Limin Bao

A Novel Approach for Evaluating the Air Permeability of Airbag Fabrics

An approach based on the shock tube experiment is proposed to evaluate the permeability of airbag fabrics. Shock tube experiments were conducted to imitate airbag inflation by fixing an airbag fabric sample near the end of an open driven section. When a plane shock wave impinges the airbag fabric, it will be reflected. Meanwhile, an increase in pressure will form at the front face of the airbag fabric and this will lead to a flow through the fabric, due to the permeable structure of the fabrics. The air permeability of airbag fabrics can therefore be determined by measuring the velocity of the reflected shock wave. It was found that at relatively high pressure the dynamic permeability results from the shock tube experiment were lower than the static results from the conventional permeability testing method. This phenomenon appears to be related to the different influences on the airbag fabric structure of the steady pressurization that occurred in the static experiments and the instantaneous pressurization that occurred in the shock tube experiments.

Mechanical enhancement of UHMWPE fibers by coating with carbon nanoparticles

Fiber-reinforced plastic (FRP) is composed of reinforced fibers and matrix resin, and has high specific strength and low-density materials. Because of the orientation of the fibers within them, FRPs are prone to buckling damage when under compression along the axial direction of the fiber, especially flexible organic ones. The compressive performance of FRP is largely dependent on fiber properties. the buckling load of FRP will increase with the increasing of fiber’s. In this study, we developed a way to improve the compressive and bending strength of ultra-high molecular weight polyethylene (UHMWPE) fibers. Carbon nanotubes (CNTs) and vapor-grown carbon fibers (VGCFs) were coated on the surface of UHMWPE fibers by pyrrole vapor deposition. The transverse compressive strength and bending strength of single UHMWPE fibers were determined by microcompression and single fiber bending measurements, respectively. The experiment result showed that coating UHMWPE fibers with CNTs and VGCFs increased both their transverse compressive strength and bending strength. It is excepted that the improved fiber would applied in FRP for better compressive performance.

Preparation of carbon fiber-reinforced thermoplastics with high fiber volume fraction and high heat-resistant properties:

In the present article, a highly heat-resistant composite with a high fiber volume fraction (Vf > 60%) was successfully manufactured using engineering plastic Nylon66 as matrix and carbon fabric as reinforcement by a solution impregnation molding method. The mechanical properties of the composite were investigated using a tensile measuring device. Mechanical analysis revealed the superior mechanical properties of the composite relative to those of previously reported carbon fiber-reinforced thermoplastics (CFRTPs). The cross section and fracture surface of the composite were characterized by scanning electron microscopy. The resin successfully impregnated the fiber bundles and the bonding strength of the fiber–resin interface was excellent. Dynamic mechanical analysis was used to evaluate the heat-resistant property of the composite. The composite exhibited a better heat-resistant property relative to that of the carbon fiber-reinforced crystalline co-polyester composite. To further verify the versatility of this method, super engineering plastic polyetherimide with a higher molecular weight was successfully employed as matrix to prepare CFRTP.

A Study on the Torsional Wave of Fiber-reinforced Composite Materials

The impact characteristics of FRP are important for structures and other applications. In this article, a CFRP pole is used to study the effect of fiber orientation on the torsional strain wave rate. A method of forecasting torsional strain wave characteristic is subsequently suggested. An experiment is conducted to verify the theory and the calculation method. Good agreement is obtained between the theoretical and the experimental values of seven types of laminated composite cylinders, unidirectional (0,90) plies, and cross-plies (15, 30, 45, 60, 75). This demonstrates that the mathematical technique developed here is satisfactory for predicting the torsional strain wave of laminated composites. Torsional strain wave rates of laminated composites vary with fiber orientation angle.

Relationship Between Uniaxial and Strip Biaxial Tensile Properties of Fabrics

Based on two basic assumptions: the Poissons ratios ν x , ν y are constants; and tensile rigidities Ex , Ey are nonlinear functions of the stress, a new nonlinear theoretical model to describe the tensile behavior of fabrics based on the orthotropic theory is presented here. This new model was used to predict the uniaxial tensile properties of fabrics from the strip biaxial test by the Poissons ratios ν x , ν y calculated from the strip biaxial experimental results. The uniaxial tensile experiments for plain knitted fabrics and for plain woven fabrics were carried out and the experimental results showed good agreement with the results predicted by the new model. It is the first time the relationship between the uniaxial tensile test and the strip biaxial tensile test has been established. The paper provides a simple and effective method for comparing the results obtained by different experimental methods.

Research in Recycling Technology of Fiber Reinforced Polymers for Reduction of Environmental Load: Optimum Decomposition Conditions of Carbon Fiber Reinforced Polymers in the Purpose of Fiber Reuse

The objective of the present study is to investigate the effect of pyrolysis time and temperature on the mechanical properties of recycled carbon fiber, based on tensile strength measurements, determining the optimum decomposition conditions for carbon fiber-reinforced polymers (CFRPs) by superheated steam. In this research, CFRPs were efficiently depolymerized and reinforced fibers were separated from resin by superheated steam. Tensile strength of fibrous recyclates was measured and compared to that of virgin fiber. Although tensile strength of recycled fibers were litter lower than that of virgin fiber, under some conditions tensile strength of recycled fibers were close to that of virgin fiber. With pyrolysis, some char residue from the polymer remains on the fibers and degrees of char on the recycled fibers were closely examined by scanning electron microscopy.

Development of a high-density nonwoven structure to improve the stab resistance of protective clothing material

The purpose of this research was to enhance the stab resistance of protective clothing material by developing a new high-density nonwoven structure. Ice picks often injure Japanese police officers due to the strict regulation of swords in the country. Consequently, this study was designed to improve stab resistance against ice picks. Most existing anti-stab protective clothing research has focused on various fabrics impregnated with resin, an approach that brings with it problems of high cost and complicated processing. Seldom has research addressed the potential for improving stab resistance by using nonwoven structures, which exhibit better stab resistance than fabric. In this research, we prepared a series of nonwoven structures with densities ranging from about 0.14 g/cm3 to 0.46 g/cm3 by varying the number of stacked layers of Kevlar/polyester nonwoven under a hot press. We then proposed two methods for producing such hot-press nonwovens: the multilayer hot-press method and the monolayer hot-press method. Stab resistance was evaluated according to NIJ Standard-0115.00. We also investigated the relationship among nonwoven density, stab resistance, and flexural rigidity, and here we discuss the respective properties of the two proposed methods. Our results show that stab resistance and flexural rigidity increase with nonwoven density, but flexural rigidity of nonwovens prepared using the monolayer hot-press method only shows a slight change as nonwoven density increases. Though the two methods exhibit little difference in maximum load, the flexural rigidity of nonwovens prepared using the monolayer hot-press method is much lower, which contributes to superior wear comfort. Finally, we investigated the mechanism behind the stabbing process. Stabbing with an ice pick is a complicated process that involves many factors. Our findings indicate that nonwovens stop penetration primarily in two ways: nonwoven deformation and fiber fractures.

Impact Force when Fabric Inflates at High Speed

Occupant protection systems for automobiles are currently highly publicized. An airbag inflating at high speed impacts an occupant with great force. Airbag safety relies on its construction with primarily woven fabrics. We have referred to a typical pressure-time history of an airbag and developed a device to measure impact load when the fabric airbag inflates at high speed. When interior pressure in the airbag increased, impact load increased. Also, the impact load on a body increased as the distance between the body and airbag decreased. The impact force of an airbag inflating at high speed was simulated by a non-linear finite element method (FEM) combined with an incremental method, where the sample was modeled by a thin elastic shell. An experiment was conducted to verify the theory and this calculation method. Good agreement was obtained between the theoretical and experimental values for two types of fabric sample. This demonstrated that the mathematical technique developed here can satisfactorily predict the impact force when an airbag inflates at high speed and that the impact force depends appreciably on the mechanical properties of fabrics.

Optimum Decomposition Conditions for Glass Fiber Reinforced Plastic Recycling by Superheated Steam

The objective of the present study is to investigate the effect of pyrolysis time and temperature on the mechanical properties of recycled fiber, based on tensile strength measurements, determining the optimum decomposition conditions for glass fiber-reinforced plastic (GFRP) by superheated steam. In this research, GFRP was efficiently depolymerized and reinforced fiber was separated from resin by superheated steam. Tensile strength of fibrous recyclates was measured and compared to that of virgin fiber. Although tensile strength of recycled fibers were lower than that of virgin fiber, under some conditions tensile strength of recycled fibers were close to that of virgin fiber. They were the optimum decomposition conditions for GFRP in our experiments. With pyrolysis, some char residue from the polymer remains on the fibers and degrees of char on the recycled fibers were closely examined by scanning electron microscopy.

Research on FRP Composite Structures with Self-Healing Function - Effect of Filler on FRP Interlaminar Fracture Toughness

In reacent years, studies on reducing the diameter of microcapsules for practical application to self-healing FRP have been conducted. This study clarifies how filler grain diameter and strength and filler volume fraction affect the interlaminar fracture toughness of FRP. The reinforcement material used in this experiment was carbon fiber fabric sheets. Acrylic particles were used as filler; the mechanical properties were similar to those of microcapsules of self-healing FRP. The filler volume fraction was confirmed to affect the interlaminar fracture toughness. The grain diameters of the hollow particles were smaller, and the Youngs modulus of the filler is larger, confirming that the interlaminar fracture toughness increased. High rigidity and small-grain diameter microcapsules are considered to be appropriate microcapsules (enclosing repair agents) for self-healing of CFRP.