Kevlar Yarns Research Articles

Experimentally validated predictive finite element modeling of the V0-V100 probabilistic penetration response of a Kevlar fabric against a spherical projectile

This work presents the first fully validated and predictive finite element modeling framework to generate the probabilistic penetration response of an aramid woven fabric subjected to ballistic impact. This response is defined by a V0-V100 curve that describes the probability of complete fabric penetration as a function of projectile impact velocity. The exemplar case considered in this article comprises a single-layer, fully clamped, plain-weave Kevlar fabric impacted at the center by a 0.22 cal spherical steel projectile. The fabric finite element model comprises individually modeled three-dimensional warp and fill yarns and is validated against the experimental material microstructure. Sources of statistical variability including yarn strength and modulus, inter-yarn friction, and precise projectile impact location are mapped into the finite element model. A series of impact simulations at varying projectile impact velocities is executed using LS-DYNA on the fabric models, each comprising unique mappings. The impact velocities and outcomes (penetration, non-penetration) are used to generate the numerical V0-V100 curve which is then validated against the experimental V0-V100 curve obtained from ballistic impact testing and shown to be in excellent agreement. The experimental data and its statistical analysis used for model input and validation, namely, the Kevlar yarn tensile strengths and moduli, inter-yarn friction, and fabric ballistic impact testing, are also reported.

Rehabilitation Glove Device Design

In hand rehabilitation, physical therapy is applied to the hands and fingers regionally. In the treatment of hand rehabilitation, it is aimed to restore the hand function, to facilitate hand movements and to restore movement. Hand rehabilitation is not only the fulfillment of the hand function, but also the pain and seizures that occur at the same time. For the rehabilitation of the hand in work, each time the rehabilitation center or the hand movement provider instead of the different cost devices designed wearable rehabilitation gloves. It is aimed to rehabilitate the hand by making finger joint measurements of the person to be used, producing rings from the three-dimensional printer on the gloves, connecting the kevlar yarn to the servo motors, and opening and closing the fingers. The device is person-specific, portable and easy to manufacture and low cost. This feature allows the person to perform the rehabilitation of the hand wherever he is without going anywhere.

Virtual ballistic impact testing of Kevlar soft armor: Predictive and validated finite element modeling of the V 0 - V 100 probabilistic penetration response

Abstract This works presents the first fully validated and predictive capability to model the V0-V100 probabilistic penetration response of a woven fabric using a yarn-level fabric finite element model. The V0-V100 curve describes the probability of complete fabric penetration as a function of projectile impact velocity. The exemplar case considered in this paper comprises of a single-layer, fully-clamped, plain-weave Kevlar fabric impacted at the center by a 17-gr, 0.22 cal FSP or fragment-simulating projectile. Each warp and fill yarn in the fabric is individually modeled using 3D finite elements and the virtual fabric microstructure is validated in detail against the experimental fabric microstructure. Material and testing sources of statistical variability including yarn strength and modulus, inter-yarn friction, precise projectile impact location, and projectile rotation are mapped into the finite element model. A series of impact simulations at varying projectile impact velocities is executed using LS-DYNA on the fabric models, with each model comprising unique mappings. The impact velocities together with the outcomes (penetration, non-penetration) are used to generate the numerical V0-V100 curve which is then validated against the experimental V0-V100 curve. The numerical Vi-Vr data (impact, residual velocities) is also validated against the experimental Vi-Vr data. For completeness, this paper also reports the experimental characterization data and its statistical analysis used for model input, viz. the Kevlar yarn tensile strengths, moduli, and inter-yarn friction, and the experimental ballistic test data used for model validation.

Effects of Kevlar volume fraction and fabric structures on the mechanical properties of 3D orthogonal woven ramie/Kevlar reinforced poly (lactic acid) composites

The proposed 3D orthogonal woven ramie/Kevlar reinforced poly (lactic acid) composite in this paper is a new type composite in which the 3D orthogonal structure has great advantages of high impact and delamination resistance due to the Z yarns and the hybridization of natural and manmade fibers provides not only partial environment friendly benefit but also efficient compensation for the relatively low mechanical properties from pure natural fibers. Eight types of the aforementioned composites were designed and fabricated. The results showed that as the volume fraction of Kevlar was increased, the tensile properties showed increasing trends, while the flexural properties were predominantly dependent on the fabric structures, especially, the weft yarns properties in the first and second layers from the upper and bottom surfaces. Furthermore, the impact strength was enhanced as the volume fraction of Kevlar increased to 5.5% and leveled off when Kevlar yarns continuously increased.

On the mechanical response of 2D plain woven and 3D angle-interlock fabrics

Abstract The present study compared the tensile and low velocity impact (LVI) response of Kevlar/basalt fabrics. Homogeneous and hybrid fabrics with structures of two dimensional plain woven (2D-P) and three dimensional angle-interlock (3D-A) were woven with Kevlar and basalt yarns. Interlacing of brittle basalt yarns with high-ductility/high-toughness Kevlar yarns enhanced the tensile strength of 2D-P fabrics by 5.39–50.29% and 3D-A fabrics by 14.80%. Similarly hybridization enhanced the energy absorption of 2D-P fabrics by 8.58–37.71% and 3D-A fabrics by 13.45–20.14%. Change in the architecture from 2D-P to 3D-A also enhanced the tensile and impact resistance of fabrics. Different failure modes induced due to tensile and LVI loads were identified.

Investigation of mechanical behavior of woven/knitted hybrid composites

The objective of this research is to develop the woven/knitted hybrid composites for improved in plane as well as out of plane mechanical properties. Two different type of structures and two different materials were used in this study. Firstly, the woven and knitted fabrics were developed with glass and Kevlar yarn. Secondly, the laminated composite samples were fabricated with different stacking sequence of fabric plies. The epoxy resin was used as matrix. The cured samples were characterized for impact, tensile and dynamic mechanical properties. The behavior of composite materials was then analyzed with percentages of different fiber and fabric types. The samples with higher percentages of knitted reinforcement gave better impact strength but failed to provide better tensile properties. Moreover, the samples with higher percentages of woven structure and glass materials gives better modulus values.

Analytical model of nonlinear twist dependency for Kevlar yarn based on local filament strain

Kevlar KM2 600 denier yarn is often twisted to improve yarn load at failure. It is noted in ASTM-D-7269 that twisting KM2 past five twists per inch can cause a lower load at failure. Understanding the physics that govern the load decrease at higher twist ratios can lead to improved yarn designs, possibly stronger than the peak values currently seen at three turns per inch. Increasing yarn strength would enable enhanced usage of Kevlar yarn, improving chord and fabric structures. This paper describes the testing and finite element analysis methods used to probe yarn tenacity as a function of twist per inch. The performed tests indicate that strength decreases as the yarn is twisted past three twists per inch and are in agreement with previously conducted trials. The finite element model results were compared to test data performed in this study and ones reported in literature. Employing the validated simulation data, yarn damage and failure pictorials were produced. The frames showing the yarn at varying displacements illustrate the yarn failure propagation at varying twist-per-turn values. It is suggested that yarn softening as a function of twist per turn is attributed to higher strains of the outer filaments, at large amounts of twist, than of the core filaments. Previous work has shown a dependency of local filament strength to its yarn radius. The focus of this paper is to derive a comprehensive filament model, using finite element analysis, that incorporates the yarn strain gradient and is experimentally verified.

Multiscale modeling of randomly interwoven fibers for prediction of KM2 Kevlar yarn strength and damage

Modeling Kevlar yarn response as a function of twist requires creating a model at the filament level that incorporates capturing the mechanical interaction of numerous fibers. The inherent complexity of building a multiscale interwoven fibrous structure manually is prohibitive for such an endeavor; therefore, computer-aided simulations are preferred. In this study, a random walk methodology was employed to generate a fibrous structure along the axis of a yarn. Since the directionality of the fibers is randomly oriented along the axis, the fibers can wind around each other and tangle or terminate on demand. The resultant geometry can represent the tortuous path that yarn filaments experience. Yarn twist can be introduced through imposing a rotation matrix to the geometry or conducting an initial analysis that applies the preload. The analysis method employed in this paper captures the correct prestress of the twisted yarns at zero, three, and ten twists per inch. The analysis then loaded the yarn until filament fracture occurred. The predicted ultimate load was within 5% for all three twists per inch analyzed. The zero twists per inch linear response matched test results to within 5%.

To improve failure resistance in joint design of composite wind turbine blade materials

In this paper the failure behaviour of composite materials in the skin-stiffener of wind turbine blade structures are investigated. In order to achieve this, the laminated composite beams were stitched using glass, carbon and Kevlar yarns before curing process. Four different moulds of T-beam with adhesive; T-beam with stitches; Box-beam with adhesive and Box-beam with stitches were studied in this work. These specimens were tested under quasi-static loading condition to compare the failure resistance of adhesive and stitched bonding methods. Experimental results indicated that stitching can significantly improve failure load and interlaminar fracture resistance of the joints in wind turbine composite blade structures. The cohesive zone modelling (CZM) technique which is known as a variation in the cohesive stresses with the interfacial opening displacement along the localised fracture process zone is also used to predict bonding failure in the skin-stiffener of wind turbine blade structures.

Microscopic deformation mechanisms of unidirectional fiber bundles under transverse compressive stresses

The high-performance filament yarns, such as carbon fiber yarn, glass fiber yarn, and Kevlar fiber yarn, have characterized as unidirectional，high parallel filament in fiber bundle. However, due to the difficulties in statistically analyzing the micro-structural characteristics of high-performance fiber bundles comprising of thousands of filaments, Nylon (PA6) filament yarns were chosen as the substitute of high-performance fiber bundles to study the deformation micro-mechanisms of fiber bundles under transverse compressive stresses. In order to evaluate the effects of different compressive stresses on the deformation properties, the synchrotron radiation X-ray micro-computed tomography (micro-CT) was used to obtain cross-section images of the fiber bundle during the compression testing. In particular, the influences of compressive stress on the fiber volume fraction, fiber distribution, fiber contact, and fiber orientation were studied. Results indicate a strong dependence of the microstructure of fiber bundles on the compressive stress.

Dynamic Material Characterization Using Digital Image Correlation

Digital Image Correlation is a non-contact optical technique for measuring the full-field deformation on the surface of a deforming specimen. The technique was initially used in quasi-static experiments, but with the development of high speed digital cameras is used also in dynamic experiments. This use of the Digital Image Correlation technique in several dynamic experiments is presented. This includes the compression and tensile split Hopkinson bar tests, a shear test for specimens made of sheet metal, a dynamic punch test, tensile test of Kevlar cloth and Kevlar yarn, and an intermediate strain rate test in compression.

Quantifying damage at multiple loading rates to Kevlar KM2 fibers due to weaving, finishing, and pre-twist

Understanding Kevlar's mechanical response at strain rates relevant to impact events is essential for the development of numerical simulations of impact events. The strength and orientation of the individual filaments may become compromised as a result of crimping, weaving, or finishing processes required to weave the Kevlar yarn into the fabric used for protective equipment. To elucidate and quantify any damage to the fibers as a result of the weaving or post treatment finishing process, single fibers were extracted from the warp and weft directions of plain woven, hydrophobically treated Kevlar cloth. The strength of these fibers was measured over a wide range of strain rates and compared with fibers extracted from an unwoven yarn. The tensile response was also measured from single fibers subjected to varying levels of shear strain. The tensile strength of the fibers was evaluated at 0.001 s−1, 1 s−1, and approximately 1000 s−1 using a Bose Electroforce test setup and a Hopkinson tension bar modified for fiber experiments. A wide range of gage lengths was investigated to find the effect of defect distribution on the tensile strength of the woven fibers. The results show that fibers taken from the weft direction of the woven fabric decreased in strength 3%–8% compared with the unwoven fiber. The warp fibers were a minimum of 20% weaker than unwoven and weft fibers at all loading rates. Twisted fibers retained 93% of untwisted tensile strength up to a shear strain of about 0.10–0.15. Measured Young's modulus as a function of strain rate and tensile strength as a function of gage length in relation to defect distribution are also presented in this paper.

Reactive Aramid Nanostructures as High‐Performance Polymeric Building Blocks for Advanced Composites

AbstractTraditionally, the field of advanced nanocomposites has relied on a fairly limited set of building blocks; many with low reactivity and of limited variability. These limitations have been addressed by the creation of functionalized nanometer‐scale aramid structures, in the form of nanofibers and nanosheets. These were obtained by deprotonating macroscale, commercial Kevlar yarns using potassium hydroxide in dimethyl sulfoxide to yield stable dispersions of nanometer‐scale aramid fibers that were then hydrolyzed using phosphoric acid (PA). To illustrate the use of these functionally‐active nanostructures as building blocks for nanocomposites, they were crosslinked by glutaraldehyde (GA), and formed into macroscopic thin films by vacuum‐assisted filtration. It was shown that the mechanical properties of these PA/GA treated films can be tuned by varying the amounts of PA and GA used during synthesis, adjusting the relative amounts of hydrolysis and polymerization. These results are the first demonstration that aramid nanometer‐scale fibers can be used to form versatile nanometer‐sized building blocks that can then be crosslinked to fabricate a wide variety of nanostructured aramid materials with tailorable properties.

The influence of surface microstructure on the scratch characteristics of Kevlar fibers

In this work, nanoindentation and nanoscratching experiments are combined with atomic force microscopy to investigate the relationships between contact geometry, apparent friction, and deformation modes of two grades of Kevlar® (Dupont) fiber—Kevlar KM2 and Kevlar 49. Changes in the relative angle between the scratching probe and the fiber surface, often termed as the attack angle, result in changes in deformation mode, which correlate with the changes in the apparent friction. As attack angle increases, the observed deformation modes of the fiber surface change from a smoothing of the surface, often termed as ironing, to fibrillation, in which the fibrils break and coalesce in front of the progressing probe. A mixture of these two modes occurs at intermediate attack angles. When fibrillation occurs, material pile-up forms in front of the progressing probe. This pile-up introduces an additional component to the frictional response that is largely responsible for an increase in apparent friction with an increasing attack angle and/or scratch length. The level of friction associated with fibrillation is measured to be up to approximately three times higher than previously reported for Kevlar yarn–yarn friction. Fibrillation of Kevlar KM2 occurs at larger attack angles as compared to Kevlar 49, which is believed to be related to a near-surface region of reduced modulus and hardness previously observed in KM2 fibers. A detailed discussion of the measured response is given based on the interactions between the scratching probe and the fibrillar network and the resulting deformation mechanisms.

SIMULATION OF THE ELASTIC PROPERTIES OF REINFORCED KEVLAR-GRAPHENE COMPOSITES

The compressive strength of unidirectional fiber composites in the form of Kevlar yarn with a thin outer layer of graphene was investigated and modeled. Such fiber structure may be fabricated by using a strong chemical bond between Kevlar yarn and graphene sheets. Chemical functionalization of graphene and Kevlar may be achieved by modification of appropriate surface-bound functional (e.g., carboxylic acid) groups on their surfaces. In this report we studied elastic response to unidirectional in-plane applied load with load peaks along the diameter. The 2D linear elasticity model predicts that significant strengthening occurs when graphene outer layer radius is about 4% of kevlar yarn radius. The polymer chains of Kevlar are linked into locally planar structure by hydrogen bonds across the chains, with transversal strength considerably weaker than longitudinal one. This suggests that introducing outer enveloping layer of graphene, linked to polymer chains by strong chemical bonds may significantly strengthen Kevlar fiber with respect to transversal deformations.

Recent developments in dynamic testing of materials

Three new testing configurations that have been developed since the last DYMAT conference in 2009 are presented. The first is high strain rate testing of Kevlar cloth and Kevlar yarn in a tensile Split Hopkinson Bar (SHB) apparatus. The Kevlar cloth/yarn is attached to the bars by specially designed adaptors that keep the impedance constant. In addition to determining the specimen’s stress and strain from the recorded waves in the bars the deformations are also measured with Digital Image Correlation (DIC). The second testing configuration is a high strain rate shear test for sheet metal. The experiment is done by using a flat notched specimen in a tensile SHB apparatus. The shear strain is measured using DIC within the notch and on the boundary. The third development is a compression apparatus for testing at intermediate strain rates ranging from 20 s −1 to 200 s −1 . The apparatus is a combination of a hydraulic actuator and a compression SHB. The stress in the specimen is determined from the stress wave in a very long transmitter bar and the strain and strain rate is determined by using DIC. The results show clean stress strain curves (no ringing).

High-Strength, Metalized Fibers for Conformal Load Bearing Antenna Applications

We propose the use of high strength, metal-coated Kevlar yarns to weave flexible, conformal, and load-bearing antennas for an emerging class of applications emphasizing multiple functionality. In particular, here we present a unified, quantitative analysis of multiple properties of conductors as load-bearing materials in stress-, weight-, and shape-critical applications (e.g., in aerial vehicles), suggesting advantageous electrical conductor configurations to be metal-coated, multi-filament, high strength fibers. We then describe the fabrication of highly conductive metal coated Kevlar yarns, their mechanical and electrical properties, and the weaving of a flexible, stretchable, volumetric spiral antenna. The high frequency response of the antenna is found to match that of a traditionally made antenna comprised of electroplated copper on a rigid ceramic (Rogers TMM4) substrate. At low frequencies, the relatively lower conductivity of the metal-coated kevlar yarn leads to higher resistive losses compared to the traditional electroplated copper. We discuss strategies for mitigating such losses, and other means of improvement. More broadly, the results described here suggest a novel direction for multi-functional antenna design and applications, enabled by the superior mechanical characteristics of the composite conducting fibers, and the flexible, conformable, woven antenna architectures they help achieve.

Mechanical Properties Evaluation of Woven Coir and Kevlar Reinforced Epoxy Composites

The utilization of coconut fibers as reinforcement in polymer composites has been increase significantly due to their low cost and high specification of mechanical properties. Whereas kevlar fibers has widely used as the core material in flexible body armors due to its great mechanical properties, such as high strength, light weight, good chemical resistance and thermal stability. The research work is concerned with the evaluation of high speed impact and flexural test of hybrid textile reinforced epoxy composites. Samples were prepared from coir yarn, kevlar yarn, interlaced of coir and kevlar yarn with different warp/weft orientation and pure epoxy as control specimen. The woven samples were produced using handloom and the composites specimens were prepared using hand lay-up technique. From the results obtained, it was found that woven kevlar composites samples displayed the highest impact properties while it exhibits the lowest flexural properties. Results also showed that the composite plate for woven coir yarn (warp) and kevlar yarn (weft) has the flexural strength and impact strength of 17 MPa and 67 kJ/m², which presented as the nearest properties to woven Kevlar composite respectively. These results indicate that coir as a natural fiber can be used as a potential reinforcing material for high impact resistance such as body armors in order to reduce the usage of synthetic materials whilst utilizing the natural resources.

Metallization of Kevlar Fibers with Gold

Electrochemical gold plating processes were examined for the metallization of Kevlar yarn. Conventional Sn(2+)/Pd(2+) surface activation coupled with electroless Ni deposition rendered the fibers conductive enough to serve as cathodes for electrochemical plating. The resulting coatings were quantified gravimetrically and characterized via adhesion tests together with XRD, SEM, TEM; the coatings effect on fiber strength was also probed. XRD data showed that metallic Pd formed during surface activation whereas amorphous phases and trace amounts of pure Ni metal were plated via the electroless process. Electrodeposition in a thiosulfate bath was the most efficient Au coating process as compared with the analogous electroless procedure, and with electroplating using a commercial cyanide method. Strongly adhering coatings resulted upon metallization with three consecutive electrodepositions, which produced conductive fibers able to sustain power outputs in the range of 1 W. On the other hand, metallization affected the tensile strength of the fiber and defects present in the metal deposits make questionable the effectiveness of the coatings as protective barriers.

1A1-I07 人間の関節を模したロボットハンドの開発 : RCサーボを用いたワイヤ駆動による指関節多リンク制御(ロボットハンドの機構と把持戦略)

We manufacture an anthropomorphic hand with five fingers and control the fingers consisted of the multi-joints to grasp various objects by wire driven actuator. The state of grasping and holding objects can be detected using servomotor torque. There servo's torque was measured using the current sensor on the servomotor. In this paper we will observe the action and the response of each servomotor based on the current sensor data. We derived calibration method for current sensor. Additional, we did the tensile test of Kevlar yarn. Also, calculate the torque of servomotor used by current sensor data. Furthermore we show the mechanism of the designed robot hand.