EFFECT OF MICROSTRUCTURE OF CARDBOARD ON ITS MECHANICAL PROPERTIES

The article is devoted to the prediction of mechanical properties on the study of the microstructure of the cross section of cardboard. The results of the work in the future can be used as an addition to standard methods for evaluating the mechanical properties of cardboard. On the basis of images of the microstructure of the cross sections of the two-layer test liner cardboard and their graphic processing using modern computer programs, the lengths of fiber contacts were determined. Guided by the fact that the most significant indicator of all geometric parameters of the microstructure is the length of fiber contacts, the main mechanical properties of cardboard were determined (bursting strength and compression resistance, breaking length, bending stiffness, interlayer strength)produced according to various technologies (conventional method of preparing recovered paper stock, dry defibration of recovered paper with aerodynamic formation of the top layer, dry defibration of recovered paper with subsequent supply of fibers to the stock and dry defibration of recovered paper with subsequent grinding in the stock). Each of the technologies allows to obtain cardboard with different mechanical parameters. It has been established that almost all mechanical indicators depend directly proportionally on the length of the fiber contact lines. The obtained dependencies can be used to predict the mechanical properties of cardboard in its production at industry enterprises.

Heating mechanisms in induction welding of thermoplastic composites

The heat generated within thermoplastic carbon composite laminates during induction welding can be attributed to one, or a combination of the three heating mechanisms discussed in the literature: (i) Joule heating of fibers; (ii) Joule and/or dielectric heating of polymer; and (iii) fiber-to-fiber contact resistance heating. The answer to the question, which of the three heating mechanisms is most dominant, remains open. This research aims to provide an answer to this question through finite element simulations using both an in-house developed numerical Whitney-elements based toolbox for induction welding simulations (WelDone), and the commercially available software, ANSYS Maxwell. The simulations are done at two levels; first, using WelDone laminate-level simulations are performed to see in which direction: fiber-, transverse to the fiber-, or thickness direction, most of the heat was generated; and second, ANSYS Maxwell was used to simulate the solid loss on a microscopic, inside fiber and resin, level with and without the presence of resin. In the latter series of simulations, contact between fibers in different layers was explicitly modeled. The numerical simulations revealed that on the laminate-level most heat is generated in the fiber- and thickness directions. The former coincides with Joule heating of fibers, while the latter can be attributed to either Joule heating of polymer and fiber-to-fiber contact resistance heating, or both. The fiber level simulations, however, revealed that both fiber-to-fiber contact and no-fiber-to-fiber contact conditions have a significantly small effect on the solid loss compared to presence of resin. Based on the latter, the heat generation in the thickness direction was attributed to a second heating mechanism; Joule heating of polymer. It must be noted that the dielectric heating of polymer was ignored due to the relatively low operating frequency at which induction welding takes place.

Studies of Microwave Electromagnetic Field Influence on Adhesion Strength of the “Matrix-Fiber” Contact Zone on the Example of the Elementary Cell of a Certified Polymeric Composite Material

The strength characteristics of polymer composites (PCM) reinforced with fibers of various nature largely depend on the adhesion strength of the components in the matrix-fiber contact zone, determined by the mechanisms of their adhesive interaction. The strength of the bonds in the contact zone depends on the transfer of the load from fiber to fiber through the matrix layer. Taking into account the order and greater strength of the reinforcing fibers in tension, compared with the matrix material, the adhesion of the PCM components has the greatest effect when the material is perceived as transverse to the direction of the fiber loads, which usually occurs in bending and interlayer shear. In the latter case, the strength of the material several times less, which determines the importance of increasing the strength of the adhesive interaction, which requires comprehensive studies and an adequate description of its mechanisms. An experimental study of the adhesion strength in the matrix-fiber contact zone after short-term exposure to a microwave electromagnetic field with different energy flux densities on the PCM physical cell model, represented as a basalt fiber bundle placed in ED-20 epoxy resin, was performed. It has been established that exposure to a microwave electromagnetic field with an energy flux density of (17-18) x104 μW/cm2 for 1-2 minutes leads to an increase in adhesion relative to the source material by no less than 32%. This method can be used as a basis for the development of technologies for increasing the strength of the interlayer shear PCM, reinforced by fibers of various nature. To clarify the mechanisms of the obtained results, it is advisable to conduct a study of the micro-and nanostructures of the “matrix-fiber” contact zone using electron and atomic-force microscopy and its phase composition..

Shape-Memory Actuation of Individual Micro-/Nanofibers

Advances in the fabrication and characterization of polymeric nanomaterials has greatly advanced the miniaturization of soft actuators, creating materials capable of replicating the functional physical behavior previously limited to the macroscale. Here, we demonstrate how a reversible shape-memory polymer actuation can be generated in a single micro/nano object, where the shape change during actuation of an individual fiber can be dictated by programming using an AFM-based method. Electrospinning was used to prepare poly(ε-caprolactone) micro-/nanofibers, which were fixed and crosslinked on a structured silicon wafer. The programming as well as the observation of recovery and reversible displacement of the fiber were performed by vertical three point bending, using an AFM testing platform introduced here. A plateau tip was utilized to improve the stability of the fiber contact and working distance, enabling larger deformations and greater rbSMPA performance. Values for the reversible elongation of εrev = 3.4 ± 0.1% and 10.5 ± 0.1% were obtained for a single micro (d = 1.0 ± 0.2 μm) and nanofiber (d = 300 ± 100 nm) in cyclic testing between the temperatures 10 and 60 °C. The reversible actuation of the nanofiber was successfully characterized for 10 cycles. The demonstration and characterization of individual shape-memory nano and microfiber actuators represents an important step in the creation of miniaturized robotic devices capable of performing complex physical functions at the length scale of cells and structural component of the extracellular matrix.

Morphologies and characteristic of glass fiber suspensions basing on various beating speeds

Glass fibers commonly flocculate in suspensions and slurries, which can be largely prevented by a beating process. In this paper, morphologies and characteristics of glass fiber suspensions resulting from various beating speeds are explored. By increasing the speed (ranging from 1500 revolutions to 12000 revolutions), glass fibers can be translated, rotated, bended and broken, which leads the drainage resistances of glass fiber suspensions increase dramatically from 19.5 °SR to 23.5 °SR, then fluctuate and settle close to 22.5 °SR. Decreasing the fiber length leads to reduction in fiber–fiber contact and improves the uniformity of fiber suspensions. The separation and random distribution of glass fibers decreases in the viscosity of the fiber suspension.

Simulation of the Friction Coefficient of Paper-Based Wet Clutch With Wavy Separators

To simulate the change rate of the friction coefficient μ with respect to the sliding speed V, that is, the μ-V slope, a model combining macroscale and microscale phenomena is proposed. The macroscale model obtains distributions of the fluid pressure and fiber contact pressure over the whole engagement face, and the microscale model obtains the friction coefficient of each fiber contact through a detailed model for single-protuberance fiber contact. An experiment was conducted to obtain the μ-V slope by changing the wave height of separator faces, and the simulation and experimental results were compared. The combined model is advantageous for representing experimental μ-V relationships at small and large wave heights in comparison with models using only the macroscale behavior. Both experimental and simulation results showed the μ-V slope becoming more negative with increasing wave height. The simulation results revealed possible causes for the negative slope. In the wavy separator, the fluid friction that contributes to the positive slope is difficult to achieve due to the large film thickness, and the load-sharing ratio of the fiber contact tends to decrease due to wedge action of the fluid film. These phenomena shift the μ-V slope to the negative.

Characterization of interlayer air permeability of thermoplastic prepreg stacks

An important mechanism for void air removal during oven vacuum bag processing for thermoplastic composites relies on void air flow to the part perimeters through the permeable pathways created by the rough surfaces of two adjacent prepreg layers. In this paper, the interlayer air permeability of AS4/APC2 carbon poly (ether ether ketone) thermoplastic prepreg was investigated before and after oven vacuum bag processing conditions. The permeability thickness product was measured with an experimental set-up and data reduced based on one-dimensional Darcy’s flow. The interlayer permeability exhibit directional dependency and are uniquely determined by the angle between two adjacent prepreg layers. Before oven vacuum bag processing, the principal permeability thickness products for lay-ups with included angle of 0°, 30°, 60°, and 90° were determined. Good agreement was achieved between the rotation matrix predicted permeability thickness products and the measured results. During processing, when temperature is above resin glass transition and below melting, the permeability of 0°/0° and 90°/90° interlayers reduces dramatically with increasing temperature and dwell time. For the 0°/90° interlayer, only a slight reduction compared to the room temperature baseline was obtained for temperature ramps up to 300℃ and dwell time up to 8 h at 240℃. The changes of the surfaces roughness were correlated to the reduction of measured permeability. The 0°/90° interlayer surface shows the evidence of fiber–fiber contact that limits the contact between layers and prevents significant drop of permeability during processing. Off-axis stacking sequences with fiber–fiber contact are advantageous for oven vacuum bag processing of large thermoplastic composite parts.

Neurosurgical patties: adhesion and damage mitigation

OBJECT Neurosurgical patties are textile pads used during most neurosurgical operations to protect tissues, manage the fluid environment, control hemostasis, and aid tissue manipulation. Recent research has suggested that, contrary to their aim, patties adhere to brain tissue and cause damage during removal. This study aimed to characterize and quantify the degree of and consequences resulting from adhesion between neurosurgical patties and brain tissue. METHODS Using a customized peel apparatus, the authors performed 90° peel tests on 5 patty products: Policot, Telfa, Americot, Delicot, and Ray-Cot (n = 247) from American Surgical Company. They tested 4 conditions: wet patty on glass (control), wet patty on wet brain peeled at 5 mm/sec (wet), dry patty on wet brain peeled at 5 mm/sec (dry), and wet patty on wet brain peeled at 20 mm/sec (speed). The interaction between patty and tissue was analyzed using peel-force traces and pre-peel histological analysis. RESULTS Adhesion strength differed between patty products (p < 0.001) and conditions (p < 0.001). Adhesion strength was greatest for Delicot patties under wet (2.22 mN/mm) and dry (9.88 mN/mm) conditions. For all patties, damage at the patty-tissue interface was proportional to the degree of fiber contact. When patties were irrigated, mechanical adhesion was reduced by up to 550% compared with dry usage. CONCLUSIONS For all patty products, mechanical (destructive) and liquid-mediated (nondestructive) adhesion caused damage to neural tissue. The greatest adhesion occurred with Delicot patties. To mitigate patty adhesion and neural tissue damage, surgeons should consider regular irrigation to be essential during neurosurgical procedures.