly and substantially decreased, in order to avoid fiber fracture in the implantation process, the Z-yarn needs to be replaced in time after 20~25 times of continuous

Comparison of Holmium:YAG and Thulium Fiber Lasers on the Risk of Laser Fiber Fracture

Objectives: To compare the risk of laser fiber fracture between Ho:YAG laser and Thulium Fiber Laser (TFL) with different laser fiber diameters, laser settings, and fiber bending radii. METHODS: Lengths of 200, 272, and 365 μm single use fibers were used with a 30 W Ho:YAG laser and a 50 W Super Pulsed TFL. Laser fibers of 150 µm length were also tested with the TFL only. Five different increasingly smaller bend radii were tested: 1, 0.9, 0.75, 0.6, and 0.45 cm. A total of 13 different laser settings were tested for the Ho:YAG laser: six fragmentation settings with a short pulse duration, and seven dusting settings with a long pulse duration. A total of 33 different laser settings were tested for the TFL. Three laser settings were common two both lasers: 0.5 J × 12 Hz, 0.8 J × 8 Hz, 2 J × 3 Hz. The laser was activated for 5 min or until fiber fracture. Each measurement was performed ten times. Results: While fiber failures occurred with all fiber diameters with Ho:YAG laser, none were reported with TFL. Identified risk factors of fiber fracture with the Ho:YAG laser were short pulse and high energy for the 365 µm fibers (p = 0.041), but not for the 200 and 272 µm fibers (p = 1 and p = 0.43, respectively). High frequency was not a risk factor of fiber fracture. Fiber diameter also seemed to be a risk factor of fracture. The 200 µm fibers broke more frequently than the 272 and 365 µm ones (p = 0.039). There was a trend for a higher number of fractures with the 365 µm fibers compared to the 272 µm ones, these occurring at a larger bend radius, but this difference was not significant. Conclusion: TFL appears to be a safer laser regarding the risk of fiber fracture than Ho:YAG when used with fibers in a deflected position.

Karakteristik Fiber Metal Laminate Akibat Beban Impak Balistik Dari Peluru Kaliber 9 mm Full Metal Jacket (FMJ)

<p class="Abstract"><span lang="EN-GB">Estimated damage levels from ballistics impact zone provide valuable information to make bulletproof materials more effective. Therefore, this study aims to determine the impact of ballistics including hole shape, hole depth, macro, and microstructure on fiber metal laminate. The characteristics of ballistics impact for each configuration target is obtained from experiment and comparison based on simulations with finite element method. Test experiments used short-barreled fire guns at a distance of 5 meters with a normal attack angle based on the National Institute of Justice standard. Simulation with Johnson-Cook plasticity models for aluminum plate and orthotropic material model for kevlar/epoxy. The experiment and simulation results showed that the projectile is able to perforate the first layer (aluminum plate) and the second layer (Kevlar/epoxy) while the last layer (backplate) is deformed to form a bulge. The aluminum plate is perforated by the failure of petaling formation on the backside and spread of dimple fracture around the area of the petal which indicates ductile fracture while kevlar/epoxy is perforated by projectile with failure of fiber fracture on primary yarn, fiber pull-out, fiber stretching and fiber rupture.</span></p>

Tensile Behavior of Geometrically Irregular Bagasse Fiber

In the present work, an investigation on the surface topography and geometry variation of bagasse fibers was correlated with their mechanical properties via image analysis. The fibers were tested under a universal tensile testing machine and the diameter of the fibers was calculated using images obtained in a digital microscope. Furthermore, surface characterization and quantification were also performed using images obtained via SEM. The results showed that the surface roughness of alkali-treated bagasse fiber increased compared to that of the untreated one. Moreover, it was observed that the diameter variation of bagasse fiber along its length and among different fibers is not only variable but also unpredictable. The tensile test results revealed that bagasse fibers showed lower stress at a rupture with considerable scatter. It can be inferred that the synergistic effect of thick bagasse fiber, bagasse fiber diameter variations along its length and among fibers, and the fiber fracture mechanism establishes a local condition for fracture and resulted in such variations in tensile properties. Finally, the results clearly showed that the two-parameter Weibull fit the experimental data fairly well (R2=0.97). The Weibull modulus (m) was found to be 1.7, indicating that the strength distribution is high.

Elucidating the mechanisms of damage in foam core sandwich composites under impact loading and low temperatures

Recent interest in Arctic exploration has brought new challenges concerning the mechanical behavior of lightweight materials for offshore structures. Exposure to seawater and cold temperatures are known to degrade the mechanical properties of several materials, thus, compromising the safety of personnel and structures. This study aims to investigate the low-velocity impact behavior of woven carbon/vinyl ester sandwich composites with Polyvinyl chloride (PVC) foam core at low temperatures for marine applications. The tests were performed in a drop tower impact system with an in-built environmental chamber. Impact responses, such as the contact force, displacement and absorbed energy, at four impact energies of 7.5 J, 15 J, 30 J, and 60 J were determined at four in-situ temperatures of 25°C, 0°C, −25°C and −50°C. Results showed that temperature has a significant influence on the dynamic impact behavior of sandwich composites. The sandwich composites were rendered stiff and brittle as the temperature decreased, which has a detrimental effect on their residual strength and durability. At 7.5 J at all temperatures, the samples experienced matrix cracking, fiber fracture, and delamination at the top face sheet. The samples impacted at 15 J at all temperatures experienced fiber fracture, matrix cracking, and delamination at the top facesheet and localized core crushing/fracture. At 30 J for all the temperatures, the samples exhibited perforation of the top facesheet and penetration into the core. As the temperature decreased, the penetration of the striker into the core increased. At 60 J for all temperatures, the samples experienced perforation of the top facesheet and core, and the back facesheet exhibited varying extent of damage. At −25°C and −50°C, the sandwich composite samples were almost completely perforated. In general, low temperatures rendered the sandwich composites stiff and brittle, resulting in an increase in the degree of damage and more pronounced damage modes. At all impact energies, the sandwich composites were rendered stiff and brittle as the temperature decreased, which has a detrimental effect on their residual strength and durability.

Novel Analytical Model of Stress Concentration around Broken Fibers of Unidirectional Composite Plate

During the fiber fracture of unidirectional composite a distribution of stress around the neighbored fibers happens, this mechanism is called the local redistribution efforts. Referring to the "shear lag" method, the researches wanted to predict the stress concentration in the surrounding area of broken fibers as well as the longitudinal resistance of the unidirectional composite which presents a fiber breaking. The goal of this paper is to develop a new probabilistic model of unidirectional composite plate to calculate the stress concentration at the broken fibers and their neighboring fiber intact. The "shear lag" method has been generalized to see the broken fibers interference on the stress concentration factor variation of surrounding sound fibers.