On the Network Strength of Meta-Aramid Fiber Suspension and Its Relationship to Formation

Because of poor surface hydrophilicity, meta-aramid fibers readily form flocs by intertwining or interlacing, and this severely affects the uniformity of meta-aramid paper. To investigate the flocculation mechanism of meta-aramid fiber suspensions, the critical flocculant concentration, shear, and compressive network strength of meta-aramid fiber suspensions were examined. A hand sheet former was used to study the influence of the yielding properties of suspensions on the uniformity of meta-aramid paper, and the relationship between the formation index and rheological properties was determined. The results showed that the critical gel concentration ranged from 0.37 to 0.68 g/L, which was much lower than that of plant fiber suspensions. In addition, the compressive yield stress ( P y ) and shear yield stress ( τ y ) of the meta-aramid fiber suspensions were found to increase linearly and exponentially, respectively, with an increasing concentration, and the uniformity index of the paper sheets was found to depend on a power of τ y ⋅ P y . This provides an effective method for predicting paper sheet uniformity.

Mechanical performance of sandwich composites with additively manufactured triply periodic minimal surface cellular structured core

Sandwich composite structures are comprised of a low-density core (commonly honeycomb) and facesheets. They are typically used in applications that require lightweight for efficient design, such as in the marine and aerospace industries. This work investigates the feasibility of adopting triply periodic minimal surface (TPMS) cellular structures as the core for sandwich composites. Sandwich structures were manufactured using a carbon fiber-reinforced polymer (CFRP) facesheet and three different 304 L stainless steel core structures (honeycomb, gyroid TPMS, and diamond TPMS). Three mechanical tests, namely edgewise compression, three-point bend, and impact test, were carried out to evaluate the performance of each sandwich configuration. The experimental results of the non-traditional sandwich configurations were compared against those of a honeycomb core sandwich composite. The edgewise compression test showed that the ultimate edgewise compressive strength increased by 7% when the honeycomb core was replaced by the gyroid core and reduced by 2% when the diamond core replaced the honeycomb core. The three-point bend test showed that the traditional honeycomb core sandwich configuration had a higher shear yield stress when compared to the non-traditional sandwich structures. The shear yield stress was reduced by 54% when non-traditional sandwich cores were used. The shear ultimate stress was reduced by 41% and 37% when the honeycomb core was replaced by the gyroid and diamond structure, respectively. Impact test results, on the other hand, showed that the peak force recorded during the impact event was reduced, while the absorbed energy was increased when non-traditional cores were used. Peak force was reduced by 28% and 39%, while the absorbed energy was increased by 9% and 16% when the honeycomb core was replaced by the gyroid and diamond cores, respectively.

Measuring material plastic response to cyclic loading in modern rail steels from a minimal number of twin-disc tests

Advances in rail materials from conventional rail steels to those with higher yield points and the potential of additively manufactured laser clad coatings to improve the durability of railway track components presents a new challenge in characterisation. Many of these new and novel materials have either limited test samples available or are more resistant to strain and therefore present challenges in characterisation. The method reported here uses twin disc tests to simulate cyclic loading experienced by rail steel in service. A sample from a single test condition is analysed, measuring the shear yield stress and the accumulated shear strain at multiple depths below the contact surface, from which a Shear Yield Stress – Plastic Shear Strain (SYS-PSS) relationship is extracted. Knowledge of the stress history of a rail sample is not required to apply the method and minimal samples are required, providing a technique which can be used on rail steel samples removed from service.

Effect of the Drying Method of Pine and Beech Wood on Fracture Toughness and Shear Yield Stress

The modern wood converting processes consists of several stages and material drying belongs to the most influencing future performances of products. The procedure of drying wood is usually realized between subsequent sawing operations, affecting significantly cutting conditions and general properties of material. An alternative methodology for determination of mechanical properties (fracture toughness and shear yield stress) based on cutting process analysis is presented here. Two wood species (pine and beech) representing soft and hard woods were investigated with respect to four diverse drying methods used in industry. Fracture toughness and shear yield stress were determined directly from the cutting power signal that was recorded while frame sawing. An original procedure for compensation of the wood density variation is proposed to generalize mechanical properties of wood and allow direct comparison between species and drying methods. Noticeable differences of fracture toughness and shear yield stress values were found among all drying techniques and for both species, but only for beech wood the differences were statistically significant. These observations provide a new highlight on the understanding of the effect of thermo-hydro modification of wood on mechanical performance of structures. It can be also highly useful to optimize woodworking machines by properly adjusting cutting power requirements.

The shear and compressive yield stress of fibrillated acacia pulp fiber suspensions

The degree of interactions between fibers and the tendency of fibers to form flocs play an important role in effective unit operation in pulp and paper industry. Mechanical treatments may damage the structure of the fiber cell wall and geometrical properties, and ultimately change the fiber-fiber interactions. In this study, the gel crowding number, compressive and shear yield stress of fibrillated acacia pulps were investigated, and the results showed that the gel crowding number of the refined pulp samples ranged from 8.7 to 10.7, which were much lower than that of un-refined pulps. As the concentration increased, both the compressive yield stress {P_{y}} and shear yield stress {\tau _{y}} of all suspensions increased accordingly, and the yield stress was found to depend on a power law of the crowding number. Moreover, the values of {\tau _{y}}/{P_{y}} were also examined and the variation of {\tau _{y}}/{P_{y}} became largely dependent on the fiber morphology and mass concentration.

Microstructure Simulation and Constitutive Modelling of Magnetorheological Fluids Based on the Hexagonal Close-packed Structure

This paper presents a new constitutive model of high particles concentrated magnetorheological fluids (MRFs) that is based on the hexagonal close-packed structure, which can reflect the micro-structures of the particles under the magnetic field. Firstly, the particle dynamic simulations for the forces sustained by carbonyl iron powder (CIP) particles of MRFs are performed in order to investigate the particles chain-forming process at different time nodes. Subsequently, according to the force analyses, a hexagonal close-packed structure, which differs from the existing single-chain structure and body-cantered cubic structure, is adopted to formulate a constitutive model of MRFs with high concentration of the magnetic-responsive particles. Several experiments are performed while considering crucial factors that influence on the chain-forming mechanism and, hence, change the field-dependent shear yield stress in order to validate the proposed model. These factors include the magnetic induction intensity, volume fraction and radius of CIP particles, and surfactant coating thickness. It is shown that the proposed modeling approach can predict the field-dependent shear yield stress much better than the single-chain model. In addition, it is identified that the shear yield stress is increased as the particle volume fraction increases and surfactant coating thickness decreases. It is believed that the proposed constitutive model can be effectively used to estimate the field-dependent shear yield stress of MRFs with a high concentration of iron particles.

Preliminary experimental evaluation of a novel loudspeaker featuring magnetorheological fluid surround absorber

<span>A novel design of magnetorheological fluids (MRF) based surround device in a loudspeaker system was studied in this article. The main objective of this research is to design a new surround device of the loudspeaker that can be easily controlled its damping. Therefore, it was predicted that the audio pressure level on the loudspeaker could be easily manipulated at a different sound source by applying a certain magnetic field. This function could not be reached using one conventional speaker system. Firstly, a set of an electromagnetic device containing MRF was designed to replace the conventional rubber surround. The magnetic circuit was then evaluated using the finite element method magnetics to study the flux distribution in the MRF area. The current was varied from 0.25 to 0.75 A by an interval of 0.25 A. The magnetic flux resulted from the simulation was then logged and used as the based value for predicting the change of shear yield stress. The base properties of the shear yield stress of the MRF against the magnetic flux was obtained from previous experimental result. Therefore, it was hopefully the prediction could be closed to the real system. Based on the simulation result, the shear yield stress varied from 43 to 49 Mpa or about 15 % increment. </span><span lang="IN">A simple experimental work was carried out. By applying particular direct current into the coil, the sound quality generated by the loudspeaker shows different values</span><span>.</span><span lang="IN"> Based on the preliminary experiment, the level of decibel decreased about 3 dB as the application of magnetic fields. The idea has been proven in this preliminary experimental evaluation.</span>

Micro-mechanical theory of shear yield stress for strongly flocculated colloidal gel

We derive a constitutive relation for shear yield stress of strongly aggregated colloidal gel as a function of interparticle potential, volume fraction, contact scale properties and gel microstructure.